The Murphy Builders Site

Posted: **Fri Feb 17, 2012 10:46 pm**

Thanks Ralph,
It sounds like you may have helped solve my problem. You mentioned that you
will not be able to install rear window. I assume this is because you are
installing shoulder straps on your rear seats??? I am not really up on the
configeration of the elite. I plan to install shoulder belts on the front
seats only. The bucket seats in the rear will have the belts supplied my MAM.
Gerry
On 2/22/03 3:59 PM, REBAKER@FTC-I.NET wrote to MURPHY-REBEL:

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-> Date: Sat, 22 Feb 2003 18:52:10 -0500
-> From: Ralph Baker <rebaker@ftc-i.net>
-> Subject: shoulder harnesses
-> To: murphy-rebel@dcsol.com
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->
-> We will be installing same in our Elite. After much thought have come
-> to the following:
->
-> Eliminate the "cross shoulder" attach point at the door upper rear.
-> Scrap straight sections of cutoff bulkhead channel will be riveted back
-> to back with a piece of 1/8" flat stock between them full length. The
-> 1/8" stock will extend an inch above (toward the floor when installed)
-> at the forward end to be drilled for the harness attach point. The
-> extended portion will be similar in shape to the outboard seat belt
-> point that extends above the door sill. A flat strip of .040 will cap
-> the fore to aft bulkhead channels and rivet to the cross bulkheads as
-> well.
->
-> The attach will consist of a short length of 1/8" cable with a swaged
-> turnbuckle fork on each end oriented at 90 degrees to each other to
-> eliminate twist. One fork to bolt to the strap fitting and one to bolt
-> to the 1/8" stock between the bulkheads.
->
-> The only decision yet is whether or not to go back one additional
-> bulkhead for additional strength. As always, these are experimentals,
-> no analysis has been done, and all decisions are yours as are the
-> results of those decisions. One consideration with shoulder harnesses
-> is that they must not cause spinal compression in a crash. I believe I
-> have seen no more than a 30 degree angle from the spine to the belt
-> specified. The attachments should be directly behind the seat centers.
-> This, of course, prevents windows aft of the wing. Small loss in my
-> opinion. Shoulder harnesses should be standard due to the greatly
-> increased safety in my opinion.
-> Ralph Baker
-> Elite 624E (reserved)

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Posted: **Fri Feb 17, 2012 10:46 pm**

We will be installing same in our Elite. After much thought have come
to the following:

Eliminate the "cross shoulder" attach point at the door upper rear.
Scrap straight sections of cutoff bulkhead channel will be riveted back
to back with a piece of 1/8" flat stock between them full length. The
1/8" stock will extend an inch above (toward the floor when installed)
at the forward end to be drilled for the harness attach point. The
extended portion will be similar in shape to the outboard seat belt
point that extends above the door sill. A flat strip of .040 will cap
the fore to aft bulkhead channels and rivet to the cross bulkheads as
well.

The attach will consist of a short length of 1/8" cable with a swaged
turnbuckle fork on each end oriented at 90 degrees to each other to
eliminate twist. One fork to bolt to the strap fitting and one to bolt
to the 1/8" stock between the bulkheads.

The only decision yet is whether or not to go back one additional
bulkhead for additional strength. As always, these are experimentals,
no analysis has been done, and all decisions are yours as are the
results of those decisions. One consideration with shoulder harnesses
is that they must not cause spinal compression in a crash. I believe I
have seen no more than a 30 degree angle from the spine to the belt
specified. The attachments should be directly behind the seat centers.
This, of course, prevents windows aft of the wing. Small loss in my
opinion. Shoulder harnesses should be standard due to the greatly
increased safety in my opinion.
Ralph Baker
Elite 624E (reserved)

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Posted: **Fri Feb 17, 2012 10:46 pm**

Ralph, the attachment to the airframe sounds good!!

However IMHO, with 18 years experience injection moulding plastic seat belt
retract mechanism components for both Bendix and TRW and witnessing their
sled tests many times (sure glad they use million dollar dummies and not
real people!), I have one concern though with your usage of 1/8" cable. The
1760lb stainless/2000lb galvanized breaking strength (and only in a smooth
even pull) of the 1/8" cable will be the weak link of your attachment, with
the cable breaking before any seatbelt straping, "D" ring fittings or
attachment bolts. I would look at something more robust for your attachment
extension, even if it's just a larger size cable (5/32 = 2900ss/3300galv lb
and 3/16 = 3700ss/4200galv . If you're going to the trouble of making sure
you are really safe, with a double shoulder harness, then you may as well
make that extension cable capable of handling 13 or 14 g's as well.
Generally Mil spec on buckle assembly is a proven load of 2500lbs (or more)
and webbing is usually good for 6000 to 10000lbs.

That said, yes I have seen 1/8" cable used in other aircraft for belt
extensions. Just because someone else used it doesn't make it right as is
clearly shown by the CH701 that I have in the hanger, that only uses about 3
frigin rivets to hold the .032 belt attach plates to the airframe!

Cheers,
Wayne

----- Original Message -----
From: "Ralph Baker" <rebaker@ftc-i.net>
To: <murphy-rebel@dcsol.com>
Sent: Saturday, February 22, 2003 6:52 PM
Subject: shoulder harnesses

We will be installing same in our Elite. After much thought have come
to the following:

Eliminate the "cross shoulder" attach point at the door upper rear.
Scrap straight sections of cutoff bulkhead channel will be riveted back
to back with a piece of 1/8" flat stock between them full length. The
1/8" stock will extend an inch above (toward the floor when installed)
at the forward end to be drilled for the harness attach point. The
extended portion will be similar in shape to the outboard seat belt
point that extends above the door sill. A flat strip of .040 will cap
the fore to aft bulkhead channels and rivet to the cross bulkheads as
well.

The attach will consist of a short length of 1/8" cable with a swaged
turnbuckle fork on each end oriented at 90 degrees to each other to
eliminate twist. One fork to bolt to the strap fitting and one to bolt
to the 1/8" stock between the bulkheads.

The only decision yet is whether or not to go back one additional
bulkhead for additional strength. As always, these are experimentals,
no analysis has been done, and all decisions are yours as are the
results of those decisions. One consideration with shoulder harnesses
is that they must not cause spinal compression in a crash. I believe I
have seen no more than a 30 degree angle from the spine to the belt
specified. The attachments should be directly behind the seat centers.
This, of course, prevents windows aft of the wing. Small loss in my
opinion. Shoulder harnesses should be standard due to the greatly
increased safety in my opinion.
Ralph Baker
Elite 624E (reserved)

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Posted: **Fri Feb 17, 2012 10:46 pm**

First, thanks for the comments Wayne. We will uprate to 3/16 cable to
avoid tooth marks in the panel.

Second, Gerry, the Elite has the option for 3 pair of additional
overhead windows in addition to the "eyebrow" windows under the
windshield. We are installing only 2 seats. The shoulder harness
attach points will run right through where the rearmost windows would
have been installed so we eliminated them. We will also be installing
the "opera" windows on either side of the fuselage just aft of the doors
for a view back and down in turns. I hope this answers your question.
Ralph Baker

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