Flap Locks

As we prepared for our first trip to Oshkosh, we were concerned with preparing the airplane to live outside for a while. This involved making plugs for the air intakes, weather stripping the windows and doors, and coming up with a way to hold the flaps in the retracted position.

Since the Bearhawk uses one-way cable tension to hold the flaps down and spring tension to hold the flaps up, a gust of wind from behind can extend the flaps. This can subject the flaps to damage, especially if the gusts are strong.

My first attempt at a control lock was to make a v-shaped piece of aluminum out of a 1/8″x2″ extrusion. I bent the aluminum to a radius that would fit outside of the flap and trailing edge at the wing root, allowing for some foam padding. This didn’t work very well, because the 2″ bar was too narrow. The same idea might work if the bent piece was much wider, maybe 6″ or so.

It was important to minimize the weight and space of the lock device, since I was going to have to be carrying it around, so a 6″ taco shell wasn’t going to be optimal. Instead, I expanded and copied a design that I saw on a Kitfox at Oshkosh one year. I started with a scrap of 3/8″x2″ hard plastic, probably Delrin.
Flap Lock Parts
I drilled two holes to accommodate two 3/8″ dowels, then padded those dowels with some hardware store tubing. Before applying the tubing, I spray-painted the whole assembly bright pink to make it more obvious during the preflight exterior inspection. Finally, I connected a short and small bungee cord that will hold the lock in place. The lock would probably stay in place without it, but I didn’t want to risk having it come off.
Bearhawk Flap Lock

External Control Lock

Flap up lock

I think the bright color looks quite nice, though it hasn’t been too durable in the sun so far.