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Old Feb 13, 2003, 12:34 PM
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byrocat's Avatar
Aurora, Ontario, Canada
Joined Mar 2002
1,614 Posts
Catapult hook position and construction

I'm doing a bit of scratch-building (mentally right now) and doing a rough set of drawings to see if I have enough dta to start a prototype.

Anyway, one of the things that I haven't been able to find a lot of information on is the catapult hook.

When I flew sailplanes, the usual hook was about an inch or so of 4-40 rod, end-threaded, which was bent to give about an inch of wire to hook the bungee's ring unto. The threaded end of the hook went through the bottom of the fuselage and through a blind nut with another nut providing the locking to keep everything from coming apart too easily. Positioning was in front of the CofG, about an inch or so for the cautious types, up to just behind for the competitive types.

The blind nut went into a short section of basswood or plywood (abut 1/4 thick by one inch wide) which was tied into two bulkheads to spread the load.

Now, for EDF's, is such an arrangement workable?

If anyone has pictures of their installation (inside and out), or scans from the instructions or plans, it would be greatly appreciated.

I'm sure that there are lots of newbie lurkers (like me) who'd like to pick up the knowledge of more experienced fliers and builders.
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Old Feb 13, 2003, 01:14 PM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
7,937 Posts
The hook needs to be farther forward on EDFs than it is on sailplanes. The average position is about 40% of the distance starting from the nose and going back to the CG. EDFs would die quickly trying to launch them as steeply as the sailplanes get launched, the wingloadins are too high. The flatter launch of a more forward location is better.

I tend to use sailplane type hooks. 4-40 rod may snap if you try to use it, and bending the threaded rod is tough without it snapping. I use a plywood plate on the inside of the fuselage.
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Old Feb 13, 2003, 02:56 PM
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gregg f's Avatar
shadow hills,ca
Joined Apr 2000
6,594 Posts
my rule of thumb, is locate it half way between the nose and wing l.e. ............g
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Old Feb 13, 2003, 05:22 PM
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Dr. Jet's Avatar
Oceanside, California
Joined Sep 2000
1,249 Posts
I wish I had a digital camera!

My newest tow hook is on the S&S F-86. I took a hunk of aluminum and milled out everything that did not look like a towhook. Afterall, this is a 7-1/4 pound beast and I use about 45# of pull on the bungee so I just couldn't use a wimpy hook! Then I epoxied a sheet of carbon fiber plate to the inside of the fuselage. The thing is attached with a countersunk 3mm FH machine screw in the back and an angled and countersunk 4-40 cap screw in the front. I'm sure someone will photograph it at the MWE and post it here (huh Gregg?? ).
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Old Feb 13, 2003, 05:32 PM
Purple power
gregg f's Avatar
shadow hills,ca
Joined Apr 2000
6,594 Posts
Re: I wish I had a digital camera!

Quote:
Originally posted by Dr. Jet
My newest tow hook is on the S&S F-86. I took a hunk of aluminum and milled out everything that did not look like a towhook. Afterall, this is a 7-1/4 pound beast and I use about 45# of pull on the bungee so I just couldn't use a wimpy hook! Then I epoxied a sheet of carbon fiber plate to the inside of the fuselage. The thing is attached with a countersunk 3mm FH machine screw in the back and an angled and countersunk 4-40 cap screw in the front. I'm sure someone will photograph it at the MWE and post it here (huh Gregg?? ).
dj: uncle joe is the official edf photographer. he's there now ......gregg
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