Crouch Strap story

In article , Robertmudd1u
writes
You may be interested in my latest crotch strap experience.

I'm still analyzing my June 2003 accident and the cause. More later on this.
The role of the crotch strap is significant and worthy of mention.

Dr. Byars, thank you for this interesting and important feedback based on real
world experience.

The standard line from the German manufactures is that a crotch strap is not
needed because the submarining hazard has been taken care of through use of the
"H point" when locating the anchoring point of the lap belts.

This system
locates the lap belt a bit further forward than in older designs with the aim
being to get the lap belt lower on your hips. This is supposed to prevent it
from being pulled out of place when tightening the shoulder harness. It does,
but I believe the lap belt has to be tightened to an un-necessary degree to get
anywhere near the effect the "H point" is credited with bringing about.

Quite. If you could predict exactly when you were going to crash, and
correctly tighten up your straps beforehand, this might work. But with
sometimes hurried field landing decisions the "pre-prepared crash
scenario" is just not realistic. Also, from other postings in this
thread, the four point harness does not seem to be very good in high
turbulence.

My experience is that the "H point" is not adequate to keep the lap belt from
being pulled up when tightening the shoulder straps. This is especially true
when flying out west in strong lift at high speed. A crotch strap helps keep
you from bouncing around thus providing more comfort and better control. The
difference is security in the cockpit is dramatic. I normally retro fit a
crotch strap to my gliders and feel a lot safer and more comfortable with its
use. This holds true even with my Genesis which used the "H point" system to
locate the lap belt anchor points.

Robert, I entirely agree with you and Ed Byars that a fifth (crotch, if
you like) strap is invaluable in a number of situations.

In my military flying, a five-point harness was normal and I spent many
hours wearing one, normally as part of Martin Baker ejection seats of
various types.

Turning to gliding, some 10 years ago another pilot at Lasham ordered a
German glider and wanted 5-point harnesses fitted during build. The
maker refused to fit them "because it has been shown that the fifth
strap is dangerous". When pressed, they quoted a report done by a car
(automobile) test organisation in Germany on five-point harnesses that
suggested that some damage might occur to the crotch area in the case of
a severe impact. Possible damage to the male genitals was also
mentioned, and this seems to have had a major impact (no pun intended!)
on people's thoughts about the fifth strap.

However, my view was that in a major crash, if the fifth strap caused
some soreness afterwards but prevented "submarining" of the body under
the lap straps, then it could reduce damage to the legs or even save the
life of the pilot. It is all very well raising emotional points about
sore genitals. The real point IMHO is in a crash in which life is at
stake or there is the possibility of the pilot becoming a paraplegic.
What is the best option to minimise these awful results in a critical
"life-or-death" crash situation?

To put it crudely, would you rather have a sore crutch for a short
while, or be dead, or in a wheelchair for the rest of your life? In any
case, the "sore crutch" effect may not be there after all, see the next
para.

I was supported in my view by Dr Peter Saundby, the medical advisor to
the BGA, a qualified flight surgeon and an RAF jet pilot himself. He
pointed out that an important function of the fifth strap was to keep
the major load-bearing lap straps from riding up too high, even if they
had slackened off during flight. The lap straps then stood a good
chance of taking the large crash loads for which they are designed, and
any tendency to "submarine" under them would be minimised.

Peter and I were able to interest Dr Tony Segal, a UK glider pilot and
graduate of the UK Aero Medical (Flight Surgeon) course with the RAF at
Farnborough. Tony had already made glider crash tests using redundant
cockpit sections. He then managed to interest the UK Defence Evaluation
and Research Agency (DERA) in the crashworthiness of four and five point
harnesses. Tests were carried out at the UK Defence site at Farnborough
using instrumented human dummies seated in mock-ups of glider cockpits
and the impact test track of the Centre for Human Sciences (CHS) at
Farnborough. The glider cockpit was modelled around a Nimbus 3.

An unclassified report was published. This was also presented to the
gliding scientific organisation OSTIV during their meeting at Bayreuth,
Germany, in August 1999 and no doubt will be available in full from
OSTIV (OSTIV = Organisation Scientifique et Technique Internationale de
Vol a Voile).

As far as I know, this paper is probably the most definitive recent work
on the subject and would probably answer most of the points raised in
this thread. Here are some details:

Title:

Four and Five Point Glider Seat Harnesses - Static and Dynamic Tests

Authors

Dr Anthony M Segal, Lasham Gliding Society, UK
Leslie P Neil, Senior Engineer Impact Protection, UK DERA
Graham A Reece, Instrumentation Engineer, UK DERA
Philip G Murtha, Impact Test Track Engineer, UK DERA

The paper is 20 pages long but para 5b is worth quoting in full (QRF =
Quick Release Fastening, that is, the harness release box)::

"5 b) Observations After the Impact Test

When a 5 point harness was being tested, both with the harness tight and
with the harness slack, the lap straps remained in the correct position
over the hip bones. The QRF also stayed in the correct position.

When a 4 point harness was being tested, both with the harness tight and
with the harness lose, the lap straps were seen to have moved up over
the abdomen until they were jammed tightly under the lower rib margin.
The QRF had moved upwards until it was in the epigastrium (the "pit of
the stomach"). This is very serious, because severe, even fatal injury
may be caused to the internal organs in the upper abdomen.

THIS IS CONSIDERED TO BE THE MOST IMPORTANT FINDING OF THE ENTIRE TEST.

Following the impact test, with a 4 point harness, the shoulder straps
were seen to be hanging loosely between the seat back and the pilot
dummy's shoulders. This was due to the upward movement of the lap straps
and the QRF."

Finally, the conclusion includes the following words:

"A 5-point harness is superior to a 4-point harness in an accident
impact situation and also under conditions of negative-g. This is
especially so if the harness is slack."

It also goes on to say: "It is recommended that the 5th strap be
designed to avoid injury to the crotch of the pilot. This design of
strap should be fitted to new gliders and be retro-fitted (where
structurally feasible) to gliders in current use".

-------------------------------

The above seems pretty conclusive to me and in my syndicate glider we
had a fifth (crotch) strap fitted in the rear cockpit. We were told
that in the front cockpit there was not a proper hard point to which a
fifth strap could be fixed. Maybe with some minor structural
strengthening it could be, this thread has reminded me that we ought to
investigate it.

--
Ian Strachan
Lasham Gliding Centre, UK