Avoid Curve

[Nicho]

Can someone please explane why the approach to landing profile ignors, in most instances, the AVOID CURVE ?

[SASless]

There have been numerous threads on that topic or included that topic in discussions about the H-V diagram...curve....chart for several aircraft. Do a search and several good discussions will show up.....usually steered by the illustrious Nick Lappos....an erstwhile Teetotaller of some repute.

[[email protected]]

Nicho , as you will find elsewhere on this forum the avoid curve is created from data gathered by brave test pilot types who fly at selected heights and speeds, chopping the throttle and entering autorotaion after a 1 second delay that equates to estimated time for recognition of a real engine failure. The aim is to achieve autorotation at minimum rate of descent speed, typically in the 50 to 70 knot speed range as this configuration gives you maximum time in the air as you are falling out of the sky slower. This also maximises your chance of a safe engine off landing as you have a minimum RoD to reduce before you hit the ground.

The reason that the avoid curve is often ignored is that the data is gathered from straight and level flight and on the approach you will generally have a lower lever position which means that a. you have slower rate of Nr decay following an engine failure as the rotor drag is reduced and b. you have less to lower the lever until you get into auto.
However, it does not mean that you will automatically be able to achieve a safe EOL if the donk quits on approach - in fact the deeper you are in the avoid curve the less likely it is. That is not to say you won't survive it - any EOL you walk away from is a good one - but bending the aircraft means someone has to pay for it!

Strictly speaking the avoid curve is not applicable to approach because the data is not gathered in that configuration.

Practically it doesn't take the brains of an archbishop to see that you are poorly placed at 50' and 10 kts compared to 50' and 50 kts. One is inside the avoid curve for most singles and the other isn't. It's up to you.

Hope this helps.

[Lu Zuckerman]

To: Crab

Nicho , as you will find elsewhere on this forum the avoid curve is created from data gathered by brave test pilot types who fly at selected heights and speeds, chopping the throttle and entering autorotaion after a 1 second delay that equates to estimated time for recognition of a real engine failure.

A Sikorsky test pilot was killed during the developmental testing of the S-58. He hit the ground hard and the gear collapsed and the helicopter rolled over and a blade stub entered the cockpit.

:sad:

[old heliman]

From memory, the HV is predicated up to the 'knee' of it at MTOWA and at max power. Above that it is based on the cruise configuration. Hence when landing it is not relevant.

[NickLappos]

The avoid curve is an approximation at best, and even then only at a specific set of circumstances. Landing procedures can often enter the curve, and if they do, testing has been done to show (to nobody's surprise) that there is no problem entering the avoid area.

Why? Because the avoid area was built with conservative rules that make it bigger than it needs to be, and because the approach configuration (part power descent) is a nice place to fail an engine and have reduced consequences. Descents are not used to make the avoid area.