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From: veeneman@mot.com (Dan Veeneman)
Newsgroups: sci.military
Subject: <None>
Message-ID: <1990Dec19.010115.24669@cbnews.att.com>
Date: 19 Dec 90 01:01:15 GMT
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From: veeneman@mot.com (Dan Veeneman)
Subject: Re: RE: Autorotation of Harriers

> From: joefish@uunet.uu.net (joefish)
>
> [...]
>
> For military helicopters, if a blade hits a tree trunk, expect the
> transmission to separate from the aircraft.

Actually, transmission separation from the aircraft is extremely unlikely.
Depending on the thickness and density of the tree, as well as the
thickness, weight, and composition of the blades, several things could
happen:

1.  The rotor blade cuts the tree without sustaining damage.  Small saplings
	and young bamboo cut rather nicely.  It is not, however, an
	approved maneuver.  :-)

2.  The rotor blade cuts the tree and deforms and/or begins to delaminate.
	This would require either refurbishing the blade(s) or, more
	likely, discarding them.  Transmission failure may or may not
	occur.  It would have to removed and inspected for 
	"sudden stoppage" to determine the extent of the damage,
	if any.  At the time of impact, the ability of the ship to remain
	in the air would be determined by the condition of the blades, not
	the transmission.

3.  The rotor blade fails to cut the tree.  The blade will definitely
	deform.  In addition, the most likely fail point would be where
	the rotor connects to the hub - the blade(s) disconnect from the hub.
	Transmission *failure* may or may not occur (not that it makes
	much difference).  Even these incidents are often survivable,
	as contact is often made at low altitudes and low airspeeds.
	(NOE is something else, of course).
> 
> If the tree is on one side the transmission goes backward, if the tree
> is on the other side, the transmission goes through the cockpit.

In the event of a catastrophic failure, the transmission gearing would
most likely shred itself and go in all sorts of directions.

>
> Joe Fischer           joefish@disk.UUCP

Dan
veeneman@mot.com