Questions about the P47 proformance (long)

[Thor^]

Hi every one i like to fly the jug and some one put up a link in another thread to zenios warbird drive in. I watched the films on the jug and got to wondering. The film is from 1943 so it couldent have been the same model jug we have now but it stated that a split S in the jug at full powere would lead to compresion and augering. So i went to test this out with the AH jug. I took clean load out and 50% fuel climed to 30k at 250 ias 400 true(got to like that =) ) i did my first split S puling backe enuf to get just a little black around the edges but no where near blacking out i droped 22400 feet. looking at my notes here i forgot to record speed but i rember it was around 5oo ias true? then i dove to 20k leveld and trimed up
at 300 ias 400 true. i split S again i droped to 15k 350 ias 425 true. i dove to 10k leveld and trimed at 350 ias (dident right down true forgot).Again i split s i droped to 4800 feet 450 ias 475 true. i climed to 5000 feet to see what would hapen 300 ias i split S droped to 1000 feet 400ias 400true. i was at full powere during the hole flight. once i puled backe hard enuf to almost black out.At no time did i ever use the dive breaks. so thats my story now my questions. what made the 1943 jug compres like it says in the vido? why dosent the P47 D model have the same problem? is this somthing that AH dident capture in modeling the plain? Or is it somthing that cant be done becus of programing?

note im not complaning about AH i love the game (would pay to play but cant aford it right now long story =( ..) Just so you all know im not squeaking im just wondering and trying to learn. im neather a piolet or a programer im just looking for info =)  

[This message has been edited by Thor^ (edited 06-26-2000).]

[Lephturn]

Those videos were made to keep new pilots from killing themselves.    At 500 Ias the P47 in AH will go into compression badly and the dive flaps must be used to pull it out.  That video was likely made before the dive flaps existed, so they had to keep the pilots from split-s ing and hitting 500 IAS or so.  If they exceeded 500 they were pretty much dead meat, so you can understand why they built some margin of error into the training films.  

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Lephturn - Chief Trainer
A member of The Flying Pigs
Visit Lephturn's Aerodrome for AH news, resources, and training data.
 http://users.andara.com/~sconrad/


"MY P-47 is a pretty good ship
And she took a round coming 'cross the Channel last trip
I was thinking 'bout my baby and lettin' her rip
Always got me through so far
Well they can ship me all over this great big world
But I'll never find nothing like my North End girl
I'm taking her home with me one day, sir
Soon as we win this war"
 - Steve Earl

[Thor^]

i can see that they hade some margen of error in there film but i dout it was that larg. I stated in my first post that i did NOT use flaps and i did go over 500 true.

So my guestions still stand and i would like a more in depth reply from thos with the knowlidge on this BBS. thank you all for your time.

[juzz]

Real pilots didn't pull lots of G in WW2 like we do in sims. Try a split-s at 2 or 3 G and see what happens.

[Lephturn]

Thor,

True Airspeed is not relevant.  Only your Indicated Airspeed counts when you are talking about compression and dive speed.  In your above post you didn't mention going over 500 TAS, and you weren't even close to over 500 IAS.

If you push a Jug past 500 Mph IAS it WILL compress, and badly in AH.  Without the dive flap it is VERY hard to recover it in this condition.  I was not talking about regular "flaps", but the special "dive recovery flap" that was installed on the later model P-47's, including the version we have here in AH.  This film was made before the advent of that flap, so if a pilot got a P-47 into compression, it was very difficult if not impossible to pull out of the dive.

I think if you try gentle 3G split-S's at full throttle in the P-47 starting from a decent cruising speed like 300 IAS you will hit 500 MPH IAS.  Notice when you hit that speed in the game your controls will freeze solid and you will be unable to pull out of the dive.  If you activate the dive recovery flap in the P-47D-30 that we have in AH, you will regain some control and pull out.  The earlier versions of the P-47 did not have this feature, so they would have likely killed a bunch of pilots in training without this kind of warning.

From what I have seen, the AH P-47D-30 is modelled very accurately.

------------------
Lephturn - Chief Trainer
A member of The Flying Pigs
Visit Lephturn's Aerodrome for AH news, resources, and training data.
 http://users.andara.com/~sconrad/
 

"MY P-47 is a pretty good ship
And she took a round coming 'cross the Channel last trip
I was thinking 'bout my baby and lettin' her rip
Always got me through so far
Well they can ship me all over this great big world
But I'll never find nothing like my North End girl
I'm taking her home with me one day, sir
Soon as we win this war"
 - Steve Earl

[This message has been edited by Lephturn (edited 06-27-2000).]

[Daff]

Lephturn, I believe it also depends on the air density, although I dont quite understand it  .
(ie it's easier to compress higher up at the same IAS than at lower altitudes).

Daff

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CO, 56th Fighter Group
"This is Yardstick. Follow me"

[Westy]

 This is not meant to be taken as anything but an observartion of an odd occurance but last night in a dogfight with a 109 at A27, after a couple of loops, rolls and turns he dove to escape and I quickly followed right on his tail at 400 yards. He out dove my P-47 handily from an almost equal start and even started pulled away to about 690. This is when I entered compression and even with throttle back all the way and dive flap employed I slow rolled to the right, out of contro and into the ground.  The 109 pulled out and up with no problem at all.  And the whole time he was pulling away. Not once did I gain on that bugger like I might have had he chopped throttle..

  -Westy

[Minotaur]

 

Originally posted by Daff:
Lephturn, I believe it also depends on the air density, although I dont quite understand it   .
(ie it's easier to compress higher up at the same IAS than at lower altitudes).

Daff

I am not so sure that this is the complete reason, or that the thicker air at lower altitudes results in a greater control surface force.



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Mino
The Wrecking Crew

"I kinda like it.. and the hell with the cat"
Hangtime

[Lephturn]

Was it a G-10?

If so I would expect it to pull away, even in a dive, at least at first.  Those suckers are FAST, and accellerate better than a Jug.  I would bet the 109 pilot was flying with trim at that point... I know those guys are used to doing it to stay alive.  I'll check out the dive speed of the 109 sometime though and see what I find.  One would expect it to tear itself to bits before the Jug would lose total control.

------------------
Lephturn - Chief Trainer
A member of The Flying Pigs


"MY P-47 is a pretty good ship, she took a round coming 'cross the Channel last trip.
I was thinking 'bout my baby and lettin' her rip
Always got me through so far"
 - Steve Earl

[Daff]

Mino, yeah, but wouldnt you get the same amount of air hitting the surfaces? (Given that the IAS is the same).

Daff

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CO, 56th Fighter Group
"This is Yardstick. Follow me"

[Westy]

 Thanks Lephturn. I pretty much discounted the initial part of the dive. I had a decent fuel load, who knows what the 109 had - let alone which model it was. And the dive was with an initial full thottle, with wep even used  for the first  few seconds.
 The odd part, imo, is after we both quickly reached the same speed in the dive ( which was steep at about 75-80 deg) and based on the range not changing we stayed that way for a good 10-15 seconds before we I found myself compressed, unable to pull out and I watched him able to do so easily.  The P-47 trim didn't help for me, course it could have for him.  And the speed flaps didn't seem to make a difference.  I'll be filming more now to find my error or anything that might be odd enought to submit to HTC for a look into.

  -Westy

[juzz]

Compression is dependant on your true airspeed in relation to the speed of sound(Mach number), and the speed of sound changes with density(altitude).

Control forces are dependant on indicated airspeed.

As for Westy's anecdote: It sounds like you were at low speed when the 109 dived. It would have a greater acceleration in that case due to its vastly better powerloading. Before you could catch it your Jug was "compressed" and you backed off. The important thing to note is that the P-47 will experience "compression" at a much lower Mach no. than the Me 109. The Me 109 is possibly even better than the P-51 in this regard.

I don't now the critical Mach number for the P-47, but I think it's just over 0.7? For the Spitfire it's about 0.83.

[Daff]

Hmm..actually sounds sensible.
Guess that at lower density, there's less air obstructing the turbulent flow and vice-versa.

Daff

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CO, 56th Fighter Group
"This is Yardstick. Follow me"

[Weave]

  Haven't have any compressability problems yet, and I love the Jug, but whats with the location of the VSI guage? HT, put the sucker where we can see it with out looking down.

...Weave

[ygsmilo]

I have been flying the Jug alot and I luv it.  I had not experienced any compression untill last nite, the funny thing was that it was not a steep dive but a shallow dive. I was at about 20K and saw a few low dots and stuck my nose down for a 300fpm dive.  By the time I had an id on the cons my speed had built up to where my controls locked up, I eased off the throttle and droped the the dive flap and eased the nose up with the trim tab and was able to recover.  Odd that is was a shallow dive though.

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JG 2's current cannon magnet

Milo