Prop to Keel Clearance

I just turned my A box to the down position. Just loosely bolted for right now. I though I would have a couple of inches clearance between the prop and the keel. As it turns out it is only 1 1/8 inches.

Is this too close for this Air Command? Can the keel flex that much at that point to strike?

I am putting new motor mounts in and some spacers that will give me another quarter of in inch but thats only 1 3/8 clearance. Not Enough?

In the up position there is just under 7 inches.

Advantages or disadvantages either way?

Thanks

Mark

What is your reason for turning it downward? Did you do a double hang test to determine where the CG was in relation to the thrust line with it in the up position? I think I'd want a little more clearance the what you have there.

Timchick said:

What is your reason for turning it downward? Did you do a double hang test to determine where the CG was in relation to the thrust line with it in the up position? I think I'd want a little more clearance the what you have there.

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No it was on the advise of someone here I trust.

Better thrust line and a couple other reasons.

But it looks like it it's going to be too tight

Thanks Tim.

Make some 1" spacers and put them under the engine, to raise it up slightly.

Mark,

I had a Tierra II ultralight that had 1/2" clearance in a similar joint where all the frame tubes converge. From your picture, it sure appears to me that your frame would never flex as much as my Tierra frame unless you are in a crash sequence?

My Brantly, factory-built helicopter had 1/2" between rotor tips vs. tail rotor tips while spooling up! You would think the fuselage could flex that much but it doesn't

BC

Even if you banged your tail in hard, the attachment points in that setup would flex the frame away from the prop.

But if your worried, just trimm an inch off each blade and pitch it up 1/2 a degree.

I would go with 1 and 3/8

Mark, I've talked to Doug at Air Command about this issue several times as I'm doing my rebuild. Doug recommends that the clearance be 1 1/4" so you should be fine. I've talked to others who like 2" or more so that when they take off from dirt runways, the blades pick up less rocks.

Thanks

Thanks

I believe this will OK with the engine lift.

Thank you all for the input. You all Rock!

This is why I ask questions here and because I work Saturdays and can't get to any of the PRA meetings!! Bummer!

Mark

Surgury Successful

Surgury Successful

Adding the spacers and new motor mounts was a success. Actually it was easier than I thought it would be. I new have 2 full inches clearance between the prop and the keel, And getting that motor mount bolt head out of the way I got my new Rotax side muffler mount on and ready for the GyroJake rehabbed muffler.

Thanks Jake for all you do for us that don't know much and a special thanks to Jerry Marsh AKA Gman that was so very kind to offer to make the spacers and mail them to me on his own time and dime. He made me two sets. 3/4 and 1 inch round and as it turned out I used both for a total of 3/4 net lift.

And thanks for all the advise and input from all of you.

Mark

That looks like it worked great.

I sure would have thought that if the keel flexed more than an inch, in the short distance between the mains and where the prop is, you would have a whole lot more to worry about than the prop hitting it. I have always been told and inch and a half is plenty.