Performance at Altitude

Hello all,

One of the many things I enjoy about DCS is that the flight models tend to be so thoroughly researched that I happily cede any disagreements I think I have regarding aircraft performance. These disagreements tend to be exceedingly rare (especially compared to some other sim out there...).

With that said, the P-47 is obviously EA, so I thought I'd ask: is the high altitude performance on-par with what people were expecting? I find that the aircraft is a joy to fly below 15,000', and is quite maneuverable (although it does bleed a lot of energy to do so). However, I thought the Jug would be a real champion above 20-25,000', but I'm finding that when fighting with P-51s (for comparison) and Fw-190Ds, the Jug seems to be a bit lackluster. The engine gauges show that appropriate power is being made, but the aircraft just seems to get beat down on energy pretty quickly.

Please do not turn this into an advice thread. I am looking to get a sense of people's thoughts on the P-47's high altitude performance.

Many thanks,

Your jug is missing its water injection.

The first question has to be this.

Are the P-51's and Doras flown by humans?

Your jug is missing its water injection.

I understand that, but at altitudes where the Jug’s turbo still allows for max power while other aircraft are starting to lose quite a bit, I didn’t think it would make that big of a difference. Below 20k is another story though...

The first question has to be this.

 

Are the P-51's and Doras flown by humans?

Both have been AI on hardest difficulty. I understand people say that the AI cheats, but they’re still quite easy to defeat. Any other matchup isn’t difficult, so I’m really just judging relative performance. The AI isn’t the issue here.

I understand that, but at altitudes where the Jug’s turbo still allows for max power while other aircraft are starting to lose quite a bit, I didn’t think it would make that big of a difference. Below 20k is another story though...

 

 

 

Both have been AI on hardest difficulty. I understand people say that the AI cheats, but they’re still quite easy to defeat. Any other matchup isn’t difficult, so I’m really just judging relative performance. The AI isn’t the issue here.

The AI is the issue. The AI flies perfectly. You do not. Compare performance against humans.

More than "AI flies perfectly," the AI never bleeds energy, which is why it would seem that the player's aircraft is bleeding energy at an unreasonable rate.

I understand that, but at altitudes where the Jug’s turbo still allows for max power while other aircraft are starting to lose quite a bit, I didn’t think it would make that big of a difference. Below 20k is another story though...

 

 

 

Both have been AI on hardest difficulty. I understand people say that the AI cheats, but they’re still quite easy to defeat. Any other matchup isn’t difficult, so I’m really just judging relative performance. The AI isn’t the issue here.

Last I tested, we're able to get 64" at 2700RPM, so we should have full power, regardless of the implementation the WI system. WI allows the engine to be run at a higher pressure setting without ejecting large chunks of cylinders, but it does not, in and of itself, increase power.

What you are more likely running into is that the P-51D and Fw-190D are still extremely capable up to 20,000-25,000ft. The advantage of a turbocharger is that it is a more efficient way to extract energy from the engine, than the gear driven supercharge is, but that difference in overall power really does not start to show up until well after 20-25,000 ft, so at 25,000ft, you are still fighting them on roughly equal terms. However, by the time of the P-47D-30, from 25,000 to 30,000ft, the turbo really is not big enough, anymore, to take advantage of the extra power available, so from 25,000ft to 30,000ft, so you're really performing at the level of a late 1943/early 1944 aircraft. It's more a measure of how exceptionally good its high altitude performance was in late 1943, that that level of performance is still competitive with a 1945 aircraft.

That's the key piece of context to remember here. The P-47 developed its reputation as a high altitude fighter in 1943 and early 1944, when its primary competitors were things like the Spitfire Mk 9, which topped out at slightly above 415mph at 22,000ft, the Bf-109G-6 (without water injection) which didn't even break 400 mph at 22kft, the Fw-190A's, which generally peaked at ~400 at 20,000ft, or the Hawker Typhoon, which generally didn't even break 20,000ft.

By contrast, the P-47C/D models were chugging along at 420-430 mph at 30,000ft. 20-30 mph faster, at 10,000ft higher than pretty much everyone else on the field. And this is where the B-17's are hanging out at the time too.

If you looks at the history of the Merlin powered P-51, and the Fw-190D, they are both direct responses to the poor altitude performance of their predecessor designs, and were largely successful at it. By contrast, the P-47's high altitude performance was never and issue; it's challenge was always low altitude performance, rate of climb and range. And when you look at the key design changes from the C-2 to the D-30, that is what is reflected: an enlarge main fuel tank for extended range, new larger paddle-bladed propellers to increase the low speed thrust, higher boost limits for the engine allowing more power below the critical altitude. But we really don't see things that increase, or even really change, the high altitude performance. As near as I can tell, the turbo charger did not get more powerful until the P-47M model, and in all of the earlier models, once its past the systems' critical altitude, the power at altitude appears to be nearly the same as the 1943 D-5 version.

So to recap, in the 20-25kft range, you're only just starting to see an advantage from having a turbo instead of a super charger, but its not a large or decisive gap. Further, the P-51D, Fw-190D, and Bf-109K all have significantly improved higher altitude performance over the earlier war aircraft, while the P-47, at high altitude, is still pretty much performing where it was in 1943, so while you should see better performance, it won't be to the margin that earned the plane its original reputation.

Last I tested, we're able to get 64" at 2700RPM, so we should have full power, regardless of the implementation the WI system. WI allows the engine to be run at a higher pressure setting without ejecting large chunks of cylinders, but it does not, in and of itself, increase power.

I thought the same but after having another discussion on another forum about the same topic this chart came along (p-47 using 150oct fuel)

http://www.wwiiaircraftperformance.org/p-47/P-47D_42-26167_Power.jpg

In the graph in this test, the 65inch power is given with and without WI. There is 200hp difference according to the power curve. Around 2450hp without WI and 2650hp with WI (there is different performance in the speed graph too).

Why there is this difference in output? No idea. As you, I always thought that the WI only prevented detonation at higher settings (thus allowing that higher MP). Maybe there are other factors that make the engine developing a bigger output but, in any case, it seems that the WI is helping giving more HP at the same MP (at least in this test and with this fuel).

Water injection cools down mixture (and indirectly the engine), it is reason why power is at the same manifold pressure different.

Water injection cools down mixture (and indirectly the engine), it is reason why power is at the same manifold pressure different.

And because it's cooling the mixture, for a given pressure it will have a higher fuel/aor density. So in theory, if we control for the inlet temperature, we should get the same power for a given MP, with or without water, but since that was a test of total power, one would expect that they used the same intercooler flow for both tests.

So that begs the question, where is the Carb Air temp gauge measuring from? Before or after the WI nozzle? Given that the manuals allow up to an additional 17C in carb inlet temperature with WI activated, I'd have to guess that it is before the water injection, so we probably don't have a measure of the true charge temperature in the plane.

Given that, I suspect we would need to do specific performance at altitude tests to determine if we are or are not getting the equivalent of WI performance at this time.

Thank you,

Voyager

Last I tested, we're able to get 64" at 2700RPM, so we should have full power, regardless of the implementation the WI system. WI allows the engine to be run at a higher pressure setting without ejecting large chunks of cylinders, but it does not, in and of itself, increase power.

 

What you are more likely running into is that the P-51D and Fw-190D are still extremely capable up to 20,000-25,000ft. The advantage of a turbocharger is that it is a more efficient way to extract energy from the engine, than the gear driven supercharge is, but that difference in overall power really does not start to show up until well after 20-25,000 ft, so at 25,000ft, you are still fighting them on roughly equal terms. However, by the time of the P-47D-30, from 25,000 to 30,000ft, the turbo really is not big enough, anymore, to take advantage of the extra power available, so from 25,000ft to 30,000ft, so you're really performing at the level of a late 1943/early 1944 aircraft. It's more a measure of how exceptionally good its high altitude performance was in late 1943, that that level of performance is still competitive with a 1945 aircraft.

 

That's the key piece of context to remember here. The P-47 developed its reputation as a high altitude fighter in 1943 and early 1944, when its primary competitors were things like the Spitfire Mk 9, which topped out at slightly above 415mph at 22,000ft, the Bf-109G-6 (without water injection) which didn't even break 400 mph at 22kft, the Fw-190A's, which generally peaked at ~400 at 20,000ft, or the Hawker Typhoon, which generally didn't even break 20,000ft.

 

By contrast, the P-47C/D models were chugging along at 420-430 mph at 30,000ft. 20-30 mph faster, at 10,000ft higher than pretty much everyone else on the field. And this is where the B-17's are hanging out at the time too.

 

If you looks at the history of the Merlin powered P-51, and the Fw-190D, they are both direct responses to the poor altitude performance of their predecessor designs, and were largely successful at it. By contrast, the P-47's high altitude performance was never and issue; it's challenge was always low altitude performance, rate of climb and range. And when you look at the key design changes from the C-2 to the D-30, that is what is reflected: an enlarge main fuel tank for extended range, new larger paddle-bladed propellers to increase the low speed thrust, higher boost limits for the engine allowing more power below the critical altitude. But we really don't see things that increase, or even really change, the high altitude performance. As near as I can tell, the turbo charger did not get more powerful until the P-47M model, and in all of the earlier models, once its past the systems' critical altitude, the power at altitude appears to be nearly the same as the 1943 D-5 version.

 

So to recap, in the 20-25kft range, you're only just starting to see an advantage from having a turbo instead of a super charger, but its not a large or decisive gap. Further, the P-51D, Fw-190D, and Bf-109K all have significantly improved higher altitude performance over the earlier war aircraft, while the P-47, at high altitude, is still pretty much performing where it was in 1943, so while you should see better performance, it won't be to the margin that earned the plane its original reputation.

This was very helpful, thank you for taking the time to write all that up.

The AI is the issue. The AI flies perfectly. You do not. Compare performance against humans.

You’re offering advice without a complete understanding of what I’m saying, and what I’m asking. What you’re saying is applicable at all altitudes. I’m specifically mentioning high altitudes. The AI is easy enough to defeat at medium to low altitudes, even if they do fly “perfectly.” (Hint: regardless of their lack of energy bleed, their BFM is far from perfect.) The performance gap seems even wider at high altitude though, which is where, if anything, the gap should be closing / starting to turn in the favor of the Jug. The explanation offered by Voyager is a helpful starting point, though.

Took her up to 31,000 feet (29.92 inHg).

Compressor got to maximum rpm, and handling got really terrible.

Only got to fly straight and level at 25,000 feet.

Ok, I wasn't with much patience, but I believe if I were lighter I would be able to get to 40,000 feet; The main problem though, was handling.

Took her up to 31,000 feet (29.92 inHg).

Compressor got to maximum rpm, and handling got really terrible.

Only got to fly straight and level at 25,000 feet.

 

Ok, I wasn't with much patience, but I believe if I were lighter I would be able to get to 40,000 feet; The main problem though, was handling.

 

You are right, the handling is bad up there. Could be that terrible handling is indicative of lots of induced drag, which makes it seem like the power is lacking. I understand it’s EA though, we’ll see where this goes. Still loving the module...

Took her up to 31,000 feet (29.92 inHg).

Compressor got to maximum rpm, and handling got really terrible.

Only got to fly straight and level at 25,000 feet.

 

Ok, I wasn't with much patience, but I believe if I were lighter I would be able to get to 40,000 feet; The main problem though, was handling.

...

Could the difference be that your true airspeed (TAS) up at 35,000 ft would be much higher than the IAS on the gauge. So inertia would be much higher among other things. At any rate, handling would be noticeably different compared to lower altitudes.

This was very helpful, thank you for taking the time to write all that up.

 

 

 

You’re offering advice without a complete understanding of what I’m saying, and what I’m asking. What you’re saying is applicable at all altitudes. I’m specifically mentioning high altitudes. The AI is easy enough to defeat at medium to low altitudes, even if they do fly “perfectly.” (Hint: regardless of their lack of energy bleed, their BFM is far from perfect.) The performance gap seems even wider at high altitude though, which is where, if anything, the gap should be closing / starting to turn in the favor of the Jug. The explanation offered by Voyager is a helpful starting point, though.

At altitude, the margin between maximum speed (Mach Number limited) and stall speed is narrowed down. Go high enough and you get into "Coffin Corner", where the two speeds meet.

Above 35,000 feet all aircraft are slugs. Acceleration is minimal. Airspeed margins are razor thin. The ability to very precisely operate the aircraft are why autopilots are required to be functional and engaged to operate in high altitude, precision airspace.

The AI has the ability to aviate very precisely in all regimes and this ability exacerbates the apparent disparity in high altitude performance. This invalidates any comparisons you may make.

If you want valid performance comparisons, compare apples to apples. Pit AI Thunderbolts against AI opponents and see what happens.

Or fly human versus human.

Just my two cents; at higher alts, the air is much, much thinner. This not only affects the amount of oxygen that you need to run your engine, it affects how much lift your wings generate at a given speed. It's a lot like you are flying at lower alts with the speed indicated by your instruments; if you have superior low speed handling, you might have some advantages over the guy whose aircraft starts getting harder to fly precisely once the speed dips below a certain line--assuming, of course that he cannot generate a higher speed at that altitude.

The specialized high altitude aircraft of that era had extended wings; think of the Spitfire Mk VII which not only had some extra 'plumbing' for the engine, but the extra pointy wing tips added. Or think of the early U-2 or the Canberra recon versions--extended wings. Until you're going at speeds mostly attainable by jets, you need a certain amount of wing surface to give you anything like the amount of control you take for granted below about 6000m, and the propeller fighters of WWII couldn't quite generate that sort of speed, and things got progressively sloppier the higher you went.

As others have pointed out, the ai controlled aircraft fly at a degree of perfection reserved for Jesus and the Angels in real life, so they're going to beat a human player's brains out 99 out of 100 times.

cheers

horseback

its a little more than that, its like low speed at lower altitude, but you're also getting dunked on by mach effects just the same as if you were flying at high speeds at lower altitudes.

so even if your airplane is good at maneuvering around at low speeds, it doesnt automagically mean you can pull the same moves at high altitudes. you can feel the difference even with modern jets, you have to be a lot more ginger about maneuvering a f-15 doing 300kias at 40kft than the same 300kias at 4kft

im just reiterating what pmiceli described really but i think a lot of people dont quite register the significance of mach when described in formal terms

tldr: the higher you go, the more you're simultaneously both fast and slow

Took her up to 31,000 feet (29.92 inHg).

Compressor got to maximum rpm, and handling got really terrible.

Only got to fly straight and level at 25,000 feet.

 

Ok, I wasn't with much patience, but I believe if I were lighter I would be able to get to 40,000 feet; The main problem though, was handling.

Next time you go there make sure there's nothing left in auxillary fuel tank. The plane can be trimmed for almost hands off flight then, even above 30,000.

Otherwise it indeed wobbles all over the place.