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.
Taperwing Typo
With reference to the article by John Hunton, starting on page 52 in the January 1989 issue of Model Aviation, there is a typo near the bottom of page 53 in the line:
Dt = 0.5 rho V^2 Cd S
The term V should be V^2, and the next line obviously used 1/32 x 1/32 (or V^2) to arrive at the value of Cd(T).
I agree that the 90 mph versus 79 mph for the GLH is based on simplified assumptions. I know nothing about either model but would expect that the drag of any aerodynamically clean model would mostly arise from skin friction for the case considered (max speed, very low CL), and the relative speeds with the same engine, prop, fuel, weight, etc., would depend mainly on the total model surface area (wing, fuselage, tail).
John W. McKee Baytown, TX
Control Line Speed model
I enjoy reading Model Aviation, and the article on the Taperwing 1/4 A Pylon Racer was no exception. I was especially interested in John Hunton's performance comparisons of the GLH and the Taperwing, as I had previously calculated the performance of a number of 1/2A CL Speed planes. For comparison purposes, the assumptions I made and the resultant performance are as follows:
- Assumptions:
- Weight: 0.5 lb
- Engine power: 0.15 bhp
- Propulsive efficiency: 70%
- Wing area: 21 square inches (required for 30 mph takeoff)
- Control lines: two 0.010 in. diameter by 42 ft long
- Results:
- Total drag: 0.43 lb
- Wing drag: 12%
- Body drag: 7%
- Line drag: 81%
- Top speed: 89 mph
As the calculation results show, the control lines are by far the largest component of total drag. It becomes immediately apparent why the engine power and propeller efficiency are so important to the success of a Control Line Speed model.
Paul Rice Richland, WA
From 1946
Enclosed are two photos of a Control Line P-51 my dad brought me back in 1946 prior to December 5. It is all aluminum except for wooden wing and stabilizer tips, riveted together. The two props I have with it are stamped "Miniature Motors P-51," and it is powered by a .29 Bullet engine. It was flown twice, both flights being successful.
Gordon T. Bland Temple, TX
Pulsemaster 64
I especially enjoyed the article entitled "Pulsemaster 64" by Bernard L. Stuecker in your December 1988 issue. After reading it and considering all that it seemed capable of doing, I wrote the author to obtain the software and one of the available connectors. Bernie was especially prompt in supplying these, and it was only a few days later that I was able to construct the circuit. The results were quite gratifying. No problems were encountered in the wiring, and the software works just as claimed.
Of even more interest, while using this unit I finally identified the real cause of erratic behavior of one of my RC models. The elevator servo was defective; it had an unusual amount of overshoot (about 12°) when its direction was reversed. No wonder we kept "chasing our tails" trying to get the model trimmed (both physically and electronically). After replacing that servo (which was almost brand new) with another of similar type, trimming was a snap. Now the model flies just as we felt it should.
I plan to take the test device, along with my C-64 computer, to demonstrate its features at our next club meeting. If there's enough interest, we will make up some adapter connectors so various kinds of equipment can be tested.
Olin K. McDaniel Florence, SC
BT-7 and BT-9 Again
In the letters section of the January 1989 issue, there is a discussion about the BT-9. For reference, your caption said "Really a BT-7." Mr. Caton is correct in his identification of the BT-9. Mr. Kaman was only slightly correct in saying the BT-9 was the fixed-gear version of the AT-6.
Perhaps I can clear this up and, at the same time, identify two North American trainers that, to my knowledge, have never been modeled.
North American produced at the same time a basic trainer, the BT-9, and an advanced trainer, the BC-1. The BC-1 was similar in basic configuration to the BT-9 with the rounded vertical fin. However, the BC-1 had a larger engine, retractable gear, and a constant-speed prop. The BT-9 had a two-speed prop. The "BC" designation for the advanced trainer meant Basic Combat.
Later, North American improved the breed. They produced the BT-14 and the AT-6. The BT-14 and the AT-6 each had the now-familiar sharp-pointed vertical fin. They were of the same rugged construction with the same honest, forgiving flight characteristics as their forerunners, the BT-9 and BC-1.
I took basic training at Randolph in the winter of 1940 when the big push was starting to produce pilots. The cadets were divided into two flying sections: one flew the BT-9 and the other the BT-14s. I flew the BT-9. I went to Brooks Field for advanced training and flew the BC-1 and AT-6. Flight characteristics and cockpit configuration were almost identical. When I graduated from Brooks, I stayed as an instructor. My cadet students experienced no difficulty whatsoever in transitioning from the AT-6 to the BC-1 or vice versa.
Kelly Field also had the same mix of BC-1s and AT-6s.
I'm retired from the USAF now, but in my travels I have seen the wonderful AT-6 around the world. Seems like no matter where I go, you will see either an AT-6 or a Gooney Bird.
Mr. Caton mentioned flying the AT-9, a Curtiss-built twin-engine advanced trainer. I can't understand why scale modelers haven't discovered this bird. It is a beautiful machine with the typical very skinny Curtiss fuselage at the empennage and a large, bulbous side-by-side cockpit. I flew them at Lubbock, and it was right sporty.
The AT-9 was designed to give cadets experience in a twin-engine bird with a high wing loading—and it did just that. If you chopped all power and dropped flaps and gear, you'd better be sure a runway was directly under the plane, because you sure couldn't glide to one. This bird was nicknamed "The Mole" because of the bulbous nose. I seem to recall that Wylam once did drawings for this plane.
I hope I have clarified some of the differences of these planes. The BT-9 was the fixed-gear version of the BC-1. The BT-14 was the fixed-gear version of the AT-6.
Del Wood Coeur d'Alene, ID
Transcribed from original scans by AI. Minor OCR errors may remain.
