Pedal turns, LTE and the Critical Wind Azimuth
There are far too many accidents caused by pilots simply not making the input they need to accomplish the job at hand. It has recently come to light that many accidents previously attributed to LTE, have been caused by nothing more than a pilot who failed to fly the aircraft. That’s right, they just didn’t put in the pedal they needed; they let the aircraft spin out of control often killing people in the process. How could anyone let this happen? The bottom line is poor pilot technique. Just because someone has a pilot’s license doesn’t mean they can fly worth a crap.
Unfortunately, this all comes right back to flight training, and those who conducted check-rides for pilots who have poor skills at best. But, let’s get back to the core of the problem; flight training; and we’ll stick with counterclockwise rotors. Every pilot should know that some rotors turn the other way, and in that case the procedures outlined in this article are opposite. So…
First things first; always apply whatever amount of pedal (or other control input) is required to accomplish what it is that you have to do at the time. Anything less just isn’t piloting the aircraft, it is letting the aircraft pilot you.
Remember that we apply left pedal to counter torque. Any time we want to maintain a stable hover on a given heading, or make a left pedal turn, we must apply left pedal to a varying degree. The helicopter tail rotor is thrusting the tail to the right (nose left). Remember this, thrust to the left and torque to the right. Generally speaking, pedal turns are only accomplished at airspeeds below 45 knots, above that speed, the turns are usually accomplished through cyclic inputs only.
Left Pedal Turns Only
During training we practice both left and right pedal turns so that students learn what is possible, and how to handle different situations. However, when a student is solo, he or she should make only left pedal turns most of the time and use caution making right turns. This is for two reasons.
- First, a pilot can easily lose control of the helicopter if a right turn begins to accelerate, which it usually will. A right turn can quickly accelerate because it does not require power to make the turn, just the torque that is already there. Pilots will always notice that a pedal turn to the right is much faster than a pedal turn to the left for a given amount of input.
- The second reason is that if you cannot complete a left pedal turn, that is if you do not have the tail rotor authority available, then you probably shouldn't fly. This is a test as to whether or not you could likely overcome a right turning tendency.
Right Pedal Turns
The above facts often confuse a pilot when they begin conducting commercial operations, and they believe that less power is required to make right pedal turns. Although this is true for slow inputs such as while in a hover, one must remember how a pedal turn is stopped.
If you are in slow flight (less than 45 knots), and you will be making a turn, this will be conducted with significant pedal. If you make this turn to the right because of the myth of the right-pedal-turn = less power demand, you will find that you cause a decrease in rotor rpm when you apply the left pedal needed to stop that turn.
The pedal authority needed to stop a turn is greater than that which is needed to enter a turn. In slow speed flight it is safer, and will require less altitude to make a pedal turn to the left than it will to the right. This is because when you stop the left turn you will be decreasing the load on the main rotor and rotor rpm will not decay.
We don't always have the option of the direction of the turn. In commercial operations, perhaps while spraying a field, every other turn is to the right. This is ok. You must increase the altitude, and lead with throttle when you apply left pedal coming out of the turns even in helicopters like the Robinson which excellent responsive governors (except turbines where you cannot lead-in with throttle as it is always full open).
One may ask why the altitude change? Keep in mind that you can recover most situations with altitude, that is, you will trade some of your altitude during the recovery. If for example you made a right pedal turn during a low altitude air taxi, when you apply left pedal to stop that turn, your rotor rpm will quickly decay. Decayed rotor = altitude loss. This is due to the fact that the immediate power for your tail rotor will come from the main rotor (flywheel effect). The engine will replenish that power shortly. There is only one recovery, the collective must be lowered. If you did not have sufficient altitude, you will do what? Yes, that is right, you will crash. The helicopter will be in more than one piece, and helicopters in more than one piece just don’t fly well.
Milk the collective? NOT! It will not work!
This is a term that you will hear sooner or later. This technique is in reference to a pumping action on the collective in an effort to regain rotor rpm during a decaying situation.
You will read this often in accident reports, always remember: milking action = accident report! Remember that the collective does not give milk, so don't try to milk it.
It is physically impossible to gain more rotor rpm through a milking technique rather than just lowering the collective for an rpm gain. Think about it, at the very best, you will have collective down only 50% of the time. It will take more altitude to regain rpm milking the collective than it will with the collective just down, and altitude is precious and limited, or otherwise it wouldn't be important would it?
The real key here is avoidance; avoid a situation where you would have to think about the consequence of, 'to milk or not to milk'. Also remember that it is necessary only to lower the collective enough to gain what you need; so it may not be necessary to fully lower the collective.
So are there any exceptions to the milking of the collective? In theory, it has been argued that by milking the collective, you can avoid ground contact as you burn fuel which in turn lightens the aircraft making more power available. The likelyhood of this working are next to none, however it is ammunition for your arsenal of accident prevention techniques.
Loss of Tailrotor Effectiveness or Loss of Pilot Effectiveness?...
Though it has never been referred to as LPE before (I hate the over use of abreviations, makes me think of the movie, "Good Morning Vietnam", but the FAA and management in industry gets stroked on abreviations). Due to a large number of accidents and a particular indvidual involved in the investigations, the causes that would have been commonly attributed to LTE have now been classified as LPE; Loss of Pilot Effectiveness. This particular individual asked the NTSB, "Why don't we just call it what it is"? This is an all new term that you are going to start hearing a lot more often.
More importantly, lets not limit it to LTE events; where it's appropriate, call it what it is. It's not very educational when an acronym such as LTE is applied simply because the helicopter started spinning before it went down, but that is basically what has been occuring. Oh there have been contributing factors as the FAA and NTSB like to call them. A lot of the reason behind that blind classification is that either the pilot was dead, or he didn't remember what lead to the crash.
Some pilots who have been involved in recent accidents, when questioned for more detail, have stated that they simply didn't make the pedal input; they have given a couple of different reasons, but none are legitimate. The bottom line is that they just stopped flying the aircraft. One pilot stated that he thought he could "fly out of it".
Though LTE in and of itself is a serious concern, the pilot not making use of available control inputs is a larger problem. I have long maintained that LTE, and it's causes have been overstressed to the point where pilots roboticlly think that if you avoid those conducive wind conditions, you will avoid LTE. This is incorrect on two fronts. First, LTE is not an automatic condition with those winds, and second, the pilot giving up because he got into a tough situation and quit flying is not LTE. A pilot I was flying with once came back into the lounge and express to other pilots that he had just experienced LTE, when in reality we had been working on down-wind hover and he had difficulty controlling the helicopter. I explained that he did not have LTE because LTE is a Loss of Control. He did not have a Loss of Control, he had difficulty controlling.
When I question even experienced pilots about procedures especially where cross-wind landings are concerned, they will give the wrong answer the majority of the time. The question is, assuming you are in a counterclockwise rotating single rotor helicopter, and you had to choose between a direct left or direct right crosswind, which would you choose? Well, they will think for a moment about their learnings of LTE, and answer that they want the wind off the right. Robotic answer, and wrong! Take the helicopter out to an airport on a windy day and try it. What the hell is going on?
I maintain that The Critical Wind Azimuth is far understressed, as it is viewed as a high altitude consideration, and as a result many accidents that get attributed to LTE were actually a result of this lack of knowledge. Unfortunately, at some point, the pilot just gives up and stops flying the aircraft. His box of tricks is empty, and his bag of luck has run out, and the resulting accident will get attributed to LTE.
During flight training, Flight Instructors should teach their students to always use whatever pedal is needed to accomplish the task at hand. An issue that comes to mind is hovering autorotations. I have heard many instructors describe the procedure to their students incorrectly time after time. They will say, "hold collective momentarily and apply full right pedal, Cyclic for position and cushion with collective". This is all correct except the redal part; you don't apply full left pedal, you apply pedal to maintain heading, whatever that takes. Preventing LTE is no different, you do whatever it is you need to do to maintain control of the aircraft, whatever it takes.
The Critical Wind Azimuth, did you know about this? Well, you should...
We were all taught about the four factors relative to LTE (left quartering headwind, left crosswind, tailwind, and the loss of translational lift), but were you aware of the Critical Wind Azimuth? I have only seen this in the Bell POH. Incidentally, the POH indicates that it is critical only at high altitude; but I can assure you that it is more important than that. It is important to note that this is relative to the direction of rotor rotation.
As a demonstration, choose a runway or other safe approach path to a safe area where you can make an approach from either direction with a direct left and right crosswind. You will see that if you take the wind off the left, the aircraft will be significantly easier to control than if you take the wind off the right. If you make your approach with the wind anywhere in the Critical Wind Azimuth, you will notice the aircraft is significantly harder to control than with the wind in any of the remainder of the disk.
Often pilots get caught off guard by this one. If you are in an OGE hover and you turn into this wind condition you will know it. It will be far worse if you are in a right pedal turn, and worse even still if your altitude is low. The helicopter will become difficult to control, and the best recovery will be to lower the nose and fly free of this condition just as you would from settling with power. Lowering the collective also helps. What ever you do, don't increase collective pitch. Keep in mind that this diagram depicts a helicopter with a counterclockwise rotor rotation. ENDJump to Top