High Hover
Joined: Sep 2002
Aviation Qualifications: CPL
Posts: 4,721
Likes: 636
From: Great South East, tired and retired
AAAAARRRRGGHHH!!!
It is NOT AUTOROTATION!
It is an engine failure in the hover. Using stored rotor energy to cushion the landing, while the RRPM decay.
It would be a triumph of engineering over laws of aerodynamics if something were able to transition from powered flight (air going from top to bottom) to autorotation (air going from bottom to top) in 15 feet. And not be going down at 1500 feet per minute.
Terminology, Bloggs!
It is NOT AUTOROTATION!
It is an engine failure in the hover. Using stored rotor energy to cushion the landing, while the RRPM decay.
It would be a triumph of engineering over laws of aerodynamics if something were able to transition from powered flight (air going from top to bottom) to autorotation (air going from bottom to top) in 15 feet. And not be going down at 1500 feet per minute.
Terminology, Bloggs!
Joined: Oct 2002
Posts: 242
Likes: 1
From: England
Never tried it myself but my instructor demonstrated an engine failure from a 40-50ft hover in an R44 and one from 50-60ft in a Bell 206. . .
Didn't do it straight off just kept getting higher and landing no probs.. .
Didn't do it straight off just kept getting higher and landing no probs.. .
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
Likes: 1,814
From: EGDC
PPF#1, I think helipolar bear was highlighting the fact that sitting into a 20 kt wind in the hover (stationery over the ground) is the same as being in forward flight at 20 kts - the disc still gets 20 kts of airflow over it. Therefore you would enter the H-V graph at the 20 kts point not at the 0 kt point; I am sure you are both arguing the same point.
Ascend Charlie - good point, there have been more teddys thrown out of cots on this forum due to confused terminology than you can shake at stick at.
Tiger Mate - in the SAR world we spend a very high percentage of our life in a 40 - 50 ' hover - fortunately there is yet to be a case of a twin engine failure in this configuration (I do not count the RN Wessex that had both engines put out by water ingestion!)
Bugdevheli - the trading off of manoeuverability for Nr might save your skin in one situation but might prevent a safe landing site being reached in another eg sitting above and close to a cliff top.
Ascend Charlie - good point, there have been more teddys thrown out of cots on this forum due to confused terminology than you can shake at stick at.
Tiger Mate - in the SAR world we spend a very high percentage of our life in a 40 - 50 ' hover - fortunately there is yet to be a case of a twin engine failure in this configuration (I do not count the RN Wessex that had both engines put out by water ingestion!)
Bugdevheli - the trading off of manoeuverability for Nr might save your skin in one situation but might prevent a safe landing site being reached in another eg sitting above and close to a cliff top.
Joined: Jan 2001
Posts: 3,008
Likes: 62
From: North Queensland, Australia
Obviously a 50 ft hovering engine failure won't allow you to get fully into autorotation before reaching the ground, but there will be a component of airflow coming from below as you descend, giving some benefit.
Unless I've missed it in some of the posts above, nobody has mentioned lowering the collective partially to save some Nr and give you a bit of lever to use at the bottom - that's what I'd certainly do...lower it 'positively' a few inches to start heading down and then raise it up around my ears at a few feet off the ground, rather than sit there waiting for the stored energy in the blades to dissipate prior to a particularly hard and painful fall.
Unless I've missed it in some of the posts above, nobody has mentioned lowering the collective partially to save some Nr and give you a bit of lever to use at the bottom - that's what I'd certainly do...lower it 'positively' a few inches to start heading down and then raise it up around my ears at a few feet off the ground, rather than sit there waiting for the stored energy in the blades to dissipate prior to a particularly hard and painful fall.
Joined: Dec 2001
Posts: 1,835
Likes: 3
From: Philadelphia PA
Little known fact-
The reason the low hover height on the HV curve is typically about 6-10' is that the FAA technique for testing the HV curve does not permit the collective to be lowered prior to it being raised.
So, when developing the low hover height point, you start increasing the height of the engine failure until you are at the point where following the engine failure you sit and wait while the aircraft falls, and then can only yank mightily on the lever to try to stop the rate of descent.
Obviously, those who are trained and prepared and proficient who hover at higher heights and know to lower the lever briskly first are doing something different than the published HV curve demonstrated.
This contributes to people treating the HV curve with less respect than it deserves.
And for Part 27 helicopters, the HV curve is not a limitation. Part 29, 10 passengers and more, it is a limitation unless you're using Category A procedures.
The reason the low hover height on the HV curve is typically about 6-10' is that the FAA technique for testing the HV curve does not permit the collective to be lowered prior to it being raised.
So, when developing the low hover height point, you start increasing the height of the engine failure until you are at the point where following the engine failure you sit and wait while the aircraft falls, and then can only yank mightily on the lever to try to stop the rate of descent.
Obviously, those who are trained and prepared and proficient who hover at higher heights and know to lower the lever briskly first are doing something different than the published HV curve demonstrated.
This contributes to people treating the HV curve with less respect than it deserves.
And for Part 27 helicopters, the HV curve is not a limitation. Part 29, 10 passengers and more, it is a limitation unless you're using Category A procedures.
