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May 31, 2018, 11:42 AM
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T - Tiny 1-cell Twin Gyrocopter


This is my Twirl Tiny 1-cell twin gyrocopter that borrowed heavily from the great Twirl autogyro design by Al Foot. I scaled down his plans to 33.8% for a rotor-to-rotor span of about 10 inches, and adapted a frame work of carbon fiber to his geometries. After adjustments and alternations over several months the power is provided by a 7mm coreless motor with 4:1 ratio gearbox, 4 inch propeller, and a 130-140mah lipo. Weight RTF is 23 grams with a Spektrum Mini-Vapor circuit board for control.

For the first flight, I had installed a 8.5mm motor and gearbox but found thrust excessive and marginally stable. Below is what I wrote on March 29, 2016 to a friend who owns the Twirl:

"Flew the Twirl Tiny this afternoon for the first time in Mom's backyard. Close to dead calm air, but not quite. Took several attempts to obtain stable flight. I added about 25% of the available left rudder trim to counter the right thrust. Plus around 5-6 clicks of up elevator, and moving the lipo fully toward the tail to counter the shallow nose dive. Once flying straight and level the Twirl Tiny is responsive to the tail surfaces. Turning well to the left and right, more or less equally. Throttle needed was only about 45-47%, but even so it was fast. Too fast to be indoor flying friendly. Fun and encouraging!

A strange behavior occurred three times. The aircraft nosed upwards and the rotors slowed until the fuselage was hanging vertically underneath the propeller, and the tail was doing the toilet bowl wobble. Just hanging on the prop with the tail feathers swinging in a circle as I look at the top of the rotors. Fortunately the 8.5mm motor has plenty of thrust to hover and I controlled the landing for a tail first touchdown. You see this behavior with your Twirl, right?

Thinking about the next steps. I want to reduce the high wing loading by replacing the 8.5mm motor with a 7mm one. This will include the smallish gearbox that I fly on the Saucer 1982. Less power should permit a smaller 140mah lipo instead of the 240mah. Hopefully not giving up too much prop thrust. Plus I can remove all of the right thrust easily. And if this change still isn't finding a reasonable balance for my Twirl Tiny then I may add a second wing below the existing one. Interesting project! "

- Curt
Last edited by CorvetteC5; May 31, 2018 at 01:46 PM.
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May 31, 2018, 01:41 PM
Way to much free time!
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After months of tuning and flying, I increased the stock wing size by about 4 times the area using cut-offs from the Parkzone Ember 2 wing. The wing halves were left overs from an Ember 2 twin-fuselage design that Dad was flying. This is a big cheat I know, but allows my Tiny to be throttled back and flown much more slowly. The rotors are mainly there for looks, drag, and stability now. Before the wing change I found the power requirements from the 1-cell lipo to be unacceptable for regular use during the indoor RC flying season. A better approach will be to create a larger 2-cell version of Al Foot's Twirl where power and thrust will not be so marginal.
Apr 15, 2019, 12:19 PM
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Flying Video!


Twirl Tiny 1-cell powered twin autogyro RC aircraft (3 min 28 sec)


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