Ken Burdick's C Speed plane, a converted Formula 40, seen at the Northwest OctoberTest in Salem, Ore., on Oct. 23, 2010. All photos by Ken Burdick.
By Ken Burdick
Yes folks, it's true.
Converting your F-40 from a bellcrank 2 line system to a mono line C speed ship will take a little work and finish time, but it's not difficult.
Photo shows both the two-wire bellcrank and the monoline unit installed.
Monoline wire has a loop typically formed around a 1/8” minimum diameter rod and must be pushed through the wing in order to reach the button of the torque unit. Additionally, the AMA specifies that for C speed, the wrap and solder that holds this loop, must be 1-3/4” long. These are your challenges.
If you were building a new model, you would slot the wing for the wire to go through and that makes it simple. In this case however, your wing is finished with either two slots for the wire to bellcrank layout or tubing set into the wing for the wires to sit in. You can either route a slot 1/4” wide all the way down the wing to the crutch, or use the front leadout position for the line and form the AMA loop AFTER the line runs through the leadout guide. You can then slide the loop back into the wing and attach it to the torque unit. This has one major drawback; the line cannot be removed from the wing so it's up to you. Primary tools, a # 11 X-acto knife and a Dremel tool with bit as shown.
Formula 40 plane before conversion to monoline.
I recent purchased a Formula 40. It had the strong Nelson engine I was looking for as well as a good pan and props. Not a bad deal, all things considered. The wing however is all basswood and the builder had installed brass tube for leadout guides. I elected to not route the wing but to use the front leadout guide instead.
The first step is to locate the torque unit into the wing, so that it is centered to the line guide in the wing. This is done by running a wire through the wing as a visual reference. Draw a T shape on the underside of the outboard wing, using a Sharpie. Be sure to make it oversize so you can adjust its position. Start with an X-acto knife and outline the T. Next keep cutting until you are 1/3 through the thickness and chip out the pieces. You should now have a rough t shape. Using a dremel and bit as shown, route out the T shape to nearly full thickness of the wing. Slot the crutch so the T unit can be dropped in place.
Remember that 1-1/2” of wire wrap and solder required by AMA? Well ... it just won't fit through the 1/8” tubing the fellow ran through the wing for lead-out guides. A 1/4” slot must be routed on the underside of the wing that is long enough to contain the wrap and solder job. I made mine 1-3/4” to be sure. The crutch will also need a slot in it now.
Don't give up and fly stunt just yet, we're almost done. If you have a good epoxy job on the T unit, very little fill will be needed, if not, I recommend this “blue stuff”we bought from an aircraft store. Microballoons and epoxy will also work fine. The slot on the inboard wing will require a cover so use your modeling skills here. All slots, holes and otherwise protrusions in the wing should be covered, filled and sanded. As shown in the picture, I used 1/64" plywood to cover the hole. Place an oversized piece of ply on top of the hole, cut around the ply leaving some extra room in the cut to hold filler. In other words, make the cutout larger than the plywood. CA the plywood in place then fill around the edges with filler
The "blue stuff" is SuperFil, available from full-scale aviation supply stores such as Spencer Aircraft in Puyallup,Wash.
If that won't float your boat, just route the inboard slot as pretty as you can and make it all the way through the wing, leaving a rectangular hole there. I promise this won't slow you down since most of the drag will be the line anyway.
There must be a dozen different ways of doing this installation, this is the one I chose for the particular airplane. Send in pictures of how you did yours, the more we share ideas, the easier it will be for a new guy who wants the help.
The Hippy, Marty Higgs, is at it again! How many good props have you ruined after spending hours on them ... for me it's been a few. Just released from Fast Hippy Products is the “Skidoo.”
Made from 7170 (very hard aluminum), the skid will bolt on to the front of your new C speed pan just in time to save that $15.00 carbon fiber prop you just reworked.
I was contacted by none other than Bill Allen the other day. He is interested in C speed and as some may know, ran his F-40 up over 165 in some hot sessions a few years ago. Bill makes awesome speed buggies. We may have lost Ted Gritz to the Phoenix guys, but we just picked up another brother...
-- Kenny-b
This page was upated OCT. 27, 2010