shaggy48

I recently ordered a couple Master Airscrew K Series props from tower hobbies. Tower's website says the prop hole is approximately 3/16th of an inch. But when I got the props, the holes are way too big. In fact, the hole on each prop isn't even the same on each side of the prop. Each prop has a small hole on one side (about 5/16th inich) and a bigger hole on the other side (about 3/8th inch). So the prop holes are tapered from 5/16 to 3/8th inch! Fortunately I only ordered two of these props, but the fact that they both came this way, makes me think this might be normal for this brand. Does anyone know if this is the case? Or did I just get two defective props?

For me to use these on an 8mm shaft I'd have to dirill or ream them and shim them to get a good fit. But I shouldn't have to do that and I don't have any shims that would work anyway. Guess I should have ordered the more expensive APC props but just wanted to test the difference between these and the wood Zingers I've been using. I know it is normal to have to ream the prop holes and their website does say approximately 3/16th. But there's a big difference between 3/16th and 3/8th! Maybe the K-Series just aren't intended for 8mm shaft engines?
Of course tower hobbies says they will replace them, but I'm concerned that the replacement will have the same problem?

Shaggy

airbusdrvr

The front side of the hole is smaller than the back side of the hole. I don't see anywhere on Tower or Master Airscrew's site where the hole size is defined prior to shipping. 8mm is about the same as 1/4 inch. I would bet the front side hole is this size. If the rear of the hole is larger than your shaft, that is no problem. The prop nut will hold it flat against the engine and the front hole should be your prop shaft size(reamed if necessary). If the hole is larger than 1/4 inch, then return them or use them on a larger shaft engine. You can never have to many props

jaka

Hi!
Most props are made that way!
Makes it more easy to have your reamer ream up the hole that way! Get a reamer if you don't have it !

landeck

My Feedback: (1)

jaka is right, you need a prop reamer. Fox makes good ones in both metric and ASA sizes.

http://www.foxmanufacturing.com/inde...ort=20a&page=2

Bruce

shaggy48

I could ream the small side to fit. But the other side is 3/8th inch. That's about an 1/8 inch too big. Only a small portion of the hub would fit snugly. Would you still use it? One little hit on the prop and it would come unbalanced. No?

landeck

My Feedback: (1)

No, it will not come unbalanced. The purpose of the hole is to center the prop on the crank shaft when you tighten the prop nut. It is the thrust washer and prop nut/washer that keep the prop on the plane.

Bruce

shaggy48

The purpose of the hole is to center the prop on the crank shaft when you tighten the prop nut. It is the thrust washer and prop nut/washer that keep the prop on the plane.

While I agree with the above in general. That only means that the ends of the prop are equidistant to the center of the prop shaft. My concern is the lateral balance. I.e. Isn't it likely that the prop wont run true if the hole is too big on one side of the prop? So yes I can try to align the side that is too big by eye, and the nut will hold the prop tight. But, that 1/8th of an inch at the shaft will transfer to a prop that wobbles at the tip of the prop. No? That is the problem I'm more concerned about and that's what I meant by unbalanced. Or am I off base here?


And for anyone interested here's the link for the prop. Just scroll down and it gives the size of the hole. Again, mine were much bigger than advertised for this prop.

http://www3.towerhobbies.com/cgi-bin...?&I=LXZ982&P=7



Shaggy

Bax

My Feedback: (11)

If the hole is centered in the propeller, then you just balance the prop by supporting it in the center and removing material from the back of the heavy blade. If the hub is properly-made, then the hole will be properly-centered. If it's properly-centered, you'll have no problems once you get the propeller installed correctly. We're not sure about your concern about the hole being too large on one side or the other. If there's a slight variance in the center at the wide part of the prop, the amount of weight difference will be negligible as long as the propeller is properly-centered on the propeller shaft.

You can get rid of all your questons by using a wooden propeller. They usually have a constant-diameter hole in the center of the prop that is almost always too small for the propeller shaft...especially on propellers intended for larger engines. You then must use a reamer or drill press to get the hole properly enlarged. If the propeller shaft of the engine has a step in size close to the drive washer, then you back-drill the prop to accomodate the step. That will give you a propeller with a perfectly-fitting hole.

landeck

My Feedback: (1)

Bax, for once I need to disagree with you. You want to remove material from the front of the prop. If you do it by removing from the back you stand the chance of changing the pitch of the prop.

Bruce

shaggy48

BAX - Actually I have been using wooden props (Zingers) with success. And they came with a constant diameter hole which I then ream to the size of the 8mm shaft. But I wanted to try the glass filled/nylon for comparison. See my first post to see what my question was and what I mean about the hole. Simply put, one side is bigger diameter than the other.

Is it normal for wooden props to have a constant diameter hole and nylon/gf props to have a tapered hole?? Or does this depend on brand? Anyone?

Shaggy.

landeck

My Feedback: (1)

Nylon/gf props do not have a tapered hole. They are two different sized holes that meet in the center of the prop. This is so that if you have to enlarge the smaller hole, the bigger hole can act as a guide. On most props, the smaller hole is 1/4 inch and fits many .25 through .50 engines. The larger hole is 5/16 inch and fits many .60 and larger engines.

Bruce

shaggy48

Ok I found the answer to my question about the Master Airscrew props. http://masterairscrew.com/manualinst...ler_Holes1.pdf

Seems tower's website simply gives the wrong size of the bore diamter. Master Airscrew's website clearly shows exactly what my measurements were. And they're all tapered rather than a constant size.


Shaggy

shaggy48

Tapered is probably an inaccurate term. What I mean is - smaller diameter hole on the front side of the prop and a larger diameter hole on the back side of the prop. That's fine, I understand now why they're made that way and as long as I can ream it to fit my engine shaft I'm ok with it. But when I'm done reaming I still want a constant diameter hole through the hub. Not a hole that although the front now fits the shaft properly, the rear is still too big for the shaft by an 1/8 of an inch.

jimmyjames213

My Feedback: (2)

thats is fine dont worry about it, the back "taper" as you call it doesnt have to touch the crankshaft as long as the front part is.

your thinking way to hard just ream the props to fit your crank and bolt them on.

The Ghost

8mm = 0.3150", 5/16" = 0.3125" Ream the prop out only 0.0025" no problem, most composite props have different sized holes from front to back, all the APC props I have bought required resizing to get to fit the engines anyway.

Cheers

carrellh

If you want a hole that is 8mm all the way through, I do not think you will be able to accomplish your goal with any MA or APC composite prop. As far as I know the hole in the back is 3/8 and that is about 9.5mm.

LSF2298

My Feedback: (4)

I spray the light side front and back with clear Poly U so I don't change the pitch. Light coats until it balances.
JMHO

landeck

My Feedback: (1)

I have done it that way too but I find the sanding approach a little faster.

Bruce

LesUyeda

You want to remove material from the back side of the prop. The front side is airfoil shaped, and you will statically balance the prop, but you will dynamically unbalance it.

Les

landeck

My Feedback: (1)

I strongly disagree! You are much more likely to dynamically unbalance the prop by taking material off the back side, thereby changing the pitch. When taking it off the front side, you will not change the airfoil if you take it off the entire width of the last 1/3rd of the blade. At least that has been my experience for the last 57 years[sm=spinnyeyes.gif].

Bruce

jaka

Hi!
Agree!
In pylonracing you sand /file the front side off a prop! The pitch is more important the the curvature of the front side of the prop.

Bax

My Feedback: (11)

Actually, the "face" of the propeller is the underside of the airfoil, which faces the engine. The "back" of the prop is the lettered side that faces forward. I guess it's a bit of how you learned the terminology.

landeck

My Feedback: (1)

I understand your terminology now and we are in agreement. I have just always considered the front of the prop as facing away from the engine and the back as facing towards the engine. And to think I have a BS and an MS in AeroSpace Engineering, maybe I need to talk to some of my old profs[sm=spinnyeyes.gif].

Bruce