From: "Tom Low" <thomas.low@sri.com>
To: <lancair.list@olsusa.com>
Subject: Canopy Jettison and Parachute Use
Date: Thu, 29 Nov 2001 11:41:41 -0800
Message-ID: <LLEMJEMDFDFMLCJGFNEGMEMOCCAA.thomas.low@sri.com>
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As an owner of a Lancer 235, I too have considered installing a
jetttisonable canopy to allow emergency egress.  I have read the opinion
that bail-out is seldom an option, but there are several scenarios in which
I would "definitely" want that possibility:
1. In the event of an in-flight (non-electrical) fire that is not
extinguished by shutting down fuel to engine.
2. If you perform aerobatics, you (and your passengers) are required to wear
parachutes.  To do so with the standard canopy configurations is of no
value.  Variations in individual aircraft configurations, CG locations, etc.
will have an effect on spin characteristics.  I know of pilots who have
intentionally spun the '235, and have successfully recovered with standard
techniques without unexpected consequences.  Nonetheless, I would not
consider spin testing my plane without a jettisonable canopy and a chute,
and 10,000 feet of air beneath me.  Even then, I doubt I would.  I am not
concerned about structural failure of my plane, as such would be a result of
my incompetence, either in maintenance, inspection or piloting.  You could
claim that an inadvertent spin would fall in to the same category, but if
you perform aerobatics in your plane, you should recognize the possibility
that a small error could result in a spin entry.
3. If you fly with non-pilot family members, especially young children, the
idea of a BRS type recovery system is attractive if you as the pilot were
incapacitated.  The engineering required to adapt such a system to a 2-seat
Lancair is significant, and while the weight of our aircraft are within the
BRS specs, our cruise speeds are not.
	The following is a discription of a canopy ejection mechanisim I am
considering.  I would welcome critical review of this concept before I
implement the design.  My aircraft is fitted with the original 4-bar linkage
canopy.  The canopy release mechanism concept I am engineering employs the
existing 4 latches, but replaces the latch element affixed to the canopy
frame (the hook) with a custom machined machined version.  The custom hook
is machined from a block of aluminum, also containing a vertically aligned
dove-tail slide. The block is hard anodized to prevent gauling. The slide
allows the recess into which the latch is locked to separate from the part
of the block that is permanently attached to the canopy frame. The two parts
of this block are locked together during normal operation with a stainless
steel ball that spans across the sliding and fixed components.  The ball is
retained with a horizontal sliding pin, exiting each of the four blocks
rearward.  A cable in a polyflow tube connects each of the release pins, and
is routed (glassed in) along the canopy frame rearward and then up an over
the rear canopy roll over structure.  The cable is exposed for 8 inches at
the center of the canopy bow, and is protected with a Velcro safety cover.
	The canopy is closed with the four over-center latches as is normally done.
In an emergency, one could reach up and grab the exposed section of cable
(after removing the safety cover) and with a firm downward pull, extract all
four pins installed in machined blocks.  This permits the balls to slide
clear of the interface between the two parts of the dove-tail, and the
canopy would then be pulled up by the low pressure air stream.  To allow the
canopy to separate from the airframe completely, the four linkage arms that
support the canopy when open are cut off one or two inchs from the canopy
frame attachment point.  Delrin plastic sleeves slide over the aluminum
rods, and these sleeves are connected to the canopy frame in the
conventional manner.  Friction is sufficient to allow the canopy to be
operated in the normal manner on the ground.  In flight, the sleeves would
slide off of the rods, allowing the canopy to separate.  I agree that it is
very likely that the fin will be struck by the departing canopy.

Hope this helps anyone considering flying with a 'cute in  their 2-seat
Lancair.

Tom Low
N31CD


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