Double Kestrel/Double Merlin: any merit in that?

[tomo pauk]

Talking about V-3420 got me thinking: would there be any benefit for the Allied war effort if there were double Kestrels and/or double Merlins available; the W form, not the X form? Data for the 'single' Merlin are well known, so we can assume double HP in the D. Merlin. The late-30's variants of Kestrel were making 680-700 HP on take off, 630 HP at 14400 ft, dry weight 960 lbs, ~21L/1300 cu in - so the pre-ww2 D.Kerstrel is at 1360-1400 HP at 1920 lbs, TO, and 1260 HP at those 14400 ft.
Wonder how much of a power increase we would see with 42 L engine, applying the applicable lessons learned from Merlin wartime development? Would it mimic the Peregrine/Vulture trouble? Any good platforms/users for the doubles?

 

[wuzak]

What about H?

There was a proposal for an H-Merlin, based on the Merlin 61. It would be two complete engines which could run independently.

I would suggest trying a version with geared together cranks, and only one set of accessories.

 

[davebender]

Wouldn't it be easier and better to perfect the Griffon engine and get it into mass production earlier?

 

[wuzak]

Wouldn't it be easier and better to perfect the Griffon engine and get it into mass production earlier?

Griffon: Wartime potential 2500hp
H-Merlin: Potential: 4000hp

 

[davebender]

Griffon: Wartime potential 2500hp
H-Merlin: Potential: 4000hp

A 2,500 hp engine during 1943 is more useful then a 4,000 hp engine during 1947.

 

[wuzak]

A 2,500 hp engine during 1943 is more useful then a 4,000 hp engine during 1947.

The proposed H-Merlin used Merlin bits - only a few new bits required. The major engine bits - crank, rods, blocks, heads, valve gear, supercharger etc, would be straight off the production line. Would need new reduction gear, new intercollers and new crank case.

A geared together one would need a new supercharger/accesories section, reduction gear and crankcase. Why would it take 5 years to get to work?

 

[wuzak]

A 2,500 hp engine during 1943 is more useful then a 4,000 hp engine during 1947.

And teh Griffon could not make 2500hp in 1943 - not, in fact, during the war either. But it did have that potential.

 

[yulzari]

Was the Rolls Royce Vulture not a double Kestrel?

 

[wuzak]

Was the Rolls Royce Vulture not a double Kestrel?

Not exactly.

 

[nuuumannn]

I think Hives of Rolls had his eye on what Whittle was up to in his little shed to bother with making the Merlin more complicated...

 

[tomo pauk]

The proposed H-Merlin used Merlin bits - only a few new bits required. The major engine bits - crank, rods, blocks, heads, valve gear, supercharger etc, would be straight off the production line. Would need new reduction gear, new intercollers and new crank case.

A geared together one would need a new supercharger/accesories section, reduction gear and crankcase. Why would it take 5 years to get to work?

Heya, wuzak,

While we can assume more or less accurately what power to expect from double Merlin, how many HP we could expect from a double Kestrel? Of course, with some plausible development.

What about the applications? Even with pre-war rating of 1300 HP it can power some bombers rather fine, and one in the nose can serve in FAA planes?

 

[davebender]

Why did it take until late 1944 for Daimler-Benz to perfect the DB605D engine? Why did Lockheed need 5 years to perfect the P-38? Why are we still waiting for Lockheed Martin to perfect the F-35 fighter aircraft?

If high tech stuff was simple, quick and inexpensive every nation would build them.

 

[cimmex]

because in Tomo's scenarios money and resources does not count....
Cimmex

 

[tomo pauk]

How much of the money is to be poured into a W variant of the tested true V engine, vs. all the Pennines, Exes, Crecies, Vultures? Let alone vs. the sleeve valve engines? Wasn't the V-3420 been a much more worthwhile thing than the Lycomings, Continentals, Chryslers that would rather melt down, than to produce anything close to 1500 HP? Or, DB-606/610 vs. Jumo-222?

 

[wuzak]

Heya, wuzak,

While we can assume more or less accurately what power to expect from double Merlin, how many HP we could expect from a double Kestrel? Of course, with some plausible development.

A double Kestrel would probably be pegged at around 1500hp. A Merlin will give you much the same, if not the Griffon will.

The best of the Kestrels was the XXX at 720hp in 1938. It was also the heaviest at around 920-950lbs.

Ad ouble Peregrine would give you more - around 1800hp - at the expense of even more weight. But that would at least have scope for improving power. But then you would have to debug the Peregrine and its double at the same time.

Solving the Vulture's problems would probably take the same amount of time, or less, an be capable of 2500hp by 1942/43 and 3000hp by 1944/45. It will also be lighter and more compact.

 

[tomo pauk]

Thanks.
That would mean like a 1440 HP in 1938, weight cost some 1900 lbs dry for the D.Kestrel?
What were the things that were holding the Kestrels power down, ie. the inability to go above 750 HP?

 

[wuzak]

Thanks.
That would mean like a 1440 HP in 1938, weight cost some 1900 lbs dry for the D.Kestrel?
What were the things that were holding the Kestrels power down, ie. the inability to go above 750 HP?

I would say the size and strength of the components. It was built from the mid 1920s, and wasn't stressed for more hp.

 

[wuzak]

Thanks.
That would mean like a 1440 HP in 1938, weight cost some 1900 lbs dry for the D.Kestrel?
What were the things that were holding the Kestrels power down, ie. the inability to go above 750 HP?

The Vulture was already getting 1800hp, or more, by then. Albeit with poor reliability. Weight was 500lbs more, though.

 

[Shortround6]

The Peregrine used the same bore and stroke as the Kestrel so that should help answer the question as to what was needed for a "high power" Kestrel. I am not sure if the Kestrel was used with glycol coolant or only with water which affects radiator size and weight.

 

[tomo pauk]

Wonder how much the bolded part is true (guess it's a typo, not 780 kW, but 780 HP?):

However it was not long before line improvements increased power dramatically; the V model provided 695 hp at 3,000 rpm with no basic change to the design, while the XVI used in the Miles Master delivered 745 hp. In 1935, Messerschmitt also tested its Messerschmitt Bf 109 V1 prototype monoplane fighter with Kestrel engine.

Increased availability of higher octane aviation fuels in the late 1930s allowed the engine to be boosted to even higher power levels without suffering from ping, and the Kestrel eventually topped out at 1,050 hp (780 kW) in the Kestrel XXX model of 1940.

From here:
http://spitfiresite.com/2010/04/the-development-of-rolls-royce-merlin-engine.html

BTW, SR6,

The Peregrine used the same bore and stroke as the Kestrel so that should help answer the question as to what was needed for a "high power" Kestrel.

Care to elaborate a bit?