"Heli-TWIRL"...  a .15 Powered, 36" rotor, Fixed pitch heli-head , direct controlled autogyro
Jim Baxter, updated November 1998
This is another light model that is slightly larger than a Minnie, yet 10% lighter, and has a rotor that is also slightly larger, therefore a better (lighter) disk loading...

Although I am not a fan of using helicopter components for autogyros... (I personally don`t consider a model with such parts a "true autogyro") I had the Kyosho Hyperfly mechanics and decided to build this model to utilize the components., and test how well it may perform... 
The advantage of this model will be the capability to utilize a larger rotor and still be able to control the model by changing the rotor blade pitch through servo control, without the rotor actually tilting like the normal DC model function.....  
The rotor will fly relatively level, while the model does the tilting and pitching while maneuvering.......  With the normal DC model, the rotor noticeably tilts first, followed by the model changing direction.

Top photos.. original version...Click on a thumbnail photo for a larger view...



Bottom photo (foreground), with the modified tail... Click on the photo for a larger view...
FLIGHT ATTEMPT #1:  This model successfully completed its first flight attempt on 15 March.   Knowing it might be a problem to get this type rotor to pre-spin, I was not surprised that an ROG attempt failed, especially since this older .15 engine did not seem to have a lot of power.   Noting that the rotor spun very well when held nose high into the wind, I elected to make a hand launch.     One never knows, with a completely new design, just how in/out of trim a model may be the first time, so I nervously released the model and hoped for the best... and IT FLEW!... The aft trim (aft rotor trim neutral) was insufficient along with the weak engine power, and even with full aft stick the model would not gain altitude and flight was aborted after about 1 to 200 feet of flight.    Roll throw was noted to be insufficient, so I feel that after adjustments in the aft tilt trim, an increase in roll throw, and an engine tuning... this model has an excellent chance of being a good flyer.   I was very satisfied with this first flight test.
FLIGHT ATTEMPT #2:  March 18th,  Completed a flight to include approach and landing.  However it flew in a right yaw, and would not turn left.  Pitch control was good,  and while turns to the right were rather strong, I was able to complete a right circling approach into the wind... Planned corrections:  increase in left throw in both the rotor and rudder.   Possible left tilt offset of a few degrees being considered. With this being a CCW rotating rotor it is not unusual to have left offset trim.requirement..
FLIGHT ATTEMPTS # 3 -4,  late march:  The installation of a few degress of left rudder and a left tilt now has the model flying without a lot of right yaw... and it -will- turn left, although not without some difficulty...  More work needed...
Flight attempt #5, in early April, continued to be plagued with severe problems of it wanting to "resist"turning.
** mid-April...  A series of short (200 feet long) straight flights were conducted to see exactly what it was doing and if -any- kind of trim would solve this mystery... well after 3-4 flts, nothing seem to work, so I REMOVED the horizontal stabilizer... and guess what, it FLEW straight as an arrow...  It required full down stick, but that`s something that should be easiily corrected.
Early May flying:  Installation of the small stab shown in the bottom photo solved the pitch problems, now with the problem of completing a "coordinated" turn still being there... the rudder size has been increased and the rotor roll rate reduced...  awaiting the next test...
Late May:   Model is flying, but is somewhat a handful... I keep getting closer to a "comfortable" flyer, but that may be just due to experience with flying it.  A slightly smaller rotor size (36") has been tried and does not seem to make any significant difference..
June... somewhat frustrated, and ready to toss it in the trash, I elected to try installing counter-clockwise blades and reversing the flybar.   The only "left handed" blades I had avail'  were some left over FA-61 (lower aspect ratio) ones...    Amazingly it has responded well to the changes.   Control is smoother and more predictable.   Hovering is now possible into a nice breeze... ALTHOUGH... as it approachs a stall at about 45 degrees nose high, the fuselage (if you relax on the rudder & tilt) will rotate horizontally (torque?) into the advancing blade.. very quickly...
I`m now satisfied the model is decent, and can be eventually re-designed / re-built to correct the scars, etc., of experimentation.
November 1998:   Model deactivated, with radio, engine, etc., all removed for a new model....
FINDINGS:  The use of a fixed pitch heli-head on a small autogyro does not result in any improved performance or control over a simple dc only gyro...   The dc model is easier to build, easier to fly, and certainly less expensive.

Model Specs:

  • Rotor diameter = 35" (currently)
  • Gross weight w/fuel = 25 ounces.
  • Low aspect rotor blades, clark Y airfoil, thin.. with a very flat bottom.
  • Blade incidence = aproximately 1 degree negative.
  • Engine = Thunder Tiger .15 gp



rev..11-18-98..jb