V-3300

[davebender]

DB603 engine development began during 1936. They had a prototype running during 1937 when RLM cancelled program funding. To me that seems like rapid development progress.

 

[Shortround6]

You NEED to get a prototype engine running in order to have much development at all. The real question is how fast can you go from the 1st prototype engine to a production worthy example.

Allison had a running "prototype" in the early 30s.
P&W had a 9 cylinder "test mule" running before they had a complete R-2800.
Wright had an R-3350 running in May 1937
Work on the Continental O-1430 stretched out for years because the army would only fund one and two cylinder test rigs.

The first prototype engine is just the start of development, not the middle let alone the end.

P&W had 3000 hours of ground testing on "prototype" R-2800s before they ever stuck one in an airplane and that was in a test mule aircraft and not an intended application.

 

[Shortround6]

I never thought about i before, but did the H-2470 have the exhausts between the banks, a la Sabre?

I would assume this would teh logical way as the engine was derived from a flat engine, so the intakes could be mounted top and bottom unmodified.

It would also seem to be to be the best way to do an H.

From the photo posted and another in an edition of "aircraft engines of the world" it appears that the exhausts were on the outside of the "H" and the intakes on the inside.

The Hispano 24Z has them on the outside as does the Arsenal 24H (Jumo 213 cylinder blocks) . I would note that these are all Vertical "H" engines and not horizontal like the Sabre.

Both French engines use two separate superchargers, perhaps being 72 and 70 liter engines it is to use the existing ones rather than trying to design a new single unit of the appropriate size?

http://www.aviationbanter.com/attachment.php?attachmentid=23388&d=1205431840

 

[nuuumannn]

From what I read about the Eagle 46, Rolls did not consider doing a bigger version of the Merlin because the Griffon proved so successful. There's no reason why Rolls would have examined making the Merlin bigger by turning it into a double powerplant. Of course, the Eagle 46 was bigger still than the Griffon, but its development was overshadowed by jet propulsion.

Rolls Royce scaled the Kestrel to make the Buzzard

The Buzzard wasn't based on the Kestrel - it was built based on the need to design a bigger engine than the 'F', which became the Kestrel. It was a much bigger engine but based on the same basic layout. Its cubic capacity was 70% bigger than the 'F's.

 

[Shortround6]

Aircraft engine designers, at any given point in time, thought there was a limit to the amount of power that could be had from a single cylinder. Once you had reached that limit the only solution was to go to more cylinders.

This limit was governed by cooling.

And by the speed of the flame front in the cylinder, you want the combustion to be about done in the 20 degrees of crankshaft rotation after top dead center and this places a limit on bore size and RPM. Bore size can be expanded some what by going to triple ignition but most (all?) designers didn't want to do that.

And byy the piston speed. About 3000fpm was considered the max Piston speed that was practical in the WW II era and only the JUMO 213, the DB603 the Bristol Pegasus exceeded it by any great amount. The Bristol Pegasus didn't use the cylinder pressures the German engines did. The piston speed helped govern the rpm.

With cylinder bore and stroke both limited in size, once that size is reached then the only answer is more cylinders.

Better fuel allows higher cylinder pressures and more power per cylinder but that is obviously fuel dependent. If you don't have the the better fuel?????

 

[wuzak]

From what I read about the Eagle 46, Rolls did not consider doing a bigger version of the Merlin because the Griffon proved so successful. There's no reason why Rolls would have examined making the Merlin bigger by turning it into a double powerplant. Of course, the Eagle 46 was bigger still than the Griffon, but its development was overshadowed by jet propulsion.

In a way the Griffon was the beigger Merlin - it just wasn't scaled up as such.

Looking at capacities:

Kestrel 21.2l/1296ci
Merlin 27l/1649ci
Griffon 36.7l/2239ci
Vulture 42.5l/2592ci
Eagle 22 46.2l/2817ci
H-Merlin 54l/3298ci

An H-merlin would have given an engine in the 3500-4000hp class faster than the Eagle 22 and would use a large proportion of components already in production.

The Buzzard wasn't based on the Kestrel - it was built based on the need to design a bigger engine than the 'F', which became the Kestrel. It was a much bigger engine but based on the same basic layout. Its cubic capacity was 70% bigger than the 'F's.

True enough.

The H (Buzzard) was a scaled up F (Kestrel).

 

[wuzak]

From the photo posted and another in an edition of "aircraft engines of the world" it appears that the exhausts were on the outside of the "H" and the intakes on the inside.

The Hispano 24Z has them on the outside as does the Arsenal 24H (Jumo 213 cylinder blocks) . I would note that these are all Vertical "H" engines and not horizontal like the Sabre.

Both French engines use two separate superchargers, perhaps being 72 and 70 liter engines it is to use the existing ones rather than trying to design a new single unit of the appropriate size?

http://www.aviationbanter.com/attachment.php?attachmentid=23388&d=1205431840

Hadn't realised that the H-2470 was a vertical engine.

Seems ;ogical to me that they could sanwich two engines together horizontally and keep the intake manifolds the same as the O-1230.

 

[Shortround6]

Or a Griffon was a repackaged Buzzard (same bore and stroke)

 

[wuzak]

Or a Griffon was a repackaged Buzzard (same bore and stroke)

And that's about all that was common between them.

 

[Shortround6]

Well, both had overhead cams and 4 valves per cylinder.

what are different crankcases, crankshafts, connecting rods, reduction gears and few hundred other minor differences between friends

It helped speed up development didn't it??

 

[wuzak]

Well, both had overhead cams and 4 valves per cylinder.

what are different crankcases, crankshafts, connecting rods, reduction gears and few hundred other minor differences between friends

It helped speed up development didn't it??

True.

They also used the Kestrel style head (parallel vertical valves). So that would have helped a lot.

And the R, based on the Buzzard, was to be used as the basis for the Griffon I, but that was abandoned.

 

[wuzak]

Well, both had overhead cams and 4 valves per cylinder.

what are different crankcases, crankshafts, connecting rods, reduction gears and few hundred other minor differences between friends

It helped speed up development didn't it??

I suppose it was also a V12 with 60° between the banks.

 

[wuzak]

Just a quick mock up of how a H-3420 might look (without a lot of bits, obviously)

And one I did before - an X-3420.

 

[Shortround6]

Nice work.

 

[johnbr]

Yes very nice work.

 

[wuzak]

If you were to do a complete redesign you could, potentially, make the H engine more compact than using the complete top end of the engine as shown there.

Have a single one piece head which has the combined exhausts.

 

[Shortround6]

That may make maintenance a bit of a nightmare, not to mention manufacture. A one piece 12 cylinder head is going going to be very heavy and hard to move, it may also be stretching the foundry capability to cast such things with an acceptable scrap rate.

the last is one of the secrets to engine "technology". The designer can draw anything he wants, If it can't be made on a mass production basis at acceptable costs it doesn't matter how good it is in theory.

 

[wuzak]

That may make maintenance a bit of a nightmare, not to mention manufacture. A one piece 12 cylinder head is going going to be very heavy and hard to move, it may also be stretching the foundry capability to cast such things with an acceptable scrap rate.

the last is one of the secrets to engine "technology". The designer can draw anything he wants, If it can't be made on a mass production basis at acceptable costs it doesn't matter how good it is in theory.

Yes, and it is a whole new engine then - not using bits readily available.

The maintenance would be regarding access to items like spark plugs - which were on the Allison, like the Merlin, located on on either side of the head.

So that would need a redesign. And I think so too would items that need regular access.

 

[Shortround6]

I was just reading about Miller designed V-12 in WW I. It was 1414 cu in and the crankcase and cylinder blocks were designed as one piece. In 1917 it was supposed to be the largest aluminium casting attempted in the US. They got a usable casting on the 3rd try. Aircraft engine designers almost routinely pushed the state of the art in foundry (casting and forging) techniques as well as pushing the state of the art in materials. There are reasons that some aluminium and even a few steel alloys in Great Briton had a RR prefix code. There is a fine line between pushing the state of the art not quite far enough and falling behind the competition and pushing too far and winding up with an unproduceable engine. The sleeve valve engines just missed this last category.

 

[gjs238]

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