Running out of pedal

[3 D]

Ok so here goes:

As a very inexperienced training pilot (Grand total of 30 hrs so far) I had a very interesting experience today whilst hovering in an R22. We were experiencing a slight wind from the starboard side approx 10-12kts (perhaps also a little from the rear) when I ran out of left pedal, fortunately we were not yawing to the right so it did not cause a problem but it was more than a little worrying to reach the end of the pedal travel!

My questions are about design, 10-12 kts is not a very stiff wind, I think, and yet it was sufficient to require all of the tail rotors control movement to keep us pointing in the desired direction. Is this normal and if so why don't we have much more powerful tail rotors to prevent this? What typically is the limiting factor on the amount of thrust available from a tail rotor is it the angle of attack of the blades or power limitations or other things?

I have of course discussed this with my instructor but would really appreciate any comments from the great wealth of experience out there and hopefully it will help me understand more and avoid a similar situation in the future.

[squawk1181]

3 D,
Please share with us the comments of your instructor. I have over 900 hours as an instructor in R22s and never ran out of tailrotor - even in winds over 35 Kts. I thought that the R22 has a very effective tailrotor.
Thanks
:confused:

[squawk1181]

P.S.:
LTE (= Loss of Tailrotor Effectiveness) can be caused by
1) left cross wind (vortex ring state in tailrotor)
2) wind from the left front (interference of mainrotor vortices)
3) tailwind (weathervane effect)
- in counter-clockwise rotating systems...

[Steve76]

Its all a combination of AUW + Density Alt.
If you require more collective you will require more LH Pedal.
The question needs to be asked as to why the helo wasn't hovering into wind?

[[email protected]]

3D, when you are hovering in a crosswind from the right, the natural tendency of the aircraft is to yaw into wind (weathercock effect) therefore you will require more left pedal to maintain your heading.
Try hovering in 4 different configurations ie intowind, downwind, crosswind left and crosswind right and make a note of your pedal and cyclic positions. Generally into and downwind will be the same apart from the extra twitchiness downwind, crosswind from the left will give minimum left pedal and crosswind from the right maximum left pedal.
If you can, also note how the hover attitude changes along with the power required - this exercise helps reinforce a lot of the groundschool stuff about TR drift and roll.
I think I am right in saying the R22 has a 15 kt downwind limit but in my experience pilots conveniently ignore this, right up to the point when they get spun round into wind due to weathercocking.

[TeeS]

Steve 76
I don't know if I missed your point but isn't it normal to teach a student to hover crosswind, downwind etc?

[the coyote]

I must agree with squawk1181. To me they seem to have plenty of tail rotor authority.

Its been a while for me in the R22, but if my memory serves me correctly the flight manual states that they are demonstrated to handle up to 17Kts from any direction. Don't quote me but I believe this may be a certification requirement for the aircraft with the FAA. In reality they can handle far more, I have done spot turns with them in 35 Kts.

Some things for you to think about:

As Steve76 pointed out, the higher you go, the less power AND tail rotor authority you will have.

How was your RPM? If the governor was on and functioning normally then presumably it was 104%, but a drop in RPM not only reduces lift but significantly reduces the capacity of the tail rotor.

Arresting a high right yaw rate can be difficult, there is a large power demand on the engine to produce the additional tail rotor thrust, and rapid or violent left pedal inputs can easily reduce your RRPM and thus TR thrust, not to mention the possibility of high stresses on the airframe/power train.

With 10 Kts or so of wind from the right, there is no chance in my view you had any LTE.

In addition to your healthy concern and a desire to further your understanding (which I admire), look beyond that and take it one step further as a student.

What would you have done had you run out of pedal and couldn't stop the turn? What situations may lead to you being in that situation, with regard to density altitude, wind, power demands, power/airspeed combinations. If you can pre-program your mind and instinctive actions/reactions it may help you when you are surprised one day with not a lot of time to act. Know the cures for any given problem, but also know the preventions.

Likewise, I am interested to hear what your instructor had to say.

Enjoy your training!

[Nick Lappos]

the coyote is onto something with the discussion of RPM reduction. If you slip down in Nr by even a bit, it can have a double effect. Here's why:
The thrust you deliver from the tail rotor creates the anti-torque, and is proportional to the pitch setting and the square of the Nr. If you reduce Nr by 2%, you reduce the thrust by 4%, which could get you close to limits in some cases.

The anti-torque that you need is proportional to the main rotor torque. If you droop Nr, the rotor needs the same power, but power is torque times Nr, so for constant power, the Main Rotor torque must go up. For a 2% droop in Nr, the torque will rise by 2%, and the anti-torque needed wil have to rise.

Thus, a given droop in Nr produces non-linear effect on the tail rotor margin.

A third effect is the need for the helicopter to point into the wind, like a weathervane. When crosswind, this effect is maximized.

Another effect that can play is vertical maneuvering. Note that a slight torque rise (manifold pressure for recips) will require a corresponding anti-torque response to maintain heading. If you nudge the collective upward and droop the Nr a bit, you can easily carve 5 or 7 knots off the side flight capability of the machine. For a hairy flare at the bottom of a too-fast approach, the main torque can be pumped to 10 or 15% above hover torque, and the tail rotor can be saturated.

There really is no such thing as Loss of Tail Rotor Effectiveness, BTW - for a given density altitude, the tail rotor always produces a given maximum amount of thrust and a given maximum effectiveness, it is just that it can be swamped by main rotor torque rises, and by crosswind effects. Generally, only marginal tail rotors experience LTE, and the vast majority of LTE events are experienced by only two types of helicopter. LTE is not a pervasive helicopter problem.

[Kirt Hood]

Nick , maybe you could answer this if you would, or anyone else here for that mater. When I was checked out on the R-22 my instuctor pointed out that when hovering in a brisk wind off to the right front the tail will want to wether vane but with the wind off the left front the tail wants to be drawn into the wind. I find this rather spooky, a few times when in a hover it would snap turn to the right (tail drawn into the wind) rather fast and I would fly out of it before to long. usually 90 to 120 deg. In a 500' hover if there is no noticable exact wind direction it's disconcerting if I get a brisk wind just off from the left and then all of a sudden it snap turns right , this being with no collective input until after the turn, then lowered with forward cyclic to fly out of it. What would be the reason for this and is there any indication to the onset of it happening or is it just the nature of the beast (R-22) and lack of experience? Hope this question makes sense.

[the coyote]

Kirt, I presume you are saying that with the wind from this direction (10-11 oclock relative) the nose of the aircraft tends to yaw right rather than weather cock into the wind. I have never really found this to occur, although I do find them noticeably twithy with the wind there. The only thing I can think of that will cause right yaw in this situation is torque reaction due to a reduction of tail rotor thrust. I believe this would be due to disturbed air from the main rotor vortices of the retreating blade passing onto/into/around the tail rotor and causing random changes in tail rotor thrust allowing the torque to 'win' and yaw it right.

Have you noticed that it is always more twitchy to hover with a left crosswind than a right one in the R22? I believe it is for a similar reason, this time disturbed air from the tail rotor itself being blown back and affecting the induced flow from it and thus causing variations in tail rotor thrust.

However I must point out I am no guru in physics or aerodynamics, so take it as my theory only. I would be interested to hear from NL or others with far more knowledge/authority in this area what they think about my theories. Aside from what I think to be the early model Bell 206's with the smaller tail rotor, I am also interested to know what other aircraft are prone to LTE?

[3 D]

To answer some of the points raised:

The governor was on and functioning normally with RRpm at 104% on the gauge.

The MAP was approx 23.5 inches (not excessive in my limited experience and less than I have used in the hover before) I did check this at the time because I wondered why I had run out of pedal and thought I may be producing too much torque with the main rotor. My Instructor also looked at this and confirmed this reading.

To explain the situation rather more accurately we were hover taxiing very slowly to a FATO not really hovering cross wind, although we do practice this of course as we have spot turns with stops at the four points. The hover taxi was one of my better efforts and we were really nice and stable so I wasn't using lots of pedal to arrest an excessive rate of yaw just a continuous need for lots of pedal to maintain the heading.

One of the main reasons I discussed this with my instructor (and other pilots) was to try to gain a better knowledge of the reasons for this happening and make sure that I have set in my mind exactly what I should do should I ever experience the same or worse situation on my own. He asked me what I thought I should do first and then explained the correct course of actions and the reasons behind them.

Assuming a similar situation but not being able to arrest the yaw with the pedal available he said if:

There was lots of nice open space then I should fly the helicopter forwards round the corner, accepting the low rate of yaw, until I come round into wind giving me sufficient tail rotor authority.

If I was in a confined area type situation where the above was not possible and the yaw not acceptable the only course of action would be to stop any movement across the ground with cyclic and lower the collective landing with the yaw if it was still present at the lower power setting.

During the flight debrief my instructor commented that he had on a flight in the same machine just half an hour before my flight had a very similar experience when he was hover taxiing (I think he was expecting it to happen on our flight so had his eye on things on the way out to see if any indications could explain it). Speaking to another instructor who flew the machine today he commented that he also noticed that more left pedal was required than normal. In conclusion the engineers will be asked to inspect the rigging as it is thought that something may need adjusting.

Hope I haven't gone on too much but I wanted to answer all that I could.

Thanks for all the great replies special thanks to Nick who as always explained something books never seem to.

As an aside have any of you had similar LTE experiences and if so what did you have to do?

P.S. I would love your comments on the hollow rotor blade idea if you ever get chance Nick.

[MightyGem]

Back in the early days of the Lynx (British Army), it was quite common to run out of left pedal when trying to spot turn to the left in a bit of a breeze. The solution, given a decent hover height, was to dump the collective a bit to reduce torque, and get the turn going again.

[Buitenzorg]

3 D, I wasn't in the cockpit with you, so I can only give you some general insight based on instructing in R22s for about 800 hours.

The R22 has very good tail rotor authority compared to most other helicopters. I've never run out of left pedal, including hovering in pretty high (~30 kts) crosswinds; hard work and twitchy, yes, but never out of control. But many students including myself have gone into a merry right-hand spin, convinced we had full left pedal in. When the instructor took over and the student relaxed, there was always found to be at least 1" of pedal travel unused and available. The student would simply be so tense that even leaning on the left pedal the tensed-up right leg would not budge. As a matter of fact, I had two students this afternoon do just that! The only way you could really be sure you used full left pedal is if you actively lifted your right foot off the pedal; if you did that during the episode you described, the tail rotor controls must be mis-rigged.

BTW, the POH states (in the Performance section, not in the Limitations section) that "Hover controllability has been substantiated in 17 knot wind from any direction up to 9,800 feet density altitude". 17 knots is the minimum required for certification, so they stopped testing (or at least documenting the testing) at that. You'll see the same 17 knots in the POH for quite a few other helicopter types.

[GIMPOSH]

Having spent the last 2000 hours in Bells wonder machine the UH-1H I have run out of TR on may occasions. Anyone who has flown the Huey (especially the earlier models with the TR on the right) hot / high / heavy (heaven forbid all three at once) will know it is not a matter of when but how fast it will turn. I always assess the approach and ACFT performance PRIOR to ETL, one of my mental checks is power / pedal position. If you seem to be using more left pedal than normal at this stage it might be time to decide if you want to get any slower, and why is it like that. Keep on top of the heading in the hover, the faster the divergence the more pedal needed to stop it and sometimes there just isn’t enough.
Just my $0.02 worth

[3 D]

Thanks for the advice and words of wisdom guys.

much appreciated

3d

[[email protected]]

3D, I think the answer is definitely related to interaction between the main rotor vortices and the tail rotor. This would not be a factor in a true crosswind hover, but as you move into a hover taxy, your relative wind starts to move forward and the main rotor wash moves backwards. The problems of tail rotor authority and running out of power used to be demonstrated on the Wessex at MaxAUM - the worst position was with a wind from half past ten to 11 o'clock , this produced high Tq as large left pedal inputs were required to control the heading. Running out of TR authority was a real factor in the Wessex at High AUM/density altitude, it is still operated in Cyprus with a weight limitation at the top of Troodos as you are at the edge of the flight envelope. I and many others have discovered the joys! of running out of pedal there and having to dive down the mountainside trying to get some speed on to recover the situation.
To other R22 gods BTW, I am always impressed by those who are not test pilots who feel utterly justified in saying "I know its not certified to do this but I'll give it a go anyway" encouraging people to fly an R22, or any other helicopter beyond it's certified limits is unprofessional. If you are prepared to exceed one limitation, where do you draw the line? Add another inch to your personal MAP limits because you know the engine won't blow up? Add a few more pounds of fuel because the last time you got airborne at MAUM there was still some power left? Spot turns at 35 kts - you must be pissed!

[the coyote]

To crab, just a quick note in my defence. I presume your comment about spot turns in 35 Kts was directed at me.

To the best of my memory, the flight manual states "hover capability has been demonstrated up to 17Kts with the wind from any direction" or words to that effect. I am not aware of it being a stated limitation, if I am wrong or there is one then I stand corrected and go back to work with my tail between my legs, everyone occasionally slips up.

I agree with you entirely regarding your comments about keeping within the limits. I reject any inferrence from you that I may be one of those pilots to throw all limits out the window, and those that know me know I don't do that. By the way no hard feelings. The reason I posted that comment was to illustrate that 10-15 kts shouldn't be a problem, and definitely not to brag or encourage someone to go out and push some limit.

As an aside, let me pose a question for thought: An aircraft has say a 20Kt downwind hover limit. Its been parked up overnight and now in the morning its blowing 25 Kts on the tail. Do you wait all day or do you go? A limit is a limit, but how accurate is the average pilots judgement of windstrength without aids?

[[email protected]]

Coyote,

If the 17 knot certification is not intended as at least a guide for sensible caution then how do you define the cross and downwind limits for the R22? Does it just mean that there are no wind limits for the aircraft and you can just keep pushing the flight envelope as long as your cojones are big enough. Will the aircraft fly faster than its certifed VNE? probably but should you do it and are you confident that you can calculate the stresses and strains the extra fatigue causes on component life?

In answer to your second question, what is your need to get airborne? Life saving or pleasure flying? Exceeding the limits of an aircraft is something that most pilots will have to do at some point in their lives but they need to be able to justify why they did it. Starting the rotors and getting airborne in 25 kts with a 20 kts downwind limit would be an acceptable risk to complete a SAR or similar mission but if you do it for a pleasure flight and cock it up you had better be ready to face the music. "Sorry boss I crashed the aircraft/hit the tail boom/overstressed the transmission, because I couldn't wait for the wind to drop/ couldn't be ar*ed to get it towed into wind/couldn't say no to the passengers" is not exactly the moral high ground.
I am sure you are not a cowboy but I am also aware that GA is not overly well policed and few pilots/owners ever seek post graduate training after gaining their PPL. A mechanical limit is relatively easy to calculate - a personal limit is usually only recognised after it has been exceeded.

[Nick Lappos]

The cayote is not in violation, and not even showing bad sense, IMHO. The crosswind demonstration is made using adequate control, usually defined by a trimmed point where there is enough pedal left to command some turn in either direction. It can be 10% remaining pedal, or any pedal at all just so that a slight yaw rate can be generated when on the pedal stops.
Doing this under controlled circumstances while in a stable hover condition is an effective way to prevent LTE, and is good training in my book. The only negative outcome is that the aircraft will not achieve the desired heading, and will stop its yaw. Worst case is that it will head up into the wind.

If it is a limit, in section I of the flight manual, then it should not be challenged, of course. The use of the word limit can't be bandied about. By LIMIT, I mean that it is expressly prohibited by the flight manual, or other publication of the government or manufacturer. A real maneuvering limit, like a stall speed in a fixed wing, might be reached and demonstrated often without violating the manual, or common sense.

LTE occurs, and tail rotor margins become dangerous, when the pilot waltzes into the problem with vertical maneuvering, usually when he arrests an approach at the bottom using a healthy extra bit of torque or manifold pressure. In such a case, the uncontrolled yaw might be so inadequate that the classic LTE spinning might occur.

I think healthy instruction as to the limits with controlled demonstartions is one way to educate and prevent LTE.

[[email protected]]

Nick, whilst I agree that the 17 kts certification is not a limit and therefore not in section 1, I have to ask you where you would advise low time pilots to draw the line regarding cross and downwind hovering? Yes, demonstrations of recovery from LTE and running out of aft cyclic downwind must be taught - but once a pilot has his PPLH, who is there to guide him as to what he should and should not attempt. If relying on commonsense were the answer there would not be half as many incidents and accidents in helicopters as there are.
As you well know, in the military an aircraft is given a release to service with limitations on just about everything but always including cross and downwind hovering limits. These limitations assume an average Squadron pilot level of skill and allow for inaccurate wind measurement but they give a very clear indication that you are approaching the physical limits of controllability of the helicopter.
The nearest the civilian pilot has to a rubberstamp from a higher authority is the certification of "acceptable control has been demonstrated in winds of up to 17 kts from all directions" with absolutely no guidance as to how far, if at all, it can be safely exceeded.
So, you can either teach people to respect the 17 kts figure or just let them go out and experiment until they find themselves spinning out of control close to the ground (not a healthy place to be, especially in an R22).
Gradually pilots will gain experience and most will be lucky and only scare themselves but the PPLH holder with 100 hrs who only flys once or twice a month and is constantly battling against skill fade is not in a great position to start exploring the flight envelope.
Post graduate training would certainly help a lot but how many want to pay for extra training once they have got their license?

PS 3D I wrote a load of bo88ocks on an earlier post having convinced myself you had been hover taxiing with a wind from the left and not from the right - sorry!