Thrust requirements for helicopter tail rotors?

Question

I'm researching what would be involved in generating temporary thrust for helicopter tail rotors for a system to be implemented in case of tail rotor failure or damage. I'm looking for specific links to find information on what amount of thrust..percentage wise or general amounts..are needed for operation of a military helicopter like a Blackhawk or any other smaller models. I'm interested in developing an emergency thrust device or system for loss of tail rotor function in combat or civilian use. I envision a jet propulsion system built into the tail and properly armored that is controlled by computer to alter it's amount of thrust as necessary depending on inputs from the pilot for course correction. Or a system of thrust vectoring of the primary engine exhaust. Such a system would provide emergency backup manuevering in the event of tail rotor loss or malfunction to provide ample time for evasion and descent in a controlled manner for both civilian and military helicopters.

Answer 1

OK....an entire book could be written here!
Firstly compensating for loss of tailrotor (LTR) depends on too many variables to have a single bullet theory. If it's a control problem (loss of pedal authority or jammed pedals) then the tail rotor is still effective and although it's a serious condition ....it's not one that necessarily leads to disaster. Most helos have reasonable control authority providing there is foward flight (airflow over the vertical stab + the rotating tailrotor ) combine to keep a run -on landing possible.
Complete loss of tail rotor + gear box will, in many cases result in a radical C of G change that will render the aircraft unflyable (too much nose down moment) so any 'emergency thruster' would be moot.
The only scenario that an 'emergency thruster' would be of any use would be a tail rotor driveshaft failure....and lets hypothesize two scenarios for that:

1) failure in foward flight - The aircraft will yaw left or right (depending on main rotor rotation) and the degree of yaw will be determined by airspeed and toque (Q) being developed.

2) Failure in the hover - In this the case the aircraft will IMMEDIATLY and VIOLENTLY yaw and begin ever increasingly fast rotations...until power is eliminated (autorotation)

Now lets talk about compensating...
Your system would have to be designed to react IMMEDIATLY upon failure. It would have sense rotational velocity and apply a descrete amount of thrust to EXACTLY compensate Q . Since Q is variable depending on flight regime....your system would need to react instantaniously to power changes....or risk aggrevating the situation for the pilot up front or be pilot controllable....but the biggest hurdle is the worst case scenario....heavily loaded, high Q, and in the hover...your system would have to react immediatly and exactly correctly...and I'm having a hard time imagining how such a system would work as solid fuel rockets can't be controlled, engine exhaust doesn't provide nearly enough 'thrust' and can't be modulated independent of power settings (at least without a complex and heavy system of vectoring)
Anyways...hope this helps a bit....but as a last word...the tail rotor system typically consumes about 20-25% of total power developed.....ie: if 2 engines are produced 1000shp then 200-250 shp is for the tail rotor..and if 1000shp holds a machine of 12,000lbs in a steady hover....then ....well you do the math!...
Anyways....keep us informed!
Cheers

Answer 2

The thrust has to match the counter force generated by the primary rotors! The tail rotors are there to prevent the aircraft from rotating on it's axis! Alternatives have already been tried through the years but go ahead and try something new! Try designing a primary that doesn't require a tail rotor in the first place! Learn everything you can about how the aircraft functions! Hopefully this will give you a few new ideas! Come up with something incredibly simple and reliable! Copy nature because it has had billions of years to try millions of differing configurations!

Answer 3

The amount of tail rotor thrust required is going to vary during the different stages of flight. I would guess that you would want to activate the emergency system right before touchdown when the helicopter is going to be pulling the most pitch and requiring the most tail rotor thrust. They have helicopters with no tail rotors (NOTARs) where the antitorque is provided by "jets" airflow. Another consideration to tailrotor failure is CG. Why is the tailrotor failed? is it more than just a stuck pedal? Stuck pedal situations are mostly manageable. If the tailrotor gear box was shot off or departs the aircraft, it not only starts to spin but will also be uncontrollable due to an extremely forward CG.

Answer 4

Save your time and energy. For decades they have tried but yet to come up with an adequate replacement for a bladed tail rotor. And weight is already a problem that far aft so a redundant system would cause more problems than it would solve for those rare tail rotor failures. They are rare you know? And even if the military could afford the addition, you'd never sell it to the civilian world. If it doesn't help a helicopter make money they don't need it. Great safety record there too anyway.

Answer 5

the thrust required will be directly related to where your arm will be in the tail boom. the further from the center of the main rotor, the less force needed to turn the helicopter. but remember, the only directional force that is absolutely mandatory is the one needed to counter act the rotational force of the main rotor. so you could focus mainly on producing a single nozzle that allows all force to be used in that one nozzle. say the main rotor turns clockwise, the fuselage will want to turn counterclockwise, if you deployed a single nozzle to counteract that counterclockwise turn, then to allow the aircraft to turn counterclockwise you only need to lower the thrust output of that one nozzle. not the most efficient way to turn but in an emergency, it would get you to the ground.

Answer 6

thrust would need to equal and exceed the amount of torque generated by the main rotor.

Simply know the mass of main rotor, speed it spins, and distance from the center of thrust that the tail rotor is acting at.