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Old 02-07-2009, 05:54 PM
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blackshire blackshire is offline
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Join Date: Jan 2009
Location: Fairbanks, Alaska
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You all are most welcome! I have seen both the Campbell and Sting Aero Products HLGs (Hand Launched Gliders) online, and that thought (that they could make fine boost-gliders) had crossed my mind as well. When I first heard of the discus HLG launch method some time ago, I thought it was some kind of F/F (Free Flight) aeromodelers' "in-joke"--until I saw photographs of it being done.

Also, this morning I found these downloadable balsa chuck glider plans on the Tom Martin Radio Control (TMRC) web site: www.tmrcsailplanes.com/plans-and-patterns.html

These are classic Jasco, Jetco, and Frank Zaic designs (they're near the bottom of the "screen-page" on the TMRC web site) that people have built and flown for years. Tom Martin also has laser-cut kits of some of these available. The Jetco Thermic 18 and Jetco Thermic B are just like pop-pod front-motor boost-gliders. In fact, you could easily convert these to boost-gliders by adding pop-pod attachment points at their front ends and by moving their vertical stabilizers to the bottom side of their fuselage booms.

Speaking of Frank Zaic, G. Harry Stine made extensive use of the information in Mr. Zaic's book "Circular Airflow and Model Aircraft" (Northridge, California: Model Aeronautical Publications, 1964) to develop his "Stine's Basic Boost-Glider Design Rules" in his "Handbook of Model Rocketry," and Mr. Zaic's book is listed in its bibliography section. In fact, Stine even wrote that "These Design Rules will also produce a very fine chuck glider for hand launching." Stine designed the MPC (now Quest) "Flat Cat" boost-glider kit using these rules.

One thing in particular from Stine's rules that I found very interesting is that (to quote him):

"And it isn't really necessary to use the classic model airplane airfoil that's curved on top and flat on the bottom. A symmetrical airfoil, such as used on [rocket] fins, will glide just as well (and perhaps better since its CP [Center of Pressure] remains at or near the 25 percent chord point [back from the wing's leading edge], whereas the CP of a flat-bottomed or *cambered* classic airfoil moves *forward* with increasing angle of attack, introducing another variable into an already complex system)."

The wings of aerobatic airplanes (both full-scale and models) use symmetrical airfoils because they work just as well when flying inverted (upside-down) as they do when flying rightside-up. Using just a degree or two of nose-up trim with either a fixed horizontal stabilizer or movable elevators is all that is necessary to make a symmetrical airfoil generate lift.

Stine also wrote that both the wings and the horizontal stabilizer of a boost-glider can have zero incidence (having them mounted on the fuselage boom at zero degrees angle of attack, that is) *if* the horizontal stabilizer is located both behind *and* below the wing. This places the horizontal stabilizer in the downwash from the wings (which "fools" the horizontal stabilizer into "thinking" that it is flying at a slightly negative angle of attack). This prevents the boost-glider (in glider mode, after the pop-pod has been jettisoned) from pitching down into the upward-angled relative airflow and diving into the ground, as an ordinary non-gliding model rocket would.
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