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I wonder if a jet plane can have helicopter rotor for vertical take off and then, when moving forward just stops that rotor and uses lift from wings like normal plane.

Since rotor blade seems thinner and smaller than wings, I guess when turned off, its drag should be much lower than wing.

So why doesn't that type of hybrid plane exist?

Or the drag of the rotor at the jet speed would be so high? If the drag is high, why is it high, since the rotor blade is also airfoil like wing?

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  • $\begingroup$ Which weight for the aircraft? Because usually helicopters are very limited in weight, due to the rotor being a small wing with limited lift, and the mast bearing all the forces. $\endgroup$ – mins May 18 '16 at 18:21
  • $\begingroup$ For your general problem, please take a look at the Sikorsky S-72 X wing experimental program. $\endgroup$ – KorvinStarmast Oct 14 '16 at 15:31
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There were actually some experiments with stopped rotor. Furthest with the actual implementation was probably the Boeing X50 Dragonfly:

Boeing X-50A.jpg
By Source, Fair use of copyrighted material in the context of Boeing X-50 Dragonfly

The main reasons I can think of why nothing like this reached production yet are:

  • When the rotor spins, the blade on one side moves aft and needs to have its leading edge face aft, but when the rotor is stopped, both sides need the leading edge facing forward. So either the airfoil must be symmetric, but that has really poor efficiency, or some blades have to turn somehow, which is complicated.

  • To be light, rotor blades are normally very flexible and rely on the centrifugal force to keep them straight under load. But when they stop, they won't have such force, so they must be much stiffer, which makes them bit too heavy to spin.

  • Having separate wings and rotor would add a lot of weight, especially since the rotor would still have to be made strong enough to resist the aerodynamic loads when stopped.

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    $\begingroup$ Reading the Wikipedia article I would say the main reason this design failed is the effect of the rotor downwash on the fixed wings. This aircraft in fact created its own massive amounts of turbulence and hence never made it to level flight in one piece. $\endgroup$ – Rob Vermeulen May 18 '16 at 17:55
  • $\begingroup$ @RobVermeulen, the reasons I write are the ones that make this approach difficult. This particular experiment did indeed fail mainly due to aerodynamic instability. $\endgroup$ – Jan Hudec May 18 '16 at 19:34
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So why doesn't that type of hybrid plane exist?

This type of plane does not exist largely because there is a simpler way to go about this that has already been done with some success. Planes like the Harrier are capable of VTOL by simply re-directing the exhaust of the jet.

enter image description here (source)

In this case you reduce the amount of moving parts by not needing both a regular jet system and a helicopter mechanism (which requires a lot of up keep) instead its simply easier to have a directed nozzle

enter image description here (source)

This idea has been carried over into the prop world with Boeings V-22 Osprey which has tilt control rotors that allow for VTOL but are also used for forward flight. In this case

enter image description here (source)

To directly answer the drag question, yes the drag would be high (some one else may be able to provide a specific number or the math) but like anything else the design could be built it just would not be very efficient. Since you can generally control the pitch of a helicopter rotor you could potentially (on an even numbered rotor system) orient at least 2 of them to act like small wings and generate very limited lift to assist you even in their static situation.

Like most things in aviation planes are built for a given mission profile. VTOL fits certain cases like anding on an aircraft carrier or in other hard to reach places but things like commercial planes already have a large runway based infrastructure to support them. Any hard to reach place that you need to land at most likely also means your loads are small and a helicopter will suffice, you would need a large hard to reach place that had constantly large loads going in and out to justify a sizable commercial plane that had VTOL capability. While there are some applications for this in the military space (carrier landings come to mind) there are other systems that have been found to be efficient to use. Interestingly enough the directed exhaust from the new F-35's has caused issues on the deck of aircraft carriers.

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  • $\begingroup$ Suggest you add S-97 and Sikorsky X2 pictures, if you are going to add Osprey. $\endgroup$ – KorvinStarmast Oct 14 '16 at 15:27
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Anything that uses a rotor to take-off vertically is most inefficent when lifting, hovering or moving slowly. This is most obvious when a helicopter is at max weight or in "hot and heavy" conditions when it might not be possible to take-off vertically.

In order to lift vertically, thrust must be greater than weight. This is not true for a "conventional" aircraft.

If you use a rotor only for lifting off, then that rotor becomes nothing but extra weight (and complexity) that you don't need. Maybe you could use the stopped rotor to generate some lift in a similar fashion to a conventional wing but as others have pointed out, to make a rotor blade which is rigid enough to act as a static wing and can still handle the forces generated when rotating is a serious engineering challenge that will add more weight and complexity (because the rotor hub must have hinges that can absorb the forces when rotating but keep the blade rigid when stationary).

You also need some complex, and therefore heavy, mechanism for tranisitioning the thrust from the rotor whilst lifting to whatever propulsion you use for forward flight.

More weight, more complexity, more maintenance, more cost, more to go wrong. What's not to like? ;)

The other answers also point out better solutions such as vectored thrust and using the same rotors to lift and to provide thrust in forward flight.

Add this all together and you have a solution for a problem which doesn't exist.

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  • $\begingroup$ See "ABC" and "X wing" development in the 70's and 80's. See also recent Sikorsky X2 and S-97 with a pusher prop to overcome some of the issues, and of course raise other challenges (to include scaling, as they hope to do with Defiant). $\endgroup$ – KorvinStarmast Oct 14 '16 at 15:29

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