"Owl" glider crash - more info

To recap, one of the SparrowHawks built for Mississippi State University
broke up in flight Oct 18. The pilot parachuted safely.

I just finished talking to Greg Cole, designer of the SparrowHawk. The
program manager from MSU visited him Monday to discuss the data from the
flight and pictures of the pieces. The short story is the pilot
inadvertently exceeded Vne while performing a rolling maneuver as part
of the test program, and the glider broke apart at 171 knots!

The speed and most of other data used in the analysis came from the data
logging system carried in the glider. A helicopter making a video
recording was following it at the time it broke up. The calculated
flutter speed, using measurements from ground-based stiffness and
frequency tests of a SparrowHawk (not the MSU glider) is 170 knots. For
this reason, and the speed of the breakup, Greg thinks it was almost
certainly flutter that caused it.

It's quite remarkable it lasted to the 171 knot speed, given it's 123
knot Vne. The demonstrated flight speed for certified gliders is Vne +
10%, which would be only 135 knots for a 123 knot Vne.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

"Eric Greenwell" wrote in message
news:GIg0h.12159$iM2.2023@trndny08...
To recap, one of the SparrowHawks built for Mississippi State University broke
up in flight Oct 18. The pilot parachuted safely.

Any word on why the pilot elected to "get out and walk" rather than ride
the BRS down? I wouldn't be the one to second guess his decision, but it
apparently came near to turning out very badly.

Vaughn

Vaughn Simon wrote:
"Eric Greenwell" wrote in message
news:GIg0h.12159$iM2.2023@trndny08...
To recap, one of the SparrowHawks built for Mississippi State University broke
up in flight Oct 18. The pilot parachuted safely.

Any word on why the pilot elected to "get out and walk" rather than ride
the BRS down? I wouldn't be the one to second guess his decision, but it
apparently came near to turning out very badly.

The breakup of the glider was so forceful, it threw him out of the
glider with the remnants of the seat attached to him by the lap belt.
The lap belts are connected to the seat, rather than the fuselage, as in
many (most?) gliders. The BRS was apparently activated when the
structure with the activation handle tore from the main fuselage.

The pilot's parachute did not open properly at first because it was
hindered by a small piece of the canopy frame that was still connected
to part of the seat pan by the lanyard that holds the canopy in the open
position on the ground. Nobody can believe the lanyard (and the little
screws that hold it) survived the breakup, but the fuselage attachment
point will be definitely be changed!

Greg said calculating the forces on the components during a catastrophic
failure like this is difficult, because you don't really know what is
deforming, how it's deforming, and how fast it is deforming, and rapid
deformation changes the strength values you have to use in the
calculations. He says they will revisit the problem and find ways to
strengthen the safety harness connection to the glider, but can't
guarantee the changes will survive such a high speed breakup (almost 50
knots over Vne).

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Eric Greenwell wrote:
To recap, one of the SparrowHawks built for Mississippi State University
broke up in flight Oct 18. The pilot parachuted safely.

I just finished talking to Greg Cole, designer of the SparrowHawk. The
program manager from MSU visited him Monday to discuss the data from the
flight and pictures of the pieces. The short story is the pilot
inadvertently exceeded Vne while performing a rolling maneuver as part
of the test program, and the glider broke apart at 171 knots!


Was the test point intended to be a roll with CASVne or was it not
possble for some reason to perform a roll without exceeding Vne?

Is there any indication of the speed at which flutter started?

Andy

Andy wrote:
Eric Greenwell wrote:
To recap, one of the SparrowHawks built for Mississippi State University
broke up in flight Oct 18. The pilot parachuted safely.

I just finished talking to Greg Cole, designer of the SparrowHawk. The
program manager from MSU visited him Monday to discuss the data from the
flight and pictures of the pieces. The short story is the pilot
inadvertently exceeded Vne while performing a rolling maneuver as part
of the test program, and the glider broke apart at 171 knots!


Was the test point intended to be a roll with CASVne or was it not
possble for some reason to perform a roll without exceeding Vne?

Greg was not certain about the reason for the test, but it was supposed
to be conducted under 100 knots. ntil a public determination is offered
for the excessive speed, I don't want to repeat prelimanary remarks that
I got third-hand,but everyone is agreed the speed build up had nothing
to do with the SparrowHawk design.


Is there any indication of the speed at which flutter started?

Based on the air data logger it carried, it broke up at 170 knots
"instantaneously". Given the rapid breakup, and the 170 knot flutter
speed from design calculations, everyone thinks that's when and what
happened.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org