Prop Mounting
03-06-2013, 08:30 AM
#27
RE: Prop Mounting
Using the the taper reamer technique is the same way one would open the hole in a servo arm with a #11 blade from both sides carefully. That also is a good technique that results in a less sloppy clevis or S' bend joint.
The bottom line is use what ever tool you may have and yes I have both taper and fractional/metric step reamers and use both.
As I stated most do not bother with the APC prop centering rings and I offered that just for information.
John
The bottom line is use what ever tool you may have and yes I have both taper and fractional/metric step reamers and use both.
As I stated most do not bother with the APC prop centering rings and I offered that just for information.
John
03-06-2013, 09:38 AM
#28
RE: Prop Mounting
ORIGINAL: jester_s1
Prop installation is one of those little internet myth depositories that just refuses to die. Here are the facts:
1. The kind of hole doesn't matter. The prop is held in place by friction on the backplate or thrust washer by design. All the hole does is center the prop so that the hub will be in balance while the engine runs. You could get a prop centered properly and then Dremel out all around the engine shaft so that it doesn't touch the prop at all and, assuming the prop was balanced right, you'd never know the difference in flying.
Prop installation is one of those little internet myth depositories that just refuses to die. Here are the facts:
1. The kind of hole doesn't matter. The prop is held in place by friction on the backplate or thrust washer by design. All the hole does is center the prop so that the hub will be in balance while the engine runs. You could get a prop centered properly and then Dremel out all around the engine shaft so that it doesn't touch the prop at all and, assuming the prop was balanced right, you'd never know the difference in flying.
2. You should never have to hold on to the thrust washer to tighten down a prop. If you are doing that you don't have enough backplate friction. I can put a prop nut on finger tight which the engine compression is enough to be able to tighten it down, and I can then turn the engine over with the prop. You'll notice the thrust washer has texturing in it to bite into the prop hub. When you use a plastic spinner, you need to add some kind of material to replace that friction. The best thing is a piece of open mesh plumber's sandcloth or either the drywall sandcloth that looks like window screen material. If you use a spinner with a metal backplate, it will have some texture on it that is adequate to hold your prop.
3. (not discussed yet but important) You have to use enough torque, especially with a 4 stroke. The little 4 way wrench you bought for glow plugs probably fits your prop nut. It's fine for snugging down the nut, but break out the box end wrench and really crank down on that thing if you want it to stay on. If you ever use a wood prop, retighten occasionally as the wood will compress a little. You don't need any kind of threadlocker on any engine if you tighten the nut hard enough to begin with.
4. Do not under any circumstances sand off the sharp trailing edge on your props. They are made that way for a good reason- drag reduction. Even rounding it off a little bit can make a significant difference at the 12-13k rpm you'll be running at most of the time. Many people will take off the casting line at the leading edge and maybe sand away the burr at the trailing edge, but you want the back of that prop to be razor sharp.
5. Balancing is worthwhile. I know beginners don't want to spend money on tools, but $20 for a good prop balancer will save you much more than that in repairs caused by vibration and even engine reliability issues cause by fuel foaming. You'll occasionally see someone tell you they have been flying unpteen years and don't bother balancing props on smaller planes. But once you get a few balanced right and get used to see how your plane runs with them, you'll know the difference instantly when you forget and put a new one on that isn't.
03-06-2013, 09:11 PM
#29
Moderator
RE: Prop Mounting
I haven't updated my profile in a while Horace. I've done a bit more since creating it 7 years ago. To be clear, I wasn't advocating one to use a prop with too big a hole in it, but rather making the point that there is very little sideload on the prop hole, making the debate between straight holes vs. tapered holes or holes a thousandth or two too big moot. As for sharp trailing edges, I've never sanded one off and after probably 1000 engine starts I haven't cut myself once. Even as a newbie trying to start engines without an electric starter I had the good sense not to flip the thing with my bare hand. Anybody that can't figure that out should really consider sticking with video games for amusement.
