What was the problem with the allison engine?

[MIflyer]

Okay then I guess it is settled.

Almost every supercharged engine built in WWII was made in a two-speed single stage supercharged version. But we could not do that with the V-1710 to give a performance peak at 5000 ft as was done with the V-1710-87 of the A-36A, and also at 20,000 ft as was done with the V-1710-81 of the P-51A. admittedly those two engines used different supercharger impellers but a happy medium must have been impossible.

Every other engine could do that if you made a two speed version, but not the V-1710.

That clears it up. Thanks everybody.

I am just glad I did not know these kinds of facts when I was working as an engineer on aircraft pressurization and pneumatics.

 

[Lighthunmust]

Okay then I guess it is settled.

Almost every supercharged engine built in WWII was made in a two-speed single stage supercharged version. But we could not do that with the V-1710 to give a performance peak at 5000 ft as was done with the V-1710-87 of the A-36A, and also at 20,000 ft as was done with the V-1710-81 of the P-51A. admittedly those two engines used different supercharger impellers but a happy medium must have been impossible.

Every other engine could do that if you made a two speed version, but not the V-1710.

That clears it up. Thanks everybody.

I am just glad I did not know these kinds of facts when I was working as an engineer on aircraft pressurization and pneumatics.

Please don't leave the discussion. I only know a little about the engine you are discussing, but find it very interesting. I now know I have been foolish to have not purchased some of the engine books I've seen. I am ordering Vees for Victory today. I seem to recall another book being available about WW2 aircraft engines that I will purchase. MIflyer and anyone else, do you have any engine book recommendations that are not for an engineer but for a layman.

 

[Shortround6]

Okay then I guess it is settled.

Almost every supercharged engine built in WWII was made in a two-speed single stage supercharged version. But we could not do that with the V-1710 to give a performance peak at 5000 ft as was done with the V-1710-87 of the A-36A, and also at 20,000 ft as was done with the V-1710-81 of the P-51A. admittedly those two engines used different supercharger impellers but a happy medium must have been impossible.

Every other engine could do that if you made a two speed version, but not the V-1710.

That clears it up. Thanks everybody.

I am just glad I did not know these kinds of facts when I was working as an engineer on aircraft pressurization and pneumatics.

OK I will bite, Just what other 2 speed engines had second power peak at 20,000ft?
2 Speed only, not 2 stage.

BTW, most sources give a power peak at 15,500ft for the V-1710-81.

Engine chart on page 271 Of "Vees for Victory" gives 950 hp at 20,000ft at 3000rpm and about 37in manifold pressure.

 

[Shortround6]

MIflyer and anyone else, do you have any engine book recommendations that are not for an engineer but for a layman.

Graham White's book "Allied Aircraft engines of World War II" gives a nice over view of the allied side.

"Major Piston Aero Engines of World War II" by Victor Bingham is a real mixed bag. Lots of information, pictures and drawings but numerous mis-prints and mistakes make it hard to rely on.
You don't have to be an expert when the book disagrees with itself or displacement figures don't agree with given bore and strokes.

Bill Gunsten's "Development of Piston Aero Engines" does help explain some of the "engineering' stuff for laymen.

 

[Lighthunmust]

Graham White's book "Allied Aircraft engines of World War II" gives a nice over view of the allied side.

"Major Piston Aero Engines of World War II" by Victor Bingham is a real mixed bag. Lots of information, pictures and drawings but numerous mis-prints and mistakes make it hard to rely on.
You don't have to be an expert when the book disagrees with itself or displacement figures don't agree with given bore and strokes.

Bill Gunsten's "Development of Piston Aero Engines" does help explain some of the "engineering' stuff for laymen.

Thanks Shortround6. I was just looking at what is available on Amazon.

 

[Readie]

I think the Lancaster (and the follow-on development, the Lincoln) was handicapped by being Merlin powered.

Four turbo charged Allisons (basically the whole engine package from a P-38J/L) would have been more effective. More allitude capability compared to the Merlin 20 series in the Lancaster (equal to the Merlin 85 engines in the Lincoln) to help get above the flak and fighters. The stronger Allison power section could handle more power longer than the Merlin (good for the long climb to allitude) with less maintenance. Most importantly, the turbocharged Allison burned less fuel than a Merlin for the same horsepower, so more bombs for the same takeoff weight.

Griffon power in the Shackleton (another Lancaster follow-on) was also less than ideal. Allison had a turbocompound V-1710 running in their test cell. A single stage single speed version of a gas sipping Allison turbocompound would have been a better match to the Shackleton than the Griffon. (Note, this assumes that Napier misfires with their diesel work. They already had data and blueprints for the Jumo 205 diesel, a Deltic version of a Jumo 205 would have been could have been winner for long range patrol aircraft. Even the 'simplified' second version of the Nomad was wayyyyy too complicated. As with the Sabre, Napier reached too far).

I'm going to stand back after I send this post, just in case a vein in Readie's forehead bursts...

Piper106

Very good...I had to smile.
Cheers
John

 

[Readie]

No such thing as free power

Much higher boost pressure is needed in a turbo for the same bhp due to pressurized air being much hotter, due to conduction from white hot exhaust manifold.

Much more complex management needed in a turbo, to control fueling and ignition due rise of boost pressure compared to a gear driven blower.

Higher pressures and temperatures encouraging detonation, turbo can be a big engine destroyer.

More intercooling needed to cool inlet air.

Much higher incidence of fire due to white hot turbo and manifold.

Compromised exhaust manifold and system function due to restriction of turbo and waste gate not letting the gas flow freely.

Waste gates are fickle things that can jam leading to your cylinder heads coming off with a bang.

Not able to use exhaust jet nozzles worth hundreds of horsepower to the non turbo engine.

Higher cost and with early installations higher weight and greater bulk.

Greater sensitivity to detonation due to unstable octane blends.

The list of exhaust driven blower cons is at least as long as that of a gear driven blower.

The reason you cant get much increase in power in your supercharger by increasing speed is because inlet wont let the air flow you cant just spin it faster. Your cramming too much air in and we all know what happens when you compress air too fast HEAT

My Eaton supercharger can produce more power than standard by spinning faster but, at a cost of a shorter life. The extra power also comes with bigger injectors,bigger intercooler ( a guy in Eastern Europe makes a cracker) bigger valves / different timing, porting and a free flowing exhaust ( pref with no cat) and a remap. All of which must be declared to the insurance company of course...
I would expect an increase from 163 to 210-225 bhp. However, dyno's and superchargers dont mix so its hard to measure exactly.
I used the word 'free' on purpose as the supercharger does take a lot of power to turn whereas a turbo uses exhaust gases which are produced anyway.
My car's supercharger gives its a lot of poke and torque,poor emissions and mpg. The turbo version is more powerfull, gives better mpg and costs less to tax.
But...its souless.
Cheers
John

 

[Shortround6]

No such thing as free power

True

Much higher boost pressure is needed in a turbo for the same bhp due to pressurized air being much hotter, due to conduction from white hot exhaust manifold.

Are we talking about cars or aircraft. Most aircraft Kept the intake ducts separated form the exhaust ducts by space and shielding. In most cases the turbine (hot) section was exposed to the slipstream. Only real point of conduction was through the shaft connecting the turbine and the bearing assembly.

Much more complex management needed in a turbo, to control fueling and ignition due rise of boost pressure compared to a gear driven blower.

Again, cars or aircraft? American aircraft used a two stage system that was designed , at least at the start, to give a constant pressure to the carburetor up to the rated altitude of the turbo. No change in fuel feed or ignition due to turbo.

Higher pressures and temperatures encouraging detonation, turbo can be a big engine destroyer.

True but since every large aircraft engine was supercharged to some degree or other it makes little difference if the if the higher pressures and temperatures are coming from a gear drive blower or a turbo.

More intercooling needed to cool inlet air.

I would really like to see some proof of this. Since there were only 3 production engines that used both turbo and mechanical drive superchargers as first stages in a two stage system. You also have to take out the variables. Like the relative efficiency of the compressors you are comparing. If compressor "A" is operating at 65% efficiency and compressor "B" is at 70% then compressor "A" will heat the intake air more regardless of how it is driven.

Much higher incidence of fire due to white hot turbo and manifold.

DO you have any statistics?

Compromised exhaust manifold and system function due to restriction of turbo and waste gate not letting the gas flow freely.

A bit firmer ground here. GM figured at 20,000ft about an 8% loss in power due to Back pressure compared to an engine with open exhaust. Back pressure at 20,000ft being much loser than sea level due to out side air being half the density/pressure. GM may have been putting a bit of a spin on things because few turbo installations actually ran at as low a back pressure as an open exhaust even at sea level with waste gate wide open.

Waste gates are fickle things that can jam leading to your cylinder heads coming off with a bang.

A more likely scenario is the turbo coming apart with a bang as the stuck waste gate causes the turbine to over speed. P-38s and some bombers didn't have "scatter shields" around the part of the turbo that faced the crew for nothing.

Not able to use exhaust jet nozzles worth hundreds of horsepower to the non turbo engine.

This is a big variable. It works better the higher you go (less back pressure) so it sort of paralleled the turbo, it works better the faster you go so it doesn't work as well for climb as it does for speed. Nozzles have to optimized for one speed/altitude condition or they are a compromise everywhere ( ok, maybe only a few percent)
They work best on V-12s. Short exhausts give best pressure/highest exhaust gas velocity. trying for short stacks on a radial can give you the cowl of a B-25. IS the extra thrust worth the extra drag?
Turbos do help a bit with high altitude cruise, Jet exhaust stacks may help but between the slower speed hurting their efficiency and the much lower mass of the exhaust the jet thrust vs prop hp ratio changes dramatically.

Higher cost and with early installations higher weight and greater bulk.

Quite true

Greater sensitivity to detonation due to unstable octane blends.

given that both American two stage systems didn't introduce the fuel until after the 1 st stage and the intercooler I am not sure how this is a factor. P-38s were often limited by their intercoolers. Intake temperature was to be held to 100 degrees F at the intake of the carburetor. The "unstable octane blends" didn't have a clue as to what happened to the air before it arrived at the carburetor. As long as it is the same pressure and temperature the inlet of the carburetor the fuel will act the same.

 

[gjs238]

What were the supercharger arrangements of the Continental I-1430 and Ford GAA?
Would they have accommodated a 2-speed arrangement, unlike the V-1710?

 

[Readie]

Neatly sums it up


View: https://www.youtube.com/watch?v=hjz8pAGRvsg

Goering remarked 'if the English had fitted Allisons's instead of Merlin's to their Spitfires we would have won...'


View: https://www.youtube.com/watch?v=Svx6tg5Ofc8

'Captain to bomb aimer.... we have a little present for those Allison boys in Scottsdale and Montrose ...'


View: https://www.youtube.com/watch?v=FojsG1oSOv4

A sound and sight to stir the blood of any true Englishman.

Enjoy

Cheers
John

 

[Shortround6]

What were the supercharger arrangements of the Continental I-1430 and Ford GAA?
Would they have accommodated a 2-speed arrangement, unlike the V-1710?

The Continental was intended to be used with a turbo charger and had a single speed supercharger drive to the engine supercharger in most versions (there were at least 13 different versions) there were one or two two speed versions and a 2 speed two stage version but many of these models never made it into an airframe for flight testing.
I don't believe the Ford engine ever made it out of the test cells to be installed in a test mule aircraft so it's actual configuration is also pretty open ended.

 

[Readie]

The Continental was intended to be used with a turbo charger and had a single speed supercharger drive to the engine supercharger in most versions (there were at least 13 different versions) there were one or two two speed versions and a 2 speed two stage version but many of these models never made it into an airframe for flight testing.
I don't believe the Ford engine ever made it out of the test cells to be installed in a test mule aircraft so it's actual configuration is also pretty open ended.

Shortround, do you know if 'turbo lag' was a factor with these turbo charged engines? I know that early car turbo engines were very prone to lag and I wondered if this technology was in its infancy the same issue would spoil performance or fly ( drive) ability.
Superchargers are pretty much instant, but would any turbo lag be negated by a 27 litre engine exhaust volume?
Cheers
John

 

[Shortround6]

Shortround, do you know if 'turbo lag' was a factor with these turbo charged engines? I know that early car turbo engines were very prone to lag and I wondered if this technology was in its infancy the same issue would spoil performance or fly ( drive) ability.
Superchargers are pretty much instant, but would any turbo lag be negated by a 27 litre engine exhaust volume?
Cheers
John

Remember that there were NO single stage turbo charged aircraft engines in WW II. ALL Planes that used a turbo back then (unlike private planes in the 60's and newer) had the turbo feeding an engine driven supercharger. Yes it can take time for one of those old turbos to spool up but it took time for the engine to speed up too. Think of the propeller as a 300-500lb flywheel. A constant speed propeller was also like a variable speed transmission. the more power you feed it the more pitch (resistance) it put on the blades.
Then there is flying technique, proper cruise with a P-38 called for low engine rpm but several lbs of boost. The turbo should have been partially wound up to begin with. That was part of the Problem with P-38s in Europe. Some local "expert" had told the pilots in England they would get better throttle response if they cruised at higher rpm and low boost. This was against the advice of both Allison and Lockheed. Not only was the turbo idling but the low pressure meant that the intake charge was too cool and proper fuel vaporization was a problem among other things.

 

[Readie]

Remember that there were NO single stage turbo charged aircraft engines in WW II. ALL Planes that used a turbo back then (unlike private planes in the 60's and newer) had the turbo feeding an engine driven supercharger. Yes it can take time for one of those old turbos to spool up but it took time for the engine to speed up too. Think of the propeller as a 300-500lb flywheel. A constant speed propeller was also like a variable speed transmission. the more power you feed it the more pitch (resistance) it put on the blades.
Then there is flying technique, proper cruise with a P-38 called for low engine rpm but several lbs of boost. The turbo should have been partially wound up to begin with. That was part of the Problem with P-38s in Europe. Some local "expert" had told the pilots in England they would get better throttle response if they cruised at higher rpm and low boost. This was against the advice of both Allison and Lockheed. Not only was the turbo idling but the low pressure meant that the intake charge was too cool and proper fuel vaporization was a problem among other things.

Thanks,I hadn't considered the propeller.

I found this as well about ejector exhausts.
Merlin 55 ejector exhaust detail, Spitfire LF.VB, EP120
The Merlin consumed an enormous volume of air at full power (equivalent to the volume of a single-decker bus per minute), and with the exhaust gases exiting at 1,300 mph (2,100 km/h) it was realised that useful thrust could be gained simply by angling the gases backwards instead of venting sideways.
During tests, 70 pounds-force (310 N; 32 kgf) thrust at 300 miles per hour , or roughly 70 horsepower was obtained which increased the level maximum speed of the Spitfire by 10 mph to 360 mph The first versions of the ejector exhausts featured round outlets, while subsequent versions of the system used "fishtail" style outlets which marginally increased thrust.

The same principle would apply to other in line engines and may be even radials?
Cheers
John

 

[davparlr]

The same principle would apply to other in line engines and may be even radials?
Cheers
John

Not much of a trade off for the P-47. The turbo supercharger on the P-47D-25 allowed the engine to generate an incredible 2300 hp all the way up to 33k. Of course, even more incredible was the P-47M/N, which generated 2800 hp up to 33k, and 2600 hp up to 35k, over twice the power of the high altitude, non turbo charged Ta-152H and 800 hp more than the dual engined Do-335A-1. Loss of exhaust thrust was insignificant compared to power gained.

 

[Lighthunmust]

Not much of a trade off for the P-47. The turbo supercharger on the P-47D-25 allowed the engine to generate an incredible 2300 hp all the way up to 33k. Of course, even more incredible was the P-47M/N, which generated 2800 hp up to 33k, and 2600 hp up to 35k, over twice the power of the high altitude, non turbo charged Ta-152H and 800 hp more than the dual engined Do-335A-1. Loss of exhaust thrust was insignificant compared to power gained.

Until I saw one at the Yanks Museum in Chino,CA the P-47M seemed like a mythological beast. Seeing your location davparir I am guessing you have seen it. If not, make time, you will enjoy Yanks.

 

[gjs238]

So, we've learned a great deal about the limitations of the Allison design.
And about the flexibility of the RR design and the genius of Sir Stanley Hooker.

What about DB superchargers?
I know about the fluid coupling w/barometrically controlled speed.
Were the earlier designs fixed-speed?
Did the design lend itself to two stages?
How did high altitude performance compare to RR and US turbo designs?

 

[Shortround6]

As far as I can find out the first 601s used a single speed drive, there may have been a 2 speed drive on an other early model. German superchargers were no better and no worse than anybody else's in 1938-40. Since the German engines needed less boost than the Merlin or Allison the same performance supercharger could supply the required pressure at a somewhat higher altitude. Once they went to higher boost (anything much over 1.42 Ata) they were running into the same problems as the allies. However by that time better performing superchargers were coming into use.

By "performance" I mean the pressure ratio and efficiency. A supercharger that can achieve the same pressure ratio with better efficiency not only uses less power to drive, it heats the intake charge less and allows slightly higher boost before detonation, the cooler charge is also denser at the same pressure and offers more power from that aspect. Super charger design tended to move in fits and starts on both sides.

The Germans certainly knew of the advantages of two stage supercharging having used it on at least two different Grand Prix cars in the Late 30s. Granted they were roots superchargers but the basic principle of slitting the work over two superchargers instead of one still applied. Two stage superchargers actually took less power than a single supercharger for the same boost and heated the intake charge less. Obviously using two added weight, bulk and cost even before you hit boost levels that required inter cooling.

 

[wuzak]

As far as I can find out the first 601s used a single speed drive, there may have been a 2 speed drive on an other early model. German superchargers were no better and no worse than anybody else's in 1938-40. Since the German engines needed less boost than the Merlin or Allison the same performance supercharger could supply the required pressure at a somewhat higher altitude. Once they went to higher boost (anything much over 1.42 Ata) they were running into the same problems as the allies. However by that time better performing superchargers were coming into use.

The DB series engines used a variable speed drive for their supercharger. Basically a fluid coupling altered the speed of the impeller depending on the altitude reached.

The Germans certainly knew of the advantages of two stage supercharging having used it on at least two different Grand Prix cars in the Late 30s. Granted they were roots superchargers but the basic principle of slitting the work over two superchargers instead of one still applied. Two stage superchargers actually took less power than a single supercharger for the same boost and heated the intake charge less. Obviously using two added weight, bulk and cost even before you hit boost levels that required inter cooling.

The Mercedes-Benz W154 used the M154 engine with two superchargers in 1938. The superchargers were of the same size, and worked in parallel, not series. For 1939 the W154 ran the M163 version of the 3l V12, which had a two stage supercharging system. One blower was smaller in size than the other.

Alfa Romeo designed the 158 for Voiturette racing in the late 1930s. I believe it had a single supercharger. Post war the 158s dominated GP racing, and were developed into the 159 with two stage supercharging.

Britain's response to the Alfa was the BRM Type 15, which was powered by a 1.5l V16 with two stage supercharging by Rolls-Royce. The supercharger was a mini Merlin 60-series style supercharger, with both stage impellers mounted on a common shaft. R-R suggested some things that would help with engine response, as centrifugal compressors work at high rpm and don't make boost low down. BRM ignored or couldn't afford R-R's suggestions.

 

[wuzak]

Not much of a trade off for the P-47. The turbo supercharger on the P-47D-25 allowed the engine to generate an incredible 2300 hp all the way up to 33k. Of course, even more incredible was the P-47M/N, which generated 2800 hp up to 33k, and 2600 hp up to 35k, over twice the power of the high altitude, non turbo charged Ta-152H and 800 hp more than the dual engined Do-335A-1. Loss of exhaust thrust was insignificant compared to power gained.

Power is one thing, but how much power is translated into forward motion is another.

At such altitudes the performance of the prop falls off, unless the prop is designed for such altitudes. And if the prop is designed for high altitudes it will be less effective down low.

Take, for instance, the Mosquito. For the high altitude types, like the XVI, "paddle blade" props were used. For Sea Mosquitoes, where performance at sea level was paramount for getting off carrier decks, "needle blade" props were used.

The later M/N Thuderbolts repositioned the supercharger such that some exhaust thrust was still available. The residual thrust on turbo installations such as on the Lightning was essentially lost. The XP-67 had the turbo with its shaft axis parallel to the engine crankshaft, with the exhaust and bypass exhaust (through the wastegate) exiting through the rear of the nacelles.