Prop Position
 

Which is the best way to install the prop on the crank to aid balance? Inline with the rod @ TDC or 90 degrees to it. I have known this in the past but have forgotten which way is proper. I am sure this has been asked a zillion times.

RE: Prop Position
 

Postion the prop for proper grip when starting

RE: Prop Position
 

I use an electric start as this is an older mag engine that is hard if not impossible to hand start. Since prop position for starting is not critical, I would like to place it for best engine balance. I think I remember that the prop lines up with the rod @ TDC, but I am not sure.

RE: Prop Position
 

I put them so they are horizontal against compression when the engine stops to protect the prop from damage

RE: Prop Position
 

I get what you are saying here....and I know this has been hashed out on here somewhere at least a time or two, but for right now the threads are escaping my search. I recall in the end that the position ends up having little affect in an attempt to balance out a single cyl engine. There was talk about having a slightly out of balance prop, positioned in an attempt to counteract the inherent imbalance a syngle cyl engine promotes....again in the end it appeared fruitless.

I would make every effort to get your engine properly tuned, cooled, and balance those props/spinners...and fly.

RE: Prop Position
 

I started doing this with my combat planes, because they don't have landing gear and you need to deadstick every landing. I now do it with all of my planes, just in case I remove the gear on a firmer landing. At least the prop will emerge unscathed. <rolls eyes>

Jack

RE: Prop Position
 

Yeah you are probably right about the necessity to do this. I just remembered reading about the influence of prop position relative to the dynamic balance of the rotating mass.The prop is the last balancing element. I am sure each engine would be somewhat different, but there was a rule of thumb to follow on positioning it if a starting position was not required. It is on a great running old Homey 30cc. Just balanced a new prop, and was toying with the position issue, I have tried it both ways and it seems a little smoother at 90 degrees. no big thing, just curious.

RE: Prop Position
 

Engine balance is influenced by the prop position. If the prop is in line with the unbalance of the total engine, it will lessen the motion along the engine axis. (like the balance stave of a chord dancer) The trick is to find out what position is best. For a two blade prop I would try out three prop positions first, each 30&deg; different to each other. Then change position either way 15&deg;, which should get you extremely close.
With a three blade prop, the effect is quite a bit less pronounced, so much even as to not to bother.

RE: Prop Position
 

Thanks for the reply! Any suggestions as to a good starting position?

RE: Prop Position
 

If the prop is perfectly balanced, then it shouldnt matter which position its in.

RE: Prop Position
 

Not true. The prop (balanced) still has influence on the mass-motion system. Also, precession forces in a two blade prop tend to oscillate, and prop position relative to the engine can dampen or increase these oscillations.

RE: Prop Position
 

I put mine on the front. Never had a problem.

RE: Prop Position
 

Guess you never has a pusher:D.

RE: Prop Position
 

So what your saying is " I don't care to think about things that don't concern me."

Hows Obama working out for you?

RE: Prop Position
 

I personally like a little wity funny stuff from time to time. Keeps it interesting and for Pete's sake it's a hobby so I don't take everything so seriously. Also, being from Canada he probably didn't get to vote for Obama.

RE: Prop Position
 

And you must of never heard of ACORN.

RE: Prop Position
 

So the bottom line is that the position for minimum vibration must be found by trial and error?

RE: Prop Position
 

"So the bottom line is that the position for minimum vibration must be found by trial and error?"
And prop position can make.

RE: Prop Position
 

More or less.
For some engines, conversions I believe, the proper position has been posted here on RCU, but I could not find it any more.
I would not bet on it that all engines find benefit in prop indexing. That would be some project to find out.

RE: Prop Position
 

Of course I've heard of ACORN but I still maintain he didn't get to vote for Obama.

RE: Prop Position
 

Whoa!Hold on fellas...

planepounder - sorry if I sounded flippant about your topic. Vibration affects us all. I do believe I asked a very similar question some years ago on this very forum - that's why I was interested to read your post. Dumb thing for me to say - I must have had a few that night.

Ralph - I'd say something witty here but I don't want to start an international incident. Sheesh - take it easy man.

Jezmo - Actually I did get to vote for Obama, Several times, while we were vacationing in Florida. Weird eh?

(Dan Quayle for Prez)

RE: Prop Position
 

LOL

RE: Prop Position
 

Hey, no offense taken, thought it was pretty funny! Guess I can learn about this concept in my leisure now as I lost the old Telemaster in the sun on final Sunday. Guess what the first thing to the crash site was-yep the old Homey! Talk about vibration now! lol.

RE: Prop Position
 

Awww man. Sorry to hear that.

(raises glass to Telemaster...)

RE: Prop Position
 

Yeah we had a great time together (sniff). I even broke out a new trash bag for her.

RE: Prop Position
 

At the flying field today my friend aligned the prop on his BME 50 with top dead center. He said he read it on the Net.

I told him about this thread and that he might need to try several positions?

He was satisfied that it ran better aligned vertical with TDC.

Looked like the same amount of vibration to me? Hard to say without an instrument to measure the intensity?

He's happy with the way it runs and he was still able to prop it.

RE: Prop Position
 

Ihad a ZDZ40 that was shaking the crap out of my H9 Cap (rhyme unintentional). Posted a question about prop alignment here on RCU. I tried every prop, every alignment, every swear word Iknew, and sent it back to Czech Rep for a look-over. Only thing that helped was switching planes. Weird.

RE: Prop Position
 

The instructions that came with my Irvine 150 say "Fit the propeller securely at the "twenty minutes to two" position when viewed from the front of the engine."

RE: Prop Position
 

Any external balancing of an imbalanced crankshaft will introduce lateral imbalance and should be avoided.
i.e it only adds to the problem.