Crutch Detail

HI
I am going to see if I can post drawings of my motor mount \ Crutch details.
The parts are put together with slow cure epoxy,
The motor mounts are cut to the same curve as the wing root and epoxy to the wing root.
The hard 3\16 balsa top of the crutch also glues to the inside top of the fuse sides.
The motor mount pads can be alum. steel. or phenolic.
This epoxies to the sides of the balsa carbon balsa doublers and fuse sides.
I will try to post them if this works

These are the balsa-carbon-balsa fuse doublers.
They have lite fuse sides.
harder balsa doublers with .5 CF mat in between.
Used slow cure epoxy. the above crutch epoxies to this, and the top block.
The basswood inserts are for the cowling mounts.

This has been used on close to 2000 models since I developed the technique the 1980s. It does work well. and absorbs vibration. makes for a stiff platform for a cowl to bolt to.

This is the cowling detail, on how I hold it in place .
I got tired of seeing pooched sides. This works very well to keep it locked down.
You can also use a few small wood or piano wire dowels to peg the front or back down

Thanks Randy,
This is very helpful stuff. I appreciate it as do many others.

I can attest to the longevity of this fuse crutch, plywood free system.

I've built some this way, and the oldest one I have is one I purchased, and that is Bill Rich's "92 Nats" Orange & White SV with the green dragons on the wing. Bill probably had over 800 flights, Eddy played with it a while and probably put on 150 flights, Jimmy Mitchell had it a while and probably added another 150 flights and I flew the STINK out of that thing as my Sunday practice plane for a while and must have over 300 flights on it.

These are all very consevative estimates I would say, never mind the sheer age of the thing!

All flights with a thumping ST60. Not one crack in the nose, motor mounts, nothing. Still fly it now and then, and probably still deadly in the right persons hands. Has a nice shiney finish still too.

Eric V.

LAST EDITED ON Aug-07-04 AT 00:35 AM (CDT)
 
Thanks for the detail. The one I finished is built that way. The plane I'm doing now is going to be done the way The Bob Hunt vidio shows compound molding.

I can attest to the longivity of the way that Randy says to do it. 10 years ago the SV11's I built lasted a long time. Thanks again Randy.

What I always liked about Randy's front ends (is that right to say?) is that they held up to the Tiger 60, if it can hold up to that, it can use one of our PAs no prob.

Here is what I a lowly advanced flier noticed. Most people need nose weight, when i build a light nose trying to be cute, i end up with lead in the front. Why not build this thing like Randy shows and put some weight in where it can do some good, not in the form of a "dumb" lead weight...

anyway i have come to understand that Randy knows what is going on, we trust him completly.

I have a peculiar method for assembling the maple sticks to the cross-grain balsa fillers. I use runny epoxy: Shell Epon 815 with DETA hardener. I brush it on the end grain, let it wick into the balsa, then brush on some more, repeating every few minutes. The balsa end graing soaks up epoxy like a sponge. When the balsa appears to be saturated with epoxy, I assemble the mess with rubber bands. After it cures, I pull on the sticks as with a wishbone. If it breaks, I epoxy it back together. This often happens two or more times, but eventually one gets a really strong assembly. Then I sand the assembly flat on a belt sander, removing all the ugly excess epoxy. Do this before adding the doubler across the balsa and maple. Otherwise, you aren't assured that the bond between the cross-grain blocks and the maple is good.

Do the rest of you now understand why it takes Howard so long to build a model? I'm telling all of you, he would *gladly* glue a crutch together 10 or 12 times if that's what it takes.

Howard may have taken so long to build his latest Impact that a "revolution" of sorts in engines may well have passed him by.

Having said that, I do something quite similar in gluing crutches...??!! If it breaks, it wasn't good enough; do it again. And we both use exceptionally good epoxy, even if preferring different brands.

As does Howard, I begin with oversize pieces, both maple sticks and balsa cross pieces. When it is finally glued together to a suitable standard I simply start shooting the assembly through a table saw. All sides get their chance at being whacked back some, the result is a nicely squared-up--and flat--piece.

We all know that when Howard decides not to fly combat, he really slows down!

BTW, double gluing has been done since the Ambroid days!

LAST EDITED ON Aug-08-04 AT 09:21 PM (CDT)
 
I have read that epoxy does not stick well to....epoxy. Double gluing may not be the answer. What about soaking the cross-grain balsa in something else, perhaps under vacuum, prior to assembly? Maybe polyester resin?

I appreciate the amount of effort Randy has put into these drawings, and his generosity in posting them. It might have been easier to put them all in one post, however. 50kb per attachment, but virtually unlimited number of attachments, FWIW. Steve

PS: Howard still flies combat. I saw him fly against Milissa Huber just a week ago, at the fab Bladder Grabber.

"""I appreciate the amount of effort Randy has put into these drawings, and his generosity in posting them. It might have been easier to put them all in one post, however. 50kb per attachment, but virtually unlimited number of attachments, FWIW. Steve""

I tried that ....For some reason it only loaded 1 of the diagrams. So I just put 3 back to back. I have no idea why I could not post more than 1 pic

> I tried that ....For some reason it only loaded 1 of the
>diagrams. So I just put 3 back to back. I have no idea why
>I could not post more than 1 pic
>
>Randy

I would guess that you didn't click the box for .gif on the 2nd and 3rd attempts. Gotta keep an eye on those pesky things. It defaults to .jpg now; didn't usta. Steve