EF5, the idea of two opposite spinning rotors for a heli is great in theory, and works equally great on the toy choppers that are available now. However with helis that carry humans the increased complexity, results in a corresponding higer cost and lessened reliability. The lowest priced choppers already cost over $250 an hour to operate, and with twice as many moving parts, it will have a catastrophic and fatal failure probably 16 times as often. And if you’ve flown the toy helos with dual rotors, they have a hard crash about once a minute…

I just saw a video of a helicopter with two rotors that spin in opposite directions which counterbalances the torque that one rotor by iself would generate. What do you think of the practicality of such an idea? Would it substantially increase maintenance?

Yes, reaction time can’t be judged, and therefore the indicator would be ostensibly meant to first provide an exact measure of “available energy”, and secondarily provide an “assumed” safety state based on “typical” reaction time of an “average” pilot (3-5 seconds). The indicator can be made to be more conservative by assuming a slower reaction time, but the idea would be to provide at least some guidance as to where in the envelop one is operating.

As to Alan’s question about H-V curve applicability for landing, yes, if one is coming in “heavy” on a hot day, the descent will likely have a significant amount of collective to keep things from getting out of control, and thus the same “high pitch / reaction time” combination that necessitates having an H-V curve WOULD also apply during landing… and another strong argument for having a real-time display of energy in the cockpit would be more helpful than a couple of static charts based on some combination of weight and temperature.

There are ever-changing factors with every flight so its MOST important to be familiar with the risks and weigh the odds, thus minimizing as many risks as possible.

Given “normal” loading and conditions, perhaps your collective setting is closer to full-down (auto) than on takeoff… but may not apply when coming in heavy, in hot weather, as Chalk 4, trying not to run over the guys in front of you and avoiding vortex ring state at the same time… The H-V is still there and you’re at high power/high pitch setting. I was taught (and experienced) that some things can’t be avoided – only managed. (Similar situation applies when coming out of a tight LZ with high trees or buildings… you know you’re in the “deadman’s curve” and pray nothing goes wonky or try to react accordingly.)

That should answer Alan’s question, too. High power (such as during takeoff and climb) equals high pitch angle, which equals a shorter required reaction time to get the collective down. And I was taught that the H/V diagram is not for landings for that very reason: you’re already close to an auto, anyway.

I flew USAF helos for 2500 hrs. I don’t understand how the H-V diagram will change based on power – either takeoff or landing. Please explain further…

The H-V diagram in the flight manual is actually showing how to survive an engine failure during take-off – a requirement during type certification.

A similar H-V diagram developped using approach power would look a lot different – the ‘avoid area’ would be much smaller.