Letters to the Editor
Editor's note: The April 1995 issue contained a Letter to the Editor from Don Tyndall that appeared in final form with a jumbled sequence of paragraphs. Apologies from our staff to Don for this unusual error; here is the correct text:
Letter: Don Tyndall
I read with interest "The Myth of the Terraced Airfoil" by Jim Petro in the February 1995 issue. While not persuaded by Jim's arguments regarding terraced airfoils, I was more intrigued by his closing statement about Bernoulli.
Poor Jakob. It's not his fault. Bernoulli never said a wing generates lift because the airflow over the upper surface has a greater velocity and therefore lower pressure; rather, he dealt with the airflow across the bottom of the wing. Bernoulli's experiments dealt primarily with hydraulics, so it's doubtful he gave much thought to airplane wings—especially since he died in 1705, about 200 years before much flying was being done.
No, the blame lies with those who seek to apply Bernoulli's discoveries where they don't belong. Yes, it's true that pressure decreases as velocity increases—we see this in our carburetor venturis all the time. And it's also true that the air pressure on top of a wing is less than on the bottom. But it's not necessarily true that this reduced pressure, supposedly caused by the difference in air velocity over the curved upper surface versus the flat bottom surface, "sucks" the wing into the air. It doesn't even play much of a part in allowing the greater pressure on the bottom to "push" the wing upwards.
Think about it. If this theory explains how a flat-bottom airfoil generates lift, then how is lift generated by a symmetrical airfoil (aerobatic airplane), or a flat-plate airfoil (simple sheet-balsa glider), or a single-surface airfoil (kite, paper airplane, hang glider)? And how are we able to fly a flat-bottom wing inverted?
The answer to this question is "with a lot of forward stick." Which is also the answer to how a wing generates lift. A wing generates lift through angle of attack. Tilt it up a little, it lifts a little. Tilt it up a lot, it lifts a lot. Tilt it up too much, however, and it stalls. Which is why the upper surface is designed with a curve in it to smooth the airflow to allow a higher angle of attack prior to stall. It's not to speed the airflow over the top to suck the wing into the air.
So let's not blame Bernoulli. He never "claimed" that top-curve airflow must catch up with lower airflow, as Mr. Petro wrote. That was done by some other fellow. Let's find out who he is, and de-myth him!
Don Tyndall Warwick, New York
Modeling in Vietnam
Maybe you are amazed to have this letter on hand. Please permit me to introduce myself.
I have been a modeler since 1947 (in North Vietnam). I worked for SALS (an aeronautical training center) from 1955 in the South in charge of the modeling section and for the House of Children (1975–1991) in the Young Pioneers/Modeler section.
We practiced every kind of model. But at the present time only the RC modelers are in full activity—the only active group in our country.
In former times, we were about 25 local adult modelers and a dozen U.S. servicemen. Now almost all of them have immigrated overseas, as well as a dozen of my new young pupil modelers!
There is no more activity at the House of Children because we no longer have facilities. But a dozen adult modelers are still active with RC, including helicopters. Sometimes we receive copies of RCM or MA from our relatives, so I have the address to write to you today!
What do you think about our modeling activity? May we call on you for help? You can learn more about us by asking Mr. Harold G. Cowan, who flew with us in 1973–75 in Saigon.
Nguyen-Quang Ru Ho Chi Minh City, Vietnam
'Fledglings' Update / Comment
I am happy to report that Joseph and David, the two fledglings in the article "Two Fledglings Earn Their Wings" (March 1995 issue), are still enjoying the hobby. Joseph has an Estes rocket-launched glider under construction at the moment, and David is working on a Great Planes Trainer .60.
The March 1995 issue of Model Aviation will always be a treasure in our family. Thank you.
Van Twelves Stuart, Florida
I've just got to tell you how much I enjoyed reading Van Twelves' article in the March issue! It brought back so many delightful memories of teaching my sons something about model airplanes—both the innocence of the kids and my own idiosyncrasies.
Doug and Jeff were 9 and 7, respectively (Doug's now 48), and were my guinea pigs in the development of the Cub Scout Special. This all-balsa, 12" stick rubber job was designed and kitted for members of Cub Scout Pack #196, Queens, N.Y. The kit sold for 35 cents, if I remember correctly, including mimeographed plan and instructions, all necessary balsa, a prefabricated front end (aluminum-tube bearing, plastic prop, a music-wire shaft, and a couple of washers). I made seven dozen kits and parts of the models were all over the neighborhood for weeks after that Pack meeting. Plans were ultimately published in an Air Trails Annual.
But it was Eric (now 48) who really latched onto model airplanes. At five, he was handy enough to be trusted with sharp tools, but he just didn't comprehend sandpaper as a shaping tool. I'd say, "make the glider wing like this," and show him a carefully airfoiled piece of wood. Then he'd produce a piece of sheet balsa with rounded edges. I was really defeated. He had the run of the shop and any non-power tools he wanted to use, but we didn't work on any more airplane projects until about five years went by and he made a model boat with a round hull. "Now you're ready," I said, and he resumed model aviation very actively and successfully until he got his first car.
Long before that came to pass, however, he decided his youngest brother Richard—then 3 or 4 years old—could have razor blades to play with while the old man was at the office. Now 31, Rich still has all his fingers and uses them with skill and artistry.
Please pass along my thanks and congratulations and a copy of this letter to Van Twelves! He did a great job—in more ways than one!
Robert Hatschek Douglaston, New York
Les Weise
I would like to make AMA members aware of some of the accomplishments of Lester (Les) Weise, a pioneer modeler from Cincinnati, Ohio.
Les built and flew his first gas model plane in 1936. Intrigued with the idea of obtaining control of his models, he developed and flew a sophisticated system of tethered flight during 1937. An article in the Cincinnati Enquirer dated August 28, 1938, features a photo of the plane and a description of the system. Les was 22 at the time.
The plane was a typical free-flight design of the period: a nine-foot-span cabin model powered by a Forster .99. The control system employed two horizontal sticks mounted below the left wing, pivoted at their center. Four lines 8 feet long were connected between the stick ends and a joystick mounted on a horizontal pole. Linkage within the plane and at the joystick allowed movement of the ailerons and elevators, plus throttle control.
From 1945 until his retirement in 1980, Les operated a popular and well-stocked hobby shop in the Cincinnati area. During that period Les' interests included model railroads, boats, and planes. His fleet of paddle-wheeled riverboat models, including a six-foot replica of the Delta Queen, has been on display on numerous occasions in connection with local events. His version of the Delta Queen was presented to the Smithsonian.
Although Les has maintained a lifelong interest and participation in model aviation, he has also been involved with full-scale projects. These have included hot-rod car construction, piloting light aircraft, and the construction and piloting of ultralights. His full ultralight was a 3/4-size Curtiss Robin, which he scaled up from an 8 1/2" × 11" drawing of the original aircraft. He flew that in 1993. His sixth ultralight is a high-wing monoplane that he designed, built, and flew in 1994.
Les Weise, a true Renaissance man, is an inspiration to fellow modelers in our area.
Robert S. Munson Cincinnati, Ohio
Hand-Launched Glider (HLG) Tips
- Grip: Avoid a grip that is too tight. A too-tight grip can tire your hand easily and cause you to lose the "feel" for the glider in your hand. Comfort—repeatable comfort—is the key.
- Footwork: You will be turned perpendicular to the target (like a quarterback when he drops back to pass—his body is turned sideways). How many steps you take to get ready to launch is up to you—only two or three steps are really necessary, but if you feel better taking several steps, do what is comfortable and something you can do consistently.
You must reach the launch point with the glider banked (right wing down) perhaps 20°, and ready to step forward with your left foot while pushing with your right foot and throwing the glider upward at an angle of 60° or more—all the while keeping your eyes on your target.
- Timing: If everything works as planned, the right back of the glider will counteract all the left-circle adjustments you have built in and the model will make one spiral to the right, rolling over and into the left glide turn.
The tricky part is getting your feet and arm coordinated so that you get all available power into the launch. If the glider lags behind your feet (early release), a weak launch will result; if the glider gets ahead of your feet (late release), you could actually throw the glider into the ground, or at least have a loopy, fish-out-of-water launch.
As with the throwing motions of other objects (balls, javelin, etc.), there is a moment of truth—a fraction of a second where, when your timing is right, the glider is cocked behind you and your weight is on your right foot—when you commit to the launch. After this instant, the launch is executed in a whoosh of motion. Your left foot comes forward, you push hard with your right leg, your shoulders rotate into the launch, and the glider whips forward and up. A sharp, almost ringing whistle will result—the unmistakable sound of a strong launch.
- Practice: Once you have achieved this launch motion, and you see the power it generates, you'll want to do it again and again. You'll be able to see and hear when a launch isn't up to par.
Now it's a matter of practice. Each glider design has its own sensitivity to adjustments, and only practice will give you a feel for what's required for successful flight. Try several designs until you find a model that suits your arm strength and flying style.
No matter what modeling discipline you eventually choose, this most basic model type can provide hours of enjoyment and teach the builder an enormous amount about the fundamentals of model flight and trim. Give HLG a try!
If you have any questions about HLG construction and trim, seek out a local expert or write to me c/o Model Aviation.
Transcribed from original scans by AI. Minor OCR errors may remain.
