From: mpaton@oakhill.sps.mot.com (Michael J Paton)
Newsgroups: rec.aviation.homebuilt
Subject: Dynamic Rollover (Was Re: Mini 500 Heli)
Date: 17 Nov 92 22:12:12 GMT
Reply-To: mpaton@tempest.UUCP (Michael J Paton)
Organization: Motorola Inc., Austin, Texas

In article <uh311ae.722024630@sunmanager> uh311ae@sunmanager.LRZ-Muenchen.DE (Henrik Klagges) writes:
>milgram@eng.umd.edu (Judah Milgram) writes:
>
>>How is direction of rotation important in a dynamic rollover situation?
>
>You'll get retreating blade stall, resulting in loss of lift on that side.
>On a standard US helicopter, that is going to be the left side, i.e. you
>roll left. On a non-standard one, you roll right ...
>

I thought at first that the above answer was a complete non-sequitur, but on
closer examination, I think the problem is one of the definition of dynamic
rollover. Before getting to that let's deal with Judah's question. The original
context of the question is reproduced below.

In article <uh311ae.721831567@sunmanager> uh311ae@sunmanager.LRZ-Muenchen.DE (Henrik Klagges) writes:
 
>d) doesn't have some of the obvious flaws that the Rotorway Exec 90 has,
>   e.g., ...
>   the Exec
>   90 has its main rotor turning into the wrong direction (all commercial
>   /military helis in the US turn counterclockwise), whis is very dange-
>   rous for pilots relying on their reflexes eg in a dynamic rollover.
 
and milgram@eng.umd.edu (Judah Milgram) asks:
> How is direction of rotation important in a dynamic rollover situation?

And I'll attempt to answer that it it is not that direction of rotation is so
important in a dynamic rollover situation, but that direction of rotation is
important in a situation where pilots are relying on their reflexes. 
 
Furthermore it really depends on what the pilot's trained reaction to a problem
actually is. Typically an engine failure or throttle chop (in say an R22) will
result in a yaw to the left, and require right pedal (amongst other very
important things). If the reaction in the pilot's head is along the lines of
"Engine failure, add right pedal!", then there will be trouble if the 
helicopter is an Aerospatiale. One might well argue that the proper reaction
ought to be, "Left yaw, add right pedal!" which wouldn't get one into trouble.

I have been flown in an Aerospatiale 350 by a pilot who had only flown 
Robinsons and to my surprise he had no trouble at all. 

Going back to Henrik's reply, he describes retreating blade stall and says
that when this happens (perhaps as a result of exceeding Vne) that a roll
develops in a direction depending on the direction of rotation of the
main rotor. This is all true, but he seems to imply that this is a dynamic
rollover situation. This might make sense, but the definition of dynamic
rollover I was taught does not include this, and solely deals with a helicopter
rolling about its skid (or wheels) aided by the application of power. If a
helicopter tips too far in this situation added power can only make things
worse irrespective of the position of the cyclic control. The only thing to do
is to lower the collective and hope to drop back on the other skid.

It is possible that attempting a run on landing and putting on the wrong pedal
input on touchdown could cause a dynamic rollover. I don't see how wrong pedal
input can cause retreating blade stall.

Michael Paton
mpaton@tempest.sps.mot.com