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Lockheed P-38 test planes and planned developments

Arjen

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Yes, it's sad. Even so: buy the book. It's a good read.
 

Bill Walker

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Apologies if this has been covered before. In cruising through Baugher's web site I see that P-38 s/n 41-1968 was modified by Lockheed with raised booms, in anticipation of tests with floats. Any pictures or drawings of this modification, or of a P-38 on floats?
 

SpudmanWP

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Source:

http://www.456fis.org/P-38_LOCKHEED.htm
 

Bill Walker

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Thanks Spudman. Those booms look pretty much stock. Do you have a date and source for this?

On closer examination, it appears the rear of the booms are kinked up. I guess the concern was spray and/or clearance on the horizontal surfaces, not prop clearance.
 
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CostasTT

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Pic links: http://www.aviationspectator.com/files/images/Lockheed-P-38-Lightning-027.preview.jpg or https://en.wikipedia.org/wiki/File:p-38E_scorpion-tail.jpg

early configuration: http://1000aircraftphotos.com/Contributions/KleinBernhard/6595.htm



Older thread: http://www.secretprojects.co.uk/forum/index.php?topic=1639.15
 

Bill Walker

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Thanks to everyone. I guess I should have searched for "P-38 floatplane", I searched for "P-38 floats".
 

Stargazer2006

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Topics merged.

When it comes to the P-38E modification with the cranked tail booms, also known as the "Piggy-Back" Lightning, the various sources do not seem to agree.

Warbird Tech No. 2 says:
Upswept tail experiment (...) may have derived from Lockheed's earlier short-lived excursion into modifying the P-38 for use on floats for ferrying; this particular iteration was an attempt to address perceived tail problems at high speed.
However, according to the much earlier Detail & Scale No. 57:
Contrary to information published elsewhere, this was not an attempt to cure tail flutter problems. Instead, these design tests were accomplished in anticipation of using the Lightning with floats. The higher tail was necessary in order to keep it out of the water as the aircraft took off or landed, but no seaplane adaptation was ever produced.
It seems that most books devoted to the Lightning go for either one or the other explanation.

However, the Polish Monografie Lotnicze No. 67 provides what may be the most convincing evidence of them all:
  • The project of a Lightning floatplane, to operate in remote areas where no airfields were available (...) was abandoned with the rapid advance of American offensive in the Pacific.
  • P-38E factory No. 5204 with stretched and raised tail (...) was introduced to reduce buffeting. The aeroplane was damaged before first flight.
  • P-38E "Piggy-Back" with the raised tail (...) was tested for fitting in the Lightning floatplane. The tailplane was raised by 33 in. This required the tail booms to be removed immediately aft of the radiators and replaced by modified section. This was the second variant of Lightning tail modification.

That publication show pictures of both experimental aircraft, which are quite different from each other. So if we are to believe the author (who obviously has pictures to back it up), the first P-38E (still with peacetime roundels) to be modified received a stretched tail that was only slightly raised, while the second one (with the early wartime roundels) received the higher raised tail. The former was to be tested in an attempt to improve the tail's aerodynamics, but crashed before it could be tested; the latter was tested in anticipation for the cancelled floatplane version.

One thing continues to bug me though: the P-38 floatplane depicted in the two company illustrations posted above has a tail that looks almost exactly like that of the first modification, NOT the second one!
 

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sienar

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I have found a NACA report that seems to conclusively prove that a raised tail was tested in attempts to improve buffeting, but it is of a slightly different design.


"Buffeting


Neither the results of force tests nor observations of the model behavior during tests gave any indication as to whether or not tail buffeting occurred. Figures 29 and 30, which give results of measurements of the wake at the position of the tail, show that with the standard tail position, the tail will come within the wake of the wing and fuselage at high Mach numbers. These results indicate that raising the horizontal tail surfaces 32 inches above the standard position should keep them out of the wake, except for Mach numbers above .0.75 at angles of attack above 2, and should thereby largely eliminate buffeting. Reference 2 makes a similar conclusion Tests were made with the tail altered as shown in figure 31. The model dimensions indicated correspond to raising the tail 32 inches and moving it back 24 inches on the airplane. Figure 32 shows the aerodynamic characteristics resulting from this change. The only effect as compared to the standard tail position was an increase in stability."


And the included images are below.
 

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Stargazer2006

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sienar said:
I have found a NACA report that seems to conclusively prove that a raised tail was tested in attempts to improve buffeting, but it is of a slightly different design.
Cool. Can you post a link to the PDF file? Thanks!
 

sienar

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Stargazer2006 said:
sienar said:
I have found a NACA report that seems to conclusively prove that a raised tail was tested in attempts to improve buffeting, but it is of a slightly different design.
Cool. Can you post a link to the PDF file? Thanks!

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092690_1993092690.pdf


There are a few other NACA reports about buffeting and the P-38. So if you want to find out everything about the P-38s buffeting problems then I can post them, but I'm guessing that is not why you asked for the report
 

elmayerle

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sienar said:
I have found a NACA report that seems to conclusively prove that a raised tail was tested in attempts to improve buffeting, but it is of a slightly different design.


"Buffeting


Neither the results of force tests nor observations of the model behavior during tests gave any indication as to whether or not tail buffeting occurred. Figures 29 and 30, which give results of measurements of the wake at the position of the tail, show that with the standard tail position, the tail will come within the wake of the wing and fuselage at high Mach numbers. These results indicate that raising the horizontal tail surfaces 32 inches above the standard position should keep them out of the wake, except for Mach numbers above .0.75 at angles of attack above 2, and should thereby largely eliminate buffeting. Reference 2 makes a similar conclusion Tests were made with the tail altered as shown in figure 31. The model dimensions indicated correspond to raising the tail 32 inches and moving it back 24 inches on the airplane. Figure 32 shows the aerodynamic characteristics resulting from this change. The only effect as compared to the standard tail position was an increase in stability."


And the included images are below.
that altered center nacelle looks very similar to what was flown on the Lightning "Swordfish" test aircraft. It would've been interesting to see it in production.
 

KJ_Lesnick

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This is P-38 related in general: I'm curious as to why there were small tailplanes mounted outside the booms
 

Basil

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From the aerodynamic perspective the wind tunnel model with the underslung symmetrical fuselage looks great.
 

GTX

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hesham said:
My dear GTX displayed those drawings before,but I repeat showing them,
with their comments.

Err...I think you might have made a mistake since that lower one is supposedly the variant proposed with a 75mm gun...which is not mentioned.
 

hesham

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Oh sorry,


I will correct it.
 

fightingirish

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Stargazer2006

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Magnificent three-view arrangement in color of the P-38E floatplane version, from Wings, August 1976:
 

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Stargazer2006

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The projected variant of the Lightning with T-9 75 mm gun:
  • Original company drawing by J. N. Moyer, July 12, 1943.
  • Three-view arrangement and cutaway view by Bob Pike.
Source: Airpower, September 1976
 

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Stargazer2006

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CostasTT said:
The swordfish has been mentioned, but there is no picture of it. Time to add one, I think. ;)
Good idea! Here is what I have readily at hand: a larger version of your Aerofiles pictures and another inflight photo seen from the side...
 

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GTX

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Stargazer said:
The projected variant of the Lightning with T-9 75 mm gun:
  • Original company drawing by J. N. Moyer, July 12, 1943.
  • Three-view arrangement and cutaway view by Bob Pike.
Source: Airpower, September 1976

Err...check out the very first post in this thread.
 

Stargazer2006

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SpudmanWP said:
Larger Swordfish and other pics
I beat you to that pic, sorry... But where are the "other pics" you're talking about?

GTX said:
Err...check out the very first post in this thread.
Oops! Didn't go back in the topic further enough. Awfully sorry about this.
I could remove my scans, but since theycame out a bit differently, some folks might want to keep both.
 

SpudmanWP

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Stargazer said:
I beat you to that pic, sorry... But where are the "other pics" you're talking about?
fixed..
 

J.A.W.

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This USAAF P-38J flight test has a summary that is.. fairly damning.

"...airspeed limitations are low... definitely objectionable & hazardous from a combat standpoint..."

& may well be reason why further performance improvements mooted for the 'K' were not proceeded with..

http://www.wwiiaircraftperformance.org/p-38/p-38-67869.html
 

RyanCrierie

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I just found a reference in FEAF files dated 27 August 1945 and signed by GEN Kenney cancelling the order for 250~ P-38 6 gun nose modification kits. Anyone ever heard of this specific mod?

EDIT: Yep, it was mentioned earlier. Here's the cancellation order.
 

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KJ_Lesnick

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Sienar

I have found a NACA report that seems to conclusively prove that a raised tail was tested in attempts to improve buffeting, but it is of a slightly different design.
Was this made to aircraft 41-1986 as well, or just a concept?

These results indicate that raising the horizontal tail surfaces 32 inches above the standard position should keep them out of the wake, except for Mach numbers above .0.75 at angles of attack above 2, and should thereby largely eliminate buffeting. Reference 2 makes a similar conclusion Tests were made with the tail altered as shown in figure 31. The model dimensions indicated correspond to raising the tail 32 inches and moving it back 24 inches on the airplane.
1. Increasing the maximum safe mach number to 0.75 instead of 0.67 or 0.68 seems like an enormous improvement. Why was it not implemented?

2. At the penalty of appearing to split hairs (I'm not) the plane was 24" longer at the position of the leading edge of the horizontal stabilizer, or the plane was 24" longer?

The only effect as compared to the standard tail position was an increase in stability."
What kind of stability? Longitudinal, directional, or both?

Neither the results of force tests nor observations of the model behavior during tests gave any indication as to whether or not tail buffeting occurred.
So, this test was based simply on measurements of the airflow pattern?
 

RyanCrierie

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From an August 20 1943 report on Reconnaissance by Elliott Roosevelt (son of FDR) to Hap Arnold:

9. Another aircraft which was examined at this factory was a two-place T-38 aircraft with two pilots' cockpits in tandem. This aircraft was regarded by the inspection party as a very desirable aircraft for photo reconnaissance if it would be procured within a reasonable length of time. The Lockheed Co. officials stated that the first one of this type would not be able to be produced for at least 18 months, inasmuch as no engineering had as yet been done on the basic design. Therefore, this aircraft was also ruled out of consideration.
 

RyanCrierie

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GTX said:
Hi folks,

Yet another P-38 development/trial - this time in the Torpedo carrying role - apparrently two torps could be carried.

Regards,

Greg
NARA II
COLLEGE PARK, MD
RG 342
ENTRY P-26
SARAH CLARK CENTRAL DECIMAL CORRESPONDENCE
BOX 3008
NND 917647

AAFMC-266-WF-6-22-42-300M

INTER-OFFICE MEMORANDUM
ARMY AIR FORCES
MATERIEL CENTER
Office of The Commanding General

JLR:fma-51

Wright Field, Dayton, Ohio

Date MAR 27 1943

E.O. 431-4-29

TO: Chief, Armament Laboratory,
Engineering Division, Wright Field

SUBJECT: Torpedo Installation on P-38G Airplanes.

1. The installation of two 2,000-lb. torpedoes under the wing of the P-38G airplane No. 43-2381 was inspected in the Armament Hangar on March 19, 1943 by personnel of the Structures Branch, Aircraft Laboratory in answer to a telephone request from Mr. M. Burr of your Laboratory.

2. Each torpedo was slung under the wing (between the fuselage and nacelle) by means of two cables which pass under the torpedo and attach to the spars of the wing at four points, two on each spar and one of which (the outboard attachment on the front spar) is the jacking point. The cables hold the torpedo up against the standard bomb support (pedestal) which has a special fairing at the lower end to fit the contour of the torpedo. Four struts, streamlined with fairing, brace from the lower end of the pedestal to the aforementioned four cable attachment points on the wing to support the pedestal and hence the torpedo against side swaying. Two more struts braced from two of these attaching points on the wing, the ones on the rear spar, to a common point near the extreme aft end of the special pedestal fairing. This point is well aft in terms of the length of the torpedo and braces the torpedo against yawing by means of a threaded pin which screws down through, the support point and seats about three-eighths of an inch deep in a hole in the torpedo. This hole in the torpedo facilitates locating the torpedo such that its center of gravity is midway between the main support cables and directly under the pedestal-support.

3. From inspection the installation seems to be adequately supported against up or down vertical loads, against fore or aft drag loads, against side loads, and against yawing, pitching, or swaying tendencies.

4. The wing is adequately strong for the flight loads due to this installation, but not for landing with the torpedoes still on. If it becomes necessary to land with the torpedoes on, it is recommended that the pilot be cautioned to make an extremely gentle landing.

5. The question was raised as to whether or not it would adversely affect the structure to release only one of the two torpedoes. The structure would not be any more critically loaded when asymmetrically loaded with one torpedo than with two, provided the air controls and lateral balance is such that the pilot can maintain normal flight and maneuvers.

6. The above-mentioned installation is structurally satisfactory, based on visual inspection, for experimental flight testing only.

R. Frichel, Capt., A.C. for
PAUL H. KEMMER,
Colonel, Air Corps,
Chief, Aircraft Laboratory,
Engineering Division.
 

lastdingo

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In 1940 Packard Motors of Detroit began building the two-speed Merlin V-1650-1 (Merlin 28) under license from Rolls Royce. This engine had 1170 horsepower in high blower with a critical altitude of 21,000 feet. Lockheed ran a study comparing a Merlin XX powered Lightning with a standard V-1710 powered variant. The reported speed difference was over 25 mph, favoring the Merlin powered airplane. Climb performance was similar to the Allison powered machine.

Another Merlin vs. Allison comparison in 1942 involved the V-1710-89/91 Allisons (engines used in standard P-38J) and the Packard V-1650-3 two-speed, two-stage Merlin used in the P-51B/C. Utilizing Military Power speed was almost identical.

Yet another study in 1944 compared V-1710s producing 1725 bhp and "advanced" Merlins using "special" fuel and producing 2000 bhp (no altitude specified). The Merlin powered version could supposedly attain 468 mph at 30,000 feet, which was considerably better than the Allison powered version.

These studies were all conducted by Lockheed and exhibit a certain amount of optimism in regard to maximum speed for both types, but the consensus clearly shows better performance with the Merlin powered Lightning.
http://www.wwiiaircraftperformance.org/p-38/p-38-wayne.html
 

sienar

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The Aviation Historian issue 23 has an extensive article on the compressibility problems of the P-38 and makes a very convincing argument that the cause was the wing/fuselage pod junction. Included are a few pictures from NACA that I havent seen elsewhere.

Also illuminating in this article;

The British manager for the P-38 had W.E.W. Petter of Westland evaluate the problem; "He says that they have invariably had trouble when they have required that the air should expand simultaneously in two planes, as for instance when a body is mounted on a wing and its streamline tail coincides with the trailing edge of a wing, or when a fin and tailplane intersect and their trailing edges are roughly in the same plane."

Lockheed took issue with the testing NACA performed, even though they found the same improvement with extending the center pod over the course of multiple tunnel test. One NACA report on this is still unavailable to the public.

Lockheed started experimenting with a lengthened pod on its own in the fall of 1941, retrofitting two aircraft (!)

Highly recommended issue!
 

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