P-38 Still has Problems

[Ack-Ack]

Originally posted by Kweassa
I always wondered about this. How large would the pitch-up movement be with the diveflaps deployed?

 In AH2, really honestly, I don't feel any kind of difference in handling whether they are applied or not(I don't use CT).

 In FB/AEP, the diveflaps virtually make the plane do a loop all by itself when deployed. It feels like the elevator trim suddenly maxed out to the top.

 So which depiction would be more correct? Or would it be somewhere in between??

The nose up pitch from the dives flaps in AH doesn't seem as pronounced as the ones I've read from P-38 veterans.  I've read some stories that sometimes they blacked out from the nose up pitch.

In AH, if you have the elevator trimmed to close to neutral, you will see the P-38's nose pitch up but it's nothing dramatic.


ack-ack

[Murdr]

Translation:
gripen: chicken bla bla chicken
Murdr: yes, well dont forget about the egg that the chicken came from.
gripen: you dont understand what your talking about, its all about the chicken.

suit yourself. The properties I described are all there and documented mr know-it-all.

[gripen]

Murdr,
Well, let's try again a bit more simple way:

"High speed wind tunnel tests of a model of this airplane, whic are reported in references 2 and 3, showed that the inboard portion of the wing between booms had a relatively low critical Mach number which was being exceeded considerably in dives at high altitude. At the supercritical speeds investigated there was little change in the angle of attack for zero lift, but there was a significant reduction in lift-curve slope accompanying the loss of lift of the center section of the wing and a shift of load to the outboard portion of the wing. The reduced lift-curve slope, the shift in span loading and reduced downwash on the tail greatly increased the static longitudinal stability, resulting in a strong diving tendency. "

Shortly this means that it was the inboard portion of the wing which caused the tuck under.

"The outboard dive recovery flaps produced favorable shift in trim by decreasing the angle of attack for the zero lift and increasing downwash on the tail, but did not alter the the mach number the diving tendency developed"

Shortly this means that the dive recovery flaps were installed to the outboard portion of the wing and nothing changed in the inboard section where the problem was. Therefore it should be easy to understand that the tuck under problem was there with or without dive recovery flaps. The dive recovery flaps just added positive pitch up moment to counter the tuck under and increased the drag considerably to keep the plane out of trouble.

gripen

[Crumpp]

==============================================
Translation:
gripen: chicken bla bla chicken
Murdr: yes, well dont forget about the egg that the chicken came from.
gripen: you dont understand what your talking about, its all about the chicken.
==============================================

Translation:

I don't know what your talking about Gripen so I will attack you since I don't want to ask questions and appear stupid.

Gripen is saying the Dive recovery flaps masked the symptoms not fixed the problem and added quite a bit of drag.  At least according to the aerospace engineers.

Gripen is presenting cold hard facts.  Which much more than anyone else in this thread has done.  Why is he being attacked?

Many times if you look hard enough you will see the pilot stories do line up with the scientific data.  If you dig hard enough I am sure you will find it.  

And if you think I've got poms-poms out for LW planes you haven't
t been in any LW threads.  I am firmly for realistic modeling of the A/C.  Otherwise what is the point of a simulation.

Crumpp

[Murdr]

Christ you are being thick.  You do understand that in order for a plane to fly you have to generate greater lift under the wing rather than over?  Do you understand that the formation of super sonic shock on the upper surfaces causes greater pressure on top?  That is the opposite of flying.  Hello? Still with me?  Deployment of the dive recovery flaps changes the shape of the wing.  The change in shape causes the shock to form further aft.  If the shock is further aft, you have positive pressure UNDER the fore of the wing, and positive pressure ON TOP OF the aft of the wing.  These forces would tend to pitch the nose up.

As speed increases the shock moves further forward until the flaps become useless.  If you re-read looking specifically for references to "upper surface shock" you will see that is what pitches the nose up.

Are you contending that the dive flaps magiclly pitch the nose up?  Or are you contending that the dive flaps form a greater supersonic turbulence under the wing than on top?  Its one or the other because you apperently are disagreeing with my statments about the shock formation being displaced.  If that were the case aerodynamically it would continue to push to the ground.

[Crumpp]

Can u not read the graphs Gripen has posted?  I am not trying to second guess the scientific data.  I am reading what the aeronautical engineers got for test results on actual aircraft under controlled test conditions.  In otherwords VALID scientific DATA.

Looks like their are a few configurations for the inboard flaps which do produce a nose up situation.  

However most of the conditions tested with the inboard flaps the P38 seems to adopt a nose down attitude.

In either situation the dive flaps produced huge amounts of drag.

So yes your pilot andectdotes are truthful.  The pilots certainly are not lying HOWEVER the nose up attiude occurs in part of the flight envelope under certain conditions.  In a normal dive profile the scientific data points the tuck under still existing.

READ the DATA Gripen posted.

Crumpp

[OIO]

the dive flaps prevented the tuck under if they were deployed before a dive (under ~300mph)... if deployed after the ~300mph the dive flaps would create a 3g  nose up pull.

38 test pilots even commented the plane would pull a neat loop all on its own if the flaps were deployed after.

[Murdr]

I had posted on the fly my previous 2 posts.  

In general, the effectiveness of the flaps increased considerably with increasing Mach number to well past the Mach number of lift divergence.  As shown in the typical pressure distribution the pressure recovery aft of the flap was less complete at hugh Mach numbers, causing a considerable increment of negative pressure over a larg portion of the upper wing surface.  Also, the upper-surface shock moved aft when the flaps were deflected.  Both of these effects contributed to the flap effectiveness.  However, there is evidence that the effectiveness will decrease sharply above some Mach number between that for lift divergence and a Mach number of 1.0

I was not at all trying to refute anything you said to begin with.  However I was pointing out how it aids in recovery when compression is reached.  You pointed out the fillets are more effective on the outside of the nacells as opposed to the inside.  That would make sence considering the distance between the leading edge and the center of the wing is shorter on the outside of the nacells than on the inside.  

You stated:

The dive recovery flaps did not change the speed where the tuck under phenomena started nor prevented other compressibility problems.

I didnt/dont disagree with that.  However with the dive flaps employed, lift characteristics at the onset of compression are starting from a more favorible position than without them.  This allowed the pilot to recover with less altitude.  Or as they summised it in NASAs history "In March 1942, after less than four months of tests in Langley's 8-Foot HST, Stack's engineers reported that they had an answer to the P-38's dive-recovery problem: a wedge-shaped flap installed on the lower surface of the aircraft's wings. They said that their tunnel tests showed that wings having this flap would retain enough lift at high speeds to enable a pilot to pull the plane out of steep dives."

[Crumpp]

So why all the nastiness?

Crumpp

[Murdr]

I dont know, I try to point out a facet of dive recovery flaps and I get talked down to as if I dont have a clue.  I had just re-read that report about a month ago after seeing a P38 and talking to a pilot.  I asked about stalls, acclerated stalls, stalls in a hard bank, the dive flaps.  So as I said, 1. I posted on the fly 2. Replies to me were snobish.

[Crumpp]

Roger that.

There is a lot of snobbishness on this BB.

Sometimes we all forget that we don't have all the visiual clues which tell us what someone is actually thinking.  The emotion icon are a poor substitute.

Crumpp

[gripen]

Murdr,
I don't know which of your posts are worth to reply?

That DSIR 23/15088 is a RAE report on dive test on the P-38 with dive recovery flaps and it contains measurements on pull out force. At 10k and mach 0,65 flaps gave about 3g pull out, at 30k and mach 0,65 about 1g pull out. Above critical mach number effectiveness of the dive recovery flaps decreased just like the NACA report indicates. "Wings of the Weird and Wonderfull" by Eric Brown contains a chapter on these tests.

I don't what has been snobish here, but it's quite strange if I first link couple reports on dive recovery flaps and after that someone starts to teach how these devices work. Anyway, in the case of the P-38 it should be noted that wing itself without fuselage did well up to and over mach 0,7 and dive recovery flaps were located to the outer section which did fine while the problems generated in the inner section. So IMHO talking about shockwaves around flaps and effectiveness of the flaps is a bit missleading.

gripen

[Crumpp]

Well, I was a Lederhosen wearing Luftwhobble....shhheeesh.

Obviously someone who has never been in a Luftwaffe thread.


Crumpp

[Murdr]

Originally posted by Crumpp


Sometimes we all forget that we don't have all the visiual clues which tell us what someone is actually thinking.  The emotion icon are a poor substitute.

Crumpp

good point

[TheManx]

One thing I've learned from this thread is that P38 fans are awfully long winded

Oh, and to answer a question about 4 pages ago, yes I've flown the 38 in AH2, found it a lot of fun. Had some good fights with someone who's name I can't recall who also flys the 38. Didn't have any problems with the flap retracting spins as others seem to. I didn't turn it as well as I used to, but I don't play often anymore so I attributed it to that more than on any real performance degrade.

I'm no expert though, and I have no real love for the 38 other than it can be a fun plane to fly in Aces High.