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  • Steve

RV-8 and the Homebuilt Electric Tug

Part 1, 5/25/24.

As I get older, I find that some things are not as easy as they used to be (I know, just me right?), particularly things that rely on strength of the body. Things like, oh, I don't know, pushing the airplane out of the hangar. Sure, that part is easy enough, but add in the fact that the taxiway is higher than the hangar floor, resulting in a small hill just outside, and things get a little harder.

Right now, I have no trouble pushing the airplane out of the hangar and up the small hill to the taxiway, of course the reverse being true, means that putting it back in is quite easy. I fear that the time may come when it will not be so easy for me to manage the hill, small though it may be. There will likely come a time when I will need help, that is if I live long enough and enjoy good health long enough.

Carl is a few years older than me, though probably in as good or better shape, but his new hangar has a few challenges as well, as did his old one. He spent a good bit of time looking at the commercially available electric tugs for moving small airplanes, and I looked a lot of them too. They all have one thing in common, they are not cheap. The reasonably good ones retail for 2.5 AMUs or more. For the uninitiated, AMU stands for Aviation Monetary Unit and is equivalent to $1,000 US (or Normal) dollars.

Due to their popularity and extreme expense, there has been a lot of interest, particularly in the home building community, in a DIY electric tow tug. There is a thread on Van's Airforce dot Net (VAF) that details one such search. There is another, somewhat shorter one as well.

Dan Horton built a number of tugs that he designed and Carl bought one of them. Compared to the commercially available units it was both cheaper and a better fit for the RV-8. Dan had some parts left over and offered to build a few more, and I considered buying one since it is such a well designed, well built unit, but I really would like to build one for myself. As I am still waiting for Van's to release the RV-15 kit, I haven't had anything to build for a while and this seems like a fun project for the mean time.

Reinhard Metz has an article in the March 2024 issue of Kitplanes detailing the unit that he built with (I hope) enough information for someone like me to be able to build one as well.

Reinhard's tug showing the unit he made and gave instructions for.

Reinhard's airplane has a training wheel, so his tug is maximized for that purpose. One of the nice features is that he has two arms that are electrically controlled to engage and disengage the nose wheel for quick connection and disconnection of the tug. My airplane has a tailwheel, so I will have to do something a little bit different. Dan H. uses a different method on his to capture the tailwheel.

Dan's tug uses a fork to capture the tailwheel.

I really like Dan's method, but his fork is welded in place and can't be adjusted for different tailwheel yokes, let alone different sized airplanes.

Forks welded to the tug.

As I hope to someday have an RV-15 as well as the RV-8, and/or I may want to experiment with different tailwheel yokes on the RV-8, I would like to have my tug be adjustable. I think I will try to come up with some kind of hybrid between Reinhard's idea and Dan's, though at the moment, I don't know quite what that looks like.

Carl showed me around his tug and demonstrated hooking it up to the airplane. I think I like that and want to duplicate it in some way.

One of the nice things about the Kitplanes article (linked above) is that it comes with a materials list and links to the actual products the author purchased. He built his a few years ago, so the prices of the things he bought have gone up, but so far, I have found almost all of the materials I need. Over the past few weeks I have been gathering the various parts needed to get started.

The first hurdle was to get material for the base and frame. The frame is made from 1" square steel tube. I thought this would be easy enough to procure form the local big box DIY store and I was right, to an extent. I found the square tube at my local Lowe's, but it was a good bit more expensive than I expected it to be. It was $28 for a 3 foot section and I needed about 8 feet, just for the frame.

I went home and tried Amazon and found something a little better, but not a lot. They had 1" square tube .083: wall for $29.50 for a 4 foot section. With free Prime shipping, it is a little cheaper, but not a lot. They also had the 1.5" square tube for the handle. At least I only needed one of those.

Where I really ran into trouble was with the aluminum plate for the base. Reinhard called out (because it is what he used) 1/4" aluminum plate for the base. The base / frame is 18.5" X 14.5", so a 24" X 24" piece is pretty much needed to start with. I couldn't find such a thing for less than about $130 + shipping. Fortunately, my Dad spent many years stopping by Boeing Surplus in Kent on his way home picking up raw stock at scrap prices. Fortunately for me , that is, since he just happened to have a sheet of 1/4 6061 aluminum that is big enough for the base plate and maybe even the other fittings needed.

Last weekend I tried to make my first cut of steel tube to make the pieces for the frame. I thought this would be a perfectly simple thing to do his my Dad has the proper tools in his hangar. I have watched him use this saw many times, but never actually tried it myself.

Nothing better for cutting small(ish) bits of material.

I was pretty proud of myself for getting the saw all set up and the tube stock marked at 45 degrees and the vise on the saw adjusted to the same angle, but when I tried to make the first cut, I ran into difficulty. I made it through about 90% of the tube, but when it got to the bottom wall, the blade jumped off the pulley's. I put it back on, but it did this for a total of three times. After the third time, I figured I'd better stop before I break something and get assistance.

At least I got a really good start.

Today, My Dad was able to come over and take a look at it to determine what I was doing wrong. Since I was doing most of it right, he figured it must be either the blade or the feed speed. I was probably trying to make it cut too fast. I put the blade back on and he tried it. I felt a little better when the same thing happened to him.

He suggested trying some cutting fluid and that seemed to do the trick. By using plenty of oil and a pretty slow feed speed, we were able to get the results we expected. After all, this is a really good saw.

Above, pointless video of saw running.

After learning that little bit of tid, the rest became very easy. I had the blade jump off one more time, but after that I got it dialed in and was able to finish the cuts pretty quickly.

Two 14.5" pieces and two 18.5" pieces.

I did some rudimentary deburring, but have to clean them up a bit more before they are ready for welding.

The basic frame.

The whole frame with cross piece.

Fortunately, the guy in the hangar next to my Dad's has a TIG welder and is not afraid to use it. I asked him if he would be willing to do the welding for me and he said sure, but he doesn't have a lot of time right now. I told him I wasn't in any hurry, so he agreed to tackle it.

The next simple step is to tackle the base plate. Fortunately, my Dad has a really nice band saw (Boeing Surplus) that will eat through that plate like butter. Once that is cut to size, there is a large(ish) cutout in the middle that needs to be made, but guess who had just the tool for that?

Stay tuned for more...

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