Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: oakranger on December 05, 2011, 11:22:48 PM
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Try to find photos of this particular 190. Interesting information behind the reason of it, but i guess it was only experimental. Any input?
(http://i393.photobucket.com/albums/pp20/skbluestem/fw190v18aw_title.jpg)
(http://i393.photobucket.com/albums/pp20/skbluestem/190C-Pic01s.jpg)
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(http://fw190.hobbyvista.com/v18.jpg)
(http://i101.photobucket.com/albums/m44/phoenix7187/fw190c8dn1.jpg)
(http://i82.photobucket.com/albums/j273/Bilkeau/Scan10169cr.jpg)
The FW 190 V18 was designed and built as a prototype for the high-altitude FW 190 C, and in V18/U1 form it had the DB 603 A engine driving a four-bladed propeller. The FW 190 C was a projected high-altitude fighter that never came to fruition; even so five prototypes were completed, the FW 190 V18, V29, V30, V32 and V33. Each of these aircraft had DB 603 inline engines, annular radiators, Hirth 9-2281 turbochargers and four-bladed propellers. The FW 190 V18 was coded CF + OY and received a white outline Balkenkreuz and Hakenkreuz. By 1944 the project had been halted by technical problems and opposition to use of the DB 603 (which was needed for other aircraft types).
V18 (W.Nr 0040) was previously used in the Hohenjager programme, and with its huge belly mounted turbo-supercharger, was nicknamed "Kangaroo".
This project came to nothing, and it was decided to convert the airframe to Ta 152H standard as part of the H-series prototype "family", but it only left the prototype shop as series production was starting, and was not used in any testing. It was used instead for pilot familiarisation, and a new wooden tail was fitted after damage sustained in a take off crash on on 23rd December 1944. (Incidentally, Ta 152H series production started after the prototypes had made just 30 hours and 52 minutes of test flights in total!)
A very intresting looking Fw-190. The bottom reminds me of the Mustang, wonder if that is where they got the Idea? Most info found through out the internet.
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A very intresting looking Fw-190. The bottom reminds me of the Mustang, wonder if that is where they got the Idea? Most info found through out the internet.
I was thinking of the same thing when i first saw the image. It sure looks like it. Great job on finding pics too. :salute
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The underside cooler is more like that of the 109H project. Large scoops were not unique to the P-51. Even the Hurricane and other 1930s designs had them.
The radiator was still around the nose (cowl flaps and all), and what you are looking at is the cooler for the turbocharger.
The system had many flaws, also relating to the reliability and cost of such a system. I believe they also had major heat issues causing failures in the ducting (the pipes you see running back) as it required special types of metal.
Overall it was found to be too heavy, too draggy, too unreliable, and too costly, considering that Germany was already developing engines with 3 stage superchargers that did the job just as well (theoretically -- these also had problems but usually on the highest third stage) or even better.
The focus was maintained on additives (MW50, GM-1, etc), higher geared engines (Jumo engine on Ta152 for example) and simply more powerful engines (DB603G which practically never manifested, for example)
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The underside cooler is more like that of the 109H project. Large scoops were not unique to the P-51. Even the Hurricane and other 1930s designs had them.
The radiator was still around the nose (cowl flaps and all), and what you are looking at is the cooler for the turbocharger.
The system had many flaws, also relating to the reliability and cost of such a system. I believe they also had major heat issues causing failures in the ducting (the pipes you see running back) as it required special types of metal.
Overall it was found to be too heavy, too draggy, too unreliable, and too costly, considering that Germany was already developing engines with 3 stage superchargers that did the job just as well (theoretically -- these also had problems but usually on the highest third stage) or even better.
The focus was maintained on additives (MW50, GM-1, etc), higher geared engines (Jumo engine on Ta152 for example) and simply more powerful engines (DB603G which practically never manifested, for example)
Reason why they took the Ta-152.
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Well the Ta152 was just one evolution of the design. There were other planes and they were also using higher-geared engines and GM-1 boost and whatnot. Ju-88S for example, relied on GM-1 for its high alt speed runs. There were also the jets and the rocket powered planes, as well. The Turbosupercharger just didn't fit with Germany at the time.
Look at the DB603, for example. On the same engine you have the one model with a FTH of about 19K with a single stage charger, and about 25K with a double stage charger. Swap out that charger to a different model and you get potentially over 30K FTH on the 603L/N (not sure if those saw the light of day outside of testing)
You could achieve the same results with existing technology.
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What I find quite extraordinary is the evolution of the cooling systems in response to the higher altitudes. To acheive these higher level flights, the cooling system had to be pressurized (closer to armstongs line...).
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What I find quite extraordinary is the evolution of the cooling systems in response to the higher altitudes. To acheive these higher level flights, the cooling system had to be pressurized (closer to armstongs line...).
When was the cooling system pressurized? Who accomplished this?
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Whats the point of the exhaust pipe being so long?
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It's not an exhaust pipe. It's taking the exhaust pressure and routing it through a turbosupercharger for high altitude performance.
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The germans did on the TA-152. The cockpit and cooling system was pressurized. Water boils at 212 at sea level, at 10k the temperature is 193 degrees. 20K, 182. The boiling point is relative to atmospheric pressure as are other things. To acheive adequate cooling, the system had to be pressurized.
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By its very nature, liquid cooling is a closed, pressurized, thing.
Your cooling system isn't affected by air pressure because it's maintained inside metal pipes. The pipes provide the pressure.
Think of it this way: When your car overheats do you open the radiator cap? Hint: Better stock up on burn cream if you try it!
We're not talking calm water boiling away due to a drop in pressure. Nor was water even used for most liquid cooling on these planes.
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When I get home I will dig through my stuff. One of the issue with high altitude flight and liquid cooled engines is the inability to cool water as a result of its boiling point decreasing in relationship to altitude. http://en.wikipedia.org/wiki/Junkers_Jumo_213 this is the wiki link, but I do have some books at home that get a bit more into the idea, one is Willy Messerschmitt, Pioneer of Aviation Design by Ebert, Kaiser, and Peters. IIRC they have some discussion on cooling challenges at altitude. More to follow.
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By its very nature, liquid cooling is a closed, pressurized, thing.
Your cooling system isn't affected by air pressure because it's maintained inside metal pipes. The pipes provide the pressure.
Think of it this way: When your car overheats do you open the radiator cap? Hint: Better stock up on burn cream if you try it!
We're not talking calm water boiling away due to a drop in pressure. Nor was water even used for most liquid cooling on these planes.
Your car runs at say, 230 degrees, why, because the gas is not allowed to expand and the fluid actually boil. So, yes it is "pressurized" in a way. But this is a car in the year 2011. The solutions developed to address this very problem were quite interesting to me from an engineering standpoint. Having tubes, radiators, blocks, gaskets, all designed to take into account the stresses of maintaining a heated fluid in its liquid state.
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Got home, nope not in the ebert book, the piece I remember seeing high altitude discussion, stemmed from the the use of MW-50 to alt, then switching to GM-1. Had something to do with engine cooling, that is why it was stuck in my mind at the time.
There is much more to this, air pressure having a lot to do with the ability of a heat exchanger to "exchange heat". Lots of stuff is out there on air cooled engines, but I am having a hard time find specifics on high altitude radiator design, inlet design, and exhaust design. The radiator has to be larger because although colder, the atmosphere is not as efficient at heat transfer (giant math stuff, nearly over my head)
http://digital.library.unt.edu/ark:/67531/metadc61946/m1/10/
Bear in mind this paper discusses air cooled engines at altitude, but the concept of heat transfer also will apply to liquid cooling if you substitute the cylinder head design and interior cowl design for radiator design.
Part of making massive power is massive cooling. There are drag engines that make 7000HP out of less than 700 Cu in, but only for 4 seconds or so. Making 1000HP for hours, now that is cool, literally.
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It wasn't that big a departure in practical application. A number of Germans told of how you could just run at higher settings all the time without fear of overheating. It was frigidly cold, if you recall, and that helps cool things down a lot more than the thinner less efficient air.
So I have no doubt you may have quite a basis in fact and truth, but in practicality I have never heard of any plane in WW2 that had problems cooling at very high alts, or any special "pressurized" liquid cooling system in any of the planes that did it.
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IIRC,the P38 had issues with too much cooling at higher alts in European theater.
:salute
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Got home, nope not in the ebert book, the piece I remember seeing high altitude discussion, stemmed from the the use of MW-50 to alt, then switching to GM-1. Had something to do with engine cooling, that is why it was stuck in my mind at the time.
There is much more to this, air pressure having a lot to do with the ability of a heat exchanger to "exchange heat". Lots of stuff is out there on air cooled engines, but I am having a hard time find specifics on high altitude radiator design, inlet design, and exhaust design. The radiator has to be larger because although colder, the atmosphere is not as efficient at heat transfer (giant math stuff, nearly over my head)
http://digital.library.unt.edu/ark:/67531/metadc61946/m1/10/
Bear in mind this paper discusses air cooled engines at altitude, but the concept of heat transfer also will apply to liquid cooling if you substitute the cylinder head design and interior cowl design for radiator design.
Part of making massive power is massive cooling. There are drag engines that make 7000HP out of less than 700 Cu in, but only for 4 seconds or so. Making 1000HP for hours, now that is cool, literally.
The GM-1 system was pressurized to turn the gas into a liquid I think when this happens the gas super cools to -127F. It helped with cooling
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Actually I think the GM when combusted created more oxygen in the cylinder, thus giving more power up where there wasn't enough power even with a super charger. GM-1 was basically nitrous oxide for street rods today.
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Officially leaving my field (geological engineering) and opening a can of worms. My point is the air at altitude does not have the ability to act as a heat transfer to the extent lower altitude atmosphere is able to. Despite very low temperatures if the engines design was not developed with high altitude operations in mind there may have been cooling problems. At least that is what I got from the article I attached, which covered radial engine cooling at high altitudes.
A chart I would l love to see is the horsepower of the 213 at 35k. I am curious what the loss in hp is in comparison to sea level. Again if there are any aero guys who want to get into thermodynamics I would enjoy the read .... Lesson
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As in.... Jumo 213?
(http://www.hitechcreations.com/components/com_ahplaneperf/genchart.php?p1=40&p2=64&pw=2>ype=0&gui=localhost&itemsel=GameData)
Note I put the Spit14 in there as well. I don't believe anything special was done to the cooling design other than making the radiators slightly deeper because of the higher-powered engine. That wasn't a HF version of it, either, just a basic F.XIV.
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As in.... Jumo 213?
(http://www.hitechcreations.com/components/com_ahplaneperf/genchart.php?p1=40&p2=64&pw=2>ype=0&gui=localhost&itemsel=GameData)
Note I put the Spit14 in there as well. I don't believe anything special was done to the cooling design other than making the radiators slightly deeper because of the higher-powered engine. That wasn't a HF version of it, either, just a basic F.XIV.
Intresting
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On the chart, speed does not equal HP. What HP is the 213 generating at 35K?
Speed can have more to do with aerodynamic efficiency than HP. Part of that aerodynamic efficiency is how to manage the larger cooling requirements (surface area=drag). The question on these charts is: Is the disparity in speed a result of aerodynamic efficiency, or the ability to cool the engine effectively to operate in a higher HP range at altitude?
An analogy:
When I cool my beer wort, if I slow the flow of water, the wort chills faster, than if I accelerate the flow of water though the chiller. The reason, a greater amount of heat transfer takes place between the water and the wort, because there is more time for it to occur. At altitude, there is a great deal less in terms of particles to effect this heat transfer. Just because it is cold does not equal heat transfer. Think of the temperature of the ISS on the sunny side vice the shade side { http://science.nasa.gov/science-news/science-at-nasa/2001/ast21mar_1/ }, both exist in a vacuum and extremely cold "outside" temperatures, yet the sunny side can overheat becasue there is nothing for the heat to transfer to.
As discussed earlier, it was these design considerations I find fasinating. I really wish I knew more about the math behind them. The engineering decisions between say radiator area creating drag, vice enhancing cooling and enabling more HP. Pick one if you know what I mean.
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1580 HP at 3,000 Rpm my book has this listed for Climb to alt and Combat for the jumo 213 E/E1 that was in 152s.
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Dirt,
try looking up the BV 155,it has a unique cooling system.
:salute
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There is just a teaser (one page or so) in the Messerschmitt book I mentioned earlier. It sure was a neat looking, and huge plane. My current love affair is with the JU-288. I have already built one scale model of it, as a proof of concept, now I need to make it a bit bigger and a bit more detailed. Read up on the engines in that biscuit, not the BMWs, the Jumos.....
Another interesting aspect of high altitude flight is propeller design. Another discussion completely.
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Everyone here needs to take a thermodynamics engineering course. It's the one class I consider the most pratical in real world engineering. It's the study of how heat and energy work.
And how come no one mentioned anything about the radiator fluid used? This had to be used to decrease the freezing/increase the boiling point temperatures.
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The P51 is a good example of dealing with the problems of high-altitude cooling. The scoop has a relatively small opening which expands in front of the radiator. This expansion slows the air and increases its pressure as it passes through the radiator and improves cooling at high altitude and speed. The remainder of the duct then converges which reaccelerates the air to the exit at the rear to approximately the same speed and pressure as the local airflow. This alone reduces drag but there is also the expansion of the air heated by the radiator which actually offsets even more of the cooling drag. You could consider it a primative ram jet. The overall cooling system still adds drag but only a fraction of the drag created by more conventional designs while providing an efficient cooling system.
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The P51 is a good example of dealing with the problems of high-altitude cooling. The scoop has a relatively small opening which expands in front of the radiator. This expansion slows the air and increases its pressure as it passes through the radiator and improves cooling at high altitude and speed. The remainder of the duct then converges which reaccelerates the air to the exit at the rear to approximately the same speed and pressure as the local airflow. This alone reduces drag but there is also the expansion of the air heated by the radiator which actually offsets even more of the cooling drag. You could consider it a primative ram jet. The overall cooling system still adds drag but only a fraction of the drag created by more conventional designs while providing an efficient cooling system.
Would this concept be similar, but improvement to what the SR-71 engine answer?
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Mace: The P-51 design actually created THRUST. The thrust overcame the drag of the radiator to begin with, for a very nice design... Essentially a drag-free radiator scoop! Not necessarily designed for high-alt. Designed for general use. It wasn't the only one like this. The MiG-3 also had a very similar design.
Dirtdart: Yes, but the speed charts are a good indicator of how much HP you're making. I've shown you a nearly linear increase up to that peak power. The question was related to LOSS in power and I was showing only a steady GAIN all the way up to FTH instead. Look at... let's see... ah-ha! The perfect example: P-40F and P-40N:
(http://www.hitechcreations.com/components/com_ahplaneperf/genchart.php?p1=118&p2=120&pw=2>ype=0&gui=localhost&itemsel=GameData)
...just to illustrate my point. These are the same airframe but with different engines. From this I can tell where they make the most power, and that at 18K the Merlin is making a helluva lot more power on 2nd speed of its supercharger than the -N's single speed can make. This speed drop is a direct correlation to the loss in power above FTH.
So the chart is helpful for getting an idea of the power curve. Though it isn't a specific number (Kilo posted one, let's use that), it does give a good idea.
I never said I'd spell it out, just gave an idea.
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Would this concept be similar, but improvement to what the SR-71 engine answer?
The principle is similar but the results are wildly different. In each case, air enters the inlet, is decelerated (in the Mustang by expansion and in the SR-71 by inlet shock waves), energy is added (in the Mustang by the radiator, in the SR-71 by fuel burned in the afterburner) and the resulting heated gas is then accelerated out the back producing thrust. The SR-71 produced tremendous amounts of trust due to the extreme heat involved but the Mustang produced only a tiny amount of thrust and only at high altitude and high speed. In fact, the "thrust" produced by the Mustang's cooling system only offsets some of the drag inherent in any radiator based cooling system, the thrust never completely offsets the cooling system drag so the net result is still increased drag. In other words, the Mustang would be faster if it had no cooling system at all but this is obviously a difficult proposition. The P51 is unique in that the cooling system design is very visible (the large, underbelly scoop) as well as effective but as Krusty mentions many other WWII aircraft used the same principle for cooling.
The main part that's relevant to the discussion of cooling effectiveness at high altitude is the issue of heat transfer from the radiator to the airstream. A radiator is affected by aerodynamics as much as any other part of the plane. All parts exposed to airflow develop a boundary layer of stagnant air near the surface. This boundary layer increases in thickness at low pressure. The same happens in a radiator and this boundary layer acts as an insulator which inhibits the transfer of heat and actually becomes a barrier inhibiting airflow. By slowing the air and increasing its pressure the boundary layers within the radiator are reduced resulting in more effective heat transfer.
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Mace thanks for explaining what I am incapable of explaining. krusty the contrast of the two p40s is great but that is also 20k which way different than 35k.
Another interesting example of trading heat for thrust is an old racing plane called the beguine (named after a song). It had wingtip radiator arranged like "ramjets".
Mace where do you reckon the cooling for the mustang was optimized. There was a YouTube link I saw recently about two mustangs flyin cross country to set the record back in the 40s. I wonder what their flight profile was would probably answer the optimum speed altitude for that airplane.
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What, radiator creating thrust?
Thats how?
At the alt of 10km, the air temperature is around -50/-70 Celsius, whats around 210 Kelvin.
Even a pressurized water cooling system cant be warmer than 130-150 celsius (no more than 450 kelvin anyway). There is no way the radiator could warmen up the 210 Kelvin air to like 300-350 (what would mean a temperature-propotional expansion, effectively the air would exhaust 350/210 times faster than it enters the radiator). Since the air spends only a moment in the radiator, its physically next to impossible to build an effective radiator like this. Also, the more effective the radiator is, the more drag its structure indicates (inside that box under the belly).
So, it will have some effect, especially at high altitudes where the difference in the temperature is larger, but i dont think it can generate "thrust" compared to a clean airframe (true, theres no place for the cooling then...)
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The principle is similar but the results are wildly different. In each case, air enters the inlet, is decelerated (in the Mustang by expansion and in the SR-71 by inlet shock waves), energy is added (in the Mustang by the radiator, in the SR-71 by fuel burned in the afterburner) and the resulting heated gas is then accelerated out the back producing thrust. The SR-71 produced tremendous amounts of trust due to the extreme heat involved but the Mustang produced only a tiny amount of thrust and only at high altitude and high speed. In fact, the "thrust" produced by the Mustang's cooling system only offsets some of the drag inherent in any radiator based cooling system, the thrust never completely offsets the cooling system drag so the net result is still increased drag. In other words, the Mustang would be faster if it had no cooling system at all but this is obviously a difficult proposition. The P51 is unique in that the cooling system design is very visible (the large, underbelly scoop) as well as effective but as Krusty mentions many other WWII aircraft used the same principle for cooling.
The main part that's relevant to the discussion of cooling effectiveness at high altitude is the issue of heat transfer from the radiator to the airstream. A radiator is affected by aerodynamics as much as any other part of the plane. All parts exposed to airflow develop a boundary layer of stagnant air near the surface. This boundary layer increases in thickness at low pressure. The same happens in a radiator and this boundary layer acts as an insulator which inhibits the transfer of heat and actually becomes a barrier inhibiting airflow. By slowing the air and increasing its pressure the boundary layers within the radiator are reduced resulting in more effective heat transfer.
OK, i knew thatthe SR-71 compacts the air giving it the ability. Thanks :salute
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What, radiator creating thrust?
Known as the Meredith Effect....
Here is a forum post on it. Quite intresting to read.
http://www.ww2aircraft.net/forum/flight-test-data/meredith-effect-p-51-a-16845.html
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Mace, you're right about boundary layers, but not about the end conclussion. The reason the P-51 scoop is offset from the fuselage with a fillet is to set it out from the boundary layer to prevent any problems. The layers is small, even at lower altitudes. The P-51 scoop has no problems at any alt unless it recieves a bullet. Then it's going down one way or another, and fast.
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Known as the Meredith Effect....
Thanks!
Trying to find a mathematical formula to calculate the effectiveness, but still there are too much unknowns...
In ideal case: (mass-flowcooling water)*(specific heatwater)*(deltaTwater)=output thrust. right?
There are middle phases as the expansion of the airflow, the losses cant be as high there...
The overall effective thrust may be a decent number... but the radiator itself causes some drag too, no im not sure.
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The layers is small, even at lower altitudes. The P-51 scoop has no problems at any alt unless it recieves a bullet. Then it's going down one way or another, and fast.
The scoop is optimized to provide the required amount of air to cool the radiator, the flow of air is regulated by the exhaust vent behind the radiator. If the radiator is hit, then OK plane is hurting, the scoop...eh who cares.....
http://www.air-racing-history.com/aircraft/Beguine.htm
As mentioned by mace, the word thurst is used very loosely. It means it overcame drag, but bu no means a "engine".
Great discussions gents.
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Read the article posted in the linke beau32 provided, dirt. (if you haven't already)
It's basically 1 step shy of a ramjet. It's a very measurable thrust. Very interesting stuff.
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Dammit...all the security stuff on our computers is not letting me see the videos.
http://history.nasa.gov/SP-445/ch5-5.htm
http://contrails.free.fr/refroid_meredith_en.php (Authors original work)
"Mustang, this jet of heated cooling air reduced cooling drag to almost
nothing. It did not eliminate it entirely, but it reduced it to the
point where cooling drag was merely "3% of the thrust of the
propeller." Corky Scott
From what I can read on the net, at any rate, leads me to believe the best a radiator based system could do was overcome drag induced by the scoop/inlet/exhaust. Merediths study did give rise to the exploration of the ramjet. This is very interesting and I think I may head down to the library (I am at the US Army Engineer School) and see what I can dig up on this. We actually have a decent library.
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Mace, you're right about boundary layers, but not about the end conclussion. The reason the P-51 scoop is offset from the fuselage with a fillet is to set it out from the boundary layer to prevent any problems. The layers is small, even at lower altitudes. The P-51 scoop has no problems at any alt unless it recieves a bullet. Then it's going down one way or another, and fast.
You misunderstand. I was not talking about the fuselage boundary layer, I'm talking about the boundary layer created IN the radiator core itself. Basically, a radiator core is a series of flat tubes and the air flows through the slots between. A boundary layer forms on these tubes as well insulating them from heat transfer (a thermal boundary layer) and, when it gets bad (i.e., lower pressures), it effectively reduces the amount of space between them to the point that the airflow is restricted. Also consider the increasing parasitic drag which rising exponentially relative to speed. In effect, the radiator essentially becomes just a big speed brake with very little cooling capability.
One option is to move the tubes further apart but then you reduce the cooling density (amount of cooling fluid that can flow through a specific size radiator) and you still have the issue of increased form drag relative to speed. The radiator can be increased in size (or multiple radiators used) but then you have more cooling drag to deal with and more need for greater horsepower and then more need for cooling, etc., etc. It's a typical issue with aircraft design, tradeoffs must be made. In this case, the additional complexity (and weight) of a cooling "system" of scoops, plenums, and exhausts can be employed to increase the efficiency of a smaller radiator by employing Bernouli's law to reduce the speed and increase the density of the air at the radiator face to allow it to operate efficiently while also reducing cooling drag.
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As HoHun points out in that thread It would in fact more properly be called the "Junkers effect" as Junkers patented the diffusor-radiator-jet combation as "Düsenkühler" ('jet cooler') in DRP 299799 on 17 January, 1915. (Von Gersdorff et al., "Deutsche Flugmotoren und Strahltriebwerke, p. 196.)
The principle obviously was well-known in the English-speaking part of the aviation industry as well. "Fundamentals of Fighter Design" by Ray Whitford notes (p. 61): "In 1926 it was realized that airflow through the radiators on liquid-cooled engines could, if properly ducted, eliminate the cooling drag and even produce a little thrust at speeds above 260 kts (483 km/h)."
The P-51's radiator design might have been more effective than most, but all WWII radiator designs were "jet-coolers".
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The scoop provides measurable thrust but it only partially offsets the drag created by it.
This is why the reno planes are starting to show up without scoops at all.
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Anybody got any detailed pictures of the P-51D scoop, especially the internal structure and the radiator itself? Pages from a specific book illustrating the key features would be most helpful.
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Google is your friend: http://www.pprune.org/aviation-history-nostalgia/387708-napier-heston-belly-scoop-first-one.html
-C+
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Read the article posted in the linke beau32 provided, dirt. (if you haven't already)
It's basically 1 step shy of a ramjet. It's a very measurable thrust. Very interesting stuff.
I read the stuff, but again I am a bit confused as to why you say this. Everything I have read refers to the effect as dimininshing the affect of drag induced by a radiator. Nothing I have seen say it offers thrust which would then equal more speed. Can you please clarify?
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I read the stuff, but again I am a bit confused as to why you say this. Everything I have read refers to the effect as dimininshing the affect of drag induced by a radiator. Nothing I have seen say it offers thrust which would then equal more speed. Can you please clarify?
Not to be overly simplistic but there are two forces that act along the longitudinal axis of an aircraft, thrust and drag. In level flight, any force which tends to move the aircraft forward is thrust and any that impedes its forward motion is drag, right? The only ways to make any airplane faster is to increase thrust or decrease drag (or both). A good cooling system would be designed for minimum drag and the P51's does this. In addition, the P51 uses the expansion of gas caused by the heat from the radiator to increase the velocity of the air exhausted by the system through a relatively small opening (i.e., a "nozzle") to produce a small amount of thrust. It doesn't offset the entire amount of cooling system drag but it is still a force pushing the aircraft forward, i.e., thrust. So, the P51's system not only reduces net drag but increases net thrust. The net result is increased speed.
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and drag is a quadratic equation. If you want to go twice as fast, you need 4x horsepower. It makes more sense to try and decrease drag before adding more power (look at the La5/La7. Same engine, less drag.)
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I don't believe the scoops created any thrust. I know P-51's seem to dive faster with holes punched in them though. :devil