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V-22 Osprey: how do its controls work?


JayPee

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Some of the controls of the V-22 remain a mystery to me. Hopefully someone here can shed some light on it, or better, provide some reference material since Google is failing me big time.

 

At 90 deg. nacelle, the Thrust Control Lever controls collective pitch to control altitude through downward thrust, just like an ordinary helicopter, where engine RPM remains the same (+/- governor corrections).

 

What happens at 0 deg. nacelle, or airplane mode? Does the TCL still alter blade pitch to control for thrust, or does it keep blade pitch constant and adjust engine RPM the way a turbo prop functions?*

 

* I know a turbo prop also has variable blade pitch but the primary channel to adjust thrust is the engime RPM.

 

Regarding yaw, at 90 deg. nacelle the pedals cause differential nacelle angle, IIRC from 83 deg. to 97 deg. At 0 deg. nacelle the pedals control the tail rudder control surfaces to yaw like a plane. Articles on the FCS of the Osprey state that controls gradually phase out based on nacelle angle. What does that mean? That e.g. with nacelles at 60 deg., a full left pedal gives a 33% rudder control surface swing and 66% differential nacelle angle? (My logic: 60 deg. nacelle angle is 2/3rd helicopter mode, 1/3rd plane mode)

 

Also, what is the procedure to gain forward (or backward) airspeed while in helicopter mode? Slightly tilting the nacelles forward (or backward) using the wheel on the TCL, again max. 83 deg. to 97 deg. IIRC? Or does the pilot give forward (or backward) stick input to have the whole airframe pitch nose down (or nose up)?

 

Thanks

-Jp


Edited by JayPee
spelling n typos

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This is from this website

http://www.navair.navy.mil/v22/?fuseaction=faq.main:

 

The process of rotating the nacelles between helicopter and airplane mode is called “transition”, and the reverse from airplane mode to helicopter mode, “conversion”. Transition and conversion procedures are simple, straightforward, and easy to accomplish. The amount and rate of nacelle tilt can be manually controlled by the pilot or can be performed automatically by the flight control system. The V-22 can perform a complete transition from helicopter mode to airplane mode in as little as 16 seconds. Conversions and transitions can be continuous, stopped partway through, or reversed as desired. A tiltrotor can fly at any degree of nacelle tilt within the authorized conversion corridor envelope. During vertical takeoff, the conventional helicopter controls are utilized. As the tiltrotor gains forward speed, the wing begins to produce lift and the ailerons, elevators, and rudders become more effective. Between 40 and 80 knots, the rotary-wing controls begin to be phased out by the flight control system. Once in airplane mode, the wing is fully-effective and pilot control of cyclic pitch of the proprotors is locked out. Because the nacelle angle can be commanded separately from the primary pitch controls of rotor cyclic and tail elevator, the conversion corridor (the range of permissible airspeeds for each angle of nacelle tilt) is very wide (about 100 knots). In both accelerating and decelerating flight, this wide corridor means that a tiltrotor can have a safe and comfortable transition or conversion, offering the combined advantages of speed and maneuverability for low level flight.

 

So it would seem that Nacelle angle can be control manually, and that conversion between airplane/helicopter control mode is dependant on forward airspeed and therefore control effectiveness of the conventional flying surfaces., which would make sense.

 

This is an interesting observation from an Israeli pilot who has tested it:

 

"The pilot uses a control stick and a system that is similar to a throttle. In one standpoint, the control stick serves to determine altitude while the 'throttle' serves to determine speed. In the other standpoint, each of them serves the opposite role. In the mid-stage you feel like you're losing control of the plane. I imagined that the fly-by-wire system would function more smoothly, but discovered that in some cases we needed to intervene."


Edited by whiteladder
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Ok this is from a retired V-22 pilot and seems to contradict the Pitch lock out.

 

"The TCL moves fore and aft just like an airplane throttle, unlike a helicopter collective. It does operate as a collective control, however, and becomes a traditional throttle during the transition. While this may seem counter-intuitive to helicopter pilots, it actually makes a lot of sense, because regardless of the mode of flight, youre always doing the same thing: controlling the thrust vector."

 

he goes on to say:

 

Once the nacelles hit zero, the next step is to autobeep the rotor r.p.m. to the cruise speed of 84 percent by briefly flipping the nacelle thumbwheel forward and letting it spring back into position. The sound and vibration levels drop significantly at this point and the Osprey is flying with about a five- to seven-degree nose high platform while accelerating through 200 KCAS all in about 15 to 20 seconds.

 

During transition, the flight controls switch from a helicopter to an airplane based upon a speed schedule contained in the flight control computers. Swashplate movements are reduced and the flaperons rise up to become very large ailerons. (One thing to note is that the TCL doesnt change its function; it still controls the thrust vector by collectively changing the proprotor pitch.)

 

So it seems fair to say that in airplane mode the FADEC maintains the rpm at 84% and that pitch controls the amount of thrust.


Edited by whiteladder
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I knew the first two paragraphs, but thanks for repeating. Especially the Israeli pilot's comments are useful.

 

Where did you get the retired pilot interview from? I think it indeed proves the blade pitch is the main channel to alter thrust, in both airplane and helicopter mode, and in between. However, as far as I understand, in airplane mode the normal operation rpm is 84% so I assume it is around 100% in helicopter mode to provide more overall power.

i7 4790K: 4.8GHz, 1.328V (manual)

MSI GTX 970: 1,504MHz core, 1.250V, 8GHz memory

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Hover taxiing can be accomplished in two ways, either with the cyclic or the nacelles. There is no magic number differentiating when to use one over the other, but its much more efficient to use the nacelles if moving more than just a couple of aircraft lengths.

 

Probably where you got your intel from as well:http://www.verticalmag.com/features/features_article/20112-flying-the-v-22.html#.UisGcT9wjIU

 

I think this answers how forward flight is achieved in helicopter mode. Although "no magical number" exists, I'm sure the military have their procedures and guidelines for this.

i7 4790K: 4.8GHz, 1.328V (manual)

MSI GTX 970: 1,504MHz core, 1.250V, 8GHz memory

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