Jammed Collective

[overpitched]

We have been sitting around debating this scenario:

Bell 206, pilot only, 40 gals fuel on departure set 85% torque 60 kias. When you level out and you go to lower the collective you find it is jammed at 85% torque. How do you get the aircraft back on the ground in one piece??

:confused: :confused:

[the coyote]

I would think that if you cant descend once you have slowed down and brought it out of translational lift then the only alternative is to wind the throttle off enough to take the Nr back towards 90% to reduce lift and then play with your airspeed/Nr accordingly.

[peter manktelow]

arh...a bit extreme but seem to recall we used to practice same thing in a 204 (Australian Navy UH-1B)

Bring the nose right up to get the speed off...zero if necessary

(the idea is to get the helicopter moving in the direction of down instead of up)

roll her on her side and pull like a mad man. Out of balance will also help.

The tricky bit is when the grounds starts looming up.

Cant remember what we did then...sorry

[Whirlybird]

Had this demonstrated at the end of my FI course, after discussing it for ages. It was an an R22, but ought to be similar for any helicopter, I think. I tried bringing back the speed, and while theoretically it works, it's horrible - you end up in a high hover and hardly descending at all, just wobbling around all over the sky (a technical term!) and risking vortex ring. What I was shown is to close the throttle a bit, at the same time starting a turn; this increases the disc loading, thus raising the RPM so that it doesn't get too low. Then keep going in a gentle descending turn until you're near the ground, and then...I can't remember!!! I guess you'd roll the wings level just before you lose translational lift, then do a run-on landing. Should work, I think.:eek:

[Thumper2]

Perhaps push forward on cyclic make a fast go around, then on final push further foward on cyclic while beeping back or reducing throttle. Once you have decended back to the area of mother earth apply aft cyclic while increasing Nr with opposite throttle or beeping. Once in the hover reduce throttle or beep again and settle gently back to earth.

Wish that could my biggest worry!

[chopperman]

Just my suggestion, for what it's worth.
After you find a suitable landing site, (I would suggest a long flat one with fire cover available), get the aircraft on the wrong side of the drag curve to start a rate of descent. As you get close to the ground the ground cushion should slow the rate of descent, if it's to high I suppose you could always try a little forward speed (but not above translational lift). If the aircraft sits on the ground cushion, gentle close throttle and overpitch onto the ground, should the aircraft run on, close the throttle(s) slowly or you will probably roll over.
Simple or what? It may sound simple, but I can assure you that this situation is a real nasty. Let's hope it never happens to you. Fly safely,
Chopperman.

[John Bicker]

Tricky this one! 85% Torque with 1 on board and 40 gallons might be hard to get on the "back side of the curve". Haven't flown a 206 for a while, it would probably hover OGE at this power setting. A really high landing site might help!

As for the theories of reducing the RRPM, be a little careful going down this track as the TR loses performance much sooner than the MR. In fact the MR on most helicopters becomes more efficient at lower RPM.

And of course as you are thinking about how to extract yourself from this position you are getting lighter!

Somebody got a 206 they can take out and see what the real numbers are?

[overpitched]

Thanks for the feedback. The configuration I have mentioned of 85% torque and 60 kias is standard climb configuration so you find yourself with these numbers on the dials everytime you fly. On a rescent flight we slowed to a hover at 85% torque and were still climbing vertically at about 500 fpm when we gave up the exercise going thru 4500 feet. Now that sounds like an awfull lot of throttle roll off to establish a descent. Any thoughts ??

[Blue Rotor Ronin]

run on landing...easy.:ok:

[the coyote]

John,

Valid point about the tail rotor. With regard to main rotor efficiency, it may become more efficient (lift vs drag ratio) at a lower RRPM but it will still produce less total lift for a given pitch setting. Lift is proportional to the square of the airspeed over the aerofoil, all other factors remaining constant.

I would think that if you were still climbing at 500 fpm at zero airspeed with a stuck collective, then you are in a bind that calls for drastic action.

In that situation I would reduce RRPM with throttle as much as I felt comfortable with (towards 90%). I would experiment with manouvreability at this reduced RRPM, considering the possible increased chance of retreating blade stall or stalling regions of the main rotor disc during manouvres. If that was the case, (probably evident by massive vibrations!) I would leave it at 97% (bottom of the N2 green band).

Then I would get it down to the ground by turning it on its side at slow speed (a tight descending turn), setting up the highest rate of descent I could. As the ground comes up and as late as possible, roll it right way up (which would rapidly take care of that ROD), lose any speed you have and roll off the throttle, all as quickly as I could before it started climbing again. Wait for what would be a significant but hopefully well survivable impact.

I would definitely experiment with it once or twice before committing myself to landing by rolling off the throttle completely. The 20kg of fuel you might burn in 15 min of experimenting in my opinion is not going to make your predicament much worse.

[Ascend Charlie]

Well, Mr Coyote, the theory isn't bad, it works in a fixed-wing as well, but in a helo it doesn't quite work out like that in practice.
All is OK until you get to the "roll it on its side at low speed and descend".

You end up turning so fast (to keep airspeed less than 20kt) it topples your eyeballs and you get dizzy well before you lose 500 feet. And rolling out puts you back in a climb.

Stick with the reduced RRPM and low-to-zero speed. It will take time to come down, but that gives you plenty of time to think about things. Don't beep the revs back, because if you suddenly need some revs, the beep is too slow, Use throttle only. BUT!!! Remember that the B206 flight manual prohibits using the throttle to control power in a practise situation. Legalities...

And if the engine subsequently quits, the TILT light comes on and the game is over.

A student can be taught to think about energy management and stuck collectives by setting, say, 16"MAP in a Robbie or 35% TQ in a B206 while on early downwind at a quiet airfield or over a large field and let them play with airspeeds and flight paths, s-turns etc to wash off speed to land at a nominated spot. The touchdown is the tricky bit, being unable to lower the lever to peg it on the ground.

[John Bicker]

Coyote gets my vote as the best solution so far. The tight descending turn gets it on the back of the curve. I would be a little careful still of using the throttle. What you are doing is removing the N2 governor from the game by resetting the Max N1 stop. I think this would complicate things more than would be benefitted from it.

Put everything you have in the left rear corner so to speak. It was standard practice moons ago in a H500 to get the things down in a narrow vertical space. Huge rates of descent can be seen with very little airspeed. From the ground it looks like an aeroplane in a spin and probably follows a similar path.

Once you get it near the ground roll out and close the throttle to idle and wait. The tail rotor still works of course so at least you would be able to keep it straight for a while. With this pitch setting though RRPM is going to vanish very quickly and you would hope to be close to the ground before it starts to rotate. Contrary to the simplistic view of some there is friction in the drivetrain.

Whichever way you slice it - nasty.

Again moons ago it was possible to get a H500 to spin around a point with 90 degrees of yaw to the extent that it would look like it was 70 degrees nose down and looked like an aircraft in a spin yet it was not descending, in fact if you were good you could get it to climb like this. The limiting factor was available power. It looked really strange and on reflection probably really stupid.

Back in the days of Young, Dumb and F............

[Whirlybird]

I haven't practised this in a B206, but as I mentioned briefly, I have done it in an R22, so perhaps some detail would be of interest.

Having discussed it: "What do you think you do?" asked the instructor. I said to slow down, wrong side of drag curve etc. "OK", he said, "try it". I can't remember how much collective we had, but we were straight and level, so I'd guess around 20". I slowed down, and slowed down, and slowed down.... Eventually we did get a ROD, but despite power curves and theory and all that, it really wasn't going to work. We were at 1000ft, very low airspeed, descending with no collective...not nice!!! So..."I'll show you", said the instructor. He rolled off throttle, at the same time putting it into a turn to raise the RPM. He controlled the RPM with throttle and angle of bank, and as far as I remember it wasn't that steep a turn. At any rate, we descended in a neat spiral in a very controlled fashion, until he rolled the wings level close to the ground, and I can't remember the details of what he did then, but I think all you can do is lose translational lift and do a run-on landing.

Now, it may be different for a B206; I don't know, though I can't think why it would be that different. And the fact that an extremely high hours instructor makes it look easy.... So I'm not trying to say what's best, and I hope I never have to find out for real :eek: :eek: :eek:. But I thought this might be at least vaguely relevant.

[Ascend Charlie]

Yes, Cap'n Bicker, that trick with the 500 must be a kiwi specialty.

We did our 500 endorsements with your almost-namesake (sounds the same when you put in his New Zillund ecksunt) in your previous employer's old bus, the C-18 machine. He kept talking about a thung called a Turtle Dick and i couldn't see anything that looked like that. It was up on the roof somewhere...

The airborne sequences included the nose-down-roll-like-crazy dive at the dirt which certainly reminded me of a Macchi in a fully developed spin. He said it was useful for losing altitude - would have been more useful if it would GAIN altitude, as mostly we are down in the weeds anyway.

But certainly an eye-opener!:eek:

[the coyote]

Ascend Charlie,

For a situation like this where you CAN descend at no airspeed and/or a reduced RRPM, by all means it is not a huge problem. And you have the ability to tweak in a bit of throttle or tickle a few knots on and run it on to stop your ROD in this situation. I am more responding to a situation where even in the hover you have a rate of climb, and thats nasty. I disagree with you re the descending turn. Try slowing it down, drop the nose and roll it into a turn, around 45 deg, then use a significant amount of pedal (as in nearly all of it) to pull it into the turn and out of balance, ie left turn, left pedal. You will find if you do it right a tight descending turn that doesn't keep winding up.

By the way, in my earlier post, you don't need to be slow in the descending turn, do it at 60K if you like. The aircraft will descend at any airspeed with a high angle of bank. At the bottom is where you need to pull the speed off, and you need to do that while you are still in the turn or it will climb too far away from the ground, so thats when you tighten it right up.

Whirly, 20" MP in the R22 with two on board, you will be able to land it relatively easily by varying airspeed alone. I am yet to hover the R22 in nil wind with 2 POB using less than 20" MP, and so it will descend by coming out of ETL. A B206 single pilot with 40 Gals stuck at 85% Tq probably equates to a 60 Kg pilot in a robbie with no fuel and stuck on 24" or more. Ask you instructor how he would land if he was still climbing in the hover.

[Hughes500]

Tried this in a line and base check on a gazelle about 2 months ago. Problem with Gazelle throttle is in the roof. We had about 65 to 70 % torque. Had to fly at minimum speed to iniate a descent - took about 15 miles to lose 1500ft !!!As we came close to ground pull back a la quick stop and she settled on the ground. A bit tricky if you had more power on though !!!!!!!!

[Blue Rotor Ronin]

Run on landing....... easy!!!:ok:

[B Sousa]

An Interesting topic and a tale from Vietnam as told to me by the Pilot who flew it. Mike Gralian (Sacramento California) was a Maintenance Officer with I believe the 1st Cav. He took minimal crew on board for a topping check in a UH-1. Basically a handful of collective and off We go to get some reading on the guages.. Problem turned out to be the aircraft had just come out of extensive maintenance and someone ( Murphy) had installed a bolt in backwards allowing the long end of the bolt to get in the way of the collective. When they were at a point ready to descend, collective would not go down. According to Mike it was panic city for many minutes. Aircraft continued to climb. He stated it was somewhere near 18000 feet that in desperation the crewchief actually stood on the collective. (You can move around in the Huey). That extreme move was enough to free the thing without losing the rotor head from sudden down collective.
Anyway they all survived and headed for the club on landing.
Things like this do happen.

[Blue Rotor Ronin]

Had it happen whilst still a student, first priority ......get her away from the ground...... steep descending turn over the airfield, with the boys in red watching. Ran on at 50 odd kts...Easy.As I've mentioned before:ok:

[Shawn Coyle]

The problem with trying this in a Bell 206 is that the throttle is not conducive to being played with, due to the limited travel between idle and fly. You need to be very careful, and if I remember rightly there is some caution about having the throttle anywhere except idle or fly.
It evidently did happen for real to a 206 a long time ago, but I don't know the details - pilot did exactly as has been discussed. But then again, the collective should never jam...

And if it did jam, would you know enough to report it as a Service Difficulty Report when you got on the ground???