A tow bar for a Stearman should:
- Be easy to move, install and remove by one person
- Utilize the towing eyes on the lower landing gear knuckles.
- Have the pins engage the eyes from the bottom up, and provide a means of locking the pin in the eye.
- Have a castering, wheeled, adjustable height support on the front of the tow bar so that it can be set at the right height for the tug hook.
- Have wheels under the gear attach ends so that it can be easily moved by hand or towed without being attached to a plane.
- Have a rigid cross member that, when engaged, will hold the two bars in place when not attached to a plane.
- Have the front towing eye on the centerline between the two bars, and the front wheeled support close to the centerline.
- Be at least ten feet long for ease in maneuvering
These were the specs set down for the following tow bar that has been in use for about 12 years, without discovering anything else that it should have or do.
The two main bars are made out of square steel tubing 2 1/4 by 2 1/4 and 1/8 in wall thickness., 10 ft long. The front towing eyes are made from 3/8 inch steel plate, and are identical.
The large hole in each is 2 1/4 in. in diameter. A short section of tubing with 2/1/4 in OD (1/8 in wall) is positioned through the bottom plate and welded in place on the bottom. The top plate is reversed and placed over the protruding stub of the 2 1/4 in tube so that it fits flat against the bottom plate. Then a large washer cut from the 3/8 inch steel plate with a 2 1/4 inch hole is placed over the stub tube and fits down against the top plate. The tube was sized to just reach the top of the washer. Put a temporary 1/32 inch spacer under the washer, and then weld it to the tube. Remove the spacer.
Now the two plates which move in a scissor like fashion, and are on the centerline, are welded into one end of the 10 ft square tubes.
For the other end, taper down the square tube and weld on an upright one inch diameter steel pin which extends 2 inches above the square tube. The top of the pin is rounded and there is a 1/2 in hole drilled in the side of the pin, half way through. This hole will receive the 1/2 in diameter locking rod. Don’t weld the pin in place until the locking rod is assembled so that the two will match properly.
Weld on three upright guides for the locking rod, each with 1/2 inch holes. Between the first two guides, there is a spring with a stop set screwed to the locking rod. This spring keeps the rod engaged into the hole in the upright pin. The rod has a cross handle in back. To engage, the handle is drawn back and the upright pin is moved up through the towing eye from the bottom. Then the locking rod is released and it slides across the top of the towing eye into the hole in the upright pin. The tow bar is then locked to the towing eye for either pushing or pulling.
Find some surplus wheels and brackets to put on the bottom of the two tow bars. Position the wheel brackets temporarily with clamps for alignment before welding.
For the front support, fab a 3/4 inch diam. aluminum rod and mount a castering wheel on one end. Get the end pieces from two 3/4 in Pony pipe clamps and
weld or braze them on the top and bottom of one of the 2/14 in bars, as close to the front as you can. The bottom clamp is reversed in it’s clamping action so that the support rod can be held from moving either up or down. Using an aluminum rod makes for good clamping action.
Near the back of the tow bars there has to be a cross bar. (19 1/2 in) This bar has close fitting pins in each end that engage with close fitting tubes brazed or welded to the sides of the bars. This cross piece holds the bars apart at the correct distance for the alignment of the towing wheels, and holds the bars in an upright position so they don’t flop over. When the tow bar is attached to the plane, one end of the cross piece is unpinned and swung over to the other bar and repinned.
During towing of the plane, the front support rod is moved up for clearance from the ground, and held in that position by the Pony clamp.
Put a mark on the front support rod that positions the front eye at just the right height for your tug. Then when the towing ball is positioned, release the pony clamp so that the eye drops over the ball, and then raise the support rod up for clearance.