11 replies to this topic

[Paolo]

OK, I guess I'm not the only Motor enthusiast who also likes planes so... here's one for you.

I was always fascinated by the design of the P39 fighter.
Especially interesting was its engine, placed after the pilot instead than forward.
The idea was to have a lower polar inertia moment and thus increase maneuverability.

This arrangement has made miracles for cars, but was a disaster with propeller planes (Airacobra was not the only try at this : there were at least an italian Piaggio and a french Arsenal fighter with similar concepts.).

Apart from its other shortcomings, it is noteworthy that P39 was NOT more maneuverable than its opponents .

I don't mean Zero , i mean Bf 109 and P40 : high wing loading fighters

Now, you cannot place the CG of an aircraft where you like : it must be not far from 25% chord anyway. So Airacobra's CG was more or less in the same position as , say, a P40 Tomahawk.

Yet it probably DID have a lower polar moment.

Why didn't it work ?

One possibility might be a shorter tail (a bad factor for maneuverability), necessary to compensate for the rearward placing of the engine. Yet P39's tail is not expecially short.

Any ideas ?

[Alvega]

An underperforming Allison engine was probably the cause of its relative failure.

[unrepentant lurker]

I'm having trouble picturing it right now. Did it have tricycle landing gear and the propellor ahead?

Could the answer be greater weight do to the longer drivetrain on it?

As Alvega mentions, it could be something unrelated. Although, it is interesting to note that it wasn't a much opted for arrangement. And there were alot of new aircraft being built in that timeframe. One would think there was an inherit disadvantage to the design concept.

[marion5drsn]

The P-39 was an aircraft designed and constructed somewhat for the wrong purpose. It was designed, as a fighter but was a better antitank weapon as proved by the Russians. It was taken out of service by the Army Air Corp and sent to the Russians as Lend-Lease and supposedly used in its more proper role. The cannon was I believe a 37mm running thru the propeller hub. A devastating weapon when used against a tanks upper surface. Supposedly the Russians loved then. Remember the Russians had the Stumavik(sp) a somewhat similar weapon but much better armored.
The use of the non turbo-supercharged Allison V-1710 engine was possibly due to the turbos, which were also used in the Lockheed P-38 that used two of them and the Republic P-47 Thunderbolt Fighter. America had plenty of aircraft it was a matter of just choosing the correct one. From what I have read about these P-39s is that the choosing of the wing section was wrong. All sorts of rumors about the P-39 also possibly created prejudice against it and it was chosen to be sent to Russia as an aid to their difficult war against Germany.

If you are genuinely interested in this aircraft you might call 1-800-826-6600 and ask them if they have any books or pamphlets on this interesting aircraft.
The Allison engine has a great book about its development from 1929 to the end of WW-II and just why it was not a great engine until much development work was done after Pearl Harbor.
This book is, “Vee’s For Victory”. By Daniel D, Whitney ISBN: 0-7643-0561-1. This engine was used on the P-38, P-39 and the P-40. M.L. Anderson

[BRIAN GLOVER]

Cars and planes are my life. I have many thousands of hours on all types of aircraft, military and civilian.

The P39 and later P63s did have high wingloads. Its a way to get speed, but the wing can stall easily, and sometimes when the wing was loaded in a steep turn, the wing would stall, which often led to a snap roll, or as the English say, whip stall. A snap roll is actually a dynamic spin entry, and if an emmediate recovery was not initiated, a full flat spin would be the result, which could not be recovered at the altitudes that that plane flew. It was actually recoverable if the spin went inverted because the rudder was in clean air. Trying to stop rotation by adancing the power, only worsened the problem and the nose went higher than the horizon. The rate of decent would only be about 800ft/min, so that would be a good time to bail.
The P63 was longer and there was more elevator authority, but still would bite the low time pilots that often flew them, as most high loaded wing airplanes do. The rudder was short coupled, and the moment was insufficient to stop rotation, whereas the P51 and P40 had the rudder far aft of the cg. The location of the CG is not a factor,` because it is the same location aft of the centre of lift for all airplanes . A long drive shaft to the propeller gearbox also worsened the 'gyro'precession effect and more rudder pressure was required for co ordinated turns. IE, if that ball goes off centre and you load the wing past critical, guess what, you have just entered a spin. Also if the ball is not centered, the cannon and the machine guns could not be sighted.
Early P51s had the same two stage auxillary supercharged Allison engine, but the P38 had turbo supercharged versions, which were never developed properly. A BF 109 became a ME 109 after 1940. Dont like the plane myself. P51 for me.

The This is a

Originally posted by Paolo
OK, I guess I'm not the only Motor enthusiast who also likes planes so... here's one for you.

I was always fascinated by the design of the P39 fighter.
Especially interesting was its engine, placed after the pilot instead than forward.
The idea was to have a lower polar inertia moment and thus increase maneuverability.

This arrangement has made miracles for cars, but was a disaster with propeller planes (Airacobra was not the only try at this : there were at least an italian Piaggio and a french Arsenal fighter with similar concepts.).

Apart from its other shortcomings, it is noteworthy that P39 was NOT more maneuverable than its opponents .

I don't mean Zero , i mean Bf 109 and P40 : high wing loading fighters

Now, you cannot place the CG of an aircraft where you like : it must be not far from 25% chord anyway. So Airacobra's CG was more or less in the same position as , say, a P40 Tomahawk.

Yet it probably DID have a lower polar moment.

Why didn't it work ?

One possibility might be a shorter tail (a bad factor for maneuverability), necessary to compensate for the rearward placing of the engine. Yet P39's tail is not expecially short.

Any ideas ?

[12.9:1]

Some time ago I read of a wondrous flying machine, pre war counter-rotating, midship mounted-
twin, supercharged straight eight Bugatti engines !! It was to be an air racer but WW2 intervened.
The context I saw it in was, it had shown up in the USA, bought for it's engines {put into cars},and
may still exist.
P-S It had that Bugatti look - sleek, modern, and distinctly different

[BRIAN GLOVER]

Jay Lenno, a late night talk show host in LA, has a 27 Rolls Royce Silver Ghost with a Merlin engine and also a Hispano Suiza car with a HS aircraft engine. Pehaps he has one of the missing engines. His latest aquisition is a Mc Laren F1.
The Discovery Channel started Discovery Wings last week and shows airplanes, 24 hours a day. Call your local cable company. Speed Channel and Discovery Wings, can a divorce be far off?

m

Originally posted by 12.9:1
Some time ago I read of a wondrous flying machine, pre war counter-rotating, midship mounted-
twin, supercharged straight eight Bugatti engines !! It was to be an air racer but WW2 intervened.
The context I saw it in was, it had shown up in the USA, bought for it's engines {put into cars},and
may still exist.
P-S It had that Bugatti look - sleek, modern, and distinctly different

[desmo]

Here is a link to a good brief article on the Bugatti plane. I'd nearly forgotten about it as I hadn't heard anything about since I was young and voraciously devoured any books on aircraft I could get my hands on. Very advanced looking- too advanced for it's day perhaps? Would that radiator scheme have actually worked?

[BRIAN GLOVER]

Thats amazing Desmo. Thanks man. I am a member of the EAA and I receive their monthly magazine, Sport Aviation. The annual convention held in Oshkosh WI, is my Meca. I have never seen this plane in this publication, or any other for that matter. First for me.
Every aviation enthusiast should make a point to visit the annual EAA convention in Oshkosh next year, as it is the 100 annerversary of the airplane. It will be the biggest airshow in the world and a replica of the Right Flyer will fly there after its flight at Kittyhawk, NC,exactly 100 years to the day since the right brothers flight. There is another replica of the Flyer in the museum.
I believe propellers on the same shaft spinning in opposite directions are contra rotating, as opposed to a P38's counter rotating props.

Oh yes, Desmo, I want to take this opportunity to thank you for this most interesting NG. I cant tell you how much I enjoy everybodies company here. I wish I could spend more time here.

Originally posted by desmo
Here is a link to a good brief article on the Bugatti plane. I'd nearly forgotten about it as I hadn't heard anything about since I was young and voraciously devoured any books on aircraft I could get my hands on. Very advanced looking- too advanced for it's day perhaps? Would that radiator scheme have actually worked?

[Roland Kunz]

Hello

Two usefull quotes:

THE BELL XP-39 AIRACOBRA


How America's Best Pre-War Single Engine Fighter
Was Ruined By The Air Corps

The story of the Bell P-39 is one that causes you to stop and think of what might have been, as opposed to what actually was. Having gone down in aviation history as the "Iron Dog", the Airacobra had from its inception, the potential to be the world's finest fighter aircraft at the beginning of America's involvement in WWII. That it instead became one of the wars most loathsome fighters, easily conceals the real potential the prototype.
Bell's XP-39 prototype was rolled out for the world to see on April 6, 1939 at Wright Field. Essentially designed around the new Oldsmobile 37mm cannon (not unlike the A-10 Warthog), the XP-39 was the second design which incorporated the 37mm to come from Bell. Their original concept had placed the cannon behind a front mounted engine, pushing the cockpit too far to the rear of the fuselage to be practical.

Bell's chief engineer, Robert Woods, went back to work and conceived an aircraft with a mid engine location, which allowed the plane's nose to be dedicated to a very heavy ( by late 1930's standards ) battery of weapons. This rather unusual engine placement was not unique. A mid-engine concept had been tried by Koolhoven of Holland with limited success due to a poor choice of powerplant and inadequate technology. Their FK-55 fighter did not live up to expectations. The general concept, however, was not without merit.

Woods' design employed the new Allison V1710 engine, rated at 1,150 hp with the new B-5 turbosupercharger. Installation of the Turbosupercharged Allison promised excellent high altitude performance. This provided for a critical altitude of 20,000 feet, about the same as the XP-38. Expectations were fully met and justified when, on April 6, the XP-39 attained a speed of 390 mph. Later flights produced speeds that flirted with 400 mph (398 mph was reported). Bell's little fighter also displayed a remarkable rate of climb, reaching 20,000 feet in 5 minutes flat! This odd looking aircraft created no small stir in the aviation community. Nothing flying in Europe could match the overall level of performance displayed by the XP-39. At least nothing having the potential for production. It should be noted that the prototype was unarmed and was not fitted with armor plate nor self-sealing fuel tanks (the last two items were not part of the USAAC specification).

Despite the superlative performance of the new Bell fighter, there were design flaws. An undersized vertical stabilizer led to problems with directional stability. Woods' also made a poor choice in airfoil section for the wing. These problems could have been overcome, and in fact, the vertical stabilizer was later redesigned to resemble that of the Curtiss P-36/P-40. Airfoil section design was not addressed until the P-63 Kingcobra, where a laminar flow wing was employed.

After the initial test flight, the XP-39 was turned over to the engineers at Wright Field. And here is where the P-39 was generally undone.

At the time the Bell was being evaluated, the AAF was deep into "streamlining" as a way to improve aircraft performance. This is somewhat understandable, due to the relatively low powered aircraft engines of the 1930's. By reducing drag, especially parasite drag, the engineering minds at Wright Field found that significant increases in performance could be attained. This was all well and good. Unfortunately, they carried it too far as it related to the XP-39. NACA engineers decided that the Bell's turbosupercharger inlet created too much drag. Certainly the inlet generated no greater drag than did the Prestone inlets on the Lockheed XP-38. Nonetheless, they were insistent, the inlet scoop had to go. They reduced the height of the canopy, chopped 2 feet off the wing span and lengthened the fuselage by over a foot. A less powerful Allison with only a single stage mechanical supercharger replaced the turbosupercharged engine. This effectively eliminated decent high altitude performance. Thanks to these changes, the Airacobra had it's center of gravity shifted further aft, exacerbating its already marginal stability. All said and done, the people at Wright Field had reversed the old cliche, and created a sow's ear out of a silk purse.

Certainly Larry Bell and Bob Woods were outraged at the butchered result. Unfortunately, there was very little they could afford to do about it. Bell Aircraft was at the edge of bankruptcy. Having only produced 15 total flyable aircraft, of any type, Bell was deep in debt. Neither Bell nor Woods were willing to go to the mat for their beautiful fighter. To preserve the company's financial viability, they would have to take it on the chin. Their pressing need was to get an order and establish some inward cash flow.

Fortunately, Bell sold the French on the P-39 and received 2 million dollars in advance on an eleven million dollar order. Later that same year (1940), Bell received orders for just under 1,000 P-39Cs and Ds from the USAAF. These were equipped with self-sealing fuel tanks and additional armor, the weight of which, only further degraded performance. Without the turbosupercharger, or even a gear driven two speed, two stage supercharger, the Airacobra was not capable of taking on modern fighter aircraft at anything above 10,000 feet. It should also be noted that the early versions of the Allison V1710 engine never produced anything close to their advertised power rating without a turbosupercharger pressurizing the intake system.

Overall handling had degraded to a point where some claimed (without a grain of truth) that if the pilot simply sneezed, the plane would spin. Some Brits flat out refused to fly the plane, one pilot saying it was more dangerous to RAF pilots than the Luftwaffe. Such extreme examples of exaggeration followed the P-39 throughout its service life.

Adding to the general unhappiness with the airplane, the 37mm Colt M4 cannon frequently jammed after only firing a few rounds. The balance of the guns, 2 .50 cal. M2 and 4 .30 cal. Brownings were inadequate by 1942 standards. One of the problems pointed out by the British was the cockpit being filled with cordite fumes after firing the guns. They also found that firing the guns would knock the magnetic compass out of whack. The RAF did admit that at low level they found the Airacobra to be a match for the Bf-109E. Unfortunately, the RAF needed a high altitude fighter. Besides, the Luftwaffe was now getting newer and far better performing fighters.

Because the Russians were seemingly satisfied with the P-39 is not indicative of the aircraft's performance as much as the Russian's desperate need for combat aircraft. Moreover, the air war on the eastern front was fought largely below 20,000 feet, and more often than not, well below that. At these heights, the P-39 possessed some marginal level of capability. Credit must be given to those Soviet pilots who, despite the severe limits of the aircraft, used them very effectively against the Luftwaffe's superior Bf 109s and Focke Wulf 190s.

Bell P-39s served in North Africa and Italy with the USAAF and several other Allies including the Free French and Italians. Airacobra service in the Pacific has been the subject of many books and articles. In a single sentence; the "Iron Dog" was replaced as quickly as possible.

Taken as a whole, the P-39 was a dismal failure of the AAF's engineering and procurement establishment to identify and develop the better attributes of an advanced and promising fighter aircraft. This was the same establishment that prevented Lockheed from installing Merlin engines in the P-38 as early as 1941. Had the USAAC (Air Corps) not stripped the turbosupercharger from the XP-39, the United States may have entered the war with a competitive single engine fighter plane already in service. Indeed, it was not until the advent of the Bell P-63 that the level of performance finally matched that of the Bell XP-39 of 1939. Of course, by that time, the P-63 was already outclassed by the P-38, P-47 and P-51. Indeed, the P-63 was too little too late. In large part, it was the Air Corps myopic vision of the future of aerial warfare that caused it to be so.



RESOURCES:
Rick Mitchell, The Complete Story of Bell Aircraft Corporation's P-39 Pursuit Fighter Plane.
Ernest R. McDowell, P-39 Airacobra in Action.
Francis H. Dean, America's Hundred Thousand.
Warren M. Bodie, The Lockheed P-38 Lightning.

http://home.att.net/...rdan/XP-39.html


THE BELL P-39 AIRACOBRA

By Patrick Masell

Bell Aircraft Corporation's P-39 Airacobra was a rather strange sight to behold. It had a cannon located in the propeller hub, tricycle landing gear (the first fighter with such a configuration), a car-type door to enter and exit the craft rather than a sliding canopy, and wings set considerably farther aft than normal. Oddity aside, it was a trim and handsome airplane in profile, but it proved notoriously poor in air to air combat. Japanese pilots found it particularly easy to shoot down. Although its dog fighting capability was limited, it enjoyed great success in the hands of Soviet aviators. They found it to be a superb ground attack aircraft, raining destruction upon German armored vehicles.

Designed by Larry Bell to meet requirements for an Army Air Corps fighter competition, the XP-39 first flew in April of 1938. This prototype sported a turbocharger, pushing the aircraft's speed to 390 mph. Its performance roughly matched that of the XP-38, especially at high altitudes. Unfortunately, the Army decided they had no need for high altitude interceptors at the time and both the XP-38 and XP-39 lost the contest to the XP-40.

Nevertheless, the Army expressed interest in the Airacobra, but insisted on a redesign to meet their specifications. They depleted the turbocharger to reduce cost and drag (replacing it with a single stage mechanical supercharger), and also chopped 2 ft off its wings. Their tinkering resulted in a drop in performance, especially at high altitudes. Larry Bell did not dare to protest because the company was facing bankruptcy and desperately needed the Army contract. By December 7, 1941 Bell had delivered 600 P-39s to the Army Air Corps.

The first main production model, the P-39D, was quite typical of the type. It was powered by a 1,150 hp Allison engine (V-1710-35). The engine was placed in the middle of the fuselage behind the cockpit in order to accommodate a 37mm cannon positioned in the nose of the aircraft. This required a very strong structure to keep the engine in place. The whole airplane was basically designed around this gun. The engine drove the propeller via a 10-foot shaft that passed between the pilot's feet. The weight of the amidships engine moved the center of gravity aft. Because of the shift in the center of gravity, Bell's designers were forced to use a then radical tricycle landing gear. In order balance the plane in flight, the wings also had to be moved aft, to a position beneath the engine. Placing the wings directly beneath the engine meant that most of the P-39's weight was concentrated in the middle of the airplane, and that made it a twitchy airplane to fly, one that tended to initiate directional changes with very little control input, roughly analogous to a car that over-steers. The engine was also apt to break loose in the event of a crash landing, with unfortunate results for the pilot sitting right in front of it. It was not a pilot's airplane.

Without a turbocharger, power from the Allison engine fell off severely even at medium altitude. The P-39s acceleration, climb rate, and service ceiling were so compromised that it simply was not competitive with the performance of the enemy fighters it would soon face. Add to that its lack of maneuverability, and in aerial combat the P-39 became "meat on the table" to Axis fighter pilots.

On the plus side, the pilot sat well forward in the fuselage where he could see quite well. The well-designed canopy provided a very good all-around view for its time. The big cannon in the nose was devastating to other aircraft at long range if the pilot could score hits with it. The plane's sleek nose and careful streamlining gave it a good top speed for its time. And the tricycle landing gear was definitely ahead of its time.

Armament consisted of the aforementioned Colt 37mm cannon firing through the propeller hub (30-60 rounds of ammunition), two 50 caliber guns in the nose (200-270 r.p.g.), and 4-.30 cal. wing mounted machine guns (1,000 r.p.g. max.). The preponderance of firepower in the nose made for an effective armament, although the mix of three different calibers with their different trajectories and points of convergence diluted that effectiveness somewhat. The Airacobra was also capable of carrying 500 lbs. of bombs.

The first mass-produced model was the P-39D of 1941. All P-39 models from the D forward were really quite similar. The D-1 temporarily replaced the 37mm cannon with a 20mm cannon. The D-2 model introduced a more powerful 1,325 hp. Allison V-1710-63 engine.

Basic specifications for the P-39D were as follows (taken from The Fighter Aircraft Pocketbook by Roy Cross): Max speed 360 mph at 15,000 ft; Best climb 2,040 ft/min. at 10,300 ft.; Climb to 20,000 ft. 11.7 min.; Range 600 miles at economical cruise; Armament 1-37mm nose cannon, 2-.50 nose m.g., 4-.30 wing m.g.; Span 34 ft. 2 in.; Length 30 ft. 2 in.; Height 11 ft. 10 in.; Wing area 213 sq. ft.; Empty weight 6,300 lbs.; Max weight 9,200 lbs.

The F model of 1942 differed from the D only in detail. A proposed carrier based version of the P-39, the XFL-1, failed its carrier qualification trials and development was abandoned in 1942.

The K and L models of 1943 had V-1710-63 engines and a new propeller. The L also had an improved nose wheel. The M and N models, introduced later in 1943, had V-1710 engines rated at 1,200 hp.

The final, and most numerous, production version was the Q, which replaced the 4-.30 wing guns with two under wing .50 machine guns. The Q-21 and Q-25 variants had a four-bladed propeller. 4,905 P-39Qs were built; large numbers of which went to Russia.

Bell's successor to the P-39 was the similar but somewhat larger P-63A Kingcobra. It was a development of the P-39 based on recommendations from the Russians, and incorporated a redesigned laminar flow wing. Deliveries of this improved version of the P-39 began in October of 1943. The Kingcobra looked pretty similar to the P-39, and was identical in gun armament to the P-39Q, but could carry up to 3-500 lb. bombs. It was powered by a 1,500 hp. Allison engine with a two stage supercharger that gave it a top speed of 361 mph at 5,000 ft. and 410 mph at 25,000 ft. Best climb rate jumped to 3,870 ft/min. at 5,000 ft. Allison engines of up to 1,800 hp (war emergency rating) powered later versions of the P-63. The P-63 was basically an export fighter. The great majority of the approximately 2,970 P-63's produced went to the Soviet Union, but some were also supplied to the Free French.

By 1941 P-39s were being produced in volume and delivered to Army Air Corps bases in the Pacific. Many were given to foreign countries through the Lend-Lease Program. The UK, because of losses during the Battle of Britain, was desperate for fighter aircraft. Still, when the first Airacobras reached squadrons in North Africa, pilots expressed their disdain for it. Six out of twelve P-39's were shot down on their very first combat mission in Europe. The P-39 was facing German fighters at high altitude, where it was greatly outclassed. In fact, the British disliked it so much they canceled the balance of their order, leaving 200 British specification P-39s in Bell's hands. The U.S. Army took over the order and renamed them P-400s.

By the time the Japanese attacked Pearl Harbor P-39s were stationed on American air bases throughout the Pacific region. When Airacobra pilots tried to engage Japanese fighters, they found they were outclassed. The Americans were as disappointed with its performance as were the British. P-39 losses to the Japanese were severe.

There was only one front where the P-39 enjoyed success, the Eastern Front in Russia. The USSR, like other countries, received aircraft from the United States through the Lend-Lease program; 4,773 of them were Airacobras. Unlike everyone else, the Russians loved the P-39. They stripped them of pilot armor and other "non-essentials" to reduce weight and enhance performance. The P-39 turned out to be well suited for combat on the icy Russian Front. Air combat there was at low altitude, where the P-39 performed best. Also, the USSR's air campaign consisted mainly of attacking ground targets, mostly tanks, other vehicles, and soldiers. This was the P-39s strong suit. Bell's fighter also enjoyed success, strangely enough, against the Luftwaffe. The German fighters, particularly the Bf 109, were high altitude interceptors, and their performance dropped considerably at lower levels. In Russia, German pilots were forced to face the Airacobra on its terms.

The P-39's lack of dog fighting capability made it one of the worst fighters of the war, but its durability, impressive armament, and low altitude performance made it an excellent ground support plane and a fearsome predator of German armor. Had it been used correctly the P-39 (which should have been designated the "A-39") might have been one of the most successful ground support airplanes of the war. If the Army hadn't insisted on deleting the prototype's turbocharger it might even have been an effective air superiority fighter.

Unfortunately, the P-39's capability as a fighter-bomber has never been fully credited. Like many other fighters, it falls into the "misunderstood aircraft" category. History remembers it as a pathetic fighter due to an unfortunate error of omission, and because it was improperly employed by everyone except the Russians. Of the 9,558 P-39s of all types built, only one remains in airworthy condition today.

http://www.chuckhawk...ary_history.htm

Other links:


http://trfn.clpgh.org/ah/p39n.html.htm
http://www.hitechcre...&threadid=44670
http://www.realtime.net/centex/p39.htm
http://www.clubhyper...ariantsms_1.htm
http://www.wpafb.af....esearch/p39.htm
http://home.att.net/~C.C.Jordan/index
http://www.elknet.pl...pokri/pokri.htm
http://home.att.net/...one/Welch2.html
http://www.zenoswarb...ation_Link.html

Usefull boards:

http://www.hitechcre...i?ubb=forum&f=9
http://wae.com/qmsgs.html
http://www.mustangsm...m/bbs/index.sht

http://www.insidethe...bs.cgi/mb118405
Now many Automotive names where involved in both; Maybach, Daimler-Benz, Pegasus, Hispano, Fiat, BMW, Rplls Royce, Packard, Debonet even Ford had a triplane ;).

But Bugatti startet a project to tear the speedrecord from the germans but the war came faster and so that got never finished. Maybe the most advanced airplane ever.

Grüsse

[marion5drsn]

These are the numbers of the engines used in the P-63 two stage. No intercooler. It did not get the variable second stage until after the war and this on the Twinboom version P-51 /P-82.
# ENGINE TYPE MODEL AMOUNT hp YEAR SPEED
1
2 V-1710-47 E-9 3? 1325 1940 2
3 V-1710-93 E-11 2521 1325 1940 2
4 V-1710-109 E22 222 1425 1943 2
5 V-1710-109A E22A 128 1425 1944 2
6 V-1710-117 E-21 2237 1325 1943 2
7 V-1710-119 F-32R 5 1500 1943 2

M.L. Anderson

[BRIAN GLOVER]

Howdy Roland.
Thanks for the article. The P39's wing was designed to accept a much more powerful engine and the choice of airfoil was ment for much more thrust than it had. In some respects, it was pretty advanced.
The 3 articles submitted, including Desmo's, had a common thread to this effect, mentioning the emploment of high laminar flow airfoils. Generally, all fighter planes since are configured this way, where the jet engine placement is in this 'mid' location. Mid engines would have been used earlier, had it not been for cooling needs and prop drives. The Wright Flyer had a mid engine.

Had the P39 had a pusher prop, which is more efficient, and also a Merlin engine, it might have been more successfull. The Japanese had such a plane with a tricycle gear prior to the P39, which saw limited combat, but they set the standard for all fighters planes to follow.
To get a high laminar flow wing to work, much thrust is required and additional pilot skills are required, which all pilots at that time did not have, save for some test pilots. Since the F86, exta thrust prevented stalls, even at high loaded turns, but caution was required at take off and landings.
To try and illustrate the difference in wing sections, let me use the following aircraft as examples:
To fly a Beachcraft Baron as opposed to Ted Smith's simirlarly powered Aerostar, will give a pilot some idea, just how different a high laminar flow wing performs. The Barons high drag, high lift wing section is docile, and one can be quite sloppy on short finals in slow flight without penalty. The Aerostar needs high power settings even over the threshold and untill ground effects is reached, just like jet aircraft. On take off, the Baron will start flying when it is ready, and you wont be able to keep it on the runway. The Aerostar will make no attempt to fly at any speed untill sufficient elevator deflection is initiated. Like any high loaded wing, at the right airspeed, one must rotate to a specific and predetermined attitude and the airfoil transitions from induced lift to laminar flow lift before sufficient lift to sustain flight is achieved. IE: a rotate speed and a lift off speed which will vary, depending on gross weight.
Many planes with such an airfoil, get bad reputations, because of untrained pilots. The Mitsubishi MU2 comes to mind.
The Baron will indicate 165kts at cruise and with the same thrust, the Aerostar will indicate 210 kts. At 10000ft the difference in true airspeed will be even more drastic. Both aircraft have pressurized versions that would allow cruise altitudes of 20 000 ft and the Aerostar's ground speed, would be 100 kks faster than the Baron. Now you know why such a wing section was desired by early fighter plane designers.


High laminar flow wings need to be flown differently. You cant fly them by the seat of your pants. You must fly them srictly by the numbers. Predetermind pitch and power settings are used for a specific performance requirement. The P39 may have gotten a bad rap because of this.

[QUOTE]Originally posted by Roland Kunz
[B]Hello

[b]THE BELL XP-39 AIRACOBRA
by Rick Mitchell

How America's Best Pre-War Single Engine Fighter
Was Ruined By The Air Corps
This rather unusual engine placement was not unique. A mid-engine concept had been tried by Koolhoven of Holland
. An undersized vertical stabilizer led to problems with directional stability. Woods' also made a poor choice in airfoil section for the wing. These problems could have been overcome, and in fact, the vertical stabilizer was later redesigned to resemble that of the Curtiss P-36/P-40. Airfoil section design was not addressed until the P-63 Kingcobra, where a laminar flow wing was employed.
, Overall handling had degraded to a point where some claimed (without a grain of truth) that if the pilot simply sneezed, the plane would spin. Some Brits flat out refused to fly the plane, one pilot saying it was more dangerous to RAF pilots than the Luftwaffe. Such extreme examples of exaggeration followed the P-39 throughout its service life.

THE BELL P-39 AIRACOBRA

By Patrick Masell

. Placing the wings directly beneath the engine meant that most of the P-39's weight was concentrated in the middle of the airplane, and that made it a twitchy airplane to fly, one that tended to initiate directional changes with very little control input, roughly analogous to a car that over-steers.