P38J at alt

[Ratpack1]

That happened to me once in a 38. Took off, went AFK and by the time I came back it was right near 30K Feet. So I went to turn her over and get back down to earth, the minute I did I went into compression nearly instantly lol. Nothing I did would pull out of it, I was a missile. 

[Murdr]

the problem i was having though, was that i would get my stall buzzer, and the shudder of the oncoming stall with even just a gentle pull out.

That's not a 38 issue.  All planes have less favorable lift/handling characteristics up high.  If anything, the P38 suffers less than many other planes at higher altitudes.  When you're thinking maneuvering, look at your IAS to judge what your maneuver options are.  Remember not to be heavy handed, and be patient because your opponent also has maneuvering issues.

i was chopping throttle when i'd go in. on one pass, there was one i'd guestimate to have been about 20k, that looked like he was focused on a squaddie. i tried to pick him, and cut to 1/2 throttle as i dove for him. i then felt the shudder of compression,(well before i got near him) went to idle, full up trim, full right rudder, everything i could think of to prevent the compression i entered. went into it anyway, and couldn't recover till about 16k.  so.....my questions?  how does one fight in the 38 at that alt? how does one fight against a 109 in a 38 at that alt? how does one prevent compression at that alt?

  This is very managable if you watch your TAS when you are going nose down for more than 5 seconds at a time...or if you're at cruising speed.  If you're in BnZ mode, you need to plan your approach so that you either do not approach at a steep angle, or so that you're transitioning closer to a level attitude by the time you get to your target.  That said, I still fight in the vertical at altitudes above 20k, but I am topping out below stall speed and coming straight down, not starting a dive while already going 250 TAS, or staying in a steep dive long enough to reach 400 TAS.  If I find myself having to chop my throttle to control my speed, I already made a mistake as far as I'm concerned.
 

[Guppy35]

Only a couple of us flew the 38J in DGS because of concerns for the high alt stuff and compressibilty.  The rest flew the 38L with the dive flaps.  As one of two J drivers I never had any problem with it, but I really watched the throttle and used lots of rudder if I started moving downhill too fast.  As Murdr stated, you have to  think more ahead of the game at alt because no one is going to turn real fast.  That being said, the 38s we had in DGS did fine up high, although as most know, I prefer low alt in a 38G

[Dawger]

Stall speed is related to Indicated Airspeed.

And it doesn't change with altitude. An aircraft that stalls at 100 mph at sea level will stall at 100 knots at high altitude (There is some variation but it is minor for the purposes of this discussion)

The difference is that indicated airspeed drops with altitude.

At sea level full power in an average late war fighter you will be around 300 MPH IAS. At 30K you might see 180 MPH IAS as an example.

Same stall speed at 1 G of 100 MPH

Stall speed increases in proportion to the square root of the G force on the airframe.

At sea level you can easily pull 4 G. There is an excess of airspeed. Stall speed at 4 G is twice the 1 G stall speed (Square root of 4 being 2) which equals 200 mph in our example.

At 30K the same 4 G turn will stall the airplane. If you are high enough, accelerating to above 200 mph so that you can pull 4 G may exceed critical mach and put the aircraft into compression.

So at high altitude you are limited by low G tolerance before stall because the air is thin. You are limited by flying at indicated airspeeds closer to stall and you are limited because you are flying closer to critical mach number.

True airspeed is not important for high altitude performance. Indicated airspeed and Mach number are the values to concentrate on.

[CAP1]

at first, like i mentioned, i wasn't sure if i should've put this here or in the general discussion forum. i'm very glad i put it here. in the general discusion, i think i'd have gotten more replies like that first one.......here though, you guys are all giving excellent info!

 now for the stupid question..........

TAS is indicated by the red needle on the airspeed indicator, correct? and the white needle is my IAS?

 if so, am i correct in the fact, that i should pretty much ignore my TAS when maneuvering in a fight at those alts?

if i were to practice fighting at those alts, does it help, hinder, or have no effect on fighting at lower alts? i'm talking in the p38 still.......regardles of my ego(what little i have left) i'm not getting out of the 38 till i can fly her and fight in her as well as i was doing in the hurris, spits, zeeks, hellkittys, etc.

 and finally......Murdr(i think) mentioned that if anything, the 38 had a bit of an advantage up that high. it looked to me like those 109 drivers were controlling themselves much better than i was controlling my ride. would i have been wrong on that one too? i mean were they most probably struggling as i was?

 i didn't(and still don't) think it was anything to do with the aircraft(my trusty cartoon p38), but rather i think(well...i KNOW) the problem was and is(for now anyway) with the pile-it behind the controls.

 again, thanks guys for all of your helpful input, and taking your time to reply to these!\

<<S>>

[Murdr]

and finally......Murdr(i think) mentioned that if anything, the 38 had a bit of an advantage up that high. it looked to me like those 109 drivers were controlling themselves much better than i was controlling my ride. would i have been wrong on that one too? i mean were they most probably struggling as i was?

Yes, they would be struggling too, however they can still out turn you by about the same percentage at that altitude as they would on the deck.  The thing that really does a planes maneuvering options in at altitude is the thrust deficit.  20-22k isn't quite high enough for a P-38 to gain that power advangae on a 109f...23k and above would preferable for that match up.

[Murdr]

True airspeed is not important for high altitude performance. Indicated airspeed and Mach number are the values to concentrate on.

Freaking Mach number is not on your instrument panel.  Cap can glance at his TAS and say "crap, I better be careful, I'm doing 420 TAS at 22K", or he can pull out his clipboard................clic k E6B...........figure out how close he is to Mach .68...that is if he knows that's the number for the P-38 (if not, remeber it), and by that time it doesn't matter, because it does not take a P-38 all that long to hit critical mach at altitude.

[Cajunn]

I would like to add something to this thread, I hear quite a few comments about the P-51 not being all it was made out to be in historical right ups. Well a while back I did a bomber escort mission in a P-51 and we got up to around 25 or 30k and got intercepted by co-alt enemy fighters of all varieties. And I was amazed at the how much better the Mustang was at the higher altitudes, I chewed everything up that I came across. And that got me thinking about the fact that the mustang was built for high Alt escort and that's where most of the dogfights took place in ww2 and that's probably why it had such a good reputation amongst the pilots that flew her. I have taken other fighters up to that altitude and it took a lot more effort to fly them and you almost feel as if your always right on the edge of out of control.

Anytime I get to 20k or better I end up in trouble unless I'm in the mustang (never flew any of the other high alt planes), and that goes double if I'm in a plane with a low compression rate (P-38).  And as everyone knows the 109's get stiff around 450mph, and if you really want to get in trouble take a K4 up at the higher altitudes where its top speed is around 440mph and try to dogfight, its almost impossible.   

[TequilaChaser]

sometimes too much "unecessary information" clouds the subject just as much as posting "wrong information"

for reporting plane performance, speeds, climbrates, turn rates etc......... most times these are reported using TAS ( True Air Speed )

for Manuevering you always want to use IAS ( Indicated Air speed ), for this is what the speed is for your plane type that is being calculated/determined by the planes PITOT tube

REMEMBER:
Use IAS ( Indicated Air Speed )  ie.... THE WHITE NEEDLE ON THE GAUGE  for MANEUVERING SPEED

Use TAS ( True Air Speed )  ie.... THE RED NEEDLE ON THE GAUGE  for determining Plane Performance

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Dawger,
in another thread on AH2Training, HellFire reported downloading one of your files or books or something? ah it was called "Dawger's BFM"  can I get a copy please, I read that it had loads of helpful info...... I am always looking for good info........... I didn't know you had your own BFM, that's outstanding! I really would like to check it out if ya don't mind, Sir ! ~S~[/list]

[BaldEagl]

Yes, they would be struggling too, however they can still out turn you by about the same percentage at that altitude as they would on the deck.  The thing that really does a planes maneuvering options in at altitude is the thrust deficit.  20-22k isn't quite high enough for a P-38 to gain that power advangae on a 109f...23k and above would preferable for that match up.

In my experience in the 38's it seemed to me that those twin thrusters gave it a vertical advantage at higher alts particularily against the 109's and 190's, which get pretty feable at anything much over 20K, but you fly them a lot more than I do so I could be wrong.

I do fly 109's and 190's quite a bit and in a 109 I'd want that fight in the 15-17K range or lower.  I'd only want it in a 190 if I could maintain a speed advantage regardless of alt although a 190 could safely dive out at any time.

[dtango]

Ah, what air density and temperature does to the performance of an airplane!  And of course God made it so that they vary with altitude which confuses and complicates it for dweebs like us!  It affects a whole host of things from lift and drag, to thrust and compressibility.

Though I'm tempted to explain the physics (along with full waving of the hands!) I'll refrain and cut to the chase with hopefully some practical stuff. 

Avoiding compressibility effects in the P-38: 

First - that dive flap on the J and L models?  It was put their for a reason - for the very purpose of dealing with the P-38's nasty compressibility effects.  It's wise to use it.

Second airspeed matters.  Of course compressibility effects kick in when local regions of the plane hit mach one.  And God would make it so that the speed of sound in true airspeed reduces with increasing altitude (at least for the realm of the atmosphere we usually fly our virtual airplanes in).  The upshot is that the true airspeed and the indicated airspeed when you experience compression reduces with increasing altitude.  So what's a poor P-38 pilot supposed to do?  Besides the good advice Murdr gives on this maybe the following chart is also helpful.



The P-38's dive speed placard says the limit is about mach .65.  I've marked up the NACA chart there with a red line to indicate where Mach .65 is.  Our handy little chart gives us where mach .65 is at various altitudes for both IAS and TAS.  The blue lines represent the range of IAS for mach .65 from sea level to 30k.  Notice how much the IAS speed ranges from: ~500mph at sea level to 290mph at 30k.  I've put blue markers for increments of 5,000 feet for you for reference so you see that mach .65 ranges from:

SL = 500 mph
5k = 470 mph
10k = 430 mph
15k = 390 mph
20k = 360 mph
25k = 320 mph
30k = 290 mph

Conversely you can look at TAS (green lines) as well which ranges from 500 mph @ SL to 440 mph @ 30k for mach .65.

Of course you can push the limit some more and move up to mach .68 as Murdr suggests.  Redraw the lines as appropriate and see what that gets ya.

Altitude effects on performance are more than just compression related - e.g. the turbosuperchargers of the P-38 greatly benefit it compared to the 109F and G series.  But for the sake of brevity I'll limit this post to the issue of compression.

Hope that helps!

Tango
412th FS Braunco Mustangs

[Dawger]

That chart cannot be used without the accompanying standard atmosphere table if you are looking for True Airspeed

The whole thing here

It is a very old chart and there are some errors in it because of its age but useful for comparing Indicated Airspeed to Mach number. Beyond that there is little utility in game and it is obsolete for real world use.

[dtango]

That chart cannot be used without the accompanying standard atmosphere table if you are looking for True Airspeed

The whole thing here

It is a very old chart and there are some errors in it because of its age but useful for comparing Indicated Airspeed to Mach number. Beyond that there is little utility in game and it is obsolete for real world use.

Hmmm....riddle me this.  Why do you need the accompanying standard atmosphere table?  The chart above is already in standard atmosphere which of course is also the atmosphere we have in AH.  It also has a correction factor for when you're not in standard atmosphere by TAS on the 2ndary x-axis and the temperature lines associated. 

And why is there little utility in the game?  As Murdr has already mentioned we don't have mach meters in WW2 in our virtual WW2 aircraft save for popping up the E6B but why would you be doing that in a middle of a fight vs. glancing at the airspeed indicator?

Tango
412th FS Braunco Mustangs

[Dawger]

 

[CAP1]

i still have that one question though?

will practicing at those altitudes help improve low alt performance of the loose nut behind the controls?