Two engines coupled together

[Geoff_H]

95.55 amongst other things states:

(b)   that has a single engine and a single propeller; 

If an engine was made from two small engines bolted together with each driving through belts or gears to an output shaft that is attached to a propeller would that be a regarded as a single engine?   One starter motor and one set of controls.

[facthunter]

Wouldn't think so. I don't advise it either.  Nev

[spacesailor]

RR Merlin 

Originally two straight sixes,  welded together. 

No one thinks it's two engines .

spacesailor

[facthunter]

Because it isn't. Nev

[Geoff_H]

I have 2 single cylinder engines. I need one engine.  A single cylinder engine has put of balance forces in the xy plane.i the engines were contra rotating and synchronised the vibration would only be in the Y plane.

[onetrack]

The answer is Yes. Plenty of big engines around that are two engines bolted end-to-end. The Detroit Diesel V16 is two Detroit V8's coupled together. Many big ships engines are built with the number of cylinders you order, they just keep adding cylinders. Many dragsters have two (or more) engines coupled together.

 

I would think CASA is more concerned about two propellors. Two single cylinder engines coupled as one must have a phased connection, so they balance each other out.

 

The problem is, generally, two engines coupled together are heavier than if all the cylinders were encased in one block. In industrial and marine applications, not a problem - in an aircraft, the weight penalty may be excessive.

 

Edited August 28, 2023 by onetrack

[onetrack]

Of course, I forgot to mention that two engines that are close-coupled are going to be a much lighter setup than two engines that are coupled using belts, chains or gearbox.

[spenaroo]

hmm it does bring a good question about what makes an engine an engine by definition.

is it the crankcase or the crank shaft?

and how's that work for stackable options like a Rotary. that can have theoretically as many crank cases bolted together as wanted,
its limiting factor is creating a crankshaft that takes the forces.

[facthunter]

 Long crankshafts are a problem with torsional effects. A coupled motor is much the same without the block integrity If you do it with  chains or gears you introduce a disconnect where some lost motion can occur. Try listening to a motor with a loose flywheel. (Just a bit)and hear the noise that's created and it will give you an idea of the extent of the forces involved. Tatra built Modular motors where sections could just be added on to get what power you wanted in Rail Motors and enabled on the job servicing also. GM in line two strokes did that a bit too.. Only one side of each main bearing wore and to a lesser extent the big end bearings also..  Nev

[facthunter]

The Junkers Jumo has two crankshaft's geared together. (opposed Pistons.) Its ONE motor. Napier deltic also..   Nev

[facthunter]

I don't like either set up. I'd prefer the Commer knocker that does it with linkages  I've designed a two stroke motor that ended up like the Commer but with variable compression ratio, Being 2 stroke and probably subject to Patents somewhere, I've long ago shelved it. Nev..