- Oct 30, 2003
- Givens Predator
- Total Flight Time
- 2400+ in rotorcraft
When discussing the use of real-world thrust number actuals as a comparative index across the many types of gyrocopters one might consider, instead of just reported HP claims and ratings, some great info is contained in this article concerning power loss through shafts and transfer cases.
Understanding drivetrain power loss, or how the clutch, gearbox, diff, shafts, et al leach away horsepower and whether the “15% rule” is indeed universalwww.superstreetonline.com
It is easy to understand that a direct-coupled Lycoming will transfer significantly more power to the prop, and thus produce more thrust per rated engine HP, than, say, a Yamaha Apex with one of Teal Jenkins' three-gear tractor FW gearboxes mounted on it; or that a Mohawk Silent Drive Hy-Vo chain drive is far more efficient than any gearbox at all.
The many configurations of redrives/PSRUs used on aircraft powerplants of all types makes it impossible to nail down a single efficiency number that fits every case.
Therefore to be summarily dismissive of thrust testing as a suitable means of determining power delivery to the prop and predicting aircraft performance is foolish, if not arrogant.
As for me, what I have tested and found personally over many years of work is what I stated prior. Prop efficiency is a mathematical equation that does not lie. It is a straight-forward trig, physics and real-world measurable of either static thrust or true air speed, with the difference being in generating the propulsion of air from a standing-still, steady state vs forward aircraft motion creating an apparent movement of air through the prop before being propelled by it. In the latter case, prop efficiency is a real-world, hard facts number determined by comparing theoretical distance to be moved over a given time period according to prop pitch compared to an actual, tested, measured distance an aircraft moves over a given period of time, or AS, and taking into account airframe drag.
Static thrust tests are lots of fun because of the noise and drama involved.
They are also easy to perform with relatively inexpensive equipment.
In my opinion based on my experience; static thrust is not an accurate representation of horsepower output or particularly useful as a flight performance predictor.
I feel there are simply too many variables
Having watched many static thrust tests it appears to me that how the propeller is pitched may have a very large effect on static thrust measured.
The size of the propeller can also have a large effect on propeller efficiency.
In my opinion the reason people use a propeller speed reduction with all its attendant problems is to be able to use a larger propeller for more efficiency without having the tip speed become a problem.
In my opinion using static thrust combined with dry weight as a way to predict gyroplane performance is both foolish and arrogant.
The Predator regularly climbs out at a steady 1,100 feet per minute when flown solo with a light fuel load (1,100 pounds takeoff weight) and regularly climbs out at a steady 600 feet per minute with two up and full fuel (1,400 pounds takeoff weight.
The static thrust didn’t change and the dry weight didn’t change; only the takeoff weight changed.
Anyone who has flown a two place gyroplane solo and two up is familiar with how takeoff weight affects the performance of a gyroplane.
When I solo someone in a two place we put weight in the passenger seat so that the performance is closer to what the client is used to.
I read lots of big talk about potential performance of a Yamaha powered gyroplane. I have yet to see that promised performance realized.