Key Features of the Heliplane Design

  1. Able to slow rotor and still be stable and controllable at high speeds.
    1. There is no fundamental reason this design cannot fly as fast as 500 mph. Speed is limited only by the tip speed of the advancing blade and available horsepower.
    2. The rotor advance ratio, known as Mu, equals the ratio of the forward speed of the aircraft to the rotor tip speed. At high speeds, this ratio will be greater than one. This has never before been achieved in manned flight and has been thought by most to be impossible or at best impractical.
      1. One of the reasons is because the retreating blade always has to produce the same lift as the advancing blade, and at a Mu above 1 the retreating blade has reverse airflow.
        1. However, the most difficult condition from a lift equilibrium standpoint is a Mu ratio of 0.75. At this condition, the velocity over the entire retreating blade is at its lowest. Therefore, its lift potential is at its lowest.
        2. We have demonstrated that our control system can maintain lift equilibrium on the rotor at a Mu of 0.75 at a rotor lift +/- 300 lbs on the current CarterCopter Technology Demonstrator. Above a Mu of 0.75, rotor lift and rotor lift stability increases so that at a Mu as high as 5 at a forward speed of 500 mph, the rotor would still be stable even with a vertical gust of 50 ft/sec (3000 ft/min).
      2. Another reason is that as the Mu ratio increases, the retreating blade, due to reverse airflow and the fact that the aerodynamic center moves in front of the blade dynamic CG, becomes increasingly unstable and will try to diverge. This can be controlled with a very torsionally stiff blade and either an advancing blade that is more stable than the retreating blade is unstable, or a very stiff boosted control system.

       

  2. Efficiency (L/D ratio) can approach that of a fixed wing aircraft.
    1. With the rotor slowed down, the rotor drag is basically a function of its wetted area, which is small in comparison to the wetted area of a wing - based on an equivalent size aircraft.
    2. The wing can be made smaller on the Heliplane because it does not have to provide the lift required for a low landing speed - its wing is sized for cruise.
    3. The total wetted area of the rotor and wings of the Heliplane need not be much different than the wing of an equivalent size airplane.
    4. Since the wing does not need any high lift devices, it can be structurally more efficienct and utilize a high aspect ratio planform to improve the aircraft's L/D.

     

  3. The Heliplane has full hover and sling load capabilities. Thrust from the large diameter propellers located on the wing provides three functions;
    1. Counters the rotor torque during hover and slow speed flight. At speeds over 100 mph there is no torque reaction required for the rotor- the rotor is in full autorotation
    2. Provides all the forward thrust requirements so the rotor can be unloaded and slowed down for high speed flight.
    3. Allows the aircraft to remain level over wide CG shifts. A net forward or rearward thrust from the propellers forces the rotor to be tilted fore or aft to keep the aircraft in one spot and as a result will cause the aircraft to pitch up or down.

     

  4. Innovations in the rotor, rotor controls, prop, fuselage construction, and landing gear allow the design to be scaled up larger than that possible using conventional technology and still have a meaningful useful load (as large as a C-130).
    1. The prop on the CarterCopter Technology Demonstrator is 8 ft in diameter, has been proof tested at a tip speed over the speed of sound, produces 1300 lbs of thrust from 300 hp and weighs 27 lbs, including the pitch change mechanism. The weight of the nearest competitor's prop is 76 lbs.
    2. The rotor on the CarterCopter Technology Demonstrator is 44 ft in dia. and could produce the required lift for an 8000 lb helicopter, yet it weighs less than 300 lbs including the hub, pitch change mechanism and 130 lbs of inertia weight. This blade weight to gross weight ratio becomes .0375 and is 1/2 to 1/3 the weight ratio of any other helicopter rotor.
    3. The composite construction technique used on the CarterCopter Technology Demonstrator enabled the passenger compartment to be proof tested to 25 psi with a large windshield only 1/4 inch thick. The door is a self locking design whereby the loads pass across the door rather than around it, which greatly reduces the stress concentration and the fuselage weight.
    4. The landing gear is a structurally efficient trailing arm design with a relatively large stroke in which to absorb energy. The landing gear has a smart mechanical valve which can in the 1st inch of landing gear travel determine the impact velocity and then regulate the cylinder pressure to provide a near constant deceleration over the remaining stroke. The prototype landing gear was proof tested at an impact velocity of 20 ft/sec. With a longer stroke available on larger aircraft such as the Heliplane Transport, the landing gear could safely absorb an unheard of impact of 50 ft/sec.