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2

You could use the second rotor to provide anti-torque function only, as Arthur Young did when developing his helicopter test models at Bell during WW2. In that case the upper rotor did all the lifting and the lower one had blades that were at 90 degrees and just made drag to generate a cancelling torque. But that is really inefficient, and Young quickly ...


5

The lift-to-drag ratio of the main rotor blades is around 10, so the tail roter has to provide a force equal to one tenth of the aircraft's weight. Of course you have to take into consideration torques and lever arms, but if we assume that most of the lift and drag is created by the outer portion of the main rotor and that the tail rotor's lever arm is ...


2

The tail rotor on helicopters indeed provides anti-torque thrust, plus thrust for manoeuvring in the yaw axis. A quote from Principles of Helicopter Aerodynamics by j. Gordon Leishman section 6.9: The magnitude of this thrust, as well as its power consumption, depends on the reaction torque from the main rotor, $Q_{MR}$, and the location of the tail rotor ...


0

Well, there is the RAH-66. Stealth helicopters are difficult to make because of the radar cross-section of the blades. Even on the B-2 the fan blades are shielded so they don't create a massive return, and helicopter blades would create a much bigger return.


2

Well there actually are stealth helicopters, from Boeing Sikorsky’s RAH-66 Comanche, to a classified low observable derivative of the UH-60 Blackhawk, which was used in operation Geronimo to kill Osama bin Laden. They’re out there but haven’t seen the light of day for several reasons. In the case of the RAH-66, It was development problems and massive cost ...


3

It's because the blade's span-wise axis is "swept" relative to its flapping hinge line, so when it flaps, the sweep angle results in the blade's effective AOA changing somewhat (for the advancing blade, reducing; that's what the feathering part means). To picture it, imaging you are standing directly in front of the tail rotor disc watching the advancing ...


9

The closest question to this currently is Why aren't modern helicopters quieter?, which one should read first. That regards sonic stealth. As for radar stealth, any rotating part, visible from the outside, is a major source of unavoidable radar reflections. In 4th generation jet fighters, the engine faces generally contribute more than half of the total ...


5

Yes, helicopters are allowed near busy (and any other) airports, because why not? Ok, seriously: helicopters in general are just as able aircraft as ones with fixed wings. General limitations for use of airspace may be in effect depending on airspace categories around aiports, but to my knowledge there are no airports in the world that would specifially ...


0

Remember that the helicopter visibility restriction also applies to IFR departures. under part 135, you can depart IFR without a takeoff alternate if you have the visibility to shoot the approach straight in, and all the equipment is working... this visibility can be cut in half unless it says helicopter vis reduction N/A. So, looking at this approach ...


50

No, the helicopters are standard production versions. The Eurocopter AS350 is a common model used for these operations. In 2005, Didier Delsalle landed a Eurocopter AS350 B3 on the summit of Mt. Everest at 29,029 feet (8848m) (twice). The only changes he made to the standard version were removing a few things like extra seats to reduce the weight, and of ...


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