The Razorback
The Razorback
Hi,
As far as I can tell, there are no compelling reasons to design a new pusher gyro, other than nostalgia or the feeling of familiarity they provide. For my money, it is tractors all the way. Every time I have tried to design a pusher, I have run into the issues of obtaining CLT without resorting to the "daddy-long-legs" approach adopted by the Dominator, a look I find personally unappetising.
I can also see no valid reason to design yet another RAF look-alike, with its cruciform tubular airframe (with or without dropped keel), chopped off pod, exposed engine, and tail feathers tight up against the prop. There are already a host of machines available with variations on this basic configuration. Why add another?
For me, the entire concept had to be re-thought. My design guidelines needed to include as must-have's:
- Tractor configuration
- Large tail moment arm
- Hidden mast pylons
- Enclosed and aerodynamic fuselage
In the "Nice to have" department were:
- JTO (or VSTO)
- Collective pitch control
- Residual Rotor Power
- Wings
In order to get the rotor head in the correct position relative to the aircraft CG, all tractor designs to date have opted for rotor pylons either fixed to the cabin roof (eg: Littlewing) or an arrangement which obscure the view of the pilot (eg:Michael Guard's tractor design, the Russian tractor featured on this forum some time back, the Raven Redrive tractor et al). I decided that this was inelegant and unnecessary, so designed a cantilevered beam reaching from behind the pilot to place the rotor head in the correct position. My initial fears were that this would place too great a strain on the beam - but is has been designed to withstand over 10G's, yet weighs very little indeed.
The next major concern was providing sufficient tail and HS authority. Try as I might, I found it impossible to provide this sort of authority by using the traditional tail surfaces fixed from below. My best attempts were marginal at best, and I did not want to resort to the main tail + side winglets solution. I think it looks yuk. It all has to do with that pesky rotor blade swinging so close... So I opted to use a "rafter" fixed to the rotor head angling down, and invert the tail feathers. This provides a guaranteed rotor clearance, and also provides more than sufficient tail authority. Sufficient clearance between rotor blades and tail can be achieved two ways: Use elevators on the tail for pitch control, and save 9 degrees of rotor incidence by fixing the rotor head in the fore/aft plane (eg: early Littlewings). In this configuration, there only needs to be 19 degrees of clearance between the blades and the tail. Or, use the more usual fully articulated rotor head design, and raise the mast to provide 28 degrees of clearance.
Finally, the enclosed fuselage. If you want to sit on a broomstick out in the open air and fly low and slow, I have absolutely no problems with this. None at all. But if you want to fly fast, and in a degree of comfort, this aspect of gyro design needs a radical overhaul. My reading of this forum over the years has highlighted a number of current concerns in this gyro community, and near the top of the current wish-list for most pilots is the desire to fly faster. Almost every discussion about engines, props or blades has as a major theme our desire to fly faster. So - design a gyro with as clean an aerodynamic fuselage as fixed wing aircraft.
In order to do this, consideration needs to be paid to construction techniques. A good enclosed fuse has to include fairing in the engine, either pusher or tractor, and this can certainly be accomplished using the traditional aluminum tubing airframe. But it is so much more elegant (in my opinion) to build the airframe out of composite materials. The lines can be more subtle, the angles more gradual. I am building a completely composite (CF/Kevlar) fuselage not only for aesthetic appeal, but also because it is hugely strong for its weight.
The remaining "Nice to have" list is optional, of course. I'll be introducing each of them after the gyro is built and flying. No rush.
That about sets the scene for the Razorback. Check out the drawing below. I've been stalled by local companies taking extended Christmas breaks of late, but everything is back on track to begin construction this month, so actual photos soon.
Regards,
Duncan