Hello All,

I've had two landings and two broken (wooden) props. Landings were ok, just a little rough, where the prop touched the ground.

However, it seems as if there is much more vibration than before.
The engine is definitely mounted securely, and the prop is balanced.

Should I think about the crankshaft being bent? How do I check for this? (I have an OS 40 LA)

Thanks!

take the prop and prop nut off.

take out the glow plug. (reduces resistance by compression)


now rotate the engine and see if the tip of the crank moves side to side at all. if you cant see any diffrence then its probably not bent, or not bent enough to worry about.

also check to see if the crank is tight as a worn bushing can cause vibration too.

Unstable, I checked the crankshaft. If it is bent, it is so minimal that I'm having a hard time noticing any deviation.

Maybe this is normal, and I'm just noticing it now. I had the plane tied down so I could run the motor, and the horizontal stab was really vibrating. Maybe it's nothing. Would engine vibration lead to difficult flying control? (as I think I had the other day--could have just been wind gusts up high)?

Hey, I had a similar problem with engine vibration which lead to other probs. I found loose engine mount screws to be the culprit. Might seem basic, but you never know, shake it around a bit and see if it moves around.

Unless you have a dial caliber it's difficult to measure the run out on that small shaft.
Try this.
Put the prop back on.
(A new prop)
Stack some books up until they just barely touch the prop tips when they point down.
With the glow plug out and one tip pointing down make a mark with a pen.
Then turn the prop slow and see how far it's from the first mark.
Do this several times,
You shouldn't be off more then the thickness of a quarter and remember wooden props are off track as much as the thickness on a match book cover.(appx 11 thousands of an inch.)
GL and let us know how you made out.

I've had realy bad vibration with a MAS prop on a 40LA, changed to APC and no probs

Were the wings installed when you noticed the increased vibration? They will vibrate more without the wings.

Wooden props will break before the crank will bend.

Dainjarouz , the engine is definitely on tight.

Whirleybird , I'll give that a try!

Woodsy , unfortunately, I replaced my wooden prop with ANOTHER Master AirScrew (this time plastic). APC doesn't make a 10 x 6, only a 10.5 x 6 (or am I wrong)?

Steve , vibration was with wings on.

ps everyone--Flight number 3 today, and NO broken prop today! (this was b/c I had the plastic prop on--it still struck the ground a little, causing the engine to quit--I wonder if this is really bad for the engine??)


THANKS FOR ALL THE ADVICE!

Here in Aus we get 10x6 APC, my 40LA and 40FP seem to like the 9x7 props

I do it all the time. Twice today. 46 FX & 70 Surpass. Never has damaged them. Gonna have to get much better before I fly the gasser. It will damage it.

Steve, I have an Ultra Stick 120 with Zenoah G23--obviously, I will not be flying this until I'm a better pilot. But, are you saying that prop strikes are more damaging to an engine like the Zenoah (than a glow engine)?

STILL HIT THE GROUND?LOL
Maybe you need a shorter prop or longer landing struts LOL
Well you left out the more important info.
With the plastic prop did the vibration go away?

That is what I have been told. I could be wrong, but I may be right. Damn you Billy Joel, GO AWAY. These voices......reverberating....arrrghhhh.

Anyone have a picture of this plane that eats props?

No, there is still vibration, but I'm going forward anyway. The plane is a Hobbico Superstar with OS 40 LA. Ignorance is bliss, I gotta go fly now.

Its a piston moving up and down its gonna vibrate and it's normal, just go fly it.

eah but he said it started AFTER the prop strike.
But as cheap as that engine is I agree and would just fly the plane
60* here today

This is a really old thread to reopen but I couldn't resist as I had exactly the same thing happen to me today. Same plane (Superstar), same engine (OS40LA), same story on the props. Ran smooth as silk on 2 wood 10x6 props. But I broke those wooden props on 2 successive days (!) and all I had left in the spares box was a Master Airscrew 10x6. When I fitted it, the vibe levels went up massively - to the point where I thought something must be loose/bent/broken. I checked everything I could think of but couldn't find a problem so I flew it and it was fine.

I bought a couple of different wood and plastic props this evening to experiment with. The wood props are so much lighter that I think they are just less inclined to beat up the engine - even if not very well balanced.

Dan

Next time, just start a new thread.

In most cases, 4 year old info is kinda risky. In this case, it's fine. A small engine like that will vibrate a bit. If the shaft were bent, you would notice it. In general, there is not enough mass on the prop or the piston to bend the shaft from a prop-strike.

When it comes to larger, especially gas engines, there is a risk of damage from a mere prop-strike due to the mass of the piston(s) and the stifness of the prop, (especially carbon fiber).

On a small engine like that it is possible, but unlikely that a prop-strike could bend the CS. I would not be afraid to run it if it were imperceptibly bent, but if it is apparent, buy a new one and if you are adventurous, replace the necessary parts. My guess is that after you re-build one glow engine, you will just buy new ones from that day forward.

MAS props flex more than wood does and can cause a liitle bit of vibration. Don't worry about it too much. Just like EVERY other plane keep an eye on the hardware for loosening and you will be fine.