fastplane

Why do gasoline engines vibrate more than glow engines? That seems to be the general info I hear. Too much vibration is not good for the planes.
Most of the gasoline are 2 cycle and so are lots of large glow engines. Is it because the gasoline engines are just bigger or just a matter of cost that would make the gasoline engines as smooth as 2 cycle engines?

SitNFly

My Feedback: (54)

Mostly just a matter of a bigger piston flying up and down. Can't fool Mother Nature. Unless you buy a twin ......

pe reivers

The gas engines are also two stroke engines, and vibrate actually less than equal sized glow engines. That is, because the glow engine's ignition is less controlled, and torque variations in a glow engine are larger. Mechanical balance is about the same, or should be.

captinjohn

Maybe you should go read the Gas/glow engine data AV8TOR has posted in "engine conversions" here on RCU. He claims a lower & smoother idle ! Pe Reivers...have any of you guys tried the Gas/Glow over there? Whats your thoughts on running that mix? Thanks John

pe reivers

Can you post a link?

rmh

My ST2300s on 5%nitro and a spark ignition were smooth as glass and the idle!! wow ticker ticker . I did use the ST 2300carb with tank pressure (1/2-3/4 psi)
converted Walbros -setup for alky were simply a lousy setup as the calibration was way off. al you could do was drill the passages and hopefully get flow right. As a engine for the F3A I thought this was the best, smoothest power setup I had seen but the guys in F3A were sold on the YS1.4 at the time -and those grossly overpriced OS things --Ohwell

captinjohn

Dick Hansen: I wonder if the new China made Tigers would run as good as the old ones? I got to sell some of my colection...and find out. I helped a guy that has a YS 1.4 and it sure was a pain in the _utt. I tried to set valve clearance and found out one valve was sticking. I got it free-ed up only to stick again. It was a very low time engine. He had to send it back and finally YS fixed it. You need to be rich to run one....you need high nitro fuel and lots of it. Capt,n

captinjohn

LINK??? just click by the yellow bar...jump to Engine conversions!!! Capt,n

fastplane

All of that is quite interesting and informative but why do gasoline 2 cycle engines seem to vibrate more than glow engines?
At least this seems to be the feeling of lots of people.

captinjohn

My guess is with a spark engine...its more of a explosion! With a glow engine..its slower burn rate. The flame front with glow, maybe does not have a fast travel rate as gas!!! Heck I don,t really know..never been inside a cylinder when it fires!!!!

pe reivers

No yellow bar on my computer, nothing to jump to, and the reference name is not OK as well. Posting links makes life a lot easier for all of us.
I did a not so quick search, and the person you mention runs a Poulan on glow/gas fuel mix, which seems to serve him well.
I still do not know what particular thread you mean, but that fuel mix makes no sense to me.
Methanol fuel on ignition is fine, and gives plenty of power, as a matter of fact at least 10% more than with gas only. The inition, controlled by a spark plug makes for decent low vibe running, like gas. Mixing in gas with the methanol only has virtue in cold weather for better starting, along with acetone. Powerwise, methanol with nitromethane is best, and cannot be beaten by any other mixture that will keep you healthy.

Bob Pastorello

My Feedback: (198)

Since we're speculating - I'd guess that most gas motors have higher piston and con rod masses, are less-effectively crankshaft counter-weighted, and have relatively more available "torque" for a given size than their glow counterparts. Usually designed for far less rpm, so perhaps I may be close with my guesses.

Don't know, really...

Truckracer

My Feedback: (19)

Go back and re-read some of the previous posts, some of your answers were there. I don't really believe that most gassers do vibrate more than glo engines. Comparing engines of similar sizes .. gas vs glo, I would think the vibration on the gasser might even be less than the glo engine. Certainly the idle will be smoother with electronic ignition if there is an advance curve. Now most gassers are larger engines so yes, they do vibrate more as pointed out earlier in this thread .... just a larger reciprocating mass from a larger piston.... compared to a smaller glo engine.

While there is way more to it than this very simple explanation, there are at least two sources (discounting the prop and spinner) of engine vibration. One coming from the rotating / reciprocating mass of the crankshaft, connecting rod and piston. The other source of vibration would come from the combustion pulses. Many factors control each of these sources of vibration. Crummy cheap engines will probably shake more from the mechanical sources of vibration than higher quality engines ... but not always. Mag ignition gassers will probably shake more at idle than EI engines ... pretty much the same at full throttle. A large gasser shakes more when converted to glo operation ... some really hammer at idle. Some of the early large glo engines were incredible shakers! How about some of the large, higher compression 4 strokes .... talking about power pulse vibration!! To be fair you just have to compare similar sized gas and glo engines to judge them fairly. Blanket statements just don't work here as there are too many variables.

pe reivers

right!
In addition, the gassers like zenoah etc are made for handheld operation which demands lowest vibration mode operation. They are produced in great numbers. There is a lot more design and follow-up effort involved in these engines than in even the best of our model engines.
The power pulses cannot be reduced, unless we leave the single cylinders and opposed twins and turn to 180 degree crank in line twins and upward. These engines will have different vibration modes, though smaller.

altavillan

My Feedback: (1)

An engine that vibrates all through the rpm range in my opinion is junk and should not be used for RC. Provided that the prop and spinner are not the cause.
An engine that is well balanced will only vibrate at or near idle if set up correctly......Causes for excessive vibration.

Flexing firewall.
Sloppy standoffs.
Too low of an idle speed.
Too heavy of a prop causing excessive power pulses.
Airframe mass inadequite to absorb the power pulses.
Harmonic matches (those times when one or more control surfaces shake but only at certain rpm settings.)

Harmonics come into play during some rpm settings in any engine/airframe setup and should be watched and monitored closely. How many times have we read posts about an airframe failing while flying at half throttle straight and level. Most probably caused by a small reduction in throttle setting witch can cause an engine to shudder a bit. If the shudder is in the range of vibration/harmonics, the airframe is being subjected to sever forces.

Kweasel

My Feedback: (29)

Modern model engines (like ZDZ) have made great efforts to reduce reciprocating mass. In comparison chainsaw engines have much heavier pistons, rods, and counterbalance for a given displacement. Mechanical vibration is hard to judge without instruments. Most perceived vibration comes from poor combustion mixture and timing.

JoeAirPort

My Feedback: (41)

Many things can cause what is perceived engine vibration. A prop out of balance. A bad spinner. Just some loose stand offs can do it. A weak or damaged engine box. Too light duty of an engine box. A rich low end will do it for sure. There's so many variables that you can't always blame the engine.

captinjohn

JUMP IN about page 25 or post# 600 http://www.rcuniverse.com/forum/m_12...25/key_/tm.htm Capt,n

yakman

I seen a zdz 80 run on both gas and glow. It was smoother at higher throttle with glow and smoother at low rpm with gas. This was an observation backed up by a few individuals. I have no explanation.

AA5BY

I have both a zenoah g-20 and a saito 125 and the zenoah gas motor is smoother than the saito 125 glo. Both run excellent but there is a vast difference in fuel cost. The zenoah burns 5-6 oz of $3 per gal gas and oil and the saito burns 18-20 oz of $15 per gal glo. Guess which gets flown the most?

fastplane

TO AA5BY, Which planes are the Zenoah g-20 and Saito 125 in? Are the airframes comparable considering strength which might be a factor in vibration? Cost of fuel is certainly one of my factors for considering gas engines for anything larger than the Saito 125.
If not even considering the cost of fuel, just performance which engine would you use?

How about a question to those that have put these engines, or similar glow vs gas, in same test stands and see if the vibrations are different.

AA5BY

I've the G20 on a hanger 9 ultra stick lite just under 10 lbs and yields unlimited vertical. The Saito 125 on a 10.5 lb Akrobat II and it does not have unlimited vertical. I think the g-20 is about as strong as the saito 125.

UASprof

Guys, your smart phone has a vibration measurement app available, VR meter. Lets end the speculation and get some numbers.

ahicks

My Feedback: (2)

UASprof - betting when those notes were written (12/07), there weren't many smart phones around?

captinjohn

I see it is your first post. Welcome to RCU. Pretty interesting about that VR meter ! Capt,n