Aces High Bulletin Board
General Forums => Wishlist => Topic started by: BnZs on October 14, 2009, 08:32:02 PM
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IL 2 is wrong. All P-38L models, beginning with the P-38L-1-Lo, were fitted with the Allison V-1710-F30. The preceding P-38J models, from the P-38J-1-Lo were equipped with the Allison V-1710-F17. The V-1710-F17 was rated at 1600HP at WEP, where as the V-1710-F30 was rated at 1725HP at WEP, for a difference of 125HP per engine, or 250HP per plane. The P-38J was rated at 421MPH at WEP, with 250HP less than the P-38L. It would be odd to say the least that a nearly identical plane with a very small increase in weight and a 250HP increase would be as slow or slower.
As a side note, in 1943, Allison developed the V-1710-G6 series engines. These engines were rated at 1725HP at military power with a two speed two stage supercharger and 2250HP at WEP with 100" of boost on water/methanol injection and 115/145 fuel. That was without the benefit of a turbocharger.
That AHII chart, by the way, is a chart for planes in a game, where as the discussion was about real aircraft.
Apparently the "WEP" setting for the P-38L in AHII actually reflect military power. Therefore, I propose the P-38L be allowed to run at its current "WEP" setting (really military) continuously, as is the case with all other plane's military power settings in-game.
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I think this is a game concession thing because if the engines were run at FMP for five minutes it was risking engine fires and wrecked turbo-superchargers.
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I think it's limited in the game to the standard limitations. When you hear about 1700hp you have field-modified and non-standard engine ratings being used. It was rampant with certain groups, and seems to have been done regularly on the P-38s.
AH models the "standard" not the "souped up hotrod", so that's probably why we have this limitation.
P.S. Our P-38 J/L make about 420mph already on WEP. Just for reference to the quote above.
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I think it's limited in the game to the standard limitations. When you hear about 1700hp you have field-modified and non-standard engine ratings being used. It was rampant with certain groups, and seems to have been done regularly on the P-38s.
AH models the "standard" not the "souped up hotrod", so that's probably why we have this limitation.
P.S. Our P-38 J/L make about 420mph already on WEP. Just for reference to the quote above.
The point is that Ls are running around at what amounts to their "mil" power settings. Not asking for any extra boost, just seems only fair they be allowed to do it continuously, like every other plane in the game.
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You want the P-38L to adopt the military rating of an engine that it did not use? :huh
As for WEP, 1725HP @ 3200 rpm was Allison's rating but that was not authorized for service use. That's why the flight manual lists WEP at 1600 hp @ 3000 rpm and why it is that way in the game.
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hey, why not give them unlimited WEP, but if WEP is on for more then 5 minutes, both engines catch fire and explode! that would be a compromise! :D
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I will get my timer.
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I think it's limited in the game to the standard limitations. When you hear about 1700hp you have field-modified and non-standard engine ratings being used. It was rampant with certain groups, and seems to have been done regularly on the P-38s.
AH models the "standard" not the "souped up hotrod", so that's probably why we have this limitation.
P.S. Our P-38 J/L make about 420mph already on WEP. Just for reference to the quote above.
The 1725HP rating on the -30 Allison in the P-38L is NOT a field modification. It was tuned and rated for that power at the factory. The USAAC detuned it to the same power level as the -17 engine in the P-38J.
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As for WEP, 1725HP @ 3200 rpm was Allison's rating but that was not authorized for service use. That's why the flight manual lists WEP at 1600 hp @ 3000 rpm and why it is that way in the game.
As I explained in the thread the quote was taken from. Allison and Lockheed tested and cleared the -30 at full power, but the USAAC did not.
It is not just an increase in RPM that yields the 125HP, it is mostly an increase in boost, the increase in RPM was just a minor factor.
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I hadn't read the other thread but clearly your original quote in this thread has been misread. Your "side note" was somehow transposed to mean that engine or power setting is what should be on the P-38L when you said nothing of the sort.
On the WEP, I wasn't implying anything about RPM, I only listed RPM because I wanted to differentiate them but I didn't want to look up the MP ratings. Although I'd bet that the main purpose of the RPM increase was to achieve the higher boost and that without the higher RPM that ultra high MP would be unattainable.
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The 38s we have are just fine. Now about that 38H? :)
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As Savage already talked about, the P38L engines came off the factory line at higher performance levels than the USAAC let them keep. So after the USAAC lowered their performance, lockheed sent reps out and showed mechanics how to get the original power back.
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FYI, this started over the fact that Il-2 has two P-38Ls. One that's like ours, and one called "P-38L late" that has a significantly better max TAS, and which also climbs and turns faster than the standard P-38L. It sounds to me like both sims are correct.
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As I explained in the thread the quote was taken from. Allison and Lockheed tested and cleared the -30 at full power, but the USAAC did not.
This begs the question.
Why would they reduce it to a lessor rating?
Just curious as to the logic the military had for this
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This begs the question.
Why would they reduce it to a lessor rating?
Just curious as to the logic the military had for this
Why would they remove the turbo from the P-39?
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Not a valid comparison. The P-39s didn't ship with them, and have them disabled by the USAAC.
The P-39 development reached a point where a decision was made, and that part omitted. Wrong or right, it wasn't "undo-able"...
Question is why did the USAAC limit the power settings on Allison engines. They probably had reasons. Also don't forget a lot of P-38s had some engine issues and cooling issues. When you have 2 you can still make it home on 1, though, so engine failure wasn't as costly as when a single-engine plane went down.
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Why are 38 drivers never,ever,ever,never,ever happy?
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deleted
I have to be nice.
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Question is why did the USAAC limit the power settings on Allison engines.
Short answer: Higher power meant higher boost. Higher boost meant more strain. More strain meant more time spent fixing the thing than flying it.
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Ding ding ding! We have a winnar!
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Why are 38 drivers never,ever,ever,never,ever happy?
You don't know many of us cartoon 38 drivers do ya? :)
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Why are 38 drivers never,ever,ever,never,ever happy?
Remember to run if you hear the sound of a "pegleg" coming towards you. If you wait too long, you're screwed. :uhoh
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Pegleg of doom....
PS: 38H please!
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Not a valid comparison. The P-39s didn't ship with them, and have them disabled by the USAAC.
The P-39 development reached a point where a decision was made, and that part omitted. Wrong or right, it wasn't "undo-able"...
Question is why did the USAAC limit the power settings on Allison engines. They probably had reasons. Also don't forget a lot of P-38s had some engine issues and cooling issues. When you have 2 you can still make it home on 1, though, so engine failure wasn't as costly as when a single-engine plane went down.
Krusty I'm not advocating turbos for the 39. Just pointing out that the military does some odd things from time to time. Sheesh :rolleyes:
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Krusty I'm not advocating turbos for the 39. Just pointing out that the military does some odd things from time to time. Sheesh :rolleyes:
I got your intention, but it wasn't really the same issue. One was a decision from the design phase, and one was a limitation called down after production.
But I did get your point.
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Also don't forget a lot of P-38s had some engine issues and cooling issues.
Since this is a discussion about the WEP limitations on the L and no other variant of the Lightning, comments about "a lot of other P-38s" having engine and cooling problems isn't really relevant considering those issues were corrected in the L variant.
ack-ack
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Fair enough, but I thought maybe it applied to the reasoning behind the USAAC's decision.
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The turbos were removed from the P-39 do to cooling problems, and the fact that the plane was not going to be used at High altitude. Also the USAAC could get more hours per engine before it cratered. The same reason that they De-rated the later 1710 Allisons. Even today in the modern warbirds that are using the 1710's most owners opt to have them derated so that they don't have to pay 500,000 dollars for a new one as often.
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I hadn't read the other thread but clearly your original quote in this thread has been misread. Your "side note" was somehow transposed to mean that engine or power setting is what should be on the P-38L when you said nothing of the sort.
On the WEP, I wasn't implying anything about RPM, I only listed RPM because I wanted to differentiate them but I didn't want to look up the MP ratings. Although I'd bet that the main purpose of the RPM increase was to achieve the higher boost and that without the higher RPM that ultra high MP would be unattainable.
No, the RPM had nothing to do with the manifold pressure. On an Allison with a turbocharger (it already has a crank driven centrifugal supercharger) the MAP (manifold absolute pressure) is regulated by throttle opening and the waste gate. It did not need to turn 200 RPM in order to get 10" more boost. All you need to do is open the throttle further and/or adjust the waste gate. Also, with a turbocharged engine, boost is also at least partially regulated by load. Of course, if you change the prop pitch to allow the engine to turn more RPM, you remove load from the engine, when you remove the load, the turbocharger boost often drops. My turbocharged V6 TType Regal is a prime example. If you rev the engine in neutral, it barely builds boost. If you rev it in gear, against the torque converter, loading it, it will build all the boost you can stand. The normal procedure for taking off in a P-38 is to hold it against the brakes (creating the load) until you make 50"+ of boost (a P-38 is supposed to have good enough brakes to sit still while you build that boost, although it won't do it in AH II).
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The turbos were removed from the P-39 do to cooling problems, and the fact that the plane was not going to be used at High altitude. Also the USAAC could get more hours per engine before it cratered. The same reason that they De-rated the later 1710 Allisons. Even today in the modern warbirds that are using the 1710's most owners opt to have them derated so that they don't have to pay 500,000 dollars for a new one as often.
An Allison V-1710 doesn't cost $500K. I've seen them selling for $200K or so.
The G series Allison V-1710 in the P-82 Twin Mustang is rated at a higher HP than any of the F series Allison V-1710 engines found the rest of the World War II aircraft. Two differences made a little difference. They added center counterweights to the crankshaft (F series engines got those crankshafts at times, late in the war) so that the engine was smoother and easier on bearings at higher RPM. The intake manifold was altered several times beginning with the F-17 series from the P-38J, to improve mixture distribution which prevents detonation.
The turbocharger was removed from the P-39 because the USAAC decided that the scoop and the cover for the turbocharger caused too much aerodynamic drag.
The problem with turning up the boost on a V-1710 Allison wasn't really the engine itself, especially after the updated intake manifolds. Usually it was a problem with fuel quality combined with maintenance procedures. Properly tuned an Allison V-1710 can easily run as much as 80" MAP in stock form, on decent fuel.
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Fair enough, but I thought maybe it applied to the reasoning behind the USAAC's decision.
The pre J model P-38 had problems with the leading edge mounted intercoolers, moving the intercoolers from the wings to the chin solved that, so more boost could be run, for longer periods. They also upgraded the Prestone radiators and the scoops, that solved any overheating problems.
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No, the RPM had nothing to do with the manifold pressure. On an Allison with a turbocharger (it already has a crank driven centrifugal supercharger) the MAP (manifold absolute pressure) is regulated by throttle opening and the waste gate. It did not need to turn 200 RPM in order to get 10" more boost. All you need to do is open the throttle further and/or adjust the waste gate. Also, with a turbocharged engine, boost is also at least partially regulated by load. Of course, if you change the prop pitch to allow the engine to turn more RPM, you remove load from the engine, when you remove the load, the turbocharger boost often drops. My turbocharged V6 TType Regal is a prime example. If you rev the engine in neutral, it barely builds boost. If you rev it in gear, against the torque converter, loading it, it will build all the boost you can stand. The normal procedure for taking off in a P-38 is to hold it against the brakes (creating the load) until you make 50"+ of boost (a P-38 is supposed to have good enough brakes to sit still while you build that boost, although it won't do it in AH II).
This evaluation is not exactly correct. Holding the brakes has nothing to do with building load. Holding brakes or not, the load on the prop will be exactly the same as the rpm increases with open throttle.
2nd the increased pressure is not do to the load on the car as you state, but it is do to the throttle being open more at the same RPM when the car is under load.
HiTech
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No, the RPM had nothing to do with the manifold pressure. On an Allison with a turbocharger (it already has a crank driven centrifugal supercharger) the MAP (manifold absolute pressure) is regulated by throttle opening and the waste gate. It did not need to turn 200 RPM in order to get 10" more boost. All you need to do is open the throttle further and/or adjust the waste gate. Also, with a turbocharged engine, boost is also at least partially regulated by load. Of course, if you change the prop pitch to allow the engine to turn more RPM, you remove load from the engine, when you remove the load, the turbocharger boost often drops. My turbocharged V6 TType Regal is a prime example. If you rev the engine in neutral, it barely builds boost. If you rev it in gear, against the torque converter, loading it, it will build all the boost you can stand. The normal procedure for taking off in a P-38 is to hold it against the brakes (creating the load) until you make 50"+ of boost (a P-38 is supposed to have good enough brakes to sit still while you build that boost, although it won't do it in AH II).
Your really close about how a turbo works, you just need to add 1 thing. The heat that the load generates is what actually makes the turbo spin faster, thus creating more boost. Boost is controlled by quality of the turbo itself, or a wastegate. Not all engines that are turboed have a wastegate, but most high performance ones do.
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This evaluation is not exactly correct. Holding the brakes has nothing to do with building load. Holding brakes or not, the load on the prop will be exactly the same as the rpm increases with open throttle.
2nd the increased pressure is not do to the load on the car as you state, but it is do to the throttle being open more at the same RPM when the car is under load.
HiTech
If the plane is not moving, there is a greater load on the engine. It takes a certain amount of energy to make the plane move. If that energy is produced by the engine at a given RPM at a given throttle opening, if the plane does not move at that speed, where does that energy go? In other words, at wide open throttle and 3000 RPM, an engine produces 1600HP, and the plane flies at 360MPH at sea level. If the same plane is sitting on the runway at wide open throttle and at 3000 RPM, where does the energy go?
No, on my car, and most other turbocharged cars, you cannot build the same amount of boost at wide open throttle in neutral as you can in gear and loaded against the brakes and the torque converter. If you simply open the throttle in neutral, the engine will rev with little or no load and create much less boost. Mine might make 5 psi even as high as 5000 RPM in neutral sitting still, but it will make 15 psi at 2500 in low gear sitting still.
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If the plane is not moving, there is a greater load on the engine. It takes a certain amount of energy to make the plane move. If that energy is produced by the engine at a given RPM at a given throttle opening, if the plane does not move at that speed, where does that energy go? In other words, at wide open throttle and 3000 RPM, an engine produces 1600HP, and the plane flies at 360MPH at sea level. If the same plane is sitting on the runway at wide open throttle and at 3000 RPM, where does the energy go?
The energy goes into drag on the prop. On any constant speed prop, the torque will remain the same for any set MP/RPM and Alt. With the throttle wide open holding breaks the prop using all the torque the engine can produce, or it would be gaining RPM. As the plane starts moving the engine torque will not increase the prop rpm will not change, but the pitch of the blades will change slightly to use the exact same torque as when the plane is standing still. Hence there is no difference.
No, on my car, and most other turbocharged cars, you cannot build the same amount of boost at wide open throttle in neutral as you can in gear and loaded against the brakes and the torque converter. If you simply open the throttle in neutral, the engine will rev with little or no load and create much less boost. Mine might make 5 psi even as high as 5000 RPM in neutral sitting still, but it will make 15 psi at 2500 in low gear sitting still.
One question, if you are running at 5000 RPM in neutral is the gas pedal (i.e. throttle) in the same position as when you are 5000 RPM and under load?
In a sense it is the load that is creating the extra psi, but really it is the throttle having to be opened more (hence more air moving threw engine) to hold the same RPM with the extra load. But on an airplane with a constant speed prop the load/torque does not change if you are moving or standing still.
HiTech
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The energy goes into drag on the prop. On any constant speed prop, the torque will remain the same for any set MP/RPM and Alt. With the throttle wide open holding breaks the prop using all the torque the engine can produce, or it would be gaining RPM. As the plane starts moving the engine torque will not increase the prop rpm will not change, but the pitch of the blades will change slightly to use the exact same torque as when the plane is standing still. Hence there is no difference.
One question, if you are running at 5000 RPM in neutral is the gas pedal (i.e. throttle) in the same position as when you are 5000 RPM and under load?
In a sense it is the load that is creating the extra psi, but really it is the throttle having to be opened more (hence more air moving threw engine) to hold the same RPM with the extra load. But on an airplane with a constant speed prop the load/torque does not change if you are moving or standing still.
HiTech
The easiest way to resolve this debate and for all to save face is just to give us the P-38H.
ack-ack
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I agree with ack ack. As usual.
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and here I was going to tell everyone to just fly the G and then you don't have to worry about WEP. But I like AKAK's idea more. :)
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P-38H
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SAPP tards :neener:
:cheers: