Varying degrees of IGE
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Varying degrees of IGE
From the wealth of knowledge out there, I was wondering if somebody could assist me answering a question I received from a student.
We are told that IGE occurs when the helicopter is one blade span above the ground (with minimal wind, not on sloping ground, not over water or grass).
Does the helicopter achieve greater IGE by being only 6 inches above the ground as compared to being 5 feet above the ground, as compared to being 15 feet above the ground?
Or is Ground Effect just standard (same value) anywhere between 6 inches and 15 feet (R22).
Thanks in anticipation!
We are told that IGE occurs when the helicopter is one blade span above the ground (with minimal wind, not on sloping ground, not over water or grass).
Does the helicopter achieve greater IGE by being only 6 inches above the ground as compared to being 5 feet above the ground, as compared to being 15 feet above the ground?
Or is Ground Effect just standard (same value) anywhere between 6 inches and 15 feet (R22).
Thanks in anticipation!
lordy lord....but I am going to say that this is a dificult one to measure scientifically and I dont know that I can help much.
I know that I once made good use of Ground Effect whilst overwater with a 212 that had lost a stove on rotation off the deck. When we levelled off (at I guesstimate about 5 feet) the Nr was veeeery low but we had airspeed and we did not want to swim so flew for what seemed a couple miles coaxing the airspeed and Nr back up to acceptable levels (sort of like flying a 47G after over pitching) before climbing out back to the beach (Bombay actually)
I really push using the ground effect when doing OEI training with the S76 to get the IAS/Nr combination back up.
Anyhow...try this for lateral thinking...if anyone knows about GROUND EFFECT , it is the boys who are playing with various "In Ground Effect Vehicles". The Russians called them "iraknoplanes" (or something similiar....not sure of spelling) and built some reall monsters ....like the size of a DC-10
interesting subject...
I know that I once made good use of Ground Effect whilst overwater with a 212 that had lost a stove on rotation off the deck. When we levelled off (at I guesstimate about 5 feet) the Nr was veeeery low but we had airspeed and we did not want to swim so flew for what seemed a couple miles coaxing the airspeed and Nr back up to acceptable levels (sort of like flying a 47G after over pitching) before climbing out back to the beach (Bombay actually)
I really push using the ground effect when doing OEI training with the S76 to get the IAS/Nr combination back up.
Anyhow...try this for lateral thinking...if anyone knows about GROUND EFFECT , it is the boys who are playing with various "In Ground Effect Vehicles". The Russians called them "iraknoplanes" (or something similiar....not sure of spelling) and built some reall monsters ....like the size of a DC-10
interesting subject...
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dzeroplus,
The ground effect is a gradual thing, it starts at about 20% thrust advantage (or power decrease, take your pick) at the point where your aircraft just breaks the ground. As you gain height, the effect reduces until by about 1.5 times the rotor diameter it is nil. The line is not straight, the per foot of height effect is strongest at low altitude, and gets weaker as you go up.
Why not try it? On a still morning, take your machine and barely lift it off, with the skids just awash, and note the rpm and power (MP). then lift it to 5 feet and sustain the same rpm exactly. Let it settle at 5 feet, don't pump the collective, let it drift up and down a bit. Note the MP there, should be noticibly higher. Now go to the highest hover the avoid area of your manual permits, and repeat this trial. Much more power yet.
For the record, the effect is not due to a "ground cushion" or "air pressure" or "a bubble of air" under the helo. The ground bends the air flow coming off the rotor, and this bend makes the rotor blades work at a lower angle to produce the same lift. The lower angle needs less power, so we see the ground effect.
The ground effect is a gradual thing, it starts at about 20% thrust advantage (or power decrease, take your pick) at the point where your aircraft just breaks the ground. As you gain height, the effect reduces until by about 1.5 times the rotor diameter it is nil. The line is not straight, the per foot of height effect is strongest at low altitude, and gets weaker as you go up.
Why not try it? On a still morning, take your machine and barely lift it off, with the skids just awash, and note the rpm and power (MP). then lift it to 5 feet and sustain the same rpm exactly. Let it settle at 5 feet, don't pump the collective, let it drift up and down a bit. Note the MP there, should be noticibly higher. Now go to the highest hover the avoid area of your manual permits, and repeat this trial. Much more power yet.
For the record, the effect is not due to a "ground cushion" or "air pressure" or "a bubble of air" under the helo. The ground bends the air flow coming off the rotor, and this bend makes the rotor blades work at a lower angle to produce the same lift. The lower angle needs less power, so we see the ground effect.
IGE
dzeroplus
I concur with the replies above however, I have a question for you. Are you a helicopter "pilot/instructor" as your profile suggests or is your experience on fixed-wing? If you are indeed a helicopter pilot, you shouldn't really need to ask the question about IGE.
My point being that knowldge of IGE/OGE performance for a helicopter is as fundamental, and as important, as knowing that you need to enter autorotation when your engine fails. (single engine!). If you are indeed a qualified helicopter pilot, might I suggest you go back to your flight school and ask for a substantial refund as you clearly haven't been thoroughly taught the essential limited power techniques. If you are a helicopter instructor; well, where do I start.........!
This isn't meant to be a dig at you by the way. However, if you missed IGE, what else didn't you get taught?
J
I concur with the replies above however, I have a question for you. Are you a helicopter "pilot/instructor" as your profile suggests or is your experience on fixed-wing? If you are indeed a helicopter pilot, you shouldn't really need to ask the question about IGE.
My point being that knowldge of IGE/OGE performance for a helicopter is as fundamental, and as important, as knowing that you need to enter autorotation when your engine fails. (single engine!). If you are indeed a qualified helicopter pilot, might I suggest you go back to your flight school and ask for a substantial refund as you clearly haven't been thoroughly taught the essential limited power techniques. If you are a helicopter instructor; well, where do I start.........!
This isn't meant to be a dig at you by the way. However, if you missed IGE, what else didn't you get taught?
J
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(OGE) Out of Ground Effect provides normal lift. Normally speaking.
(IGE) In Ground Effect provides greater lift. But, as Gordon Leishman says "The [ground] effect has long been recognized but the aerodynamics are still not fully understood."
(UGE) Under Ground Effect provides the greatest lift. But, it is even less understood.
This phenomenon is most noticeable at six feet under. Most people say that one hovers like an angel. Others, who have been naughty, dispute this and say that there is one hell of a sinking feeling.
(IGE) In Ground Effect provides greater lift. But, as Gordon Leishman says "The [ground] effect has long been recognized but the aerodynamics are still not fully understood."
(UGE) Under Ground Effect provides the greatest lift. But, it is even less understood.
This phenomenon is most noticeable at six feet under. Most people say that one hovers like an angel. Others, who have been naughty, dispute this and say that there is one hell of a sinking feeling.
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Not wishing to hijack - but someone mentioned the Russian ground effect planes. (These things first appeared on the satellites during the Cold war and frightened the s**t out of the USA miltary - 250mph flying battlecruisers could move entire divisions.)
Anyway, a tale. Three years ago I got to fly on a Russian-built ground-effect plane. A Malaysian investor had procured a Russian design and engineering team and set them up in the Bahamas to develop civilian versions of the ground effect plane.
The one I went on was about the same size and shape as a six-seater twin - but with very short stubby wings. It behaved like a boat up to 50 knots - going through an "up on the plane" stage at about 25 knots. Then the magic happened - the buffeting stopped, the speed climbed to 100 knots and we were flying about 20cms above the water on ground effect. Gobsmacking. I will try to post some links if I can find the stuff.
The lead engineer was ex-military - looked like your standard movie Russian hardman soldier. Extremely fit, double sixpack etc. I asked him what he did before he got involved in this programme : "KGB". And - er - where were you based? "Oh I was at university in Israel."
OK - these things are called WIG vehicles (Wing In Ground effect) and here's a good link http://www.aerospaceweb.org/question...cs/q0130.shtml
Anyway, a tale. Three years ago I got to fly on a Russian-built ground-effect plane. A Malaysian investor had procured a Russian design and engineering team and set them up in the Bahamas to develop civilian versions of the ground effect plane.
The one I went on was about the same size and shape as a six-seater twin - but with very short stubby wings. It behaved like a boat up to 50 knots - going through an "up on the plane" stage at about 25 knots. Then the magic happened - the buffeting stopped, the speed climbed to 100 knots and we were flying about 20cms above the water on ground effect. Gobsmacking. I will try to post some links if I can find the stuff.
The lead engineer was ex-military - looked like your standard movie Russian hardman soldier. Extremely fit, double sixpack etc. I asked him what he did before he got involved in this programme : "KGB". And - er - where were you based? "Oh I was at university in Israel."
OK - these things are called WIG vehicles (Wing In Ground effect) and here's a good link http://www.aerospaceweb.org/question...cs/q0130.shtml
Last edited by headsethair; 1st Sep 2003 at 17:41.
The 1.5 times rotor diameter is a standard definition of the range within which the a/c can be considered IGE. As an example, the B-212 FLM OGE graph states a 60 ft hover. The skid to head is 12 feet which makes 72 feet, and the rotor diameter is 48 ft. Voila!
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I have been an instructor for over 20 years and before that I practiced thousands of confined areas,most of them at MGW. Definitively hovering at 5 or 6 inches of the ground you get more lift than at 5 0r 10 feet.Many times I approched and hovered at 100% torque with a 206 at 6 feet of the ground. Lowering the aircraft at 3 to 10 inches of the ground I would reduce the torque to 95%
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(UGE) Under Ground Effect provides the greatest lift. But, it is even less understood.
This phenomenon is most noticeable at six feet under. Most people say that one hovers like an angel. Others, who have been naughty, dispute this and say that there is one hell of a sinking feeling.
Visual indications: When you see plant roots in the cockpit windshield, you are there.
This phenomenon is most noticeable at six feet under. Most people say that one hovers like an angel. Others, who have been naughty, dispute this and say that there is one hell of a sinking feeling.
Visual indications: When you see plant roots in the cockpit windshield, you are there.
