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:

Cyclic, cyclic, cyclic?

Yes, unless I have been flying under a total misaprehension these last thirty years, I think someone is confusing the control names.

A more complete explanation, also covering V22 survivability in general:

http://www.globalsecurity.org/milita...22-survive.htm

An excellent site.

Yes, but it over-hypes the advantages of the tilt rotor over the helicopter. Most of the the so-called advantages also apply to helicopters.

Helicopters can also be flown at altitudes where small arms fire is a tiny threat. The SA threat becomes almost negligable at surprisingly low altitudes.

Helicopters can also be given full anti-ice / de-icing protection. The Norwegian Super Pumas flying the North sea have been so equipped for over twenty years.

The tilt rotor will NEVER truly replace the helicopter, except in some specialised (or heavily politically sensitive) roles. It is a specialised aircraft, trading lifting power and low speed handling ability for the "Holy Grail" of a higher cruise speed.

ShyTorque, Spruit's attempt at 'educating' you was downright hilarious! Do they have any idea who you are?

I agree with your point; the tiltrotor concept is in some ways like the autogyro: a courageous attempt at combining the best of a helicopter with the best of an airplane. Sadly, it ends up a compilation of the worst traits of the two modes of flight. Makes you wonder how Bell/Agusta is going to do with their 609. At least it will be able to autorotate. The FAA would never be as cavalier as the Pentagon has been in waiving that requirement. Or would they?

What does the V-22 exactly give the Marines? Speed? Range? Over a short range the Osprey's speed advantage over a helicopter is negligible. And why would they need long range? We're not fighting the USSR anymore. There's got to be a secure airfield within a hundred miles or so of any battlefied, where Marines can get out of a plane and into a helicopter for the last leg of the journey. Nobody likes airport layovers but c'mon...

Rev

Agreed. It strikes me that the V-22 is a rather flash answer to a question that doesn't exist (or maybe did exist but doesn't anymore).:confused:

Revolutionary, No matter, I'm only a mere pilot but I've been around for a while; as a pre-flight I do have a look at what folks have on their profile.

I'm still intrigued by the theory that pushing a collective forward gets a helicopter out of VRS. If there's enough adrenaline around, this might result in something interesting - like the grip end of the collective being pushed off.

Subscribe to OTH warfare and you will understand the importance of the tiltrotor to my brother Marines. The aircraft is going to have further teething problems no doubt, but the concept (if not the aircraft) is a strategic leap in warfare.
Another area is NEO operations. Study even just a bit about the embassy evacuation in Somalia in 1991. The mission was accomplished, despite the equipment available, not because of it.
Even in short range operations there is a large advantage to faster, more capable aircraft. A few minutes may not seem much to an armchair quarterback, but could be the difference between life and death to a grunt in a firefight.

Gents,
The reason why the USMC is so wedded to the concept of the tiltrotor is indeed range. Not in the traditional sense of invading the USSR, but due to the new "Visions" of Sea Basing and Ship-To-Objective-Manoeuvre (STOM). This argues that, rather than conventional amphib doctrine where you assault a coast, build up combat pwr then strike inland to the enemy centres of gravity you simply fly, direct, to the CoG - thus, the arguement goes, providing shock, dislocation and denial of manoeuvre to the enemy (now removing doctrine bulls**t book from ars*). To go 200 miles plus inland from over the horizon offshore requires a fast(ish), survivable (yet to be proved in the V-22's case) aircraft with good range, hence V-22. But, to deliver the same combat effect in one wave as a Sqn of Ch-53s you're going to need an awful lot of them, or launch the -53s a long time before the V-22s and RV at the IP..
Shytorque, you clearly need to be less subtle in your banter.....

Can't the V22 put the rotors forward (as in forward flight) and land like a STOL aircraft in an emergency?

According to a recent whitespace Bell/Boeing presentation, the current recommended solution for 'busting out' of VRS is to apply 2° nacelle tilt using the maximum (=normal) rate of conversion. IIRC, this results in 400–500ft altitude loss. The V-22 is susceptible to entering VRS at descent speeds between 2000-5000fpm and airspeeds up to 40kt.

Not all the way forward to 0°, since this would result in proprotor ground strike. The civil BA609 shares the same drawback.

I/C

Low Observable:
Well I gave a recent example of an autorotation and engine off landing in a twin engine rotary. Your 757 does have a 2 engine out mode - it's called gliding - and it has been useed in anger on large commercial twin jets in recent times. Two examples off the top of my head would be the Airbus the glided about 200 miles into the Azores and the hijacked Ethiopian 767 that ditched off the Comores after running out of fuel.

The point is that double engine failures do occur, often for unpredictable reasons. To design an aircraft that, to use a media term, falls out of the sky following a double engine failure seems unwise to me. Many people owe their lives to the fact that most fixed wing and rotary aircraft can be placed on the ground with a good chance of success following the failure of all engines.

The V-22 has been evaluated by people who know how helicopters work and hence measure its performance against that. A bit like the British Army's initial evaluation of the Tank by Cavalry officers in 1916. The V-22's eventual operational performance will either save it or kill it.

Anyone with an interest in the civil requirements for the tilt rotor (Bell 609) will find details here http://www.faa.gov/aircraft/draft_do...rt%20basis.doc

ShyTorque, if pushing the collective forward doesn't get you out of VRS I suppose you could always get out and push the helicopter forward, no?

Evalu8ter, you clearly have a very sophisticated understanding of the modern battlefield (I myself have none) and I can see now where the V-22 would come in handy. Having said that, as Fg Off Max Stout points out, double engine failures do occur. I just cannot understand how the Pentagon could go forward with an aircraft (one meant to carry a whole complement of troops no less) that is unable to deal with this particular emergency. Is it just a waiting game now to see when the first V-22 malfunctions spectacularly?

You need sinkrates in excess of 1600-1800fpm to enter VRS in V-22. Most aproaches end up with no more than 400fpm sink/flare. At roughly 1000fpm, bitching betty comes on & yells, "sink rate" - should you choose to ignore it, & find yourself entering VRS, a 3-second application of Forward Nacelle & add power to fly out of it results in virtually no altitude loss.

One of the early V-22 crashes resulted because the test pilot kept resetting his master reset & eventually bled all his hydraulics away. The computer analyzes & contains hydraulic leaks through a protocal, but when master reset is iniated, it assumes all is well & must run through the protocal again.
Many of the small problems that are supposed to crop up during DT&E and OT&E have done - the overwhelming majority of them have been fixed.

My understanding of the autorotate deal was compromise. Original design for rotors was actually much larger diameter & sufficient energy was stored in them. In order to accomodate shipborne ops & folding blades, the size was reduced to the point autorotation was ineffective.

Current single engine safe speed is roughly 40-50kts, so you're going to "roll on" (shattering your rotors when you do) with 25-30+ knots of forward airspeed. That's emminently survivable on a hard surface - not so much on an unprepared surface - particularly with a top-heavy beast like the Osprey (probably a lot of tumbling).

Single engine failure in most helos results in arriving at the scene of landing - it merely cushions the autorotation. The same is true of the Osprey. Dual engine failure requires that forward airspeed mentioned in paragraph above.

The Osprey is not, nor was it ever, a helo replacement. It is a different animal entirely. Many USAF brass view it as a Pave Low replacement - it isn't. But those are political problems, not aircraft problems...

"The Osprey is not, nor was it ever, a helo replacement"

Herk
For the USAF or the USMC? If the later, I might have to disagree. The -46 is long in the tooth. Been a number of years since I've been on one, but the Vietnam bullet hole patches were plentiful. If you're talking about a leap in capabilities far beyond a simple one for one replacement with a newer generation helo, then yes.
One thing you didn't mention in the debate over the lead service was the number of times the program was almost killed by the DoD. Then SecDef Cheney tried on many occasions to end it all. Finally after some open warfare within congress quietly led by Marines operatives Cheney relented. To paraphrase him, "OK, just don't shove them down my throat" The Marines enjoy a tremendous reputation within the beltway, I don't know if the USAF would have the political clout to pull off the mission given the tenuous situation it was having with procurement.
One could also argue, the Marines have as much experience as any of the services in introducing vertical lift in to the inventory.

US Herk, "Dual engine failure requires that forward airspeed mentioned in paragraph above". Do you mean the 40-50 knots? So the h/v curve isn't so big after all? To be sure I understand: let's say you're at 1,500 feet and 100 kts with nacelles up in helicopter mode and at that moment both engines decide to quit. What happens next?

Cyclic, collective, schmollective... Jeebus, can't a guy make a mistake? I had been out picking beets on the Agricultural Cooperative No. 541 "V.I. Lenin" and the word was on my mind.

For both.

It's not a helicopter. Period. End of discussion.

People want to put things in nice neat boxes. Well, there's a new box to put stuff in - tiltrotor.

Yes, the USMC wants to replace the CH-46 because they're old. They bought the Osprey. It will do the -46 mission, but that doesn't mean it's a -46 replacement.

Too much semantics? Perhaps.

Same with AFSOC.

If someone wants heavy rotary lift, buy Chinook.

First, I doubt you'd be in those conditions. You would be in transition mode with nacelles at some intermediate angle. In which case you'd continue your forward speed to the crash site...errr...landing site.

Most of the approaches occur low & fast with a near immediate stop. There is no long straight down hover. It will terrain-follow in at 100' & 220+ kts, enter approach mode & take a 4* glidepath down to 50'/0kts. If it all goes pearshaped at 50', well, that's how far you fall. A lot of pure helos will hurt themselves from 50' w/no forward velocity as well - simply not a lot of energy stored in the rotors.

Once again, I'm not an Osprey pilot. But we do have a program here where I can fly it - I'm trying to get my stuff in one sock so I can do so. :ok: