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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Explain this to me please,,,,
09-08-2006 06:15 AM  14 years ago
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wurthless

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Redding Ca.

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Explain this to me please,,,,
1.5...2 times lower inertia moments of the helicopter; ability to perform a pedal (flat) turn within the full flight speed range; the best vertical rate of climb and hovering ceiling.
OK I understand what the pedal turn is,,,but whats the first part talking about and what is a hovering ceiling?
This is a few of the specs for a the Russian KA-5- Black Shark http://www.chelbi.net/ka50/
QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-08-2006 06:29 AM  14 years ago
Aaron29

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USA

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A ceiling is always a reference to highest altitude flight.

Hovering ceiling is usually lower than forward flight due to effective translational lift. And there are two hovering ceilings:

IGE - in ground effect, close to the ground, and
OGE - out of ground effect

Helicopters can hover higher in ground effect.
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09-08-2006 06:39 AM  14 years ago
wurthless

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Redding Ca.

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Still not sinkin in my hard head.
Helicopters can hover higher in ground effect.
A hover is a hover is a hover,,,, be it 2 feet off the ground or 500 feet. Once your high enough to be OGE your "hovering" higher then when you were IGE,,,I'm confussed still
effective translational lift.
I read what this is once but dun forgot it,,refresh me please
QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-08-2006 06:43 AM  14 years ago
Aaron29

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USA

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The non-aerodynamic answer is it rides a cushion of air underneath it and can thus attain a hover at a higher altitude.

The long version involves change of effective blade angle of attack and induced drag due to reduced downwash. I'll be glad to explain it in detail later. It's bed time.
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09-08-2006 06:44 AM  14 years ago
wurthless

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Redding Ca.

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yep I have a "brain sweat" goin here QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-08-2006 07:21 AM  14 years ago
Furious Predator

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Kitchener, Ontario, Canada

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you can test the ground effect on the sim and in real life with a model heli.

go up about 10 feet on a calm day. let the heli decend SLOWLY at a constant rate. and without touching the collective, the heli will slow down and transition from a decent into a steady hover. this normally happens within a height of 1/2 to 2/3 of the rotor diameter, same with planes, but 1/2 to 2/3 of the wingspan. i have done this on G2, Reflex, and in real life just to see if i can detect the ground effect.

normally you dont notice it unless your looking for it, the effect is pretty small on these things.
Shawn
Team Leisure-Tech
Team HelixRC
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09-08-2006 09:45 AM  14 years ago
bagobitz

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saddleworth,lancs,UK

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My understanding, is that the ige/oge are dependent on GROUND altitude (wether barometric or actual above sea level)
there's a video of a successful takeoff from an Everest camp. The pilot could not get into forward flight and therefore translational lift,therefore, as the ground dropped away, he came out of ground effect, lost lift and control and piled it.


My understanding is that a heli will hover in ground effect at higher altitude than it's oge max.


do I have it right?
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09-08-2006 02:03 PM  14 years ago
w8qz

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Grand Rapids, MI - USA

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1.5...2 times lower inertia moments of the helicopter
I assume that the reference here is to the inertia moment about the main shaft - ? (didn't bother to look up the URL)

- at any rate, in layman's terms, inertia moment is the tendency of an object to continue to rotate once started, or the resistance to start rotating when at rest.

Lower inertia about the main shaft (i.e. axis of tail rotor control) would mean better response to 'pedal' inputs - quicker response, and quicker stops, with less 'overshoot'. This would give better control to the pilot.

With our models, inertia moments are relatively small when compared to the control force available, and are not a major concern in normal piloting (extreme 3D excepted!). I assume that with full scale helicopters, inertia is a much more important factor.
"The helicopter is much easier to design than the aeroplane, but is worthless when done. W. Wright"
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09-09-2006 04:44 PM  14 years ago
wurthless

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Redding Ca.

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Yes I too have expermented with the IGE/OGE with my Sky Robo. I can approach a table top at a slow rate of speed , just inches above the table hieght and as I come over the table the heli lifts up with out me giving it any input. Opposite happens when I fly off the table into clean air.
there's a video of a successful takeoff from an Everest camp. The pilot could not get into forward flight and therefore translational lift,therefore, as the ground dropped away, he came out of ground effect, lost lift and control and piled it.
I did not know a heli could fly at an altitude that it could not hover in. The heli at Mt Everest had to fly into land or hover IGE but could not get going again into FF without being IGE. You say at first it's a video of a successfull T.O. but then you say he "piled it" Did he crash or not?
w8qz,,
thanks for clearing that up. The link is to a Russian built heli that uses XRB rotors and it must be quicker turning in that arrangment.
Thanks for all the help,,you guys are smart!!!!
QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-09-2006 06:04 PM  14 years ago
AirWolfRC

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42½ N, 83½ W

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Yes, he crashed & burned, literally.
He might have made it if he had climed to at least one rotor diameter before going off the edge of the plateau.

I have that video in my archives . . . somewhere.

Wolfgang
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09-09-2006 06:46 PM  14 years ago
Chief_USN

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Chesapeake, VA

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I seen a close call with this effect first hand a few years back. We were standing on the flight deck launching an MH-53E with a full load of fuel and cargo. The helo started to lift off and the LSE(Landing Signalman) gave the signal to drift left to clear the ship and start forward flight. As soon as the MH-53E got out fom over the deck, it dropped down, almost smacked the main rotor on the scuffing(edge of flight deck), and went out of site below flight deck level. All of our mouths dropped and then we started smelling fuel. The pilots reacted just fast enough to flip the fuel dump switch and started dumping fuel to lighten the load. The only thang that really saved them was getting that cushion of air back as they got closer to the water.

This can also be felt in flight getting ready to land. I've flown onto the ship before and it is a nice and smooth descent until the bird gets over the ship and you can actually feel the bird lift up a little and then it gets rough because of the turbulance created by the downwash and the flight deck obstructions and angles.

Chad
Team HeliProz 12-14
US Navy Chiefs...Unity, Service, & Navigation to the Fleet since 1893
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09-09-2006 08:33 PM  14 years ago
wurthless

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Redding Ca.

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That was close!!!
Would like to see the video of the other crash if you can dig it up, AW
QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-10-2006 05:50 AM  14 years ago
jschenck

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La Vista, NE.

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I have experienced a very similar flight dynamics when hovering a blade CP. I put a 2'x2'x2' cardboard box in the middle of my basement - then try to land the BCP on it. weird, when 1/2 the rotor disk is over the box it's really hard to control. It's like there is a bubble of air over the box and your heli is constantly being pushed off/falling off the bubble.
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09-10-2006 04:48 PM  14 years ago
wurthless

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Redding Ca.

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I can see where having half the disk over an object and half over clean air would be very unsable.QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-10-2006 10:54 PM  14 years ago
AV8TOR

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Fort Worth, TX

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Helicopters can hover higher in ground effect.
Ground effect with a rotor aircraft is 1/2 your rotor span so what are you saying "higher"? Less power maybe?
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09-11-2006 05:51 AM  14 years ago
wurthless

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Redding Ca.

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If I'm folowing the facts correctly it means a copter can hover IGE at a higher ALTITUDE (like over a mountain top) but could not hover OGE at that same altitude. So a pilot could not just stop and hover at 10,000 feet(guessing here), but if he stopped over a spot of ground at that hieght he could hover over it (IGE).QUICK! ,,,can someone turn the gravity off for just a second,,,,
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09-11-2006 09:56 AM  14 years ago
bagobitz

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saddleworth,lancs,UK

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As wurthless has said.
OK, imagine hovering next to a mountain..the mountain is sheer-sided,up to your hover-ceiling.....then it goes off to a gentle upward slope.
you cannot hover any higher today,because of the altitude-density of the air.you drift across to the slope, which is LESS than 1 1/2 rotor-widths beneath you...lo and behold, you start going up again...you slowly drift up the slope.....eventually you'll reach the point where the ground is rising,but the Heli isn't .....that's the ceiling IGE.

it will, of course vary according to air-density...which is why an altimeter has to be constantly "loaded" with the prevailing barometric-pressure,in order to give a correct altitude .

don't forget, altitude and height above sea-level are NOT the same thing.
this is a simplified explanation (i think) hope you can make sense of it.
jschenck,s experiment illustrates the principle..the "bubble"is a constant -thickness layer over the terrain...when the heli runs out of breath,you can put a "bubble" under it and give it a bit of a "leg-up"
you can also visualise that it gives the rotor something solid to push against.
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