Hi everyone, I'm flying a superstar 40 trainer plane,and always been using a 10x6 Top Flight propeller with no vibrations an being a beginner I've been through a few. The guys in the club told me that I should switch to a Plastice type prop which I did (Master Airscrew). I bought a balancer an always made sure that the spinner and props are balanced correctly, but everytime I put the Master Airscrew on the plane I get a vibration, an when I switch back to the Top Flight the vibration goes away. Is there any explanation as to why this happens? All nuts, bolts, screws on the plane are tight. And the Engine type is an OS FP max 40. the Vibration is at lower rpm 1/4 throttle or less an nothing above that from what I can tell. Thanks again for any advise and support.

Sounds strange considering your prop is in balance........couple of questions....
Have you tried a different Master Airscrew prop?
Is the prop hole reamed out larger than your engine's prop shaft?
Is the spinner a tighter fit with the MA prop than it was with the TF prop? (is it touching the prop anywhere)

madmanmike:
This sounds a bit familiar as I had the same problem with some props in the past.
I balance my props and have encountered the same thing you describe.
Some prop's center hole is off center and will be only be off by a fraction.
I balance them, then remove the prop from the balancer and flip it and remount it in the balancer.
You'd be surprised how many props will not be balanced once flipped.
By flipping I mean having the back of the prop facing you when you balance it initially, then have the front of the prop facing you to double check the balance.
Also if the reamed hole isn't perpindicular to the prop it could cause probelms as well.
I hope this helps.

Tom

Mike:

Make sure you're doing all of the above, and also when you balance the prop, balance it so it's balanced horizontally, so that the blades balance along the horizon, and also balance it vertically. Horizontal balance can be fine, but it can still be out vertically. There was an article a few months ago about this in some magazine- I forget which one. You should also check everything else out like engine mountings, loose bolts and nuts anywhere on the plane, etc. in the event that this is just a fluke, and the real problem isn't your prop.

MadScientist, what powers the A-10 that you have on your avatar? When I'm ready to move up in this hobby, I want an A-10. Is it jet or ducted fan? How fast?

I was wondering of designing an A-10 on autocad with a single regular glow 2 strk. engine mounted b/n two turbines inside the 2 ducts by some type of chain. Imagine the piston shaft connected with the 2 cam shafts in a car engine. The piston shaft is like the engine and the two cam shafts are like the two turbines. Well, it's just a concept of mine. I haven't even started flying yet. I'm very much a newbie. I'm imagining again. Sorry.

Thanks guys for the replies, just got home from work, and after supper I'll try balancing the prop the way you all have suggested, and maybe a different prop altogether. And yes, I had to ream out the hole to make it fit the shaft, but I still made sure it was a snug fit. I also went through the plan from top to bottom anc check all bolts,nuts,screws and everything check out fine. The only thing I could not check for balance, is the spinner nose cone, It's a plastic type with no center hole, but if you all think that could be the problem I can get 1 tomorrow at the hobbie shop. thanks again for your concerns.

Hi again guess what? I've done what you all suggested and still that vib. is still there, went to the hobbie shop and bought a new alum. spinner checked it for balance and mounted it on the plan along with a new master screw prop and the bad vib is still there Now I'm really stumped. My guess is I'll just bring it to the feild and have the Instructor look it over. and just maybe I'll just have to stick to the wooden Top Flights. Thanks again for all of your help, an I'll keep you all posted with in the next couple of days.

I tried a half dozen Master Airscrew 10/6 props awhile back and I couldn't get them to balance vertically. The blades would balance no problem with very little work they would hang from 9-3 o'clock on the money, but tip it just a little either way and one side of the hub always wound up on top. I don't think it was an off center hole either, it looked good and to be that far off I am sure it would have been noticeable. The hub needed to be almost ground off on one side to get one to balance, it is beyond being airworthy, but I got frustrated and decided to get it balanced no matter what. I have gone back to APC scmitars and havn't had as much trouble getting them balanced.

BTW,
You said earlier that you had a plastic spinner, then you went to an aluminum one and it still vibrates, don't forget to check the CG!!! You have added alot of weight way out front on the nose by doing that I would suspect, better safe.(also the balance of the spinner needs checked.)

If I can find the prop I balanced I will post a pic. It will show better than I can explain.
rod

Thanks again everyone, I went back to the wooden Top Flight prop, and it works fine , also had to rebalance the plane. You were right! It needed some weight on the tail . Sure thing Rod I would like to see a pic or post of a prop that you have balance. thank you

OK, this may sound weird but I suspect it's not a vibration at all. The FP is a bushed engine and the problem is only evident at low revs, in other words the notorious (but harmless and inescapable) rattle. Why it's only happening with the heavier prop had me wondering but I'm guessing that the lighter wood prop is more easily moved back and forwards so that there's less impact when the crank slops either way (good techo term ).

Madmanmike,

After thinking about your description of the vibration problem I suspect you have either worn out the bearing in the front of the engine or possibly bent the crankshaft a little bit (can't imagine how that could happen ). The key, I think, is that you don't see the problem when running the Top Flite wood props, and you do see the problem when running the plastic props. My thinking goes something like this. The wooden props are extremely rigid as compared to the plastic props. Try flexing the tips of a wooden prop and you'll see what I mean. With a plastic prop you can flex the tips of the props, not much I grant you, but some. So, if the prop shaft is running out of round this could cause the tips to flex while the engine is running, and the problem should be more noticeable at lower RPM's when the tips will have time to move. As you increase the RPM's you would reach a point where the blades are getting around faster the the tips can flex and the vibration will stop. I have no idea how you might determine if the prop shaft is bent or not, or if you have a worn bearing for that matter. Maybe someone with machinist training will offer some information about that.

Bill Sindel

master airscrew props aren't my prop of choice. when you bring it up to full throttle, the tips sometimes bend forward making a buzzing sound. they don't have a lot of power, and they do vibrate a lot, balanced or not. i would reccomend apc. they are more expensive, but you get a lot of power, they are so much quieter it isn't even funny, and they are a fiber/plastic prop and are really tough. they aslo come pretty well balanced

I've also noticed that MAS props sometimes vibrate more than other makes. They certainly are more flexible, and flexible is a bad thing with props.

I suspect you either have a prop that is out of balance vertically as Rod described, or the prop has a bit of variance that causes one blade to flex more than another. Did you remove the molding flashing from the edges? I've noticed that the flashing can affect prop performance. I think it's possible that the prop might be statically balanced, but not dynamically the same, either because one blade is lifting more than the other or some other reason. How did you balance the prop when you first balanced it? I assume you removed plastic from somewhere, how much did you have to remove, and from where? Maybe it changed the airfoil shape a tad or changed the individual blade's CG causing one blade to twist a tad more than the other.

One thing about vibration, it's common to think it "goes away" at higher rpms, but it usually doesn't so much go away as "hide" as the frequency goes up, it's harder to notice.

Oh, and all single cylinder engines vibrate at some RPM ranges. It's possible the MAS prop is just putting the engine in a slightly different RPM range for the engine and causing a resonence or something simular, in other words, it might not be the prop at all.

there is also a chance that the particular noise that prop makes resonates well with your plane. my os 50 sx on an 11x7 mas prop will sound really awful on 3/4 throttle, but it's the covering streached along the light trussle frame that is making the noise

Took awhile to find this prop, it isn't airworthy anymore due to the amount of hub I removed to make it balance. My flying buddy mic'ed the leading edges and the hub that is left and said they are not the cause of the bad balance and by guessing the diameter of the hub and center hole he believes it was probably pretty close to centered. I just went back to the stouter APC scmitars, yes they are a little more $ but not that much for a 10" prop. I ran out of balanced props a couple of weekends ago so I strapped on one that hadn't been checked(practicing cross wind landings, they all were passable, but whenever I would make my turn-around to taxi back I would catch too much air under the upwind wing and tip over and knick the prop. I don't care if it just looks cosmetic on the tip, if I nick a prop I trash it and start over.) After just one flight the servo tray was almost unscrewed and the cover over my fuel tank flew off just after I landed. Even a little vibration sure can cause havock with the structure. I will try to get a picture in this, it's my first time so have patience. BTW I learned to use the ailerons to control the wing while I turn and didn't loose a prop this weekend!!
rod

no wonder...

So I go out and fire up my OS60FX with my 12x6 MAS prop. I hit the throttle and watch the prop "flex" forward! Wow. Now is this only because I'm holding onto the plane, or would it still "flex like that when it's in flight with only the natural drag of the plane? My engine manual recommends not flying any prop other than a wood prop. Is it a good idea to fly with a non-wood prop?

yes, as a matter of fact, i think wood props are very outdated and unneficient. apc's props are really efficient, quiet, and don't bog down your engine even though they are heavier. About the prop flexing, it will still flex like that, but not quite as much. when you are flying, while the pitch of the prop may be 6, the number of inches the plane actually travels can be really low like .5 or .25 so the prop flexing at full throttle in the air may be equivelant to 3/4 throttle on the ground.

Actually, wood props can flex less than most of the smaller plastic props out there, including APC. So a good quality wood prop can actually be more efficient than even an APC. That said, I don't fly wood anymore myself.

The engine instructions probibly recommend wood because they want the prop to break with out stressing the crank shaft or other engine parts if the prop hits something. However, these days, you're not likely to break the engine that easily, so I would't worry about it. I suspect the engine company keeps that in the instructions as a CYA thing, or maybe they just haven't updated their instructions in years. Way back, there were only wood and nylon props. The old nylon props flexed way more than even the MAS props do, and many people (myself included) would say never to use one of those props. The fiber-reinforced props like the black MAS props and the APCs really haven't been around all that long. I remember when APC first hit the market. (sometime around 1990, I think, plus or minus a year or two).