Couple of Early P-38 FM Observations

[niklas]

ups, while i was writing my posting, some new postings did appear  

so letīs wait for the next patch  

niklas out

[wells]

Niklas, 3400 kg is 7490 lbs  (454 grams/ pound).

[wells]

F4UDOA,

The Cl comes from the lift equation

L = Cl * WA * V * V * density / 2

rearranging for sea level

Cl = 391 L / (WA * V^2)

V is in MPH and WA (wing area) is in square feet.  The Lift force is in pounds.  The constant 391 works out the units and is only good for sea level calcs...makes things a bit easier.  Note, that L = weight * G factor.

The drag equation is the same as lift, only Cl is replaced with Cd.

[wells]

Niklas, let's take it a step further and factor in thrust and zero-lift drag at different speeds, 150, 200, 250, 300, 350 mph

I'll assume that 350 mph is the top speed of both planes at sea level(not far off).

Starting with max speed, so I can figure the Cdo where T = D.

109G10 (1800 hp)/P-38L (3200 hp)

350 ~ 1700 lbs/3040 lbs
Cdo (using wing area) ~ 0.031/0.030
f (equivalent flat plate area) ~ 5.4/9.8

(Thrust, Zero-lift drag)

300 mph ~ 109(1850, 1250)/ P38(3330, 2230)
250 mph ~ 109(2170, 870)/ P38(3930, 1550)
200 mph ~ 109(2590, 560)/ P38(4760, 990)
150 mph ~ 109(3040, 310)/ P38(5820, 560)

Excess thrust = T - ZLD

Plane 109 / P38
300 mph ~ 600/1100
250 mph ~ 1300/2380
200 mph ~ 2030/3770
150 mph ~ 2730/5260

Acceleration due to excess thrust(ft/sec^2)

Plane      109/P38
300 mph ~ 2.59 / 2.01
250 mph ~ 5.62 / 4.35
200 mph ~ 8.78 / 6.89
150 mph ~ 11.8 / 9.62

So the 109 should get an advantage here.  For the 300 mph 4G example, there's just enough in the 109 to overcome it's disadvantage and the planes are about equal.  When pulling max G's, the advantage goes to the P-38 above about 250 mph.

Personally, I didn't notice any change in the P-38 for patch 2, even though Pyro said he made a big change to induced drag.  Sustained turn speed was about the same as in patch 1 at 175 mph.

[Gator]

> Of course the L model had dive flaps which could prevent this from happening, but the flaps did this mainly by slowing the plane down in a dive.

Hmmmm, it is my understanding that the dive flaps had more to do with increasing lift and controlling the boundary layer air flow under the wings than by slowing the plane down.

[Minotaur]

 

Originally posted by Gator:

Hmmmm, it is my understanding that the dive flaps had more to do with increasing lift and controlling the boundary layer air flow under the wings than by slowing the plane down.

From my recent research this is my understanding also.    

The compressability problem had to do with the speed of air passing over the wings.  Even though the A/C was below Mach speed the airflow passing over the wings was above Mach.  Air at Mach speed reacts more like water than air.  This caused the center of lift for the wing to be shifted rearward, forcing the nose down.  This effect was called "Mach Tuck".

The first batch of "Dive Recovery Flaps", "Dive Flaps" or "Compressabilty Flaps" were fitted to the P-38J (P-38J-25).  They were fitted to the lower wing outboard of the tailbooms and were 4' 10" long.  From the picture that I have, I am guessing the flaps were about 3 to 5" wide.  Electricaly operated by a button inside the cockpit, the flaps would deploy or retract in about 1 second.  Full open deployment was 35 degrees.

The purpose of the flaps was not to act as a "Dive Brake", but to alter the air flow over the lower surface of the wing.  Altering the air flow over the wings to shift the wings center of lift.  

Actually, the flaps only delayed compressability and did not prevent its occurance.  They simply raised the speed for which it happened.  My guess is this speed was high enough to not be an issue later on.

Tony LeVier, a Lockheed test pilot at the time wrote.
 

The dive flaps did three things (All positive):
1) They produced a slight stalling moment.
2) They created some added drag to help slow the plane down.
3)The produced a slight gain in lift of (the) wing area affected by (the) dive flaps.

(LOL I have the same problem with forgetting to use "the's")

Tony also went on to say that the flaps for all intents and purposed fixed the compressabiliy problem.

Now a P-38 with dive flaps could perform Split-S manuvers with ease.  Mixed with the hydraulically boosted ailerons, it became truly the dogfighter that it was intended to be.

The silly part to all this was that the flaps had been tested as early as Feb 1943.  However; the paradigme mind set was that it was the ussual design of the "Twin Boom Tail" that was causing the problem.  Not high speed airflow over the wings.  

Who knows what history might have written about the P-38 had it beaten the P-51 to the ETO with the issue of compressability solved.

BTW, can any one explain to me what is meant by the expression "They produced a slight stalling moment"?  Thanks!  



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Mino
The Wrecking Crew
Trainer

[niklas]

first, please excuse my mistake that i didnīt convert correctly lb <>kg   Again, after the failure of the satellite, a disastrous error due to the convertion of metric to us-units

wells, there is a difference beween patch 1 and 2. At least i get about -1550ft/min now, and 250mph in the 4G test. Still very good i think, but not too good.

For the 1700lb~350mph, did you substract the induced drag? Did you substract later for the thrust also the induced drag? With F=P/v i get higher values for the thrust.

I tried a 4G test for 180° turn, starting from 300mph. P38 is better, comes around at 220mph G10 at 200mph.

"When pulling max G's, the advantage goes to the P-38 above about 250 mph"
So, friends of the P38, here is the ultimativ tactic instruction if you have a lot of speed and you have a fight with a 109 : Pull as hard as you can at your stick to get max. Gīs and withit the advantage  

niklas

[funked]

Mino, I think the engine reliability and the maintenance and fuel expenses would have still kept the P-38 from supplanting the P-51D.

The only dimension I can find for the dive flap span is that 58" figure.  From eyeballing them in person I would estimate the chord at about 18".

[This message has been edited by funked (edited 03-05-2000).]

[SnakeEyes]

Leonid and others who think I was attempting to bait... not so.  I'm merely questioning why so many of the AH aircraft seem to experience so many same flight model problems that Warbirds had?  You'd think that HTC would be more able to account for those issues, given previous experiences...

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SnakeEyes
o-o-o-
=4th Fighter Group=

[funked]

SnakeEyes:

"You'd think that HTC would be more able to account for those issues"

SnakeEyes, you might have noticed that HTC released two patches within 24 hours to correct mathematical errors in the P-38 FM parameters.  They are more than able to account for those issues.  

"I'm merely questioning why so many of the AH aircraft seem to experience so many same flight model problems that Warbirds had?"

What are those problems exactly?  What I'm noticing is that AH has so FEW of the same flight model problems that Warbirds still HAS.    

[This message has been edited by funked (edited 03-06-2000).]

[blur]

 

Originally posted by SnakeEyes:
Leonid and others who think I was attempting to bait... not so.  I'm merely questioning why so many of the AH aircraft seem to experience so many same flight model problems that Warbirds had?  You'd think that HTC would be more able to account for those issues, given previous experiences...

Considering the amount of work these folks pump out, I for one am willing to cut them a little slack when a value in an equation is found to be a little off.

[SnakeEyes]

Granted, I don't presume to speak with authority about the physics of it all... you guys know far about that stuff than I do.

However, it seems that I've heard the same complaints regarding performance at altitude (for many aircraft), the P38 not bleeding E like they should (I assume this is the issue fixed?), complaints in general about Otto (ground based), and I found that the P51 seemed to have a bouncy nose that reminded me very much of WB 1.1x.  I also found the Beta to be very microwarpy... of course, alot of that is just the nature of the Net IMO.

Granted, I stopped playing after Beta... so I don't know how many of these were fixed (I understand you guys now have flap/gear limits and such).

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SnakeEyes
o-o-o-
=4th Fighter Group=

[Kieren]

I can only speak from my perspective, so here goes:

Nose bounce in AH51 vs. WB51- not even close. If your controls are set up properly the 51 flies as if on rails. You will see it drift up or down based on trim, but that is what is should do.

Warp WB vs. AH- again, no contest. We all know well the microwarp escape plan patented by the P38 and 190 in WB. It just doesn't happen here (to me, anyway) the way it did there. People do warp (find any online game that doesn't) but the effects aren't nearly as pronounced.

Airframe limits have long since been added, as well as speed restrictions on flap/gear deployment. There is no appreciable difference in this area.

Control was crisper to some extent in WB, but I'm not sure this is necessarily accurate. YMMV.

One guy's opinion! I'd say you need to activate the account and test a current version before you pass judgement.  

[SnakeEyes]

Hehe... only 3 things would get me to consider that:

1) Latewar uberbirds (F8F, Ta152 [Nice book VERM], Tempest, P51H, etc).

2) A Mac version (several members of the WB squad I'm in fly Macs).

3) WB totally disintegrates/AH is proven to be completely superior.  Right now, even if the FMs truly are superior (seems like eye of the beholder these days), I found the gameplay to be lacking.

PS - I flew in AH off and on right up to the end of the Beta, and I'm not at all convinced that the smoothing code here is better.  In fact, my experiences (using 3 different connections) is that it was worse.

Not a rip, just one guy's opin...

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SnakeEyes
o-o-o-
=4th Fighter Group=

[Gator]

> Mino, I think the engine reliability and the maintenance and fuel expenses would have still kept the P-38 from supplanting the P-51D.

  I agree with the conclusion that it is unlikely the P-38 would have supplanted the P-51D, but for different reasons.

  While Kelly Johnson proposed replacing the turbo-supercharged Allisons with Merlins and mechanical superchargers to solve the problems with the poor quality British fuels, the Merlins were already in demand for other fighters and unavailable for use in the P-38.

  With only so many P-38's to go around, it's not surprising that with the high altitude problems with the turbo-supercharged Allisons and the British fuels, the demands for P-38's in the Pacific, by the Fifteenth in Italy, and for low-altitude work with the Ninth that the Eighth would go with the Mustang.

  Then add in the fact that the Lightning was more expensive, could not be mass produced as easily, was more difficult to maintain and more difficult to fly for the average pilot than a single engine fighter.

  One of the amazing things, to me, about the large numbers of P-38's built is that it was not originally designed for mass production and was originally, as Martin Caidin says, essentially a hand-made machine since Lockheed was led to believe that the Air Corps would buy no more than fifty!