Crouch Strap story

I sent the following to our magazine nine months ago and didn't receive an
acknowledgement or receipt. I guess it was not suitable for them so I
thought I would share it with ras to maybe provoke some safety discussion.

efb10-11-03-rev.6-5-04

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.

The last half dozen gliders I've had I added a crotch strap (usually
available from Wings & Wheels), which easily clicks into the bottom, front
or 5th slot of the standard Gadringer belt hardware. I secure the other end,
which terminates with the belt into a triangular link, with a quarter inch
hole that I bolt to the seat pan with a large "wood" washer behind the seat
pan. My gliders are Experimental category so this is legal.

I always heard that the main purpose of a crotch strap was to keep the lap
belt across the upper thighs and prevent it sliding up to the stomach area.
I have since learned better.

It of course depends on the direction of the accident loads and the
direction of the inertia of the body as to how all restraint straps come
into play.

Many glider accidents involve "dropping in" vertically wherein the tailbone
(in the L-1, L-2 area) or higher are damaged so the belts don't help much.
You seldom see accidents with lap belt overload, but it happens. I have a
sad memory of helping remove a dead friend from an inverted Ventus cockpit
where the lap belts on both sides had pulled lose from the seat pan.
Fortunately rare but it happens.

In my "incident" the nose of the glider hit hard ground at about a 60 plus
degree angle. The "load" was about along the longitudinal axis of the
glider. Since in our modern gliders (ASW-28 in my case) we recline (sit
supine), the inertia of my body was toward the nose with only the crotch
strap to resist. Actually Waibel designed the seat pan to take some of this
forward load against the bottom of the thighs. In this seating the knees are
bent more upward.

The nose of the glider (along with my feet) was crushed in a calculated
energy-absorbing manner. Thank you Gerhardt Waibel! I think his design and
the crotch strap saved my knees.

I was conscious and lucid until the helicopter dropped me off at the
Medical College of Georgia Trauma Center.

After that I really was not with it for a couple of weeks, but after that
time I suddenly noticed that my groin area was still quite swollen. I
realized that my crotch area had sustained a significant load and that all
things considered had kept my body from moving more forward and no doubt
helped minimize the leg/knee damage. I had no shoulder strap or lap belt
marks or soreness.

Since my guess is that a significant number of glider accidents impose loads
and body reactions similar to mine, I recommend a crotch strap. Trying to
distribute the load to the pelvic area by wearing an athletic "cup" may be
good for some flights, but for some flights there are other disadvantages.
Many contest pilots regularly wear a male external catheter and I don't
think both would work. With just the crotch strap I always had to be
careful that the strap was adjusted somewhat to the right, was not too
tight, and did not interfere with the flow from the catheter that was to the
left.

I suggest reading Chip Bearden's posting which appeared in the
rec.aviation.soaring newsgroup on Nov.20 1998 which outlines a more complex
but better seat belt design.

I hope this discussion will create more thought about glider accident
safety.

Ed Byars

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.

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 Mudd

"Robertmudd1u" wrote in message
...
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.

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 Mudd


After reading Ed and Robert's posts, I intend to install a crotch strap in
my Nimbus. At the very least, it will let me get the shoulder straps REALLY
tight without pulling the lap belt up too high.

When you are riding 10 - 15 knot mountain thermals with a stiff carbon wing
you just can't be strapped in too tight.

Bill Daniels

"Robertmudd1u" wrote in message
...
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.

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 Mudd


After reading Ed and Robert's posts, I intend to install a crotch strap in
my Nimbus. At the very least, it will let me get the shoulder straps REALLY
tight without pulling the lap belt up too high.

When you are riding 10 - 15 knot mountain thermals with a stiff carbon wing
you just can't be strapped in too tight.

Bill Daniels

"Ed Byars" wrote a good piece on belting yourself in.

Before you just go and install marginal belts, look at what is available in
the sports car world
and choose the correct parts. Crotch belts or "5 point harnesses"
were developed for upright seated positions. They worked by holding the lap
belt
in the proper position over the hips and weren't designed to take impact
loads
without "stuffing your balls through your throat". As cars became faster
and aero considerations
moved drivers to the supine driving positions used today, "6 point systems"
evolved.
The load path in grontal impacts could no longer be absorbed by the lap
and shoulder belts because the vectors were wrong. What has evolved is a
belting method
that creates a web seat secured to the lap belt attach points. This
prevents the driver from
sliding forward out from under the belting system.

My SCHROTH harness hooks up like this.
Connect lap belt.
left 6 point go's under my leg, around my upper thigh, over to the
left lap belt anchor, thru a loop and back to the buckle.
Same for right side
connect shoulders
done.

What this does is transfer any decelleration loads into the upper
thigh/lower butt
area and is quite comfortable. It virtually eliminates soft tissue bruising
..
I would not fly a 5 point harness as I feel they are unsafe, the risk of
internal injuries to
the soft stuff is too high. BUT the 6 point harness works very very well.
I have
had the unfortunate "experience" of stuffing a formula car and know exactly
what works,
and what doesn't.

I don't have good pictures, but looking at the WILLANS web site gets the
message across.
Look at the way all the sub straps create seats to support you against
sliding forward.


http://www.willansharness.com/

Scott Correa

The 'crotch strap' is what used to be known as a 'negative-G'
strap. Usually it works to keep your skull away from
the canopy during the bumpy bits of sky; rarely, it
helps you in a crash by preventing submarining. However,
a single strap is both inconvenient and potentially
painful. A better design is a double strap, like an
inverted V, but it needs two hard points. Another
variation is an upright V, with one hardpoint and some
secure way to fasten the ends of the V to the lapstraps
rather than the buckle.

The conventional 4-point or 5-point harness shows its
ancestry from the lapstrap by having the primary mounting
[the buckle] on the lapstrap. Would a better design
not have the buckle assembly permanently mounted to
the [adjustable] negative-G strap and the two lap and
two shoulder straps plugging in later ?

Ian




At 15:00 06 June 2004, Bill Daniels wrote:

'Robertmudd1u' wrote in message
...
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.

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 Mudd


After reading Ed and Robert's posts, I intend to install
a crotch strap in
my Nimbus. At the very least, it will let me get the
shoulder straps REALLY
tight without pulling the lap belt up too high.

When you are riding 10 - 15 knot mountain thermals
with a stiff carbon wing
you just can't be strapped in too tight.

Bill Daniels

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

On 6 Jun 2004 16:55:50 GMT, Ian Cant
wrote:

The 'crotch strap' is what used to be known as a 'negative-G'
strap. Usually it works to keep your skull away from
the canopy during the bumpy bits of sky; rarely, it
helps you in a crash by preventing submarining. However,
a single strap is both inconvenient and potentially
painful. A better design is a double strap, like an
inverted V, but it needs two hard points. Another
variation is an upright V, with one hardpoint and some
secure way to fasten the ends of the V to the lapstraps
rather than the buckle.

I followed the link to Willans Harnesses in "plastic guy's" post and
moused round the site a little. They supply a Y-strap that's designed
to connect to the 5th slot on their quick release fitting, passes
under your legs and attaches to the lap strap hard points. They say
its designed to upgrade their 4-point racing car harnesses to 6-point
standard.

This looks potentially like a quick and easy way to upgrade a 4-point
harness because it requires no extra hard points in the glider.
Presumably the lap strap hard points are already designed to take the
full deceleration loads in a crash so fitting it would not put
additional loads on them.

Does anybody on here know if this upgrade has been done?

If so, how does it compare with a traditional 5-point system with
regard to anti-submarining and negative-G properties?

Are our 5-point rotary action quick-release units the same as the car
racing gang use?


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Dale Thompson and I had an inverted V crotch strap in our 1-35. It served to
keep the lap belt in position. More important was the assurance that the
legs and hips would probably take the stress instead of other more
"important" parts that could not be so easily repaired.

Fortunately, we never had a test of its effectiveness.

The design is very simple and easily made. Our was made by Alan Silver, in
the San Francisco bay area, who repacked our chute. I do not think he is
still in business.


"Martin Gregorie" wrote in message
...
On 6 Jun 2004 16:55:50 GMT, Ian Cant
wrote:

The 'crotch strap' is what used to be known as a 'negative-G'
strap. Usually it works to keep your skull away from
the canopy during the bumpy bits of sky; rarely, it
helps you in a crash by preventing submarining. However,
a single strap is both inconvenient and potentially
painful. A better design is a double strap, like an
inverted V, but it needs two hard points. Another
variation is an upright V, with one hardpoint and some
secure way to fasten the ends of the V to the lapstraps
rather than the buckle.

I followed the link to Willans Harnesses in "plastic guy's" post and
moused round the site a little. They supply a Y-strap that's designed
to connect to the 5th slot on their quick release fitting, passes
under your legs and attaches to the lap strap hard points. They say
its designed to upgrade their 4-point racing car harnesses to 6-point
standard.

This looks potentially like a quick and easy way to upgrade a 4-point
harness because it requires no extra hard points in the glider.
Presumably the lap strap hard points are already designed to take the
full deceleration loads in a crash so fitting it would not put
additional loads on them.

Does anybody on here know if this upgrade has been done?

If so, how does it compare with a traditional 5-point system with
regard to anti-submarining and negative-G properties?

Are our 5-point rotary action quick-release units the same as the car
racing gang use?


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

For me six point harness is far preferable to a five
point one which would simply be impossible for long
flights. The borrowed Std Cirrus I fly at present
has a non-approved 6 point harness designed for race
car use that uses a 4 point buckle and no additional
attachment points. I think it is a little different
from that described in the earlier post.

The shoulder and lap straps are as normal except that
there is a strong metal ring attached to the top of
each lap strap about 3 inches lateral to the buckle.
The 4th and 5 straps are attached by metal clips under
the seat pan to the fuselage (not seat pan) mounted
attachment points also used for the lap straps. The
upper, business, end of the 2 thigh straps is a loop
not a buckle. The straps run forward and medially
under the seat pan for about 8 inches and emerge through
slit shaped cut outs in the seat pan under the inside
of each upper thigh - giving virtual attachment points
there. With only the laps straps buckled the left
thigh strap comes inside and over the thigh to the
metal ring over the top of the thigh, through it and
then turns upwards and inwards towards the top of the
buckle area. Then the metal tongue of the left left
shoulder strap is inserted throught the thigh strap
loop and into the buckle. Same on the right.

This arrangement pulls down on the lap strap assembly
from the top strap's tongue but the extra straps come
in at an angle from the side and do not cover the buckle.
When the buckle is undone the shoulder straps are
instantly free of the 4th and 5th straps which just
fall away through the metal loops on the lap straps.

When we first looked at the glider we did not understand
that the extra straps attached to the shoulder straps
and thought they were suppsed to attach to the lap
straps which would not have been easy to get out of
in a hurry. I only refitted the extra straps today
as a result of thinking about this thread and it seems
to work really well. I feel secured firmly in the
seat pan and can't slide forward. The lap straps are
held well down in place and at last I don't have to
feel squashed down by shoulder straps - which can be
safely left comfortable. I will be able to pee no
problem too.

I recall from attempts to get six point straps fitted
to a new glider about 3 years ago that the manufacturer's
view was that it was impossible for them as there were
no LBA approved 6 point straps. Damn shame.

John Galloway