What was the problem with the allison engine?

[wuzak]

The R-3350s in the B-29 were turbocharged. The V-3420s in the XB-19, being tested as a backup for the R-3350s, were also turbocharged, but used an experimental turbocharger - for installation in teh XB-39 the turbochargers were deleted. The XB-44 was the first B-29 to be fitted with R-4360s, but were not turbocharged. The XB-50 used turbocharged R-4360s.

 

[wuzak]

When did they consider liquid cooled engines essential? Who in USAAC/USAAF thought they were essential? I am well aware of various studies and trials, but do not recall hearing anything on the essential need for liquid cooling.

How much more vulnerable? As much as billions of coolant system piercing pieces of flak can create. Liquid cooled engines may have made a stronger case for the use of more HMG instead of more cannon on Luftwaffe fighters. More bullets to pierce versus less shells to burst.

The only thing wrong with the mechanical vulnerability of the B-29 power plant aside from the engine cowling was that its first name wasn't P&W and its last name 2800.

In the early '30s it was considered that an air-cooled engine of the power required for future bombers would be impractical for aircraft use.

Armour plate could have been used to protect vulnerable systems if need be.

 

[Lighthunmust]

Not really a good analogy. Battlecruisers were quite successful when used for what they were designed for, fighting armoured cruisers. They were not intended to be fast battleships no matter what the press releases said.

Without these manufacturing break through's in casting, forging and machining the aircooled engine could have hit dead ends. At times during the 30s the future of the aircooled engine's ability to compete with the liquied cooled engine didn't look good. The air cooled makers managed to keep pulling tricks out of their bag but betting on what would happen 3-5 years down the road was never a sure thing.

Even though I have yet to receive and read those engine books we corresponded about, I think you are overstating your case and underestimating mine.

I think the battlecruiser analogy it is far better than you are giving it credit.

What was the fate of most Battlecruisers? A record of failure and obsolescence more than success. Why? Because of an over emphasis of one aspect of warship design due to the influence of Jackie Fisher's fantasy. A fantasy that you will always hold the advantage in any combat engagement due to your weapons, speed, and tactics. Fisher forgot the combat rule that you are a target more often than a shooter, and you are only dead once. If you make something that looks like a battleship eventually both sides are eventually going to treat it as a battleship. If you make something that looks like a tank both sides are going to treat it as a tank. The analogy fits the inline versus radial issue just fine with regard to sacrificing protection for performance. Engines protect the crew from crashing to the ground. Using an engine type with marginally more performance when the stakes are life and death for the crew and the nation is wrongheaded thinking. The hope that the expected inline performance would balance against the advantages of radials is a mistake as much as the 1930's thinking that bombers would run away from or shoot down attacking swarms of fighters. Claire Chennault understood this in the 1930's.

Regarding the supposed preference for inlines:

From the Curtiss A-12 entry in Wikipedia:

The A-12 entered service in 1932 and remained in service until 1942.
Engine - "1× Wright R-1820 "Cyclone" 9-cylinder air-cooled radial engine, 690 hp (515 kW)"

"The most obvious difference between the A-12 and the A-8 is the air-cooled, radial engine in the A-12, which replaced the A-8's inline, water-cooled engine. This was a response to the USAAC's move toward a preference for radial engines, especially in attack aircraft. The rationale behind this preference is that the radial engine has a lower profile, making it less vulnerable to ground fire, and a simpler cooling mechanism, which is also less prone to groundfire, as well as overall maintenance problems."

From "American Combat Planes" - Ray Wagner:
"The second example (of the YB-9) was flown November 13, 1931, with Curtiss V-1570-29 Conquerors, the last inline engines to be used on an Army bomber for over 11 years"

In the early '30s it was considered that an air-cooled engine of the power required for future bombers would be impractical for aircraft use.

Armour plate could have been used to protect vulnerable systems if need be.

Pages 195-231 of Wagner's ACP covering the years 1931-1945 are filled with over a dozen bombers having radial engines. The only exceptions are the experimental one-off XB-38 and the experimental two-off XB42. If the gentlemen running USAAC in the 1930's preferred inlines; they did little to implement that preference.

I have requested the search terms that Readie and gjs238 used to find reference to an inline preference by the gentlemen running the USAAC in the 1930's. I would really like to see the article. Perhaps the three engine books I just ordered, partly due to Shortround6's, recommendation may contain the reference to preference. Damn right that rhyme is intended! For now I think the gentlemen of the USAAC might have preferred blondes (inlines), but certainly married brunettes (radials). Inlines are fine if you're flying within you're own lines, use a Radial to avoid foreign burial. All rhymes double damn intended!

Not enough armor plate could be used without unacceptable lose of performance. If it could have been practical we would have a great many less HE-111 crash sites in England.

Guys help me out. Show me the light by making a better case for your opinions. As always: Thanks for the education.

 

[Shortround6]

, I think you are overstating your case and underestimating mine.

The analogy fits the inline versus radial issue just fine with regard to sacrificing protection for performance. Engines protect the crew from crashing to the ground. Using a engine type with marginally more performance when the stakes are life and death for the crew and the nation is wrongheaded thinking. The hope that the expected inline performance would balance against the advantages of radials is a mistake as much as the 1930's thinking that bombers would run away from or shoot down attacking swarms of fighters.

You have to understand the thinking of the time rather than apply 70-80 years worth of hind sight. At times they were not looking for marginally more performance but rather substantial jumps in performance. In some cases they over reached and in other cases technology moved faster than expected.

Regarding the supposed preference for inlines:

From the Curtiss A-12 entry in Wikipedia:

The A-12 entered service in 1932 and remained in service until 1942.
Engine - "1× Wright R-1820 "Cyclone" 9-cylinder air-cooled radial engine, 690 hp (515 kW)"

"The most obvious difference between the A-12 and the A-8 is the air-cooled, radial engine in the A-12, which replaced the A-8's inline, water-cooled engine. This was a response to the USAAC's move toward a preference for radial engines, especially in attack aircraft. The rationale behind this preference is that the radial engine has a lower profile, making it less vulnerable to ground fire, and a simpler cooling mechanism, which is also less prone to groundfire, as well as overall maintenance problems."

Well, this shows a little bias right here. Lets yank out a 1926-27 water cooled v-12 and stick in an up to date 1932 radial engine with 15% more power and then tell ourselves how clever we are. OK, a bit of an exaggeration but the V-1570 Conqueror had pretty much reached the end of the line before the 20s were out. It was finished off with merger of Curtiss and Wright in July of 1929. Curtiss-Wright didn't care which engine they sold so no more development was put into the Conquerer.

From "American Combat Planes" - Ray Wagner:
"The second example (of the YB-9) was flown November 13, 1931, with Curtiss V-1570-29 Conquerors, the last inline engines to be used on an Army bomber for over 11 years"

Pages 195-231 of Wagner's ACP covering the years 1931-1945 are filled with over a dozen bombers having radial engines. The only exceptions are the experimental one-off XB-38 and the experimental two-off XB42. If the gentlemen running USAAC in the 1930's for inlines; they did little to implement that preference.

I would note that just about every one of those bombers used pretty much versions of standard commercial engines until at least 1939-40. The USAAC spent darn little money on R&D of radial engines. They were feeding Allison, Continental and Lycoming for Liquid cooled projects. Continental was little more than a parts supplier for the army at times. They simply made parts and ran test to army designs and specifications for the hyper engine project. Both the Continental and Lycoming started out as flat 12s that could be buried in the wing for better streamlining by eliminating the the engine nacelle. Try that with an air cooled radial without a very fancy gear box. This idea got over taken by technology, as the 30s went on airfoils and wing structure changed and fat wings went away. Unless you had a really big bomber (B-15/B-19) the wing wasn't going to be thick enough to hide even a flat 12.
The Army was also trying for high altitude flight with the turbo charger. They were afraid the much thinner air at altitude wouldn't properly cool the air cooled engines.
Then there is keeping up with the "Jones's". With France, Germany and Great Britain all using liquid cooled engines for large numbers of their warplanes it would take a might confident man to ignore liquid cooling in the 30s.

Not enough armor plate could be used without unacceptable lose of performance. If it could have been practical we would have a great many less HE-111 crash sites in England.

Nobody was armoring much of anything in airplane in the 30s.

You might also want to consider that the liquid cooled early P-40 had 22% less drag than the radial powered P-36, confirmed by flight tests. That is total drag not engine drag. Look at the A-8 and A-12 again. The liquid cooled A-8 was slightly heavier and yet was 6mph faster despite the A-12s radial having 15% more power. The Conquerer had a higher service ceiling despite having NO supercharger, none, nada, zip, zilch. Of course this is wike and ceilings might not be correct.

 

[Lighthunmust]

You have to understand the thinking of the time rather than apply 70-80 years worth of hind sight. At times they were not looking for marginally more performance but rather substantial jumps in performance. In some cases they over reached and in other cases technology moved faster than expected.


Well, this shows a little bias right here. Lets yank out a 1926-27 water cooled v-12 and stick in an up to date 1932 radial engine with 15% more power and then tell ourselves how clever we are. OK, a bit of an exaggeration but the V-1570 Conqueror had pretty much reached the end of the line before the 20s were out. It was finished off with merger of Curtiss and Wright in July of 1929. Curtiss-Wright didn't care which engine they sold so no more development was put into the Conquerer.


I would note that just about every one of those bombers used pretty much versions of standard commercial engines until at least 1939-40. The USAAC spent darn little money on R&D of radial engines. They were feeding Allison, Continental and Lycoming for Liquid cooled projects. Continental was little more than a parts supplier for the army at times. They simply made parts and ran test to army designs and specifications for the hyper engine project. Both the Continental and Lycoming started out as flat 12s that could be buried in the wing for better streamlining by eliminating the the engine nacelle. Try that with an air cooled radial without a very fancy gear box. This idea got over taken by technology, as the 30s went on airfoils and wing structure changed and fat wings went away. Unless you had a really big bomber (B-15/B-19) the wing wasn't going to be thick enough to hide even a flat 12.
The Army was also trying for high altitude flight with the turbo charger. They were afraid the much thinner air at altitude wouldn't properly cool the air cooled engines.
Then there is keeping up with the "Jones's". With France, Germany and Great Britain all using liquid cooled engines for large numbers of their warplanes it would take a might confident man to ignore liquid cooling in the 30s.


Nobody was armoring much of anything in airplane in the 30s.

You might also want to consider that the liquid cooled early P-40 had 22% less drag than the radial powered P-36, confirmed by flight tests. That is total drag not engine drag. Look at the A-8 and A-12 again. The liquid cooled A-8 was slightly heavier and yet was 6mph faster despite the A-12s radial having 15% more power. The Conquerer had a higher service ceiling despite having NO supercharger, none, nada, zip, zilch. Of course this is wike and ceilings might not be correct.

I think I have some understanding of the thinking in the 1930s only because it has not changed much as far as the American military is concerned. I think you may be right about throwing money at inlines. The longer we debate, the more I am remembering things read years ago. I do think their real preference was for power. The kept finding that in radials with the benefit of also desired dependability under adverse conditions. Really, they were worried about cooling at altitude? Had none of them seen what Mallory was wearing to climb Everest? Had none of them ever been 10,000 feet above sea level? No doubt they were envious of the those so sophisticated europeans and their flashy seaplane air-racers and slick monoplane fighters powered by inlines. With commercial aviation providing the funding for radials, why not throw money at glamourous inlines? It is not so much my use of hindsight as their narrow mindedness, petty resistance to anything upsetting the status quo, and shortsightedness that was the problem. That and Army and Navy brass determined to limit the autonomy of the USAAC.

I agree about armor not being on their minds. The minimal engine power available would alone preclude much thought of adding additional weight. After all Bomber pilots wouldn't be caught and if by luck a fighter showed up it would be promptly dispatched by a socket mounted .30cal.

Obviously someone thought the A-12's marginal decrease in performance was worth the gain in dependability. The best way to measure performance is with reproducibility. Coming back from the mission to fly another mission was the best measure of the performance of an engine.

 

[Shortround6]

It is not "military" thinking I was referring to, but the thinking of many people in the aeronautics industry. The 'debate' over liquid cooling vs air cooling had been going on since before WW I. As technology ebbed and flowed, First one side would have an advantage and then the other.


the problem with cooling at high altitude is not the temperature, which is obviously lower but the density. At 33,000ft the air is one third the density of sea level. The engine is cooled by XXX pounds of air per minute flowing through the fins or radiator. While you can supercharger the engine to get the power what do you do to "supercharge" the cooling system?

I really do have to question this part of your post.

"No doubt they were envious of the those so sophisticated europeans and their flashy seaplane air-racers and slick monoplane fighters powered by inlines. With commercial aviation providing the funding for radials, why not throw money at glamourous inlines? It is not so much my use of hindsight as their narrow mindedness, petty resistance to anything upsetting the status quo, and shortsightedness that was the problem. That and Army and Navy brass determined to limit the autonomy of the USAAC."

There is really no way to debate that kind of thinking and there is no need to try to 'goad' people into giving you information.

I think I will check out of this discussion for a while.

 

[billswagger]

The Allison attached to the P-51 was said to have performed better.
Maybe i'm stating the obvious, but the air frame will effect performance more so than the engine.
I think the Allison gets its reputation of lower performance at higher altitude because it was never designed to be operated at the heights the military required of it.
This point was probably made earlier in the thread, but the P-40 was a lower to mid altitude fighter and the Allison performed quite well when compared to other liquid cooled V-engines. The poor altitude performance reputation probably comes from the lack of performance the P-40 experienced, but that may also be due to weight, wing loading, drag....etc.
For example, a contemporary 109 Db601 puts out around 1000hp at 17000ft, and less than 900hp above 20,000ft.
The 109 is lighter and requires less power to gain similar performance.
Similarly, with the Spitfire, but i don't have figures for the Merlin, only that it had a better FTH.
When compared at lower heights, the Merlin and Allison were nearly the same.
The Merlin was a good engine, but i've also read that the Allison was much more durable from an RPM standpoint.
I refer to racing boats of the 1950-1960s era that used both surplus engines of ww2, and the Allisons were said to be better suited for the RPMs required for boat racing and both types of engines achieving similar outputs.

 

[wuzak]

The Allison attached to the P-51 was said to have performed better.
Maybe i'm stating the obvious, but the air frame will effect performance more so than the engine.
I think the Allison gets its reputation of lower performance at higher altitude because it was never designed to be operated at the heights the military required of it.
This point was probably made earlier in the thread, but the P-40 was a lower to mid altitude fighter and the Allison performed quite well when compared to other liquid cooled V-engines. The poor altitude performance reputation probably comes from the lack of performance the P-40 experienced, but that may also be due to weight, wing loading, drag....etc.
For example, a contemporary 109 Db601 puts out around 1000hp at 17000ft, and less than 900hp above 20,000ft.
The 109 is lighter and requires less power to gain similar performance.
Similarly, with the Spitfire, but i don't have figures for the Merlin, only that it had a better FTH.
When compared at lower heights, the Merlin and Allison were nearly the same.
The Merlin was a good engine, but i've also read that the Allison was much more durable from an RPM standpoint.
I refer to racing boats of the 1950-1960s era that used both surplus engines of ww2, and the Allisons were said to be better suited for the RPMs required for boat racing and both types of engines achieving similar outputs.

The Allison attached to the P-51 performed better at low altitude because its installation was slightly less draggy, and at low altitude the engine performance was similar or better than the Merlin, because the Merlin was a high altitude version. A low altitude version would have fared better at low altitudes.

The Allison's main problem, when not coupled to a turbocharger, was that it had a single speed supercharger. Later they developed the two stage supercharger with variable speed auxiliary stage, but single stage engines remained single speed. That could have been rectified if so desired, but it wasn't to be the case.

 

[gjs238]

That could have been rectified if so desired, but it wasn't to be the case.

It seems the Allison design left less room for "rectification" that other designs.

 

[Lighthunmust]

I really do have to question this part of your post.

"No doubt they were envious of the those so sophisticated europeans and their flashy seaplane air-racers and slick monoplane fighters powered by inlines. With commercial aviation providing the funding for radials, why not throw money at glamourous inlines? It is not so much my use of hindsight as their narrow mindedness, petty resistance to anything upsetting the status quo, and shortsightedness that was the problem. That and Army and Navy brass determined to limit the autonomy of the USAAC."

There is really no way to debate that kind of thinking and there is no need to try to 'goad' people into giving you information.

I think I will check out of this discussion for a while.

Did you think I was referring to you or members of this forum with this comment?
The narrow mindedness etc.,etc, was referring to members of the USAAC hierarchy. I was not attempting to goad anyone, apparently it came off that way and I apologize for my lack of clarity. I do however think a discussion of the impact on aircraft technical development by pre-war attitudes and politics of the USAAC, and Army and Navy leadership would be interesting.

 

[buffnut453]

The Allison attached to the P-51 performed better at low altitude because its installation was slightly less draggy, and at low altitude the engine performance was similar or better than the Merlin, because the Merlin was a high altitude version. A low altitude version would have fared better at low altitudes.

The Allison's main problem, when not coupled to a turbocharger, was that it had a single speed supercharger. Later they developed the two stage supercharger with variable speed auxiliary stage, but single stage engines remained single speed. That could have been rectified if so desired, but it wasn't to be the case.

Wen the Mustang MkI entered service, none of the other RAF fighters had two-stage superchargers but the Allison still lacked altitude performance, hence the Mustang was assigned to army co-op tasks.

 

[gjs238]

Wen the Mustang MkI entered service, none of the other RAF fighters had two-stage superchargers but the Allison still lacked altitude performance, hence the Mustang was assigned to army co-op tasks.

"none of the other RAF fighters had two-stage superchargers"
But then wouldn't those fighters also lack altitude performance?
Or was it that they had two speed blowers?
Or perhaps the single-stage single-speed blowers were optomized for a higher altitude?
Or perhaps the single-stage single-speed blowers were better designed?

 

[Readie]

The Pratt Whitney R-2060 Yellow Jacket was a liquid-cooled aircraft engine project developed for the United States Army in the early 1930s.The engine had five banks of four in-line cylinders, and displaced 2,060 cubic inches. Designed to produce 1,000 hp, the engine produced 1,116 hp on its final run after 35 hours of testing. The engine was cancelled in favor of continuing development of Pratt Whitney's air-cooled R-1830 Twin Wasp radial engine. (source wiki)

Another dalliance with liquid cooling by the Americans. I must confess I had never heard of the 'yellow jacket'

Cheers
John

 

[Readie]

Piston Engines

This is interesting. The US Navy recognised the weight advantage of the radial for its own carrier borne aircraft.

1930 - 1939 Military Aircraft

A long list here. Showing the use of inline and radials by designers.
I'm not making any particular point, just posting the link for general interest. There are some obscure aircraft listed !!
Cheers
John

 

[davparlr]

The discussion on liquid cooled inline engines verses air cooled radials took me back to my childhood growing up in Pensacola. I remember one of the innumerable airshows put on by the Blue Angels that I attended that they had a demonstration of a P-51 and an F8F. It was one of those hot, humid summer days Pensacola is so famous for. The P-51 flew first. It took off and flew a few demo runs and then came around and landed. The announcer, obviously a Naval aviator, said that the P-51, due to its liquid cooled engine had overheated and had to land. Next came the F8F. It took off and flew a few demo runs and then came around an landed. The announcer said that the F8F had overheated.

 

[Shortround6]

"none of the other RAF fighters had two-stage superchargers"
But then wouldn't those fighters also lack altitude performance?
Or was it that they had two speed blowers?
Or perhaps the single-stage single-speed blowers were optomized for a higher altitude?
Or perhaps the single-stage single-speed blowers were better designed?

It is a little bit of everything, it is also the fact that the Allison powered planes were heavier than the Spitfire, Hurricane, Bf 109, etc. An Allison powered Mustang can tip the scales at over 8000lbs with only 630lb of internal fuel (105 US gals?) so even if you had shoved a Merlin 45 into it it would have been a bit lacking in high altitude performance compared to a MK V Spitfire being about 1400lbs heavier (about 20%). Merlin 45 was single speed. It was also good for 1185hp for take off.

engine..........take-off .........military power/low gear......WEP/Low...........Militay power/high.... WEP high
Allison-39........1150..............1150/11,700ft..................1490/4,300ft.......------..............-------
Allison-81........1200..............1125/15,500ft..................1410/9,500ft.......------..............------
Merlin 45.........1185..............1210/18,250ft..................1515/11,000ft.....------..............------
Merlin XX.........1280..............1260/12,250ft.................1485/6,000ft......1175/21,000ft......1490/12,500ft

Merlin XX and 45 used the same supercharger.

 

[gjs238]

The Pratt Whitney R-2060 Yellow Jacket was a liquid-cooled aircraft engine project developed for the United States Army in the early 1930s.The engine had five banks of four in-line cylinders, and displaced 2,060 cubic inches. Designed to produce 1,000 hp, the engine produced 1,116 hp on its final run after 35 hours of testing. The engine was cancelled in favor of continuing development of Pratt Whitney's air-cooled R-1830 Twin Wasp radial engine. (source wiki)

Another dalliance with liquid cooling by the Americans. I must confess I had never heard of the 'yellow jacket'

Cheers
John

That's neat. Why must a water cooled engine be an in-line? Radial water cooled is cool.

 

[davparlr]

Then the roughly 400 hp advantage of the 3350 would probably continued as altitude went up. The additional 1600 hp per plane would be like having an additional engine.

 

[davparlr]

is a mistake as much as the 1930's thinking that bombers would run away from or shoot down attacking swarms of fighters. Claire Chennault understood this in the 1930's.

I don't think the idea was as much of a mistake as was the understanding of the rate of advancement that was occurring at the time. When the B-17 was conceived, the proposed fighters at the time was not significantly faster than the bomber and defensive system would be more effective. However by the time the bomber was deployed, technology in fighters had significantly improved and implemented much faster than bomber advancements could. The concept of speed as an superior advantage for a bomber has never been disproved nor abandoned, starting with the amazing Mosquito. In the 50s, the Mig 15 had a devil of a time, and as far as I know never succeeded, trying to catch a B-47s, as they buzzed Russian airfields. This is would have also been true with the Mig 21 trying the catch the equally fast B-58, and the tri-sonic B-70 was killed by advancements in anti-aircraft missiles, not by a fighter threat.

 

[Messy1]

I have been following this thread closely. Learned a lot. Thanks to all contributors!