FM Question/New F4U's climb slower??

[Widewing]

Originally posted by straffo
So it's faster than a yak.

Yes, but it's more complicated than that.

First we need to examine acceleration. I measured acceleration for the F4U-1A, Yak-9U and P-51D. All were loaded with 25% fuel. Testing was done at 50 feet ASL. Recorded time required to accelerate from 150 mph to 250 mph and from 150 to 350 mph.

150 mph to 250 mph-

F4U-1A: 23.37 seconds
Yak-9U: 22.50 seconds
P-51D: 24.32 seconds

150 mph to 350 mph-

F4U-1A: 1:37.06
Yak-9U: 1:47.04
P-51D: 1:38.56

So, the Yak has a very slight advantage to 250 mph. However, at 270 mph its rate of acceleration has already fallen behind that of the F4U. Where the Yak shows its greatest edge is between 150 and 230 mph. Over the whole speed range from 150 mph to 350 mph, the Corsair gets there first, with the P-51D close behind and the Yak trailing well back.

Now, we know that the Yak doesn't have a WEP setting, so it can run at max speed for as long as it has fuel. On the other hand, both the F4U-1A and P-51D have just 5 minutes of WEP, whereupon they are limited to MIL power. So, I measured max MIL power speeds and compared them to the Yak's max speed. Tests were done at 50 feet ASL.

F4U-1A: 352 mph MIL power
Yak-9U: 357 mph
P-51D: 355 mph MIL power

Let's assume that all three are in a tail chase, with the Mustang and Yak chasing the F4U.

Since the F4U-1A accelerates best (especially over 300 mph), it will pull away. Even when the Corsair peaks at 366 mph, the P-51D cannot close on it having the same max speed. Meanwhile, the Yak is falling steadily behind. After 5 minutes both the F4U and Mustang run out of WEP. The P-51D cannot close on the F4U until the Corsairs speed bleeds below 355 mph. That will take longer for the F4U, than for the Mustang or Yak (I'll discuss speed bleed later). It will take the P-51D quite some time to chase down the F4U, assuming WEP is not used again by either.  Our Yak, which has fallen way behind might as well turn around. Its 5 mph advantage will require a long chase to catch up. Probably too long to bother.

Personally, if I were flying the F4U, I'd drag it away from the Yak and kill it... Then I'd go after the Yak, which is generally outclassed by the Corsair.

Speed bleed... A measurement of how fast the airplane sheds E when power is pulled off to idle. This can be a factor in a tail chase. I measured the time required to bleed down from 350 mph to 150 mph. Altitude was 300 feet using auto-level. This should be a function of drag, but moreso of mass.

F4U-1A: 46.12 seconds
Yak-9U: 27.93 seconds
P-51D: 37.69 seconds

So, the F4U-1A bleeds off speed slower than the P-51D and much slower than the Yak-9U. This hints toward the reason that the F4U zoom climbs better than many other fighters... Greater potential energy for any given speed.

To balance this, I decided to measure E bleed over a 180 degree 5g flat turn, beginning at 350 mph, max power. All three fighters began at 350 mph, speed at the end of the turn is recorded.

F4U-1A: 308 mph
Yak-9U: 302 mph
P-51D: 306 mph

Not a huge difference, but it tends to show that the Yak can pull a tighter turn from high speed as it bleeds more E in the process, which tightens the turning circle. Of course, simply pulling off some power can change the entire relationship.


My regards,

Widewing

[straffo]

Thank for you post , it confirm my intuition .

Originally posted by Widewing

F4U-1A: 46.12 seconds
Yak-9U: 27.93 seconds
P-51D: 37.69 seconds

I'm pretty surprised byt the E bleed of the Yak (even if again I expected this from  my AH experience) what can justify this ?

Aerodynamic differences ?

Mass differences ?

A La7 is a comparable to the yak in size/weight should it bleed E like a Yak ?

[Widewing]

Originally posted by straffo
Thank for you post , it confirm my intuition .

 


I'm pretty surprised byt the E bleed of the Yak (even if again I expected this from  my AH experience) what can justify this ?

Aerodynamic differences ?

Mass differences ?

A La7 is a comparable to the yak in size/weight should it bleed E like a Yak ?

My inclination is to believe that mass is the primary factor.

I will test the La-7 and compare it to the Yak. If the La-7 holds E much longer than the Yak, it would be something to discuss with Dale and Pyro.

My regards,

Widewing

[Viking]

Originally posted by Widewing
F4U-1A: 46.12 seconds
Yak-9U: 27.93 seconds
P-51D: 37.69 seconds

This sounds awfully wrong. The P-51D has an empty weight of 7,635 lbs, the F4U-1a 8,982 lbs, and the Yak 5,526 lbs. With internal fuel the P-51 and F4U is rather even in weight, difference being only a couple of percentages. The P-51D is obviously the most aerodynamic plane of the three with the Yak a close second, both having inline engines with the Merlin offering 220 hp more than the Klimov. The F4U with its radial engine producing in excess of 2000 hp (2250 with water) is obviously the most draggy, only able to match the 1720 hp P-51D in speed. Being close in weight, but more draggy, the F4U should decelerate quicker than the P-51D, probably closer to the Yak.

[Widewing]

Ok, I tested the La-7 for speed bleed. Here's how they match up, speed 350 mph TAS, pull off power to idle, time to bleed down to 150 mph is recorded.

F4U-1A: 46.12 seconds
Yak-9U: 27.93 seconds
P-51D: 37.69 seconds
La-7: 39.41 seconds

For the La-7, it cannot be correct. It weighs just 7,300 lbs compared to the Yak which weighs 7,050 lbs. Moreover, the Yak certainly has a lower drag coefficient than the air cooled Lavochkin. So, I would believe that they should bleed speed at a similar rate.

However, that is not the case. The La-7 holds its E better than the much heavier and extremely clean P-51D. There's no way that the radial-engined La-7 has a lower Drag coefficient than the .0176 of the Mustang.

I think we have partly discovered why the La-7 is so uber in Aces High.. It has the E retention of a much heavier aircraft without actually suffering the associated weight penalty. Obviously it doesn't require perking, just fixing.

My regards,

Widewing

[Widewing]

Originally posted by Viking
This sounds awfully wrong. The P-51D has an empty weight of 7,635 lbs, the F4U-1a 8,982 lbs, and the Yak 5,526 lbs. With internal fuel the P-51 and F4U is rather even in weight, difference being only a couple of percentages. The P-51D is obviously the most aerodynamic plane of the three with the Yak a close second, both having inline engines with the Merlin offering 220 hp more than the Klimov. The F4U with its radial engine producing in excess of 2000 hp (2250 with water) is obviously the most draggy, only able to match the 1720 hp P-51D in speed. Being close in weight, but more draggy, the F4U should decelerate quicker than the P-51D, probably closer to the Yak.

I read somewhere that the La-7 had a CDo of .0223, and taken with it's wing area of about 190 sq/ft, that equates to a flat plate area of 4.24 sq/ft. Compare that  to the P-51D with a flat plate area of 4.10 sq/ft. Now add in the far greater weight of the P-51D and it should be no contest. Yet, as modeled, the La-7 bleeds speed SLOWER than the P-51D... Has to be a modeling issue.

My regards,

Widewing

[Viking]

Sounds like there is more than one plane that is affected by this anomaly. For all we know the entire FM needs remodeling.

Makes me wonder if HTC do any testing themselves?

[hitech]

Widewing: In your deaccel test, you have not taking the prop into account at all.

Other than that Ill take a look at the numbers.

[Widewing]

Originally posted by hitech
Widewing: In your deaccel test, you have not taking the prop into account at all.

Other than that Ill take a look at the numbers.

I appreciate you having a look.

I realized that the prop would have some effect, but since there's no way to eliminate it in game...

Another round of tests could be done by simply shutting off the engine, but I don't know if that would make much, if any difference. I will try that later this afternoon and compare the results.

Again, thanks.

My regards,

Widewing

[Squire]

Its interesting to throw in the Mosquito in there...with 100 percent fuel "clean" (and an a/c of low drag), its @ 20,000 lbs, and I tested it using the above method and it decelerates from 350 to 150 in 40 seconds. Almost the same as an LA-7 of 1/3 the weight.

Spit VIII at 25 gas does it in 30 sec, im assuming thats a function of the much reduced inertia from a lighter a/c.

[Widewing]

Some additional data concern speed bleed.

I tested the original four fighters again, this time shutting off the engine. There was no difference in bleed-down time, all were within 1/10th of a second of the original numbers. There was one exception, and that was the P-38L. When you shut down the engines on the P-38s, the props go into feather, greatly reducing drag.

Here's the shut down bleed times... From 350 mph to 150 mph, 25% fuel (except where noted) and zero burn. Altitude was 300 feet ASL.

F4U-1A: 46.08 seconds
Yak-9U: 27.88 seconds
P-51D: 37.78 seconds
La-7: 39.34 seconds

Here's some additional types tested.

190D-9: 36.46 seconds
109K-4: 35.72 seconds
SpitVIII: 30.91 seconds
N1K2-J: 35.53 seconds
P-38L: 33.41 seconds (85.47 seconds if props feathered)
Tempest: 30.28 seconds
Typhoon: 30.21 seconds
P-47D-40: 49.84 seconds (54.25 seconds with 100% fuel)

I find it odd that the Brit fighters bleed E faster than the others. I expected than the P-47 would bleed slower by adding weight (full fuel) and it did. The Typhoon and Tempest were virtually identical, but the Tempest did have a lower drag wing design... I expected a difference. The N1K2-J and 109K-4 bleed speed at similar rates. I suspect that the 109's smaller flat plate area was offset by the N1K2-J's greater weight. Looking at the three American fighters, they tend to bleed speed according to the relationship of their relative weights. Again, this is what I expected.

On the other hand, the lightweight La-7 retains speed like a much heavier fighter would without the weight penalty. However, the Spitfire Mk.VIII, with a similar weight to the La-7 and 109K-4, bleeds speed like crazy. This is despite having a very low drag wing design.

I also do not understand why the Tempest and Typhoon bleed speed as rapidly as they do. Especially when compared to the 2,000 lb lighter 190D-9. Can the prop diameter/design make that much difference?

My regards,

Widewing

[Squire]

Yes, despite the 100,000,000 posts from the "Spit Haters Club" (tm) concerning it "not bleeding E", its an interesting result.

[Saxman]

The thing with the Spit isn't that it doesn't bleed E, it's that it can pretty much instantaneously get it BACK.

Could the F4U's wing configuration have anything to do with its substantially increased E-retention over the P-51? It WAS determined that the gull design reduced drag on the airframe.

[Squire]

Well, post a film of it getting it back "instantaneously" and post it. I will look at. I have been in AH for almost 5 years, and have never come across such a thing yet.

...and the criticisms were precisely that: "wouldn't bleed E" (supposedly).

Trouble was, when asked to test and show a result, it was never forthcoming, just hot air.

I dont like the over use of the Spits in the MA either, and thats really what the problem is, not the flight model.

...In any case, I wont hijack the thread (every AH thread turns into a Spit thread at some point, its like a scientific constant in AH BB), but I would also like PYRO to look at the relationship with weight and drag with some of the types mentioned above.

Later.

[Krusty]

Right when HTC changed the airflow code, folks mentioned the 109s, saying "I used to never have to slow down, now I have to sideslip, use rudder and flaps, all just to land!" so that might be a side-effect or bug from the code change.

Widewing: The prop is a huge brake. It's still spinning and the wind is pushing it, so you're slowing down a lot. When you're in AH and you shut the engine off, you "coast" a lot longer if you reduce RPMs as far as they will go. This lessens the bite of the wind, and might show better deaccel times. I don't know if a feathered prop on the P38 has the same drag as a reduced RPM prop on other planes, though. I suspect the 38 would still have the advantage.