Letters to the Editor
All letters will be carefully considered; those of general interest will be used. Send to Model Aviation, 815 15th St., N.W., Washington, D.C. 20005
Gas Power for Electric Spitfire
I am very impressed with the Electric Spitfire in the October 1981 Model Aviation. However, I do have a couple of questions.
I am currently flying a General Skyfarer, 6-ft. span (fixed rudders, twin tail) with controls for aileron, elevator, throttle, and nose wheel (coupled with aileron servo). All-up weight is 6 1/2 lb., 700 sq. in. area. I am using an Enya .29 swinging an 11-4 prop with a 2 1/4-in. spinner. It gets off very well on pavement, will loop and do rolls, but I still consider it underpowered.
I should like very much to build the Spitfire, and I do have an ST.23 which has very little time on it. It seems to do well on a 9-6 or 10-4. My question: What was the prop diameter and pitch on the .23 version? With a 3 1/2-in. spinner, this doesn't leave much blade sticking out.
I realize that the Spitfire has an extra 190 sq. in. over the Skyfarer, but even at 5 lb., the wing loading figures at about 8 oz., while my Skyfarer is close to 15. Based on charts by Jack Burns in a 1976 Model Aviation, the Spitfire falls in the "light glider" area and the Skyfarer in the "heavy glider" area.
The article on the Spit mentions swinging a 12–13–14 diameter by 8 pitch prop on electric. Please advise on the .23 engine, or should I go to an OS .35?
Don Boardman Swanton, VT
Designer/author Don Sittell responds: I flew the Spitfire on both an ST.23 and an OS .30 with good success. I preferred the OS because it had a little more pep and a lower, more reliable idle. I used a 10-3/4 prop on the .23, and used 10-4s and 11-4s on the .30. They all worked well even with the 3 1/2-in. spinner. I would recommend the .35 if you want a little aerobatic performance; the .23, however, will fly the Spitfire well—even if a bit more sedately.
Wants Electric Power Specs
I think AMA President John Grigg's "pitch" for the merits of electric-powered model aircraft recently was extremely sound and farsighted. Considering the public's dislike for those noisy glow engines (especially when our members fly their planes close to residential areas), his support of electric-powered model flying is wise—very wise, indeed.
However, if the manufacturers of these electric propulsion motors for model aircraft continue to fail to provide the serious modeler with the products' optimum design ratings (particularly the motor's voltage and wattage ratings), their efforts to expand the interest in electric flying and win more enthusiasts for "silent flying" may well prove to be less productive than they might wish. In short, as a serious model builder, I hesitate to invest my hard-earned dollars into more than one electric flight system. I presently have an Astro Flight 05 for RC flying, because most current manufacturers of these systems do not provide sufficient technical information with their motors. As much as they might wish to capture the entire battery-supply-and-sales portion of this area entirely for themselves, their short-run advantage here might kill more overall growth and use of their type of power systems in the future.
Dr. Cy Stow Conyers, GA
Since Doug Pratt, MA assistant editor, has had a good bit of experience with electric-powered models, we called on him for thoughts on the matters that Dr. Stow raises. Here's what Doug says: Dr. Stow has a very good point. The folks who manufacture glow ignition engines make available all kinds of technical data on their products. With the growing interest in electric propulsion, it's high time we had some hard engineering data. Bob Boucher's book, The Silent Revolution, is a fine manual for the beginner, but with the new hot-wind motors and high-voltage battery packs coming on the market, we need more specifics. General Electric publishes an applications handbook for Ni-Cd batteries that is extremely useful; it can be purchased from Ace RC (see January "Product Review" section, page 50). Many of us would like to see manufacturers' engineering data in print. Electric propulsion works, most everyone admits; now we need to know the hows and whys.
Common Meeting Ground
I was very pleased to see the construction article and plans for Pieces on page 64 of the January Model Aviation. This release coincided with the start of our 1981–82 indoor model program in Kansas City, and it was well received. Pieces obviously is a good design from its records, and the construction article by Walt Van Gorder was well done.
We have found that indoor models can provide a common meeting ground for Radio Control, Free Flight, and Control Line interests. Thank you for helping to promote indoor models.
Roger J. Schroeder Overland Park, KS
We've got to admit that we were looking at the calendar when we scheduled the Pieces Indoor Easy B construction article. Peanut Scale is another activity with much greater interest. We recommend taking a look at the Fury Peanut Scale in this issue.
Intermeshing Twin-Rotor Autogiro
In the article "Let's Talk About the RC Autogiro" by Jack Headley (November 1981 MA), the author questions the lateral stability of the intermeshing twin-rotor type of autogiro. As I am building this type of whirlybird from the plans referenced in the article (MB plan #9791 for $5), I would like to point out that one-half the rotors are anhedral, the other one-half dihedral. The author states that the rotors rotate forward, which is only partly true. According to the plans, the rotors rotate forward in the dihedral sections of the rotors; this part of the rotors, thus, produces the majority of the lift. This means the autogiro has exceptional lateral stability.
Philippe Chibolas Danville, KY 40422
Author Jack Headley responds: Since the article was published, I have received a letter from George Chaulet, who has developed this type of model extensively in France. He comments that lateral stability in turns is no problem. The biggest problem is that, occasionally, the blades run into each other. Much chafing of balsa results. Mr. Chaulet's explanation seems to be verified by the above.
Another letter about the same article follows.
"Let's Talk About the RC Autogiro" by Jack Headley is an interesting, informative article, and hopefully it will stimulate interest in this type of model. They are an interesting challenge. For anyone interested in the single-rotor autogiro, I offer the following additional comments.
Obtaining lateral stability seems to be the problem. By using flapping blades, unbalanced rotor lift is eliminated, but the stability problem persists. The inertia and the aerodynamic damping about the roll axis is much smaller than that of a conventional plane (or of a twin-rotor autogiro). Is that the cause of lateral instability? If so, layout may be critical. Small wings (to scale) or a rate gyro may be necessary.
One advantage of the autogiro over the helicopter is that the autogiro rotor head is much simpler. With three or more blades, each blade must be hinged (free to flap). Drag hinges are not required; collective pitch control is not required; cyclic pitch control is obtained simply by tilting the rotor shaft. The blades do not rotate about their pitch axis, and no swashplate is used.
Machined rotor heads are impressive, but a usable rotor head can be constructed from hardwood, brass tubing, and music wire with ordinary modeling tools and techniques. A two-blade rotor could be a simple see-saw arrangement. However, there is an indication that two-blade rotors are slow to start autorotation (may not start at all), and under some flight conditions the rotor of a model autogiro has a tendency to stop turning! A two-channel single-rotor autogiro should be practical. The autogiro definitely can be landed dead-stick, with no problem. Rudder is ineffective and not needed. Elevators are effective; they eliminate the need for a pitch-axis tilt of the rotor head. Rotor tilt or aileron can be used for roll-axis control. If rotor tilt is used, locate the roll-tilt axis high on the mast as close to the rotor as practical. Use a good, strong servo to tilt the head about plus/minus 10 degrees.
William J. Kuhnle Richardson, TX
Nostalgia: K&B .61-Powered Model
Harold Benjamin would be interested to know that someone else shares a similar nostalgia. My K&B .61-powered model isn't as elaborate, but it has been lots of fun and a pleasure to onlookers. I was surprised to discover how well it flies. It originally was a tail-dragger and had wing spoilers linked to the rudder. It was rebuilt following a radio failure—at which time a trike gear and standard controls were installed. Be confident, Harold Benjamin, you have a fine airplane.
Leland W. Sloan LaVerne, CA
Organization for Electric Power Fliers
Electric power for model aircraft has been proven to be efficient and practical. With this in mind, a group of electric power enthusiasts have decided to form the Society of Electric Aircraft Modelers (SEAM), a national organization dedicated to the advancement of all forms of electric-powered model aircraft.
SEAM is to be affiliated with the AMA, and it is intended to serve in an advisory capacity to the AMA in all matters relating to electric-powered model aircraft. The ultimate goal of SEAM is to provide the following services to the modeler:
- Information exchange: quarterly newsletter, reprints of technical and experimental data sheets, direct member-to-member information exchange, product information brochures.
- Contest rules: forum for all types and classes of free flight and radio control electric-powered model aircraft.
- Promotion: regional electric-powered aircraft activities of all kinds through local SEAM clubs.
- Business directory: for dealers who stock electric motors, batteries, chargers, and suitable aircraft kits.
Any readers who are interested in any form of electric-powered model aircraft and who may have an interest in an organization of this sort, please send your name, address, and telephone number, plus a stamped, pre-addressed #10 (business size) envelope to:
SEAM, c/o Frank Hecox 11632 Flamingo Dr. Garden Grove, CA 92644
Special interest groups in many areas of airplane modeling have been very helpful in coordinating activities and seeing to the well-being of their interests. Perhaps SEAM will soon take its place alongside the others.
Transcribed from original scans by AI. Minor OCR errors may remain.
