If...........?

[twistgrip]

Guess I’m a bit thick where aerodynamic theory threads are concerned; fascinating though they undoubtedly are. . .. .But – practical theory; well, that can be an interesting issue too.. .. .Twin engine, S & L, cruise speed, near MAUW, three or four thousand feet to play with and jammed collective.. .. .Probably been discussed many times. But, interesting to see the theories.. .. .How to get down……..?

[greenarrow]

1.Jump.. .2.Fly to an area where the ground comes up to meet you.. .3.Cyclic step down but to accept a high speed run on.. .4.In a twin retard one engine to ground idle, check your available power on the other, ie I'm I still flying S/L, Slowly reduce the Nr at achieve a ROD of no more than 200ft per min check you can increase this back to flight. If not bring the idle engine back in to help, then just take your time. (I tried this once in the Lynx Sim and it worked).

[Droopy]

The problem of getting the speed off can be addressed by racking the aircraft round in constant tight turns, slowly washing off the airspeed. The idea is that at a suitable point you can level the aircraft and you will have a brief period at low speed before the fixed pitch will cause the aircraft to climb again or accelerate. This is the point at which use of the throttle can control a descent [need to be careful with tail rotor authority]. Obviously you'd need to practice this several times at altitude before committing yourself to the manoeuvre at low level.

[sprocket]

That scenario gives me the willies. I’m not a pilot so I cannot give any answers to your question, but I’ll be watching for replies.. .FWIW, I was a pax in a 500 when that situation occurred. We were straight and level, about 1000’ AGL when the pilot tried to lower the collective. It was jammed solid!. .We cruised around for a while thinking that the engine was going to fail next just to make things even more interesting. After a bit of a conversation with him, we toyed with the idea of rolling off the throttle slightly and doing some turns, to lose altitude with the intention of ‘running it on’ when we got to the ground. He did not risk raising the stick in case it put us into a climb that we could not get out of.. .The pilot eventually loosened his harness to get a better look at the collective stick and noticed that the seat bottom had shifted slightly across and part of it was now under the lever preventing him from lowering it. The Velcro under the seat prevented him from sliding the seat back to its proper position, so the pilot had to completely undo his harness and raise his bum high enough for me to drag the seat back.

[[email protected]]

I'm with droopy on this one - the turning technique used to be taught on the Wessex and works in both the Lynx and Sea King sims. Hopefully having lost both altitude and airspeed you will be in a position below min drag speed where you can balance power available against speed and achieve a gentle wings level descent (avoiding vortex ring)to land. This would be the time to consider reducing Nr to assist.

[Nick Lappos]

twistgrip,. .. .this one's easier than you think.. .. .First maneuver around and dive down to the deck near a large airport, which should get rid of altitude, don't sweat Vne, you've got bigger problems. From Vcruise to 1.1 Vne should give you well over 2000 ft/min descent. Level off at 100 feet above the deck, line up with the runway, and get ready to pull a rabbit out of your hat. Slow down to Vrsuise again when you level off, of course.. .. .Assuming all other controls are in good shape, bring back the rotor rpm with careful reduction in engine levers. A 10% reduction in Nr is a 20% reduction in thrust and power. Use this to slow the aircraft down, and descend the last few feet. Stall is a problem at high speed, don't get below 90% Nr until down below slow cruise speed, then reduce the lever even more.. .. .Also, increase drag as much as possible, drop gear, blow floats, jettison doors, etc. Arrange a touchdown at 80% Nr or so, then pull levers back further to stop.. .. .Use breaks to roll out.. .. .Try it in the simulator! <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />

[heedm]

There was a story about this, I think in a Bell 47. The collective wasn't stuck, but came detached and the blades somehow went into a very high collective pitch. The solution? Open the door, crawl around the helicopter in climbing high forward speed flight, insert needlenose of leatherman tool into flight controls (while yelling at pilot to move collective little bit up...little down...oops just passed it) reconnect the collective, land and write some new advertising for leatherman.. .. .Okay, maybe it's just an urban legend. Hard to tell nowadays.. .. ._________________. .. .Seriously, one thing I would be concerned with is why is my collective stuck? Stabilize your flight, examine the controls. If you move your thermos coffee cup, maybe you'll be able to lower collective. If you suspect FOD, maybe you can raise a bit of collective and shake things loose. If it's a hydraulic problem, what else are you likely to lose? Each of these situations would alter my action plan.. .. .Personally, I would have been hesitant to dive to 1.1 Vne. Now that Nick mentions that, I will consider it. . .. .Prior to that, I would have beeped the rotor down and sped to Vne (based on actual Nr) to see what kind of descent that gave me. If that gave me 300 fpm and I figure 10-13 minutes of this was fine, then I would carry on. To increase that descent rate I would spiral. No need to be aggressive here unless I have to get to the ground immediately...30 degrees, no reversals will do.. .. .I would set myself up on a single engine profile, use the engine lever to pull one engine out of governing range, but keep it running as high as I can so I can quickly bring it back in for an overshoot. Fly a 3 degree glidepath at about 65 KIAS, flare for a high speed run on landing.. .. .Remember, with most emergencies, the first thing you should do is wind your watch.. . . . <small>[ 17 March 2002, 17:59: Message edited by: heedm ]</small>

[Lu Zuckerman]

To: heedm. .. .Your urban legend is partially correct. It was a Bell but not a model 47. It was a Huey in Vietnam. The crew was pulling maintenance on the helicopter and all of the seats and some of the decking was removed. The mechanic was sitting on a wooden box while running the helicopter. The wire drive on the collective servo broke and the servo went to the high end. The mechanic and his assistant tried laying their full weight on the collective but to no avail. The mechanic tried maintaining directional control but his seat (box) was moving all around. From what I understand he ended shutting off the fuel and the helicopter made a rotating landing damaging the skid shoes but with little other damage.. . . . <small>[ 17 March 2002, 19:39: Message edited by: Lu Zuckerman ]</small>

[Rob_L]

I seem to remember a similar attempt to operate a Bell 47 controls by levering on the swashplate.. .Sadly crewmans head and the stabiliser bar attempted to occupy the same space at the same time.

[helmet fire]

Any Kiwis out there remember an incident about 5 years ago in this vein? I think it was a Hughes 300. Stuck high pitch discovered at level off, machine kept climbing at speed. Pilot could see broken collective to pitch connection. Pax, under instruction from pilot, climbs on to skid, reaches broken bit and they fly helo down to ground for a change of shorts.. .. .I will search NZ database soon to see if I can substantiate. . .. .I was taught to go with the large angle of bank, high G turn to lose height - I hadnt considered the 1.1 VNE. Any reason not to do the turn Nick, or is it just one more way to skin the cat?

[Nick Lappos]

helmet fire,. .The turns are ok I think, but the high g of the turns are perhaps worse than the high speed, considering rotor blade stall. However, whatever works, works, I think.. .. .I teach a trick for pilots to finesse their low speed power and airspeed control. Set level flight at half to 2/3 of the best rate of climb speed (40 knots for big Sikorskys), and let the instructor take the collective and don't let it move. On a clam day, the below works well.. .. .Using only cyclic, adjust airspeed to set a descent or climb at will. Remember that if you speed up, you will climb and if you slow down, you will descend. After a bit of practice, slow down and start a descent, pick a spot and approach it. If falling short, increase speed a bit, if landing long, slow down slightly to steepen up the approach.. .. .I found that most helo pilots can learn to make precision approaches without collective control after a bit of practice!. .. .This fits the original post because, if the stuck collective case has power that is below hover OGE power, you could also slow down until you get the airspeed to the level flight point (perhaps 25 or 30 knots) and then just do the airspeed control trick to land. You will climb a few thousand feet burning off the speed, but you can descend afterward, once speed is under control.

[twistgrip]

I think one way or another (hadn’t considered the 1.1 vne technique before, Nick) it’s probable you could get down to landing height with only slightly sticky trousers.. .The real problem I think comes with the run on landing, which is what most posts advocate. Any high/medium speed landing is going to run into directional difficulty with loss of tail rotor control as the Nr droops, possibly resulting in a roll over – which is a pity after all the sweat. Remember you’re at a high collective pitch setting and the aircraft is going to be very light on the wheels/skids during those critical seconds.. .I think as near a zero speed as you can get, (which I why I like the tight turn scenario) offers the best chance. Pulling back both (or probably one – as you’ll have the other back anyway) engines at the critical moment will probably result in the beginning of a rotating landing, but if it’s at or near zero speed and close to the ground as you can get, you’ll maybe bend the aircraft but not yourself.. .The main problem with this however is that it’s almost certainly a once only attempt, as it would be difficult to fly away from if you screwed it up. Whereas you can have as many goes (fuel permitting) as you want at the run on technique.. .Not sure if simulators can accurately represent the aircraft in this scenario (low NR vs tail rotor thrust).

[heedm]

twistgrip, initially I caught myself in a high governor vein of thinking that led me to consider pulling both engines back. That works fine if you have pitch control, but when you pull both engines back with a high pitch setting, your rotor will droop very dramatically. I don't recommend this.. .. .The run on landing doesn't require any considerable drooping. Beep down and/or pull one engine back to initiate a descent. When you flare at the bottom of the descent, your speed will slow, but your Nr shouldn't change much. Once on the ground you'll want the engines pulled back and the nose lowered quickly. I'm not sure if this would work well in a skid equipped helicopter.

[twistgrip]

I guess it all depends on how much speed you can wash off heedm. If you can get it down to a point where the brakes will be immediately effective, I agree. So a few practice goes first and if that doesn't work, back up to height and the zero speed option. By which time you should have quite an audience!

[sling load]

This was shown to me 19 years ago in a Hughes 300 by my instructor, he only did it once and my memory of it is a little hazy, but we were doing emergency procedures training and jammed pedals and fixed collective was shown.. .. .As I recall, he selected a BROC airspeed and slowly reduced airspeed as we climbed, the aircraft got to a stage where it would not climb anymore with the reducing airspeed. At this point the cyclic was sluggish and as I recall, this was close to the vortex ring state as the aircraft started to descend. He increased the airspeed slightly and regained full cylic effectiveness.. .. .As I recall, he had a descent happening and he flew the aircraft at a speed which he controlled the rate of descent. We didn't do a full touchdown, however he got a descent happening and by use of airspeed controlled the rate of descent. I can't recall how high we climbed till all this took place, but it was 2or maybe 5 thousand feet. . .. .This was so long ago, I have probably forgotton the precise technique, but it was shown to me as part of his training school syllabis.. .. .I have never had the technique shown again in any other machine, multiengine or single turbine.. .. .As I said, this was one event 19 years ago, but he did display a technique that appeared to work, I cant remember the manifold pressure, but it was cruising power.. .. .Maybe Nick could elaborate, is this another method?

[helmet fire]

An excellent suggestion Nick. I remember we used to practice the airspeed thing for the UH-1H with fully jammed closed anti ice vanes (I think) which gave a max power of 25 psi (about 50% of power for those more modern chaps). I can see it would work equally well for this scenario. Great tip - thanks.. .. .twistgrip: I see no problems running on with the skid equipped aircraft, and in fact used to practice just that in the UH-1H and 212/412. As to loss of tail rotor authority - I agree with you on the UH-1H as that could run out of left pedal with 100% RRPM, but not so on 212/412 & 205A1. I believe you would get to an unrecoverable RRPM before noticeable left pedal loss, but this is only a theory as I have not bled them to that extreme (thats what Nick gets paid to frighten himself doing!)

[Geoff Williams]

You may remember from your training, the Power verus Airspeed curve. Its the one with the start at zero airspeed and power required to hover, then rises in power required until about 15 knots then falls in power required as airspeed increases to VBROC then rise again after the lowest power required point as airspeed still increases to Vne. VBROC point is also the MROD and max power available point.. .This curve is for a constant height so if the collective is stuck, hopefully not at a very high power setting, then in order to lose height you must fly either to the left or right of the VBROC/MROD point.. .I much prefer to land at a speed on the left of that point as if you must meet the ground with limited control, the slower the happier!. .Adopting a Power/Speed combination, preferably into wind for lowest G/S, with a "comfortable" rate of descent is an exercise I have often done with students.. .. .Doing turns aids in loosing height initially however diving at the ground makes slowing down difficult as when the nose is raised, up you go again.. .Takes a bit of time to get down, but it works.

[CyclicRick]

I remember (hopefully correct)hydraulics off in a Gazelle placed the pitch lever in such a position that it gave (at the right airspeed) approx 300-500ft rate of decent which then enabled you to concentrate on holding the cyclic. By varying the airspeed you could control the approach onto the ground where you could run on, the only problem then was to get the collective down. The principle is almost the same.. .In the Bell 205 we let it settle and then slow down using the stick to a lower airspeed ( roughly 40kts) and then beep down into a gentle decent. Fighting the collective is a waste of time unless you weigh in at about horse level