The Ptug from Hell
Back in 1981, I became interested in Ultralights and bought a Pterodactyl Ptug. The Ptug was originally designed as a hang glider tow plane, but without the draw bar, it was also called the Ascender because it's climb rate was about 1000 fpm. Jack McCormack told the story about how, when it was first designed, he took it to Ultralight Fly ins and was told not to terrify the public with full performance climb outs. They limited his climb rate to something like 250 fpm, on the idea that at the excessive climb rates the Ascender could manage, that the plane might break the upward sonic barrier (which, as all ultralight fly-in officials knew, was at that time was exactly 251 fpm.) and fly apart, frightening the public. Back in those days, I did try a few aerotows, but the way the tow line was fastened to the basetube and the top of the control bar seemed to limit the feasibility of aerotow.
In 1995, I learned to aerotow behind a Dragonfly, and became interested in reviving my Ptug as a modern tow plane. I did some tests with the stock configuration Cayuna 430 including restoring the original expansion chamber for more peak power and switching to a lower pitch prop to get more horsepower. Doing the best I could, my climb rate pulling a hang glider was only 150 fpm, which meant that it took nearly 15 minutes to climb to 2000 ft. This wasn't acceptable.
A friend told me he had a Rotax 532 engine that needed some work, carburetors, an exhaust system and a cooling system. It was rated for about double the horsepower of the Cayuna 430 and it's dry weight was only a little more. I bought it, and began the daunting task of installing a watercooled, heavier engine with twice the horsepower on my Pterodactyl. Rapidly the shopping list for installing the big engine got really long and expensive. I had to design an engine mount plate that would fit on the Ptug and get it built at a machine shop. I found an aluminum motorcycle radiator, no small task as most are made of brass, and weigh like they are made of lead. I quickly found that even converting to a 2 carb throttle from a 1 carb throttle was a design issue. I got a factory Rotax exhaust system, but found that even it needed modification and welding just to install it. I had to change the water fittings on the engine as I was mounting the engine upright instead of upside down and add a thermostat. The thermostat, usually a luxury on an ultralight, was necessary when flying the Ptug down rapidly while idling to keep it from getting too cool and cold seizing. The draw bar for towing the hang gliders was designed for a 54" prop, which was a little small for the horsepower available to me, so I had to get a special high pitch Ivo 3 blade prop trimmed to fit into my draw bar. I had to change the struts on the Ptug on which the engine mounted from 1" to 1 1/8" internally reinforced. The list went on and on. New instruments, new landing gear. A new draw bar mount was designed to isolate the tow forces to the engine.
The airframe got special consideration as well. All of the wood plugs were changed out for polyethelyne and any suspect tubing was replaced as well. I elected to keep the spars stock because of the cost in changing out virtually every tube in the wing and the keel as well. I built all new flying wires, with the outside set of 1/8" instead of 3/32" and changed the U bracket to which the cables attached to tangs instead, adding NeverKinksâ at each thimble. I also considerably reduced the dihedral, copying Dave Froble's Pterodactyl I had flown at Sun-N-Fun. This greatly improved the crosswind takeoff and landing characteristics of my Ptug when coupled with my Spoilerons which were hooked to my aircraft style steering petals, but at a cost that the stick pressure needed to operate my tip rudders was greatly increased. I even had to design a new mirror mount so that I could see the glider behind me when I was towing and find a place to put all of the extra instruments. Water temp, dual EGT, Tach/hour meter, altimeter, rate of climb, air speed, GPS, Kitchen sink. No fuel gauge since in theory, I could see the fuel tanks in the mirrors.
The final result cost me a lot of bucks, and I still didn't even know if the thing would fly slow enough and climb fast enough to tow hang gliders well. So, I did a few test flights with it, and took it to Sun-N-Fun '96 to tow my SuperFloater. I carried it in my SuperFloater Trailer with two SuperFloaters and several hang gliders. I stopped at Quest Air on the way to Sun-N-Fun to put it together and do some test tows. The first test tow with the big engine was towing the SuperFloater with me flying the SF and Jack McCornack, the original PapaDac at the stick of the Ptug. He stamped his seal of approval on it. Then I towed a pilot on a WW Ramair. He complained that I was towing too fast. I figured that I had to get used to the increase in power but my primary goal was to get to Sun-N-Fun. So, early next morning, in company with a Dragonfly powered by a similar engine and piloted by a foreign pilot who didn't really know the way, I flew XC to the Lakeland Airport. The Ptug had excellent fuel consumption cruising at 45mph and considering that I was flying IFR, (I fly roads) we still made good time. I noticed that I had used only 2/3 the fuel that the other tow plane had. I assumed that it was because of the lighter weight of my plane which was FAR103 legal, weight wise anyway and must have weighed almost 200 lb. less than the other plane.
So there I was at Sun-N-Fun with the most overpowered ultralight around. Dave Froble, PapaDac II, started talking about a certain twin engine ultralight design which always did a high performance climbout during the Manufacturer's showcase, claiming I should challenge it to a climb out contest. I happened to mention this to one of the hang glider pilots and was promptly laughed at. Sooo, when the Manufacturer's showcase started, and Dave Froble and I rolled out our two Pterodactyls, I decided to do a genuine high performance climbout to the 500' ceiling to which we were limited. Here was Dave Froble in his nice shiny freshly built Pterodactyl, and me with my Butt Ugly Ptug with patches on the sail, bits of hardware stuck every where, a canard which looked like it had gone through the World War, (the first world war!) including the rusty ring where a can of paint had been left on it for several years, and a number of stick-on patches, spoilerons which had only been painted partly on one side and none on the other, the radiator mounted with several old sawed off Hang glider deflexors and attached to the air frame with u-bolts. Not a miracle of cosmetics, form follows function, I always say…. I jammed my throttle to the stop, held my Ptug on the ground until it was going 45 mph, and then pointed back on the stick. I had a considerable headwind, so it seemed like I went straight up and somewhat backwards. Fifteen seconds later I was at 500 ft., cut back the throttle and nosed it level. Dave followed me up with his over-powered, but not well tuned Ascender III and arrived about 15 seconds later. The hang glider pilot who laughed at me, showed up as I landed and admitted that he had never seen anything quite like it.
Meanwhile, Jack McCornack was standing on the sidelines and watching his vindication as I proceeded to tow everything in sight at the Sun-N-Fun hang glider showcase in front of thousands of people. The tow speed of the Ptug seemed to be a little faster than the Dragonfly but not as fast as the trike towplanes. The climb rate was excellent. I could pull a hang glider to 500 ft in 45 seconds.
Over the next few years, I cleaned up the Ptug. I put on a new sail. Built a new canard. Came up with a way to deploy both spoilerons at once to act as spoilers while allowing them to move separately as ailerons, and added elevator (oops, canard) trim. I replaced a lot of the tubing and generally improved it's appearance and function. I even towed a Woodstock sailplane with Gary Osoba, and did a 30 mile XC towing a SuperFloater back from an XC.
It's still probably the only active Ptug in the world, but it is also one of the few FAR 103 legal tow planes in existance. It's winter now, and I can hardly wait for a new year to get towing again.