Mustang, was it's wing really laminar flow? Very long
Charles K. Scott
Was the Mustang's laminar flow wing laminar or not?
That is a question asked often in several groups and recently, after
finishing "Pursue and Destroy" by Leonard "Kit" Carson, I believe I
have found a definitive answer.
Mr. Carson's credentials are that 1. He flew the Mustang in combat. 2.
He was an engineer who understood aerodynamics. 3. He was a test pilot
for a while after W.W.II. He goes into extreme technical detail while
telling about the Mustang and his career flying it.
Carson begins his analysis of the Mustang and it's laminar flow wing
back in the late 20's and early 30's when NACA, the National Advisory
Committee for Aerodynamics began it's research on airfoils, airflow,
and other aspects of flying. The airplane companies were in no
position to do this research because they did not have the money to
develop and build wind tunnels. He described airfoil research prior to
NACA as piecemeal, with many airfoils being developed by the OTLAR
method (Oh That Looks About Right, my words, not his)
It was during the thirties that NACA established the relationship
between turbulent flow and drag. Their measurements indicated that the
3/32 inch rivets heads and lap joints on the typical metal airliner
"dissipated" 182 horsepower. On one airplane they were measuring, they
found that a coat of paint cost the airplane 91 horsepower over the
same airplane with bare aluminum. They learned that mere dust, fine
sand or a piece of scotch tape "would cause the smooth laminar layer
next to the wing surface to jump over To a turbulent, high drag
condition."
Then, in 1938, in a wind tunnel designed to smooth out the airflow
through the tunnel (designed by Jacobs and Dryden, prior to this wind
tunnel, flow through the tunnel was too turbulent to test laminar
theories) a new type of airfoil was tested that set new and incredible
drag coefficients compared to any airfoil previously tested. It
recorded a drag coefficient of .003 "which was about half of the lowest
ever recorded before for an airfoil of similar thickness."
Further tests conducted in England "demonstrated that laminar flow and
a reduction of drag could be obtained for a considerable distance over
a smooth full scale wing."
This was in the wind tunnel, however, and it turned out that an
enormous gulf existed between test aircraft and the wind tunnel and
combat aircraft.
The following reasons were given by Carson explaining why in real life
laminar flow simply did not occur on the P-51's wing.
1. The effects of propeller Slipstream. Airflow within the arc of the
prop is very turbulent, "the whole fuselage and inboard section of the
wing next to the fuselage operate in that turbulent stream. Tests in
the Langley wind tunnel revealed that airflow within the arc of the
prop (the prop was 11 feet in diameter which meant that turbulent air
was encountered all the way out to within 13 inches of the inner gun
position) was "90 to 95 percent turbulent" (in other words non laminar)
2. Vibration: "Engine and propeller vibrations transmitted through the
structure will induce transition to turbulence." Tests indicated that
laminar flow on twin engine aircraft was greater with one engine
feathered than with both running. Engineers surmised that the lack of
engine/prop vibration on the dead engine side promoted laminar flow.
Honest, that's what the book said. Of course with both props turning,
more of the wing would be bathed in the prop slipstream which as has
been mentioned above, trips laminar flow to turbulent.
3. Airfoil surface condition: "Mud, dirt, ice and frost will induce the
transition to turbulent conditions." "Fuel truck hoses, ammo belts,
tools, guns and large feet in GI. shoes found the way to the tops of
wings" the scrapes and dents this servicing caused had negative effects
on laminar flow.
4. Manufacturing tolerances: "The Mustang was the smoothest airplane
around in 1940, but there is a practical limit in construction. We're
talking about surface roughness or waviness of .01 inches which will
cause transition to turbulence." (remember the afore mentioned dust
and scotch tape which was observed to trip airflow to turbulent). Some
aerodynamicists have stated that true laminar flow did not occur
outside the wind tunnel until the advent of Burt Rutan's Vary E-Z in
the early 70's with it's incredibly smooth fiberglass over carved foam
wing and aft mounted engine which of course kept the wing ahead of the
prop slipstream.
5. Wing Surface Distortion in Flight: Flight brings flight loads which
can and did distort the wing and cause ripples in the wing surface
which were fully capable of tripping the laminar flow to turbulent.
Carson went on to state: "The Mustang wing was a high lift
configuration, as well as low drag. . . the Mustang in squadron service
was not laminar to the same extent as the wind tunnel development
models. Not one day in the past 34 years (the book was written in 74)
has it performed in that manner for any or all of the reasons just
given."
So if it wasn't the laminar flow wing that gave it it's high speed and
extensive range, what was it?
The most prominent speed secret was the dramatic reduction of cooling
drag. Placing the airscoop on the belly just in front of the rear edge
of the wing removed it as far as was practicable from the turbulence of
the prop and placed it in a high pressure zone which augmented air
inflow. Tests in the wind tunnel with the initial flush mounted scoop
were disappointing. There was so much turbulence that cooling was
inadequate and some doubted that the belly scoop would work. The
breakthrough was to space the scoop away from the surface of the belly
out of the turbulent boundary layer of the fuselage. Further testing
showed that spacing it further out would increase cooling but at a cost
to overall drag. Various wind tunnel tests established the spacing at
the current distance which represents the best compromise between
spacing out from the turbulent flow of the fuselage, drag and airflow.
With the flow into the scoop now smooth and relatively nonturbulent,
the duct leading to the radiator/oil cooler/intercooler was carefully
shaped to slow the air down (the duct shape moves from narrow to wide,
in other words a plenum chamber) enough from the high external speeds
to speeds through the heat exchangers that allowed the flow to extract
maximum heat from the coolant. As the air passed through the radiators
and became heated, it expanded. The duct shape aft of the radiator
forced this heated and expanded air into a narrow passage which gave it
considerable thrust as it exited the exhaust port. The exhaust port
incorporated a movable hinged door that opened automatically depending
on engine temperature to augment the airflow. The thrust realised from
this "jet" of heated air was first postulated by a British
aerodynamicist in 1935. The realization of thrust from suitably
shaped air coolant passages is named after him and called the "Meredith
Effect". Some have said that at certain altitudes and at a particular
power setting the Meredith effect was strong enough to actually
overcome all cooling drag; this is not regarded as being accurate by
most aerodynamicists. It greatly contributed to overall efficiency of
the cooling system but never equaled or overcame cooling drag.
Combine the low overall drag of the Mustang with significantly greater
internal fuel tankage than either the Spitfire, Messerschmitt or
Focke-Wulf 190 and you can easily see how it could fly so far. Add the
two 105 gal external wing tanks and the Mustang was fully capable of
flying to any target the heavy bombers could attack in the ETO. Kit
Carson mentioned that he flew more than 35 missions during which he was
in the cockpit for more than 5 hours.
Finally, Carson was interested to find, while reading flight test
reports in research for his book, that the quoted top speed for the
P-51B was less than what was attained during test flying. The
information is as follows:
Report: NA-5798
Title: "Flight Test Performance for the P-51B-1
Date: January, 1944
Test Weight: 8,460 lbs
High Speed: 453 mph true airspeed at 28,800 feet at 67" HG and 1298 HP,
war emergency power, high blower, critical altitude.
The quoted top speed for the B model Mustang is 440 mph.
I can only speculate that it is likely the test airplane used in the
above mentioned flight was a well maintained and unblemished Mustang.
It's probable that the actual combat aircraft would not be able to
quite equal that performance. Never the less, Carson notes this
information and concludes with the following:
"It's easy to see why many pilots preferred the P-51B, including
myself, even if it did have only 4 guns and the "birdcage" canopy. If
you can't hit'em with 4 guns, two more aren't' going to make your aim
any better."
Corky Scott
David Lednicer
Charles K. Scott wrote:
> The following reasons were given by Carson explaining why in real life
> laminar flow simply did not occur on the P-51's wing.
>
> 1. The effects of propeller Slipstream.
Recent NASA tests have shown that laminar flow can exist on a wing in
the slipstream of a prop. However, it exists on an intermittent basis,
which leads to higher drag.
> 2. Vibration:
Maybe
> 3. Airfoil surface condition:
Yes - and don't forget all the paint lines - NACA wartime data, taken
in flight on a P-51 showed that sanding the paint down improved the
laminar run.
> 4. Manufacturing tolerances:
NACA found surface waviness to be the biggest factor in killing the
laminar flow. By reducing the waviness to less than approximately .004
inches over a 2 inch span, they were able to get the laminar flow
> 5. Wing Surface Distortion in Flight:
This couples with 4.
-------------------------------------------------------------------
David Lednicer | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc. | email: da...@amiwest.com
2133 152nd Ave NE | tel: (206) 643-9090
Redmond, WA 98052 USA | fax: (206) 746-1299
Maury Markowitz
In article <5da4hg$g14$1...@dartvax.dartmouth.edu>,
Charles...@dartmouth.edu (Charles K. Scott) wrote:
Good post, but I must comment...
> The following reasons were given by Carson explaining why in real life
> laminar flow simply did not occur on the P-51's wing.
[snip]
> So if it wasn't the laminar flow wing that gave it it's high speed and
> extensive range, what was it?
I've never heard of a laminar flow wing that is completely laminar,
although perhaps some of the active sucking systems NASA's worked with
are. Laminar flow in this context means "more laminar flow" not
"completely laminar flow".
Airfoils of most of the aircraft of the day (and to some degrees, now)
had the critical point as far forward as 1/2 of the chord, and close to
2/3rds on most (which I think is close to the point on the C-150's and
such). Laminar flow wings move this rearward, reducing the turbulent
area.
All the reasons mentioned are true for disturbing laminar flow, but they
do the same thing on a normal wing too. Think "more laminar flow", and
this is indeed what the P-51 had. It also had a much higher critical mach
number, which for planes in this performance range was very important.
Maury
Matthew Saroff
Maury Markowitz (ma...@softarc.com) wrote:
: In article <5da4hg$g14$1...@dartvax.dartmouth.edu>,
: Charles...@dartmouth.edu (Charles K. Scott) wrote:
: Good post, but I must comment...
: > The following reasons were given by Carson explaining why in real life
: > laminar flow simply did not occur on the P-51's wing.
: [snip]
: > So if it wasn't the laminar flow wing that gave it it's high speed and
: > extensive range, what was it?
: I've never heard of a laminar flow wing that is completely laminar,
: although perhaps some of the active sucking systems NASA's worked with
: are. Laminar flow in this context means "more laminar flow" not
: "completely laminar flow".
: Airfoils of most of the aircraft of the day (and to some degrees, now)
: had the critical point as far forward as 1/2 of the chord, and close to
: 2/3rds on most (which I think is close to the point on the C-150's and
: such). Laminar flow wings move this rearward, reducing the turbulent
: area.
: All the reasons mentioned are true for disturbing laminar flow, but they
: do the same thing on a normal wing too. Think "more laminar flow", and
: this is indeed what the P-51 had. It also had a much higher critical mach
: number, which for planes in this performance range was very important.
Hi,
I have always been told that while the laminar flow wing may have
improved performance, the main contributor was the fact that the radiator
was an extremely efficient job of packaging. By using a configuration
that diverted boundry layer air away from the radiator, you could have
extremely small frontal area for the radiator.
--
-- Matthew Saroff| Standard Disclaimer: Not only do I speak for
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/ o o \ | personalities and the spirits that I channel
______|_____|_____| disavow all knowledge of my activities. ;-)
uuu U uuu |
| In fact, all my personalities and channeled spirits
Saroff wuz here | hate my guts. (Well, maybe with garlic & butter...)
For law enforcment officials monitoring the net: marijuana, cocaine, cia
plutonium, ammonium nitrate, militia, dea, nsa, pgp, hacker, assassinate.
Send suggestions for new and interesting words to: msa...@pobox.com.
CDB100620
Some tidbits about the P-51:
In Sept. '44 flight restrictions were placed on P-51s operating in the ETO
because of reports of the aircraft breaking up while in level flight. At
least 15 cases were witnessed. Trouble traced to weak horizontal
stabilizer/elevators.
On Sept 1, Mustangs of the 325, 31 and 52 FGs straff German airfields in
what was the most destructive single such mission of the entire war: 342
e/a are destroyed or damaged.
On Sept. 11, Mustangs of 339, 55 and 359FGs escorting B-17s engage in a
huge air-to-air near Leipzig. Credited with destroying 116 e/a for the
loss of 15 P-51s.
On Nov. 2, Mustangs of 20, 55, 352, 359 and 364FGs escorting B-17s to
Mersburg fight another huge air battle, downing 134 e/a for the loss of 8
P-51s.
Ten days later, on an escort mission to the same target, they destroy 73
for the loss of 3.
On Nov 21 on an escort to Hanover, they destroy 110 for no losses.
On Nov 27, escort missions result in the destruction of 98 e/a for the
loss of 11 Mustangs.
On Apr. 7, '45, 15 and 21FGs fly first P-51 escort missions over Japan.
On June 1, 148 Mustangs fly an escort mission to Honshu; 27 are lost,
mostly due to terrible weather conditions. It is the greatest single
operational loss of P-51s during the entire war.
By June 22, 1945, it is concluded the Mustang effort over Japan has not
been sucessful. Have embarked on 832 sorties, but only 374 have been able
to reach Japan. Credited with destroying 64 e/a and damaging 180 in
straffing attacks, but only shoot down 10 in air-to-air combat. Eleven
P-51s are shot down in air-to-air. An unknown number more which do not
return to base may have perished due to the effects of battle damage on
the long return flight.
P-51 pilots in the Pacific sang a ditty about the Mustang, the chorus of
which ran:
"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, of course, is to the great amount of altitude lost in
combat maneuvering.
One verse went:
"They taught me how to fly,
and they sent me here to die;
Where the sky is full of Zeros
and kamikaze heros."
A story was passed around of a desperate pilot calling for assistance:
"I've been hit and am losing coolant. What should I do?"
Assuming the pilot was green, some P-38 pilots called back and told him to
calm down: "Just feather the engine and trim for single-engine flight.
You'll get home okay."
To which the response was, "Feather it, hell. I'm in a P-51."
In immediate post-war interviews, Japanese pilots in the CBI and SWPA
(including the P.I.) cite the P-38 as their most feared opponent. In the
Central Pacific it is the F6F, and over Japan, it is the P-51.
AAF encountered difficulties with P-51 in setting up air strips in
SWPA/PI, because it has little cross-wind component. Many are lost in
landing accidents in cross-wind situations. P-38 had no such problems.
In CBI, P-51 was preferred because it used less fuel than the P-38 and has
comparable range.
Scott Chan
Corky Scott Posted,
>In "Pursue and Destroy", Kit Carson states that the P-51H saw limited
>service in the last few weeks of the war against Japan.
Then CDB100620 posted some interesting history about P-51s over Japan
>"By June 22, 1945, it is concluded the Mustang effort over Japan has not
>been sucessful. "
This leads to another question... which Allied fighters did make it over
Japan?
How did they perform? I'm thinking of the long-range P-47N (or was it
P-47M?)
Was it too dangerous for the USN to put carriers close enough to use
Hellcats as escorts? I suppose the whole issue was moot anyway, since the
defenders were very low on fuel and trained pilots, and posed little threat
to the B-29s.
--
Scott Chan
Maury Markowitz
In article <5dair4$2...@news.erie.net>, msa...@moose.erie.net (Matthew
Saroff) wrote:
> I have always been told that while the laminar flow wing may have
> improved performance, the main contributor was the fact that the radiator
> was an extremely efficient job of packaging. By using a configuration
> that diverted boundry layer air away from the radiator, you could have
> extremely small frontal area for the radiator.
Makes sense to me, but then why didn't the Dora do so well? It's
radiator was a thing of beauty. More to the point, the placement of the
radiator did not give the wing bigger internal volume for fuel tanks! :-)
Maury
CDB100620
Maybe the P-51's high performance came from its general low drag profile.
Drag coefficient was 0.0176. Flat plate area was 4.10 sq. ft. (for D
model)
Compare this with the Navy's hottest ship, the F4U:
Drag coefficient = 0.0267. Flat plate area = 8.58 sf (for -1D model)
CDB100620
The April 7 first escort to Japan involved 96 Mustangs of 15 and 21FGs
escorting 103 B-29s of 73BG, flying at between 12,000 and 18,000 ft.
Intercepted by over 100 Japanese planes, mostly Tojos and Nicks with some
Tonys. Japanese fighters ignored the P-51s and went for the B-29s.
15FG bore brunt of fighting. First P-51 shot down was in 21FG, however.
H. Crimm, a veteran of the ETO and CO of 531FS was worried when he saw how
low B-29's were flying, automatically thinking it put them in ideal range
of German 88mm flak. He destroyed the first Japanese fighter nailed on
this mission, a Tony which he downed while it was concentrating on a
bomber. He noted that unlike German pilots, the Japanese pilots continued
to attack the bombers, even when they themselves were under attack by the
escort fighters. A German pilot would break off his attack and dive for
the protection of the anti-aircraft batteries, whereupon the American
pilot would be forced to abandon the chase and the German could try his
attack again. He noted the Tojos were so fast that it was almost
impossible to draw proper lead on them.
The P-51s dropped their 110 gal wing tanks upon sighting the Japanese
fighters, and engaged them at combat power settings for appx 50 mins.
using the fuselage tank. Policy was to save the 184 gals in wing tanks
for going home on. Many, however, had been forced to tap into this
reserve because of the length of the air fight. Iwo Jima was 600 miles
south, the first friendly airfield. Frank Ayers 47FS, was one of these.
When he realized he didn't have enough gas to get home, he began to shake
with fear for about a minute before he was able to get control of himself.
He recalls that he clearly heard a voice telling him, "Don't worry,
you'll be all right." Whereupon he calmed down immediately. He tucked in
under a B-29 and got within 200 miles of Iwo before he had to ditch. The
B-29 pilot let down through heavy overcast guiding Ayers until they broke
out at 100 ft over the ocean, which was ruffled by gale force winds and 20
ft. waves. The B-29 led him to a picket destroyer. Ayers buzzed him,
then pulled up into the overcast and bailed out. After some time floating
he was picked up by sailors who dove off a whaleboat from the DD. Rescue
effort was harrowing for all concerned. Pretty typical experience for
many a P-51 pilot. Many pilots who did make it back had 5 gallons or less
usable fuel left.
3 B-29s were shot down on the raid as were 2 P-51s. The P-51 pilots
claimed 21 air-to-air kills, a figure which was fairly significantly
overstated.
These escort missions, dubbed VLRs (Very Long Range), were so hazardous
that a pilot only had to carry out 15 to complete his combat tour.
On the April 12 mission, only 82 Mustangs were able to make the flight to
Tokyo, escorting 102 B-29s. City was obscured by smaze and smog rising to
15,000 ft. Bounced by appx. 100 Japanese fighters, including a number of
Jacks. James Garnett, 46FS got on the tail of one of these, which
executed what he described as an incredibly fast snap roll and dived away
into the murk. His gun camera film showed some hits so he was officially
credited with a probable, but he believed the plane suffered no
significant damage. In another encounter, two P-51s were bounced by a
Jack. Element leader James Beattie reversed and battled the Jack in a
fierce dogfight with maneuvers so violent his wingman was unable to stay
with him. While trying to shake the Jack from his tail, his Mustang shed
control surfaces and then its wings ripped off. The last his wingman saw
of it, the fuselage was plunging straight down, spining like a top with
Beattie trapped inside. The Jack sprinted off after the bombers,
seemingly none the worse for the encounter. His wingman, Richard
Musgrave, who had served a tour with the 4FG in the ETO, said he had never
witnessed a dogfight with such violent manuevers over Germany. "The
Germans yo-yoed, and broke off the engagementThere are no unread articles
in Techno Talk.
Would you like to list all articles?make it to Iwo and ditched in vile
weather. Four P-51 pilots died over Tokyo, and one who ditched was not
recovered. Mustang pilots put in claims for 16 kills, which seems, again,
to have been optimistic.
Will check out details of P-47, P-38 action over Japan and post a summary.
CDB100620
The Richard Musgrave quote is garbled in my previous quote. It should
read:
The Germans yo-yoed and broke off combat by diving away if forced into a
dogfight situation. The Japanese would fight you with aerobatics and not
quit till you or they were shot down. Every fight with a Japanese was a
one-on-one duel to the death. Fighting the Germans, I felt I was in a
sparring match. I could sense they were guys just like me with no
particular desire to kill me, just beat me in a rough game. It was like
playing football--you could get hurt, but it was incidental to winning.
But I could sense no humanity in the Japanese. They wanted to kill me no
matter what, even if that meant they might die, too. I was deathly afraid
of them because once you entered combat with them, they wouldn't break it
off. You HAD to shoot them down if you wanted to survive."
Jim Chow
> I've never heard of a laminar flow wing that is completely laminar,
>although perhaps some of the active sucking systems NASA's worked with
>are. Laminar flow in this context means "more laminar flow" not
>"completely laminar flow".
>
>do the same thing on a normal wing too. Think "more laminar flow", and
>this is indeed what the P-51 had. It also had a much higher critical mach
>number, which for planes in this performance range was very important.
>
Good points...but I think even "more laminar flow" under normal P-51 operating
conditions would probably be a stretch (or at best, give a very minor
advantage). At cruise Reynolds number conditions
for the P-51, it wouldn't take much of a surface disturbance to trigger
transition instabilities...once you get past about a million Re #, a few
thousandth's imperfection can cause alot of trouble. Since many disturbances
will probably be near the leading edge, the fact that the theoretical design
transition point occurs at 3/4 chord isn't terribly useful.
Jim
Dennis Wilson
CDB100620 <cdb1...@aol.com> wrote:
: By June 22, 1945, it is concluded the Mustang effort over Japan has not
: been sucessful. Have embarked on 832 sorties, but only 374 have been able
: to reach Japan. Credited with destroying 64 e/a and damaging 180 in
: straffing attacks, but only shoot down 10 in air-to-air combat. Eleven
: P-51s are shot down in air-to-air. An unknown number more which do not
: return to base may have perished due to the effects of battle damage on
: the long return flight.
How can that be? On the April 7th mission alone(escorting B-29s
attacking Tokyo) the P-51s scored 21 for the loss of 2. On the 12th, the
P-51s scored another 15. These were all in air combat mind you. I don't
see where you would have gotten 10 air-to-air kills from.
Keith Wilson