I've seen several inquiries on towbars and towing lately. My towbar is based on ideas from a really old "MonInk" newsletter. (Published by Monnet Aircraft, then later INAV, predates the current Sonerai Newsletter published by Fred Keip.). It dispenses completely with the fuselage cross tube the "plans" tow-bar (very sketchily described) uses to hook into the fuselage. The design I copied grabs onto the tailwheel and it's spring bar. Here's the original description and sketch out of the newsletter:
"For towing my plane I made a very simple tow bar which works great. I use it for holding plane to make power checks, etc. I used 1/2' x 1-1/2' John Deere (steel) crating material. All John Deere dealers have tons of this steel as all garden tractors come crated this way.
I've tried all angles up/down, sideways to get the plane to unhook before I towed it, but when the tail spring and wheel is fastened to the bar, it won't come loose. I was concerned about breaking or bending the axle but I've taken many trips to the airport (3 miles one way) without any problems (wings folded).
To install I just lift plane up by bottom of rudder with my left hand--holding bar in my right--slip "hook" over tail spring axle- -set tail wheel in between studs--hook-up to ball hitch-- install hold down plate with wing nuts and off to the airport. Time: about 15 seconds (if you're slow). Reverse to unhook."
My own towbar used flat bar instead of the oval tubing of the example, and added a couple of braces top and bottom to keep things torsionally rigid. I haven't gotten around to it, but I also have a caster to put on per the next set of suggestions.
Also from "MONINK", here are some comments on towing in general, along with more pictures:
"NEWS FROM BUILDERS
#44511 711 East St.
Ft. Atkinson, WI 533538
Last year at Oshkosh, Glenn told me about how he keeps his Sonerai in his garage, regularly folds his wings, tows it back & forth to the airport every time he wants to fly, and can be ready to fly in 10-15 minutes! I knew this would be a great article for the newsletter and something you would be interested in. One day in late April, Glenn few over to INAV (to get some parts for his Moni he is currently building) and I had a chance to talk to him again about his "at home" Sonerai. He just hadn't had time to write anything so I interviewed him then & there.
Here's the scoop:
Before Glenn bought his Sonerai he sent out a questionnaire to many builders about folding, trailering, and keeping their Sonerai at home. He only found one builder who actually folded and trailered theirs regularly. Most thought it was too difficult, no one said they could do it alone, many never folded their wings at all. But Glenn felt it was designed to fold and it could be done. So 5 years ago he bought a ready made Sonerai from Kelly Dunn. Then he set about refining some things to make the folding process easy and fast.
Here are some of his refinements and tips;
*Polished the spars to an exact perfect fit.
*Modified the wing fold. He extended the stationary part of the slide tube on the spar. Glenn adds you need a wife with small hands to put back on the bolts, nuts and washers inside!
*Put a spring load on the main spar taper pins.
*Put a floating captive nut on the trailing edge spar pins.
*In order to line up the spars for the pins, he developed a tool made of 1/2" aluminum rod about 8" long, machine tapered to 1/4"' using the same taper as the pin. By sliding this into the hole you can line up the spar perfectly. Insert the pins and tap in place with this tool that has a hammerhead screwed on the 1/2" end made of 1" round aluminum which is soft and won't damage anything. (see photo)
*To fold the wings - Remove rear spar pins with a small ratchet, 9/16" socket. He welded a 9/16" nut on the top end of the small pins. Remove main spar pins. He ground his so that a socket (any size) would fit on them. Remove them by rotating slightly. Push with finger and they will slide right out.
*Pulling the wing out was difficult as there was no place to grasp and pull so Glenn made another tool(see photo). He took a piece of left over tubing and a starter rope with a handle, cut a piece of tubing 6" long, drilled a hole in one end, made a loop with safety wire, joined with safety wire so it is inside the tube so it won't scratch the wing, tied rope on.
To establish a convenient rope length, stand at end of wing with arm outstretched and the tube in the wing-folding hole on the wing. Adjust rope length for you.
*To pull out the wing just put this handy tool in the wing folding hole (since this is attached to the spar it is a very solid safe place) Pull the spar out, rotate 90 degrees, and fold in the designated manner.
*Before he assembles each time he wipes the spar very clean so there is no grit to cause it to bind and sprays it with a greaseless lubricant.
*On the spar box Glenn used a dremel tool and ground the sharpness off the pinholes on the spar box to prevent shaving aluminum off the spar.
* On the spars themselves, he rounded the ends to make it easier to insert them in the box.
Under the tow bar at the trailer hitch, he put a caster under the hitch so it can be rolled . (see photo) Glenn adds he never trys to back into the garage but always unhooks and pushes it in by hand!
So there you have it. With these refinements and tools, Glenn says he can take down or set up all by himself in 10 minutes, altho he usually allows 15. He claims it doesn't take him any longer to fold up his wings, hitch up, and head home than for most people to put their plane in a hanger. One advantage of having your plane at home is for maintenance. Glenn can work on it right there whenever he has time, get it done and not put it off.
Here are some interesting stats Glenn sent me:
The plane has been towed to the airport and set up, flown, folded, and taken home 100 times now! It has been towed to Oshkosh for 5 years from '81 to '85. It has almost 1500 miles of towing on it!!
If any of you have any questions, just send a SASE and Glenn would be happy to respond."
Here is Glen's current address, according to BigYellow:
Eisenbrandt, Glenn R
711 East St, Fort Atkinson, WI 53538-2621
Phone: (414) 563-6502
Apparently, Sonerai builders don't move much.
Another refinement I've seen mentioned is to saw the bar that skewers the wings to the fuselage in half. That way you can shish-kabob each wing separately.
This is about the best picture I've seen of the A-frame towbar alluded to, but not detailed, by the plans.
Finally, in order to reduce wear on the tires while under tow, the wheels need to be set with Zero Toe-out, I.E. in line with the aircraft's centerline. This slightly degrades directional stability on landing roll out. If you are NOT towing your Sonerai, you may want to consider shimming a little tow-out into your wheels at the axle attachment.
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