Stuck Pedals

[dimit]

I've heard of and tried a variety of methods for "diagnosing" a high-power, neutral, or low-power stuck pedal. Personally, on a JR the method I've had best results with is to fly at 60 mph and see how much Tq is required to centre the ball. If it's more than hover Tq it's high-power, less than hover Tq is low-power. Then I have a better idea of what to expect at the bottom end of my approach. I don't really know why this method works, though. At 60 mph the tail fin is working pretty hard, when hovering it ain't... Makes me scratch my head and wonder. I've tried this method in an Astar at 60 kias and it turned out that the indication was quite wrong.

 

What method do you prefer? Why do you like it? Can you explain why it works?

 

Look forward to your replies,

 

DM

[canukav8tor]

Dick, it's probably because on the JR's power-required curve, the two points and 60 kts and at/or near IGE hover require the same t/r power (effectiveness). In the IGE hover regime the anti-torque is required to balance the effect of the main rotor working against induced rotor drag, while at speed (~60 kts for the JR as you note) the anti-torque is required to balance the power applied to the main rotor to maintain that cruise speed, less the straight aerodynamic positive stability due to the fin/boom. Aerodynamically, every single m/r helicopter should have two such points where hover power and a certain forward airspeed result in equivalent required t/r power settings.

 

I remember that rule of thumb, it was very close for the Kiowa as well, and the 212 and 412 have similar behaviour.

 

Although not specific to t/r power requirements, the NAVSCOLSCOM site does have some good discussion about power required, particularly the part about the helicopter's equivalent to a high speed jet's 'coffin corner' where IGE hover and min power required points intersect/overlap as extreme altitudes (Mt. Everest).

 

Naval Aviation Schools Command - Helicopter Power Available vs Power Required

 

Cheers

AV8

 

[dimit]

Thanks, AV8. That link leads to a nice presentation on power.

 

I understand your point to be that the T/R power required at ~60kts may be similar to that required at the hover. What confuses me about this is that ~60kts is around the bottom of the JR total power required curve. M/R Tq is significantly lower at ~60kts than in the hover, PLUS there's the tail fin effect, so less T/R should be needed. In fact, hovering a JR at gross weight requires positive power pedal setting, whereas cruising at (basically) Vy requires a neutral or perhaps even slightly negative power pedal setting.

 

What have I missed here?

 

Thanks,

 

DM

[Guest 47yrLowTimer]

Hey Dick,

 

For what it's worth

 

An old Vertical post from 2009

 

http://helicopterforum.verticalreference.com/topic/11654-stuck-pedals/page__view__findpost__p__84392

 

I tried this on Friday with a stuck Left, though not severe worked like a charm on a Jetranger.

[canukav8tor]

Dick, I haven't had a look at a 58/206A RFM in a long time, I had thought min power required was somewhere in the 35-40 kt range. The points you raise are quite valid, so I'll have to dust off my Ray Prouty books and see if there's an answer hiding somewhere in them.

 

I remember an old UH-1 instructor telling me about having plenty of stuck pedals, most of them ironically left, and he noted his preferred technique was to come in a little shallower than the school house taught at Fort Rucker, and gently roll the Nr down as well so that the stop and spin left at the end was less pronounced. I seem to recall the 205/212 family Nr limit power on was 91%, but he mentioned he had several left pedals that he used mid-80's to keep the nose from swinging too far to the left. Never had a stuck pedal in anger, but sure practiced them a lot...the knack on the rights was being careful not to let your speed bleed off too much to the point where you would snap the nose further right trying to regain airspeed or arrest sink rate. For the rights, I recall always bringing the Nr down to mid-90's so that you had a bit of fudge either way to tweak the nose when you got that final speed just right to keep the nose straight.

 

Regards

AV8

[dimit]

47: Haven't tried the 70-80kts-level-read-the-ball diagnosis technique. I wonder if 70-80 is the point on the power curve that matches hover power, as referred to by AV8?

 

AV8: 206B3 Vy is 52kts.

 

Who else can weigh in with a stuck pedal diagnosis method?

 

Thanks all!

 

DM

[Over-Talk]

(The comments below refer mainly to a Bell (clockwise) rotor system, though the basic technique (but opposite pedal) also applies to French machines.

 

First of all, be careful to avoid a hasty definition of "stuck left", and getting committed to a landing technique that may not be appropriate.

For example, if the left pedal is stuck a little left of center, this may be too much pedal to land if you are alone and light on fuel, but it would be not enough pedal to land with a bunch of people/cargo on board.

 

So I try to fly at about 40 knots (maintains minimum steering effect of the tail-fin, and it's a probable maximum safe run-on speed) and apply enough power to simulate a landing at that gross weight/altitude. Can you go this slow?? If so, which "pedal" are you needing, or have too much of???

 

From this you can decide if you have enough "pedal" (or not) to land smoothly with power.

 

Set-up a long approach, and try to get the helicopter going as slowly as is safe...as long as the nose is centered or to the left. DON'T let it go right until at your landing area.

Note, if you don't have much pedal available, you may be traveling very quickly on the approach.

Get to your landing/run-on area and use the throttle as necessary to make the landing (this maneuver is the subject of another thread).

 

A 'stuck' pedal usually allows time to think about what you should do. Use that time well.

A 'loss' of pedal requires an immediate response (i.e, chopping the throttle). Good luck.