Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on December 28, 2005, 08:53:38 AM
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My stupid question for this year,
The R2800B engine (F4U-1/F6F-3/5) used ADI to reach 60" MAP using 100 octane Av-gas. This ADI serves two functions.
1. Cooling
2. More importantantly- Anti-detonation.
However the P-51B/D uses the same fuel (100 octane) and has a mile power rating of 61" MAP and a War Emergency rating og 67" MAP.
The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?
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F4U, what is the CR of the 2800 and 1650?
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Is it possible the liquid cool engine had a lower cylender head temp, And could hence run a higher pressure?
And as milo suggest Crompression ratio would have a big impact.
Sorta curious my self about this.
HiTech
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Higher temperatures in the cylinder will help promote detonation. Increase of cylinder pressure will also prompt detonation. Design of combustion chamber shape and mixture motion, spark plug location and piston design can all make an engine more or less inherently prone to abnormal combustion. Spark timing and fuel quality are at the top of this list as well.
Two different engines, different animals in the "engine kingdom".
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HT, I have my handy dandy POH's ready for action.
Well Cylinder head tempatures of the F4U-1 R2800-8W B-block are max 500 degrees Farenheit in both Mil and WEP.
On the F4U-4 R2800-18W and 42W are both 473 degrees F. So from the B to C block the head temps are marginally lower however my engine charts only show 60"MAP on the chart for WEP so higher temps if alloable are not shown.
My P-51D POH only shows coolant temp not cylinder head temps. The coolant temp is much lower at 135 Degrees C (275 F). Indeed there is no mention of Cylinder heads throughout the manual however they do warn against pre-ignition and detonation due to increased engine temps caused by too lean a mixture etc.
Based on this I would have to say that your explanation is correct although I would like to know what the head temps of the P-51 really are. Apparently there is no gauge to inform the pilot of this so he is just looking at his coolant temps and listening for cylinder knocking.
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The asnwer for your question : INTERCOOLER on the P-51D. It provides the same as ADI, cooling of the charge.
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Hm... Below is the induction system of the F4U from Zeno's site. What can be seen in the right side of the picture (marked as F)?
Regarding the temp, PW redesigned the R-2800 entirely during the war to improve cooling.
gripen
(http://www.zenoswarbirdvideos.com/Images/F4U/F4UIS.gif)
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Morph and I know from owning (and building) high output turbo or supercharged cars that many many factors can change the amount of boost an engine can run without detonation. As he stated, piston shape, combustion chamber shape and finish, spark plug location, turbo/supercharger size, cylinder head material, can all have huge effects on an engines inherent resistance to detonation.
My car for example (Ford 2.3 stock Iron head) is running 20lbs of boost right now. I can turn it up to 23lbs but it makes no more power because the head just wont flow more. Detonation is more likely because the turbo is having to work harder to develope the extra PSI and is heating the carge unnecessarily. The same engine, but with an aftermarket aluminum head can make much more power, but a lower boost (18PSI) because the head can flow more allowing the turbo to heat the carge less.
Basically what I am getting at is unless you compare two identical engines it means nothing, and also more PSI does not always equal more HP.
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I think the bottom line is that the typical radial engine does not discipate heat with a high degree of efficiency. Thus, cylinder head temperatures can rapidly rise to levels where engine oil breaks down and essential lubrication fails. On the other hand, the typical fluid to air heat exchanger is far more efficient and is able to discipate heat much better.
One reason you don't see cylinder head temp gauges in liquid cooled aircraft is that water temperature tells you everything you need to know. Head temps can't rise any higher than the fluid cooling them. Heat is transmitted through the heads and block into the ethylene glycol, which is pumped to the heat exchanger (radiator) and then back to the engine (just like your automobile).
Running high boost in liquid cooled engines has its risks as you can burn valves, melt piston crowns and over-stress connecting rods, wrist pins, melted spark plug electrodes and the like. As long as the the cooling system has the means to remove heat from the block and heads, there is usually no danger to the engine. However, one can increase boost to the extent that the intake charge intercooler and radiator can no longer maintain acceptable temperatures and damage will eventually result. I've seen fluid bath type intercoolers used for turbocharged drag racers. These are more efficient than fluid to air over a short time span, but rapidly become heat saturated. Ok for the short period of operation required for drag racing.
Most radials used in high performance fighters used intake charge intercoolers to lower the temperature enough to improve power (a cooler charge has greater density) and keep cylinder head temperatures reasonable . However, radials almost always operate at higher temperatures than liquid cooled powerplants. This is normal and accounted for in the engine design. Radials depend more on a cool supply of oil as the oil greatly helps carry heat out of the engine. For example, the R-2800 installed in the P-47 had an oil tank with a 28 gallon capacity, while the P-51 tank held just 12.5 gallons. Since oil is more important to cooling a radial than it is for a liquid cooled V-12, the engine must hold a greater volume of oil and that is reflected in the size of the tank. Radials are also more prone to leaking oil... Another good reason to make sure there's plenty onboard. I can't count how many pushrod tubes I've repacked (replaced seals)....
My regards,
Widewing
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What Widewing said. I will also add that the same thing can be seen in motorcycles. The air cooled engines depend on the oil in the system to remove heat from the cylinder head and move it to the sump where it dissipates. When an aircooled motorcycle comes to a stop at a traffic signal cylinder head temps can (and do) skyrocket, if it were not for the oil acting as a heat removal agent the engine would have a very short life, while the water cooled engines run at essentially a constant temperature either stopped or moving at highway speeds. This is the same thing as the 28 gallon oil tank example he gave, but on a smaller scale.
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Question about ADI and MAP
My stupid question for this year,
The R2800B engine (F4U-1/F6F-3/5) used ADI to reach 60" MAP using 100 octane Av-gas. This ADI serves two functions.
1. Cooling
2. More importantantly- Anti-detonation.
However the P-51B/D uses the same fuel (100 octane) and has a mile power rating of 61" MAP and a War Emergency rating og 67" MAP.
The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?
The answer is because the Mustang didn’t have an INTERCOOLER, it had an AFTERCOOLER. And while Kurfurst used the wrong name for the system, I believe he was correct in pointing it out.
An intercooler is a heat exchanger between superchargers. An aftercooler is a heat exchanger between the supercharger(s) and the engine. An aftercooler reduces induction air temperature better than an intercooler. Higher manifold pressures can be tolerated the lower the induction air temperature is kept. Induction air temperature is key.
An aftercooler is more efficient than an intercooler in lowering induction air temperature. Using an aftercooler system, induction air temperature in the Mustang was low enough that a higher manifold pressure could be tolerated. The Corsair’s intercooler and ADI system was apparently unable to reduce the induction air temperature enough that higher manifold pressures could be utilized.
Had the Mustang used an intercooler instead of an aftercooler, it probably would have needed ADI to achieve its boost. Conversely, had the Corsair used an aftercooler (and P&W tried to develop one), it probably would not have had to use ADI to achieve the same manifold pressure.
The obvious manner to achieve higher manifold pressures (on the same fuel grade) on an engine with an intercooler (ie. Corsair) is increase the amount of ADI injected into the engine. The quantities of ADI required increase in a linear manner with the desired power level. The more ADI dumped into the system, the more cooling of the induction air temperature, and the greater manifold pressure that could be tolerated.
100/130 grade fuel could be boosted to very high levels (I’ve seen as high as nearly 90” hga) as long as the induction air temperature was kept low enough. The Mustang's aftercooler did it better than the Corsair's intercooler and ADI.
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Yup, P-51 had an aftercooler because both blowers were rigged in series. Blower #2 compressed the air blower #1 fed it, and ran the intake air up to temps that were too high for the engine to digest. So they plummed in an aftercooler to reduce the air temp between blower #2 and the carb. See p104 (fig 143) and p363 of America's Hundred Thousand for diagrams on the inline blowers and aftercooler layout.
As a side note: the max CHT for any aluminum head is 450F. Any higher than that and the head starts to lose structural strength. The 500F limit noted by DOA above is for short periods (takeoff, max-speed flight, emergencies) according to P&W and not a sustained limit. Absolute max operating CHT is 450F, but P&W suggests holding 50F lower than that to make sure the cylinder head material maintains high operating strength. Lycoming and Continental both recommend CHT remain lower than 420F for their air-cooled (non radial) engines built today.
http://www.avweb.com/news/columns/182084-1.html
About 3/4 the way down on that page is an excellent chart from P&W regarding CHT, along with a quote from a manual they published. Deak still has copies of P&W's "The Aircraft Engine" for sale. He's asking $100 per copy over at http://www.advancedpilot.com/store.html There's also a few other books available for any aircraft nut.
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Flakbait [Delta6]
(http://www.wa-net.com/~delta6/sig/geek.gif)
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Hi F4UDOA,
>So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?
While there is plenty of good stuff in all of the above posts, let me point out that boost pressure in itself means nothing - you'd have to compare the pressures in the combustion chamber right before ignition.
It comes down to absolute boost pressure multiplied with compression ratio as a key parameter for comparisons.
Due to the complexity of real life, it's only an approximation, but I'd expect it's a rather good approximation. (Hooker et al. go into considerable detail there, but I have only skimmed the book so far and don't quote it as a source here :-)
With regard to cylinder head temperatures, I believe the indicated values might not be directly comparable between different engine types since the temperature is not evenly distributed, and the sensor is probably placed in a convenient location for each engine type, reading a bit higher or lower depending on the exact installation.
I don't think that liquid-cooled engines actually have a great advantage with regard to peak temperatures as it's my impression that the detonation usually is caused by small hot spots in places that are as difficult to cool by liquid as they are by air.
(As pointed out above, liquid cooling has several advantages, but I think they mostly concern handling and not necessarily performance.)
Just some impressions from a few books and one or two NACA reports - I might be wrong, but thought I'd add my thoughts to this thread anyway :-)
Regards,
Henning (HoHun)
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Originally posted by ShortyDoowap
The answer is because the Mustang didn’t have an INTERCOOLER, it had an AFTERCOOLER. And while Kurfurst used the wrong name for the system, I believe he was correct in pointing it out.
I often seen the Merlins "aftercooler" referenced as an "intercooler". And while you are correct with your points, and certainly understand the subject far better than me, let me note that, as I heard, the British and the Americans use different terms to describe the same thing, the former call it an IC, the latter know it as an AC.
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BTW, one thing I can think about is the rather vast volume difference between the rather small Merlin (27 liter) and the R2800 (well over 40 litres). I'd believe that to provide the same pressure for a larger volume, much larger amount of air need to be compressed, and it may be that leads to higher temperatures in the charge eventually in the larger engine. just a guess.
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Never seen the term "aftercooler" in any period documents(NACA, P&W etc). In fact this is the first time i have ever seen it used...
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Originally posted by Kurfürst
I often seen the Merlins "aftercooler" referenced as an "intercooler". And while you are correct with your points, and certainly understand the subject far better than me, let me note that, as I heard, the British and the Americans use different terms to describe the same thing, the former call it an IC, the latter know it as an AC.
An aftercooler is after the supercharger. An intercooler is between the the 2 stages of the supercharger.
justin, the P&W H-3730, the Chrysler IV--2220 and the Allison V-1710-119 had aftercoolers. Pics show the cooler between the supercharger and the induction manifold.
description of the V-1650
The supercharger is a two-stage two speed gear driven unit with intercooling and aftercooling. Two stages are used to obtain relatively high pressure ratio's efficiently, two-speed operation allows improved performance at high altitude without the loss of power at sea-level which is inherent at high blower speeds, and intercooling and aftercooling significantly reduce charge temperature, allowing higher boost without detonation.
For low speed operation, the supercharger turns at 6.391 times crankshaft speed, for high speed the blower spins at 8.095 times crankshaft speed. The supercharger is driven through a gear train coupled to the spring drive through the supercharger driving gear in the wheelcase. Three independent planetary gear trains are arranged at 120 degree intervals around the driving gear, the driving gear thus driving three planetary pinions. The ring gears for the three planetary drives have internal and external teeth, the external teeth are coupled to the supercharger pinion which directly drives the supercharger, the internal teeth are coupled to planetary gears coupled to planetary pinion gears. For low speed, the planetary pinions are directly locked to their respective ring gears through planetary gears and clutches, so the ring gear is turning at the speed on the input to the planetary geartrain. For high speed, the planetary gears are allowed to rotate about the sun gear, increasing the speed of the ring gear with respect to the input shaft. A hydraulic clutch (three really, one for each planetary gear train) combined with over-running "sprag" clutches is used to effect speed changes. The hydraulic clutch uses moderate engine oil pressure controlled with 24V electrically actuated solenoid -- the solenoid is actuated to apply oil pressure for high speed, and pressure is released for low speed operation.
The supercharger itself consists of two impellers on the same shaft, both turning the same speed. The first stage uses a 12.0" diameter impeller, while the second stage uses a 10.1" impeller. The intercooler is an integral part of the intermediate volute case, located between the first and second stage impellers. The compressed air from the first stage passes through the cooled volute and passage to the second stage. The aftercooler is located between the exit of the second supercharger and the intake plenum, and is a conventional air/water heat exchanger (liquid/air radiator). A separate cooling system with its own pump was provided (permitting cooler water than is possible by using the engine coolant) was provided for aircraft use -- a 40% reduction in intake temperature was reported by Rolls-Royce at maximum speed and power with a coolant flow of about 30 gallons per minute. For boat racing, the aftercooler is usually replaced with simple plenum tube (called a tube or ADI tube) due to disruptions in airflow and mixture which occur in the aftercooler matrix at very high power levels -- at least some of which is though to result from air-fuel-ADI separation.
An automatic boost regulator is standard equipment for aviation use. The boost regulator automatically retards the throttle as full boost is reached, eliminating manual control of this critical function. War emergency boost is often provided whereby the pilot can over-ride the regulator when necessary, an indication such as a broken seal is usually provided to alert maintenance that the engine has been overstressed. For planes with ADI, there is usually an interlock provided that restricts maximum boost to a lower setting when ADI is not functional.
http://www.unlimitedexcitement.com/
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NACA Technical Note No. 794, Feb. 1941
An intercooler is a heat exchanger, and the name "intercooler" was chosen because this heat exchanger was interposed between two stages of compression. The name now has come into widespread aeronautical use as meaning any heat exchanger used for cooling the engine air, regardless of its position in the induction system.
NACA Technical Note No. 795 uses the term "intercooler" in reference to single stage superchargers...
"Intercooler" was the term in use at the time, which was the point I was making.:rolleyes:
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Originally posted by justin_g
NACA Technical Note No. 794, Feb. 1941
NACA Technical Note No. 795 uses the term "intercooler" in reference to single stage superchargers...
"Intercooler" was the term in use at the time, which was the point I was making.:rolleyes:
The only US plane to use the aftercooler in any number was the P-51 with the Merlin engine. That's a post 1941 aircraft.
T.O. No. 1F51-D-1 "Pilot Training Manual For The F-51D Mustang," 20 January 1954, properly refers to the system as an aftercooler.
So did AAF Manual 51-127-5 "Pilot Training Manual For The P-51 Mustang," 15 Aug 1945.
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The differences in the charge cooling can't really explain the differences in the reachable MAP between the Merlin and R-2800. The E-series V-1710 (same compression ratio as in the B-series R-2800) with auxilary stage as used in the P-63 was rated at for 75" with ADI (no intercooler) while the highest rating for the B-series R-2800 with ADI and intercooling was around 64" (and R-2800 probably needed richer mixture). With ADI the Merlin would have reached even higher MAP, IIRC Merlin was type tested for +36lbs with water injection (probably with grade 150 fuel).
The reasons for lower MAP are much more likely in head cooling.
gripen
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Gripen, it all goes together. Remember, hot spots could ignite a hot charge easier than a cooler charge. That’s the reason the charge needed to kept as cool as possible. The Intercooler/ADI system of the Corsair/Hellcat was unable to reduce the charge temperature enough that high manifold pressures could be used. The Mustang's aftercooler system could reduce the charge temperature enough that higher MAPs could be used.
The simple fact is that if the Corsair or Hellcat was to use a higher MAP on the same fuel grade, it had to find a way to reduce the charge temperature further. Pratt and Whitney tried to develop an aftercooler, but abandoned the attempt after realizing that it would have required a major redesign of the engine and supercharger system. Therefore, the only other way was to increase ADI flow. That was hard. As it were, the Corsair carried only about 10 gallons of ADI, and the Hellcat 16 gallons, both set for a flow for 15 minutes use, IIRC.
Also, comparing the Merlin, R-2800 and Allison is difficult. They all had different types of superchargers, and engine cooling methods. As you know, the R-2800 was air/oil cooled, the Merlin was mostly liquid cooled, and the Allison as a combination liquid/oil cooled engine.
The V-1701 in the P-63 had no intercooler or aftercooler, true. But it also has a single speed 2nd stage supercharger, compared to the two speed 2nd stage supercharger in the Mustang’s Merlin. The Allison’s 2nd stage supercharger compressed much less, and imparted much less heat to a charge than did the Merlin’s 2nd stage supercharger. Couple that with the fact that the P-63 carried a huge amount of ADI (25 gallons for 15 minutes use) and you can see why the Allison could obtain 75” hga.
The simple fact is that if higher MAPs are to be used on the same fuel, the charge temperature has to be reduced.
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Based on my rading HiTech is right on this. Water cooling reduces hot spots in the cylinder so you can typically get more MAP out of a water cooled engine without detonation.
The cylinder head tolerances you see in most engine specs have to do with the temperature where the cylinder actually loses it's strength and may experience structural failure.
It's hard to argue this is about an intercooler when we are comparing engine models with two stage superchargers that both take advantage of large intercoolers.
-Blogs
Originally posted by F4UDOA
HT, I have my handy dandy POH's ready for action.
Well Cylinder head tempatures of the F4U-1 R2800-8W B-block are max 500 degrees Farenheit in both Mil and WEP.
On the F4U-4 R2800-18W and 42W are both 473 degrees F. So from the B to C block the head temps are marginally lower however my engine charts only show 60"MAP on the chart for WEP so higher temps if alloable are not shown.
My P-51D POH only shows coolant temp not cylinder head temps. The coolant temp is much lower at 135 Degrees C (275 F). Indeed there is no mention of Cylinder heads throughout the manual however they do warn against pre-ignition and detonation due to increased engine temps caused by too lean a mixture etc.
Based on this I would have to say that your explanation is correct although I would like to know what the head temps of the P-51 really are. Apparently there is no gauge to inform the pilot of this so he is just looking at his coolant temps and listening for cylinder knocking.
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The Merlin made up for its smaller displacement with a higher max RPM. But this only places more stress on the ability to cool the engine.
-Blogs
Originally posted by Kurfürst
BTW, one thing I can think about is the rather vast volume difference between the rather small Merlin (27 liter) and the R2800 (well over 40 litres). I'd believe that to provide the same pressure for a larger volume, much larger amount of air need to be compressed, and it may be that leads to higher temperatures in the charge eventually in the larger engine. just a guess.
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The original question was why could the Merlin use utilize higher MAPs than the R-2800 on the same fuel.
The answer is that the induction system on the Merlin was able to introduce a charge with a temperature sufficiently cool enough that detonation wouldn't be experience at its rated MAPs. The induction sytems in the Corsair and Hellcat could not introduce a charge that was cool enough to sustain the same MAPs as the Merlin. The Mustang's induction system could cool a charge enough that it could tolerate 67" hga. The Corsair's couldn't.
The engine was what it was. The way an engine created and disipated heat was hard to change without a major redesign of the engine. The way to increase MAP, then, was the reduced the charge temperature, or switch to a higher octane fuel. Temperature was reduced by way of an intercooler, aftercooler, ADI, or a combination of any or all of them. For the most part, when manufacturers and the Military wanted to increase ratings, they didn't redesign cooling systems, they added water injection.
And that you can get higher MAP out of a watercooled engine is not always correct. Maximum ratings for the P-38 were only about 60" hg - with the utilization of an intercooler. And the Allison was considered to have better cooling properties than the Merlin, and also had a less compressive 2nd stage supercharger than did the Merlin.
Whatever the cylinder head temperatures were in the engines discussed is incidental. If you introduce a 220 degree charge into a Merlin, it will detonate quicker than than a 200 degree charge, even if the cylinderhead temp is the same. The induction systems had to deal with the engine temperatures. The Merlin's induction system was better able to cool a charge, and thus deal with the engine heat better than the R2800's induction system could.
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And BTW, when you say
It's hard to argue this is about an intercooler when we are comparing engine models with two stage superchargers that both take advantage of large intercoolers.
remember the Mustang and the Corsirs had significantly different induction systems.
The biggest heat inducer to a air/fuel charge is the 2nd stage supercharger.
The Mustang's system sent the charge from the second stage supercharger to the aftercooler. The benefit was that the charge didn't have to go thru another heat-inducing compression.
The Corsair's system sent the charge from the 1st stage supercharger to the intercooler, and from there it was compressed again (and heated again) by the 2nd stage supercharger.
Again, P&W realized and aftercooler was better, but could not develope one for its engines.
Want higher MAPs, then the charge has to cooled more. Again, when the military wanted higher MAPs, they didn't improve engine cooling, they strove to reduce charge temp.
Engine heat had everything to do with it. But MAP ratings were determined by how cool a charge could be made. As charge cooling was improved, MAP ratings increased.
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Originally posted by ShortyDoowap
Whatever the cylinder head temperatures were in the engines discussed is incidental. If you introduce a 220 degree charge into a Merlin, it will detonate quicker than than a 200 degree charge, even if the cylinderhead temp is the same. The induction systems had to deal with the engine temperatures. The Merlin's induction system was better able to cool a charge, and thus deal with the engine heat better than the R2800's induction system could.
Cylinder head temps are a factor just as charge temp, combustion chamber shape, flow capability of the ports in the head, and all the other things said. Yes, charge temp is the most critical factor, but it is not the only one. A cylinder head (either water or air cooled) can have localized hot spots and cause detonation no matter cool the carge temp.
Its not an either/or situation, there are many interrelated factors that all contribute to the amount of boost an engine can handle which is why unless they are identical, not just similar, its meaningless to compare them.
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I didn't say it was the only factor, in fact, I specifically said it wasn't. I said all these thigs are interrelated.
Having an engine with hotspots sufficient to detonate a charge "no matter how cool it is" would not have been usual and would been an indicator of a serious cooling problem.
Nevertheless, the answer to the question remains that the Mustang's system could deliver a charge cool enough that it could deal with the heat and all the other stuff that factors into detonation such that it could tolerate 67" hga. The Corsair's couldn't.
When Vought and P&W wanted to run the Corsair at higher MAPs, they added water injection, they didn't modify the cowling so that the engine ran cooler.
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Here's what Graham White says in "R-2800: Pratt and Whitney's Dependable Masterpiece"
(http://members.cox.net/us.fighters/induction.jpg)
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LOL....I'm very aware of how charge cooling works and its ramifications, I have 3 cars with turbo's, one of them making 300+ HP out of 2.3ltr's.
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Calm down, Grits, that wasn't intended for the experts.
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Originally posted by ShortyDoowap
Gripen, it all goes together. Remember, hot spots could ignite a hot charge easier than a cooler charge.
Well, if there is no "hot spots", less charge cooling is needed for given MAP, right?
Originally posted by ShortyDoowap
The simple fact is that if the Corsair or Hellcat was to use a higher MAP on the same fuel grade, it had to find a way to reduce the charge temperature further. Pratt and Whitney tried to develop an aftercooler, but abandoned the attempt after realizing that it would have required a major redesign of the engine and supercharger system.
Actually Pratt and Whitney choosed to redesign entire R-2800 to improve cooling and the result, R-2800 C-series, was used in the late F4Us and P-47s. The C-series could reach 70-72" with similar charge cooling systems as earlier B-series.
And at least I'm not aware that Pratt and Whitney tried to develop an aftercooler for the R-2800; basicly they (as well as Allison) made standard single stage, single speed engines which could be coupled with auxilary stage (mechanical or turbo) for better altitude performance. Infact the report quoted by justin_g above is written by P&W employee and it's states that it is generally inconvenient to provide charge cooling after second stage in the case of the radial engines.
Originally posted by ShortyDoowap
Also, comparing the Merlin, R-2800 and Allison is difficult. They all had different types of superchargers, and engine cooling methods.
These engines can be easily compared with similar supercharger configurations; the R-2800 B-series with neutral blower (ie single stage) was limited to about 54" without ADI while the single stage V-1710s could reach 57-60" and the single stage Merlins could reach +18lbs (both without ADI and without intercooling). Note that single stage Merlins were capable to reach +25lbs with grade 150 fuel and no intercooling nor ADI.
In the case of the turbos, the V-1710 in the P-38J could reach 60" with intercooling and without ADI, while the B-series R-2800 of the P-47D was limited to 52-54" in similar configuration and it was initially limited to 56-58" with ADI (later raised to 60-64").
Originally posted by ShortyDoowap
The V-1701 in the P-63 had no intercooler or aftercooler, true. But it also has a single speed 2nd stage supercharger, compared to the two speed 2nd stage supercharger in the Mustang’s Merlin. The Allison’s 2nd stage supercharger compressed much less, and imparted much less heat to a charge than did the Merlin’s 2nd stage supercharger.
Hm... I can't really follow your logic here. The engine stage of the two stage mechanically supercharged V-1710s (as used in the P-63) was with 8,10:1 gearing so it could not reach high MAP (say over 60") without auxilary stage. The auxilary stage of the V-1710 was a variable speed unit with hydraulic coupling. If we assume a given MAP (above 60"), the V-1710 with auxilary stage and the two stage Merlin compressed charge overall just similar amount and there was probably not much difference in overall charge heating during compression (despite variable speed unit) because these V-1710s were limited to 58" without ADI.
gripen
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Hi F4UDOA,
>The R2800B engine (F4U-1/F6F-3/5) used ADI to reach 60" MAP using 100 octane Av-gas.
>However the P-51B/D uses the same fuel (100 octane) and has a mile power rating of 61" MAP and a War Emergency rating og 67" MAP.
Hm, I found two different compression ratio figures for different models the R-2800 (6.65 and 6.75), and only one for a different Merlin model than used in the P-51 (6.00).
Whatever the correct figures, a direct comparison should follow this pattern to calculate peak charge pressure:
R-2800: 60" Hg * 6.75 = 405" Hg
V-1710: 67" Hg * 6.00 = 402" Hg
This is a bit rough since the charge will actually heat up during compression, generating a higher final pressure, but this effect will be very similar for both engines, so our result can be considered a fair approximation.
Note that the R-2800 requires the use of alcohol-water injection to achieve the same final pressure as the V-1710. However, at least we have learned now that the V-1710 does not actually exceed the R-2800's peak charge pressure.
Regards,
Henning (HoHun)
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Originally posted by HoHun
Hm, I found two different compression ratio figures for different models the R-2800 (6.65 and 6.75), and only one for a different Merlin model than used in the P-51 (6.00).
Whatever the correct figures, a direct comparison should follow this pattern to calculate peak charge pressure:
R-2800: 60" Hg * 6.75 = 405" Hg
V-1710: 67" Hg * 6.00 = 402" Hg
This is a bit rough since the charge will actually heat up during compression, generating a higher final pressure, but this effect will be very similar for both engines, so our result can be considered a fair approximation.
Note that the R-2800 requires the use of alcohol-water injection to achieve the same final pressure as the V-1710. However, at least we have learned now that the V-1710 does not actually exceed the R-2800's peak charge pressure.
Hm... The B-series R-2800s (as used in the F4U-1, F6F and P.47D) had exactly same compression ratio as (most of) the E- and F-series V-1710s ie 6,65. The CR value 6,75 is for C-series R-2800 and later.
Besides it seems that you are mixing V-1710 (Allison) and V-1650 (Merlin) here some how.
gripen
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Well, if there is no "hot spots", less charge cooling is needed for given MAP, right?
That would seem to be correct. But doesn’t detract from the fact that the Mustang could reach higher MAPs in 100/130 Fuel than could the Corsair because its engine was fed a charge cool enough that it could tolerate those MAPs. The Corsair’s system was unable to cool the charge sufficiently for MAPs as high to be tolerated.
Actually Pratt and Whitney choosed to redesign entire R-2800 to improve cooling and the result, R-2800 C-series, was used in the late F4Us and P-47s. The C-series could reach 70-72" with similar charge cooling systems as earlier B-series.
THAT’S a “major redesign” I was talking about. I wrote --- The way an engine created and disipated heat was hard to change without a major redesign of the engine.
Subsequent comments pertain to the planes being discussed, the Mustang and earlier Corsairs that could not reach higher MAPs.
BTW, the F4U-4 with R-2800-18W “C” engine was cleared for 70” hga on 115/145 fuel. On 100/130 grade fuel, WEP MAP was still limited to 60” hga.
And at least I'm not aware that Pratt and Whitney tried to develop an aftercooler for the R-2800; basicly they (as well as Allison) made standard single stage, single speed engines which could be coupled with auxilary stage (mechanical or turbo) for better altitude performance. Infact the report quoted by justin_g above is written by P&W employee and it's states that it is generally inconvenient to provide charge cooling after second stage in the case of the radial engines.
If you have Graham Whites book on the R-2800, read page 135, which talks about the desire for an aftercooler to cool the charge coming from the 2nd stage compressor, and their attempts to develop and aftercooler, which they abandoned.
Again, an aftercooler is preferable to an intercooler because if cools the charge after the most heat inducing stage – the 2nd stage. A charge that flows thru and intercooler still has that 2nd stage to pass thru, with no way to cool it.
And “inconvenient” doesn’t equal “undesirable.” P&W couldn’t develop a suitable aftercooler because of the supercharger arrangement. In all R-2800s, the 2nd stage compressor lied between the carb and the engine. Ducting the charge from the carb to an aftercooler back to the 2nd stage compressor no doubt would have been “inconvenient,” nevertheless; P&W understood it was desirable. The extreme inconvenience of a major redesign is the reason the R-2800 never had and aftercooler.
These engines can be easily compared with similar supercharger configurations; the R-2800 B-series with neutral blower (ie single stage) was limited to about 54" without ADI while the single stage V-1710s could reach 57-60" and the single stage Merlins could reach +18lbs (both without ADI and without intercooling). Note that single stage Merlins were capable to reach +25lbs with grade 150 fuel and no intercooling nor ADI.
Merlin superchargers had a liquid-intercooling jacket around them. Not the same as an intercooler, but it reduced the operating temperature of the supercharger, thus it reduced the charge temperature.
Which single stage Merlins were rated for 25lbs boost without intercooling? I’m not talking about a special test engine, but rather which single stage Merlin was rated for 25lbs boost for wartime service?
Hm... I can't really follow your logic here. The engine stage of the two stage mechanically supercharged V-1710s (as used in the P-63) was with 8,10:1 gearing so it could not reach high MAP (say over 60") without auxilary stage. The auxilary stage of the V-1710 was a variable speed unit with hydraulic coupling. If we assume a given MAP (above 60"), the V-1710 with auxilary stage and the two stage Merlin compressed charge overall just similar amount and there was probably not much difference in overall charge heating during compression (despite variable speed unit) because these V-1710s were limited to 58" without ADI.
gripen
I’m not talking about the 1st stage (auxiliary stage) supercharger, I’m talking about the 2nd stage supercharger.
The point was this is the most compressive point for the charge, thus the most heat inducing. Both engines were capable of High MAPs. The Merlin dealt with it using an aftercooler and no ADI. The V-1710 had to use copious quantities of ADI, 25 gallons for 15 minutes, to achieve similar ratings.
Read Vees for Victory, I think you have it. Page 342, second column, second to last paragraph:
Regarding superchargers:
An inefficient design requires more horsepower, and any inefficiency is power that shows up in the mixture as undesirable heat. Such heat, if above a threshold temperature determined by the quality of the fuels being used and the physical design of the combustion chambers will immediately cause detonation.
Again, it comes down to charge temperature management.
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Which single stage Merlins were rated for 25lbs boost without intercooling? I’m not talking about a special test engine, but rather which single stage Merlin was rated for 25lbs boost for wartime service?
The Merlin 25 at least, and others in the 20 series as well, iirc.
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My Mosquito manual with the Merlin 25 shows a max rating of 18lbs.
And weren't 25lb boost ratings on 100/150 grade fuel???
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My Mosquito manual with the Merlin 25 shows a max rating of 18lbs.
25 lbs would only havbe been used on some Mosquitos in 1944 and 1945. Earlier and later manuals won't show the higher rating. I've got a complete test report on the Fb VI done at 25 lbs, and a bit about Mosquito NF XIXs running both 25 lbs boost and N2O injection (394 mph at 2,000 ft)
Neil posted from Avia 6/587
"boost pressure increased to 25 lbs /sq.in has been authorised for use in Merlin 25 engines in service"
And weren't 25lb boost ratings on 100/150 grade fuel???
Yes.
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IIRC none of the Mosquito units ever received 150 grade fuel, so +25 for them, is a bit theoretical. Perhaps some 'anti diver' units used it briefly in mid-1944, but that's it.
Moral of the story, +25 lbs w/o intercooling was appearantly done with NO2 injection serving as ADI and/or 150 grade fuel.
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Originally posted by ShortyDoowap
That would seem to be correct. But doesn’t detract from the fact that the Mustang could reach higher MAPs in 100/130 Fuel than could the Corsair because its engine was fed a charge cool enough that it could tolerate those MAPs. The Corsair’s system was unable to cool the charge sufficiently for MAPs as high to be tolerated.
IMHO you just can't admit here that the problem was cooling of the heads. If the B-series R-2800 had got an aftercooler, it would not have reached same MAP values as two stage Merlin.
Originally posted by ShortyDoowap
BTW, the F4U-4 with R-2800-18W “C” engine was cleared for 70” hga on 115/145 fuel. On 100/130 grade fuel, WEP MAP was still limited to 60” hga.
At least the datacollection which is available from F4UDOA's site lists WEP rating 70" for the F4U-4 (Oct. 44 ie before 115/145 became available and before F4U-4 entered service).
Originally posted by ShortyDoowap
Again, an aftercooler is preferable to an intercooler because if cools the charge after the most heat inducing stage – the 2nd stage.
No one has argued otherwise here, but comparison with similarly supercharged engines like V-1710 and C-series R-2800 show clearly that the problem was not charge cooling because these other engines could reach higher MAP with similar induction systems or even with less charge cooling.
Originally posted by ShortyDoowap
I’m not talking about the 1st stage (auxiliary stage) supercharger, I’m talking about the 2nd stage supercharger.
The point was this is the most compressive point for the charge, thus the most heat inducing. Both engines were capable of High MAPs. The Merlin dealt with it using an aftercooler and no ADI. The V-1710 had to use copious quantities of ADI, 25 gallons for 15 minutes, to achieve similar ratings.
I don't know what you are arguing here, there seem to no particular difference between these engines in overall charge heating when the charge goes through superchargers.
Originally posted by ShortyDoowap
Again, it comes down to charge temperature management.
Or similar results can be reached by improving the cooling of heads as Pratt and Whitney did when they redesigned entire engine.
gripen
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IMHO you just can't admit here that the problem was cooling of the heads. If the B-series R-2800 had got an aftercooler, it would not have reached same MAP values as two stage Merlin.
There’s nothing to admit! There was no PROBLEM. It was a characteristic of the design. It was-what-it-was and it was dealt with in the best manner possible. Like I’ve been stating, whatever the issue was with the head temperature, the charge had to be cool enough to deal with it. The Corsair’s system couldn’t cool a charge enough to use 67” hga like the Mustang could. Easy concept.
And you have no idea if the B series would have been able to make better MAP with an aftercooler or not. I happen believe it would have, and P&W must have as well or they wouldn’t have tried to develop one. Even Allison went to aftercoolers with later V-1710s. You seem to think they didn’t make any more difference than an intercooler. P&W and Allison did. Forgive me if I go with them.
The fact is is that REGARDLESS of the head temperature, it’s not easily manipulated because it’s incidental to the power that needed to be developed. The easiest way to increase MAP was to reduce charge temperature.
The simpler fact is is if the Corsair’s system had been able to reduce the charge temperature more, more MAP could have been obtained. But it couldn’t.
At least the datacollection which is available from F4UDOA's site lists WEP rating 70" for the F4U-4 (Oct. 44 ie before 115/145 became available and before F4U-4 entered service).
By December 1944, 75,000 barrels of 115/145 grade fuel had been produced for testing purposes (See AAF Historical Study 65: Aviation Gasoline Production and Control). So it was certainly available for testing – the very kind of test you are referring to.
There is also a F4U-4C performance data sheet on his site that clearly lists the WEP rating of the plane with the R-2800-18W engine as 60” hg dated 5/21/46. You must have missed it. 1946. 115/145 grade fuel did not become standard naval aviation fuel until the summer of 1947 (See Naval Aviation News, March 1947, page 29). It was in used by some 20th AF fighter Groups late in the war.
Additionally, the NAVAER performance and characteristics sheet on the Navy website shows 70” performance on 115/145 grade fuel.
No one has argued otherwise here, but comparison with similarly supercharged engines like V-1710 and C-series R-2800 show clearly that the problem was not charge cooling because these other engines could reach higher MAP with similar induction systems or even with less charge cooling.
Gripen, your logic is flawed.
The issue is absolutely charge cooling. It’s the most important element in avoiding detonation. Graham White and Daniel Whitney both say it their books, and Allison and P&W both knew it as they continually strove to reduce charge temperature by improving (or at least attempting to improve) their induction systems.
And your assertions regarding the V-1710 and R-2800 seems very odd. Both operated at low maps unless something was done to reduce induction air temperature. The P-38 and P-47 used intercoolers (and ADI for the P-47), yet neither developed the kind of MAP the P-51D did on the same fuel. It took a major redesign of the R-2800 (B series to C series) before the R-2800 was capable of it. And no V-1710 developed the sort of MAP the Mustang did until the P-63, and that accomplished by dumping huge amounts of ADI into the charge.
Again, induction air temperature is the most important aspect with respect to detonation.
I don't know what you are arguing here, there seem to no particular difference between these engines in overall charge heating when the charge goes through superchargers.
Again, I don’t understand your logic.
On the Merlin, the charge was compress twice, THEN cooled by the aftercooler before going into the engine.
On the V-1710, the charge was compressed and the hot charge went to the engine, to be cooled by ADI.
It was all about cooling the charge.
Or similar results can be reached by improving the cooling of heads as Pratt and Whitney did when they redesigned entire engine.
gripen
I ALREADY said that. But that didn’t happen with the earlier Corsairs. Their inductions systems were inadequate to cool a charge enough so that 67” hag MAP could be used. The Merlin’s was adequate.
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Originally posted by ShortyDoowap
There’s nothing to admit! There was no PROBLEM. It was a characteristic of the design. It was-what-it-was and it was dealt with in the best manner possible. Like I’ve been stating, whatever the issue was with the head temperature, the charge had to be cool enough to deal with it. The Corsair’s system couldn’t cool a charge enough to use 67” hga like the Mustang could. Easy concept.
Well, if the cooling of the heads was not a problem, then the B-series R-2800 should have reached over 70" with intercooling and ADI just like V-1710 did with ADI alone. But in reality it did not do that.
Originally posted by ShortyDoowap
And you have no idea if the B series would have been able to make better MAP with an aftercooler or not. I happen believe it would have, and P&W must have as well or they wouldn’t have tried to develop one. Even Allison went to aftercoolers with later V-1710s.
The B-series R-2800 would have done better with aftercooling but not very much and AFAIK series produced V-1710s with two stage mechanical superchargers never got intercooler nor aftercooler.
Originally posted by ShortyDoowap
You seem to think they didn’t make any more difference than an intercooler. P&W and Allison did. Forgive me if I go with them.
I'm merely pointing out that if the cooling of the heads would have been better in the B-series R-2800, it would have reached MAP close to V-1710 with similar induction system.
Originally posted by ShortyDoowap
The fact is is that REGARDLESS of the head temperature, it’s not easily manipulated because it’s incidental to the power that needed to be developed. The easiest way to increase MAP was to reduce charge temperature.
I wonder what you are trying to argue; no one tries to deny advantages of the charge cooling here. But if the head temperature can be reduced some how, the MAP can be increased.
Originally posted by ShortyDoowap
Gripen, your logic is flawed. The issue is absolutely charge cooling. It’s the most important element in avoiding detonation.
Basicly not so well head cooling prevented the B-series R-2800 to reach same MAPs as other engines with similar induction system.
Originally posted by ShortyDoowap
And your assertions regarding the V-1710 and R-2800 seems very odd. Both operated at low maps unless something was done to reduce induction air temperature. The P-38 and P-47 used intercoolers (and ADI for the P-47), yet neither developed the kind of MAP the P-51D did on the same fuel. It took a major redesign of the R-2800 (B series to C series) before the R-2800 was capable of it.
I wonder did you understand at all what I said about turbo charged V-1710 and B-series R-2800: "The V-1710 in the P-38J could reach 60" with intercooling and without ADI, while the B-series R-2800 of the P-47D was limited to 52-54" in similar configuration and it was initially limited to 56-58" with ADI (later raised to 60-64").
This comparison shows clearly how the B-series R-2800 was more limited than the V-1710 with similar induction system. With ADI Allison tested V-1710s of P-38 at 75" which is higher than 72" claimed for C-series R-2800 of P-47M.
Originally posted by ShortyDoowap
Again, I don’t understand your logic.
On the Merlin, the charge was compress twice, THEN cooled by the aftercooler before going into the engine.
On the V-1710, the charge was compressed and the hot charge went to the engine, to be cooled by ADI.
It was all about cooling the charge.
Hm... You originally said that:
"The V-1701 in the P-63 had no intercooler or aftercooler, true. But it also has a single speed 2nd stage supercharger, compared to the two speed 2nd stage supercharger in the Mustang’s Merlin. The Allison’s 2nd stage supercharger compressed much less, and imparted much less heat to a charge than did the Merlin’s 2nd stage supercharger."
Which is quite different you said now. In both engines the charge was compressed twice and I don't see any reason why there should have been a notable difference in the charge heating during this process at given MAP. Note that I did not say anything about charge cooling
Originally posted by ShortyDoowap
I ALREADY said that. But that didn’t happen with the earlier Corsairs. Their inductions systems were inadequate to cool a charge enough so that 67” hag MAP could be used. The Merlin’s was adequate.
Or the head temperatures of the B-series R-2800 were simply too high for 67".
gripen
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Well, if the cooling of the heads was not a problem, then the B-series R-2800 should have reached over 70" with intercooling and ADI just like V-1710 did with ADI alone. But in reality it did not do that.
Still, it’s not a “problem.” It was inherent in the design. Once the engine is designed, the way the detonation issue is dealt with is thru the induction system – by way of heat exchangers and ADI.
The B-series R-2800 would have done better with aftercooling but not very much and AFAIK series produced V-1710s with two stage mechanical superchargers never got intercooler nor aftercooler.
So says you, with no evidence to support your position. Again, Allison and P&W felt differently enough that P&W tried to develop an aftercooler, and Allison did.
Allison knew it had to find a way to increase power in its engines to be competitive and developed the V-1710-119 (F32R) for the proposed P-51J. It was rated on 100/130 grade fuel. In order to achieve the desired manifold pressures, a huge aftercooler sat on top of the superchargers. The P-51J was not developed as the Merlin P-51 was preferred.
The last plane to use an Allison was the F-82 Twin Mustang. It didn’t use an aftercooler or intercooler, but did use ADI. It wasn’t rated on 100/130 grade fuel, but rather on 115/145 grade fuel which could tolerate higher temps before detonating.
I'm merely pointing out that if the cooling of the heads would have been better in the B-series R-2800, it would have reached MAP close to V-1710 with similar induction system.
Fine. And I agree. But once the engine is developed, the way to avoid detonation is to cool the charge. The cooler the charge, the higher the MAP that can be tolerated.
And as far as the statement “B-series R-2800, it would have reached MAP close to V-1710 with similar induction” goes - it already did. For instance the maximum rating for the turbosupercharged R-2800-59 (P-47D-27 thru -40) was rated for 64” hga on 100/130 grade fuel. Maximum rating for the V-1710-111/113 (P-38L) was 60” hg on 100/130 grade fuel.
Now the V-1710-117 of the P-63C was rated at 76” hga on 100/130 grade fuel. It didn’t use an aftercooler or intercooler. But it used obscene amounts of ADI – more than 1.5 gallons per minute – to do it. It used so much ADI that it increased MAP by 15” hga over its dry WEP rating of 61” hga. That was how Allison chose to tackle their detonation issue.
The only engines I think that are really directly comparable (by virtue of their induction systems), are those on the P-38 and P-47. The induction systems on the P-63 and F4U used different methods to achieve what they did.
I wonder what you are trying to argue; no one tries to deny advantages of the charge cooling here. But if the head temperature can be reduced some how, the MAP can be increased.
What I am saying here is that improvements in MAP could be obtained without improvements in head cooling. Head temperature wasn’t a “problem” because these were good engines. If a way could be found to ever decrease the charge temp, MAP ratings would continue to rise. That happened for a while, until it was no longer a practical way to increase the efficiency of the induction system.
Detonation limitations were affected by many things, among them head temperature and induction air temperature. Induction air temperature was the more variable of them.
Basicly not so well head cooling prevented the B-series R-2800 to reach same MAPs as other engines with similar induction system.
Lemme ask you this? What was the temperature of the mixture discharged into the engine in the Corsair’s R-2800-8 engine (6.65:1 compression ratio pistons) at 60” hga? I don’t know. But I do know what it was for the Allison V-1710 and the V-1650 engines.
In the late V-1710s (6.0:1 compression ratio pistons) a mixture discharged into the engine at a temperature of 230 degrees Far developed 63” hga. (The V-1710-111/113 in the P-38L used 6.65:1 compression ratio pistons and developed a maximum of 60” hga.)
In the two stage, aftercooled V-1650 (6.0:1 compression ratio pistons) a mixture discharged into the engine at a temperature of 180 degrees Far developed 67” hga.
I think the engines are comparable enough to say that the major difference here is that the Merlin’s induction system cooled the charge better than the Allison’s so it was able to utilize higher MAPs. When Allison wanted to cool the charge more to develop higher MAP, it utilized ADI. I’d hazard to say the charge temperature in the Corsair's R-2800-8 was probably hotter than it was in the Merlin making it impossible to achieve the MAPs on the R-2800 that the Merlin could achieve on the same fuel grade.
I wonder did you understand at all what I said about turbo charged V-1710 and B-series R-2800: "The V-1710 in the P-38J could reach 60" with intercooling and without ADI, while the B-series R-2800 of the P-47D was limited to 52-54" in similar configuration and it was initially limited to 56-58" with ADI (later raised to 60-64").
This comparison shows clearly how the B-series R-2800 was more limited than the V-1710 with similar induction system. With ADI Allison tested V-1710s of P-38 at 75" which is higher than 72" claimed for C-series R-2800 of P-47M.
Those figures for the R-2800 SEEM to suggest a limitation. 64” hga doesn’t seem like much when the engine is intercooled and has ADI. In actuality, that was probably very conservative rating, and not a true reflection on the limitation of the engine. It was capable of more.
The Commanding General of the Material Air Command set those limitations (64” hag) in a letter dated 26 May 1944 – Subject: Extra Boost in P-47. He wrote that 64” hga was now approved for use in the P-47 with ADI, after acknowledging that the engine could withstand 75” hga for several hours (on 100/130 grade fuel).
There may be an element of conservatism in the MAP limitations set for the Corsair with the B series R-2800 as well. Nobody seems to have thought of that. Maybe the Corsair was like the Thunderbolt in that it had a conservative rating when it was known it actually could handle a higher boost.
But if the MAP limitations for the Corsair really were set at the point just before detonation, then it appears it was because the induction system was incapable of reducing charge temperature enough to achieve more.
Or the head temperatures of the B-series R-2800 were simply too high for 67".
Obviously not. The P-47s was rated to 64” hga, and was known to be able to withstand 75” hga. 67” hga was certainly achievable if the charge temperature could have been reduced enough. The Corsairs induction system doesn’t appear to have been able to do it.
Based on this alone, we could conclude the B-series R-2800 could handle MAPs up to and in excess of 67” on 100/130 grade fuel, because the P-47 did it. If the Corsair couldn’t, it’s because of an induction system limitation, not an engine limitation.
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Originally posted by ShortyDoowap
Still, it’s not a “problem.” It was inherent in the design. Once the engine is designed, the way the detonation issue is dealt with is thru the induction system – by way of heat exchangers and ADI.
F4UDOA asked why the V-1650 could reach higher MAP than B-series R-2800. And the main reason is head cooling. At similar configuration (without ADI) B-series R-2800 was limited to about 52-54" so there is roughly 15" MAP difference. The V-1710 could reach 60" at similar configuration so we know that head cooling accounts about 6-8" of the difference. The rest can be explained with differences in compression ratio and charge cooling.
Originally posted by ShortyDoowap
So says you, with no evidence to support your position. Again, Allison and P&W felt differently enough that P&W tried to develop an aftercooler, and Allison did.
Actually the rating of the two stage V-1710 with ADI and no intercooling ie 75" is a very good and supported evidence. And also comparing these engines without ADI is another. The use of the aftercooler would have resulted only minor advantage if compared to the better head cooling.
Originally posted by ShortyDoowap
Allison knew it had to find a way to increase power in its engines to be competitive and developed the V-1710-119 (F32R) for the proposed P-51J. It was rated on 100/130 grade fuel. In order to achieve the desired manifold pressures, a huge aftercooler sat on top of the superchargers. The P-51J was not developed as the Merlin P-51 was preferred.
The last plane to use an Allison was the F-82 Twin Mustang. It didn’t use an aftercooler or intercooler, but did use ADI. It wasn’t rated on 100/130 grade fuel, but rather on 115/145 grade fuel which could tolerate higher temps before detonating.
One of the main differences between the F-serie and G-serie (used in the V-1710 powered F-82s) was lower compression ratio, which was same as in the Merlin.
Originally posted by ShortyDoowap
Fine. And I agree. But once the engine is developed, the way to avoid detonation is to cool the charge. The cooler the charge, the higher the MAP that can be tolerated.
Well, F4UDOA asked the reason and charge cooling simply can't explain the difference.
Originally posted by ShortyDoowap
And as far as the statement “B-series R-2800, it would have reached MAP close to V-1710 with similar induction” goes - it already did. For instance the maximum rating for the turbosupercharged R-2800-59 (P-47D-27 thru -40) was rated for 64” hga on 100/130 grade fuel. Maximum rating for the V-1710-111/113 (P-38L) was 60” hg on 100/130 grade fuel.
You should also mention that the P-47D utilized ADI while the P-38L did not. With ADI the P-38 should have reached 75" as tested by Allison.
Originally posted by ShortyDoowap
Now the V-1710-117 of the P-63C was rated at 76” hga on 100/130 grade fuel. It didn’t use an aftercooler or intercooler. But it used obscene amounts of ADI – more than 1.5 gallons per minute – to do it. It used so much ADI that it increased MAP by 15” hga over its dry WEP rating of 61” hga. That was how Allison chose to tackle their detonation issue.
Some how you forget here that P-47D, F4U and F6F also carried ADI for the WEP and they should have reached similar MAP as the P-63 or even a bit more because the intercooler.
Originally posted by ShortyDoowap
The only engines I think that are really directly comparable (by virtue of their induction systems), are those on the P-38 and P-47. The induction systems on the P-63 and F4U used different methods to achieve what they did.
Comparison between the P-47 and P-38 show clearly that at similar configuration V-1710 reached higher MAP as noted several times above.
Originally posted by ShortyDoowap
What I am saying here is that improvements in MAP could be obtained without improvements in head cooling.
No one try to deny that here. But I'm answering to F4UDOA's question and you should too.
Originally posted by ShortyDoowap
Lemme ask you this? What was the temperature of the mixture discharged into the engine in the Corsair’s R-2800-8 engine (6.65:1 compression ratio pistons) at 60” hga? I don’t know.
Neither do I.
Originally posted by ShortyDoowap
I think the engines are comparable enough to say that the major difference here is that the Merlin’s induction system cooled the charge better than the Allison’s so it was able to utilize higher MAPs.
The difference between V-1710 and V-1650 can be explained with compression ratio and charge cooling. But these can't explain the difference between V-1710 and B-series R-2800 or V-1650 and B-series R-2800.
Originally posted by ShortyDoowap
Obviously not. The P-47s was rated to 64” hga, and was known to be able to withstand 75” hga.
As I noted above initial rating with ADI was 56-58" later raised to 60-64".
Originally posted by ShortyDoowap
Based on this alone, we could conclude the B-series R-2800 could handle MAPs up to and in excess of 67” on 100/130 grade fuel, because the P-47 did it. If the Corsair couldn’t, it’s because of an induction system limitation, not an engine limitation.
Any engine could handle high MAP for short periods.
gripen
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Shorty, sorry for collapsing your foundations for argumentation but Gripen is entirely correct. E.g. in the P-47B the maximum allowed carburetor air temperature is 35 deg (95 deg F), i.e. well below the allowed for the Merlin.
Besides, P&W made the foolish choice to attempt high power with highish CR which is not the way to get good detonation resistance.
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Originally posted by pasoleati
Shorty, sorry for collapsing your foundations for argumentation but Gripen is entirely correct. E.g. in the P-47B the maximum allowed carburetor air temperature is 35 deg (95 deg F), i.e. well below the allowed for the Merlin.
Besides, P&W made the foolish choice to attempt high power with highish CR which is not the way to get good detonation resistance.
For comparison's sake, max carburetor air temp for the Allison V-1710-111/113 engines is 45 C (113 F).
My regards,
Widewing
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F4UDOA asked why the V-1650 could reach higher MAP than B-series R-2800. And the main reason is head cooling. At similar configuration (without ADI) B-series R-2800 was limited to about 52-54" so there is roughly 15" MAP difference. The V-1710 could reach 60" at similar configuration so we know that head cooling accounts about 6-8" of the difference. The rest can be explained with differences in compression ratio and charge cooling.
He specifically asked about the R-2800 in the F4U and F6F. And the reason is induction air cooling. You pointed out correctly that the R-2800 B in the P-47 could develop, and was rated for, 64” hga on 100/130 PN fuel. The Material Air Command directive that allowed that rating stated that same engine could withstand 75” hga for “several hours.” Therefore, the R-2800 B was capable of 64”, 67” and up to 75” hga on 100/130 fuel – with the right induction system.
The base engines for the P-47 and the F4U/F6F are virtually the same, as they are both B series engines. The main differences lie in the induction systems. If the P-47 could achieve high MAPs, and the F4U could not, both with the same base engine, then the reason was due to differences in the induction systems.
BTW, when I say induction system, I am referring to the induction/intercooler(or aftercooler) arrangement, as well as ADI if applicable.
Actually the rating of the two stage V-1710 with ADI and no intercooling ie 75" is a very good and supported evidence. And also comparing these engines without ADI is another. The use of the aftercooler would have resulted only minor advantage if compared to the better head cooling.
My point was you said the R-2800 would not have benefited much from an aftercooler. There is no evidence to support that. But there is evidence that P&W felt otherwise, as they attempted to develop an aftercooler for their R-2800, but abandoned attempts. If they didn’t think it was better, why try?
And as far as the Allison goes: the reason Allison went with ADI instead of an aftercooler was because the plane would have to fly with the added weight of an aftercooler all the time, but the ADI weight would get used up. That was their logic. It’s documented in Whitney’s book. To achieve the high MAPs with ADI alone, they had to use huge quantities of ADI fluid. The P-63C carried 25 gallons of ADI which was enough for just 15 minutes. That’s an astonishing amount of ADI.
One of the main differences between the F-serie and G-serie (used in the V-1710 powered F-82s) was lower compression ratio, which was same as in the Merlin.
That’s correct. Nevertheless, all Fs were rated on 100/130 fuel, and all Gs were rated on 115/145 fuel. 115/145 can withstand more heat than 100/130 without detonation.
Well, F4UDOA asked the reason and charge cooling simply can't explain the difference.
It certainly does, and you helped explain it. Go back to the P-47 and F4U engine comparison. You brought it up. The P-47 could achieve high MAPs and the F4U couldn’t. The main difference was in the induction systems and how well they cooled the charges.
Again, both planes had the same base R-2800 B series engine. But their induction systems were different, both in design and efficiency. If one could do it, and the other couldn’t, then the answer lies in the induction system which was responsible for creating, compressing, cooling and delivering the charge.
You should also mention that the P-47D utilized ADI while the P-38L did not. With ADI the P-38 should have reached 75" as tested by Allison.
As I stated, the 64” hga rating for the P-47 was very conservative. It was already known the engine could withstand 75” for several hours.
Some how you forget here that P-47D, F4U and F6F also carried ADI for the WEP and they should have reached similar MAP as the P-63 or even a bit more because the intercooler.
Yes, the P-47, F4U and F6F carried water. But none of them used it in the quantities the P-63 did.
To achieve 2,200 hp, the base R-2800 required a little less than 8.5 pounds of ADI per minute, which is about 1 gallon per minute. The P-63 used about 14 pound of ADI per minute, which is about 1.67 gallons per minute.
ADI flow rates between the P-47 and F4U/F6F varied. And they all carried different quantities of ADI. The plane that carried the least was the F4U, something like 10 gallons. If the flow rate had been increased to the point where it cooled the charge sufficiently to reach 67” hga, it would have used up its ADI in minutes. The P-47 carried the most, something like 30 gallons for about 25-30 minutes use. The P-63 carried 25 gallons for 15 minutes use.
The P-47, F4U and F6F appears to have sipped ADI compared to the P-63, which guzzled it.
BTW, P&W tested the R-2800 B series engine to 3,800 HP (during ADI system development). 3,800 hp was equivalent to 150” hga. In order to achieve that phenomenal power, Frank Walker (P&W’s ADI development chief) simply continued to increase ADI. No doubt that at 150” hga the air/fuel charge was dwarfed by the ADI charge.
So, there is no doubt the engine in the F4U could have reached the same MAP levels as the P-51, and could have surely exceeded them. But it’s induction system held it back. It needed more ADI, or a better intercooler, or both.
Comparison between the P-47 and P-38 show clearly that at similar configuration V-1710 reached higher MAP as noted several times above.
They weren’t rated all that different, although the P-47 with ADI was rated higher.
You stated earlier that Allison tests showed if water was used on the P-38, 75” hga could be obtained. That’s what could be obtained on the P-47 with water. The 64” limit was a conservative rating.
No one try to deny that here. But I'm answering to F4UDOA's question and you should too.
No, you want me to agree with you. I have answered it. And you’ve unwittingly supported me by bringing up the F4U/P-47 comparison.
The P-47 could obtain MAPs equal to, or in excess of, 67” hga on 100/130 grade fuel. The F4U apparently could not. Since they have the same base engine (R-2800 B), but different induction systems, then the answer lies in the induction systems. (But I do believe there is a little conservatism built into the 60" hga limit for the F4U.)
There is no reason to believe the F4U could not have been boosted to 67” hga + if it could be done in the P-47. What the F4U needed was a cooler charge, which apparently could not be provided by its induction system.
Since the P-47 and the F4U has the same heads, the answer is not the heads, but rather induction system capability.
The difference between V-1710 and V-1650 can be explained with compression ratio and charge cooling. But these can't explain the difference between V-1710 and B-series R-2800 or V-1650 and B-series R-2800.
I compared the V-1710 with 6.0:1 compression ratio pistons to a Merlin with 6.0:1 compression ratio pistons. I did it intentionally for as close a comparison as possible. You left that part out of your quote. Therefore, the difference is mainly the induction air temp.
As I noted above initial rating with ADI was 56-58" later raised to 60-64".
Reread what I wrote. The maximum rating allowed was 64” hga, even though the person who gave that directive knew the engine was capable of “75” hga for several hours." 64" hga was a VERY conservative rating.
64” hga is very close to the 67” hga of the Merlin, and 75” hga is well above it, all on 100/130 grade fuel
Any engine could handle high MAP for short periods.
gripen
“75” hga for several hours” isn’t a short time. It’s a helluva long time.
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Shorty, sorry for collapsing your foundations for argumentation but Gripen is entirely correct. E.g. in the P-47B the maximum allowed carburetor air temperature is 35 deg (95 deg F), i.e. well below the allowed for the Merlin.
Besides, P&W made the foolish choice to attempt high power with highish CR which is not the way to get good detonation resistance.
You haven’t collapsed anything, though you may like to think you have.
You fail to take into account that the most compressive stage of supercharging (and most heat inducing stage) is the 2nd stage compressor. On the R-2800, V-1710, and V-1650, the 2nd stage supercharger lies BETWEEN the carb and the engine. Therefore, the charge that flows into the engine is much hotter than the air that flowed into the carb.
In fact, both stages of the supercharger lie between the carb and the engine on the V-1650. But it has a feature the other engines don’t – an aftercooler. Therefore, a hot, compressed charge flows into the engine of the R-2800 and the V-1710. But the charge that flows into the engine on the V-1650 just flowed thru an aftercooler.
All you’ve added to this discussion is irrelevancy. You said nothing that detracts from the FACT that the F4U induction system could not provide a cool enough charge to develop 67” hga, while the P-47's could. The argument Gripen made that “the head temperatures of the B-series R-2800 were simply too high for 67" is refuted by the fact that the B-series R-2800 on the P-47 could reach and exceed 67”.
Again, the difference is in the induction/intercooler/ADI systems. The P-47 proved 67" + could be reached on a R-2800 B on 100/130 fuel. If the F4U couldn’t do it, it’s because its induction system failed to cool the charge sufficiently.
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Originally posted by ShortyDoowap
He specifically asked about the R-2800 in the F4U and F6F. And the reason is induction air cooling.
No, the induction cooling difference between the aftercooler of the Merlin and intercooler of the B-series R-2800 is very small if compared to the difference caused by cooling of the heads and compression ratio. There is about 13-15" difference in dry rating and about half of this is caused by head cooling and most of the rest is caused by CR leaving very small part to induction cooling.
Originally posted by ShortyDoowap
The Material Air Command directive that allowed that rating stated that same engine could withstand 75” hga for “several hours.” Therefore, the R-2800 B was capable of 64”, 67” and up to 75” hga on 100/130 fuel – with the right induction system.
USAF and NAVY had certainly good reasons to set the limits of these engines as they did.
And P&W had also good reasons to redesign entire engine (during war) to improve cooling.
Originally posted by ShortyDoowap
The base engines for the P-47 and the F4U/F6F are virtually the same, as they are both B series engines. The main differences lie in the induction systems. If the P-47 could achieve high MAPs, and the F4U could not, both with the same base engine, then the reason was due to differences in the induction systems.
The main difference between F4U/F6F and P-47 is that auxilary stage is mechanically driven in the first one and turbo driven in the later. Otherwise both systems had same basic features; intercooler, ADI and the the engine itself was basicly same (with known cooling problems).
There is no large difference in ratings, in the beginning these were about same and later USAF was a bit less conservative.
Originally posted by ShortyDoowap
My point was you said the R-2800 would not have benefited much from an aftercooler. There is no evidence to support that.
The ratings quoted above are very strong evidence.
Originally posted by ShortyDoowap
But there is evidence that P&W felt otherwise, as they attempted to develop an aftercooler for their R-2800, but abandoned attempts. If they didn’t think it was better, why try?
Based on evidence, it seems that benefits of the aftercooler were quite small, so why waste time on small improvements.
Originally posted by ShortyDoowap
And as far as the Allison goes: the reason Allison went with ADI instead of an aftercooler was because the plane would have to fly with the added weight of an aftercooler all the time, but the ADI weight would get used up. That was their logic. It’s documented in Whitney’s book. To achieve the high MAPs with ADI alone, they had to use huge quantities of ADI fluid. The P-63C carried 25 gallons of ADI which was enough for just 15 minutes. That’s an astonishing amount of ADI.
That is logical because the installation lacked inter- or aftercooling.
Originally posted by ShortyDoowap
The P-47 could achieve high MAPs and the F4U couldn’t. The main difference was in the induction systems and how well they cooled the charges.
Actually there is evidence that F4U with B-series R-2800 could tolerate at least 65" (see P-51 vs F4U comparison) with some modifications. The P-47D had to be modified same way to reach higher MAP (PPF kit + larger water jet).
Originally posted by ShortyDoowap
If one could do it, and the other couldn’t, then the answer lies in the induction system which was responsible for creating, compressing, cooling and delivering the charge.
The F4U and P-47 with B-series R-2800 could both reach higher MAP than ratings by USAF and NAVY. But there certainly was good reasons for given ratings.
Besides, the dry rating for the P-47 seem to be lower than for F4U/F6F.
Originally posted by ShortyDoowap
Yes, the P-47, F4U and F6F carried water. But none of them used it in the quantities the P-63 did.
To achieve 2,200 hp, the base R-2800 required a little less than 8.5 pounds of ADI per minute, which is about 1 gallon per minute. The P-63 used about 14 pound of ADI per minute, which is about 1.67 gallons per minute.
Some how you forget again that P-47 featured intercooler just like F4U/F6F.
Originally posted by ShortyDoowap
BTW, P&W tested the R-2800 B series engine to 3,800 HP (during ADI system development). 3,800 hp was equivalent to 150” hga. In order to achieve that phenomenal power, Frank Walker (P&W’s ADI development chief) simply continued to increase ADI. No doubt that at 150” hga the air/fuel charge was dwarfed by the ADI charge.
USAF and NAVY did not rate engines based on bench test with special cooling devices but ratings were for actual installations.
Originally posted by ShortyDoowap
So, there is no doubt the engine in the F4U could have reached the same MAP levels as the P-51, and could have surely exceeded them. But it’s induction system held it back. It needed more ADI, or a better intercooler, or both.
The limiting factor was head temperature in the given installations (P-47, F4U and F6F). After short time heads would overheat and cause detonation.
Originally posted by ShortyDoowap
No, you want me to agree with you. I have answered it. And you’ve unwittingly supported me by bringing up the F4U/P-47 comparison.
The difference between inter- and after cooling simply can't explain the difference.
Originally posted by ShortyDoowap
I compared the V-1710 with 6.0:1 compression ratio pistons to a Merlin with 6.0:1 compression ratio pistons. I did it intentionally for as close a comparison as possible. You left that part out of your quote. Therefore, the difference is mainly the induction air temp.
Hm... I don't know what you are trying argue. I compared the V-1710 of the P-38 (6,65:1 compression ratio) to the V-1650. That comparison has the same CR ratio as B-series R-2800.
Originally posted by ShortyDoowap
Reread what I wrote. The maximum rating allowed was 64” hga, even though the person who gave that directive knew the engine was capable of “75” hga for several hours." 64" hga was a VERY conservative rating.
Reread USAF ratings, all those engines were rated with similar standards and they certainly had good reasons for the limits.
gripen
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Ok, have at it Gripen. Now you are arguing for the sake of arguing. You shot down your own argument earlier. You are wrong, plain and simple. The difference was that the induction system couldn't deliver a charge cool enough to develop 67" hga. If you want to believe something else, and continue to argue to make yourself feel better about being wrong, that's up to you.
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Well, my opinion is that the main reason for the differences in the ratings was head cooling and that can be easily proved with dry ratings. Of course anyone has right to believe whatever he/she wants to believe.
gripen
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Gee, do you think it might have been a bit of both?:rolleyes:
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I have no anykind of data on charge temperatures of the R-2800 at intake manifolds so it's difficult to say if the charge temperature of the Merlin running at 67" was lower than the charge temperature of the B-series R-2800 running at 60" with ADI.
Anyway, comparison between dry ratings using V-1710 as baseline, indicate quite clearly that most of the difference is not caused by differerence in after- and intercooling.
Temperature values posted by pasoleati indicate that Merlin could tolerate higher charge temperatures than B-series R-2800.
gripen
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Originally posted by justin_g
Gee, do you think it might have been a bit of both?:rolleyes:
:( I tried to make that point when I said it was all interelated. I said that several times.
The point I was trying to make was that 67" ISN'T intolerable in the Corsair IF the charge is cool enough. Once the engine is designed and installed on an aircraft, the way to increase manifold pressure is to find ways to cool the charge. When the AAF want more power in the P-47, they added water, they didn't cut away the cowling.
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Originally posted by gripen
Temperature values posted by pasoleati indicate that Merlin could tolerate higher charge temperatures than B-series R-2800.
gripen [/B]
What pasoleati posted doesn't speak to the issue of charge temperature and it in no way suggests the Merlin could tolerate higher charge temperatures.
As I stated ealier, the Mustang's aftercooler, labeled here inaccurately as an intercooler, reduced charge temperature to 180 degrees F.
(http://members.cox.net/us.fighters/aftercooler2.jpg)
Specific charge temperatures MAY be irrelevant anyway. A temperature tolerable in one engine may not be tolerable in another. I suspect they are all pretty close, but I don't know for sure.
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Shorty,
F4UDOA's question was following:
Originally posted by F4UDOA
My stupid question for this year,
The R2800B engine (F4U-1/F6F-3/5) used ADI to reach 60" MAP using 100 octane Av-gas. This ADI serves two functions.
1. Cooling
2. More importantantly- Anti-detonation.
However the P-51B/D uses the same fuel (100 octane) and has a mile power rating of 61" MAP and a War Emergency rating og 67" MAP.
The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?
Claiming that cooling the charge of the R-2800 enough that it could reach 67" is not an answer to F4UDOA's question. First two replies by Milo Morai and hitech cover most of the reasons for the difference.
1. Compression ratio; 67" with CR 6:1 results roughly same total pressure as 60" with CR 6,65:1.
2. Head temp; liquid cooled V-1710 could reach 60" without ADI with same compression ratio as B-series R-2800, cooling problems of the R-2800 are also well known.
There might be difference in charge temperature but that can't be large and actually charge temperatures might had been lower in the R-2800 given the use of ADI.
Regarding the "cut away the cowling"; those aircraft utilized NACA cowling so cutting away something does not mean improved cooling. Probably cowlings were made to give maximal cooling allready.
Regarding the intake temperature; the single stage Merlins did not utilize charge cooling and these could still reach 67" or even +25lbs (grade 150 fuel). Note that engine stage of the R-2800 (ie neutral blower or second stage in two stage systems) at 60" had FTH around 1k with RAM (F4U-1) while the single stage Merlins (as an example in Mosquito) had FTH with RAM well over 10k at +18lbs.
gripen
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Gripen, you are trying to make this harder than it is.
You are STILL ignoring your own argument you made earlier. The P-47 with the R-2800 B engine could reach those high MAPs, and more, on 100/130. The F4U didn't. Later you stated something like the R-2800 B couldn't tolerate 67" hg. That's absolutely wrong.
The fact is that the engine in the F4U-1 COULD tolerate 67". All it needed was a cooler charge. But the limtiation of the induction system prevented that. The Corsair carried a tiny amount of ADI compared to other comptempory planes: 10 gallons vs 16 (Hellcat), 30 (Thunderbolt), 25 (King Cobra). An increase in ADI flow would have cooled the charge more making higher MAPs tolerable, but it would have used up its ADI in minutes.
You can talk about compression ratios, NACA cowling, inlet air temperature all you want. It doesn't detract from the fact that to achieve higher MAPs, a cooler charger was needed, and the Corsair was pretty much at ther limit of how much it could cool the charge. If it could cool it more, then 67" would have been very tolerable in the engine.
Your argument that the R-2800 B couldn't tolerate 67" is nonsense.
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I understand what Shorty is saying now. The lack of an aftercooler is what limited the boost. I'll give an example of one of my cars since it is something I have firsthand data on and it relates directly to what we are talking about on a theoretical level.
Stock my car has no aftercooler/intercooler. The intake charge goes directly from the turbo to the intake manifold. The most boost I can safely run in that configuration is around 18PSI and the intake charge is above 300deg F. With a large intercooler (aftercooler in really, but people call them intercoolers) I can not only run more PSI (up to 23PSI, but 20PSI makes just as much HP with lower intake charge temp) but the charge temp is down around 210-220 deg F. More PSI and lower charge temp because of an aftercooler, which the F4U lacked.
What Shorty is saying (I think maybe I'm wrong) is that the lack of an aftercooler caused by the limitations of space to locate it in the F4U and the resulting inability to further cool the intake charge is what limited boost on the F4U, not an inherent problem in the design of the R-2800.
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Originally posted by ShortyDoowap
Gripen, you are trying to make this harder than it is.
I don't know what might mean, I'm answering to F4UDOA's question but you are not.
Originally posted by ShortyDoowap
You are STILL ignoring your own argument you made earlier. The P-47 with the R-2800 B engine could reach those high MAPs, and more, on 100/130. The F4U didn't. Later you stated something like the R-2800 B couldn't tolerate 67" hg. That's absolutely wrong.
There is evidence that B-series R-2800s were tested (both planes, P-47 and F4U) at more than 60" or 64" but that required increased amount of ADI + other modifications. USAF or NAVY never rated engines at higher MAP (except with grade 150 fuel). Apparently there was problems, cooling of the heads being the most probable.
Originally posted by ShortyDoowap
Your argument that the R-2800 B couldn't tolerate 67" is nonsense.
Well, USAF and NAVY probably had very good reasons for their ratings. Note that C-series R-2800 was rated up to 72", Merlin up to 80" and V-1710 up to 75" with similar standards.
gripen
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Grits, I'm not saying the the Corsair's R-2800 necessarily needed an aftercooler to achieve 67". I'm simply saying it needed a cooler air/fuel charge. That can be tackled in a number of ways, the easiest being to increase the amount of ADI injected into the engine. In tests the R-2800 B series ran at 150" hg, developing well over 3,000 hp. The T-bolt was authorized to operate at 64" hg, and could tolerate 75" hg for several hours. So there is no reason to believe 67" was out of the question for the Corsair.
There was nothing inherently wrong with the Corsair's engine. (Now I am saying that.) It just appears the limits of its intercoolers and ADI system to cool the charge had been reached for 100/130 grade fuel. Had someone endeavored to install a larger ADI reservoir and increase ADI flow to the engine, or undertaken a more difficult task of increasing intercooler efficiency, then 67" could have easily been obtained.
67" isn't all that high, whether its obtained with 6.0:1 or 6.65:1 compression ratio pistons.
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OK, I got ya now, I was misunderstanding what you were trying to say. I agree 100%.
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F4UDOA’s question was: The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?
The answer was that its fuel charge was sufficiently cool to avoid detontation at that manifold pressure. In the P-51’s case, it was due to a very efficient aftercooler.
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Originally posted by ShortyDoowap
In tests the R-2800 B series ran at 150" hg, developing well over 3,000 hp.
That was bench test with special cooling devices as noted above.
Originally posted by ShortyDoowap
The T-bolt was authorized to operate at 64" hg, and could tolerate 75" hg for several hours.
As noted above the P-47D required modifications to reach 64". The limiting factor was cooling of the heads which was also the reason why P&W redesigned entire engine during war.
Below are the ratings used by 8th AF at spring 1944 (they had their own ratings). Note that modifications were required even for increase from 58" to 61".
(http://www.onpoi.net/ah/pics/users/852_1136366286_p47a.jpg)
Originally posted by ShortyDoowap
There was nothing inherently wrong with the Corsair's engine. (Now I am saying that.) It just appears the limits of its intercoolers and ADI system to cool the charge had been reached for 100/130 grade fuel. Had someone endeavored to install a larger ADI reservoir and increase ADI flow to the engine, or undertaken a more difficult task of increasing intercooler efficiency, then 67" could have easily been obtained.
As noted above the F4U-1 was tested at 65" with similar modifications as used in the P-47 (increased water flow). Below is a bit from Slaker's site showing use of the 65".
(http://www.onpoi.net/ah/pics/users/852_1136367341_f4ub.jpg)
Such rating was not authorized for service use probably for cooling problems.
Originally posted by ShortyDoowap
F4UDOA’s question was: The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?
The answer was that its fuel charge was sufficiently cool to avoid detontation at that manifold pressure. In the P-51’s case, it was due to a very efficient aftercooler.
As noted above by several people, the main reason were:
1. Compression ratio
2. Good cooling of the heads.
3. Charge cooling.
As noted above, the charge cooling was not needed in single stage Merlins for +18lbs which underlines limitations of the B-series R-2800. The engine stage of the R-2800 supercharger compressed air at amount less than 2 at 60" while the super charger of the single stage Merlins compressed air at amount over 3 at +18lbs.
gripen
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That was bench test with special cooling devices as noted above.
Just water injection. That’s all it took.
As noted above the P-47D required modifications to reach 64". The limiting factor was cooling of the heads which was also the reason why P&W redesigned entire engine during war.
Of course it needed modification. Whenever a boost increase is needed, some sort of modification is required.
Below are the ratings used by 8th AF at spring 1944 (they had their own ratings). Note that modifications were required even for increase from 58" to 61".
If the original boost had been limited to 42”, it would have required modification to achieve 58”. Do you know how a P-47 throttle works?
BTW:
(http://members.cox.net/us.fighters/boost.jpg)
As noted above the F4U-1 was tested at 65" with similar modifications as used in the P-47 (increased water flow). Below is a bit from Slaker's site showing use of the 65".
Such rating was not authorized for service use probably for cooling problems.
Yet nowhere in the report from which that excerpt comes does it state the Corsair overheated.
As noted above by several people, the main reason were:
1. Compression ratio
2. Good cooling of the heads.
3. Charge cooling.
As noted above, the charge cooling was not needed in single stage Merlins for +18lbs which underlines limitations of the B-series R-2800. The engine stage of the R-2800 supercharger compressed air at amount less than 2 at 60" while the super charger of the single stage Merlins compressed air at amount over 3 at +18lbs.
gripen [/B]
LOL, why does the capability of the Merlin “underline” a limitation of the R-2800? In fact, there was no inherent limitation. As stated, the engine was perfectly capable of 67” or more on 130 grade fuel as long as the charge was kept cool enough to avoid detonation.
You could have taken the Corsair and made no other alteration to it except increase the flow of ADI and link the throttle to achieve 67” and it would have been perfectly capable of achieving 67”.
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Check Torque Meter issue "Volume 2, NUmber 3", page 18. It has Fuel-air ratios for various engines at various airflows. It clearly shows than on a same fuel the V-1710-111 needs far leaner charge to operate at high power settings than even a C-series R-2800 (that had much better head cooling due to forged heads as Gripen said) as it requires far less overrich mixture as internal coolant. Thus there is substantial difference in their respective cooling capabilities.
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Flakbait claims that 450 deg F (232 deg C) was supposedly a temp limit for aluminium heads. That is wholly untrue. E.g. the Centaurus V (that has aluminium heads) has a maximum continuous lean mixture limit of 300 deg C. The Centaurus tolerates the higher temperature due to the vastly better sleeve concept.
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As noted above, the charge cooling was not needed in single stage Merlins for +18lbs which underlines limitations of the B-series R-2800.
So the charge cooling (aftercooler) was not needed in the single stage Merlins. The Mustang didn't have a single stage Merlin. The Mustang's Merlin had a two-stage supercharger. Two stages compress much more, and impart much more heat, than a single stage supercharger. Therefore, an aftercooler was required on the Mustang's two stage Merlin.
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According to "Rolls-Royce and the Mustang" by David Birch, the charge temp in a 60 srs Merlin (probably at +18lb) was reduced from 200 deg C to 120 deg C by the aftercooler. I.e. where did the 180 F figure originate from? That 120 deg C figure is also mentioned in the Spitfire bible.
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The pic comes from "Vees For Victory" from the chapter The Rolls Royce Merlin V-1650 vs. the Allison V-1710.
The text of the book states air discharged from the supercharger discharged at 396o F. The temperature of the charge injected into the engine "never exceeded 212o F."
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Originally posted by ShortyDoowap
Just water injection. That’s all it took.
That was a bench test, certainly not with the engine installation of the P-47 or F4U/F6F.
Originally posted by ShortyDoowap
BTW:
(http://members.cox.net/us.fighters/boost.jpg)
There apparently was problems because 75" or anything over 64" (grade 130 fuel) was not authorized by USAF. Besides that might had been bench testing again.
Originally posted by ShortyDoowap
Yet nowhere in the report from which that excerpt comes does it state the Corsair overheated.
Well, there apparently was problems because such rating never entered service. And P&W improved cooling of the heads large amount in the C-series R-2800.
Originally posted by ShortyDoowap
LOL, why does the capability of the Merlin “underline” a limitation of the R-2800? In fact, there was no inherent limitation. As stated, the engine was perfectly capable of 67” or more on 130 grade fuel as long as the charge was kept cool enough to avoid detonation.
The single stage Merlins could reach without charge cooling 67" and compress charge more than 1,5 times more than B-series R-2800 in the F4U-1 (neutral blower ie single stage configuration 54"). That underlines very well the effect of the good head cooling.
gripen
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Still, the answer to the question is its fuel charge was sufficiently cool to avoid detontation at that manifold pressure. In the P-51’s case, it was due to a very efficient aftercooler.
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I wonder if you could ever admit that cooling of the heads and compression ratio can explain the difference as well or better than the aftercooler.
gripen
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Hi
I just compared P-51D climb chart with 1650-7 to F4U-4 engine operating chart with a 2800-18 engine
In 8 minutes, the 1650 burns
13 gal @ 47"
22 gal @ 61"
the 2800 burns
27.2 @ 47"
37.6 @ 60"
The MAP is comparable. Now the interesting is increase of fuel consumption from 47" to 60" or 61"
1650: +70%
2800: +40%
So there are 2 possibillities:
1) the 1650 needs much more fuel at high power
2) the 1650 is much better at cruising settings.
I found some power specs and the ratio of the PW2800 to the V1650 is at given MAP:
@47" : 1700/1050 = 1.61
@60" : 2500/1490 = 1.67
So the ratio stays close together, what does not support possibillity 2. There remains possibillity 1: The V-1650 needs much more fuel at high power settings in relation to the power gain, and imo this can only explained by one theory: Without the possibillity of waterinjection, the V-1650 must use a large amount of the fuel for innercooling effects at high power settings.
niklas
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Originally posted by gripen
I wonder if you could ever admit that cooling of the heads and compression ratio can explain the difference as well or better than the aftercooler.
gripen
If you took the aftercooler off the two stage merlin, would 67" have been possible on 100/130 PN fuel????????
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Originally posted by ShortyDoowap
If you took the aftercooler off the two stage merlin, would 67" have been possible on 100/130 PN fuel????????
The V-1710 could do about same total pressure with intercooler and still having lower SFC than Merlin. So if assume that RR had choosen same approach as Allison and P&W, the resulting two stage Merlin would have needed more intercooling capacity and installation to airframes, allready in production, would not have been so easy.
gripen