Free Flight: Old-Timers
Bill Baker
1902 Peter Pan, Norman, OK 73072
Z-model compressed air motor
My Italian correspondent Ferdi Gale sent me one of the Z-model compressed air motors sold in this country by Bert Pond and described a few issues back by John Worth. I am not going to do a detailed review, but will just say that the motor runs, is easy to operate, and could be the answer for those who are looking for quiet power for flying lightweight models.
The handful of people who fly the SAM compressed air event have taken to the motor, and Bert says all the compressed air flights at the 1990 Nationals in Lawrenceville were made with the Z motor. He says the Hungarian expert Benedek flies a light built-up 55-in.-span RC model with the Z, and Ferdi Gale says the factory may market a twin-cylinder version. He thinks this motor, if produced, will allow for lightweight RC free flight and RC models.
The factory literature indicates that the operating pressure range of the motor is one to 12 times atmospheric pressure, with the tank listed to seven atmospheres. Bert Pond says:
"I use a one-liter soda bottle in place of the Z model's 0.76-liter tank for more volume and a greater safety margin. The one-liter bottles don't burst until well over 200 psi, and the SAM rules limit pressure to 150 psi. In fact that is about the only rule at the present time for compressed air models."
He goes on to say that many fliers adapt the motors to larger propellers such as the yellow P-30 type plastic propellers and use electric pumps driven from a car cigarette lighter socket instead of the hand pump furnished with the motor. Bert's instructions, which are supplied with the motor, include details on reinforcements you'll want to use on the cylinder head if you are going to use more pressure than you get with the hand pump.
The clever design of this motor may influence future CO2 engine design, but it should be made clear that this is not a CO2 engine, and it will not tolerate such pressures. This motor does not have much, if any, more power than the ancient brass Hoosier Whirlwind three-cylinder job (which Bert also makes and sells), but it is so much lighter (seven grams for the motor with a 30-gram weight for the supplied tank) that it is possible to fly smaller models and handle some wind better. The traditional compressed air model had to be huge (a 60- to 70-in. span) and very lightly built in order to get a wing loading low enough to fly in early morning calm. They were fragile and flew at low speeds—almost like indoor models.
The English magazine Aeromodeller (April 1990) has an article about the Z motor by scale expert Doug McHard which features photos of his Piper Super Cruiser, 40-in. span, built from a 1940 Comet plan. The article has much technical data about the power plant, including drawings of the valving, which is (to me, anyway) quite new, and very different from CO2 motors, which haven't changed much in design—only in size—from the OK CO2 of the 1940s.
If this sort of valve system is adaptable to CO2, I predict that this form of power could become very popular, as the duration of run would be much extended by this very efficient system.
On the other hand, I have one of Bert's three-cylinder classics. It runs as smooth as a Singer sewing machine. If I were to build a model for it, I would want to make one from a 1920–1930 plan, one contemporary with the engine, and if I wanted to fly it in SAM competition (I don't) I would be a mite upset about all the modern technology.
I am not going to build a model for the Z at this time. Frankly, I can get better performance from a few strands of rubber; but then I would have to make my own motor noises and risk being thought even more eccentric than I am now.
Bert Pond
- 128 Warren Terrace, Longmeadow, MA 01106
Kustom Kraftsmanship (Joe Klause)
I recently heard from Joe Klause of Kustom Kraftsmanship, who says:
"Thank you for your kind words in the March issue of Model Aviation. One minor comment: In 1975 we bought out Kinn Kraft. Subsequently, in 1976 and 1978, we modified the original Kinn Kraft needle valve so that today it is a far superior needle valve assembly."
Joe sent me a sample of his popular transistorized ignition which includes a high-tension lead with the proper resistor to eliminate RC problems from ignition noise.
The most exciting thing Joe sent me was the news that the K.S.B. clockwork starter is again available, in both the version that pinches off the fuel line and one modified with a microswitch to shut off ignition engines. You need his catalog. I was really impressed; it has been a couple of years since I've seen one, and there is a lot more stuff in it now. Control Line fliers need this catalog too, as well as Old Timer fans, and anyone who runs Cox engines or high-performance engines.
Kustom Kraftsmanship
- P.O. Box 3010, Fallbrook, CA 92028
- Catalog: $1 (probably costs more than the labor to produce and mail)
The Bat Sheet and aniline dye technique
The Bat Sheet, newsletter of the Stratobats of Seattle, Washington, carries all the regional Free Flight news and often has some good original material. Mark Sexton, 8717 17th NW, Seattle, WA 98117, offers subscriptions for 12 monthly issues at $12 (U.S.), $13 (Canada, in U.S. funds), and $14 (other countries, U.S.).
The February issue described a source and technique for the use of aniline dye to give a light translucent enhancement to doped tissue colors, which tend to fade in the sun and be sort of pastel even when new. The cost is about $24 per pound for the dye. It will not dissolve in dope or thinner but will dissolve in alcohol.
One-eighth teaspoon of dye powder in two tablespoons of methanol will color about 2½ ounces of clear dope. This then needs to be sprayed onto tissue that has two or more coats of clear, dry dope on it. It may look dull, but a top coat of clear will restore the brilliant candy-apple look. The top coat is also needed to keep the dye from running, as it is water soluble. The author (I assume it is Mark) says it looks sharp on clear-doped wood such as carved balsa propellers, and he suggests using it to "spruce up some faded contest veterans."
Dye source:
- Keystone, Pacific Division, 13787 Milroy Place, Santa Fe Springs, CA 90670
That's all the room they let me have. Let's go hunt some thermals.
Transcribed from original scans by AI. Minor OCR errors may remain.
