Why didn't Allison quickly develop a one-stage 2 speed Supercharger for the P-40

[oldcrowcv63]

(Don't know if this has been covered elsewhere in the forum.)

Thinking of the time-frame of 1941-42. I understand the emphasis on the Turbocharger short-circuiting the development of the two-stage unit but was an upgrade to a two speed unit for the Allison 1710-39 engine beyond Allison's capability or were their other technical issues that prevented or slowed development of a two-speed, one stage unit. 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.

Seems like a 2 speed unit would have been pretty useful on both the P-40E subsequent non-Merlin powered models and for the P-39 as an interim fix. ???

 

[wuzak]

Considering the route they took for the 2 stage engine was to have a variable speed auxiliary stage supercharger, I wonder if that is a route they could have taken to improve the single stage engine's performance?

Neither a variable or 2 speed drive for the supercharger will help much with the altitude performance - unless the fixed gear ratio used was a compromise so as to not take away too much low altitude performance.

 

[Shortround6]

Two speed does very little for altitude use. The big gain is usually in reducing the power needed to drive the supercharger at low altitude buy using a low gear, This also heats the intake charge less and allows the throttle to be opened more reducing pumping losses.

Best illustration is the Merlin III and the Merlin X.
Merlin III used an 8.588 gear with a 10.25 in impeller for an impeller tip speed of about 1151fps. Power was 1030hp at 16,250 ft (no ram). Take off was 880 hp.

Merlin X used a 6.389 low gear and a 8.75 high gear. Impeller speeds were about 857 fps and 1173fps. Power was 1075hp for take-off, 1130hp at 5250ft in low gear and 1010hp at 17,750ft no ram.

Since the power needed to drive the supercharger goes up with the square of the tip speed low gear needed about 53-54% of the power that high gear needed and since about 30-40 percent of the power used is turned into heat over and above the heat resulting from the compression of the air take-off/low altitude performance can be much improved.

On the high end the supercharger is limited to a tip speed below supersonic (around 1100fps at standard sea level pressure and temperature) and while the conditions inside the supercharger allow for slightly higher tip speeds there is a definite limit to how fast you can turn the impeller. IF the tip speeds go supersonic inside the supercharger it sets up shock waves (little sonic booms) that severely impact airflow through the supercharger.

The vast majority of two speed engines in the US ( P&W and Wright radials) used their two speed superchargers to pick up several hundred hp at low altitudes. Critical height ( or full throttle height) in high gear usually being under 15,000ft.

Once Allison got the 9.60 gears to work ( the gears had to be made wider to stand the load, the original thickness 9.60 gears broke) the Allison was giving about as good as it was going to get with that particular supercharger (inlet, impeller, diffuser).
Allison had to redesign the gear case and change the casting patterns (molds) to accommodate the wider gears.

 

[GregP]

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.

 

[wuzak]

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.

The US government did not own the V-1710 design.

They were, however, the only customer for the engine, since the civilian aircraft market was either for cheap, lower powered engines or sewn up by Pratt Whitney and Wright. In any case, the V-1710 was not available for airliner development before WW2.

Thus, without prospects for orders of 2 stage or 2 speed engines Allison did not put their own money into developing them (Allison was small, but they were owned by GM at that time, and if a business case for a 2 stage or 2 speed engine could be made I'm sure GM would have funded it).

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.

Allison did develop a 2 speed supercharger. I am doubtful that the Army or government specified that it had to be a remote unit - as in not an integral 2 stage supercharger like the Merlin's. I would think that Allison's ethos of manufacturability and inter-changeability led them to develop the remote system, whereby a single stage unit could be made into a 2 stage unit by simply bolting on some new parts.

The initial 2 stage units had the liquid to air intercooler, and the carburettor mounted on the auxiliary stage supercharger. Then they moved the carby back to the engine stage supercarger - but that required a different carby with the intercooler. And then they ditched the intercooler and had the same base engine as for a turbocharged installation.

 

[GregP]

The US Government absolutely DID own the V-1710 design and production authorization.

They funded the development with rights and it was proprietary to the Department of Defense.

Wayne, I clearly stated "integral 2-stage supercharger." Allison never developed one. The auxilliary unit was external to the engine, not integral. Joe has two ready for overhaul and sale, should anyone be interested.

 

[tomo pauk]

Where we can read that US Government was the owner of V-1710 design?

Hi, Oldrcrow,

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.

Maybe you mean '2-stage units'?

 

[oldcrowcv63]

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."

 

[oldcrowcv63]

Thanks SR6. That's just the kind of detailed answer I was looking for and also to Wuz and Greg for their added perspective.

 

[Conslaw]

The Allison 1710 was designed with a simple integral supercharger because it was contemplated to be augmented by an external turbocharger when necessary. No external turbo would be necessary for use by airships. By late 1941, the P-47 program crossing over from paper to metal, and its turbocharged R-2800 was extremely promising. The P-38 was flying at nearly 400 MPH with turbocharged 1710s. The P-40 was a stopgap plane to be used until the turbocharged fighters could be delivered in quantity. The one-stage two-speed supercharger was also bested at this time by the two-stage, two-speed supercharger in the F4F Wildcat and similar unit in the prototype F4U Corsair. In essence, the Air Force knew that the single stage two-speed supercharger would not be good enough, and better alternatives were already in the production pipeline. By the way, at this time two-stage two-speed superchargers, probably weren't a realistic option either. There were a shortage of two-stage supercharged engines available to Grumman for its Wildcat production, so some planes had to be delivered with a single-stage unit. These were the maligned F4F-3A models.

 

[Shortround6]

It seems there are a few misconceptions. The Allison was NOT designed as an airship engine. Allison did get money form the Navy for an airship version after the Army told them they had no money for a development contract at that time. The Airship version had NO supercharger of any kind.
Turbo Allisons had been used in at least one (or more ?) Bell Airacudas and the XP and YP-37s.
The lot of early turbo engines used 6.23 gears on the engine driven supercharger and when Allison switched to an "altitude" rated engine without turbo they went to 8.80 gears. They lost of bit of low altitude power doing so but this was masked by the adoption of 100 octane fuel and the fact that the Allison was not used in bombers.

As for the US government "owning" the Allison design, I would certainly like to see some sort of proof.

1. Getting permission to export military goods is different than the goverment owning the design.
2. Getting permission to 'bump' delieveries to a later date than called for in a contract in order to fill foreign orders is not evidence of government "ownership".
3. The Government did NOT present Allison with plans/blueprints for the V-1710 and ask/tell them to build it. This last is closer to what they did with the 'Continental Hyper engine' with much of the 'theory' and initial specifications/drawings coming from the army with Continental just building what they were told.
4. The Government did enter into development contracts with Allison, paying ONLY for work or tests successfully completed. Engine fails on test Allison has to fix/repair engine out of it's own pocket and retest before it gets paid the original contract amount.
5. By the Spring of 1939 the Government OWES Allison over $900,000 dollars for work already done.
6. To get permission to export the engine Allison has to forget about the governments $900,000 debt.

There is little wonder that Allison wasn't falling all over it self developing new versions at it's own expense. Until the Spring of 1939 the Government (read Army) was neither paying it's bills or ordering engines in quantities large enough for Allison to make a profit ( GM had already sunk over 1/2 million into Allison).

 

[tomo pauk]

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?

Okay, thought it was a typo.
I've checked out the Vee's for victory book, and here is what it says about the two.
The -57 was intended for the Curtiss' ill-fated P-53 fighter, using the supercharger desinged by Birmann's TEC (Turbo Engineering Company; the supercharger itself was NOT of turbo variety here). Impeller was bigger, 10.25 in, same as Packard Merlin V-1650-1. The inlet elbow was also new, as it was the carburetor ("Holy Carburetor"). Test engine was completed on April 24, 1942. The gearing was 'Allison typical', using 6.44:1 (as early engines used on P-38 ) and 8.80:1 (as on early P-39 engines, and most of the P-40s). Power at altitude was 1150 HP at 16000 ft; almost as good as with V-1650-1, and slightly better than Allisons with 9.60:1 gearing that were to be produced from second half of 1942 on - in other words, there was no great advantage going for the -57, and as such was canceled.

The -131 (V-1710-G3) was intended for use on variants of the C-54, the 1st engine tested in December 1946. There is also shown the advantage of having a slightly bigger impeller, 10.25 in diameter.

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."

If we discount the -57 as being a co-effort of Allison and TEC, and if the engine was really there in late 1945, then it will really be the 'Allison's 1st' 2-speed engine.

One thing to add - in Feb 1941 (before the USAC's XP-51 flew), the NAA (Lee Atwood) wrote to the GM and Air Corps recommending the Allison to develop a 2-speed supercharger for engines for the future V-1710s for P-51; NAA's engineers considering back then that a perspective Continental V-1430 would be a difficult thing to install in the P-51, due to it's intercooler.

All in all, considering that a two-stage engine was in works, there was no much point in a two-speed supercharger, since it would not improve P-40s main failing, namely the weak hi-alt performance.

 

[oldcrowcv63]

Conslaw, The P-47, F4U and even the P-38 were years from operational deployment in the Fall of 1941 when it began to dawn on USAAF pilots flying the P-40E that they would be essentially ineffective in intercepting high flying bombers (above ~25,000 feet). As you point out, the F4F was handicapped by insufficient numbers of doubly supercharged radial P&W 1830's. Indeed, the P-40 was a stopgap plane until deployment of the P-47 P-38, but it was an inadequate stopgap so the question as stated was based on the assumption that a single stage, 2-speed Supercharger might have been quickly developed for the P-40 that would have incrementally improved its high altitude performance in the time-frame of 1941-42. Instead, the USAAF fielded the P-40K in the Summer/Fall of 1942, which did nothing to improve the aircraft's high altitude performance but did provide additional performance for the overweight aircraft to get off the ground. SR6 has provided the rationale for why it wasn't pursued: little benefit to be achieved, and of course the fact that at about the same time, the single staged, two-speed variant of the Packard-Merlin engined P-40(F) was coming on line which was perhaps a far simpler solution to the problem than a dedicated Allison development.

 

[tomo pauk]

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.

 

[GregP]

You can read about it in Dan Whitney's Vees for Victory and in Graham White's Allied AIrcraft Piston Engines of WWII. In both it is clearly stated that the Allison V-1710 was funded by the US Navy and the US Army Air Corps. In those days, NOBODY in the government would fund a development of a military engine and leave the result in private ownership. If they funded it, they owned it and the rights. If Allison had funded it, and had then offered it to the government, and if they accepted ... they'd still have a provision for government approval for sales and exports to other than US-military customers. It works that way today, too. The only way for Allison to have retained control of the design and manufacturing rights would have been for Allison to fund it, sell to private individuals and/or other countries, and THEN have the US government express an interest. Allison would then have been in a position to accept or reject government control by saying "no" to the controlling provisions. That didn't happen.

If the US Air Force of then or now funds an aircraft, they own the rights and would have approval oversight for any sales to outside entities. Ask Boeing or Lockheed-Martin! If you win the lottery, go try try to buy an F-22! You can't do it and also can't buy the engines or any other parts. Same as in pre-WWII days.

All the government would have had to do to deny Allison sales was to say "no!" That is defacto ownership, just as it is in 2013.

 

[rinkol]

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 original intent seems to have been that a turbo-supercharger would be used if high altitude performance was a priority. In this case, the turbo would be the first stage in a two stage configuration where the second was the mechanically driven supercharger. Since the turbosupercharger provided variable boost, the mechanical supercharger could get by with a single speed and was also suitable for use by itself at lower altitudes. The mechanical supercharger used in most of the V1710 variants seems to have been physically integrated with the engine block and adding a two speed drive would have required major changes. It probably seemed best to continue the original strategy where types such as the P-38 were produced with turbosuperchargers for applications where high performance, particularly at high altitudes, was a priority while types such as the P-39 and P-40 would be produced for low altitude operations. This avoided production disruptions at a critical stage of the war.

 

[P-39 Expert]

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.

 

[swampyankee]

Even today, defense contractors do not have unlimited rights even to products developed at their own expense; this was actually tightened under the Reagan administration, when the DoD had to pass on any article submitted for publication even if no military application was considered.

 

[tomo pauk]

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.

Actually, the main pupose of a low gear was to increase power at lower altitudes, especially the take off power. We know that V-1710s with 'low' gearing were making better power down low than those with 'high' gearing. Everybody was using throttling, not just Allison on their engines. Turbo was not an easy strap-on piece of gear on aircraft that usualy used V-1710, and variable-speed drive was pretty late in game vs. 2-speed dives used on many engines already from late 1930s.
Granted, since the 1-speed V-1710 was rarely powering bombers (apart from the A-36), lack of 2-speed S/C wasn't that much of a problem. Lack of mechanically-driven 2-stage S/C, that would've required a 2- or variable-speed drive to be efficient was a more pressing need. Even the 9.60:1 drive was too late to matter for crucial 1942 year.

 

[wuzak]

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.

You can keep saying this utter bollocks, but it won't make it true.

Single stage Merlins had automatic boost control. They tended to have less power than a V-1710 at low altitudes, but more at high altitudes.

The 2 speed Merlin XX had more power down low than the similar single speed 45, and had more power up high. And the Merlin XX had automatic boost control too.