Free Flight: Old-Timers
Bill Baker, 1902 Peter Pan, Norman, OK 73072
When I began writing this column about six years ago, I wondered why we are called contributing editors instead of columnists or writers. Well, the aptness of the term editor becomes more apparent with time, as I spend more energy deciding what to include and what to leave out than I do writing.
I do wish I could be more timely and write monthly—I am writing this in January—so as to be able to keep up a sort of dialog... but I will try to bloom where planted.
Winding, Power, and Trim
In my March 1993 column, I drew a rough graph to show the relationship of turns to torque for a rubber motor. One of the points to be made from the graph is that about 80% of the motor's potential power comes from the last 20% of turns.
If you wind to about 80% capacity, the decrease in power is rather gradual, so the trim won't change much. This makes it possible to fly models of limited performance, such as most scale models and many sport designs, which have small, nonlifting stabilizers and centers of gravity (CGs) at 25–33% of the chord.
For outdoor duration models, in both Old-Timer and current AMA-FAI events, you have to get all the energy possible into the climb in order to be competitive. So you wind as tight as you dare, to get full use of the "burst," which will produce a very rapid climb for a few seconds.
This short but very strong release of energy can be tamed somewhat by the air-brake effect of large, high-pitch props. The trim problem is really the rapid change in power as much as the very high power itself.
A lifting stabilizer with the CG about 60–70% does help a lot. While there are many trim schemes that will work, the fundamental one is to use enough left rudder and/or stabilizer tilt to give the desired left glide circle, combined with down and right thrust.
There needs to be enough right thrust to keep the model turning right (it's okay if it goes straight during the initial burst), and enough downthrust to keep it from looping. What is desired is a right spiral climb that will transition smoothly into a left glide.
If the right turn gets too tight—threatening to spiral the model in—the left rudder tab should become more effective because of increased airspeed, which will tend to open up the right turn. That is what makes this setup so safe. There are some disadvantages—and some interesting alternatives—but I will save those for later.
Motor Run Durations
I questioned O.F.B. Jim O'Reilly on the duration of rubber power runs. His figures for modern contest practice are roughly:
- Wakefields: 30–35 seconds
- Coupes: 25–30 seconds
- P-30s: about 40 seconds
- Unlimited Mulvihill models I have seen: about 50–70 seconds
The spread has to do with the choice of cross section versus length and the size of propeller, as discussed in the last column.
Old-Timers and Motor Choices
For Old-Timers, the above may be helpful insofar as the motor sizes correspond to current events. For example, I flew my Lanzo Stick and Cabin and my Korda Dethermalizer (each about 300 sq in) with the same motors used in my Mulvihill—about 90 grams, 34 inches long. Since the Mulvihill ran about a minute, the OT ships ran a bit less—about 45 seconds—because the propeller used on OT had to be smaller in diameter to be legal.
If your run is very short, you may want to increase the load on the motor—more prop—or change to a longer motor with a smaller cross section.
If you try to get a run of two minutes, for example, you are going to have to fly indoors or on very calm mornings. A long, slow climb seldom works outdoors. I am talking here about competition duration models.
Scale Models at FAC Meets
The scale models I have seen fly at Flying Aces Club (FAC) meets are the exceptions. They get very long motor runs and long flights with low model weight, so low-cross-section motors of great length—two or even three times the length of the model—can be used. The models are not wound to a strong burst level, so they have a very long cruising flight, and seldom get very high unless lift is encountered. They don't worry about glide—they generally land with the propeller still turning, like an indoor model.
Prop Carving, Instructions, and Reprints
Because of questions I get about laying out propeller blanks, I will try to give you all the necessary data in my next column. I am not going to write a detailed how-to-carve article here, as that has been done well many times.
I have a reprint of an article Dick Korda wrote a half-century ago that can hardly be improved upon, and I will make a copy for you for the usual business-size SASE, plus a loose stamp to pay for copy expenses.
My old buddy George Schroedter of Champion Model Products (CMP) offers the same deal. His kits for modern Wakefields and Coupes have very fine carving instructions; he will send you a copy for a SASE plus an extra stamp. For an even better deal, send him two bucks for his catalog and ask for the instructions in addition.
Champion Model Products 880 Carmen Court, La Verne, CA 91750 Tel.: (714) 599-3348
Prop Kits and Oldtimer Model Supply
Looking through my Oldtimer Model Supply (OMS) catalog for about the hundredth time, I see for the first time a "prop kit" consisting of a 12-inch drilled and sawed prop blank and written instructions, for $3.95—what a deal!
If you don't have the OMS catalog, you haven't been reading my column long. The catalog is $2; orders have a $3 charge for shipping and handling, so if you want the prop kit as described it will cost you $6.95. The best thing might be to get the catalog first, then order lots of stuff, which will all be sent for the same three bucks.
Oldtimer Model Supply P.O. Box 7334, Van Nuys, CA 91409
Campbell Custom Kits and New Releases
Campbell's Custom Kits recently sent me a new kit release, an Aerobee, for .020 Replica and Pee-Wee .030. This is a scale-on of an .020-powered model. It is a fine kit, with nicely pre-cut ribs and other precut parts, good wood, and good tissue. This one I can highly recommend, and it appears to have all the requirements of a competitive design.
The fuselage is sort of diamond-shaped and may not be as easy to build for a first model as a rectangular cross section, but with the clear plans it should pose no problem to experienced builders.
This is a welcome addition to the available selection of .020 Replica competition models, and it maintains the high quality standards that recent Campbell releases have featured.
Campbell Custom Kits 401 Executive Center Dr., Suite H-108, West Palm Beach, FL 33401 Tel.: (407) 686-7824 Price (direct): $21.98 plus $4 shipping and handling
Terry Rimert has put together a collection of Nostalgia-era (post–WWII through 1956) plans from various magazines and published them in book form, available from Campbell's for $10 plus $2 shipping and handling. He calls this The Third Nostalgia.
Free Flight Unlimited (R. Linwood Cochran)
One outfit that handles the Campbell line is Free Flight Unlimited, operated by R. Linwood Cochran:
Free Flight Unlimited R. Linwood Cochran 6769 Angeles Lane, Tucker, GA 30084-1344 Tel.: (404) 493-1032
He not only lists the .020 Replica Aerobee, he also has the .19 size for SAM Class A Pylon competition. Cochran's catalog covers a lot: CO2 and internal combustion motors, Jetex fuel and motors (tiny rocket motors made in England), and the extensive Canadian Easy Built line, which includes many Old-Timer rubber-built duration ships and scale models in light stick-and-tissue construction.
Linwood says he will send you his catalog free; it runs 12 sheets and takes 56¢ postage, so I suggest sending him a buck.
Closing
I keep recommending these cottage-industry catalogs because they have the bits and pieces you need. I appreciate your questions and problems; they give me ideas to write about. Please send photos and other data if you want them considered for discussion.
Transcribed from original scans by AI. Minor OCR errors may remain.
