Military helicopter tail rotor solutions?

Question

Is anyone working on solving loss of tail rotor function from RPG's as seen in the movie "Black Hawk Down"? I've wondered this for many years, whether or not it's possible to design a system whereby tail rotor loss of function could be minimized by some kind of emergency jet propulsion in the tail section to produce the necessary thrust for safe control of the helicopter or by directing engine exhaust in a sidewards manner much like an engine reverse thruster to minimize or eliminate torque thrust. I'm also wondering why the military does not employ the NOTAR system in combat zone helicopters to mitigate being brought down by RPG's. Any helicopter engineers or pilots wish to comment?

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. If Kelley Johnson and his engineers could build the SR-22 in an era of slide rules, we should be able to do this as well.

Answer 1

Loss of tail rotor authority is an emergency situation simulated and practiced by commercial pilots all the time. On a conventional main rotor-tail rotor helicopter design, the recovery for loss of tail rotor thrust is simple - reduce power if at high speed, and shut down the engine(s) and enter autorotation at low speed. It does take practice and skill to get it down safely. But a complete loss of the tail rotor would be an unrecoverable situation as the center of gravity would move too far ahead to make the helicopter controllable.

There are already several proven tail rotor-less designs in use on helicopters today:

1. Counter-rotating coaxial rotors like the Kamov KA-32,

2. Counter-rotating non-coaxial rotors like the Boeing BV107 and 234, and the Kaman K-Max, and

3. NOTAR system which uses a slotted tailboom as a sideways air foil to counteract MR torque using the Kwanda effect, and low pressure air nozzles to provide directional control.

Another type of tail rotor-less helicopter design is the tip-jet design, where pressurized gases are pumped out of the MR blade tips rather than torque in a main rotor drive mast, so there is no torque effect. This design requires a very complex swashplate and has never caught on.

You specifically mention the NOTAR system employed exclusively by MD helicopters. I've flown it a little, I like the authority and control (not to mention the safety benefits) in all sorts of maneuvers below about 80 knots, but at high speed they are twitchy. The only real problem with the NOTAR system is the rest of the helicopter - its an MD product which are notoriously uncomfortable, noisy, unreliable, and backed up by non-existent factory support. Give me a Bell, Sikorsky, or Eurocopter any day, even if they have a tail rotor!

But in general I think loss of the tail rotor is a very minor detail when you are hit by an RPG! The bottom line is that a properly designed, maintained, and flown tail rotor is perfectly safe.

Answer 2

With out the tail rotor it will gyrate uncontrollably.It functions like a steering wheel in a car.I am not a helicopter pilot and would not wish to put you or anyone else off inventing any life saving device that may prove to be effective under these circumstances.So keep up the good work and to test any ideas that you think may function requires small remote models to test out any new ideas that are invented.Good Luck.

Answer 3

It's a wonder why more helicopters do not use a twin counter rotating top rotor instead of a tail rotor. Kamen aircraft had used them for years as have the Germans and the Russians with various designs. The Ka-50 Russian Attack helicopter is so agile that the nose gun is fixed in place.

Answer 4

The problem isn't just with the tail rotor, but the whole tail assembly. As long as forward speed is kept up with just the tail rotor not functioning, it is more difficult to control, but not impossible. Pilots are taught in every course to do a run on landing in case the tail rotor quits. The landing is similar to landing a fixed wing airplane, hard on the skids, but it can be done.
At low speeds or in a hover, it is almost terminal.

Answer 5

There is a company developing the concept you talked about. Everything is on paper right now, no hardware yet.