Allison V-3420- Anyone have information on it? It seems like it would have been perfect for the XB-42.

[GrauGeist]

Pretty sure a Merlin can drive a turbo - my friend had a Mitsubishi turbo on his Kawasaki 650 motorcycle.

If a 650cc engine can drive one, I suspect a 27 liter engine might be able to...

 

[Shortround6]

There are a number of factors that come into play with turbo-charging.

RR thought they had a good thing going with exhaust thrust. They thought they were getting 89hp from a Merlin XX at 30,000ft from the exhaust thrust thrust compared to the 778hp they were getting at the propshaft. Which is a fraction of what you could get with a proper turbo, however the exhaust thrust cost them around 30-40lbs (?) or whatever the nozzles weighed on that version of the Merlin engine.
A GE "B" series turbo went around 130lbs, it needed to be mounted a number of feet away from the engine. You needed exotic alloys to make it. Or some clever cooling of the turbine blades. You also need an intercooler. Air to air or air to liquid but you need something or you are not going to get a lot of benefit. and you need some ducting (text book from the early 40s figured you needed about 10 cu ft for a turbo charger installation (turbo, ducting and intercooler) for a 1000hp engine, there may have been some economy of scale and you don't need 15 cubic ft for a 1500hp setup but the 10 cu ft set up won't work for 1000hp.

people can argue about the cost/benefit of the turbo but you need a bigger fuselage on a single engine plane. and bigger nacelles or wings on multi engine planes.

In theory the turbo can be set up to provide the same back pressure to the engine that the engine would see at sea level and present the same cooling load to the cylinder head/exhaust valve area. In practice this did not seem to quite work out, especially when they started using the turbo to provide WER. (shut the waste gate sooner).

Somehow the Merlin, with it's suspect cylinder head cooling (?) seemed to be able to stand up quite a bit of power late in the war. Burning enough fuel in the cylinders to generate the several hundred horsepower in the cylinders to power the 2nd stage of the supercharger was harder on the engine than routing the lower amount of exhaust gas to the turbine?

I have seen no figures on the exhaust thrust of a two stage Merlin engine.

Exhaust thrust doesn't work as well for climb.

Exhaust thrust is the weight of the exhaust gas (or intake charge) times the exit velocity of the gases through the nozzle.

however Exhaust Horsepower is HP = T * V / 375
T = Thrust (FT/LB)
V = MPH
375 is a constant.

If you have 0 mph you have 0 HP regardless of what the thrust is.
The higher the speed the more HP you get from the same amount of thrust (until you are well into jet engine speeds = supersonic)

 

[BlackSheep]

The Allison W-3420 had potential. to be sure, and four were fitted to a B-29.

View attachment 693509

It was faster than the normal R-3350 version, but would have also interrupted production. You'd think they could have anticipated that had it been adopted, it would have interrupted production since they declined to improve the F6F-5's rolling characteristics for the exact same reason ... it would have interrupted production.

They also tried an Allison-powered B-17, though they were V-1710s rather than W-3420s.

View attachment 693510

It was also faster than the radial-powered variety but, are you ready for it, it would have interrupted production! Go figure, huh?

Looks like Uncle Joe wasn't the only one who subscribed to "quantity has a quality all its own"

 

[don4331]

In theory the turbo can be set up to provide the same back pressure to the engine that the engine would see at sea level and present the same cooling load to the cylinder head/exhaust valve area. In practice this did not seem to quite work out, especially when they started using the turbo to provide WER. (shut the waste gate sooner).

Somehow the Merlin, with it's suspect cylinder head cooling (?) seemed to be able to stand up quite a bit of power late in the war. Burning enough fuel in the cylinders to generate the several hundred horsepower in the cylinders to power the 2nd stage of the supercharger was harder on the engine than routing the lower amount of exhaust gas to the turbine?

In trying to be object: Not only is there less power to the supercharger, but the engine weighs less - probably by equivalent weight of turbocharger as it may now be a single stage, single speed supercharger & supercharger itself is smaller as it only has to make peak boost at ground level (I'm assuming turbo maintains ground level density through critical altitude). The boost control is simplified as it is only controlling wastegate, not both throttle and supercharger speed control.

Unfortunately, the GE turbo compressor is less efficient than RR one, so intercooler needs to be larger but I would still use water-cooled aftercooler as temperatures post the mechanical supercharger are highest which allows the package to be most efficient.

In theory, you can design a turbine set up so the engine would see the same back pressure as engine with open exhaust. But that requires exhaust piping/turbine to have same equivalent resistance to flow and as noted merely maintaining atmospheric pressure. But when using a turbo, designers really wanted to achieve (or exceed) atmospheric density - no point in losing all the gains you made with supercharger because it achieved pressure increase due to heating. And most turbocharger installations require many feet of exhaust tubing.

So, the numbers from General Electric show 18" Hg increase in back pressure due to piping, turbine & additional pressure you need for intake piping, intercooler core resistance and temperature increase due to compressor inefficiency to get back to atmospheric density.

That 18"+ Hg back pressure of 1,700° F exhaust gas puts more heat load into head than the few hundred ponies driving the 2nd stage supercharger. P-47M at WEP was up to 28" Hg back pressure.

For both 2 stage mechanical and turbo supercharged, there's very short limit on how long full power can be used before things overheat.

 

[Shortround6]

For both 2 stage mechanical and turbo supercharged, there's very short limit on how long full power can be used before things overheat.

that is certainly true. The P-2800s generally ran water injection for anything over 53-54in of MAP (12 lbs?) helped cool everything.
They also used water injection on the two stage mechanical superchargers.

If the intake charge is running hot (for US practice the intake charge was over 100 Degrees F at the carb intake) they started to have problems. Granted with the RR intercooler set up we are measuing things at different point.

Criticizing the RR for not doing well with a turbo for similar problems sees a bit harsh.

Things also changed in just a few years. People were just figuring out what the limits of 100/130 fuel were in different engines in late 1941 and 1942. In 1944 they were trying to figure out the limits of 150 octane fuel. Maybe RR could have redesigned the heads for better cooling with turbos? but why bother, they were getting almost 1700hp out of the Merlin at 18,000ft with 100/130 fuel.

the few hundred ponies used by a 2 stage supercharger are at a lower power level than that.

 

[OldGeezer]

Daniel Whitney's monumental "Vee's for Victory" has an interesting little note in the V-3420 section: "Just as the V-1710 was doubled to create the V-3420, V-3420's could be 'doubled' to create a DV-6480. In November 1946 such a proposal reached the point that Allison built a reduction gear for such an engine. It was probably intended to be a competitor to engines such as the Lycoming XR-7755."

 

[ddwhitney]

Why didn't Allison work harder on developing it? Did it have some serious flaw? (Hard to believe because the V-1710 seemed to be more reliable and easier to build than the Merlin. I'm beginning to think that the Allison got a really bad rap.) Like the P-38, a 1942 XB-42 COULD have gotten one (or two) good turbochargers... Of course the XB-42 might have been even better if it was a tractor ala the R2Y than a pusher...

There are a lot of erroneous posting in this thread.
First, the US Air Corps wanted a double V-1710 to power the XB-15 back in 1934. Concurrent development of the X-3420 and V-1710 meant slow progress on both. When Bob Hazen took over as Chief Engineer in 1936 he got the Air Corps to back off of the 3420 project while he got the V-1710 through Type Testing by promising them a better V-3420 based upon his improved V-1710E/F models. This was done and the V-3420-1(A1) first ran in April 1938, although the Air Corps continued to support its development, they did not have a project needing the engine at the time. In September 1940, during the Battle of Britain, the Air Corps suspended all V-3420 work to focus on desperately needed fighter engines.
When the B-29 project got into trouble because of problems with the R-3350 the Air Corps restarted the V-3420 project in February 1941. Focus was on engines for the XB-19A and XB-39, both powered by turbosupercharged V-3420A engines. Allison was awarded a contract for 500 engines, enough to support 100 B-39s. When the R-3350 issues were mostly resolved, and the continuing need for V-1710s, the B-39 project was terminated. For a more comprehensive look at the V-3420 see Vee's For Victory! by Dan Whitney.
The V-3420B engines had contra-rotating crankshafts, ideal for powering similar turning propellers. This engine was adopted for the Fisher P-75 and the questioner is right, it could have been utilized in the later XB-42, which had two V-1710s, each driving parallel drive shafts to the aft mounted coaxial propeller gearbox. The V-1710s had the advantage that one engine could be shutdown and the other operated at full power, a measure of redundancy. This was not possible with the V-3420B.
The single-stage Merlins did have a slightly more efficient supercharger, which also could operate at either of two speeds. This improved its service ceiling.
Not everyone understands that Allison and Rolls-Royce were both working to develop two-stage engine driven superchargers at the same time, and both entered service in 1943.
Allison had wanted to introduce a two-stage supercharged V-1710 in the North American X-73, the Mustang prototype in 1941 (See V-1710 and V-3420 Designs and Concepts by Dan Whitney and John Leonard). The Air Corps did not want Allison to divert engineering and manufacturing effort into this project, so it was delayed. Their argument was that they had sponsored the development of the successful GE Turbosupercharger since WWI, the V-1710 was designed to work with a turbo, thereby giving it "two-stage" capability, e.g., X/YP-37, P-38, XP-39. Prior to the war they saw no need for mechanical two-stage superchargers.
The V-1710 was a very reliable engine. End of War TBO was 500 hours, while the Merlin never exceeded 400 hours, even on P-51s in the 1950s. Examples of V-1710s achieving over 1,000 hours on the wings of P-38s without removal are available.

 

[tomo pauk]

Thank you for the very informative post.

Not everyone understands that Allison and Rolls-Royce were both working to develop two-stage engine driven superchargers at the same time, and both entered service in 1943.

Merlin 61 entered service in second half of 1942. The 2-stage supercharged V-1710 aboard the P-63A entered service in late 1943. That is more than a year of difference. Merlin 60s and 70s offered better power above 20000 ft.
Merlin 60 was in service earlier than the Merlin 61.

 

[GregP]

I'm not sure if the RM.17SM flew, but it was cleared for flight testing at (IIRC) 2,380hp in late 1944.

If it did fly it would have been in one of Rolls-Royce's test hacks.




The RM.17SM was very much a Merlin. Most of the changes were internal and to the supercharger.

To fit it in an aircraft fitted with a 2 stage Merlin should not have required very many modifications, if any at all.




You asked if the RM.17SM flew, and then state that it did not.

I am not sure, but it was cleared for flight testing.

The V-1710-127 was a turbo-compound. The turbine added ~1,000hp to the power output.

I'm sure Rolls-Royce could have done the same for the Merlin, though it would have taken more re-engineering to get it to work, since it was less modular than the V-1710.

The V-1710-127 was based on the 2 stage engine, which was long to begin with. And then there is a large turbine bolted on the back of that. It would take considerably more engineering to fit that to an existing airframe The only proposed use for the engine seems to have been the XP-63H.

To my knowledge, the V-1710 was never type tested (the RM.17SM was), and was never cleared for flight.

Reliability was an issue, as the exhaust temperature at WEP was too high for the turbine. Had it continued, Allison would have designed a new turbine with air-cooled blades. But that didn't happen before the project's cancellation in 1946.

When did the V-1710-127 first run on the test bench?

Yes, the V-1710 passed a 150-hour type test ... in 1937 the Allison V-1710 became the first American engine to qualify at 1,000 horsepower for the new 150-hour military type test.

 

[wuzak]

Yes, the V-1710 passed a 150-hour type test ... in 1937 the Allison V-1710 became the first American engine to qualify at 1,000 horsepower for the new 150-hour military type test.

No, did the V-1710-127 pass a type test.

It appears unlikely, as by the time the engine was built there was not much demand for it.

I imagine that each new variant would have to go a type test to get the power ratings.

 

[wuzak]

Merlin 61 entered service in second half of 1942. The 2-stage supercharged V-1710 aboard the P-63A entered service in late 1943. That is more than a year of difference. Merlin 60s and 70s offered better power above 20000 ft.
Merlin 60 was in service earlier than the Merlin 61.

The second half of 1942 being July 1942. First combat victory for the IX on July 30, 1942.

I don't believe he Merlin 60 ever saw service, and only 75 were built.

 

[ThomasP]

I have read that the Merlin 60 saw service in some of the early-production Wellington Mk VI, plus I ran across a reference to the Mk VI Pilot's Notes in the National Archives at Kew:

AP No. 1578F Vol I, Pilot's Notes, Wellington VI Aircraft Two Merlin 60 or 62 Engines

 

[Geoffrey Sinclair]

V-3420 production,

Number	month
1	Jun-40
1	Sep-40
1	Dec-41
2	Jan-43
4	Feb-43
4	Mar-43
2	Apr-43
2	May-43
1	Jun-43
5	Aug-43
3	Sep-43
4	Oct-43
1	Nov-43
2	Dec-43
5	Jan-44
2	Feb-44
2	Mar-44
6	Apr-44
1	May-44
2	Jun-44
11	Jul-44
11	Aug-44
13	Sep-44
28	Oct-44
17	Nov-44
14	Dec-44
4	Jan-45
1	Mar-45
1	May-45
2	Jun-45
1	Aug-45
1	Sep-45

Total 154.

V-1710 2 stage production,

No.	Month
1	Dec-42
0	Jan-43
1	Feb-43
1	Mar-43
3	Apr-43
32	May-43
47	Jun-43
33	Jul-43
2	Aug-43
1	Sep-43
42	Oct-43
92	Nov-43
260	Dec-43

then 2,867 in 1944 and 1,645 in 1945. V-1710 post war for military, 10 in 1946, 603 in 1947 and 145 in 1948

Merlin 60 production from November 1941 according to Rolls Royce, Merlin 62 from April and Merlin 61 from May 1942. Wellington VI serials W5795, W5797 to W5815, DR471 to DR504, DR519 to DR528. Fitted with Merlin 60 W5795? (no card), W5797 to W5815, DR471 to DR482, DR484. Fitted with Merlin 62, DR483, DR485 to DR528 except DR490 and DR493 mixed Merlin 60/62, there were 29 built January to June 1942, 35 built October 1942 to February 1943.

Wellington VI on strength with 109 squadron, W5801 23 March to 1 July 1942, W5802 26 March to 17 May 1942, DR481 11 December 1942 to 29 January 1943, rest on mark VI have no squadron service.

First Spitfire IX production June 1942.

 

[GregP]

No, did the V-1710-127 pass a type test.

It appears unlikely, as by the time the engine was built there was not much demand for it.

I imagine that each new variant would have to go a type test to get the power ratings.

All engine dash numbers were not run through a type test for ANY engine type.

The V-1710 as a power system DID pass the type test, but not that particular dash number. Each new dash number had to pass testing, but not type testing.

 

[wuzak]

All engine dash numbers were not run through a type test for ANY engine type.

No, but would need to be for major revisions to the engine and to certify new ratings.

Dash numbers could change for minor variations, such as what accessories are on the engine.

But there must have been type tests to clear the engine for new ratings.

The V-1710 as a power system DID pass the type test, but not that particular dash number. Each new dash number had to pass testing, but not type testing.

I would think that the whole system would need to be type tested to set the engine rating and confirm acceptable reliability.

 

[PAT303]

I don't know how you are going to fit this into any single seat fighter

Allison V-1710 Turbo-Compound aeroengine

 

[wuzak]

I don't know how you are going to fit this into any single seat fighter

Allison V-1710 Turbo-Compound aeroengine

Put it in the middle.

Or make a twin!

 

[PAT303]

A Merlin could be bolted into almost anything, that thing requires a plane designed for it.

 

[tomo pauk]

I don't know how you are going to fit this into any single seat fighter

Allison V-1710 Turbo-Compound aeroengine

Don't do it like that?
Put the 2-stage V-1710 instead of the R-2800 on the P-47, use parts of the turbo infrastructure to drive the turbine, connect the turbine with the V-1710 via a shaft. Result is a very rangy P-47.
Not that far fetched, the P-72 was supposed to have a 10-ish ft shaft connecting the R-4360 and the auxiliary S/C (engine powered the aux S/C in this case).

 

[PAT303]

Don't do it like that?
Put the 2-stage V-1710 instead of the R-2800 on the P-47, use parts of the turbo infrastructure to drive the turbine, connect the turbine with the V-1710 via a shaft. Result is a very rangy P-47.
Not that far fetched, the P-72 was supposed to have a 10-ish ft shaft connecting the R-4360 and the auxiliary S/C (engine powered the aux S/C in this case).

That just sounds like a mess to me, having a 10 foot driveshaft spinning between your legs is going to end badly when a few AP cannon shells hit it.