Jammed Controls

A jammed control won't be leaving a sweet taste in your mouth...

A jammed control doesn't mean that someone has spilt their favourite marmalade jam over the cyclic in front of them, as comical as it sounds. Unfortunately it's a fairly serious emergency that could be encountered in flight for a number of reasons but as I'm assured by my instructors is a rarity. We need to prepare for it nonetheless to be a competent pilot that can respond to any emergency in flight. Essentially a jammed control means that it has become locked into it's current position by a mechanical failure or more likely a pen, pencil, ruler, ring (careful with those marriage proposals!), phone or any other small item could have fallen into the mechanics of the control limiting it's movement.

Once you realise that the control is jammed you immediately go into a state of panic. No, in contrast you follow a set of prior learned techniques to put the machine safely on the ground. Firstly you try some moderate force on the control in an attempt to break or move the locking item out of the jamming position. If this fails we have an abnormal situation that potentially requires some assistance to get on the ground safely so we need to let others know. We do so in the form of a "PAN PAN" call, essentially a call that says we have an issue in flight that is not perilous (that would be a MAYDAY call) but may require some assistance (potentially freeing up all available runways, watering down runways so they're slippery, getting someone on the phone that can help talk us through the situation, etc) and have emergency crews ready to respond to us on the ground. An airport would be the ideal place to land (large, flat and hard surfaces to run the machine on to) but we may have to put the machine down in a paddock, on a road or any other place that would safely accommodate the chopper depending on our location at the time of the jammed control and whether we could continue flying to a further, safer location in our current predicament. Once we've let others know we need to get the machine safely on the ground and the way we do that is different depending on which control is jammed.

Jammed collective

The hand-brake looking control is the collective. The throttle is the grip at the front end (right in this photograph) that you can wind on and off with your left hand.

The collective is the hand-brake looking control to the pilots left that collectively raises the pitch (and therefore lift generated) on all the blades equally and hence makes you go up if you raise it and down if you lower it. As you can imagine it takes more power to go up and less to come down so, via a few other mechanical and computerised links between the collective and the engine, increasing the collective also increases the power supplied by the engine and lowering the collective also decreases the amount of power supplied by the engine. This essentially means that the rotor blades continue to spin at the same RPM independent of where the collective is situated. Clever! 

If the collective is jammed you obviously can't go up or down using this control input. To put it simply, every control input has a primary effect (in the case of the collective to go up or down) and a secondary effect(s). In normal flight with no controls jammed you're constantly counteracting the secondary effects of the control inputs to keep the aircraft flying the way you want it to. To continue flying the machine in a jammed control situation we need to utilise the secondary effect of the other controls. In the case of a jammed collective we can decrease the throttle a touch so that the blades are not rotating as fast as in normal flight (only a few % lower) which means less lift generated by the blades as they're travelling slower through the air. This will initiate a slight descent. 

Then, as long as we maintain a forward airspeed, we can use the cyclic (the joystick-like device that allows you to tilt the disk and therefore move the helicopter in that direction) to change our height. Pushing the cyclic forward will make the rotating disk and therefore the helicopter tilt forward and speed us up as it simultaneously starts us descending. Similarly we can climb by pulling the cyclic aft which will point the nose up and slow us down as we climb. Essentially you trade airspeed for height and vice-versa with the cyclic in this situation. Furthermore, if we wash off enough airspeed by bringing the cyclic aft we will lose translational lift (that's the extra lift we get from moving through the air at speed, covered earlier). Once we lose translational lift the blades essentially become less efficient and we start to descend. We can use this technique to maintain the speed required to bring us down at a steady 300 feet/minute to our landing site. 

Now, the hover generally requires a decent amount of power so unless the collective became jammed during the climb (when the collective is raised significantly and hence we are using heaps of power) the power setting that the collective is jammed at won't be enough to sustain a hover when we reach the ground. In this case we need to do a limited power landing. When we're power limited we need to use the translational lift we get from forward flight to help slow our rate of descent. As such, a limited power landing means we come in at speed and slide along the surface, using the friction of the skids against the ground to slow us down. The lower the power setting the faster we will need to be coming in so that there is sufficient translational lift to reduce our rate of descent. As we approach the ground we can "cushion" the landing by increasing the throttle slightly (bringing the RPM of the blades back up and hence their lift production) prior to touch down so that we "kiss" the ground as opposed to a heavy landing. Once sliding on the ground, decreasing the throttle will decrease lift production, increasing our relative weight on the surface and hence increase the friction which will slow us down quicker. We need to be straight with the pedals as we slide along the ground so as to prevent a rollover.

Jammed pedals

The foot pedals change the pitch and hence thrust produced by the tail rotor.

The pedals control the tail rotor and are sometimes referred to as the anti-torque pedals. Remember, the reason we have the tail rotor is to cancel out the torque that the engine is producing to rotate the main rotor. The engine torque tries to yaw (spin) us right (in an R22), in the opposite direction to the blades. Therefore the tail rotor will produce thrust on the tail to the right to yaw the helicopter nose left and keep us in balance. So the pedals work like this: left pedal increases the thrust generated, allowing the tail rotor to win the torque battle and yaws the helicopter nose to the left; conversely the right pedal decreases the thrust generated and allows the engine torque to win in the torque battle and the machine yaws right. Simply put: Left pedal yaws us left, right pedal yaws us right.

In addition, at the back of the helicopter near the tail rotor we also have a little fin which is referred to as a "vertical stabiliser". The vertical stabiliser essentially generates a force in forward flight (exactly like a wing on a plane) that pushes the tail right which helps reduce the workload and hence reliability on the tail rotor. Thus a jammed pedal in forward flight will make the flight uncomfortable but the real considerations for jammed pedals is in the hover when there is no air moving over the vertical stabiliser.

The vertical stabiliser, as the name suggests, is the vertical fin that (perhaps paradoxically) generates a force on the tail to the right in forward flight. This reduces the workload for the tail rotor.

The tail rotor is situated on the far back left side of the tail boom when looking forward.

Jammed left pedal forward:

If the pedals jam with the left pedal forward in flight the situation is heavily dependent on how far forward the left pedal is jammed. With the left pedal forward you will crab through the air with the nose off to the left of your track and it will feel like you're sliding to the right. The machine will even roll a bit to the right as the air pushes agains the large surface area of the machine. To land you make a normal enough approach to your designated landing area, remember you still have collective (power) and cyclic to move the aircraft around. 

It's when you transition from forward flight into the hover that you require more power from the engine (increase the collective) as the blades lose translational lift and become less efficient. This produces more torque on the machine and requires sufficient anti-torque (left pedal). If the left pedal is jammed just a bit forward it may not be enough to win in the torque battle and the machine will begin yawing right. In this scenario we can decrease the throttle (RPM of the blades) to take some torque away whilst increasing the collective to compensate the lift lost. This will keep us straight and cushion the landing.

If the left pedal is too far forward then as you come into a hover it will be producing too much anti-torque to compensate for the engine and the chopper will begin rotating left. In this case we increase the collective to increase the torque which will level us off above the surface and stop us from yawing. Then a process of lifting the collective whilst winding off the throttle will keep us straight whilst descending to the ground. The third alternative is that the left pedal is jammed at the ideal location for the torque battle to be a tie when you enter the hover making the landing a normal one.

Jammed right pedal forward:

Now if the right pedal is forward when the pedals jam up then you are only going to yaw right when you try and enter the hover as there is insufficient anti-torque to compensate. The rate of right yaw may be quite substantial depending on how far forward the pedal is jammed. One of the landing techniques in this situation is to land at speed since you require less anti-torque (left pedal) due to the efficiency of the main rotor whilst the blades are in translational lift and the vertical stabiliser is playing its part. However with run-on landings we need to be straight, something we usually obtain with the pedals. So we need to do a "trial" run, coming in above the surface at different speeds to ascertain which speed (which directly relates to translational lift and vertical stabiliser inputs) will require the correct amount of power, and hence torque from the engine to exactly cancel the amount of anti-torque produced by the current jammed setting of the tail rotor. So essentially we come in at different speeds until we ascertain which is the speed which keeps us straight and then use this speed to run the helicopter onto the ground, cushioning with the collective. We can make fine scale adjustments to keep us straight with the throttle; winding it on will produce more torque and therefore yaw us right, winding it off will hence yaw us left. 

The other option (and the one preferred as it is suggested by the pilots operating handbook) is to enter autorotation. An autorotation is essentially an unpowered descent. If you take away the power produced by the engine (and therefore torque) you don't require an anti-torque mechanism to cancel the forces so the tail rotor becomes obsolete. This option also allows us to land in a smaller and not necessarily flat or hard piece of land.  

Jammed cyclic:

The cyclic control input. The buttons on the front are to navigate through different radio channels and the red "trigger" on the back side is to communicate with air traffic control and other aircraft.

I think the cyclic is probably the scarier of the control inputs to become jammed. To summarise, the cyclic is the joystick-like device that changes the pitch of the blades at different locations as they spin around the disk. The end result is that it tilts the disk and hence takes the helicopter toward the location that you point the cyclic. To come from forward flight back to a hover you essentially pull the cyclic aft until your airspeed is zero (and pull sufficient power to compensate for loss of transitional lift). So to reduce airspeed without the cyclic we can increase the collective, the secondary effect of which is to bring the nose of the aircraft up and will therefore slow us down. Initially we will climb as we have increased the collective, but once we get slow enough we will lose translational lift and begin to descend as the blades become less efficient. We have now slowed down and are descending. To turn we can use the pedals since the secondary effect of using the pedals is to roll and hence turn the helicopter in the direction you've pedalled. Once approaching the ground we need to cushion the landing by increasing the collective and keeping straight with the pedals. If we are not completely level this is something we have little control over fixing and hence the slower we are the better chance we have of not rolling the helicopter. However being this low and slow prior to touchdown will significantly increase our chances of walking away if the helicopter rolled due to being unlevelled as we run the aircraft slowly on to the ground.

Summary

It does sound pretty scary to have to fly the machine without all the control inputs but learning about how to compensate in flight using the secondary effects of the other inputs has actually been pretty fun and gives me more comfort flying the machine. It'd be similar to driving a manual car and the brakes failed and you needed to bring it to a stop ASAP. Sure, you could just try to run it off the road into a barrier or trees to slow it down, or you could just change down the gears and allow the engine resistance to slow the car down. It may not do a world of good for the engine, but as long as you and your passengers walk out of the situation alive and well then isn't that all that matters? Some of the recovery situations above may result in a bent, scratched and potentially rolled helicopter but, if executed properly, all should walk away to enjoy yet another beautiful day :)