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With contrarotative propeller (or not, if twin engine), cyclic and collective blade control.

Would such an aircraft be safely flyable, and how efficient would it be, assuming it can have perfectly smooth wings (and tailplane)?

In case of engine stop (allowing axle free spin and control on blades), could it control its glide and land on the runway, with the propeller's blades in an almost feathered autorotation configuration, allowing attitude control and minimum disk drag?

(like autorotating one reversed Kamov on its rotor-head, in a skydiving wind tunnel blowing a bit slower than terminal velocity)

Edit: If it goes twin engine and tailless (and still controlesurfaceless) how active cyclic pitch control would be necessary to allow use of non-reflex wing's airfoil?

enter image description here

Edit2: Switch from thrust + attitude control mode, to no-thrust + attitude control "reversed autorotation" mode. Reversed rotation allows most efficient use of blade's airfoil camber. enter image description here

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  • $\begingroup$ Are you describing an Autygyro? $\endgroup$
    – Dan Pichelman
    Dec 4, 2017 at 13:50
  • $\begingroup$ @DanPichelman no, like a Cessna 172, lift is generated by the wing; engine-propellers makes it fly fast enough for the wings to sustain flight. $\endgroup$
    – jkztd
    Dec 4, 2017 at 13:58
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    $\begingroup$ aircraft without elevators, ailerons, rudder? no problem! $\endgroup$
    – szulat
    Dec 4, 2017 at 16:01
  • $\begingroup$ @szulat good point, even if powered hang gliders look too much like a fixed wing autogyro. (still better than autogyro) $\endgroup$
    – jkztd
    Dec 4, 2017 at 16:05
  • $\begingroup$ @szulat also weight shifting control doesn't allow reverse flight, or any control while negative loading and AoA, since system becomes unstable, reversed pendulum. $\endgroup$
    – jkztd
    Dec 4, 2017 at 16:56

3 Answers 3

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An interesting thought. Control the aeroplane through its propeller(s), like a helicopter does.

  • Propeller torque differential would control roll
  • Propeller cyclic would control both pitch and yaw
  • Propeller collective would control engine thrust, like already done in constant speed propellers.

The thing that immediately comes to mind is moment arm for pitch and yaw. Helicopter blades are relatively long, and the rotor is mounted about halfway along the fuselage. The prop is limited in its blade length due to ground clearance.

enter image description here

With a configuration like above, longer propeller blades can be mounted so the pitch and yaw moment arms can be extended. As @Sanchises points out, placing of the propeller like this creates a coupling between pitch and thrust - not a bad thing, increasing pitch controllability by controlling thrust. A strong nose wheel might be required for take-off.

Not sure about your reference to the skydiving Kamov, but the aircraft could glide down after engine failure while keeping enough RPM to control cyclic. It would be a bit draggy though, with the drag comparable with a parachute of the same diameter as the propeller. Autorotation works best with a large blade moment of inertia, and the propeller would definitely not have the optimal blade length for that.

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  • $\begingroup$ If you glide straight forward at best L/D, blade's pitch will be close to feathered, at minimal drag. Eventually propeller will stop spinning, unless you want to roll, and therefore apply differential pitch between contrarotatives, increasing rpm, inducing torque, (and roll) Same for pitch and yaw. Each input increases blades rpm and authority to do whatever change in attitude. Low inertia due to relative small prop diameter helps these rpm variations. Most of the time, blades are aligned with relative wind. It could be less draggy than one stadard C172 prop idling. $\endgroup$
    – jkztd
    Dec 4, 2017 at 14:15
  • $\begingroup$ That would mean that in order to pitch or yaw the aircraft you would have to spin up the propellers first in autorotation, causing a time delay in the response. Roll response would be immediate because the spinning up is roll response already. $\endgroup$
    – Koyovis
    Dec 4, 2017 at 14:19
  • $\begingroup$ Exact, spin stop idea was to illustrate close to zero angle of attack while gliding. One minimum rpm should be set in order to minimise delay and authority on pitch & yaw, relative to drag produced by spinning. $\endgroup$
    – jkztd
    Dec 4, 2017 at 14:24
  • $\begingroup$ Except for increased propeller blade length, offsetting the propeller does not change anything; control forces are almost a pure torque on the propeller shaft, and a given amount of torque has the same effect on a body regardless of position. Only a force benefits from a longer arm, but the only significant force is thrust, which now creates a large moment around the c.o.g. which needs to be counteracted by your cyclic. $\endgroup$
    – Sanchises
    Dec 4, 2017 at 14:25
  • $\begingroup$ @Sanchises axis of rotation has an effect on moment of inertia. $\endgroup$
    – Koyovis
    Dec 4, 2017 at 14:32
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This will work as long as the propellers produce enough thrust and blade pitch can be adjusted fast enough to outrun all eigenmodes.

As soon as you need to throttle back (and eventually you must, to come down again), the control effectivity of the propellers will be greatly reduced. Granted, you can float down in autorotation like an autogyro, but the landing will be more a crash than anything else.

Note that the Boeing V-22 Osprey is not capable of power-off landings because the propeller inertia is too small to support the landing deceleration. It can glide down in autorotation but cannot perform a soft landing. Your configuration looks quite similar and will similarly not be capable of autorotation landings.

If you want to control the plane with propeller forces, the propeller must spin at high speed all the times to have sufficient thrust potential available when it is needed for stabilization. For artificial stability you have no time to spin up the prop first! Thrust is controlled by pitch only, but the higher-than-normal prop speed will cause its own inefficiency.

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  • $\begingroup$ This actually isn't autorotation like an autogyro or helicopter, since it's not providing lift + attitude control. It only provides attitude control. Each attitude correction slows you down. When gliding straight, blades are close to feathered. Wings provide lift, propellers provide best control/glide ratio $\endgroup$
    – jkztd
    Dec 4, 2017 at 16:18
  • $\begingroup$ autogiro should be autogyro. $\endgroup$
    – user
    Dec 4, 2017 at 16:33
  • $\begingroup$ @Peter Kämpf, since blade's asymmetric airfoil usage should be optimal during non powered flight, shaft rotation may be reversed in this case. Think HAWT windturbine mode, having positive AoA even if not providing thrust. $\endgroup$
    – jkztd
    Dec 4, 2017 at 18:53
  • $\begingroup$ @qqjkztd: How do you think the feathered props will contribute to stability? Without a significant blade loading they cannot do much in terms of pitch or roll control. The best you can do is to let them run at windmilling angle but at full RPM, so loads can be created quickly. And for approach and landing you cannot afford to have much thrust or even reverse thrust. $\endgroup$
    – Peter Kämpf
    Dec 5, 2017 at 15:43
  • $\begingroup$ @PeterKämpf by reversing rotation direction of the blades, compared to rotation direction while powered by the engine. Airfoil's camber should be used in its best lift producing possibility, which means reverse spin direction when unpowered, free rotating. $\endgroup$
    – jkztd
    Dec 5, 2017 at 16:47
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from an engineering design standpoint, the performance of (for example) a small aircraft like the seaplane pictured above is not in any practical sense limited by the presence of an empennage carrying an elevator and rudder. For this reason, alternatives like cyclic pitch changes on the propulsion propellors have not been actively researched for pitch and yaw control.

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  • $\begingroup$ Cyclic control on propellers is not meant to suppress the empennage. It may allow its suppression anyway, but primary goal is to have clean airfoils with no control surfaces, and get rid of the parasite drag they provide, on wings and stabilizers. $\endgroup$
    – jkztd
    Dec 7, 2017 at 12:39

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