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Allison was a relatively small firm. They were ramping up to produce engines at the time, and tyhey asked their primary customer, the Army / Navy, twice if they wanted to fund the development of a 2-stage supercharger. The Army / Navy answered "no" twice. Allison had no other market since the US government owned the V-1710 design, and they could not afford to produce expensive new designs on their own.
So the US government got exactly what it ordered … engines by specific part number. And the government never did authorize Allison to develop an integral 2-stage supercharger on Department of Defense money, so they never got one from Allison.
I've seen documentation (referenced in this forum) that seems to suggest Allison 2-speed units did appear somewhat later in the war but were not used on any fighter aircraft until much later.
Where we can read that US Government was the owner of V-1710 design?
Hi, Oldrcrow,
Maybe you mean '2-stage units'?
Tomo,
Check out:
ModDesig for the engine models described in our forum's thread:
http://www.ww2aircraft.net/forum/engines/allison-v-1710-supercharger-impeller-15753-2.html
On our forum from a discussion in 2008:
Specifically the engine models listed in Kool Kitty89's post number 16:
V-1710-57 -131 although I may have misunderstood the labeling in the chart and Kittys description. It may be the single stage, 2 speed unit was rarely used operationally and was more a developmental step toward the purportedly two stage system used in the P-63 and F-82?
Also, cryptically I found this obscure reference on:
The Allison V-1710 V-16 Engine
to a to a planned upgrade of the DC-3 called the DC-8 Skybus:
"This low-winged contra-rotating pusher transport powered by two V-1710's was announced by Douglas Aircraft in October 1945 as the "Transport of Tomorrow" -- the post-war successor to the DC-3. This airplane had a drive configuration similar to the XB-42 but placed the engines under the floor in the passenger compartment. It's 39,500 gross weight was sufficient to accommodate 48 passengers in a pressurized cabin sitting five abreast. The plane would have been 50% faster than the DC-3, at half the operating cost. The engine was expected to be a derivative of the V-1710-E29, but would have achieved the required altitude performance with a single-stage two-speed supercharger, an Allison first. The airlines were concerned about the maintenance costs of the unconventional propulsion arrangement and chose to purchase conventional Convair 240 and Martin 2-0-2 airlines. The DC-8 designation would be reused for the company's successful first jet transport a decade later."
The main 'driver' for a two speed V-1710 might've been a bomber, not a fighter. However, historically the V-1710 overwhelmingly served in fighter planes, so that 'driver' was not existing.
The main purpose of low gear in a two speed engine is to keep the pilot from overboosting the engine at takeoff.
Allison accomplished this in their single speed engine by throttling the engine at TO and gradually opening the throttle as altitude was gained and air became thinner.
By mid '42 the automatic boost control (automatic manifold pressure regulator) automatically prevented the engine from exceeding a set manifold pressure at any altitude. So the pilot could select full throttle and not overboost the engine at any altitude.
This single speed arrangement provided plenty of power at lower altitudes (peak WEP was under 9500') and adequate power at higher altitudes since the single speed was in effect high gear. It was also lighter and simpler than a two speed arrangement.
The auto boost and variable speeds of the turbo and mechanical auxiliary stage rendered a two speed Allison unnecessary.
The main purpose of low gear in a two speed engine is to keep the pilot from overboosting the engine at takeoff.
Allison accomplished this in their single speed engine by throttling the engine at TO and gradually opening the throttle as altitude was gained and air became thinner.
By mid '42 the automatic boost control (automatic manifold pressure regulator) automatically prevented the engine from exceeding a set manifold pressure at any altitude. So the pilot could select full throttle and not overboost the engine at any altitude.
This single speed arrangement provided plenty of power at lower altitudes (peak WEP was under 9500') and adequate power at higher altitudes since the single speed was in effect high gear. It was also lighter and simpler than a two speed arrangement.
The auto boost and variable speeds of the turbo and mechanical auxiliary stage rendered a two speed Allison unnecessary.