Big single vibrating

[pe reivers]

Most confuse power stroke vibration with engine unbalance vibration. Power stroke vibration at one rpm range will excite the airframe into resonance. Lighter frames will resonate at higher speed than heavy frames.
Large one-cylinder engines have more powerful power strokes, but so have large twins. However, the large twins have more seismic mass which also is better balanced around the shaft to counteract these strokes.
It is the nature f the beast.
At one time, someone invented the zero stroke engine, that would rev up indefinately and ran vibration free. Let's wait for some entrepreneur to take it into production.

[Aerobat]

Make sure the prop and spinner will hold any position on the balancer, not just horizontal. Other than that, get a twin.

[pipercub123]

I know I want a twin for sure, I just like the price of a single. I like 3W's 55 cc twin for smaller planes. I wish DA would catch on with a small twin. My DA 50 shakes the plane pretty good. Why isn't anyone using soft mounts? I've seen soft mounts where they seem too soft and than I have soft mounts on my US 41cc aeromaster and it doesn't shake badly and no you can't see the engine flop around either. Yeah the US engine is heavy so maybe that's it. Our lighter engines could be the issue as there's no engine weight to soak up things.

[Tired Old Man]

You can help offset the natural imbalance of a single with prop blade location. It won't be as easy to hand flip but it smooths things out a tad. Not a thing you can do for the power stroke. Balance the prop and hub best you can and make sure everything is tight. Don't try to obtain an idle where you can count the blades, just one low enough so the plane does not roll on a smooth surface. A higher and smoother idle is possible when flying off grass but it still needs to be low enough to land.

A thumper is a thumper, and the larger they are the worse it gets. Quadra made (makes) a 100cc single. You should see that one bang around...

[pipercub123]

	Quote: Originally Posted by Tired Old Man
	You can help offset the natural imbalance of a single with prop blade location. It won't be as easy to hand flip but it smooths things out a tad. A thumper is a thumper, and the larger they are the worse it gets. Quadra made (makes) a 100cc single. You should see that one bang around...

WOW, a 100 cc single is pretty big! I'd like to take a look at the jug on those.

I position the prop so it's at the 1-2 o'clock position at TDC. What would be the position to help with the imbalance? The 10-11 o'clock? I'm going to try it and see.

What's the truth with the DA 85 and its vibrations? People say it's almost as smooth as a twin. I take it it'd be smoother than a DA 50? I kind of wonder because as you said the bigger the singles get, the more they vibrate. If it's worse than a DA 50, I don't know. I do plan on trying one next year though or I may just go for the DL 100. Twins are awesome, but I like the idea of saving weight and the price of less exhaust to buy and a cheaper engine. Most say it'll fly a 100 cc plane better, but for a real rocket get an 85cc plane. I want a rocket so that'll be next hopfully. Don't mean to hijack the thread, but I'm hoping everyone will find your reply useful.

[Mithrandir]

Another thought is to turn the engine sideways... this way the "Up and Down" vibration from the piston going up and down is parallel with the ailerons and elevators and maybe doesn't beat up the servos as bad???

[pipercub123]

	Quote: Originally Posted by Mithrandir
	Another thought is to turn the engine sideways... this way the "Up and Down" vibration from the piston going up and down is parallel with the ailerons and elevators and maybe doesn't beat up the servos as bad???

Yeah, it's worth a shot. I might try that sometime. An elbow on side mount exhaust to deflect the exhaust down would probably be good for exhaust.

[Tired Old Man]

Good thought about rotating the engine, but how many will want the jug hanging out of one side?

The RCGF rear induction 100 twin weighs in at 5 lbs., 2 ozs. or so. No more than 5 lb., 4oz. A little more power they say than the side carbed version. Good runner as well so you might want to consider a 100cc twin for less or equal to an 85cc single. It's a pretty well made engine.

If you have a single you can help offset some of the combustion pulse by mounting the heavy blade of the prop opposite to the piston position. Not much, but some. That's when not balancing a prop can be helpful.

[RTK]

Pe--what is a zero stroke engine?? I have heard of a wobble plate engine where the cylinders all pointed forward.

[pe reivers]

That's a phantastic engine I once read about. Since it has no stroke, piston wear is non-existant, so is vibration, fuel and oil demand. Power is what you assign to it.

[JoeAirPort]

	Quote: Originally Posted by pe reivers
	That's a phantastic engine I once read about. Since it has no stroke, piston wear is non-existant, so is vibration, fuel and oil demand. Power is what you assign to it.

Power is what you assign to it.....lol.....that was my favorite.

And it can run Amsoil 10000:1 with no carbon deposits.

[Aerobat]

	Quote: Originally Posted by JoeAirPort
	Power is what you assign to it.....lol.....that was my favorite. And it can run Amsoil 10000:1 with no carbon deposits.

While pulling through an inverted cross box zero of eight, no less...