AR-1 gyro manufacturer
- Oct 31, 2011
- Tampa, FL
- Total Flight Time
- 3600+ .. New to gyroplanes
No I did not cut up McCutchens. Just tried them for testing (the 29 foot ones we were supplied for testing) and decided not to use them because of their divergent behavior above 70 mph. McCutchens were really flexible and that actually was part of the problem but in torsional axis.
You want clearance yes. Its not a bad thing but remember what you see by tilting it back is a little meaningless in the sense that in a blade flap you will be at least 1.5 feet lower than that. The blade is not straight when blade sailing, flap is happening. It has a wave in it. It will likely go above the prop arc and droop down in a wave and hit the tail and next time (rev) the wave may catch one prop blade and another a bit lower and so on. It depends on the frequency and engine RPM and all of those interactions. Nothing straight in that phenomenon so this article from BCAR Sec T and from ASRA is not done by someone who understood gyroplanes or even rotorcraft. Its a blind prescriptive rule. It doesn't hurt though. One may argue that it helps if you have a blond moment and let go of the stick when starting pre-rotation (may be). It however needs to be understood that in a blade flap, blade sailing and in flight unloaded rotors, this rule will not do much. The rotors will droop down and touch something. Because all machines in Australia via ASRA system must meet this rule and yet I am sure if you search you can find many examples of gyroplanes with blades cut tails etc. from there.
Remember for a spinning rotor to touch the tail on an AR-1 or MTO where the tail at full aft stick and touching back teeter stop is into the tail a bit, the rotor RPM without flapping has to be pretty darn low. Obviously I can easily takeoff pre-rotating to 150 RRPM and pull the stick fully back and move forward and takeoff so without flapping the rotor RPM has to fall way below 160 to touch the tail. Or you are into a flap or in the air you are unloaded. If you are in those disaster scenarios it doesn't matter what the symptoms are. You have much bigger problems.
The Aero-elastic study of autorotative rotors was done in this Ph.D thesis in the UK and they used "McCutchen" blades.
Not necessary to read and understand the 241 pages of the thesis. Just read the abstract (first 5 pages) 4 times and understand what conceptually was found. Basically torsional rigidity, flexure, position of mass balance in the blade compared to its elastic axis all have to be considered. I can tell you McCutchen blades certainly the large ones did not understand or cared for this stuff and when I offered help to correct it, well I got some words back to the effect that I was in diapers when they were making blades or something like that