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Low-G Quick Stop?


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#1 r22butters

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Posted 15 April 2018 - 13:51

Has anyone ever heard this before?

The high-time Robinson flight instructor Simon Spencer-Bower, owner of Wanaka Helicopters in New Zealand, has recently argued for an alternative low-G recovery technique: coordinated application of down collective, aft cyclic, and right pedal (as in a quick stop maneuver) which will reduce the tail rotor thrust that is contributing to the right roll and reload the rotor disc at the same time.


In thirteen BFR's and five trips to the safety course I don't ever recall anyone mentioning (nor have I ever thought of it) lowering the collectve or pushing right pedal during low-G recovery,...just gentle aft cyclic.

Its from a very long article about Robby's mast bumping issue.

https://www.vertical...rmined-reasons/
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#2 Eric Hunt

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Posted 18 April 2018 - 23:21

A secondary effect of lowering collective is the nose drops down. Not what you want when trying to use back cyclic to re-load the disc...


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#3 r22butters

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Posted 21 April 2018 - 14:08

A secondary effect of lowering collective is the nose drops down. Not what you want when trying to use back cyclic to re-load the disc...


Done a lot of quick stops over the years, never had an issue with the nose dropping!

,...aft cyclic kinda takes care of that. :)
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#4 Wally

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Posted 21 April 2018 - 16:26

Done a lot of quick stops over the years, never had an issue with the nose dropping!

,...aft cyclic kinda takes care of that. :)

At cruise speed?  High cruise, loss of positive load, it will want to tuck lowering the collective makes it worse.

Aft cyclic and positive loading the disk is the whole intent.  Why reduce collective, complicate, delay the end result?

From what I've read, the catastrophic outcome occur before any pilot input is possible.  Makes me think you can cause a poor result by inappropriate control input, but otherwise you've alread survived the incident when you start remediation.


Just a pilot (retired, so I have a LOT of time)...


#5 r22butters

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Posted 21 April 2018 - 17:22

At cruise speed?  High cruise, loss of positive load, it will want to tuck lowering the collective makes it worse.
Aft cyclic and positive loading the disk is the whole intent.  Why reduce collective, complicate, delay the end result?
From what I've read, the catastrophic outcome occur before any pilot input is possible.  Makes me think you can cause a poor result by inappropriate control input, but otherwise you've alread survived the incident when you start remediation.


If you're at high cruise in mast bumping conditions then you're ignoring rule one, slow down in turbulance!

Now I've never done a quick stop from 70kts, but I am curious about this suggestion?

However, it was brought up by a New Zealand pilot and they don't have a good track record with Robby and mast bumping, so,...?
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#6 WolftalonID

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Posted 21 April 2018 - 17:41

Next flight you go up...settlle in at a brisk 90 kias...and punch that collective to the floor....then you will see what aft cyclic is like if you delay input. You said low G recovery...Low G is experienced primarily at cruise speeds vs slow speeds because it happens so much faster. One pushes over to decend or suddenly level off ....or a little gust will push you over.....say in Mountainous terrain where winds are more sudden than most flat landers can fathom.

You can quote safety notices all day till your blue in the face...but they were written because people can be stupid. Having spent the last two years teaching flight in high alltitude, as well as flying in it....I have seen first hand on many occasions where a flatlander came up to get experience at altitude and argues with me over how to do something...only to scare the sh*t out of themselves before I take controls and recover.
My boss, and other CFIs here see it as well more than we care to.

Text book lessons are just that. Good in a book. When you take into account the many different environments pilots can fly in...its remarkable how many seem to think a cookie cutter action works the the same across all places.

I feel the kiwi who is out there demoing this recovery may be good at it...but he knows its coming and knows when he is going to recover. So his timing and control may be in sync. Thats not going to be the case for a pilot who gets behind a two bladed machine and ends up tucking that nose in a roll over at cruise speed.

Edited by WolftalonID, 21 April 2018 - 17:46.

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#7 r22butters

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Posted 21 April 2018 - 18:24

I hate to disappoint you but not all pilots desire to fly in the mountains!

The last time I did (in a 44) I slowed it down to 70 (just like some pointless safety notice suggests) so I'm not sure why you want me to "punch that collective to the floor" at 90?!

Even then, this "quick stop" like respose suggests lowering the collective, not "punching it to the floor", if you're doing that, then I don't know where you learned to do a quick stop, but yeah, you'll scare the sh*t out of this flatlander!

Oh yeah,

,...and its not a flatlander telling you to lower the collective, its another one of you pointylanders!

Edited by r22butters, 21 April 2018 - 18:39.

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#8 Hand_Grenade_Pilot

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Posted 21 April 2018 - 21:27

Has anyone ever heard this before?



In thirteen BFR's and five trips to the safety course I don't ever recall anyone mentioning (nor have I ever thought of it) lowering the collectve or pushing right pedal during low-G recovery,...just gentle aft cyclic.

Its from a very long article about Robby's mast bumping issue.

https://www.vertical...rmined-reasons/

Until you mentioned it, I was not aware of that technique. My best guess is that, in theory, adding right pedal reduces the rate of roll by decreasing T/R thrust and reducing collective (torque) keeps the aircraft in trim. Based on a previous experience, I do not see this being practical.

I have only encountered a low-g induced roll once, and it was inadvertantly. I was flying an R44 at max cruise speed and hit a massive updraft; almost immediately the helicopter banked hard to the right (I would estimate 70-80 degrees). On impulse, I applied a slight amount of aft cyclic and the helicopter immediately returned to level flight. Start to finish the entire event lasted 3-4 seconds. I did not have time to think about the corrective action; I applied aft cyclic because I was surprised and was conditioned to slow down when something goes amiss while flying fast. It was purely instict.

Because a low-g roll can be catostophic in semi-rigid helicopters (mast bumping), it is not a maneuver that can be safley practiced (atleast in my personal opinion). Expecting a pilot to reduce collective and apply right pedal, without the muscle memory from repeated practice, is not realistic.

The best solution is to keep the recovery as simple as possible; aft cyclic. From the past experience mentioned above, I know that aft cyclic will work. No sense in re-inventing the wheel. Discuss it in detail on the ground (cause, effect, recovery and most importantly, prevention). But keep the recovery technique as simple as possible.

Edited by Hand_Grenade_Pilot, 21 April 2018 - 21:31.

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#9 Hand_Grenade_Pilot

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Posted 21 April 2018 - 21:59

An additional afterthought; in forward flight, most helicopter pilots instinctively reduce anti-torque pedal and reduce collective when they apply aft cyclic (otherwise you will be out of trim and gain altitude). When I encountered that low-g roll, it is very possible that I reduced collective and added right pedal without being consciously aware of it. The one control input that I do distinctly remember is applying aft cyclic.

In that context, the technique in question makes sense.
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#10 Eric Hunt

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Posted 22 April 2018 - 00:27

 

 

Done a lot of quick stops over the years, never had an issue with the nose dropping!

 

Butters, I was talking about the Effects of Controls, lesson number one in learning to fly.

 

Lower the collective, the nose drops; pull the collective up, the nose comes up (among other things).

 

And when you are doing a quickstop, you will be pulling cyclic to raise the nose, without seeing that you are pulling a bit more due to the secondary effect of lowering the collective.


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#11 r22butters

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Posted 22 April 2018 - 01:10

About a couple hours ago I was out tooling around and just as I got a few miles from home, going about 85kts, I did a mini quick stop style tapping of the brakes, as I would imagine this Kiwi is thinking we should do for low-g.

Nothing special happened. The nose didn't drop because this is a coordinated maneuver, like low-rpm recovery, not a "dumping of the collective" reaction to a throttle chop!

Would this make it easier to get out of low-g before bumping? No frickin' clue, as unlike so many other maneuvers, I have no muscle memory technique for low-g,...only what they drilled into me a thousand times. Gentle aft cyclic!
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