Posted: Thu Feb 17, 2011 5:21 pm Post subject: High G R22 takeoff (video) + Helicopter G limits?
I found this video on youtube. The pilot accelerates to around 65 knots and pulls pretty hard for the takeoff.(takeoff at 0:33) Watch this Video in a New Window
Is that bad for the helicopter/dangerous?
Also, in the R22 POH, it doesn't talk about G limits at all. There is no maneuvering speed. Does that mean that no matter what speed you are at (you can't go much faster than NE because of retreating blade stall), you won't exceed any G limits? (basically, NE is below the maneuvering speed)
I am guessing that some other helicopters have maneuvering speeds.
Joined: Feb 14, 2008 Posts: 888 Location: Stavanger, Norway
Posted: Thu Feb 17, 2011 8:22 pm Post subject:
The only thing is at high speed and low height you might be close to the lower part of the HV diagram, which most people tend to forget about.
Things to remember are that in the US Vne is 102kias unlike the 92kias in the UK. The CAA restricted Vne due to control sensitivity at high speeds, but retreating blade stall was never encountered during certification of the R22, they simply couldn't get it fast enough (doesn't mean it's not possible). Power and transmission limits were met first. It may be possible to get it during turns with high rates of bank, or high altitude like any other helicopter. _________________ ATPL(H) IR(H): SK92, AS355, EC120, R22/44
"When the tough gets going, the tough eat haggis!"
Joined: Feb 14, 2008 Posts: 888 Location: Stavanger, Norway
Posted: Thu Feb 17, 2011 8:44 pm Post subject:
Ask your instructor to show you a high speed low level EOL... note his reaction to the question. We used to demo 20ft/70kias if I remember correctly. It's been a while since I flew the R22 and am a bit rusty with the numbers.
Posted: Thu Feb 17, 2011 8:50 pm Post subject: Take off from a taxiway?
He does however seem to be taking off from a taxiway?
I seem to remember that style of centreline marking is limited to taxiways - mostly so fixed wing types can follow it with their nose wheel and know the wheels following won't fall off into the soft stuff...
Having said that it does look like a normal take-off to me - sans any radio chatter but that might be the camcorder not picking it up or being connected to do so?
Where I fly from (EGNM) they've recently changed procedures and we now have 2 heli aiming points, rather than being treated like fixed wing we're now expected to hover taxi to the point and depart direct from there - unless of course the runway is preferable due to Wx (or wheels ala S76 / Dauphin etc). It does sharpen up the approach slightly more if you aim to be in a hover above the triangle, somewhat less forgiving than a nice long runway where you need to cruise along 1/2 of it to reach the apron anyway
Assuming the place was big enough for full ATC (taxiways etc) I'm surprised the guy would be cleared to depart from it - unless he's free to do his own thing by local procedures?
Check in the back of the POH, safety notices and you will find a section on negative G and the dangers of mast bumping. (low g pushovers prohibited).
Also going back to taxi speeds, I was told the speed at which you are taxiing is the speed at which you will hit the ground if the engine fails. I was then asked "if the engine does fail, can you keep the helicopter straight once on the ground at this speed?"
This is something I aways bear in mind when in a hover taxi.
I am in the US and we usually do takeoffs on a helipad placed on one of many taxiways (at my home airport).
I forgot that - the HV diagram says you should stay below 10 feet and begin the climb at 45-50 knots. Pilots aren't supposed to exceed 55 knots below 10 feet
So the takeoff shown in the video is outside the limits of the HV diagram. If I understand correctly, this means that if they had an engine failure during the later portion of that takeoff, they might not have been able to safely autorotate.
But what about G limits, can a pilot fly to any airspeed in an R22 and pull hard on the cyclic until airspeed is 0? Is that ok?
Do other Helicopters have G limits/maneuvering speeds? (paddy, I am talking about positive Gs)
Btw, what is the purpose of vne if there is no retreating blade stall?
It's late, been a long 36 hrs and relaxing with rum so I satand to be corrected here....
I can't see the gauges on my netbook clearly enough to get the figures - maybe you can and that's how you got to the question and know it is outside the h/v recommendations. Don't forget that that the figures are obtain in a specific set of conditions. I assume you don't know the elevation of the airfield so the altimeter might not be showing the AGL...
Yes, some helicopter I believe have G limits - not sure how you measure them though in something like the R22! Negative G is/was also a problem on other helicopters - eg the Huey.
Here it gets a bit hazy as the brain is addled... if you pull hard on the cyclic I am thinking the following might happen.
- the disk will tilt back and remove the tail so everything else is academic.
- unless you drop the collective you will climb rapidly.
The vne thing was covered on the Robinson safety course but I don't have my notes here and it was a while ago so I can't remember the offical response but I would think it is either due to the fact they couldn't get a high enough speed for RBS without exceeding other posted limits or it is due to structural design limits.
W. _________________ In memory of Skippy the Dog - "www.pilotsnpaws.org" - RIP Scruffy.x
As I understand it (and I'm pretty certain I'm about to get corrected...), the issue is with negative G, particularly on teetering-head systems, and it is the secondary motion that causes problems.
UH-1H pilots 'discovered' it in Vietnam - they would buzz along low-level, and hop over hills by applying a little aft cyclic to climb over, then forward cyclic to drop down and recover airspeed....... the pendulum action of the fuselage following the rotor disc meant that as they crested the hill their tail was high, and as the pilot levelled out after the hill, if he was a little enthusiastic, rotor disc and tail-boom had an impromptu meeting!!!
Joined: Aug 23, 2006 Posts: 25 Location: Hall Green
Posted: Fri Feb 18, 2011 1:57 pm Post subject:
It's the pilots action on encountering negative G that causes the problems.
If you unload the disc, ie from a climb shove the cyclic forward and the momentum of the cab is still upward whilst the disc is not, the anti-torque from the tail rotor is now excessive. The aircraft will yaw (in a Robbo to the left) and the parasite drag on the now side-slipping aircraft will cause it to roll to the right. Natural instinct is to apply left cyclic to overcome the roll but this will actually exaggerate the angle of the disc to the mast causing mast bumping and possible separation. Remedial action is always to reload the disc before applying lateral cyclic.
As far as positive G is concerned I've never come across published limits for a Robbo but if you load the disc up to the point at which it goes one way and the cab goes the other you've overdone it! _________________ Chief Pilot: Mickey Mouse Airlines
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