Turboprop firing sequence

[kkobayash]

I recently read in one of my lectures how a (turboprop) engine used in an aircraft (4 cylinder piston etc.) has a firing sequence where: two cylinders combust simultaneously, then the next two.

i.e instead of like a regular 4 cylinder engine, where is fires like 1-3-2-4 (or whatever), ones used in aircrafts are setup so that 1&3, then 2&4 fire together. Do you get what i mean?

Well if my above explanation is OK, i just wanted to know why this is so. Im guessing it has something to do with the power output being the same, but mean torque lower?? which would allow the powerplant to last longer.
Or i was also thinking its to make it smoother with less vibration (although now that i think about it, i dont think that this would be the case, as more gap between cycles).

Well, if anyone has an answer, id really appreciate it.

Thanks

[DaveKillens]

We need to clarify the terminology. A turboprop is a gas turbine (jet engine) that also uses the hot exhaust gas to spin turbine(s) that drive a shaft that turns a propeller. Basically, all parts are circular, and in balance.
A reciprocating aircraft engine uses the traditional piston, crankshaft, and valve technology familiar in cars. But usually, in a four cyclinder reciprocating aircraft engine the engine is an opposed four, just like the old VW Bug of years gone by. These are traditionally used in light personal aircraft. Six cylinder opposed engines are also common.
In an aircaft opposed engine, one each side, the pistons move in and out together, giving perfect primary balance.
The next URL will answer your question, the second is just for cool engine pics.
http://www.prime-mover.org/Engines/GArt ... ALANCE.Lyc

http://www.aviation-history.com/index-engine.htm

[kkobayash]

ahh!! ok Thanks Dave. Really helpful.

I always thought turboprop just meant 'open' propellers or blades. Like on a small cessna or something.

[Monstrobolaxa]

You meant a Pistonprop.

[Tom]

What you first said made me think of the 1.1-1.6l Citroen/Pergeot petrol engines. Instead of a distributor they had a similar device which fired two cylinders at once. It had no real advantages except its simplicity and I suppose it might have helped remove unburnt fuel.

[DaveKillens]

Just simplicity Tom, there is no real advantage or disadvantage to firing the spark plug at top dead center during the idle stroke. You just need to have one instead of two ignition methods.