q8cub

I bought a used 30% yak with da-50 on it. It has been flown for almost 3 seasons (3d flying).

The other day, and during a hover, I heard a knocking or clicking noise which I thought in the beginning some guy at the field was knocking something with a hammer but then realized it was coming from the engine. I also thought something could be loose in the frame then landed and checked the plane, and there was nothing loose. Everything is fixed firmly. I flew again, and during the hover, I heard the same sound again.


Should I be worried about this sound?

Could it be the fuel-oil mix. I have a 50:1 mix of unleaded gas/sythytic oil. I am using the same fuel which was mixed a year ago and stored inside room temperature for months. Could this be it?

I would appreciate any opinions on this issue!

Thanks in advance!

skip1320

Check prop bolts,when they start to losen it shows up in hover I have found a few times,good luck.

q8cub

I checked the bolts before the flights and made sure they were very tight..

Any other possibility?

Thanks.

w8ye

My Feedback: (16)

It may be detonation and pinging?

I've heard DA-50's make this sound. The owners sent them back to DA.

Never heard the cause

Truckracer

My Feedback: (19)

My DA 50 made that sound once .... sent it back to DA and they replaced the crankshaft and main bearings. Has been fine since and the repair was at no charge. Engine was out of warranty at that time too.

Tired Old Man

My Feedback: (1)

I'd be VERY worried about the sound. You're burning your engine up through lean mixtures, poor prop sizing, bad cooling airflow, or any combination of those.

A crank can be broken and main bearings can be severely damaged through detonation.

JOHNS3D

My Feedback: (5)

send to DA cause they offer warranty on engines...but not in the airplane and electronics..which is the real money is after a crash.

Truckracer

My Feedback: (19)

My engine showed no signs of lean runs, etc. and had a great track record over a several year period. One day it just broke and I would suspect it was a bad bearing that caused it. I never understood why DA replaced the crank .... there was no problem with the crank as far as I know. I guess it was one of their updates. Strange, the DA50 and one other gas engine were the only gassers I have ever sent in for repair.

spaceworm

I would suspect the fuel, it being that old. Unless it has had some stabilizer added. That little oil combined with stale gas may be the problem.

I would try some fresh fuel with good oil at a higher oil percentage.

It may be too late, if you are hearing knocking; pinging may be a transient condition caused by the fuel. JMHO.

Good luck.

Sincerely, Richard

Tired Old Man

My Feedback: (1)

The affects of excessive knock are accumulative. A slightly lean condition may not be readily apparent but componenets inside the engine are repeatedly experiencing impacts of the condition over hundreds of thousands of revolution cycles.

Old fuel may have octane degradation as Spaceworm noted. Change gas and perform some tuning.

Jezmo

On my original DA50 the wrist pin loosened up in the piston causing a sound similar to what you are describing. (That was after just over a year of hard 3D with two different people bashing on it, er I mean flying it) Replacing the wrist pin, piston, ring and upper rod bearing got me another year and a half before the crank, rod and lower bearing had to be replaced. The crank main bearings were replaced at that time and it remained nice and tight until sold. Still running great last I heard.

q8cub

Sorry guys but I discovered an issue that could be related to the crackling sound during hover: Landing gear shoe screw loose.

I just noticed one of the landing gear shoes screws was loose (more than half of the screw was sticking out of its place). I had a chance today to speak with the guy who sold me the yak. He confirmed that landing gear shoe could be the source of the knocking sound (sounded like piece of metal).

I will test it tomorrow and see how it goes.

Thanks again.

q8cub

Did a test today, and did not notice the same sound I described earlier. I did tighten the "loose" landing gear shoe screw which I think was the reason for the knocking sound. I need to do another test to confirm this.

Once 100% confirmed I will report this back here.


Thanks guys for the help.

rmh

It is possible that detonation plus worn rod/crank is making th noise
At Top Dead cente - the prop will have a little loose feeling (prop can move a little left to right as yo u gently twist the spinner back and forth
if it feel s "free" for a inch or so - you may have pounded out bearing.