Elevator Bellcrank Fabrication

The rear elevator bellcrank assembly is comprised of control horns cut from 1/8″ 4130 alloy steel welded to 3/4″ tube.  The process starts with the cutting of the steel plate using our water-jet.  Using some custom-machined tooling we temporarily fasten the control horns onto the tube.  A quick fit check on the aircraft is followed by welding all of the parts together.  Eye bolts are installed both on the control horn and the elevator and then linked with a push-pull tube for actuation.

The dxf files for the control horns are loaded into the water-jet software where the layout and machine setup take place. The parts on the screen will take 10 minutes to cut and use about 7 pounds of abrasive.
The 4130 alloy 1/8" plate is loaded and clamped to the bed of the machine.

The water-jet in action.

After the completed cut you can see a risidual layer of the abrasive on the plate. The spent abrasive collects at the bottom of the tank. After about a year of use we drain the tank and remove the used abrasive and waste material from the parts.
Close-up of the cut parts. Note that we added tabs so that the relatively small parts don't fall between the slats and sink to the bottom of the 'swamp'.
Note also the precision of the cut. After minimal deburring the parts are ready for assembly.
Here we do a quick tolerance test on the 3/4" holes. The fit is so perfect that the control horns hold their position on the tube.
Next, using the lathe, we machine some aluminum tubing that will be used to firmly hold all the parts together for welding.
The tooling is in place and checked against the drawing for correct alignment. Threaded rod is used to fasten the assembly in place.
After the assembly has been welded, we will remove the fasteners and unfortunately have to destroy the tooling because it cannot be removed without cutting it free.
The center control horn has been tack welded here. Now we do a final fit check of the assembly installed on the tail boom prior to completing all of the welding.
All welding complete.
Completed assembly installed.
Since we do not have all of the linkage hardware at this time we quickly modeled the missing fork bolt and 3D-printed a couple so that we could connect the control horn to the elevator and test the elevator range of motion.
The 3D-printed fork bolts are threaded into the elevator push-pull tube and attached to the corresponding eye bolt for a quick test. The 3D-printed parts have just enough strength to do the test. They will eventually be replaced with flight certified hardware.
A view from the other side.

Checking the throw on the elevator bellcrank linkages.  The bright green 3D-printed fork bolts are for testing only and will be replaced prior to flight.

Leave a Reply

Your email address will not be published. Required fields are marked *