P-40 Performance - Allison versus Merlin

[RCAFson]

You had several things going on at once. The early "C" engines in the P-40B&C (Tomahawks) had a problem with the propeller reduction gears. Some of the other parts may not have been the equal of even a 1941/42 manufactured engine.

Fuel was another big "IF" factor in the early part of the war. The Allisons were developed using US spec 100 octane fuel. This is different than either British 87 octane or British 100 octane. British 87 octane fuel had a fair amount of "aeromatics" in it and performed better (allowed higher boost)than than some 87 octane fuel but it was never really measured. American 100 octane fuel had very little allowable ( 2% max) "aeromatics" and while a richer mixture allowed a bit more boost there was no real jump in allowable boost pressures. In fact a few batches of US 100 octane gas performed at worse than 100 octane rating when running rich.
British 100 octane fuel at the time of the BoB and shortly after had 20% aeromatics minimum and while not tested for a while, it performed much better under rich conditions than lean. Once they did come up with test procedures and and a rating system it was found that most batches of British 100 octane had a rich mixture response of between 115-120PN. Or 100/115-120. Once they had that figured out the British began specifying 100/130 fuel. The US meanwhile shifted to a 100/125 fuel specification.

Sorry to be a bit long winded but it helps explain why British units in North Africa could use higher boost numbers than the US army approved for it's identical engines at the same time. While few people were using 75in of boost at the time a lot of them were running way over the "BOOK" numbers of 40-44 in MAP. Some claim ( and others say they didn't) The Flying Tigers used some rather high boost settings too, but I don't know were their fuel was coming from. British or American stocks? This fuel discrepancy carried over into the P-40E's at least and maybe into the P-40Ks. At some point in 1942 the British and Americans standardized on the 100/130 fuel specification. Trying to use 60-70 in of boost on 1940 US 100 octane fuel could be a very iffy proposition. Given ideal conditions you might get away with it. Less than ideal might mean pushing into the 50s could wreck the engine.

As far as other "technology" goes a number of parts were changed along the way, Crankshafts went from "plain" to shot peened to shot peened and Nitrided (early 1942) for an almost doubled allowable stress level, and that is before the 12 counter weight crankshaft shows up in early 1944. Other parts like connecting rods changed. Valve springs changed on the later engines. Even the way the crankcases were cast was changed.
Trying to wind an early engine AS BUILT to 3400-3600rpm could (and often did) result in disaster. Doing it to a rebuilt engine using late model internal parts could very well be a different story.

On page 7:

http://www.wwiiaircraftperformance.org/japan/intelsum85-dec42.pdf

there's an example of a p-39 trying, and failing, to use 70in of boost, on US fuel.

 

[tomo pauk]

The engines we build today are mostly later series and perform to stock levels. The rated rpm is 3,000 but the design was good for a LOT more. We have some customers who run them at 4,500+ rpm, but not in airplanes.

The thing is, the American engineers and Army acceptance peoplpe were very conservative. The Allison can pull over 100" of Mercury MAP, but was rated VERY conservatively and tested conservatively. You almost can't FIND a test report at over 57" of MAP and 3,000 rpm .... but we can easily get 75"+ and 3,400 - 3,600 rpm if we want. We CAN get to 115" of MAP for a race engine. Most owners don't becasue there is almost not reason to do so.

The entire point is, when we DO, the engine handles it very well!

Hi, Greg,
IMO, stating what today's piston engines are able to do, and then drawing the conclusions about ww2 era engines is just messing the thread. It's what the V-1710 was able to do vs. Merlin/V-1650, during the war time.

The Allison is tougher than the Merlin and holds a tune-up MUCH longer; MUCH more trouble-free. NOTHING wrong with a Merlin; you get what you expect to get with one, no argument there. It's just that you get so much MORE than you expect with a well-overhauled and properly-tuned Allison. We have several in Jurca Spitfire replicas and they give 95+% of the performance of the real aircaft despite having only a single stage supercharger rather than a 2-stage unit. If they had an equivalent two-stage, they'd kick-butt, and do anyway in tractor pulls where sea level performance is imnportant.

What altitude is where those 95% of the performance is reached? SL, 15000 ft, 30000 ft?

No single-stage ALlison is great at 25,000+ feet compared with a 2-stage Merlin, but the aux-stage and turbo models were ... and ARE. ALL Alisons were VERY comparable to the single stage Merlins, particularly from a serviceability standpoint. They were VERY good engines hamstrung by a government committee that controlled the ordes. if they order a V-1710-39, thath's what you deliver ... not some BETTER engine. To do that would violate the contract.

Single stage Allison is worse above 15000 ft than the single stage Merlin, period. 2 stage engine was capable to do in 1944 what the 2 stage Merlin was capable to do in 1942. The turbo V-1710, in order to reach what the 2 stage Merlin was doing, needed much more space weight.

In the post-war unlimited hydroplanes, the merlins that eventually took over from the Allisons were all 2-stage units. The single-stage Merlins mostly lost to the sinlge-stage Allisons. Guy Lombardo was the US Champion for 1946 - 1949 and won EVERY trophy on the circuit with Allisons. I have two pistons from one of his Championship-winning boats. When Merlins "took over," they were the 2-stage units and won mostly due to lack of knowledge of how to tune-up Allisons.

Nobody in RR was interested in development of the 1-stage Merlins past, say, mid 1942?

When they made the movie "Madison," Joe Yancey built the Allisons for the 20+ old hydroplane boats in the movie. He built them to STOCK configuration and they almost all ran 20+ mph faster than they did in "back-in-the-day" competion during the filming of the movie simply becasue the guys trying to "hot rod" the Allisons didn't know what they were doing. They ALSO put over 70+ hours on most of the boats during the filming and the engines never broke.

All fine and well, but again, no bearing to the time frame, and hence to the topic of the thread.

 

[Shortround6]

Thank you. The report is dated Dec of 1942, The actual flying tests may have been some months earlier?

Of interest is not only was engine detonating with the attempt at 70in for take-off or sea level but that 52in of MAP could only be maintained until until 4500ft at climb speed.

Power charts for some early model Allison's are available and use NO RAM at all so flying even at climb speed would show an improvement. The -33 engine used in the P-40B&C and Tomahawks was good for 1090hp at 3000rpm at 38.9 in MAP at 13,200ft. At 5,000ft the engine was good (assuming it did not blow up and these early engines did NOT have the improvements of the later engines) for 1440hp at 3000rpm and just over 52in MAP. Continuing down to sea level the engine should have made just under 1700hp at 61in of MAP. Getting more than 61in of MAP requires either forward speed providing RAM or over revving the engine or both. This engine had the 8.77 supercharger gears and any Allison engine using the 9.5in dia impeller and the same (or 8.80?) gear is going to give about the same pressures at the same altitudes. Differences in carburetors, inlet manifolds, backfire screens and inlet guide vanes on the supercharger inlet can affect things a bit. Big changes are the supercharger gears. With the 7.48 gears used in the A-36 there is little chance the engine could make 70 in at any altitude or speed. With the 9.60 gears used in late model Allisons getting to 70-75 in at low altitudes in fairly easy. Surviving is a lot harder.

Impeller speeds at 3000 rpm for the 7.48 gear is 22440rpm. for the 8.80 gear it is 26400rpm and for the 9.60 gear it is 28800rpm. power to drive the supercharger goes up with the square of the speed. approximately 30% of the power is turned into heat in the intake charge. The hotter charge is less dense and doesn't give the proportional power increase and the hotter charge is more likely to detonate. Allison was afraid that units that were used to operating at 56in and above with the 8.80 gears would wreck engines running those pressures with the 9.60 gears.

 

[Dan Fahey]

Would love to revive this conversation.
Some questions..
The Reno Races over the last few years have a P40, P51A and think a P38 taking laps.
There was a comment that the 3 blade prop of the Mustang and Warhawk limited the top speed.
Can a modern day Allison be built to compete with the super Unlimiteds?
Would that require a different propeller?
What HP could be expected?
Would operating at 3200/3400/3600 rpm be doable?

Conversations with Chris Fahey with Planes of Fame.
He noticed the P51A climbed a bit better than the P51D to 10000 ft.
This is when they were doing photo ops.

Then again do not know what octane they were regulated to use.
Think they all use the 100LL as standard for most of their flying.

Dan

 

[Shortround6]

The Reno Races over the last few years have a P40, P51A and think a P38 taking laps.
There was a comment that the 3 blade prop of the Mustang and Warhawk limited the top speed.
Can a modern day Allison be built to compete with the super Unlimiteds?
Would that require a different propeller?
What HP could be expected?
Would operating at 3200/3400/3600 rpm be doable?

A newer prop might well be beneficial. However as a general rule of thumb the higher you go the more prop you need. at sea level on a 59 degree day you can use a much smaller prop than at 20,000ft even for the same power. Air density at Reno altitude and well over 100 degrees IS????

A modern day Allison might be able to compete with the unlimiteds but it needs a much different supercharger to do it. It also needs a much different cooling system. It would certainly require a new propeller as you are now dealing with 3-4000hp and not 1200-1500hp.
Using the 12 counter weight crankshaft is a start for high RPM but for how long???

Greg may have better answers

Conversations with Chris Fahey with Planes of Fame.
He noticed the P51A climbed a bit better than the P51D to 10000 ft.
This is when they were doing photo ops.

Here you need information on the two planes involved. The P-51A was lighter in military form than the P-51D.
As "warbirds" are they carrying weight to simulate guns/ammo?
I don't believe anybody is still flying with self sealing tanks/liners (they deteriorate over time and become a hazard=blocked fuel lines/filters)
Armor? new radios?

and are both pilots accurately reporting rpm and boost used in the climb?

 

[Dan Fahey]

A newer prop might well be beneficial. However as a general rule of thumb the higher you go the more prop you need. at sea level on a 59 degree day you can use a much smaller prop than at 20,000ft even for the same power. Air density at Reno altitude and well over 100 degrees IS????

A modern day Allison might be able to compete with the unlimiteds but it needs a much different supercharger to do it. It also needs a much different cooling system. It would certainly require a new propeller as you are now dealing with 3-4000hp and not 1200-1500hp.
Using the 12 counter weight crankshaft is a start for high RPM but for how long???

Greg may have better answers



Here you need information on the two planes involved. The P-51A was lighter in military form than the P-51D.
As "warbirds" are they carrying weight to simulate guns/ammo?
I don't believe anybody is still flying with self sealing tanks/liners (they deteriorate over time and become a hazard=blocked fuel lines/filters)
Armor? new radios?

and are both pilots accurately reporting rpm and boost used in the climb?

Well earlier conversations commented that the D was about 1000 lbs lighter in civilian trim.
Don't think they are using full tanks of fuel either.
Then again modern day radios are a lot lighter than the tube with heavy transformers.
Be interesting redesigning the Mustang cockpit with modern instruments!

Figured the P51A flying at Reno was using 100 LL octane fuel for the Silver and Gold Races.
Hitting 350 mph laps. Which seems consistent with WW2 tests.
The P40 was not far behind.

Lot of new Allison FAA upgraded approved parts are available.
Because the original equipment is gone or worn out.
So new ones got manufactured.

Reading about the tractor pull races using Allison's.
Figured those upgrades could be used for Reno coming up in mid September!

Was the oil system in the Allison high pressure low volume or low pressure high volume?

Dan

 

[FLYBOYJ]

Folks, understand that the the P-40 and P-51A ( and similar heat aircraft) are there more for show. Look at the qualifying times and their final placings in the unlimited. BTW comparing lap speeds at Reno to original testing is like comparing apples to bowling balls.

2017 Unlimited Qualifiers

 

[FLYBOYJ]

Lot of new Allison FAA upgraded approved parts are available.

Hmmmm... Please explan

 

[Dan Fahey]

Hmmmm... Please explan

What was said in the Allison engine builders web site!
They remanufactured the parts and got FAA certifications.
Plus exceeded original factory specification!
Www.aceallisons.com

 

[FLYBOYJ]

"Upgraded FAA approved parts." The correct term.

I'm curious about this as I could not find any Type Certificate Data Sheet for the V-1710. Most if not all unlimiteds are running in Experimental category. FAA approval for any change in configuration would only happen if modifications are restricted on their aircraft's operation letter. Ace Allison's is not listed as an FAA repair station so I'm wondering on what basis this guy is making this claim. Maybe Greg has some info.

 

[GregP]

With regards to post#41, a P-39 trying and failing to use 70" MAP, the date of the report is Oct 1942. Grade 150 fuel wasn't widely available until after summer 1944. I'm guessing the P-39 was running grade 100/130 fuel. Not challenging the report at all, just noting the report date and when fuel was improved to grade 150.

Reference here: 150 Grade Fuel Summarized below.

USAAF Materiel Command held a "Conference on National Advisory Committee for Aeronautics Test Program to Investigate 150 Grade Fuels" on 27-28, January 1944. It was concluded that "The program outlined should permit conclusive data to be obtained and should indicate the relative advantages of the various high octane fuel components for the preparation of satisfactory rich and lean rating fuels. It should also indicate the military value of these fuels for long range patrol or bombardment operation". It was recommended that "the program outlined should be carried out as expeditiously as is possible".

With regard to Post #48 above, ACE Allisons: They make/made new parts because they don't have any originals to speak of. I have seen at least a eight ACE Allisons while taking them apart. My recommendation is to use genuine Allison parts when you can, and they ARE available, including piston rings.

If you are serious about an Allison, ask ACE's Bud Wheeler what his Allison guarantee is and what constitutes engine abuse. Ask him to seat the rings on a run stand before he ships it. Ask him if he'll ride in it with you. Then go ask Joe Yancey (Yancey Allisons) and/or Jose Flores (Vintage V-12s). Might as well get info from several builders. Decide for yourself and good luck whatever the choice is. Last, post pics of your new Allison chariot!

 

[Kevin J]

With regards to post#41, a P-39 trying and failing to use 70" MAP, the date of the report is Oct 1942. Grade 150 fuel wasn't widely available until after summer 1944. I'm guessing the P-39 was running grade 100/130 fuel. Not challenging the report at all, just noting the report date and when fuel was improved to grade 150.

Reference here: 150 Grade Fuel Summarized below.

USAAF Materiel Command held a "Conference on National Advisory Committee for Aeronautics Test Program to Investigate 150 Grade Fuels" on 27-28, January 1944. It was concluded that "The program outlined should permit conclusive data to be obtained and should indicate the relative advantages of the various high octane fuel components for the preparation of satisfactory rich and lean rating fuels. It should also indicate the military value of these fuels for long range patrol or bombardment operation". It was recommended that "the program outlined should be carried out as expeditiously as is possible".

With regard to Post #48 above, ACE Allisons: They make/made new parts because they don't have any originals to speak of. I have seen at least a eight ACE Allisons while taking them apart. My recommendation is to use genuine Allison parts when you can, and they ARE available, including piston rings.

If you are serious about an Allison, ask ACE's Bud Wheeler what his Allison guarantee is and what constitutes engine abuse. Ask him to seat the rings on a run stand before he ships it. Ask him if he'll ride in it with you. Then go ask Joe Yancey (Yancey Allisons) and/or Jose Flores (Vintage V-12s). Might as well get info from several builders. Decide for yourself and good luck whatever the choice is. Last, post pics of your new Allison chariot!

From what I've read on the Soviet experience with the P-39, WEP wasn't available for use until the P-39K.

 

[Dan Fahey]

Jack Rouch built Merlin Engines for the Reno Mustangs with a lot of his modifications.
My original comment was the possibility of building a competitive Allison engine.
Would not be surprised that the remaining Allison engine builders have to manufacture unavailable parts.
And collaborate how and what to do and get them past FAA certification!

 

[GregP]

Not sure anyone these days is running Roush parts on Merlins or Allisons. Would be great to find out, though.

 

[FLYBOYJ]

And collaborate how and what to do and get them past FAA certification!

There is NO FAA certification for experimental engine or engine parts unless there is a Type Certificate issued against that engine.

 

[Dan Fahey]

There is NO FAA certification for experimental engine or engine parts unless there is a Type Certificate issued against that engine.

Merlin's and Allison are not experimental engines!
Even though they are souped up!

 

[FLYBOYJ]

Merlin's and Allison are not experimental engines!
Even though they are souped up!

Evidently you know nothing about aircraft certification.

If they do not hold a Type Certificate Data Sheet (issued by the FAA) they cannot be installed in an aircraft unless that aircraft is certificated under EXPERIMENTAL category. There is no FAA certification process for the manufacture of these engines (or their parts) unless a TCDS is issued. The FAA may issue on a case-by-case/ individual aircraft basis a requirement for inspection if any part of the airframe or engine is modified under the individual aircraft's operation specifications and experimental airworthiness certificate.

So far I have not found a TCDS for either the Merlin or Allison

Again, for certification and civilian operational certification purposes, these aircraft (to include engines and propellers) are EXPERIMENTAL

 

[GregP]

Joe Yancey built up a racing Allison for an Australian Yak last year flown by Graeme Frew. Graeme's number, 35, was taken directly from Burt Munro's (World's Fastest Indian) motorcycle.

I have been asked by Joe not to disclose what was done to built up the engine and I won't. The issues they had centered around the fact that the Yak's radiator was NOT up to the task of cooling the Allison at race power levels. It ran hot EVERY time they ran it.

They had to put back in Graeme's stock Allison due to heat issues and finished last in the Gold final, but their goal was to get to Reno and compete. They managed to get bumped out of Bronze and transferred to Silver, then transferred to Gold. They not only competed, they bumped two classes and finished the Gold class! That's pretty good for a first attempt, I'd say. They never got to race the Allison that was built up for the task due to too small a radiator.

It may or may not happen again, but everyone who heard Joe's racing Allison was impressed. The best comment came from Matt Nightengale. He said to Joe that he had never heard an Allison sound like that before after Graeme's first takeoff. Graeme climbed out at about a 30° angle, but quickly came back with a hot engine!

I'd love to say more about his race engine, but Joe is my friend and he has specifically asked me not to do so.

 

[MACHIA]

Does anyone know anything about the engine for the XP-40Q? All I have read is that it had a two-stage supercharger and a higher rated Allison. Was this the same arrangement as the P-63?

From earlier reading I recall an Allison V1710 1,475 hp was used and the P-40Q and attained a speed of 422 mph in straight and level flight . The V1710's used in the P-38's were of the same horsepower . Although I'm not sure that this engine was installed in the P-63 . Anyone care to comment on that ?

 

[Big Jake]

Firstly, if the aircraft and engine are "as built" and conform with the Type Certificate then the aircraft can be registered in Limited or Restricted categories, not necessarily Experimental. This also applies to Warbirds. Through the years, many alterations were allowed by the FAA on Warbirds.
Secondly, in Reno some Warbirds are "Stock" (certified in Limited or Restricted categories), very limited in the way of modifications, or "Experimental" (the "Big Guns".) As far as I remember, a stock one never won an un-limited race in Reno - just didn't have the performance.
Thirdly, you cannot build a P-51 or a Merlin engine from scratch unless you own the Type Certificate and have a production authorization from the FAA. All the engines and aircraft in circulation have an original placard from the original manufacturer. You can build a new aircraft around a placard but you have to be careful - you need to show the Feds that it is a "restoration" or "major repair"... In addition to a number of fighters, right now a "new" B-17 is being built basically from scratch following this method.
If you change an engine on an aircraft and that new engine is not on the aircraft Type Certificate - talk to the FAA first.
My two cents...