Author Topic: P-38 MANEUVER Flap 8 Degrees?  (Read 6035 times)

Offline Randy1

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #45 on: September 01, 2014, 01:36:51 PM »
Check out the old P-38 help page http://www.hitechcreations.com/ahhelp/models/p38l.html

Wow what a find.

I looked at my handy protractor to get a good idea of what 8 degrees is and it looks like the angled upper track may drop 8 degrees albeit a WAG.

Now, could 50% be travel on the track not angle?   Could it be then at 50% of the flaps travel the angle is 8 degrees?

As Murder pointed out the lower track stops letting the drop in the upper track push the flap into a steeper angle as it travels back.  The point at which the lower track stops and the flap turns down my give it an 8 degree drop and be 50% track travel.  And we know it happens in 3 seconds.

That would make the 8 degrees and 50% flap agree.

What do you think Murder and FLS?
« Last Edit: September 01, 2014, 01:58:59 PM by Randy1 »

Offline FLS

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #46 on: September 01, 2014, 02:34:08 PM »
Randy the track angle is different than the flap angle.

Murdr there's an article by Hall Hibbard where he states the dive flaps extend 40 degrees. The manual says 35 for dive flaps.
Since there are still P-38's it shouldn't be impossible to find the correct answer. In any case approximately 35 degrees for wing flaps is close enough to my assumption of 40 to maintain my belief that the maneuvering position is nearer 20 degrees than 8.
« Last Edit: September 01, 2014, 02:54:32 PM by FLS »

Offline Murdr

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #47 on: September 01, 2014, 03:18:00 PM »
Murdr there's an article by Hall Hibbard where he states the dive flaps extend 40 degrees. The manual says 35 for dive flaps.
Umm yea, that's where the image came from.  Just out of curiosity can you point out where the 35 degree reference is?

Offline Murdr

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #48 on: September 01, 2014, 03:37:04 PM »
That would make the 8 degrees and 50% flap agree.

What do you think Murder and FLS?

It still doesn't explain away the photographic appearance of the flaps at 50%.  Some of that could be resolved by assuming the reference angle is the chord/thrust line as opposed to the aft underside foil.

Offline FLS

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #49 on: September 01, 2014, 03:43:40 PM »
Umm yea, that's where the image came from.  Just out of curiosity can you point out where the 35 degree reference is?

POH AAF 51-127-1  Page 52  The illustration shows 35 degrees.

Offline Randy1

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #50 on: September 02, 2014, 06:28:30 AM »
Randy the track angle is different than the flap angle.  . . .


It is FLS at the moment the bottom slider hits its stop.

I found another fowler flap curve that shows the maximum wing cord extension vs travel angle occurs at about 8 degrees.  The extended wing cord of course improves lift.  Again most bang for the buck.

http://books.google.com/books?id=NG2_qiSjmMEC&pg=PA533&lpg=PA533&dq=flap+extension+definition&source=bl&ots=O72hwzKCIg&sig=C2y0r-riJPEZNLv00ymtbimMkGk&hl=en&sa=X&ei=R6IFVMmeHsGBygT124KACg&ved=0CF0Q6AEwBg#v=onepage&q=flap%20extension%20definition&f=true

I am really starting to believe the 50% is of flap extension not flap angle when talking about Fowler flaps.

If 50% extension is where the bottom track hits its stop then 50% and 8 degrees may be the same thing.

Interesting no matter how this comes out.

Offline Randy1

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #51 on: September 03, 2014, 04:05:53 PM »
After a bit of comparing photos and drawings I came to the following conclusions.

From Murder's pictures  and drawing and AK-AK's links It looks to me like the back roller on the top guide is sitting right next to the beginning of the decline in the top track when full retraced.  When the flap starts to extend the back roller follows the down slope of the top rail pushing the back trailing edge of the flap down to clear the trailing edge of the wing pocket the flap sits in retracted.  Before the front roller starts down the track decline the flap angle is somewhat less than the slope of the track decline.  The further down the track slope the front roller goes, the closer the flap gets to the track slope.  When the front roller hits the upper track decline the flap angle is equal to the track down slope.  Once there the bottom track-stop stops the bottom holding rod and the rod 's attaching point to the flap becomes the pivot and the flap makes a large change in angle in a the final extension. 

From this one can see the angle change on the flap during extension is much smaller in the beginning than the end.  If 50% represents travel then by the pictures, 50% is just before the upper front roller hits the down slope of the upper track. 

I feel fairly confident that 50% travel and 8 degrees are the same thing.  I would say I am 75% confident.  That sure would explain why some very creditable sources are both right.  In AH from all our post and especially Murder's, the Maneuver setting is notch one.

Offline earl1937

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #52 on: September 08, 2014, 06:58:21 AM »
After a bit of comparing photos and drawings I came to the following conclusions.

From Murder's pictures  and drawing and AK-AK's links It looks to me like the back roller on the top guide is sitting right next to the beginning of the decline in the top track when full retraced.  When the flap starts to extend the back roller follows the down slope of the top rail pushing the back trailing edge of the flap down to clear the trailing edge of the wing pocket the flap sits in retracted.  Before the front roller starts down the track decline the flap angle is somewhat less than the slope of the track decline.  The further down the track slope the front roller goes, the closer the flap gets to the track slope.  When the front roller hits the upper track decline the flap angle is equal to the track down slope.  Once there the bottom track-stop stops the bottom holding rod and the rod 's attaching point to the flap becomes the pivot and the flap makes a large change in angle in a the final extension. 

From this one can see the angle change on the flap during extension is much smaller in the beginning than the end.  If 50% represents travel then by the pictures, 50% is just before the upper front roller hits the down slope of the upper track. 

I feel fairly confident that 50% travel and 8 degrees are the same thing.  I would say I am 75% confident.  That sure would explain why some very creditable sources are both right.  In AH from all our post and especially Murder's, the Maneuver setting is notch one.
:airplane: One thing is for sure, this has been an interesting thread, but I think it is now time to see what comments are made from this statement: maneuvering flaps are used for what purpose?
The question is, what advantage does the maneuvering flap setting give the pilot during combat maneuvers? To extend that question, which flight control on the aircraft does the maneuvering flaps assist? To extend that question a little further: At what angle of attack of the wing does the 38 have the best turn performance while maintaining maximum combat airspeed?
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Offline FLS

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #53 on: September 09, 2014, 01:49:57 AM »
We don't have a gauge for AOA Earl. Maximum combat airspeed occurs flying straight so I'm not sure what turn performance you're asking about. We generally describe your best instantaneous turn and your best sustained turn.

The advantage of the maneuver flap is to lower your stall speed without the added drag of full flaps. You typically get more than half of the lift increase in the first half of flap extension and more than half of the drag in the second half of flap extension.

Offline Dobs

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Re: P-38 MANEUVER Flap 8 Degrees?
« Reply #54 on: September 12, 2016, 10:46:15 AM »
Interesting read....and more interesting conclusion.

Here is test report from WWII aircraft performance.
ARMY AIR FORCES PROVING GROUND COMMAND
EGLIN FIELD, FLORIDA
SUPPLEMENTARY REPORT
ON
TACTICAL SUITABILITY OF THE P-38G TYPE AIRPLANE
AS COMPARED TO THE P-38F
3 May 1943

Conclusions

                 a.    All conclusions and recommendations applying to the P-38F, apply to the P-38G.

                 b.    Inasmuch as the general maneuverability of this aircraft is probably the lowest of any type of current fighter aircraft, and in view of the competition facing the P-38G in the European Theatre, all possible effort should be made to improve its rate of climb and high speed.

                 c.    The P-38G turns much better than the P-38F (will close 180 in 360 circle) due to maneuver flaps.

But the other half of the coin is stall speed in AHIII seems high...

From
PILOT'S FLIGHT OPERATING INSTRUCTIONS
FOR ARMY MODELS
P-38H Series, P-38J Series, P-38L-1 L-5 and F-5B AIRPLANES

15. STALLS.
a. With power OFF, the airplane stalls at the following
indicated airspeeds at the gross weight noted:
                                                                                            (RPM max, boost min)  (RPM min, boost min)
                                             15,000 Ib. 17,000 Ib. 19,000 Ib.   AHII 17K 38L               AHII 17K 38L
Flaps and landing gear UP        94 mph     100 mph    105 mph     110mph                          118ish
Flaps and landing gear DOWN  69 mph      74 mph     78 mph
b. As stalling speed is approached, the center section
stalls first with noticeable shaking of the airplane, however,
the ailerons remain effective.
c. In either "power-on" or "power-off" stalls with
flaps and landing gear up, the airplane "mushes" straight
forward in a well-controlled stall. With flaps and landing
gear down, there appears to be a slight tendency for
one wing to drop. There is, however, no tendency to
spin. Under these conditions, the nose drops slightly
and, as the speed increases, the wing will come up.

IN AHIII, the plane drops off to left clean stall....

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