Intermeshing rotor projects

[Basil]

...

The symmetrical configuration of the rotors as in this NorthropGrumman concept (Flettner, but not necessarily controlled by rotor flaps) looks very attractive, especially since even at higher speeds lift and propulsion remain symmetrical. It is not totally clear to me why no manufacturer except Kaman has pursued this concept of intermeshing rotors at least for high speed (attack) helicopters (Kaman's concept is only designed for comparably low speeds due to the flap control).

Currently two Swiss UAV manufacturers are using this concept:

ANAVIA HT-100 - the most advanced VTOL system worldwide.

ANAVIA develops and manufactures innovative UAVs focusing on vertical takeoff & landing systems (VTOL) of up to 500 kilograms.

anavia.eu

SwissDrones Long-Range VTOL

SwissDrones is specialized in the development, manufacturing, and operation of long-range unmanned helicopter systems for commercial and public safety applications.

www.swissdrones.com

Some time ago Kamov also introduced a scale model with intermeshing rotors (although their trademark is the of course the coaxial configuration).

 

[yasotay]

I will defer to the aero-engineers here, but not all rotor systems scale up well. The heaviest intermeshing rotorcraft to my knowledge was the Kellett XR-10 at 11,000 lbs. https://en.wikipedia.org/wiki/Kellett_XR-10.

For smaller VTOL UAS it seems reasonably viable.

 

[TomS]

I will defer to the aero-engineers here, but not all rotor systems scale up well. The heaviest intermeshing rotorcraft to my knowledge was the Kellett XR-10 at 11,000 lbs. https://en.wikipedia.org/wiki/Kellett_XR-10.

For smaller VTOL UAS it seems reasonably viable.

K-Max manages 12,000 lbs MTOW with a sling load. But that does tend to suggest there might be an upper bound.

Kaman K-MAX - Wikipedia

en.wikipedia.org

 

[riggerrob]

I will defer to the aero-engineers here, but not all rotor systems scale up well. The heaviest intermeshing rotorcraft to my knowledge was the Kellett XR-10 at 11,000 lbs. https://en.wikipedia.org/wiki/Kellett_XR-10.

For smaller VTOL UAS it seems reasonably viable.

K-Max manages 12,000 lbs MTOW with a sling load. But that does tend to suggest there might be an upper bound.

Kaman K-MAX - Wikipedia

en.wikipedia.org

K-Max may be a great flying crane, but it is not very fast: max. 100 knots clean, but only 80 knots with a slung load. K-Maxs spend most of their working life doing short lifts.

 

[Basil]

The rotor flaps of a Kaman are not suited for high speed flights. For a high speed helicopter a (semi-)rigid intermeshing rotor system needs to be applied.

 

[TomS]

K-Max may be a great flying crane, but it is not very fast: max. 100 knots clean, but only 80 knots with a slung load. K-Maxs spend most of their working life doing short lifts.

100 kts seems to be the top speed for most of the intermeshed-rotor helos I can find -- the XR-10, the Huskie, and K-Max all top out around there.

 

[yasotay]

I will make a wild guess that without significant dampening the vibration levels increase significantly with higher speeds. Assuming the retreating blades are on the inside (over the fuselage) the torsion and drag must also increase significantly and may be compounded by turbulent air over the nose of the helicopter. Crayon aerodynamicist here.

 

[TomcatViP]

@Basil said it all. I would add that they are not inherently quite suitable for a fast manned rotorcraft (rigid rotors behave like a delta wing doing NoE). At least while intermeshing is tight.

However, intermeshed rotors with disjuncted hubs could be more promising, once appropriate rotor's tips clearance features are introduced.

 

[Basil]

... just some concept art how an aerodynamic refined intermeshing rotorcraft without servoflaps could look (I do not know the artist except from this website).

Kaman SFTR-720 USCG Concept

Hi there. I spent some time refining the model, shaders and details. I ditched the design for the air intakes at the “nose” of the craft. Will have to figure out a different way to get the airflow to the engines. Maybe I will post some sketches later on. @ GrimZA: Yes I modeled the...

blenderartists.org

 

[yasotay]

Hmm... 8 rotorblades, gonna need good dampning for the 8 per vibration levels. But it can be done. Beware the SWaP.

 

[Basil]

Hmm... 8 rotorblades, gonna need good dampning for the 8 per vibration levels. But it can be done. Beware the SWaP.

Yes, could be too much. Kellett had 3 per rotor, all other intermeshers seem to have two in practice.

 

[flateric]

one of Kamov V-80 iterations

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ÐаÑало ÑÐ°Ð±Ð¾Ñ Ð¿Ð¾ Ð±Ð¾ÐµÐ²Ð¾Ð¼Ñ Ð²ÐµÑÑолеÑÑ Ðа-50 (заводÑкой ÑиÑÑ Ð-80) даÑиÑÑеÑÑÑ ÑнваÑем 1977 года. РазÑабоÑка велаÑÑ Ð²

www.aex.ru

 

[GTX]

Interesting though that assumes that the system will work and hasn't itself been damaged...when you have need to eject

 

[Basil]

one of Kamov V-80 iterations

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ÐаÑало ÑÐ°Ð±Ð¾Ñ Ð¿Ð¾ Ð±Ð¾ÐµÐ²Ð¾Ð¼Ñ Ð²ÐµÑÑолеÑÑ Ðа-50 (заводÑкой ÑиÑÑ Ð-80) даÑиÑÑеÑÑÑ ÑнваÑем 1977 года. РазÑабоÑка велаÑÑ Ð²

www.aex.ru

Thanks! Always great to read documents about soviet / russian developments from non-western sources.