Perk the P51 B

[Karnak]

Just for giggles, here is RAF results of the Mustang Mk III, Spitfire Mk XIV and Tempest Mk V with 150 octane fuel:

[funkedup]

Now THAT would be a perk Mustang.  

[Wilbus]

LoL, those would serious perks overall!

[Vermillion]

Nahh..... if we get a perk mustang, we need the P-51H Now THAT was a beautiful beastie !!

[Fancy]

Perhaps this is not so much an argument to perk the pony B as it is an argument to unperk the Ta152.

[Soulyss]

And the P-51 did have a water tank for WEP.

I'm looking at America's Hundred Thousand and on page 362 under "Engine and Water Injection System" is says:

"No water injection system was used on any production models prior to the P-51H"

[Wilbus]

No Fancy but you understand my argument

This is actually more fix the Ta152 then unperk it or perk the P51 B.

[Soulyss]

I asumed at was kinda obvious from the start when you said

Ok, well, actually, I don't want the P51 B perked

but I guess that got a little over looked.

[-ammo-]

just wanted to add this info that I got froma  newsgroup. I had posed the topic there and was given some great info. Basically, the following information puts the p-51 speed issue to bed IMO. Be advised, alot of you know and understand all that isn said  in this post, and the majority (me included) do not. Thx Peter.. In several parts--

This is going to be redundant for a lot of people, but I've reviewed
the Bulletin Board thread that's been referenced as part of this
question, and, if you don't mind, I'd like to take the opportunity to
do a small bit of teaching for those who'd like to learn where these
numbers come from.  A lot of you know this stuff, so please bear with
me, and if I've typo'ed or Thinko'ed something, please jump in and
correct me.

Let's start with a Glossary.  Some of it's pretty basic, but we'll
need it to get all the ducks in a row.  These are the things you need
to know if you want to figure out if a performance report is valid:

Flight is a balance of four forces: Weight, Lift, Thrust, and Drag.
When the sum of Weight and Lift is 0, you are in level flight.  When
the sum of thrust & drag is 0, you are at the maximum speed.

The Air:  Air, of course, is vital to making an airplane work.  For
our purposes, there are 3 properties of the air that are important.
The Pressure, (P), the Density (Rho), and the Temperature (T).  These
values change as altitude increases.  How these values change can vary
from day to day, and from location to location.  To get past these
differences, the "Standard Atmosphere" was developed.  This is a
mathematical representation of the atmosphere's changes from a given
set of start conditions, how they vary with height, and from this can
be determined the changes due to, say, a difference in temperature or
pressure at ground level.  This definition has changed through time,
in order to reflect our better understanding, and better ability to
measure these conditions.  For this purpose, I'm using the ICAO 1979
Standard Atmosphere, which does vary somewhat from the 1930s NACA
Standard Atmosphere.  (It's not that significant at these altitudes)

The thing that affects an airplane's flight the most is the Dynamic
Pressure, or 'q',  This is the pressure generated by the movement of
air.  q varied with the square of the velocity, so if you go twice as
fast, q is increased by 4 times.  

Because the Pressure, Density, and Temperature of the air decrease as
you travel higher in the atmosphere. (Actually, temperature is
constant about 36,000' or so, but that's not relevant here), the q
generated by a particular airspeed is less than it is at lower
levels.  This has led to the definition of several different measures
of airspeed.  These are:
True Airspeed - the actual speed of movement through the air.
Equivalent Airspeed - the airspeed at sea level corresponding to a
particular q.
Calibrated Airspeed - the Equivalent Airspeed corrected for the
compressibility of the air at that height and speed.  At the speeds
we're talking about, it may amount to 3 or 4 mph.
Indicated Airspeed - The airspeed that shows on the pilot's Airspeed
Indicator.  This can be affected by the location and orientation of
the pitot tube used to measure 'q', and internal system peculiarities.
The difference between CAS and IAS is called Position Error, and
varies with the speed of the aircraft.  It can be as high as 10-15
mph.  We're not actually concerned about it here.

Weight: How much an airplane weighs.  Weight doesn't necessarily
affect speed much, but it has big effects on Excess Acceleration, and
therefore Excess Power, and thus Rate of Climb and Maneuverability.
There's a whole bunch of weights, though.  There are:

Empty Weight: The weight of an airframe without fuel, oil, crew,
Ammunition, Bomb load, or removable equipment.

Basic Weight, or, sometimes, Empty Equipped Weight.  This is the
weight of the airframe with crew, removable equipment, oil, and
unusable fuel. (More or less the true minimum weight that an aircraft
can have.

Normal Loaded Weight: The Basic Weight, plus full internal fuel, and
ammunition.

Maximum Weight: The absolute most weight that you can have without
exceeding some limit. (Like Landing Gear Strength, or strength at some
G load, or engine-out rate of climb, etc.)  This usually, for fighters
requires some amount of external load.

Note that there can be a big difference between a
After World War II, the U.S. Department of Defense, in order to help
make sense of it all, came up with the idea of "Combat Weight", Combat
Weight is a stylized representation of what the weight of an airplane
will be as it may be actually engaged in combat.  It is defined as the
Basic Weight, + 60% of the Internal fuel (In most cases), plus, in the
case of some bomber aircraft, internal bombs.
This affects some aircraft more than others.  In a World War 2
context, there's a lot more difference between a P-51B's Basic Weight,
and its loaded weight, than, say, for a Spitfire or an Me 109.
Most of that difference is fuel, or course.

Here's a quick comparison, with weights expressed as a percentage of
Basic Weight:
P-51B Spitfire IX Me 109G-6
8190# 6650# 6550#
Basic weight 100% 100% 100%
Loaded Weight 120% 110% 110%
Combat Weight 112% 104% 106%

When you consider the difference that a relatively small weight change
can make on maneuverability and climb, you'll see that there's a lot
more difference between a Mustang at it's loaded weight, and a Mustang
over the target area than there is for its contemporaries. (Just for
the record, a P-51B carried about 1600# of gas internally.  The Spit 9
and 109G both could squeeze i about 650-660# of gas.  You can see why
the idea of Combat Weight was considered important.

Lift:  What's required to keep you separate from the ground.  This is
done by, if you will, "fooling the air" into generating a lower
pressure on the top of the wing vs. the bottom of the wing.  For a
given weight, in level flight, Lift is the same as the weight.  How
hard the wing has to work to achieve this lift is measured by the Lift
Coefficient, Cl.  Lift is defined as Cl * S (Wing Area) * q.  As you
can see, since q decreases for a particular True Airspeed with
altitude, the higher you go, the harder the wing has to work.  There's
a maximum limit for CL for each airfoil, called Clmax.  This limits
how much lift a particular wing can generate.  For purposes of Maximum
Speed, Clmax isn't important.

Drag: Drag is the resistance to something moving through the air
generated by pressure on the front parts, friction over the surfaces,
vacuum (low pressure) over the back parts, and drag produced by
generating lift.  Basically, for the speeds involved in this
discussion, this can be divided into 2 components, the Profile Drag
(Drag due to shape), and the Induced Drag (Drag due to Lift).  
These are expressed as the Induced Drag Coefficient (CdI), and the
Profile Drag Coefficient (CdF).  The forces that these produce are
defined, similar to lift, as Coefficient * q * S, where S is a measure
of surface area.  There's some difference of opinion over whether to
relate the Profile Drag coefficient to Wing Area (Easy to measure,
usually) or Wetted Area, which takes into account wing, tail, and
fuselage area exposed to the airstream. (Easier to determine the
effects of changes to clean up an airframe aerodynamically)  We can
get past that by relating profile drag as an Equivalent Profile Area,
which expresses the drag in terms of an imaginary flat plate with a
Drag Coefficient of 1.0 - basically, the draggier the airplane, the
bigger the plate.

Induced Drag is the drag that's generated by the lift that the wing is
producing.  The Coefficient of Induced Drag is defined as:
CdI = (Cl*Cl)/(pi * AR * e)
[pi is of course, pi, as in 3.14157..., AR is the Aspect Ration of the
wing, best calculated as (span * span)/Wing Area, and e is an
efficiency factor related to the shape of the wing.]
As you can tell, Induced Drag, depending on how hard the wing is
working to generate a certain amount of lift, is small at large values
of q. (In other words, it's less as you go faster and/or lower).

Thrust: How much force is being exerted by the aircraft's powerplant
to push it through the air.  This is a toughie.  Reciprocating engines
don't produce thrust directly, they produce power.  (Which is defined
as Torque * rotational Speed - don't sweat that).  Power doesn't
directly translate into thrust, so we'll have to do a bit of
arithmetic:
1 HP = 550 ft-lb/sec.  Now, thrust is lbf (pounds force), since we're
on Earth, we can safely assume 1G - 32.2 ft/sec^2 and not sweat it)
So, to get lbs out of a horsepower number, we divide by 550
ft/sec. (Hey ft/sec, that's speed!) so, if we do a bit more figgering,
to get the speed part down, we end up with T (Thrust in lbs) = HP *
550/v (v in ft/sec).   As you can see, at low speeds, we get bags of
thrust per horsepower.  At high speeds, the thrust decreases.
Here's another table that shows this: (remember that 550 ft/sec = 375
mph)
       Speed      Thrust (1 HP) HP (1# of thrust)
       100 mph      3.75# 0.266
       200 mph      1.88# 0.533
       300 mph      1.25# 0.800
       400 mph      0.94# 1.067
       500 mph      0.75# 1.333

[-ammo-]

continued--

As you can see, as speed goes up, thrust drops off alarmingly.  But,
of course, there's more to it.  A reciprocating engine generates its
thrust by turning propeller, which is basically a set of rotation
wings, which turn torque into thrust by moving a large volume of air
from in front of the propeller disk to behind it.  This of course,
isn't 100% efficient.  While the propeller can be considered a set of
wings, it moves through a complicated airmass.  The airspeed that a
propeller's airfoil sees is defined by the rotational speed of the
propeller, and by the forward motion of the airplane.  There are also,
of course, altitude effects.  An airplane propeller stalls at low
speeds, and has transonic problems at higher airspeeds.  The
efficiency of a propeller isn't constant.  At low speeds, it can be
rather poor, and it drops off at high speeds.  The altitude effects
also mean that a given propeller setting is only most efficient at a
particular combination of Torque, RPM, airspeed, and altitude.  This
led to problems in the 1930s, when airplanes with wide speed ranges
were beginning to be developed, and supercharged engines, which
produced their best power at higher altitudes, were introduced.  As an
example, the Boeing Monomail transport prototype, with a supercharged
Pratt & Whitney Hornet engine, couldn't take off with its propeller
set for the cruising design point of the airframe/engine combination -
the propeller efficiency was too low.  When the propeller was set for
takeoff performance, there was  a hefty hit on cruise speed.  This was
resolved by producing variable pitch and constant speed propellers.
Basically, the pitch change allows the peak efficiency to be
maintained over a wide combination of engine power/ airspeed and
altitude combinations.  What this means for this analysis is that the
thrust produced for a particular horsepower isn't dependant on
altitude.  

Oh, yeah, there's one other factor as well.  Because the combination
of airplane airspeed and the propeller's rotational speed can get
quite high, there's a loss of efficency as the propeller's blades
approach the speed of sound.  To get past that, the propeller shaft is
geared down to keep the total speed low.  The Mustang's V1650 had a
gear ratio of 0.479.  For every 1000 engine RPMs, the propeller turned
479.

The efficency of an airplane propeller is best referenced by the
Advance Ratio, or 'J'. 'J' is defined as J = V(true airspeed) /
n(rotational speed)* d (diameter). For a typical WW 2 fighter airplane
propeller, the highest efficiencies are reached at Js between 1.5 and
3.5.

Now that we've got the propeller out of the way, we need to take a
look at what is driving it.  All WW 2 fighter engines were
supercharged.  Most airplanes started the war with single-stage (one
compressor) single-speed (one peak altitude) superchargers.  This
gives the maximum engine performance at a particular height.  There
are two problems with this combination - It takes engine power to run
the supercharger, so the more you want it to compress (better at
higher altitudes), the less power is available for the propeller.
This leads to less power being available for takeoff, and at lower
altitudes.  There were basically 2 ways to get around this.  One was
to have multiple ratio gear drives, like a car's manual transmission,
to drive the supercharger.  With a slower drive speed, the peak power
was developed at low altitude, and less power was used to drive the
supercharger.  Another possibility was to have a variable speed drive
for the supercharger, like the torque converter on a bulldozer or
tank.  This meant that the supercharger used only as much power as
needed to produce a certain engine power, but at a cost in
efficiency.
 
There is also a limit for how much a single compressor can squeeze
the air.  This limited just how high an airplane engine could go and
produce peak power.  (Typically about 20,000').  This was solved by
using multi-stage superchargers, basically using two superchargers in
tandem so that the main stage (engine stage) supercharger is working
on the already compressed air of the initial (auxiliary stage).  This
could take a number of forms.  Turbosupercharged engines, such as the
Allison V1710 on the P-38, and the Pratt & Whitney R2800 of the P-47,
are one form.  The turbosupercharger delivered "sea level" air
pressures to the single-speed engine supercharger at heights ranging
from Sea Level to over 25,000', with no additional cost of shaft
horsepower to run th  auxiliary stage.  There are drawbacks in that
the turbosuperchargers were fairly heavy, took up a lot of volume, and
required tens of yards of ducting to move air all over the place
within the airframe.  Another approach was to have a separate
Mechanical supercharger, that could be shifted when appropriate to
deliver the best power.  This was the type used on the F4U Corsair and
F6F hellcat.  The drawbacks to this type are also the weight of the
system, and that the power consumed by the supercharger reduces the
power available to the propeller.  (For example, at 20,000', for the
same RPM and Manifold pressure, the R2800 on an F4U produces about
1650 HP, while the turbosupercharged R2800 on a P-47 produces 2000
HP.  The missing 350 HP is driving the supercharger.
Another possibility, which saved weight and bulk, was to have s ingle
supercharger drive that ran both compressors.  This was the type used
on the V1650 Merlin on the Spitfire and P-51.  The advantages are that
the engine wasn't much bigger or heavier than the single-stage
Merlin.  The disadvantages were that it still consumed Shaft
Horsepower, and required very careful design to match the performance
of the two compressors.  Luckily, Rolls had Stanley Hooker, who was
able to sort this all out.

Oh, yeah, and still another thing!  If you design the intake system to
you superchargers right, you can take advantage of thy dynamic
pressure you're generating to basically fool the engine into thinking
its at a lower altitude.  This is referred to as "Ram Recovery", and,
for typical airplanes is in the range of 65-80%.  Well designed
systems can give recoveries higher than 90%.  This is why an
airplane's max speed can occur at altitudes higher than the engine's
best altitude, and for purposes of finding an airplane's maximum
speed, can be critically important.

The data that is presented in the popular references is not a good
basis for accurately determining what the true performance of an
airplane is.  While the data reported is correct, as far as it goes,
context information, which is vital to determining if the numbers are
valid or not, is lacking.  You've basically got to have the following
data before an airframe's performance can be determined - Airspeed,
Specific Excess Power, Altitude, Weight, and Power produced by the
engine(s) . (Note that Max Speed is a case where Specific Excess Power
= 0.)
You'll generally get a Max Speed Number, sometimes an Altitude to go
with it, and, very rarely, a weight.  Power setting information is
almost impossible to find.  In fact, in most references, anything
other than the takeoff power of the engine is impossible to find.

Now to the subject of testing.
Well, there was (And still is) a _lot_ of non-contractor testing that
is performed for any military aircraft.  This testing takes the form
of flying instrumented aircraft over instrumented ranges, wind tunnel
testing, systems testing, the whole gamut.  After acceptance, the
aircraft are often run through test series other times, in order to
provide, for instance comparisons to other aircraft.
The date provided in these tests is normalized, or corrected to
whatever the Standard Atmosphere of the era is, so that comparisons
can be quickly and accurately made.

The data from these tests goes into developing the performance tables
in the Pilot's Operating Handbooks, and also into the data presented
in the (In the U.S. case), Standard Aircraft Characteristics (A
distilled summation of aircraft performance data used as a Staff
Reference ).

Now, for some time, I've been a bit leery about the P-51s Standard
Aircraft Characteristics data.  (A reasonable source for some of these
numbers is Ray Wagner's _American_Combat_Planes_ (Doubleday, several
editions).  The performance numbers he presents are apparently taken
from the "Basic Mission" table of the current "Standard Aircraft
Characteristics".  I've found this correspondence in about 40 test
cases, so it's fairly safe to presume that the data is from a reliable
source.)

At that time, the USAAF performed their testing at, basically, 5,000'
intervals, measuring the performance at SL, 5,000', 10,000, etc.  These
numbers in themselves are accurate, but they don't necessarily
represent the actual points of peak performance of the airplane.  
Not a big deal, really, unless you're an obsessive gearhead/Wing Nut
who plays with CFD for fun. (Guilty)

[-ammo-]

continued--

Now, to the case of the P-51.
I have immediately available to me a number of reports, or data from
reports, that include P-51B/C performance.  These are the Central
Flying Establishment graphs that Guy mentioned in another post, the
comparison report of the P-51B and a pair of F4U-1s made by the Navy
Flight Test Center at Pax River, Also mentioned by Guy, although I'd
obtained my copy from the Navy Historical Office in DC a few years
back.  It, BTW, provides excellent context, describing what was done
to clean up the airplanes before the tests. (And, yes, the Corsairs in
the tests definitely were cooked.)
Other reports are from a test series at Eglin Field as part of the
P-51B acceptance trials, and performance test series EE393 conducted at
Wright Field in early 1943.  I'm not counting the Tactical Reports by
the British Air Fighting Development Unit at Farnborough, but they
make interesting reading.  If Mike Williams is listening in, Thank
You!  The work that you've done obtaining and putting the A&AEE
reports on the web have been invaluable.
Another useful resource is the NACA Technical Reports Server.  Some of
the good folks at NASA have been spending a not inconsiderable amount
of time digitizing and cataloging thousands of the older Tech Reports,
Research Memoranda, and Wartime Reports from 1921 onward, covering
everything from determining the turning circle of a Los Angeles class
rigid airship to Anti-Satellite vehicle trajectories.
Wartime Report L-108 was most useful.  This was a study of a number of
mid-war aircraft tested in the Langley Full Scale Wind Tunnel to
determine the effects of cleaning up these airframes.

As a cross check of these numbers, Rate of Climb figures were
calculated and compared to test figures, if they were available.  The
rate of climb, and best speed for rate of climb crosscheck the drag
and thrust calculations at a mid-point in the performance, rather than
just at the end points.

Anyway, here are the performance numbers

CFE Report, Mustang III (P-51B/C with V1650-7 engine at 61" MAP/3000R
Test Weight 9200#
Max Speed     438 mph @ 27500'
              412 moh @ 14000'
Rate of Climb 2600'/min @ 23000'
      3420'/min @ 11100'

The rate of climb numbers match within 5%, and the best climb speed is
175 mph IAS.

These numbers yield an equivalent Profile Area of 4.1702 sq ft, and a
Ram Recovery of 95%

U.S. Navy Patuxent River Comparison Tests V1650-3 engine at 67" MAP/3000R
Test Weight 9423#
Max Speed   450 mph @ 29200'
    426 mph @ 12600'
No Climb data specifically called out.
Equivalent Profile Area is 4.1812 sq ft, with a Ram Recovery of 95%
Best Rate of Climb speed is also 175 IAS.

Eglin Field tests V1650-3, 67"/3000RPM
Test Weight 9640#
Max Speed   435 mph @ 27000'
    420 mph @ 13100'
No Climb Data
Equivalent Profile Area 4.3315 - note - this aircraft had the wing
pylons attached.  Ram Recovery 85%

Wright Field EE 393 tests      V1650-3 67"/3000RPM
Test Weight 9200#
Max Speed 450 mph @ 28200'
420 mph @ 15300'
Rate of Climb 2666'/min at 28550'
3450'/min at 11857
Equivalent Profile Area 4.0763 Ram Recovery 95%
Note - Calculated Max Rate of Climb at 12000' is 3400'/min at 175 IAS.

NASA Wartime Report data on P-51B
"Beat Up" CdF,     0.0208, for an E.P.A. of 4.84 sq ft.
"Cleaned up" CdF    0.0173, for an E.P.A. of 4.0309 sq ft.
So, the numbers I'm getting fall into the middle of the range,
corresponding to polishing the airplane and sealing up the gun ports.

As a check, I ran data for an "Average" P-51B with a CdF of 0.01800,
and a Ram Recovery 0f 90%.  At a weight of 9200#,
With a V1650-3, this gave me the following numbers:
Vmax, 67"/3000R (Emergency Power) 450 mph @ 30000'
  427 mph @ 19000'
  350 mph @ Sea Level
Vmax, 61"/3000R (Military Power)  445 mph @ 31000'
  425 mph @ 20500'
  335 mph @ Sea Level
Vmax, 46"/2700R (Normal Power)   415 mph @ 34000'
  380 mph @ 22000'
  300 mph @ Sea Level
The logic I'm using for when the supercharger speeds should shift may
need some tuning.

All in all, I'd say that the numbers that are in the reports quoted
above are valid.  They match with NACA's drag data, and they are
internally consistent.

Note that it's rather pointless trying to pin things down too
closely.  Individual airplanes vary, and engine performance varies as
well.  Even coming off the factory floor, a variation of about 5% or
more in the performance numbers is to be expected.

As for the Soviet numbers, I'd be interested in more detail.  From
reading reports from Soviet Pilots flying Merlin Engines Hurricanes
and Spitfires, they seem to have had some trouble getting the full
amount of oomph from their Merlins.  Although the slightly over 400 mph
number at 22,000' sounds pretty close for a V1650-3 airplane in low
blower/Max Cont. Power.  As for limits using 100 Octane rather than
100/130, I had an opportunity to ask a P-51 owner about that way back
when. (Don Davidson, when he owned "Double Trouble II") about running
his airplane on 100LL rather than 100/130.  He limited his power to
61" for takeoff. (Which was the usual value.)  Of course, he didn't run
it at more than 46"/2700 very much.  Since at that time, a Merlin only
cost a quarter of a million bucks, we can safely assume that he
wouldn't risk it needlessly.

and there is more--

Lots of testing gets done on any aircraft by the customer before
acceptance.  Anybody who believes that the U.S. Army doesn't wring out
an aircraft before selecting it for service should check out the
history of the Curtiss P-46, the annointed successor to the P-40, and
an immediate precurser to the NA-73 (P-51 prototype),  This failed
testing so miserably that Curtiss decided that they's start with a
clean sheet of paper (And did no better with the P-60 series), and
sold the engineering data to North American, who used it as an example
of what not to do.  The Brits had been testing P-51s before the
U.S. had.  After all, it was designed to their specifications.  There
was some disbelief on the part of the RAE about the Mustang's
performance numbers as reported from California, but testing of the
first examples to reach the U.K. showed that the numbers were valid.
(The stuff that Guy's pointed out was part of that testing)  It's
possible that the story you've had posted was a conflated version of
that.

There were, of course, a number of tests run on every model of the
P-51 throughout its career.  
I've been able to pull useful data from 4 test series, and use them to
reverse-engineer the basic aerodynamics of the airplane.  
I'll digress a bit here and there, to bring up a few interesing bits
about sources, and other such stuff.
What I've done was to take information from official tests and
technical literature, apply all the basic rules of aerodynamics to
them to determine the basic coefficients that define how an airplane
is going to perform, and then recalculate the airplane's performance
through it's entire flight envelope. (This allows me to crosscheck the
date vs. things like Rate of Climb, Cruise Speed, and Ceiling data.
If they match as well, then the numbers I'm generating are
consistant.)

The tests that I'm using are:
Appendices E and F of a report by the British Central Flying
Establishment, 1946.  These are charts comparing the speed/altitude
and climb/altitude performance of a Mustang II with a V1650-7 engine,
a Spitfire XIV, a Hornet I, and a Meteor III.  The tests were done in
early '46. (In fact, they're the same ones that Guy pointed out.  Mike
Williams has done some great work by ferreting out these reports, and
should be recognized.)  The second set of numbers comes from a test
series flown at Eglin Field in early 1943.  The third set is from Test
Series EE 393, performed at Wright Field in early mid '44,  The last
numbers come from comparison tests of the P-51B vs. two versions of
the F4U-1 Corsair, performed by the U.S. Navy at Patuxent River.
(Guy also managed to find an online copy of this report as well.  I
got mine from the Navy History Office a few years back)
I also cross-checked this data with NACA Wartime Report WR-L-108,
which was a series of tests performed in the Langley Full Scale Wind
Tunnel on various mid-war aircraft with a view to improving their drag
coefficients.

Here are the numbers, and the results of the run. (The data for each
test run turns out to be about 80-100 pages, so I'll just distill it
down a bit.  The data points are at the critical altitude for both
supercharger gear ratios for the appropriate power setting.

CFE: Mustang III with V1650-7 engine, Military Power (61"/3000R)
     Test Weight: 9200#
     Vmax: 438 mph @ 27500'
   412 moh @ 14000'
     These numbers give a CdF of 0.0179, and a Ram Recovery of 95%

Eglin: P-51B with V1650-3 engine, Emergency Power (67"/3000R)
     Test Weight: 9690# (Pylons attached)
     Vmax: 435 mph @ 27000'
   420 mph @ 13100'
     This gives us a CdF of 0.0185, and a Ram Recovery of 85%

EE 393: P-51B with V1650-3 engine, Emergency Power
     Test Weight 9200#
     Vmax: 450 mph @ 28200'
   430 mph @ 15300'
     This gives a CdF of 0.0175, and a Ram Recovery of 95%

Pax River:  P-51C with V1650-3 engine, Emergency Power
     Test Weight 9423#
     Vmax: 450 mph @ 29200'
   426 moh @ 15600'
   CdF 0.017945 Ram Recovery 97%          
 
CdF is the profile drag.  Ram Recovery is the efficency of the
supercharger inlet duct in capturing the dynamic pressure of the air
moving through it.  This can increase the critical altitude of an
engine by, in this case, 6000'.

[-ammo-]

lastly---

So, we've got 4 tests, with these results for CdF:
    0.0179
    0.0185 - with wing pylons.
    0.0175
    0.0179

The NACA Wartime Report L-108, "A Summary of Drag Results From Recent
Langley Full-Scale-Tunnel Tests of Army adn Navy Airplanes", 1945,
shows the P-51B to have an initial CdF of 0.0208 (Beat-up condition)
which was reduced to 0.0173 (Cleaned up, with cowling gaps sealed.)
The drag coefficents seen above are consistant with aircraft having
had a moderate clean up, basically a wax job and taping the gun ports.

I can go into much more detail later, if you'd like.  But, I'd have to
say that the numbers reported here are correct.  They check out
mathematically, and are within the basic coefficents are in line with
what NACA determined as part of their testing.


Again, thx to Peter for providing this information.

[F4UDOA]

Please define cooked? As in the F4U's were cooked?

I am always curious to hear how test were cooked to change a flight simm 60 years later??