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Lockheed AH-56 Cheyenne and derivatives

F-14D

I really did change my personal text
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Jeb said:
Triton said:
Does an X2 compound rotorcraft have an advantage over tilt-rotor when flying in contested environments?
I can only think of two.
[list type=decimal]
[*]The X2 doesn't have a translation time for the rotors to go from vertical to horizontal. I don't know how fast the tiltrotors can convert or if there are maneuvering restrictions during translation, but in the abstract I'd consider that a disadvantage.

[*]The X2, if equipped with door gunners, doesn't have as much firing arc restriction as a tiltrotor would have while flying in airplane mode. Or, for that matter, in helicopter mode, since the TR's rotor disc spans out much wider than the X2.
[/list]

Regarding acceleration, speculation is that starting from a steady state hover, a comparable X2 would have an acceleration advantage at the beginning because while its pusher is smaller than the proprotors on a comparable Tilt-Rotor, it is already in position to provide full thrust. The Tilt-Rotor would accelerate at first like a normal helicopter. As speed increased, the more towards the horizontal the proprotors translate, the more aft thrust they're going to provide and they will surpass the thrust of the pusher by a good bit, which would up the acceleration significantly. One advantage there is that once wingborne, 100% of the engine's power is available for thrust, whereas with an X2 the majority of power is always going to keep the thing in the air.

Transition time will be a function of what the required performance for a give bird is, and how the engineers choose to meet it. There are no maneuvering restrictions during transition (either way) inherent in Tilt-Rotor technology, AFAIK.

Although neither an X2 or a Tilt-Rotor are going to be using door guns when they are traveling at their higher speeds, unquestionably at lower speeds a Tilt-Rotor has a wider rotor arc so consequently can't elevate the door guns as far, which would be relevant in a tight bank. Helicopters have shot themselves down by inadvertently firing through the rotor arc.

Other possible X2 advantage , depending on the size of the vehicle, could be weight and lift efficiency at very low speeds/hover. With a Tilt-Rotor, the wing is always there. As the vehicle gets smaller, the weight of the wing becomes a larger percentage of total vehicle weight so the helicopter, lacking a wing gains and advantage. I am saying helicopter because given the extra weight of two vs one rotor, that big mast and big transmission inherent to X2, I don't know know how much those factor into the weight equation for X2.

Again, the Tilt-Rotor always has that wing there. That wing, while providing very efficient lift in wingborne flight relative to a rotor, is always going to be in the downwash when in rotorborne flight. This is going to cause a hit to Tilt-Rotor's low speed/hover efficiency. Some of this can be mitigated because a Tilt-Rotor can put a lot more twist on its blades (because it doesn't have to push the blades through the air sideways at higher speeds), but it's not enough to overcome the penalty of wing in the downwash while rotorborne.
 

yasotay

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F-14D said:
Jeb said:
Triton said:
Does an X2 compound rotorcraft have an advantage over tilt-rotor when flying in contested environments?
I can only think of two.
[list type=decimal]
[*]The X2 doesn't have a translation time for the rotors to go from vertical to horizontal. I don't know how fast the tiltrotors can convert or if there are maneuvering restrictions during translation, but in the abstract I'd consider that a disadvantage.

[*]The X2, if equipped with door gunners, doesn't have as much firing arc restriction as a tiltrotor would have while flying in airplane mode. Or, for that matter, in helicopter mode, since the TR's rotor disc spans out much wider than the X2.
[/list]

Regarding acceleration, speculation is that starting from a steady state hover, a comparable X2 would have an acceleration advantage at the beginning because while its pusher is smaller than the proprotors on a comparable Tilt-Rotor, it is already in position to provide full thrust. The Tilt-Rotor would accelerate at first like a normal helicopter. As speed increased, the more towards the horizontal the proprotors translate, the more aft thrust they're going to provide and they will surpass the thrust of the pusher by a good bit, which would up the acceleration significantly. One advantage there is that once wingborne, 100% of the engine's power is available for thrust, whereas with an X2 the majority of power is always going to keep the thing in the air.

Transition time will be a function of what the required performance for a give bird is, and how the engineers choose to meet it. There are no maneuvering restrictions during transition (either way) inherent in Tilt-Rotor technology, AFAIK.

Although neither an X2 or a Tilt-Rotor are going to be using door guns when they are traveling at their higher speeds, unquestionably at lower speeds a Tilt-Rotor has a wider rotor arc so consequently can't elevate the door guns as far, which would be relevant in a tight bank. Helicopters have shot themselves down by inadvertently firing through the rotor arc.

Other possible X2 advantage , depending on the size of the vehicle, could be weight and lift efficiency at very low speeds/hover. With a Tilt-Rotor, the wing is always there. As the vehicle gets smaller, the weight of the wing becomes a larger percentage of total vehicle weight so the helicopter, lacking a wing gains and advantage. I am saying helicopter because given the extra weight of two vs one rotor, that big mast and big transmission inherent to X2, I don't know know how much those factor into the weight equation for X2.

Again, the Tilt-Rotor always has that wing there. That wing, while providing very efficient lift in wingborne flight relative to a rotor, is always going to be in the downwash when in rotorborne flight. This is going to cause a hit to Tilt-Rotor's low speed/hover efficiency. Some of this can be mitigated because a Tilt-Rotor can put a lot more twist on its blades (because it doesn't have to push the blades through the air sideways at higher speeds), but it's not enough to overcome the penalty of wing in the downwash while rotorborne.
Superb analysis.

I will see you and raise you two.

a. Tilt rotor wing provides sunk cost space for things like jammer/aux fuel/(restricted) weapon pods location
b. Tilt rotor can trail things behind it like refuel hose& drogue, countermeasures or antenna.

Now before F-14D calls my raise, I do realize that the question regarded mostly hover and acceleration. I would offer that IF the Tilt Rotor has more rotor flexibility (exact term alludes me at the moment), and nacelle rotational speed it will move out better than a conventional helicopter, without necessity to change fuselage pitch angle. Given a standing straight line start I would have to agree that the compound would initially out accelerate the tilt rotor. However, in practical terms since we are talking about leaving a landing zone, we have to consider that most have obstacles around them that must be cleared as well. So with an "up and out", I am not sure there is much difference between the two honestly (given all power performance is equal).
 

hesham

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Look for this;

https://apps.dtic.mil/dtic/tr/fulltext/u2/a040189.pdf
 

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Triton

Donald McKelvy
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Par Tool Lockheed AH-56A Cheyenne Navy

Model of Lockheed AH-56A Cheyenne in Navy livery manufactured by Par Tool Company found on eBay

Source:
https://www.ebay.com/itm/Navy-Attack-Helicopter-Lockheed-AH56A-Cheyenne-Manufacturers-Display-Model/123247072253?hash=item1cb21913fd:g:~40AAOSwNOJbR7FZ
 

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hesham

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From L+K 20/1965.

it had estimated speed of 600 km/h.
 

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