Letters To The Editor
All letters will be carefully considered; those of general interest will be used. Send to Model Aviation, 1810 Samuel Morse Dr., Reston, VA 22090.
Piper Skycycle
You and author Ken Wilson are to be commended on the excellent Piper Skycycle article in the March issue of Model Aviation.
Up until now I had only heard a few mentions of this airplane and was unaware that it had ever been kitted by model manufacturers in the past. I had acquired a set of plans for the Skycycle from Cleveland Co. some years ago, and that was the extent of my knowledge of the model.
The many interesting facts Mr. Wilson described certainly held my interest. It's obvious that the Piper Skycycle was a plane designed before its time. Were it marketed today, especially in kit form, it probably would be a business success.
I'm looking forward to seeing someone publish plans for an RC model of it, following this article by Ken Wilson.
Alvin E. Johnson Oxford, PA
More: Airfoils and Moments
I feel that I should respond to Mr. Brownlee's remarks in his critique of my article in his letter to the editor in the February issue.
In his letter he confuses the Aerodynamic Center (AC) with the Center of Pressure (CP). It is the Aerodynamic Center about which there is no movement for a symmetrical section (or a small but constant negative moment for a cambered section). The CP is simply the point through which the resultant of the lift vector envelope acts — in other words, where the lift acts for a given angle of attack. In cambered sections the CP does move — aft with decreases in angle of attack and forward with increases in angle of attack.
Secondly, with some upturned elevon even a Clark Y section can be suitable for a tailless configuration, as long as the CG is properly placed.
After reading his letter, I am still wondering what he had tried to say.
Brad Powers San Diego, CA
Center of Pressure
I must congratulate you on your excellent choice when you printed Mr. Brownlee's letter in the February 1986 issue of Model Aviation, although it did surprise me a bit to see this type of letter. In this otherwise excellent letter there is, however, one sentence in particular that bothers me: namely, the one that says that the CP is where the moment is zero. This sort of language, I feel, would be more appropriate when talking about chordwise bending stresses in a wing panel.
This is how I picture what is meant: A force must be applied to a wing panel to balance the lift, and if this force is strategically located, it will also balance the pitching moment. The location of such a force is called the center of pressure, and if moments are taken about this point, they will add up to zero.
I could stop right here, but you might feel that I am nitpicking. So I will add that regardless of what point is chosen to take moments about, they will add up to zero. Therefore, the CP is not a unique point in this respect.
I also feel that the sooner the CP concept is buried and forgotten about, the better for all concerned.
James E. Brock Amboy, WA
Another MAP Conversion
My compliments to Dick Sarpolus and Bernie Raad on their excellent Model Analysis Program in the January 1986 issue. It took some of the mystery out of model parameters for me. However, even though the program operation is rather straightforward, it was a little awkward to use for repeated calculations, and it uses a lot of paper. This is understandable, since it was intended as a "bare bones" program. So after a couple of runs, I wrote an updated version for my Atari computer. It allows you to make repeated calculations and prints out the data only when you are ready.
There are probably several modelers out there who would like to use the Model Analysis Program but are finding the original a little difficult to work with. I, therefore, am making this version available on a 5 1/4‑in. diskette to anyone who is interested. There is no charge for the program. The system requirements are as follows: Atari computer (except the new 520ST) with at least 32K of memory, disk drive, and a compatible printer with interface. Since the program does not use any special commands, it should work with most printers.
If you would like to try this program, send a SASE with your blank disk to me. Please allow room for the written instructions which are included. The Atari version of MAP will be added to the disk and returned. In addition to the features mentioned above, a special file will be added which will allow the program to load and run automatically. Hopefully, this will make it easier for those with less computer experience. It would be best to enclose your disk in one of the sturdy mailing envelopes made for this purpose. Please make sure your disk is blank. If it contains any files, it will be returned to you unchanged. I hope that many people will find this program useful, and I encourage programmers of some of the other personal computers to join in and help our fellow modelers. Remember, when we share our knowledge, everyone benefits.
Ken Rusnok P.O. Box 116 W. Chicago, IL 60185
Poem: "We've Filed a Criminal Complaint"
Thus, we've filed a criminal complaint, with charges against this guy For shooting down our airplanes, while flying through the sky. It's been a lengthy battle, to prosecute this sin. And as we come down the home stretch, I hope that we will win.
Now, before I leave this office, I have a recommendation to state: Let's finish up our court case, and then forget about our hate. We've lived through three years of problems, and for some of us, it's been rough. Let's get on with the sport of model aviation — we've suffered long enough.
Mike Barklow Appleton, WI
In an accompanying letter, Mike said that the foregoing poem was written in 1983 when he was stepping down as president of the Valley Aero Modelers. It was for the club's newsletter but not printed due to a suit then in progress. Despite best efforts the club lost that flying field and was in the doldrums for a brief period, but by maintaining a positive attitude, the group was able to establish a new flying site and rebuild itself so that it is now bigger and better than ever. "This was very gratifying to me and to our organization," Mike notes.
My only comment on this incident is to repeat something I've said several times previously: consider a pair of safety glasses when starting your model and when working in your shop.
Have a safe month.
John Preston 12235 Tildenwood Dr. Rockville, MD 20852
Transcribed from original scans by AI. Minor OCR errors may remain.
