My experience tell's me that with a isolation mounts and balancing props and Spinners , there isn't a problem,.... of course if you don't even little 4 bangers and glow engines with do damage

[scaleguy]

Originally Posted by Don M.

My experience has been that a gas engine will destroy a 14 lb. balsa / plywood airframe in no time. That small, delicate fiberglass fuse should desinagrate right before your eyes.

Don,

That's an iteresting statement considering some of the maller gassers that are available today like the MVVS 1.6 and the RCS 140 & 180.

Please relate some of the experiences you have had with a/c in this weight range and small gassers. It would be helpfull to those of us considering the switch. But perhaps you could start a new thread in Giant Scale or Big Engines forum so we don't hijack this one.

OK here you go. I had a Brison 2.4 in a Midwest 300S, actually the weight of this bird was about 15 lbs. In 150 flights I had to replace the cowl ( Aeroglass ) twice because it cracked in several places and I got tired of fixing them, replaced the canopy which gradually got so full of stress cracks it looked awful, the covering ( although it has been used successfully on other glow powered planes ) kept coming apart at the seams after every 5 flights or so and the Kevlar tail braces would break in flight quite often. The engine was "soft" mounted on B & B soft mounts, it was sent to Texas ( Brison ) twice and came back with a clean bill of health. I suspected the ignition system so I sent it to C & H in Whyoming and they replaced the ignition system and sent it back saying it was one of the strongest 2.4's they had ever tested ( 7500 rpm on a Zinger 20 - 10 ). So last year I decided to give it another try and put it in a Topflite ARF P-51 ( now this one is 20 lbs. ) you guessed it after 15 flights the fuse is starting to crack down each side right behind the canopy and again the engine is soft mounted on a GP isolation mount.

I also have a Q42 which was mounted on a Byron Pitts in the late 1980's and that engine tore up the cowl and foam fuse very bad also ( again soft mounted ) the engine has been sitting in my attic since 1990. I am going to try another 1/3 Pitts ( GP's ) but I have a Saito 270T to put in this one. Even my wife who likes to go to the field with me always asks - " do you have that stinky plane today" ( meaning gas ) if I do she stays home.

So you can see my luck with gas engines has not been good. The Brison which I bought in 1996 now stands me about $1500.00 with all the trips back and forth to the US and has supplied me with about 165 flights. The Q42 cost me $350.00 in 1989 and has given me about 100 flights and destroyed 1 plane.

Sorry to be so long winded and I know not everyone will agree and lots of guys will say it must be something I'm doing, but you asked.

[KevinPerry]

Your soft mount is too loose . Any single will tear an airframe apart with to loose a iso mount . I have many many single gasser's and have no trouble what so ever, mounting them to the firewall . I tried one soft mount and started having airframe probs in a proven engine/ plane combo. Took it back out ...no more probs

just a thought


KP

Actually the 3 different kinds of soft mounts I had in the 3 aircraft were what I would consider very "stiff" soft mounts but I have also considered "hard" mounting a gasser to the firewall, maybe I'll give it one more try. I have an e-mail into Jim Bisson and if he can buid me a "quiet" muffler ( another thing I dislike about gassers ) I might get to like them.

We have in all probability "taken over" this thread so maybe we should move on.

[Guest]

Well read the warrantee with those mufflers they state there is no warrantee if the engine is soft mounted so that should tell you something right there. I have not soft mounted a gas engine since I sold my last quatra. There is one guy in the club running a RCS 1.4 in a GP 1/4 Spacewalker no problems and another hard mounted in a GP PT 19. I have a Brisson 2.4 hard mounted in a GP 1/3 Pitts Special, Brisson 2.4 in an 80 inch World Models Mustang hard mounted no problems. Yep I'd say it may well be something your doing wrong. And these are only a few examples. I am sure there are many more. Invest in some experienced help next time and I think your experiences may indeed be better.

Dennis

[nony]

Still, it is interstesting reading other peoples experiences..... Both my gassers are hard mounted mainly because there is no room for any kind of soft mounts.... I have seen soft mounted engines, but never heard of those sort of problems with either system - mind you, I did not go around asking either......

Correction...my G-38 shook both muffler bolts and the engine mounts loose. Thread locker fixed that, though.....

Originally Posted by Propworn

Yep I'd say it may well be something your doing wrong. And these are only a few examples. I am sure there are many more. Invest in some experienced help next time and I think your experiences may indeed be better.

Dennis

Actually I did ask for help when I first got into gas and was told by several people to soft mount them ( and still am ), there's a guy with a post in the engine section right now who says his Extra 300 / DA 50 is breaking up in the fuse from vibration and said he wishes it was soft mounted, so who's right and whose wrong. In any case it's sarcasm like yours that keeps me from asking too many questions anyway.

[AJCoholic]

in the 4 or 5 years I have been running with gassers, I have tried it both ways....

I now prefer to hard mount my engines. Not due to anyone telling me to, but 100% from my own experiences.

Example: in my AC-2 giant scale sport plane, I was running a Brison 4.2 soft mounted. The whole plane was shaking so bad all the bolts came loose and the tail wires would break every few flights. Going to a hard mount stopped this violent shake.

However, I have tried to soft mount some of my other gas engines (allways on my own home made soft mounts) they either ran as well or maybe slightly smoother but not enough to warrant using it.

My Ohio Extra 300L has the ZDZ 60 hard mounted and its really smooth, and nothing is breaking or cracking after a lot of flying (its a used plane as well)

My 2nd Ohio extra now has my 4.2 Brison on it and we'll see how it fares this coming season (its hard mounted).

Don, dont stop asking questions or sharing your experiences, OK? They are as valid as any other's.

[ronm]

Don, it is a very good question, with no single correct answer.
Vibration harmonics are weird science, and every setup is different!
Keep on asking!