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Discussion in 'Aviation' started by gjs238, Jun 20, 2012.
Could a V-3300 have been created from the V-1650 the way the V-3420 was created from the V-1710?
Rolls-Royce did do a proposal (?) for a H-Merlin. That was essentially two complete Merlin 61s mounted on the same crankcase and driving coaxial propellors - the same concept as the Fairey P.24. Each half operated independently, had its own two speed two stage supercharger, intercooler (cooling of supercharger involute) and aftercooler.
The cylinder blocks were placed in an H - with cylinders mounted vertically.
The power would have started at about 3000-3200hp, for about 3600lb (IIRC) dry weight - slightly more than two Merlin 61s. By the time it would have appeared it would have been capable of around 3600-4000hp - or more power for less weight than the Eagle 22.
The downside to doing it this way is that some components can't be brought across.
Obviously things like cranks, rods, pistons, blocks and heads can. Supercharger impellers as well. But the intake manifolds, supercharger housings/involutes, aftercoolers, etc all had to be different.
I wonder if an H Merlin with the two cranks geared together and one supercharger system would have been lighter and just as powerful? - Maybe using two Merlin first stage impellers feeding aa Griffon 1st stage impeller?
Certainly it COULD have been done.
Questions remain. The German flirtation with the W-engien was not a success. Allison did it and it was not nearly the problem child the He-177 flew with and did't tend to catch fire, but it never made it into mass production either.
My question is simple. Why would Rolls Royce try that when two other attempts at the same thing did not really succeed?
According to Wikipedia the V-3420 has a first run date of 1937, so at that point I'm not so sure what success or failures would have been known.
Almost anything can be created if you are willing to pour enough money into the program. The atomic bomb and B-29 bomber are examples of high tech American programs that succeeded only because the programs were given a blank check.
Is the V-3420 engine program valuable enough to warrant a blank check?
Allison V-3420s were produced in token numbers. And were tried on B-29.
Was there something wrong with DB-610 and/or V-3420?
It worked. However a purpose built 24 cylinder engine such as the Jumo 222 has a superior power to weight ratio and is more compact.
As did the DB-604a and c.
That is true.
However, coupling engines allows for more common components.
The DB606, DB610, et al, had the advantage that they used the whole original engines almost completely unchanged. And they could shut down one half in flight to save fuel.
A H-engine using cranks, rods, cylinder blocks, etc, from the original engine would be more compact too.
Wasn't there a French H-24 based on Jumo 213 components?
Not sure what you mean. A coupled engine has more components (i.e. the coupling gearbox) and therefore more things that can malfunction.
The only real advantage I can see is some nations such as Germany had extensive experience with coupled engines going all the way back to WWI. So coupling two engines together should not be a major engineering challenge.
Of course you've got to build the engine cowling right whether the engines are coupled or not. Otherwise you get problems similiar to early model He-177As.
Apart from the gearbox and the opposite hand supercharger system for one of the engines the coupled engines are identical to the source engines.
In teh case of the V-3420, the crankcase, accesories and reduction gear sections are all new, but the cranks, rods, pistons, valves, head, cams, etc, are the same as the V-1710. Same goes for the intake manifold.
With an engine like the Vulture, DB604 or Jumo 222 many more new components have to be designed and tested. You could use the block, heads, and top end from a V-1710 or Merlin, but you will need a whole new bottom ende (crank, rods, crankcase), reduction gear and accesories section. All the new components need design and testing.
There was. There was also a French H-24 based on the Hispano Y series V-12. The Lycoming company stacked ( actually flipped them on their sides) a pair of O-1230s to make the H-2470.
Doing this cut development time as they already knew what was going on inside the combustion chamber. Many engine designers of the time did not like to depart very far from what they knew worked.
Rolls did build an 'H' engine; the Eagle 46, first built in 1944 - not to be confused with its first aero engine in service. It was fitted to only one aeroplane; the Eagle 22 in the Westland Wyvern prototype. Here's some data from British Piston Engines and their Aircraft on the Eagle 22:
3,500 h/3,500 rpm, +28lb boost 24 cylinder, horizontally opposed H-shaped, 70-30% water, ethylene glycol, pressure cooled, sleeve valve. Bore/stroke 5.0 x 5.125 in Vol. 2,807 cu in (137 x 130 mm, 46 lt). Compression ratio 7:1, two-speed, 3:1 3.67:1 two stage supercharged, geared, spur.2985:1 LH/RH counter rotating tractor drive. Coffman starter. First flown in a Wyvern 16/12/46.
The engine owed little to the Merlin (apart from its supercharger design) but followed the design of the Napier Sabre.
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.
The DB603 was essentially a scaled up DB601. Why not take the same approach with the RR Merlin or Allison V-1710? That should shorten development time while retaining a power to weight ratio similiar to the original engine. Engine diameter increases by a relatively small amount so you don't need the much larger cowling required by a coupled engine.
You still have to do all the testing of components to make them work.
Rolls Royce scaled the Kestrel to make the Buzzard, and the Buzzard had to have extra strengthening.
That's necessary no matter which approach you take. More hp requires a larger cooling system, larger oil pump, larger bearings and crankshaft etc.
If you have two halves like the V-3420 then you can use the two oil pumps, coolant pumps, whatever, of the original. The bearings will be the same.
Same deal if you do an H-Merlin in the style of the Fairey P.24. All the major internals are the same. You only have to design and check new stuff.
Also, there is a practical limit to the size you can make an engine. At some stage you need to have more cylinders.
Scaling up an engine doesn't shorten the development time by much. It shortens the drawing time for the initial blueprints but that is about it.
A 5in cylinder (127mm) has a perimeter of 15.7in while a 6in cylinder has a perimeter of 18.84, a 20% increase. However the area went from 19.625sq in to 28.26 sq in, a 44% increase. you are burning 44% more fuel with only 20% more cylinder wall to dissipate the heat through. You also have longer path from the center of the piston head to the piston skirt/wall to get the heat through.
Lengthening the stroke works if the starting rpm is low enough. If you are starting with a 6 in stroke and a 3000rpm top limit you have a piston speed of 3000fpm which was pretty much the max in WW II for piston engines with only a couple of exceptions. The Griffon ran at 2750rpm which kept it's 6.60in stoke to a 3025fpm piston speed. Decreasing your max rpm by 8-10% is that much less power in your "scale up".
Intake flows get weird also. Flow rates though pipes go up at a much faster rate than the simply increase in diameter. For the Allies without fuel injection getting the proper distribution of the fuel/air mixture to the cylinders was a big problem that is seldom talked about except for the problems in the Wright R-3350. The engine is only as strong as the mixture in the leanest cylinder (it runs the hottest and will detonate first). Mixture distribution even in the 60s and 70s was causing problems in prototype car engines so I doubt it was an 'automatic' solve in the early 1940s.
Different sized parts will vibrate at different frequencies and harmonic vibration was a great problem in all aircraft engines. What you know about the smaller engine may help, or not.
There is a lot more to making a reliable aircraft engine than simply drawing the blueprints.