Is this normal?
 

A friend gave me a 4-5 year old Avistar with an OS LA 40 engine that has 6-8 tanks of fuel through it and runs very well, the first problem I have is at idle and through most of the mid range the fuselage seems extremely noisy. It's hard to describe but it sounds like there are loose metal pieces laying in the bottom and they are bouncing off one and another. I've went over the engine and mounting several times and everything is tight. I wonder if this plain bushing motor is just noisy by nature?
The second thing I question is during flight if I roll the plane right to inverted the engine will stumble as it goes inverted( Makes things very exciting) but then it seems to be fine it doesn't seem to do it if I roll left to inverted. It will fly around all day inverted and not miss a lick, and doesn't miss when I roll back upright.
I have an older Magnum 40 Pro I'm considering trying.
Any advise/ comments would be appreciated.
Puzzled
Thanks Kev

RE: Is this normal?
 

Kev,

First point - the rattly idle: this is perfectly normal for the LA and its predecessor, the FP. Many plain bearing engines do this. It's caused by endfloat of the crankshaft which manifests itself as a rattle at idle but clears up as the revs increase when the thrust of the prop pulls the crankshaft forward.

Second point: the fuel tank may need looking at. LAs tend to draw their fuel pretty well so I'd expect the problem exists in the tank or clunk. Perhaps the clunk is getting stuck on a roll to starboard.

RE: Is this normal?
 

Rattle on idle. It could be the model is the problem and not the engine. It can act as a drum and amplify/resonate as it moves with the engine. This is a well known problem in the automotive world and small changes can have dramatic effects. EG sticking a bit of felt on to the inside of a back wing [ fender ] .As an experiment you could see if holding the fuselage in different places with the engine on idle makes a difference.

RE: Is this normal?
 

The pushrods in my SS60 resonate at about 1/2 throttle with a ST.75 in it. Sounds like the plane is coming apart. Been doing it for 8 years with this engine. I use steel rod in tubs. It still does it even with nyrod spacers installed every 3" on the steel rod. Look for loosness in pushrods, formers, hinge points, glued joints and such. As for the the engine crank rattle, most bushing engines I've heard and had did this. It goes away when you throttle up and the crank has a load on it. Not an issue and just my opinion. Could be a combination of both.
Edwin

RE: Is this normal?
 

Yeah...and it "could" be loose electrons rattling around in the NiCd pack too, but so that you don't drive yourself insane....

As stated earlier in the thread, bushing motors tend to make a clatter at low speed. It's the nature of the beast and there's nothing to get worked up over.

Get your tank lined up with the carb to fix the other issue and go fly the thing.

'Race

RE: Is this normal?
 

Thanks everyone, I appreciate your comments.
Just put the new tank in there and remember checking the clunk but wouldn't hurt to pull it out and check again.
Don't have much invested in it except radio gear but so far I've had a lot of fun with it.
Thanks Kev

RE: Is this normal?
 

The stumbling when you roll inverted is probably due to the tank being too low when it is upright (causing tank to be too high when inverted). To help insure you are tuned correctly and not too rich on the high speed needle. Another thing to try would be to move the tank so the spray bar of the carburetor is about lined up with the center of the tank (or real close), this may be difficult to do on that plane. Another thing that may help if the above does not help is to get a hotter glow plug.

RE: Is this normal?
 

Though I'd say thanks again and let you all know what I found. After pulling the tank I discovered the pickup tubing was perhaps 1/8" to long and the clunk wasn't free to fall when the plane rolled over. Shortened it up about 3/16" and today I finally got to fly it the wind was only blowing about 20 mph. The plane rolled perfectly. The rattle I'm learning to live with. Again thanks Kev.

RE: Is this normal?
 

The way we eliminate resonance on big electrical machines is increase or decrease weight to throw off harmonic frequency.Everything has it 's own harmonic frequency and if by any chance oscilating frequency of motor equals frequency of the plane or covering or walls of fuze it start 'rattle' .It not too critical in model airplane but somewhere in a buildings or bridges it's VERY CITICAL.
I've heard stories that some times in Ukraine and Africa buildings arent built to the codes and resonance frequency sometimes interfere with frequency of aircondtioners or vent fans and it in its turn destroys buildings.
As for your application i'd add some sticky tape to the inside of the fuse.Tape the walls or if weight limits allows you glue piece of aluminum to the walls etc. The idea is to throw resonance off.

RE: Is this normal?
 

Mitty..
I and wife are often in Ukraine at visit to her family in Kyiv in Ukraine, there are lot of aircondtioners, vents etc.. in both new and older buildings and it is hot days in summer. In Russia and Ukraine + former of Soviet countries around Russia has same buildings after Nikita Khrushchev decided all peoples of Soviet shall live in same buildings of governments standard after Stalin period was ended. Never heard about buildings was collapsed of aircondtioner in eastern europe..

Jens Eirik