Hi Bob

I have seen an ASW20 where the wings departed the fuselage together-
ripping the main spar out of the fuselage. The accident entry was
exactly the kind of situation one would typically envisage a BRS handle
being reached for. Pilot did something stupid, went way over Vne
recovering from the resulting unusual attitude. A little flutter
combined with high G pull up and structural failure.

My conclusion is that - if you were to attach the BRS bridle exclusively
to either the wing spar, or the fuselage you would have problems.
Picture the pilot plummeting vertically in his perfectly streamlined
fuselage, while the wings drift down under the BRS. Alternatively
picture the pilot after the BRS rapidly decelerated the fuselage, but
not the wings which are now displaced some feet forward of their
original fitting.

Seriously- the loads have to be designed for - and I doubt there are
many gliders that this would work on. I don't know what the design work
was on the Schempp-Hirth gliders, and I know that the BRS systems have
chokes on the shrouds to reduce the shock loading. But still...

Personally I will go with a decent personal chute, Flarm and some
dedicated use of the Mk1 eyeball.

Bruce



On 2011/01/25 12:55 AM, Bob Kuykendall wrote:
On Jan 24, 12:30 pm, Martin
wrote:
...
By 'exposed spar stubs' I meant that there's no obvious tunnel, or top
and bottom guide channels, that the BRS webs could could go round the
outside of so they are guaranteed to be round the spars after the glider
is rigged: you'd need something like that to keep the webbing loop open
and let the spar stubs fit easily through them...

On the surface, it seems to me that attaching the parachute bridle to
the wing main spar stubs is not the optimal way to do it. In general,
I think I'd rather attach the bridle to the aircraft structure at the
forward and aft lift pin fittings. My thinking is that the lift
fitting structure is closer to the pilot along the primary load path
between the wings and the fuselage.

At issue is that there is usually no direct structural connection
between the wings and the fuselage at the wing main spar stubs, and
there are many conceivable failure modes that could disengage the
wings from the fuselage while leaving the fuselage otherwise intact.
That being the case, I'd rather grab the fuselage directly at its
strongest points rather than grab the wings that may or may not be
attached there.

Thanks, Bob K.

--
Bruce Greeff
T59D #1771 & Std Cirrus #57