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helicopter nose up pitch up attitude

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helicopter nose up pitch up attitude

Old 19th Nov 2016, 13:14
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helicopter nose up pitch up attitude

I was browsing the internet regarding max allowable helicopter nose (pitch up) attitude during normal take off and landing for a single engine aft CG configuration. Generally we know that as and when mission is about to be completed helicopter CG moves towards AFT. Any mention in rotorcraft flight manuals about helicopter pitch attitudes during take off and landing especially for a 3Ton class helicopter. Can some body throw some light on this. It will be helpful.
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Old 19th Nov 2016, 13:40
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Generally we know that as and when mission is about to be completed helicopter CG moves towards AFT.
On the one's I used to fly it didn't for a given payload.
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Old 19th Nov 2016, 15:56
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It depends how the fuel tank/tanks are positioned and how the C of G moves with fuel usage (all other factors being equal).
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Old 19th Nov 2016, 17:00
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The C of G on the type I fly moves forwards with fuel used. Unless I take off after forgetting the co-pilot...

But either way, if there is a written limitation on nose up attitude, the RFM is the place to look.
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Old 19th Nov 2016, 18:22
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The S76 had a limit of 10 degrees nose-up for landing, but that was due to flaring to slow down and avoiding a tailstrike. The normal flight attitudes were nowhere near that.
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Old 20th Nov 2016, 04:50
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helicopter nose up pitch up attitude

you are right at the time of take off it will be mid-aft CG then depending on the type of mission at the time of landing it will go further AFT CG. So in all probability there will be some allowable nose up pitch attitude subject to tail guard inclination w.r.t skid. In some light helicopters like tail rotor mounted on longitudinal axis, what will be the limiting nose up pitch attitude at the time of landing/takeoff. Am looking for Augusta 119, Bell 407 AND 429, eurocopter AS350 and Aérospatiale Alouette helicopter data. Some body from forums can help me in getting these data.
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Old 20th Nov 2016, 04:56
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There might also be a connection between pitch attitude and fuel remaining, in a low fuel state to ensure the pitch attitude keeps the fuel within the collector in the bottom of the tank.
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Old 20th Nov 2016, 05:38
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Any mention in rotorcraft flight manuals about helicopter pitch attitudes during take off and landing especially for a 3Ton class helicopter.
Yup. Its called the "Weight and Balance Section".

Stay within the limits = "happy days".

Nothing to see here.
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Old 20th Nov 2016, 06:05
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Generally we know that as and when mission is about to be completed helicopter CG moves towards AFT.
Not (always) true-you are probably only referring to the helicopter you know, but a lot of modern helicopters have a "smart" fuel management, making sure that the CoG stays within limits throughout the whole flight.
 
Old 20th Nov 2016, 21:17
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I don't understand all your terminology, but some of your assumptions appear to be mistaken. Terminology- "max allowable helicopter nose (pitch up)", relative to what? "3ton helicopter"? which I guess means an aircraft 0f less than 6,000 lbs?

I can't help you with Agusta 119 or Bell 429, but I have lots of experience with the AS350 and variants, no Bell 407 but tons in the earlier 206 that it is based on.

First, I can't remember a light airframe in which the CG moves aft with fuel burn, with the limited exception of the 206 Long Ranger in certain situations, the exception is limited and I'll talk about in a bit.

The AS350 fuel tank sits beneath the main rotor and aft of the allowable CG envelope except at very light loads, and even then the fuel load is in the aft envelope. Besides the fuel tank, the only loadable area that can move the CG aft is the aft baggage compartment, which has limited capacity. You can load this type such that you exceed the aft envelope limit, but it hasn't happened to me more than a couple times in 30 years on type when the aft compartment had an unusually heavy load snuck into it. The nose came up unusually into a fully controllable hover, no danger to of a tail strike. In fact, the few times I've busted the CG envelope, the aircraft was absolutely controllable in normal powered flight. And that's the trap, you lose an engine or are otherwise required to use an unusual amount of control in one or more axis, and you're a test pilot because now you may not be able to control the aircraft normally.

With the fuel aft, burning fuel moves the CG forward, typical in light helicopters. The exception is the Long Ranger, and I think the 407, which have 2 smaller tanks under the middle cabin seats. They fill at a midrange and burn at the midrange, so while the saddle tanks are being depleted the CG does move aft. The fuel burn is from the top of the main (behind and under the rear seats) moving the CG forward, then the middle/saddle tanks are emptied, moving the CG aft, and then the remaining main tank fuel is consumed. That was 25 years ago, so check your RFM...

What seems to happen as the aircraft burns fuel is that one can often increase paylod, especially if the CG envelope expands forward like the AS350 does. It's not unusual for me to leave base in my HEMS configured AS350B2 with a patient weight limit of 250 lbs for CG, and then have 350-400 lbs cg limit on the stretcher weight.
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Old 25th Nov 2016, 14:12
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Limitations

For helicopters certificated by the UK, US, or EASA (or military) there will be a limitations section in the certification documents and PFM/RFM. That information will provide the operator with any limits applicable to the helicopter. There are helicopters with nose up, nose down, and roll limitations for takeoff and landing. The Russian helicopters I have flown have similar limitations.
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