Autorotation and Yaw Control

[Dave_Jackson]

During a full-down autorotation, is the ability to control yaw of more importance during the descent or during the landing?

Thanks.

[Flingwing207]

Yes
.
.
.
OK - a no-power full-down. On the descent there is little need for changes in T/R thrust once you reduce the initial pitch of the T/R (right pedal). However, if the helicopter is out of trim, the ROD will be a lot higher, result: more inertia to arrest with the flare.

If you keep the left pedal in at cruise position, you may not be able to maintain adequate control (depending on how much power you were pulling when you entered).

When you flare and start changing RPM/pitch, the mechanical drag of the transmission will drag the nose of the helo in the same direction the main rotor is turning, so you need to increase right pedal to keep the skids aligned with ground track. If you are doing a zero-groundspeed touchdown, the yaw isn't so critical, but if you are running it on, it might just be.

So that's why the initial answer!:8

[NickLappos]

Dave,
I know of one experimental NOTAR that ran out of yaw in the descent portion of an auto, he crashed.
I know of several older helos that ran out of yaw at the bottom, they crashed.

Let's guess the correct answer is "C" - All of the above!

[Ascend Charlie]

This is like asking "When you fall into the sea, is it more important to hold your breath, or to swim?"

Each is important, but by itself, neither will keep you alive.

If you aren't pointing straight for a running touchdown, you will have troubles. If you touch down straight but then don't KEEP straight, you might run into a ditch or some other trouble.

During the descent, you have full T/R authority, with the RPM at normal or even above-normal revs. After the flare and pitch-pull, revs are reducing quickly and so is authority, but if it is judged properly, it all works fine.

[Dave_Jackson]

Thanks for the information. The question is an attempt to get a better understanding of the coaxial, and perhaps the intermeshing, helicopter.

The pedal actions are reversed in a coaxial helicopter during autorotation. Apparently, the Kamov helicopters do this mechanically, so that the pilot does not have to think about 'which pedal does what' during this emergency. I assume that this mechanical changeover is the result of the position of the collective lever. This would mean that the yaw during the descent is quite conventional.

The interesting part would appear to be the landing, when the pilot is raising the collective to use the inertia of the rotors. If pedal was being applied while the collective was being raised, then the pilot would temporarily loose yaw control as the collective passed through this changeover zone.

Any thoughts?

[Ascend Charlie]

With a coaxial, you won't have the innate tendency to yaw anyway - no torque to counteract, no drag from the transmission. So, all you are doing is making minor corrections here and there.

So, if the nose goes left, you squeeze on the right pedal - the aircraft decides how to do it, but the end result will be that the nose goes back to the right as requested. The changeover zone would only be a poofteenth of a second, and you again end up with the desired result.

But this is a guess, I have little idea of how these work.:uhoh:

[Flingwing207]

Hi Dave,

What little I know about autos and synchromesh helos was relayed to me by a K-Max pilot who stopped at KTIX while ferrying a ship south-to-north. When he landed, I noticed that he didn't set the ship down like a feather, in fact he pretty much "plunked" it down.

I asked about autorotations, and indeed you are right, when the collective is below a certain setting, the mechanical mixing of the pedals reverses. I asked the same question about the transition point, and basically the pedals' "effect" goes to neutral as you go from full down throught the transition and into the "power" range of collective travel. Since in autorotation you pass through this "null zone" pretty quickly (both on entry and while cushioning), it's not an issue.

However, when setting down a lightly loaded K-Max, you start to lose some pedal touch just as you touch down, so the tendancy is to lower collective briskly on a normal touchdown.

(Or so he said - he could have easily been pulling my chain about this last part and just made a cheesy set-down, but since he was a factory pilot, I'll take his word for it!)

[Dave_Jackson]

Thanks for the additional information.