Author Topic: p38 dive recovery flaps  (Read 812 times)

Offline df54

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p38 dive recovery flaps
« on: April 20, 2009, 05:20:18 PM »
   

   I may be opening a can of worms here but im going to anyway,
   Have read that dive flaps as modeled in ah will not slow the plane
   down and will not cause the nose to pitch up(with ct on). However   
   have noticed in warbirds that the ship noticeably slows down but the
   nose does not pitch up. In 1946 the nose rises and slows down. which is historically correct.

























           















 

Offline StokesAk

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Re: p38 dive recovery flaps
« Reply #1 on: April 20, 2009, 05:51:34 PM »
This is a common mistake.The P-38L model have Dive Brakes not Flaps. This will help you get out of a compression by making air flow over the elevators again giving you the abilaty to pull up. So they aren't flaps but they will make you turn a little better than you normaly would.
Strokes

Offline Ack-Ack

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Re: p38 dive recovery flaps
« Reply #2 on: April 20, 2009, 06:04:09 PM »
This is a common mistake.The P-38L model have Dive Brakes not Flaps. This will help you get out of a compression by making air flow over the elevators again giving you the abilaty to pull up. So they aren't flaps but they will make you turn a little better than you normaly would.

Well, there are three common mistakes that I see in both of the previous posts.

First, the P-38L has dive flaps and not dive brakes.  Second, the flaps did not act as a speed brake, they affected the center of pressure distribution so that the wing would not lose its lift.  However, because of the positive nose pitch it would bleed energy from the P-38.  There are numerous stories from P-38 pilots using the dive flaps to aid in high speed turns.  They'd deploy the flaps at the start of the turn and then immediately retract them as soon as the turn was finished, otherwise because of the nose up pitch the P-38 would bleed energy quickly.  Third, the only time the dive flaps would aid in turning is at high speed and would be useless under 300mph IAS.

The dive flaps do work in the P-38L in Aces High as long as you are not using Combat Trim and are properly trimmed.  In fact of any flight sim that has a P-38L modeled that I've played, AH is the only one that has it modeled correctly.

The way the P-38L dive flaps are modeled in IL2 is not historically correct.  From what I've gathered from playing it is the energy loss stems from the flaps being deployed themselves and not the energy loss as a result of the sudden nose up pitch.



ack-ack
« Last Edit: April 20, 2009, 06:17:10 PM by Ack-Ack »
"If Jesus came back as an airplane, he would be a P-38." - WW2 P-38 pilot
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Offline Murdr

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Re: p38 dive recovery flaps
« Reply #3 on: April 20, 2009, 06:49:48 PM »
Just to reiterate, dive flaps on the P-38 are not intended to slow the plane down.  The help reduce the mach tuck effect to aid the pilot in dive recovery.  They do cause some drag, but it is inconcequential to "slowing down" if you're above critical mach in a dive.

Offline Delirium

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Re: p38 dive recovery flaps
« Reply #4 on: April 21, 2009, 12:12:46 AM »
Murdr and AKAK said it perfectly, but I do want to add one thing.

Keep in mind, if you're in an earlier model P38 (that doesn't have dive flaps) you can always cross control if you're afraid of becoming too fast, nose low. If you often fly that fast and need to fall back on dive flaps or cross controlling, you need to re-examine how you are flying the P38.
Delirium
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Retired AH Trainer (but still teach the P38 selectively)

I found an air leak in my inflatable sheep and plugged the hole! Honest!

Offline Delirium

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Re: p38 dive recovery flaps
« Reply #5 on: April 21, 2009, 12:19:10 AM »
This is from another forum, Guppy/Corky has some contacts that would amaze and astound.

Quote from: Guppy35
I asked Lloyd Wenzel, who flew 38s with the 474th about his thoughts on the difference between the early Js and the later Js and Ls with power assisted controls, as well as dive flaps.  His reply is below.  Not exactly sure what he means by flat plate area or neutral point,  so maybe one of you gents can translate.  I did think his reply was interesting enough to share.

"Power assist on the controls was on the ailerons only and it made the 38 a differant
bird.  Loads on the aileron control were very high and resulted in slow rate of roll and
lots of effort by the pilot.  The early versions had problems with the neutral point but
were quickly solved--we all loved alieron boost.  The dive brakes were very
effective-electrically accuated and quickly deployed.  Being under the outer wing panel,
it was a good idea to deploy them before reaching the critical speed in case only one
deployed and control would be lost.  They were hooked up for only both  to deploy but who
knows.  In low alt work they were not used much unless you were jumped by other birds and
there was occasion for quick descent at times.  With low drag, it was easy to get to the
critical Mach.  The flat plate area of the bird was about the size of a folding card
table and it went like hell with the nose down."
Delirium
80th "Headhunters"
Retired AH Trainer (but still teach the P38 selectively)

I found an air leak in my inflatable sheep and plugged the hole! Honest!

Offline Dawger

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Re: p38 dive recovery flaps
« Reply #6 on: April 21, 2009, 01:07:36 PM »
Just for edification the Flat Plate he refers to is an aerodynamic calculation of Equivalent Flat Plate Area.

http://www.kathrein-scala.com/tech_bulletins/FlatPlate.pdf

The P38 has a very small EFPA which is most of the reason it got into critical mach so easily.