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From: (CDB100620)
Subject: Re: P-51 bob weights and rudder tabs
Date: 16 Sep 1997

The Merlin P-51 had a lot of teething problems, but, for some reason, they
are largely overlooked.  It had problems with the canopy frosting over,
with jamming guns, with the engine cooling system and the engine
itself--and with shedding the tail.  In fact, the plane had so many
problems initially that Col. Don Blakeslee, CO of the 4FG, called it "an
experimental aircraft" and expressed doubts that it could be successful.
The P-38 had gone through its teething troubles the previous fall and with
the introduction into ETO combat of the J model well-pleased its pilots.
FGs getting the P-51 were unhappy and pilots grumbled that they would
rather have the Lockheed.  It was not uncommon to have almost 30 percent of
P-51 sorties aborted for mechanical reasons during the winter and spring of
1944 (typical abort rate for all causes for all USAAF aircraft was 8 percent).
When the D model became available in quantity in the summer, cases of the
aircraft losing its tail surfaces in flight began to be reported.  Flight
restrictions were placed on the aircraft and the tail surfaces were beefed
up.  Wing failures were also reported due to control stick force reversal
in high-speed dives.  The bobweight was added to the elevator control
system to fix this problem.  But for the aircraft to be even marginally
stable, the fuselage fuel tank had to be less than half full.
The Mustang still had problems a year later when the 7AF began B-29 escort
missions to Japan.  Incidences were reported of tail surface failures in
dogfights. In one instance in April, 1945, a P-51D got into a dogfight with
a Mitsubishi Raiden.  During the violent maneuvering, the Mustang first
shed its tail control surfaces and then its wings were torn off.  The
pilot, 2Lt. James Beattie, did not get out.  The Raiden apparently suffered
no damage from the severe loads placed on it during the dogfight.

All that said, the Merlin Mustang was a very effective fighter, but its
greatest successes came in the ETO, where its high abort rate would not
result in equally high pilot fatalities.  Over the vast reaches of the
Pacific, the P-38 was the fighter of choice.  Mustangs suffered their
greatest operational loss of the war on an escort mission to Japan when 27
out of a force of 148 went down.  Most of the losse were weather-related
(always a greater danger than the enemy in those days) rather than
mechanical failures, but the Mustang seemed dogged by bad luck and had
little success battling Japanese fighters over the home islands.  The
contrast with its sweeping victories over the Luftwaffe is striking.
P-38 pilots relate the story of an apparently new-in-theater pilot who
called over the radio, "Mayday!  I've been hit and am losing coolant.  What
should I do."  To which a P-38 pilot replied, "Calm down.  Just feather the
prop and trim for single-engine flight and you'll get home okay."  There is
a long pause, and then the first pilot says, "Feather it, hell!  I'm in a P-51."
Mustang pilots in the PTO sang a ditty that went:

"Don't give me a P-51.
It was all right for fighting the Hun,
But if fighting the Jap you try,
You'll run out of sky.
Don't give me a P-51."

(The reference to "running out of sky" refers to the great amount of
altitude lost in dogfighting the maneverable Japanese fighters.)

In contrast, they sang about the Lightning:

"The P-38 is some machine,
The answer to a flyer's dream.
She'll dive, loop and climb
And turn on a dime.
To every pilot,  she's the queen."

It's interesting  that these two ditties imply that pilots thought the
P-38 was more maneuverable than the P-51.  It could be that they simply
trusted the Lockheed not to come apart during violent  maneuvers, and were
leery of pushing  the North American fighter.  It's even more interesting
that in the MTO and the ETO, apparently, P-38 pilots were a little afraid
of their mounts and hesitated to dogfight Luftwaffe fighters.  Go figure.

From: (CDB100620)
Subject: re: p-40
Date: 26 Sep 1997
Newsgroups: alt.history.what-if

>Wasn't the p-40 the design upon which the later p-51 was based?

The P-40 was the starting point for the P-51 design:  North American set
out to design a fighter with superior performance than the P-40 that would
use the same engine (Allison V-1710) and be more or less the same size.
The prompt was a British Purchasing Commission request for North American
to build P-40s under license, as it wanted to order more of them than
Curtiss could build.   Britishers often say that the Mustang was built to
British specifications. That's oversimplifying.  The design was essentially
North American's, but the BPC did specify that NA buy the wind tunnel and
flight test reports of the Curtiss XP-46 fighter to be used to help develop
the NA fighter.  NA engineers claim that although the company acquired this
material, it was not used in the development of the P-51.
The P-51 design used a boundary layer gutter that separated the cooling
air intake from the fuselage, preventing the intake from ingesting the
boundary layer (the layer of turbulent air close to the skin of the plane.
It was a brilliant idea, and folks are still squabbling over who suggested
the idea.  Some say it was Irving Ashkenas, an NAA aerodynamics engineer.
(He is also credited with moving the radiator air duct from the nose to the
belly of the plane.)  Others say D.B. Shenstone, a Rolls-Royce engineer,
suggested it.
The P-51 also used a laminar flow wing, which greatly reduced drag.  The
wing design was based on work done by NACA (predecessor of NASA).  The
square wingtips were based on pre-war work done by German researchers (Bf
109 had square wingtips).  The laminar wing greatly reduced drag, but it
gave no warning of an impending stall, making the airplane a tricky one to fly.
It was British input that replaced the Allison engine with a Merlin.  The
Allison was a smoother engine than the Merlin, but it only had a
single-stage, single-speed mechanical supercharger, thus limiting engine
performance at altitude.  The Merlin version put in the P-51 had a
two-stage, two-speed mechanical supercharger, which allowed the engine to
perform well to high altitudes.
The shift from first to second speed in the first stage of the
supercharger was barely noticeably, a mild kick at about 8,000 ft., sort of
like downshifting your car from 4th to 3rd at 30 mph.  But the shift from
the first stage to the second stage of the supercharger, which occurred at
about 17,000 feet, was an abrupt lurch, like downshifting your car from 4th
to 3rd at 60 mph.  Sometimes the supercharger would hang up and not shift
when it should, which could be a real problem in combat.
The best solution to high-altitude performance in a piston engine was the
exhaust-gas-driven turbo-supercharger such as was used in the P-38 and P-47
(plus the bombers and transport aircraft, including postwar piston jobs
like the Constellation and DC-6).  It maintained sea level horsepower right
up to 35,000 ft. and more.  But it took up a lot of space and I doubt the
P-51 had room for it.  Then again, the XP-37 variant of the P-40 airframe
was equipped with a turbo-supercharger.  It was mounted under the engine.
And the P-39, a smaller plane than the P-51, was originally equipped with a
turbo-supercharger.  The go-ahead to equip the P-51 with the Merlin may
have been a logistical one.  Packard had built a factory to produce Merlin
engines and there was no airplane to put them in.  The Allison was being
used by the  P-38, P-39 and P-40, and GE was at capacity producing
turbo-superchargers, so the suggestion to put the Packard-built Merlin with
its associated mechanical supercharger into the Mustang, where it fit
neatly with no major re-engineering needed, must have been a very welcome
one merely from a production point of view.  The boost in performance the
Merlin gave the Mustang was an unlooked for plus.

The P-40F was equipped with a Packard Merlin, mainly because of a shortage
of Allisons.  It's performance was about the same as Allison-powered P-40s,
suggesting that the airframe was the limiting factor in improving the
Curtiss fighter's performance.  That the P-51's performance jumped so much
when the Merlin was installed is an indication of just how advanced its
airframe was.

From: (C.C. Jordan)
Newsgroups: rec.aviation.military
Subject: Re: P38 vs P-51 vs 109 vs 190 (was Re: Lindbergh in a Mustang Over
Date: 8 Dec 1998 23:58:22 GMT

On 8 Dec 1998 06:07:50 GMT, (MLenoch) wrote:

>Carlo asks:
>> maximum control input speed,
>>BTW what is this speed for the P-51D ?
>This speed is approximately near the cornering speed of 270 kts/ 310 mph.  Now
>granted, cornering speed allows maximum  turn performance; it not a structuraly
>safe speed for max turn performance COMBINED with maximum roll performance.  To
>put in max pull plus max roll would probably damage the wings.  (I understand
>that the F-16 has a flight control computer that limits max roll against max
>pull and vica- versa to prevent exceeding the wing loads due to control
>>BTW what are the control forces like at 200 kt, 250 kt, 300 kt etc in
>>the P-51 ?
>I dont have numbers to quote this. I would enjoy doing a test flight program
>with the Mustang such as done by the EAA for some of the homebuilt aircraft as
>flown usually by Dave Moruss(sp?).
>My guesses are:
>             full  aileron    3G pull
>200kt     20 lb                  20 lb
>250kt     25 lb                  30 lb
>300kt      ? high!              45 lb
>These numbers would be interesting to research and verify.
>V. Lenoch

Your figures are remarkably accurate. I have data that indicates that the
P-51D, at corner speed, measures 48 lbs in a 3g pull. Up to 86 Lbs at
5g's. The P-47D, OTOH, requires just 16 lbs at 3g and 27 lbs at 5g's.
The testers state that the Mustang was a true "two hander".

My regards,
C.C. Jordan

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