F, C, L or F, L, C!!

[Thomas coupling]

Following from the tail rotor control thread that MG started. I Have another scenario that appears to be a modification from my military days:

I'm from the school of:. .Flare, Check, Level at the bottom of an auto/engine off.. .Recently though, I've noticed the alternative:. .Flare, Level, Check is being advocated.

Is one better than the other, or is there a choice.. .NL, your opinion would be appreciated?

Regards

http://www.animationlibrary.com/Animation10/Nature/Sun/Fire_sun.gif

. . <img src="confused.gif" border="0">

[ 26 January 2002: Message edited by: Thomas coupling ]</p>

[Nick Lappos]

Thomas,. .I assume that by "check" you mean the application of some collective pitch (we used to call it a bit of "initial pitch") to brake the descent, if so, here goes:

This is a good one for "it depends". The driving questions are 1) How good is your helo at autorotating? and 2)How much do you love your helicopter vs how much do you want to walk away?

For wonderful aircraft, which have excess energy at the bottom, the flare, level, check will work well. For most helicopters, which must be carefully threaded through a small window of energy management, a flare, check, level is proper use of the energy.

For some heavy helicopters, with little energy to spare, flare, check, land while banging the tail is actually fine and dandy.

The operative issue is how effective the flare is at stopping the descent. If the aircraft can fully stop the descent in the flare, the landing is almost a formality, so go ahead, waste some energy and level the nose first. If the flare results in a reduction of rate of descent, but the world is still rushing up to meet you, check with a collective pull, or the level-off you try will vastly increase your rate of descent, and you may land hard.

If the aircraft treats the flare as a new attitude, with little reduction in rate of descent, then pull collective but keep the nose mostly up, bang the tail on the landing.

Two additional thoughts for consideration:

1) the practice may be easy and the actual hard. If you practice in a light helo at a low altitude, autos seem nice, because the energy in the flare is applied to a lesser gross weight, and the rotor has more thrust. Also, the rotor energy in the pull is applied to less gross weight, and the rotor is more efficient there, as well.

Take that same helo to a 4000 foot spot, and get up to max gross weight and it will be a much harder bird to auto to touchdown. The flare will seem to have less "bite" (the same back stick/nose up will result in less vertical G, and the rate of descent will not be arrested as quickly). Also, the pitch pull at the bottom will seem mushier, where the up collective used to produce a comforting vertical G, it will seem less effective, and will have to be pulled faster for the same effect.

2) Some helos are naturally worse at autos, by design.

The flare effectiveness is almost all due to light disk loading. As we build bigger, faster and heavier helicopters, we load down the disk. A light piston helo with a Vne at 80 knots can be as little as 3 pounds per square foot, a 160 knot twin turbine can be 7 psf, a monster three engine can be 14 psf, and a tilt rotor can be 25 psf. Pilots can intuitively sense how effective the flare will be just by how much "bite" the flare has. The less bite, the less you have to work with at the bottom.

Also, the rotor inertia that fuels the pitch pull at the bottom can be different for different birds. Two bladed Bells have wonderfully heavy, structurally inefficient rotors, and store lots of energy, so the pitch pull can be long slow and even done twice (I used to demonstrate a touchdown auto in a Cobra, then lift up and turn 90 degrees!). Other machines have little excess energy, and so need careful management to keep from wasting the pull. It is not nice to do an auto and reach the collective stops before the aircraft reaches the earth! The last few inches are all free, courtesy of Newton's apple, and you are really just a passenger with responsibility.

A note on autos in general -they are good to do, important as confidence maneuvers, but they are not how helicopters make money. They are corners of the envelope that seem more important to those who train and practice, but when you go out to work with the machine, they are an after thought. For most helos, the pilot and his/her judgements are easily 10 times more important for safety than the autorotational capability.

Another thought: Watch the Space Shuttle land, listen to the Astronauts brag about the landing, and count how many seconds they have to level off and find the ground! Piece of cake, and a real testament to all you rotorcraft ppruners who can auto a helicopter, where the flare, pull, touchdown might take 3 seconds on a good day!

[ 26 January 2002: Message edited by: Nick Lappos ]</p>

[heedm]

A couple other things I'd consider before reaching the bottom of the auto are tail rotor clearance and landing area.

If you're low and using the flare to arrest forward speed, then your nose-up attitude may be endangering tail rotor clearance. In this case FCL may work better.

If the landing area is long and flat, then an extended flare, which gradually turns forward speed into rotor inertia may work best. If the landing area is a small confined area, then using some rotor inertia to arrest your forward speed may be required to precisely stop over the only appropriate area.

If you have wheels and a runway is looming in front of you, the auto can be succesfully done by flaring only. Maybe use collective on the runway to aerodynamic brake.

. .In any case, consider this stuff NOW. If you wait until the bottom of an auto (or even the entry) to decide what technique you'll use, you'll be making a bad situation worse.

[Vfrpilotpb]

Nick, . .I have read your post twice, and sorry to seem a little dim, but do I understand from your post that the higher in altitide and up to max weight will create a greater problem at the bottom, than at max weight and lower altitude, I practice Autos as often as I can, as you say to give my mind the background that "It may work on the day", and I have done the same with a full weight R44 and B206, but that was from entry at 1500ft, if it had been much higher, would it be affected by the max weight and the prolonged influence of gravity ?

My regards

[Up & Away]

Flare(cyclic) Check(lever) if neccessary Level(attitude) does it every time!!!

Flare Level then 'Cushion' also works but its too late to 'check' could end up with fast run on!

Flare first increases Rrpm so. .Just make sure you don't 'Check' first ie. loss of Rrpm

topilot or to pprune. . <img src="smile.gif" border="0"> <img src="rolleyes.gif" border="0"> <img src="smile.gif" border="0">

[MightyGem]

TC, as you probably recall the Gazelle was FCL cushion on, where as the Lynx was FL cushion on. Forgot where I was one day and did FL cushion in a Gazelle. Seemed to work quite well.

VFRPB, Peter, I think Nick is talking about the ground being at 4000'. Not a problem we generally have over here.. . <img src="eek.gif" border="0">

[Vfrpilotpb]

Mighty,

Ah, I now understand, had a cell down and could not see that, as you say, we dont have that prob.. .Thank you. .My Regards