still 090 twin cylinder

[jackumac]

Have any of the 090 enthusiasts out there ever seen the military drone/uav engine based on the pair of 090 heads? Is called the Limbach 275 and has been around for 20 some years now.

 

[ray benson]

Only this pic
http://www.limflug.de/doc/eng/produkte/L275e.htm

 

[Mange]

If they fire simultaneously it is in my opinion not a real Two cylinder machine.

 

[WRW]

If they fire simultaneously it is in my opinion not a real Two cylinder machine.

Why not?

 

[Mange]

It is something I take for granted about all multiple cylindered engines, like 2, 3, 4, 5, 6, 8, 10, 12, cylinders.
Who would think of asking if more than one cylinder fires at the same time?
In my opinion it is more technically challenging to make a engine that fires one at the time.
It some how seems as their not going the hole distance, with simultaneous fire.

 

[Max]

Ouch!

There goes another million brain cells!

 

[056kid]

different thinking

 

[WRW]

Mange,
I think I see what you're saying, but it is two cylinders on a common crank. With that engine configuration, I would think it would be a lot smoother running engine.

 

[begleytree]

looking at Rays pic, it has 2 pickups , one running each plug
-Ralph

 

[Mange]

Mange,
I think I see what you're saying, but it is two cylinders on a common crank. With that engine configuration, I would think it would be a lot smoother running engine.

Think about this for a minute, If that is a common crank as in a regular 090, there is no simultaneous combustion.

 

[Crofter]

Two throws,offset; pistons move in opposing directions and con rod masses cancel each other. Much easier to balance. Power pulses not as smooth as alternate firing motor.

 

[Mange]

Ray's pic clearly states:"Firing Order : both cylinders simultaneously".

I understand this is better than one cylinder twice as big, but what i can not figur out is why they did not go all the way?!

 

[Crofter]

Ray's pic clearly states:"Firing Order : both cylinders simultaneously".

I understand this is better than one cylinder twice as big, but what i can not figur out is why they did not go all the way?!

Balance!

 

[Mange]

Balance!

Now I am cofused, is there better balance in this than alternate firing?

 

[Crofter]

Think about it. Opposing masses cancel reactions. crank shafts dont have to be counterweighted to balance piston masses. Balance still is not perfect because there is still rocking imbalance due to pistons being offset lenghthwise and not perfectley opposite. I belive a three cylinder with two small and one large opposing, all firing simultaneously has be tried. It also removes the need to separate crankcase compartments to control base compression.

 

[sedanman]

It'd the k.i.s.s. princepal. Keep It Simple, Stupid (I'm not calling anyone stupid) Alternate firing would require a more difficult to make and potentially weaker crankshaft and either 2 flywheels or a distributor type ignition system. This design uses the least number of parts and the simplest machining.

 

[glens]

It would also require a greater fore/aft offset of the cylinders and a sealing mechanism on the crankshaft to isolate the bottom ends.

 

[jimbo1490]

Lots of 'boxer' style engines (that's what this is) do this. Opposing pairs fire simultaneously. But opposed engines are pretty straightforward, really. V's can get wierd, OTOH.
On an aside, the fave engines of the giant scale crowd are based on the Dolmar line, prob'ly because Dolmar squeezes the most power/displacement of most other makers. The really interesting thing is that a model engine based of the Dolmar 134 (100cc, IIRC) costs MORE than the chainsaw from which it is stripped down! No oiler, gas or oil tanks, bar/chain, cases, handles or even a freakin recoil, but more money! Go figure!

Jimbo

 

[eyolf]

There are a few advantages to the "boxer" plan, and glens is going down the right path on that. The engine can be made quite narrow, as it only needs the 1/2 the offset of a "regular" twin. The balance thing is important, too.

another advantage to the boxer-style opposed twin in a two stroke is good cylinder midrange filling because of good crankcase pumping...it has to do with the ratio of volumes in the crankcase with two pistons pumping vs one. The downside is that at high RPMs. It's hard to get enough air into that smaller space to fully charge both cyls.

As a youth, I played around with a fair number of Rotax 370 cc opposed twins. Excellent mid-range torque; those old Skidoos would pull a pretty long gear (secondary drive sprockets) for speed, but trying to rev one past about 7500 was foolish. Moving the ports around for more duration was never much use, either, but gains could be made by welding the crankcase and machining for Johnson-eveinrude reed blocks making the engine a reed-valve, even higher crankcase pressure to pump the cyls full.

 

[ScooterDrew1983]

one currection it actually isn't an opposed twin, its a 180 V-twin. oppossed twin use the same journal & V-twin uses two journals.