Hovering Limitation - Time
Thread Starter
Joined: Feb 2004
Posts: 144
Likes: 0
From: A place with no name
Hovering Limitation - Time
Hi Guys,
Being a non-rotorhead I am not sure about this. I have a work mate who was talking to me about some hovering limitation where a chopper cannot hover for too long as it creates a vacuum "or something" which causes said machine to fall out the sky.
Immediately I thought, no way. And even now I wonder if he got the wrong end of the stick. Is there any truth to the matter?
Being a non-rotorhead I am not sure about this. I have a work mate who was talking to me about some hovering limitation where a chopper cannot hover for too long as it creates a vacuum "or something" which causes said machine to fall out the sky.
Immediately I thought, no way. And even now I wonder if he got the wrong end of the stick. Is there any truth to the matter?
are there any limitations to hovering besides fuel, MAUW and weather? Oh and skill of driver doing such.
Joined: Feb 2006
Posts: 292
Likes: 0
From: Sydney
Helicopter flight physics
I wouldn't be too hasty to dispell the vacuum notion. I know for a fact that, when I first learned to fly helos, concrete helipads had an inverse square law repulsive effect on the chopper, the closer I got to the pad the harder it was to put the machine down.
As the years have passed this localised gravitational anomaly seems to have have removed itself from the physical laws of the universe.
However we all know that choppers don't really fly, they simply beat the air into submission. So it is not beyond the bounds of possibility that enough beating could trigger a quantum mechanical implosion therby generating a localised vacuum?
As the years have passed this localised gravitational anomaly seems to have have removed itself from the physical laws of the universe.
However we all know that choppers don't really fly, they simply beat the air into submission. So it is not beyond the bounds of possibility that enough beating could trigger a quantum mechanical implosion therby generating a localised vacuum?
Joined: Jun 2006
Posts: 51
Likes: 0
From: Wellington, New Zealand
Perhaps he thought that hovering in the same place could create a vortex ring? It may be wrong, but at least it makes a bit of sense.
22clipper: I thought it was because they vibrated so much, that gravity no longer had an effect of them, like lightwaves or radiowaves or something.
22clipper: I thought it was because they vibrated so much, that gravity no longer had an effect of them, like lightwaves or radiowaves or something.
Joined: Jul 2005
Posts: 59
Likes: 0
From: Melbourne
Well,
Don't know about a vacuum, but the AS365N3 has a tailboom limitation on hovering at certain OATs...the exhaust heat/composite tailboom combination etc..
Oldbeefer, I think 22clipper is referring to 'concreteitis'
Don't know about a vacuum, but the AS365N3 has a tailboom limitation on hovering at certain OATs...the exhaust heat/composite tailboom combination etc..
Oldbeefer, I think 22clipper is referring to 'concreteitis'
Joined: Jun 2006
Posts: 6
Likes: 0
From: 62n150w
Out of Ground Effect settling
Out of ground effect settling when holding position (hovering) will bring you downward in still air when you create your own verticle vortex of a downward moving localized air column. Effect goes away as you approach ground effect at the bottom of the air column. Not desirable to experience, since rate of descent is not controlable, and ability to recover requires sufficient altitude.
Not the same as holding relative horizontal ground position in a headwind.
This effect has not been personally verified -- but I scared myself once -- is supposed to be a situation whose rapidity developes porportional to the gross weight, and increases if additional collective is used to maintain height or stop rate of descent. Instead this increases the rate of descent -- a visual nearby reference is necessary to determine if holding altitude, or already descending, since IVSI would probably not be accurate.
Controls get real mushy and response to input negligible.
Solution is to decrease collective, increase forward speed and fly out of the downward moving column.
In ground effect, no wind ground-shyness is caused by increased air pressure under the rotor swept plane and greater lift produced by the denser air on the blades when they have relatively the same lift on the advancing and retreating blades. Watch the dust with a hovering aircraft in still air, you'll see the vortex pattern, and can imagine the drag slowing the air escaping from under the aircraft as it comes into contact with the ground, this drag is what increases the pressure, adding lift -- hence "ground effect"....
Not the same as holding relative horizontal ground position in a headwind.
This effect has not been personally verified -- but I scared myself once -- is supposed to be a situation whose rapidity developes porportional to the gross weight, and increases if additional collective is used to maintain height or stop rate of descent. Instead this increases the rate of descent -- a visual nearby reference is necessary to determine if holding altitude, or already descending, since IVSI would probably not be accurate.
Controls get real mushy and response to input negligible.
Solution is to decrease collective, increase forward speed and fly out of the downward moving column.
In ground effect, no wind ground-shyness is caused by increased air pressure under the rotor swept plane and greater lift produced by the denser air on the blades when they have relatively the same lift on the advancing and retreating blades. Watch the dust with a hovering aircraft in still air, you'll see the vortex pattern, and can imagine the drag slowing the air escaping from under the aircraft as it comes into contact with the ground, this drag is what increases the pressure, adding lift -- hence "ground effect"....
Joined: Oct 1999
Aviation Qualifications: ATPL
Posts: 7,371
Likes: 926
From: Den Haag
In turbine engine aircraft their may be a limitation based on engine limits if you are not MGB torque limited.
So, apart from oil temperature, engine limits, hydraulic temperature and tail boom temperature, there are no time limits on hovering!
So, apart from oil temperature, engine limits, hydraulic temperature and tail boom temperature, there are no time limits on hovering!
Joined: Aug 2002
Posts: 70
Likes: 0
From: UK
Young SoundBarrier has obviously never met a pinger has he! I have sat for many of an hour in the dip with the 'body' in the water! The main limitation is fuel and trying not to fall asleep in the right hand seat!
Joined: Jan 2000
Posts: 1,113
Likes: 1
From: UK
There is a vertical cliff face in Snowdonia where with the correct wind speed (20kt+) and wind direction (up the valley) it is not possible to hover (at least in a Wessex or Seaking) for more than about a minute.
As you stop along side the cliff face in the vertical updraughting air you can hover on around half power for a few seconds before the lever has to be gently raised to maintain position. If you hold position you will start to run out of power and must fly out. Happens every time.
As you stop along side the cliff face in the vertical updraughting air you can hover on around half power for a few seconds before the lever has to be gently raised to maintain position. If you hold position you will start to run out of power and must fly out. Happens every time.
Joined: May 2002
Aviation Qualifications: ATP+Mil
Posts: 18,633
Likes: 1,072
From: Downeast
Nigel,
You left out the most important factor for ageing pilots....bladder limits. Chug down a couple of cuppas of Earl Gray and that time limit shrinks quickly.
That is why we older guys prefer shuttling to long transits.
You left out the most important factor for ageing pilots....bladder limits. Chug down a couple of cuppas of Earl Gray and that time limit shrinks quickly.
That is why we older guys prefer shuttling to long transits.