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Round-the-Pole Circle Whirly - The Jumpin' Giro
Annual 1958 Air Trails Hobbies for Young Men

Annual Edition 1958 Air Trails
Annual Edition 1958 Air Trails Cover - Airplanes and RocketsTable of Contents

These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

Here is an unusual project for the control line enthusiast. Bob Tennenbaum's Jumpin' Giro is an autogyro craft that due to its potential for slow, helicopter-like flight, can be flown in a small area. That makes Jumpin' Giro a good subject for old-timers who don't suffer spinning in circles well anymore. It is designed for an .020 glow fuel engine, but a small electric setup can be easily substituted. The rotor span is only about 14-15 inches, and as designed there is no form of control; it simply flies in circles on its own. There is probably not enough centrifugal force on the tether line to provide positive control, but use of an R/C controlled electric motor would add to the fun. My guess is it should only be flown in no wind or very light wind conditions. That leaves out most days in my Erie, Pennsylvania locale. Mr. Igor Bensen had recently (1955) introduced his Bensen Gyrocopter when this article appeared in the 1958 Annual edition of Air Trails magazine, which was featured in all the hobbyist and do-it-yourself magazines, so that could have been the motivation for Jumpin' Giro.

Round-the-Pole Circle Whirly - The Jumpin' Giro

Round-the-Pole Circle Whirly, Annual 1958 Air Trails - Airplanes and RocketsBy Bob Tennebaum

Jumpin' Giro is an ideal model for schoolyards, small parks and gyms. Any place where an 8 to 14-foot tether line can be accommodated is room enough to fly this RTP model. It is almost indestructible and it cannot stall. Four-bladed rotors provide over three-quarters of the lift, small stub wings are for lateral stability and model can be flown without these. The pylon around which the model flies should be from 30 to 36 inches high with a good strong base.

Round-the-Pole Circle Whirly: The Jumpin' Giro - Airplanes and RocketsThe new Pee Wee or old Infant .020 takes this model up nicely; no larger engine should be used as the speed would be too great. Our Infant was shock rubber band mounted, which helps when you have to put in some more side or down thrust. The small stub wings plug in so you can experiment with different flight trims. A 5x3 wooden prop provided the thrust. This model is ideal for air pick-up tricks or other similar stunts. I would suggest a large tank to provide longer time in the air.

Construction is very simple. Entire model is of medium grain 1/16 inch sheet balsa. Build the crutch, then cement two sides to it. Add formers B2, C, D, E, F. Cement in dowel and box for wings. Install lead out wire and landing gear. Build pylon as 1/6, 1/32, 1/16 inch sheet balsa sandwich with the 1/16 SWG wire shaft in between. Cement to fuselage. Sheet top and bottom. Cement stab and rudder with offset in place, install tail skid. Build stub wings for tight fit in the box. Give four coats of clear dope and two of fuel-proof color dope.

The Jumpin' Giro: Round-the-Pole Circle Whirly - Airplanes and RocketsBlades are 1/16 inch sheet hard balsa. Straightened paper clips or 1/16 inch SWG wire is cemented to each blade leading edge, then soldered to a tin disc which is the rotor hub. This hub can be made from a V-127 film spool disc (sand off black enamel). The bearings are 1/16 inch ID copper tube about 1/4 inch long soldered to disc. Make sure it is truly vertical. Blades should have about 2 to 3° negative incidence, and add a slight bit of dihedral. The rotor spins counter-clockwise.

Model should balance 1/2 inch back from engine mount, but no farther, and should be nose heavy to increase stability in flight. Let it taxi into wind. This is important as wind will start the blades rotating sooner, and let model ROG sooner. It should take off in about 4 to 5 feet from point of release.

Nylon fishing line can serve as a tether.

Round-the-Pole Circle Whirly: The Jumpin' Giro Plans, Annual 1958 Air Trails - Airplanes and Rockets

Round-the-Pole Circle Whirly: The Jumpin' Giro Plans



Posted January 16, 2021

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