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Myths & Legends. Why your textbook is wrong.

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Aesquire

Well-Known Member
Joined
Jul 28, 2014
Messages
3,731
Location
Rochester, NY, USA
I thought a thread on misconceptions, historical, aerodynamic, and other, might be a good idea.

I have several posts in mind, but I'll start with a Historical one.

It is often said that the P-39, P-40, and other fighters in WW2 were crippled because the Allison engines they were stuck with didn't have a Supercharger, limiting their high altitude performance.

That's just not so. Except for a few experimental engines, and a few for PT boats, The Allison V-1710 was made with a built in, gear driven, mechanical supercharger, from the beginning.

The Story of Aviation in WW2 can be considered the Story of Supercharging. If you had better superchargers, you could fly higher, and in some cases, above where the enemy could reach you. Or reach you easily. The High Ground isn't just a Star Wars notion.

The Allison engine story is interesting since it's a tale of hard work, conflicting demands from the customer, and delays because of various causes, not least were the demands of the Air Corps for More Production, Now! So Drop What You're Doing and Make Engines!

The Air Corps staked everything on attaining technological superiority against already superior forces. One linchpin of their strategy was the Turbo-supercharger, which General Electric had been working on since the 1920's, including hauling engines up to the top of Pikes Peak to test them at high altitude.

So the Air Corps insisted that the next generation of fighters and bombers would use Turbo-supercharging. ( Hereafter simply called "Turbo" ) This meant that the supercharger already built into the Allison V-1710 would be geared for sea level operation, and boost for higher altitude would come from the Turbo. This was implicitly written into the contracts.

As it happened the only fighter with an Allison that used Turbos in a production airplane was the Lockheed P-38. But first, it was tried in the Curtis XP-37, & Bell XP-39.

The Curtis airplane was the first to really try to make a turbocharged modern fighter a reality, ( testing with older models goes back to the 1920's ) this redesign of the P-36 Hawk had lines reminiscent of the Bee Gee racers, with the cockpit moved way back to give room to stuff it's turbocharger and intercooler in behind the engine. Visibility and drag issues ( mostly with intake scoops and cooling ) kept the XP-37 from going into production, but it was a great advance in aviation, funky though it looked, and spent a lot of time in a full scale wind tunnel at Langley, and some good hard engineering science came out of the program. It did, however, lead to the P-40, the Only front line fighter available at the beginning of the U.S. entry into WW2.

Curtiss_YP-37_(15952957118).jpg

The Bell XP-39 was another story. The Turbo was mounted on the belly of the plane, and the intercooler ducting on the side. The photo below shows the big intercooler duct, and you can just see the Turbo, and 4 waste gates sticking out of the belly of the plane. Drag city. The XP-39 couldn't make the performance requirements, ( 360 mph asked for, 400 promised ) so...... off to the wind tunnel.

After much testing, the engineers came to 2 conclusions. 1. The Turbosupercharger was not ready, yet. 2. with an "altitude rated" engine, ( with a higher geared mechanical supercharger to provide more boost at altitude ) it would be fast enough to meet expectations. So, even though the engines specified didn't exist yet, that was the Plan. The P-39 got a lot of bad press, but did excellent service in the hands of the Soviet Allies, and P-39s were used for training in the U.S. with a small number sent to the Southwest Pacific, most notably, at Guadalcanal. Most P-39s were shipped to the Soviets. ( one Soviet ace caught a load of hurt when he publicly preferred his P-39 to Soviet planes. In Stalin's Russia that was a big load ) All service P-39s had the mechanical Supercharger built into the Allison, and no Turbo. ( i hope to do another post on the P-39, soon, if this thread is well received )

xp39-17.jpg

The P-38 deserves it's own book... in fact there are several. This is the Best one IMHO.
https://www.abebooks.com/book-search/title/lockheed-p-38-lightning-it-goes-like-hell-kelsey/
The Lockheed P-38 It Goes Like Hell-Kelsey by Warren Bodie.
Since most models of the P-38 had Turbos, it's not relevant to this discussion.



The XP-37 not being considered quite practical, Curtis went after the 1938 Fighter Competition with several variations on the P-36 that was the previous winner for the company. One was to adapt an Allison Engine to the P-36 airframe, with minimum changes. The coolant pipes for the belly mounted Radiator actually were just run along the bottom of the fuselage, on the outside. Again, it was back to the wind tunnel, to clean up the design. The result was a full 50 mph faster than the previous front line fighter, a huge jump after decades of 10-20 mph increases. The P-40 series went on to mass production, and was used by the English, and the U.S. in every theater of the war. Most notably in the African Desert, and in the hands of the American Volunteer Group ( AVG ) in China, the famous Flying Tigers. ( who stole the sharks mouth paint job from the English Tomahawks flown in Africa )

The P-40 is a strange example of the perfect storm in procurement. Allison wanted to make altitude rated, high altitude capable engines, but the Air Corps wouldn't buy them, being dedicated to turbos. Curtis desperately needed altitude rated engines to make the P-40 a success. Behind the scenes, it was arranged to allow Allison to make the engines, and Curtis took credit for the high altitude version, as did Allison, and the Air Corps, each claiming they were the Genius behind the success. ( it was Allison ) In the 1970's Don Berlin, the designer of the P-36 & P-40, while being interviewed, was informed of the reality behind the decision, and laughed. "no wonder they responded to our request ( for high altitude engines ) so quickly!"

xp-40_864.jpg

Here's an Allison V-1710 drawing, showing the Supercharger.

allison_cutawaya.jpg

A pic from the Air Force Museum, of a cutaway V-1710

070703-F-1234S-020.jpg

And... perhaps the Ultimate V-1710, with Turbo-compounding, where the exhaust turns a turbine, that feeds through a reduction gear set, back to feed, not one, but two stages of supercharging, and the crankshaft. A late war development, I don't think this one ever flew, but golly.

turbocompound.jpg

References include, but are not limited to. The excellent Warren Bodie book linked to above,

https://www.amazon.com/Vees-Victory...r1&keywords=v's+for+victory+the+allison+story

Vees For Victory! The Story Of The Allison V-1710 Aircraft Engine 1929-1948 by Daniel D. Whitney

https://www.amazon.com/Allied-Aircraft-Piston-Engines-World/dp/1560916559

Allied Aircraft Piston Engines Of World War II: History And Development Of Frontline Aircraft Piston Engines Produced By Great Britain And The United States by Graham White


and a footlocker full of Wings & Airpower magazines. I keep seeing articles in new magazines that are blatant rip -offs of articles I read 20 plus years ago.

Thank you for your patience. Any errors are mine. ( although I will blame Autocorrect ) I welcome feedback.
 
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