Engine technology free-for-all

[wuzak]

Hardly surprising then, that it never did do properly - 'what it said on the tin'..

An X (actually *) -configuration with simultaneous firing, - plenty of harmonic horrors - where is Manolis on this..

Is that an assumption?
Looking more closely, if you think of each pair of cylinders in a row the firing order for a row is like a 3 cylinder radial.

So, for the first row the firing order is:
2-1-4-3-6-5

(seems the rotation is opposite the numbering).

Row 2 is:
5-4-1-6-3-2

Row 3 is:
3-2-5-4-1-6

And Row 4 is:
6-5-2-1-4-3

Rows 1 & 2 fire together and rows 3 & 4 fire together.

That two cylinders fire together does not necessarily mean that there are "harmonic horrors".

[J.A.W.]

Did the Jumo 222 ever run reliably - or in any respectably competitive power-to-weight - flight program?
Certainly its failure was not due to want of prototypes.. ..if a machine ever was a "harmonic horror.."
..very likely it was.. ..be cool to see a Manolis simulation of the device..

Were any successful large aero-engines of X/star configuration &/or featured simultaneous firing cylinders?

[Tommy Cookers]

FWIW I have the idea that paired firing is not necessarily bad
because the firing frequency is halved it would not necessarily be worse wrt harmonics - it might even be better

this could have relevance today eg in MotoGP (fuel-limited but free design) - fewer main bearings etc
and race 4 cyl twostroke (motorcycles) always had it (inline or square 4) or something close (near-square 'V')

the argument against paired firing is that the combustion torque peak on the crankshaft is doubled
but combustion loads became less important and inertial loads more important as rpm/piston acceleration historically rose
today inertial loads are dominant, certainly in racing

ok in aircraft the engine-propellor dynamics are a minefield
and you would might even want the firing frequency to be above some prop blade frequency, not below it

[wuzak]

Were any successful large aero-engines of X/star configuration &/or featured simultaneous firing cylinders?

No.

But that doesn't necessarily mean that the engines were "harmonic horrors" or that simultaneous firing was bad, or that the two were connected.

Engines such as the Cub, which didn't have pairs of cylinders opposed, would not have had simultaneous firing of cylinders, but it wasn't a success either.

[J.A.W.]

The Napier Cub is an interesting case, unusual in being an unequal angle X-type, yet it appeared to run well..
..its 'failure' was AFAIR, more a matter of application,(lack of airframes able to cope with a 1 ton/1000hp mill),
than a mechanical issue..

As T-C mentioned, aero-engines were generally given particular design attention to detail, gear drives rather than chain,
& with the notable exception of the (non-flying) Ford V12 Merlin analogue, the multi-banks ran sans-offset.

[J.A.W.]

This 'Flight' article has some details of the final generation of large British piston aero-engines.
& how that rapid development coincided with the coming of the gas turbines that finished them.

Also - the contrast of dimensions/characteristics/consumptions/outputs between the similar cubic capacity..
.. R-R Griffon V12, Bristol Hercules 14cyl radial, & Napier Sabre H24..
http://www.flightglobal.com/pdfarchive/ ... 01810.html

[wuzak]

This 'Flight' article has some details of the final generation of large British piston aero-engines.
& how that rapid development coincided with the coming of the gas turbines that finished them.

Also - the contrast of dimensions/characteristics/consumptions/outputs between the similar cubic capacity..
.. R-R Griffon V12, Bristol Hercules 14cyl radial, & Napier Sabre H24..
http://www.flightglobal.com/pdfarchive/ ... 01810.html

Thanks.

[J.A.W.]

This SAE paper - reproduced in 'Flight'- makes some interesting points about C.I. 2-stroke efficiency attributes..
http://www.flightglobal.com/pdfarchive/ ... 02903.html

[J.A.W.]

This article shows some of the effort P&W put into their R-2800, ( eventually replacing the whole mill,
.. 'cept for bore & stroke dimensions), but getting pretty remarkable results, for a conventional radial design..

http://www.enginehistory.org/NoShortDay ... kshaft.pdf

[J.A.W.]

Here is some history on the American GM-Allison V12, some ~70,000 of which were built..
http://www.thunderboats.org/history/history0323.html

The Allison did well in turbo form (including in race boats),
& V12 engine guru Mike Nixon reckons this due to the discretely bridged twin exhaust ports per cylinder,
being capable of accepting the inherent heat/backpressure, something the R-R Merlin - which lacked this
feature - could not endure..

However, for flying, such as in the Reno unlimited air racing, Merlins have the GM unit beat..

[wuzak]

Here is some history on the American GM-Allison V12, some ~70,000 of which were built..
http://www.thunderboats.org/history/history0323.html

The Allison did well in turbo form (including in race boats),
& V12 engine guru Mike Nixon reckons this due to the discretely bridged twin exhaust ports per cylinder,
being capable of accepting the inherent heat/backpressure, something the R-R Merlin - which lacked this
feature - could not endure..

However, for flying, such as in the Reno unlimited air racing, Merlins have the GM unit beat..

The theory of the turbo in WW2 terms was that it maintained sea level air pressure to the engine. It was also the theory that the back pressure in the turbo system was no more than for an open exhaust system.

Turbo Allisons therefore didn't have to cope with higher back pressure than Merlins did without.

The Merlin's exhausts have dual ports per cylinder, which merge near the flange face.

http://upload.wikimedia.org/wikipedia/c ... inHead.JPG

[J.A.W.]

W, AFAIR, R-R never produced a factory turbo Merlin, Allison did develop their V12 with factory turbo installation.

Mike Nixon was referring to sports use such as in boats & tractor pulling, & turbos have not done well at Reno..

The extra meat in the Allison cyl head ( discrete exhaust ports right out to the turbo collector manifold face)
- was seen as the significant difference & a failure point issue when turbos are applied to the Merlin.

& I doubt that stub-ejector exhausts create back-pressure at the exhaust valve - equivalent to a turbo collector..
..since it was the value of high speed ejector thrust for R-R to determine that properly sorted mech' supercharging
was overall - the better deal for fighter mills..

[J.A.W.]

Back in the `70s there was an abortive attempt to utilize Cosworth F1 tech in F750 motorcycle G.P. racing..
..with Norton..

& a few decades later it was tried again in Moto G.P. ..with Aprilia.. .. well - it sounded great.. ..but didn't work..

http://www.motorcyclistonline.com/april ... otogp-bike

[wuzak]

W, AFAIR, R-R never produced a factory turbo Merlin, Allison did develop their V12 with factory turbo installation.

No, Rolls-Royce did not produce a turbo Merlin. Nor, in fact, did Allison.

The fact is that the airframe manufacturers were responsible for the turbo installation. I don't think a V-1710 was actually tested with a turbo until well into the war.

[J.A.W.]

I'd reckon.. W..
.. that USAAF V-1710 turbo installations were run by Allison - in a factory test cell - well prior to flight..

& Bell did one such V-1710 turbo scheme (for P-39, but subsequently aborted) long before U.S. entry into WW2..