V-22 can't autorotate. Say what?
 

This week's Time Magazine carries an article on the V-22 Osprey which is set to see duty in Iraq this fall for the first time. The article is highly critical of the V-22 program and I was quite surprised to read that apparently the V-22 cannot autorotate in helicopter mode. The author makes a big deal out of this so I don't think it's a matter of a layman misunderstanding the capabilities of the aircraft. As per the article, the V-22 has a dead-man's curve that extends all the way to 2,000 feet and 200 knots (in helicopter mode, presumably). The Pentagon quietly struck the autorotation requirement from the program after it became clear that the V-22 was going to be unable to do it without extensive (and expensive) modifications, citing the relative rarity of dual engine failures.

Granted, there are only a few scenarios possible where a tandem rotor twin would ever need to autorotate but Iraq doesn't strike me as the place where you would want to explore the odds of one of those scenarios unfolding. Anyone here experienced with the V-22?

Defense Industry Daily article covering the issue.

I take it that there is a sync shaft so in the event of a single engine failure, the remaining engine can drive both props / rotors (or whatever they are called on this aircraft).

To not have an autorotation capability seems 'unwise' to say the least - can this really be true? Double engine failures are rare but they do happen. I know the crew that autorotated an RAF Chinook to an engine off landing after what was more or less a double engine failure in recent years. It's very 'brave' or foolhardy to believe it will never happen to you. Just wait and see the lawsuits and the mod programs after the first multi fatal crash.

Looking at its short, stubby wings, I bet the glide performance in aeroplane mode is appalling and terrifying. In helicopter mode, even if the blades could autorotate, the empennage would lead to some unusual handling issues and surely a massive nose down moment. Is the Osprey the worst of both worlds, helo and plank, rather than the best?

"I take it that there is a sync shaft so in the event of a single engine failure, the remaining engine can drive both props / rotors (or whatever they are called on this aircraft)."

It would appear not. After reading the journal article I found the following:

"The Osprey's big problem is that it risks losing lift in just one of its two engines, in which case it will flip over and begin to fall upside down. This has led to previous test flight crashes which were fatal to all concerned."

:(

You know, I think that the designers probably thought about that.....:rolleyes:

The Osprey can carry 24 combat troops, or up to 20,000 pounds of internal cargo or 15,000 pounds of external cargo, at twice the speed of a helicopter. It includes crosscoupled transmissions so either engine can power the rotors if one engine fails. The rotors can fold and the wing rotates so the aircraft can be stored on board an aircraft carrier or assault ship.

See http://www.boeing.com/rotorcraft/mil...2_overview.pdf

Hardly likely. :hmm:

http://avia.russian.ee/helicopters_e...tol_osprey.php

Beaten to it. :)

Plus - Performance

Service ceiling, ft (m) -- 26,000 (7,925)
Service ceiling, one engine inop, ft (m)
11,300 (3,444)

What, all concerned? Even the designers and Mrs Miggens whose garden it flew over?

:mad:in' journos.

I believe there is a basic problem with tiltrotors. Either engine can power both rotors if one engine fails (like the Chinook). But because the rotors are on either side, if the power from the rotors gets wildly out of sync, it’s possible for the aircraft to go into an uncontrollabe roll. The so-called Vortex Ring State (VRS) is one way this can happen, and that was what caused at least one of the 3 fatal accidents that have dogged Osprey since it first flew in 1989. That - 18 years - is how long it’s been in development. 30 people died in the three accidents - and in 2000 development was grounded. The Pentagon gave two years for the programme to be sorted out. It was sorted out - basically by restricting the aircraft so that it never gets into that vulnerable corner of the flight envelope. That’s why it now has warning systems for VRS, and improved training for pilots in VRS awareness.

Osprey achieved its successful operational evaluation in June 2005, and the Pentagon approved full scale production in September 2005. Now it faces its greatest test, in operational service.

Btw, I also blinked at what nacluv quotes
I believe there’s an error there - the report should perhaps refer to ‘rotors’ in this sentence, rather than ‘engines’.

airsound

That's the problem with selective quotation. The following sentence makes clear the issue and the context:

.....The Osprey's big problem is that it risks losing lift in just one of its two engines, in which case it will flip over and begin to fall upside down. This has led to previous test flight crashes which were fatal to all concerned. As the OT-IIG report states, "When descending at a high rate with low forward speed, the rotor can become enveloped in its own downwash, which can result in a substantial loss of lift. … Should one rotor enter VRS and lose more lift than the other rotor, a sudden roll can result, which quickly couples into a[n inverted] nose-down pitch."

Sorry chaps but a vortex ring state affects conventional helicopters just as much as Osprey. The only difference is the potential for a lift asymmetry in the V-22.

It's still a very bad day out for any chopper.

c-bert - sorry, I didn't mean to imply that VRS was exclusive to tiltrotors, and I'm aware that it'll ruin the day of any chopper. But, if I've understood correctly (not guaranteed, by any means), the asymmetric aspect has become a virtually insurmountable problem for tiltrotors, whereas conventional choppers manage mostly to avoid the worst results of VRS.

I'm prepared to be corrected!

airsound

I'm afraid I don't know enough about the project to really comment, other than to say logic implies that VRS is an irrecoverable condition for a tilt rotor.

That said, I'm sure with the advanced control software the thing must have they should be able to prevent/limit control inputs that would allow it to occur.

Can someone explain why you'd need to autorotate in a twin-engine aircraft? After all, the 757 that I took from LGW to EWR the other day doesn't have an official two-engine-out mode.

Of course there have been all-engine losses due to fuel tanks inadvertently becoming filled with air, or trying to make the RB.211s breathe volcano dust... but why are helos particularly susceptible?

On the VRS issue, to clarify - all helos are susceptible and it can be serious, but the worst case is that the helo sinks - pilot pours on pitch and power - sink gets worse - pilot says B***er, it's VRS, pushes collective fwd, flies out of vortex.

In the Marana crash, VRS struck first on one side which made the aircraft roll, not sink. Pilot instinctively reacted with opposite stick, but more power/pitch makes VRS worse, so the controls were effectively reversed.

Tactics and training have been changed to avoid VRS - the approach to the landing zone is fast, low, quiet and exploits the fact that the V-22 comes to a rapid screeching halt when the nacelles go vertical. The result is a short slow vertical descent rather than a long descent where the pilot wants to go fast to speed transit through a vulnerable zone.

Well the V-22's first combat deployment started today, they left USS Wasp in the Red Sea last night and flew via Jordon to western Iraq.

Really? What exactly happens when you push the collective forward in a helo? :confused:

The helo moves forward and leaves the vortex behind. VRS happens in high descent rates when the helo descends into its own downwash, so the trick is to fly out of the downwash column.

Now I'm no rotor-head, but if the thing is in VRS and you push the cyclic forward it seems to me not much is going to happen...

...or should I just shut up?

Not being an Osprey guy, but being posted where the OCU is, I can tell you there's lots of mis-information in this post - to include all articles linked. In fact, too much mis-information to debate singly.

Having been an alternate to field acft as initial cadre (I wasn't selected ultimately), I do know quite a bit about it. Additionally, my best mate out here is one of the contract instructors for the bird.

Some truths:
Can't autorotate - has to do with both aiflow over/through/around the acft AND the engines. One engine can drive both props. Losing the main transmission in an Osprey is just as bad as losing the main transmission in a helo. You quit flying.

It IS fly by wire & the computer DOES think it's smarter than the pilot. Some aspects of flight performance are, in my opinion, adversely impacted by this.

Recovery from VRS is a well-detailed drill in the simulator. I believe, the answer is to push nacelles forward to gain forward velocity, but I haven't done this, so I'm an unreliable source of info. I do know that the controls are what take the most time to get used to - both rotary & fixed wing pilots have bad habits to overcome at critical phases of flight.

OPINION - The lengthy development of the Osprey can be partially blamed on USMC as lead service. There was a GAO investigation about 2-3 years ago that looked at transferring lead service duties from USMC to USAF. Didn't happen. The concern (which I share) was that USMC had no experience developing aircraft. The counter-concern was USAF recent experiences in contracting were fraught with corruption (for lack of a better word).

Low observable, so the drill is to push the collective forwards? Collective controls forward flight? I didn't know that.

Spru, Thanks.

I had a look but after the glaring error in line three of the explanation, I lost interest. :oh: