[3e] Lockheed AH-56 Cheyenne

[Phaelen Bleux]

Lockheed AH-56 Cheyenne
Lockheed's only endeavor in helicopter design began in 1967 when it submitted a proposal for the U.S. Army's requirement for a heavily armed gunship helicopter. An unusual design, the four-bladed helicopter also featured a pushing propeller to the rear, which not only increased speed and handling, but also allowed the rotors to be unloaded during level flight (that is, the wings provided a majority of lift while the propeller provided thrust, allowing the rotors to be underpowered to conserve fuel). The AH-56 was accepted in 1968 and dubbed the Cheyenne. An initial request for 375 machines was submitted to Lockheed, but severe problems with rotor stability (involving the death of one test pilot) caused the U.S. Army to halt the production program as it sought other options. Lockheed continued to pursue the design, but as the cost per unit ballooned from an initial $500,000 to $5 million, Congress terminated the contract in 1972 at a severe loss to Lockheed. Only 10 prototypes were every produced; of these three were lost in testing accidents.
The Cheyenne was to have featured a heavy armament of one 7.62mm MG in a 100-degree arc chin turret, as well as a large 30mm cannon in a 360-degree belly turret. Both would be controlled by the gunner, who sat forward of the pilot in the cockpit. The belly turret could also accommodate a 40mm grenade launcher with 780 rounds.
The body hardpoints could carry 450-gallon drop tanks or missiles. The wing hardpoints would typically carry TOW missiles or 2.75" FFAR rocket pods.
The Cheyenne uses 205 gallons of jet fuel per hour at routine usage. A full tank of fuel costs $1,314. Ammo for the cannon costs $15,276; ammo for the MG costs $1,292. Disposable ordnance cost varies by payload.

AH-56A Cheyenne
Subassemblies: Body +4, (Standard) Wings +2, Rotor +0, full-rotation turret [Body:U] +2, limited-rotation turret [Body:F] +0, 3 retractable wheels +0.
Powertrain: 2,927-kW HP gas turbine with 2,927-kW TTR, 2,300-kWs advanced battery.
Fuel: 438 gallons jet fuel in self-sealing standard tanks (one 300-gallon plus one 78 gallon plus one 60 gallon) (Fire 12) [Body].
Occupancy: 2 NCS.
Cargo: None.

Armor
All: 3/10

Weaponry:
30mm autocannon [Turret/Body:U] (2,010 rounds).
7.62mm MG [Turret/Body:F] (11,750 rounds).
6 TOW Rockets [Wings:U].
2 70mm 19-shot Rocket Pods [Wings:U].

Equipment:
Body: Long range radio with scrambler (300-mile), laser range finder (5-mile), autopilot, light amplification, precision navigation instruments, IFF, dedicated targeting computer, flight recorder, duplicate controls, two 2,000-lb. hardpoints. Wings: Four 2,000-lb. hardpoints.

Statistics:
Size: 60'x50'x13' Payload: 2.63 tons Lwt.: 12.94 tons
Volume: 355 cf. Maint.: 18 hours Price: $1,178,410

HT: 8. HPs: 452 Body, 193 each Wing, 201 Rotor, 100 large Turret [U], 9 small Turret [F], 41 each Wheel.

aSpeed: 253 aAccel: 3.5 aDecel: 19 aMR: 5 aSR: 2
Stall Speed: 0.

Design Notes:
Body is 355 cf; stub wings are 100 cf, wheels are 17.75 cf, full-rotation turret is 35 cf, limited-rotation turret is 6 cf. Wing volume was reverse-engineered from actual wing area (258 sf). Structure is Medium, Expensive with Fair Streamlining. Armor is Expensive Metal. Mechanical controls. Design aSpeed was 317 mph; the historical top speed is shown. Design HT was 8.5; this was rounded down due to the design's poor performance record. GM's wanting a design with some of the bugs worked out may allow HT 9.
Design loaded weight is 32,456 lbs. with 12,000 lbs. of ordnance (but see below). Design empty weight is 12,743 lbs.; this is 8% over the real-world value of 11,693 lbs. Typical combat weight would have been 16,960 lbs., with a maximum takeoff weight of 25,880 lbs. The design's lift potential is 29,270 lbs.
Since this design never made it past the prototype stage, none were ever armed. The amount of rounds carried seems excessive, but these were values I found. Also, sources state that each of the hardpoints was capable of a 2,000-lb. load. They are designed for that capacity, but it should be noted that the wing structure will only support a combined load of 7,740 lbs., which is more than adequate for the typical load-out described above.

[ed_209a]

Here's an interesting bit of trivia about the Cheyenne.

The gunner's entire seat and console could rotate inside the cockpit. A little like (and possibly inspiring) the cockpit of the Gunstar from The Last Starfighter.

[omeyer]

Originally Posted by Phaelen Bleux

Lockheed AH-56 Cheyenne
Lockheed's only endeavor in helicopter design began in 1967 when it submitted a proposal for the U.S. Army's requirement for a heavily armed gunship helicopter. An unusual design, the four-bladed helicopter also featured a pushing propeller to the rear, which not only increased speed and handling, but also allowed the rotors to be unloaded during level flight (that is, the wings provided a majority of lift while the propeller provided thrust, allowing the rotors to be underpowered to conserve fuel).
[...]
Subassemblies: Body +4, Stub wings +2, full-rotation turret [Body:U] +2, limited-rotation turret [Body:F] +0, 3 retractable wheels +0.
Powertrain: 2,927-kW HP gas turbine with 2,927-kW TTR, 2,300-kWs advanced battery.

I'm a bit puzzled by your writeup. I'd expect both "normal" wings and a rotary wing, and both the helicopter drivetrain and a propeller, possibly powered by the same turbine.

Systems which use the same subassembly as both fixed and rotary wings would be the TL8 Canard Rotor Wing (VXi3) or X-Wing Stopped Rotors (VXii8). Getting the benefits of both wings and rotors at TL7 should require both wings and rotors -- compare the tilt-rotor for a similar case, VE34.

[Phaelen Bleux]

[QUOTE]

Originally Posted by omeyer

I'm a bit puzzled by your writeup. I'd expect both "normal" wings and a rotary wing, and both the helicopter drivetrain and a propeller, possibly powered by the same turbine.

The "stub" descriptor is probably not entirely accurate, but I used it since this is still a helicopter craft. Since I used real-world SA, you can call them true wings if you like. I should have added a propeller subassembly, but I have no idea how much thrust the aft prop contributes.

However, the design (using all helicopter-based performance calcs--i.e., 1.6x thrust) is still faster than the real-world aircraft, so I felt no need to dabble in augmenting the aSpeed with the aft propeller.

Systems which use the same subassembly as both fixed and rotary wings would be the TL8 Canard Rotor Wing (VXi3) or X-Wing Stopped Rotors (VXii8). Getting the benefits of both wings and rotors at TL7 should require both wings and rotors -- compare the tilt-rotor for a similar case, VE34.

Looking at those design options, neither is quite right, and I think both are too advanced. The U.S. Army treated it as helicopter, despite its eccentric tail-prop, and I think it essentially works (if anything) like a helicopter-with-a-dash-of-autogyro.

[omeyer]

Originally Posted by Phaelen Bleux

The "stub" descriptor is probably not entirely accurate, but I used it since this is still a helicopter craft. Since I used real-world SA, you can call them true wings if you like. I should have added a propeller subassembly, but I have no idea how much thrust the aft prop contributes.

The thrust propeller needs no subassembly, but the rotor does.

Originally Posted by Phaelen Bleux

Looking at those design options, neither is quite right, and I think both are too advanced. The U.S. Army treated it as helicopter, despite its eccentric tail-prop, and I think it essentially works (if anything) like a helicopter-with-a-dash-of-autogyro.

That was why I was suggesting rotors and wings.

I think it should have these subassemblies:

• Body

• Retractable Wheels (two or three)

• Standard Wings (two of course, and called "standard" to set them apart from "STOL" or "high-agility")

• Top-and-Tail Rotor

• Full-rotation Turret (for the cannon)

• Limited-rotation Turret (for the MG)

The nominal propeller power could be scaled to get the listed cruise speed on propeller thrust alone, without the helicopter drivetrain.

[Phaelen Bleux]

Originally Posted by omeyer

The thrust propeller needs no subassembly, but the rotor does.



That was why I was suggesting rotors and wings.

I think it should have these subassemblies:

• Body

• Retractable Wheels (two or three)

• Standard Wings (two of course, and called "standard" to set them apart from "STOL" or "high-agility")

• Top-and-Tail Rotor

• Full-rotation Turret (for the cannon)

• Limited-rotation Turret (for the MG)

The nominal propeller power could be scaled to get the listed cruise speed on propeller thrust alone, without the helicopter drivetrain.

Ah, now I see the problem. I forgot to list the rotor subassembly. It is in the design; just missing from the writeup. I'll correct the OP. The rotor and wing HPs were used in performance calcs, etc.