Astro Challenger (oz14610)
About this Plan
Astro Challenger. Radio control sport model. Wingspan 70 in, wing area 630 sq in, for electric power with Astro Cobalt 05 motor.
Note plan shows installation of both direct drive and geared motor.
Direct submission to Outerzone.
Update 9/6/2023: Added article, thanks to RFJ.
Quote: "A Nationals winner in electric competition! Astro Challenger, by Bob Boucher.
I began designing the Challenger right after our tenth annual Astro Championships in February 1984. At that contest Mike Regan amazed everybody with the fantastic climb of his electric Mirage sailplane. Mike used the new Astro Challenger Cobalt geared motor with seven Sanyo 800 mAh nicads. I figured that with a model designed especially for the geared motor, I would have an unbeatable combination for the Reno Nats.
Using my IBM computer program I tried various combinations of wing area, wingspan, and airfoil sections. For these calculations I assumed that the model would weigh 38 ounces complete with motor, battery, and radio. The actual model weighed 39 ounces. The computer said that the model with the best still air time after a one-minute motor run would have an Eppler 193 airfoil, a span of 6 feet, and a wing chord between 8 and 9 inches.
Using these parameters I began to lay out the model. I wanted to try a flat center section and an open frame wing for minimum weight and minimum work. In order to eliminate the requirement for washout to alleviate tip stall, I chose an elliptical planform for the wing tips. I matched this with an elliptical stab for a distinctive and pleasing appearance. This wing/ tail combination really works. The glide is superb and the model just won't tip stall. Another bonus of eliminating washout is that with the power on, the Challenger will fly inverted and do nice rudder rolls. The Eppler 193 is thick enough so that the MonoKoted wing is torsionally stiff to resist flutter, even in steep descents.
The power train consists of the Astro Cobalt 05 geared motor and seven Sanyo 800 mAh fast charge nicad cells. I chose the small Geist prop (13x7) and the Astro electronic switch. The total power system weighs 19.6 ounces. My model with radio weighed 19.9 ounces.
Using the computer simulation of the model glide polar combined with a simple model of the propeller characteristics, we can calculate expected climb altitude as a function of lift coefficient. Table 2 shows the results of these calculations and indicates that climb altitudes of almost 1,400 feet can be obtained with a one-minute motor run. Best altitudes are obtained when climb angle is held between 20° and 30°. From this altitude still air glide times of over 16 minutes can be expected.
Table 3 repeats the same computer simulation but with a direct-drive 8x4 propeller installed. The climb performance is a bit less dramatic, but nonetheless the Challenger can easily max in still air with a one-minute motor run.
CONSTRUCTION: The construction of the Challenger is straightforward. The wing and tail use conventional open frame construction. The wing has spar webs extending all the way to the wing tips for maximum strength. Both spars and the leading edge are bent backward to achieve the elliptical planform. I built the original wing dry, but if the bending of the spars and leading edde seems difficult, the wet the spars and leading edge, towel dry, and you should have no trouble bending them..."
Update 9/11/2023: Added kit review from Model Builder, February 1989, thanks to RFJ.
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User commentsI've been looking/waiting for this one to surface! My dad got into electrics (away from the icky gas engines and boat distractions) and this was one of the first planes he built (for electric). He got good at doing conversions for the guys in his clubs :D
des - 09/06/2023
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