Allison V-3420 implementation
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wuzak
Captain
Definitely could have replaced the R-3350s in the B-29 (made B-39s).
Was proposed to replace R-2800s with V-3420s in B-26s. Would have been worthwhile (B-26s got the less powerful A-series engines).
Bear in mind that while some R-2800s could get 2800hp with lots of boost (for an air-cooled radial) and ADI a V-3420 rated at 2600hp was barely breaking a sweat. Basically being two V-1710s geared together power of well over 3000hp should have been easily possible. Later models should have approached 4000hp+. For comparison, when the R-4360 was introduced near the end of the war it was rated at around 3000hp.
The V-3420 was fitted to the XB-19 and XB-39 (made from a YB-29) with a quick engine change module that was designed to replace R-3350 installations. It easily fitted inside the nacelle profile when including all its coolers. On the XB-19 the V-3420 was fitted with an experimental turbocharger, which damaged its chances of going forward on the B-29/B-39. When fitted to the XB-39 it only had the single speed single stage supercharger.
The V-3420 could be configured with crankshafts rotating in the same or opposite directions. Thus it would have been relatively easy to have a contra-prop arrangement.
Perhaps they could have tried a V-3420 in a Curtiss XP-60 (why not - everything else was tried) or even a P-47 - they tried the Chrysler IV2220, I'm sure the V-3420 could have fitted quite easily.
- Thread starter
- #3
Weren't more B-29's and lives lost due to R-3350 engine failures than enemy action?
- Thread starter
- #4
Wonder how it would look perform in a F4U.
Readie
Chief Master Sergeant
In 1937, at the behest of the United States Army Air Corps, the Allison Engine Company agreed to design and build a large-displacement high power aircraft engine. The resulting V-3420 was essentially a pair of 12 cylinder Allison V-1710 engines mated to a common crankcase with a 30° angle between the inner cylinder banks. The crankshafts of the two V-1710 engines were geared together to drive a common propeller shaft. Most V-3420 parts were interchangeable with those for V-1710-E and -F engines.
The V-3420 had a power-to-weight ratio of 1.6 kW/kg or 1 hp/lb, excellent for its time. It was envisioned as a powerful yet compact engine for several advanced Air Force projects of the day, including the Douglas XB-19, the Boeing XB-39 Superfortress, the Lockheed XP-58 Chain Lightning, and the General Motors P-75 Eagle. As none of these designs reached full-scale production, only about 150 V-3420s were built.
Rolls Royce had a go at the X with the Vulture aero engine developed shortly before World War II that was designed and built by Rolls-Royce Limited. The Vulture used the unusual "X-24" configuration, whereby four cylinder blocks using the earlier V12 Kestrel cylinder bore and stroke dimensions were joined by a common crankshaft using a single crankcase. The engine was originally designed to produce around 1,750 horsepower, but continuing problems with the Vulture design meant that the engines were derated to around 1,450-1,550 hp in service by limiting the maximum running speed.
The H Sabre was a British H-24-cylinder, liquid cooled, sleeve valve, piston aero engine, designed by Major Frank Halford and built by Napier Son during WWII. The engine evolved to become one of the most powerful inline piston aircraft engines in the world developing from 2,200 horsepower in its earlier versions to 5,500 hp (4,100 kW) in late-model prototypes.
The first operational aircraft to be powered by the Sabre were the Hawker Typhoon and Hawker Tempest; however, the first aircraft powered by the Sabre was the Napier-Heston Racer, which was designed to capture the world speed record. Other aircraft using the Sabre were the Martin-Baker MB 3 prototype and one of the Hawker Fury prototypes. Later it became used in the early production of the Blackburn Firebrand.
The German DB 604 was unique among the DB aircraft engines by having its 24 cylinders being arranged in an X, i.e. 4 rows of 6 cylinders. The DB 604 was also unique amongst the X-24 engines, in that it was not conceived as a further development of existing Daimler-Benz aircraft engines such as the DB 601, DB 603 or DB 605. For example the Rolls-Royce Vulture was basically two Rolls-Royce Peregrine engines joined at the crankcase, thus producing the X-configuration of the cylinders.
The DB 604 was a completely new Daimler-Benz engine design featuring a perfectly square stroke ratio of 135 mm x 135 mm. The square stroke ratio enabled the relatively high engine speed of 3,200 rpm. The first engine tested in 1939 on the engine test stand achieved a power output of 2,350 hp.
Further development of the first test engines led to the DB 604A/B. The only difference between the DB 604A and the DB 604B was the direction in which the crankshaft turned. The DB 604A/B was equipped with a two-speed supercharger, achieving 2,500 hp whilst testing.
Development of this promising engine was canceled by the Reich Air Ministry in September 1942.
Fascinating engines.
Cheers
John
The V-3420 had a power-to-weight ratio of 1.6 kW/kg or 1 hp/lb, excellent for its time. It was envisioned as a powerful yet compact engine for several advanced Air Force projects of the day, including the Douglas XB-19, the Boeing XB-39 Superfortress, the Lockheed XP-58 Chain Lightning, and the General Motors P-75 Eagle. As none of these designs reached full-scale production, only about 150 V-3420s were built.
Rolls Royce had a go at the X with the Vulture aero engine developed shortly before World War II that was designed and built by Rolls-Royce Limited. The Vulture used the unusual "X-24" configuration, whereby four cylinder blocks using the earlier V12 Kestrel cylinder bore and stroke dimensions were joined by a common crankshaft using a single crankcase. The engine was originally designed to produce around 1,750 horsepower, but continuing problems with the Vulture design meant that the engines were derated to around 1,450-1,550 hp in service by limiting the maximum running speed.
The H Sabre was a British H-24-cylinder, liquid cooled, sleeve valve, piston aero engine, designed by Major Frank Halford and built by Napier Son during WWII. The engine evolved to become one of the most powerful inline piston aircraft engines in the world developing from 2,200 horsepower in its earlier versions to 5,500 hp (4,100 kW) in late-model prototypes.
The first operational aircraft to be powered by the Sabre were the Hawker Typhoon and Hawker Tempest; however, the first aircraft powered by the Sabre was the Napier-Heston Racer, which was designed to capture the world speed record. Other aircraft using the Sabre were the Martin-Baker MB 3 prototype and one of the Hawker Fury prototypes. Later it became used in the early production of the Blackburn Firebrand.
The German DB 604 was unique among the DB aircraft engines by having its 24 cylinders being arranged in an X, i.e. 4 rows of 6 cylinders. The DB 604 was also unique amongst the X-24 engines, in that it was not conceived as a further development of existing Daimler-Benz aircraft engines such as the DB 601, DB 603 or DB 605. For example the Rolls-Royce Vulture was basically two Rolls-Royce Peregrine engines joined at the crankcase, thus producing the X-configuration of the cylinders.
The DB 604 was a completely new Daimler-Benz engine design featuring a perfectly square stroke ratio of 135 mm x 135 mm. The square stroke ratio enabled the relatively high engine speed of 3,200 rpm. The first engine tested in 1939 on the engine test stand achieved a power output of 2,350 hp.
Further development of the first test engines led to the DB 604A/B. The only difference between the DB 604A and the DB 604B was the direction in which the crankshaft turned. The DB 604A/B was equipped with a two-speed supercharger, achieving 2,500 hp whilst testing.
Development of this promising engine was canceled by the Reich Air Ministry in September 1942.
Fascinating engines.
Cheers
John
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wuzak
Captain
The Vulture was not, as it has been stated many times, two Kestrel/Peregrines joined together. It had different bore spacing (the same as the Merlin in fact), but the same bore and stroke. A version with the same bore as the Merlin could have been made.
Power for the Vulture MkV is listed around 1800hp at 2800rpm, where maximum rpm was to be 3200. The speed was reduced for reliability. The reliability issues were all (or almost all) solved by the time of its axing in 1941/2. And the Vulture was tested to 3000hp on the bench at that time.
Had production continued the Vulture would have received an epicyclic propellor reduction gear system, which would have saved an estimated 400lb of weight.
The original proposal for the V-3420 saw it using 4 cylinder banks and heads from the V-1710 in an X configuration, but not the same way the Vulture was designed. I can't remember the angles, but I think the bottom banks were 120° apart. Sort of like the Napier Cub.
Allison weren't too keen on the design, and it was quite heavy. It also was to use direct fuel injection, IIRC. In the end Allison engineers swayed the Air Corps to their idea of the coupled V-1710 to become the V-3420.
Power for the Vulture MkV is listed around 1800hp at 2800rpm, where maximum rpm was to be 3200. The speed was reduced for reliability. The reliability issues were all (or almost all) solved by the time of its axing in 1941/2. And the Vulture was tested to 3000hp on the bench at that time.
Had production continued the Vulture would have received an epicyclic propellor reduction gear system, which would have saved an estimated 400lb of weight.
The original proposal for the V-3420 saw it using 4 cylinder banks and heads from the V-1710 in an X configuration, but not the same way the Vulture was designed. I can't remember the angles, but I think the bottom banks were 120° apart. Sort of like the Napier Cub.
Allison weren't too keen on the design, and it was quite heavy. It also was to use direct fuel injection, IIRC. In the end Allison engineers swayed the Air Corps to their idea of the coupled V-1710 to become the V-3420.
johnbr
2nd Lieutenant
On the DB-604 they wore at the time the axe come down working on the DB-604c that was 50L engine and hoping for 3500hp to 4500hp.
I think the V-3420 had the potential to be a more reliable and more powerful engine than the R-3350 had it been fully developed. As you all know, the B-39 was a contingency in case the B-29 could not reach operational status with the R-3350's. Wright made enough progress with the R-3350 during the B-29's development that the A.A.F. decided to go ahead with the aircraft, though the engine did prove troublesome in service. Part of the problem was the B-29 was somewhat underpowered, and if the V-3420 was indeed capable of well over 3,000 h.p. (and I agree with wuzak that it was) it would have made a better aircraft. In fact, one has to wonder if the B-39 would have made the B-50 redundant.
- Thread starter
- #9
Yeah, this is another of those great what-if's.
The Fisher Body Aircraft Development Section was tasked with developing the B-39.
According to the inscrutable Wikipedia, Fisher was directed to concentrate on the P-75, which turned out to be a dead end project anyway.
It is quite possible that had the B-39 succeeded, we wouldn't have lost so many aircraft, and crewmen, to fires from overheated engines.
The Fisher Body Aircraft Development Section was tasked with developing the B-39.
According to the inscrutable Wikipedia, Fisher was directed to concentrate on the P-75, which turned out to be a dead end project anyway.
It is quite possible that had the B-39 succeeded, we wouldn't have lost so many aircraft, and crewmen, to fires from overheated engines.
wuzak
Captain
XB-39
Boeing : XB-39 : by San Diego Air & Space Museum Archives, on Flickr
Boeing : XB-39 : by San Diego Air & Space Museum Archives, on Flickr
Boeing : XB-39 : by San Diego Air & Space Museum Archives, on Flickr
Boeing : XB-39 : by San Diego Air & Space Museum Archives, on Flickr
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wuzak
Captain
XB-38
Boeing : XB-38 : by San Diego Air & Space Museum Archives, on Flickr
Boeing : XB-38 : by San Diego Air & Space Museum Archives, on Flickr
Boeing : XB-38 : by San Diego Air & Space Museum Archives, on Flickr
Boeing : XB-38 : by San Diego Air & Space Museum Archives, on Flickr
davebender
1st Lieutenant
IMO cancellation of the DB604A engine during September 1942 and Jumo222A engine during December 1942 makes some sense as the excellent DB603 and Jumo213 V12s were entering service. When fully developed both engines had the potential to produce over 2,000 hp.
Cancellation of the Allison V-3420 is more difficult to understand as the U.S. Army Air Corps lacked a liquid cooled engine more powerful then the V-1710. I guess it's just part of the American bias in favor of air cooled radial engines.
Cancellation of the Allison V-3420 is more difficult to understand as the U.S. Army Air Corps lacked a liquid cooled engine more powerful then the V-1710. I guess it's just part of the American bias in favor of air cooled radial engines.
Shortround6
Major General
I am not sure that the Allison V-3420 was actually canceled as much as it may just withered away due to a lack of application. The P-75 wasn't canceled until Oct of 1944 at any rate.
davebender
1st Lieutenant
I have no idea whether the Allison V3420 worked as advertised. But if it did why wouldn't aircraft manufactures want to use it? I can picture an American version of the Fw-190D9. Only in this case it's a F4U powered by the new liquid cooled engine.
Shortround6
Major General
It wasn't a "new" engine. It had been mocked up in single crankshaft form in 1935. this was soon changed to the two crankshaft form and information given to selected air frame manufacturers in Jan of 1938.
Reasons for it not being used more are two fold.
1. It was not developed to a satisfactory level. It was not two V1710s joined by a gear box. While it did use two V-1710 power sections it used a single supercharger for both engine sections and had mixture distribution problems. It also used a modified ignition timing. left engine did not fire at the same time as the right engine even though both turned in the same direction.
2. While it was a powerful engine it was also a large engine. It was 60in wide compared to the 52.5in of of an R-2800 but it was lower. it was also longer than the an R-2800 with a two stage supercharger by about 9in. The real problem was weight. An "A" series V-3420 could weigh 2665lbs for 2600hp, but that does not include the weight of the radiators and coolant. It is also the weight of an engine with a single speed/single stage supercharger. Adding the turbos and inter-coolers is going to add a lot more weight. A "B" series R-2800 weighed 2480lbs with a two stage supercharger but without inter-coolers.
A "B" series V-3420 with a two stage supercharger (mechanical drive) weighed 2750lbs but that is without the remote gear box used in the P-75. As used in the P-75 with the reduction gear box, the two extension shafts to the gear box and the two prop-shafts the engine weighed 3,275lbs. This version was rated at 2,600hp for take-off at 51.5 in pressure. 3,000hp emergency at 60in pressure and 2,300hp at 21,750ft. Military power (not WEP).
An R-4360-4 weighed 3,390lbs and offered 3000hp for take-off, 3000hp military at 1500ft and 2400hp at 13,500ft from a single stage variable drive supercharger.
You can add roughly 600lbs for radiators and coolant to the V-3420 weights.
Reasons for it not being used more are two fold.
1. It was not developed to a satisfactory level. It was not two V1710s joined by a gear box. While it did use two V-1710 power sections it used a single supercharger for both engine sections and had mixture distribution problems. It also used a modified ignition timing. left engine did not fire at the same time as the right engine even though both turned in the same direction.
2. While it was a powerful engine it was also a large engine. It was 60in wide compared to the 52.5in of of an R-2800 but it was lower. it was also longer than the an R-2800 with a two stage supercharger by about 9in. The real problem was weight. An "A" series V-3420 could weigh 2665lbs for 2600hp, but that does not include the weight of the radiators and coolant. It is also the weight of an engine with a single speed/single stage supercharger. Adding the turbos and inter-coolers is going to add a lot more weight. A "B" series R-2800 weighed 2480lbs with a two stage supercharger but without inter-coolers.
A "B" series V-3420 with a two stage supercharger (mechanical drive) weighed 2750lbs but that is without the remote gear box used in the P-75. As used in the P-75 with the reduction gear box, the two extension shafts to the gear box and the two prop-shafts the engine weighed 3,275lbs. This version was rated at 2,600hp for take-off at 51.5 in pressure. 3,000hp emergency at 60in pressure and 2,300hp at 21,750ft. Military power (not WEP).
An R-4360-4 weighed 3,390lbs and offered 3000hp for take-off, 3000hp military at 1500ft and 2400hp at 13,500ft from a single stage variable drive supercharger.
You can add roughly 600lbs for radiators and coolant to the V-3420 weights.
wuzak
Captain
Hey SR, had the V-3420 been two joined V-1710s it would have been heavier. The crankshafts could be arranged to rotate in the same direction or in opposite direction - I belive the V-3420 for the P-75 was the latter.
No doubt the development for the V-3420 was lacking - because the government weren't pushing too hard for it (it was cancelled and reinstated several times) and Allison didn't bit the bullet and fund development by themselves (if Allison didn't have the funds I am sure that parent company GM did).
I have little doubt that the V-3420 could have competed with the R-4360 for power, if not weight. The V-3420 could have been available earlier than the R-4360, hence the XB-39 version of the B-29 and not an earlier XB-44 (2 stage supercharged) or XB-50 (turbocharged) R-4360 powered version.
Had Allison gone the traditional X route (90° between banks) with a single crankshaft, rather than the odd angled version they decided upon, then the V-3420 would have been more compact. Maybe slightly larger than the Vulture (0.5in longer stroke).
FWIW the Vulture was basically a 2000hp engine in 1940 (reliability not withstanding). I calculate that the equivalent power of a Vulture to a Merlin XX in mid 1940 (with 100 octane fuel) to be about 2480hp. When the Merlin went to +18psi boost with the two stage engines it was capable of 1700hp, and the equivalent Vulture would be just under 2900hp. IIRC the Vulture weighed about 2400lb dry, but a new reduction gear drive would have reduced that substantially.
No doubt the development for the V-3420 was lacking - because the government weren't pushing too hard for it (it was cancelled and reinstated several times) and Allison didn't bit the bullet and fund development by themselves (if Allison didn't have the funds I am sure that parent company GM did).
I have little doubt that the V-3420 could have competed with the R-4360 for power, if not weight. The V-3420 could have been available earlier than the R-4360, hence the XB-39 version of the B-29 and not an earlier XB-44 (2 stage supercharged) or XB-50 (turbocharged) R-4360 powered version.
Had Allison gone the traditional X route (90° between banks) with a single crankshaft, rather than the odd angled version they decided upon, then the V-3420 would have been more compact. Maybe slightly larger than the Vulture (0.5in longer stroke).
FWIW the Vulture was basically a 2000hp engine in 1940 (reliability not withstanding). I calculate that the equivalent power of a Vulture to a Merlin XX in mid 1940 (with 100 octane fuel) to be about 2480hp. When the Merlin went to +18psi boost with the two stage engines it was capable of 1700hp, and the equivalent Vulture would be just under 2900hp. IIRC the Vulture weighed about 2400lb dry, but a new reduction gear drive would have reduced that substantially.
Shortround6
Major General
The V-3420 was sort of in between. it used two V-1710 power sections (blocks and cranks) but used a common accessories section at the back. It either used a gearbox at the front of the engine or a remote gearbox/propeller drive.
Biting the bullet could have involved hundreds of thousands of dollars and thousands of man hours, while the money may or may not have been there the man hours weren't. every hour spent on the V-3420 was an hour not spent on something else. Like a two stage supercharger for the V-1710 or a better crankshaft or the new intake manifold in 1943.
The V-3420 was available earlier than the R-4360, in fact it was first running not long after the R-3350. The problem apparently was getting it to run right.
"Had Allison gone the traditional X route (90° between banks) with a single crankshaft, rather than the odd angled version they decided upon, then the V-3420 would have been more compact. Maybe slightly larger than the Vulture (0.5in longer stroke)."
There were engineering drawings and even a full sized mock up of an "X" engine although not with 90 degrees between banks. It was both more compact and lighter but only by about 100lbs or so. It might also have been a complete disaster. Nobody ever got a good "X" engine into production. 4 pistons on a single crank throw using articulating rods seems to have been a deathnell. Alison did not know this at the time but again, Allison was actually a very small company until 1939/40. in 1938 they had 25 people in the engineering dept and that included blueprint boys. If they didn't keep things simple they wouldn't have gotten anything done.
Allison had the the two crankshafts geared together but operated the cranks out of phase with each other. On the "B" engine one crank was 150 degrees ahead of the other so the firing impulses were spread out and torsional vibration held to a minimum.
I am no engineer but apparently there is a lot going on the more cylinders you add. Nine cylinder radials have different vibration problems than 7 cylinder radials and 18 cylinder radials have problems that 9 cylinder and 14 cylinder radials do not.
In hind sight it is easy to see that trying to feed a double V engine with a single supercharger may have been a mistake. Wright had trouble with an 18 cylinder radial
Maybe they were trying to save weight or though it would be easier to keep the engine "balanced" (left side running the same pressure as the right) I don't know, but we do know that gas flow though manifolds and ports was not as well understood back then as it is now.
Biting the bullet could have involved hundreds of thousands of dollars and thousands of man hours, while the money may or may not have been there the man hours weren't. every hour spent on the V-3420 was an hour not spent on something else. Like a two stage supercharger for the V-1710 or a better crankshaft or the new intake manifold in 1943.
The V-3420 was available earlier than the R-4360, in fact it was first running not long after the R-3350. The problem apparently was getting it to run right.
"Had Allison gone the traditional X route (90° between banks) with a single crankshaft, rather than the odd angled version they decided upon, then the V-3420 would have been more compact. Maybe slightly larger than the Vulture (0.5in longer stroke)."
There were engineering drawings and even a full sized mock up of an "X" engine although not with 90 degrees between banks. It was both more compact and lighter but only by about 100lbs or so. It might also have been a complete disaster. Nobody ever got a good "X" engine into production. 4 pistons on a single crank throw using articulating rods seems to have been a deathnell. Alison did not know this at the time but again, Allison was actually a very small company until 1939/40. in 1938 they had 25 people in the engineering dept and that included blueprint boys. If they didn't keep things simple they wouldn't have gotten anything done.
Allison had the the two crankshafts geared together but operated the cranks out of phase with each other. On the "B" engine one crank was 150 degrees ahead of the other so the firing impulses were spread out and torsional vibration held to a minimum.
I am no engineer but apparently there is a lot going on the more cylinders you add. Nine cylinder radials have different vibration problems than 7 cylinder radials and 18 cylinder radials have problems that 9 cylinder and 14 cylinder radials do not.
In hind sight it is easy to see that trying to feed a double V engine with a single supercharger may have been a mistake. Wright had trouble with an 18 cylinder radial
Maybe they were trying to save weight or though it would be easier to keep the engine "balanced" (left side running the same pressure as the right) I don't know, but we do know that gas flow though manifolds and ports was not as well understood back then as it is now.
Marshall_Stack
Senior Airman
Is the V-3420 different than what was used in the XB-42 Mixmaster?
Douglas XB-42 Mixmaster - Wikipedia, the free encyclopedia
Douglas XB-42 Mixmaster - Wikipedia, the free encyclopedia
Shortround6
Major General
Yes, in the XB-42 each V-1710 drove one of the contra-rotating propellers. The right hand engine drove the rear propeller and the left hand engine drove the forward propeller. In the XB-42 the gear box was modified so that single propeller operation was possible and each prop had separate governing and feathering controls.
wuzak
Captain
Lacking resources didn't stop them proposing the V-3420 in the first place. It also didn't stop them from redesigning the Liberty as an inverted vee with air cooling, no creating an X-24 Liberty.
The design for an X-3420 would have been little different to the V-3420 - both needed new crankcases to bolt the V-1710 cylinder banks to. The X needed a new crank and possibly a master rod and slave rod system. But, they could very easily have designed the X using the standard fork and blade rods from the V-1710. If they did so it would mean the engine would have been slightly longer, but would have cut down on the new bits required. The Rolls-Royce Eagle used 2 sets of fork and blade rods mounted on a single crank throw for the Eagle XVI, and it was considered for further development of the Vulture, had it continued.
In both instances they needed a new accesories section, and new reduction gear system.
So, basically the big difference between an X-3420 (with 90° bank spacing) and the V-3420 was the new single crank needed.
I believe that the original X-3420 was rejected because of the articulating rods.
