Dragonwings on Mini-500
First, I must state categorically that a stock set of gyrocopter blades must not be mounted on a Mini-500. The connection between blade and grip isn’t strong enough.
The Mini-500 has a single 5/8” diameter bolt that carries most of the centrifugal load. To accommodate helicopter loads, a special root doubler had to be incorporated that allowed transfer of centrifugal load between spar and blade grip.
Also, the twist used in the gyro version is detrimental to helicopter hovering efficiency.
As many individuals know, modern helicopters use cambered rotor blades in the interest of efficiency rather than the traditional symmetrical sections first used by the pioneers beginning in the 1940s. That knowledge has been slow in filtering down to amateur helicopter designers.
Gyros can squeak by with rotor blades that have nose down pitching moments and that aren’t balanced about the aerodynamic center. Helicopters can’t. Tail heavy rotor blades, if they don’t flutter, will become divergent at the higher tip speeds used on helicopters.
Knowing all these things, Ernie decided to have a go at DWs on a Mini-500. He built up a set of untwisted blades with reinforced root fittings and with 3.5 lb. brass tip weights.
Subjectively, the performance increase was amazing. A throttle chop and needle split from a low hover results in a slow settling in without touching the collective as a result of reduced rotor drag and increased rotor inertia.
From a low hover, permitting the rotor speed to drop into the yellow can be powered out of simply by rolling on more throttle whereas the original blades will settle in no matter how much power is applied.
Performance was improved in all flight modes; the reduction of rotor power leaves more power available for maneuvering and no doubt would improve engine durability and reliability.
Many of the fatal accidents with Mini-500s have been the result of engine failure combined with marginal autorotational performance. Low drag, high inertia rotors would mitigate those risks.
Quantitative measurements require more instrumentation than is incorporated on a Mini-500.
With 4-stroke engines, manifold pressure is a good relative power indication but is not applicable when using a Rotax 582.
A main rotor shaft torque meter would have been nice, as would have been a sensitive fuel flow meter.
I have a number of photos but the attachment link doesn't work.
First, I must state categorically that a stock set of gyrocopter blades must not be mounted on a Mini-500. The connection between blade and grip isn’t strong enough.
The Mini-500 has a single 5/8” diameter bolt that carries most of the centrifugal load. To accommodate helicopter loads, a special root doubler had to be incorporated that allowed transfer of centrifugal load between spar and blade grip.
Also, the twist used in the gyro version is detrimental to helicopter hovering efficiency.
As many individuals know, modern helicopters use cambered rotor blades in the interest of efficiency rather than the traditional symmetrical sections first used by the pioneers beginning in the 1940s. That knowledge has been slow in filtering down to amateur helicopter designers.
Gyros can squeak by with rotor blades that have nose down pitching moments and that aren’t balanced about the aerodynamic center. Helicopters can’t. Tail heavy rotor blades, if they don’t flutter, will become divergent at the higher tip speeds used on helicopters.
Knowing all these things, Ernie decided to have a go at DWs on a Mini-500. He built up a set of untwisted blades with reinforced root fittings and with 3.5 lb. brass tip weights.
Subjectively, the performance increase was amazing. A throttle chop and needle split from a low hover results in a slow settling in without touching the collective as a result of reduced rotor drag and increased rotor inertia.
From a low hover, permitting the rotor speed to drop into the yellow can be powered out of simply by rolling on more throttle whereas the original blades will settle in no matter how much power is applied.
Performance was improved in all flight modes; the reduction of rotor power leaves more power available for maneuvering and no doubt would improve engine durability and reliability.
Many of the fatal accidents with Mini-500s have been the result of engine failure combined with marginal autorotational performance. Low drag, high inertia rotors would mitigate those risks.
Quantitative measurements require more instrumentation than is incorporated on a Mini-500.
With 4-stroke engines, manifold pressure is a good relative power indication but is not applicable when using a Rotax 582.
A main rotor shaft torque meter would have been nice, as would have been a sensitive fuel flow meter.
I have a number of photos but the attachment link doesn't work.