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Shoulder harness restraint

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fklein(at)orcasonline.com
Guest

Posted: Mon Dec 03, 2007 12:14 pm Post subject: Shoulder harness restraint

Hi guys,



Just wanted to share a solution to the issue of raising the shoulder 

harness restraint sufficiently to minimize the potential for spinal 

compression during a rapid deceleration event.



This approach allows for one to sit upon the existing head rest while 

entering and exiting the aircraft, does not encroach upon the access to 

the baggage area, confines all forces to the CM rather than 

transferring them to the fuselage shell, and can easily be added to a 

completed and upholstered cockpit.



Although the riser weighs but 10 oz., it is robust enough to withstand 

the compression load generated by a 1500# tension load on the straps 

measured at an angle of 90 degrees to the slope of the back of the 

headrest; testing was done using a 20 ton hydraulic press. Assuming an 

upper body wgt. of 100#, it would be good for 15 Gs.



Comments appreciated!



Fred

A194



PS: If anyone wants to duplicate this as a nice little winter project, 

I could be persuaded to put together some kits of the hot-wired foam, 

hinges, acft. plywood, and instructions...contact me off-list.



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sidsel.svein(at)oslo.onli
Guest

Posted: Mon Dec 03, 2007 12:59 pm Post subject: Shoulder harness restraint

Fred,



Ingenious with respect to structure and "hinging out of the way", but:



Do you see a risk in the harnesses cutting into each side of your neck when 

under significant tension, since the two harness parts are restrained in the 

center just behind the neck?  The normal spread angle between the two parts 

(supposedly comfortably snug on each side of the neck during normal flight) 

will tend to narrow under tension, will it not?



Best regards,

Svein

LN-SKJ



---

jrgowing(at)bigpond.net.a
Guest

Posted: Mon Dec 03, 2007 1:45 pm Post subject: Shoulder harness restraint

Fred

Your headrest looks fantastic! I think it is the best solution I have seen 

yet. Looking forward to seeing a lot more of it!

JR (Bob) Gowing UK Kit 327 in Oz



---

ptag.dev(at)tiscali.co.uk
Guest

Posted: Mon Dec 03, 2007 2:26 pm Post subject: Shoulder harness restraint

Hi! Fred

Similar to my suggestion some time back about taking the harness over my

head BMW head rests.  If you have the original belts are they long

enough or do you need longer ones?



Regards

Bob Harrison. G-PTAG



--

fklein(at)orcasonline.com
Guest

Posted: Mon Dec 03, 2007 3:24 pm Post subject: Shoulder harness restraint

 	  Quote: 	
		   

 <ptag.dev(at)tiscali.co.uk>



  If you have the original belts are they long enough or do you need 

 longer ones?



 Regards

 Bob Harrison. G-PTAG


	


Bob,



The original belts are more than adequate for me (6'-1" and 195#). I'd 

wondered about that very thing but after trial fitting the side mounts 

for the seat belt, climbing aboard, buckling up, and making suitable 

airplane noises, everything was aok.



Fred

A194

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fklein(at)orcasonline.com
Guest

Posted: Mon Dec 03, 2007 3:39 pm Post subject: Shoulder harness restraint

 	  Quote: 	
		   Do you see a risk in the harnesses cutting into each side of your neck 

 when under significant tension, since the two harness parts are 

 restrained in the center just behind the neck?

 Svein

 LN-SKJ


	


Svein,



Not really...if you consider the rear attach point where the 2 shoulder 

straps begin and the points where they attach to the seat belt in 

front, you will trace straight lines which diverge from one's neck 

rather than "scissoring" it under tension.



Thanks for your comment,



Fred

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ami(at)mcfadyean.freeserv
Guest

Posted: Tue Dec 04, 2007 1:54 pm Post subject: Shoulder harness restraint

Fred,

Nice execution of a good idea.

CSA-VLA provides little guidance:



http://www.easa.eu.int/doc/Agency_Mesures/Certification_Spec/decision_ED_2003_18_RM.pdf

See pdf page 100 (or pages 2-8 and 2-9 at the back.



It merely advises for "..adequate separation of ...straps to minimise... 

chafing of wearer's neck...."  but recommends a maximum separation of 8" and 

maximum included angle of 60 degrees.



Was your load testing applied to the straps as fitted to the device in the 

aircraft or merely to the device sat on a strong surface? And would it be 

better to wrap the forward edge of the device around the front edge of the 

headrest, to reduce the eccentricity of loading on that corner? thereby 

maximising the resistant of the front face of the headrest



Would prefer to see the guides at the top made as part of (or recessed in 

to) the moulding, with broad rounded edges.



Duncan McF.

---

fklein(at)orcasonline.com
Guest

Posted: Tue Dec 04, 2007 10:14 pm Post subject: Shoulder harness restraint

Duncan,



Thanks for your input and questions...answers indented below.



 	  Quote: 	
		   -> Europa-List message posted by: "Duncan & Ami McFadyean"  

 <ami(at)mcfadyean.freeserve.co.uk>



 Fred,

 Nice execution of a good idea.

 CSA-VLA provides little guidance:



 http://www.easa.eu.int/doc/Agency_Mesures/Certification_Spec/ 

 decision_ED_2003_18_RM.pdf

 See pdf page 100 (or pages 2-8 and 2-9 at the back.



 It merely advises for "..adequate separation of ...straps to  

 minimise... chafing of wearer's neck...."  but recommends a maximum  

 separation of 8" and maximum included angle of 60 degrees.


	


	I really didn't want to re-invent the wheel here, so one of the  

starting points was to not alter the attach point of the shoulder  

straps...and to secure the "riser" to the same hard point used for the  

straps. If our shoulder straps had had individual bolts to the hard  

point(s), I would have maintained them; since they go back to a single  

point, that's what this design works from. The key to  

"minimise...chafing of wearer's neck" is the location of where the  

shoulder straps connect to the seat belt; in my opinion, there is no  

cause for concern here.



 	  Quote: 	
		   Was your load testing applied to the straps as fitted to the device in  

 the aircraft or merely to the device sat on a strong surface?


	


	I've done no testing with this "riser" bolted to the CM. The photo  

below shows the test rig I used. The riser is mounted on a piece of 4 x  

10 wood with an angled face, set to duplicate the angle between the  

back and top of the head rest. Unseen beneath the strapping are two AN3  

bolts which correspond to those bolts which penetrate the hard point on  

the back of the headrest and flank the AN4 bolt which secures the  

typical shoulder straps; see other photos. Note that I've substituted  

2" wide cargo straps for the standard issue shoulder harness straps;  

since I'm testing this little "riser" and not the shoulder harness, I  

thought this would have no effect. Note also that the straps are  

clamped beyond the edge of the "flap"; the riser is held in place  

solely by the two AN3 bolts (under the straps).



	Also visable in the photo is a gauge resting on a loop in the straps  

with a pressure plate beneath a 2 x 2 steel tube which receives the  

force from a 20 ton hydraulic press.



	The test rig presumes that tension forces on the shoulder straps will  

be transmitted to the "riser" at its apex which has a radius of  

3/8"...so the big question was...Would the "riser" be crushed?  Well, I  

really didn't want to destroy it, so I stopped at 1500#; this load was  

reached incrementally...it was not an instantaneous load.



	Full Disclosure: My buddy with the hydraulic press uses this gauge to  

measure the tongue weight on trailers he uses w/ his business...he  

swears that it measures weight in pounds. However, as you can see in  

the next photo, the gauge is labeled in psi. You can note the size of  

the pressure plate in relation to the 2 x 2 steel tube...it appears to  

be about 2.5 inches in diameter...which means its area is just under  

4.9 sq. in. This then implies (to this non-engineer) that the force on  

the straps would be more like 7359# rather than just 1500#. Could this  

be so? Help!



 	  Quote: 	
		   And would it be better to wrap the forward edge of the device around  

 the front edge of the headrest, to reduce the eccentricity of loading  

 on that corner? thereby maximising the resistant of the front face of  

 the headrest


	


	Though it appears greater in the photos, the front face of the riser  

is only about 1/4" back from the face of the head rest...the  

intersection between the top and the front faces of the head rest has a  

radius...I sized the "riser" so as to not extend beyond the start of  

the radius. Personally, I'm unclear as to what portions of the loads  

are transmitted to the front face and what portions are distributed  

over the top head rest surface. The head rest construction appears to  

me to be the same on all faces, so I didn't think aligning the front  

faces would be significant.



 	  Quote: 	
		   Would prefer to see the guides at the top made as part of (or recessed  

 in to) the moulding, with broad rounded edges.


	


	The beauty of homebuilt aircraft is the latitude (at least here in the  

US) it gives to allow for personal preferences. The design I developed  

was intended to both satisfy the functional requirement and be  

sympathetic to the tapered forms of the head rests...guess I could live  

with the "ears"!



	Ron Pagoris has suggested I do some load tests of side loads such as  

those which might be encountered in a ground loop...so notwithstanding  

the pixs of these puppies on my CM, I guess it's back to the lab for a  

bit.



Fred

A194

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hurstkr(at)redzone.com.au
Guest

Posted: Tue Dec 04, 2007 11:40 pm Post subject: Shoulder harness restraint

Fred,

  

 I'm very  impressed with (and jealous of) your harness riser idea.

  

 The only  problem I can see with it is that you invented it too late !  You could  have been more thoughtful and done it before I bit the bullet and made a solid  riser !! <grin>

  

 Ah well,  thems the breaks !

  

 Keep up  the good work

  

 Kingsley

  

 do not  archive

    [quote][b]

kheindl(at)msn.com
Guest

Posted: Wed Dec 05, 2007 6:32 am Post subject: Shoulder harness restraint

Fred,

  

 This is a really well designed mod. I like the simplicity and the fact that it is not taking away any usable space. I would hope that the Europa Club mods people will take this on as a standard mod with PFA approval.

  

 Karl



<html><div></div></html>

 [quote]  Date: Tue, 4 Dec 2007 22:13:00 -0800

Subject: Shoulder harness restraint

From: fklein(at)orcasonline.com

To: europa-list(at)matronics.com



   .ExternalClass .EC_EmailQuote {margin-left:1pt;padding-left:4pt;border-left:#800000 2px solid;}  Duncan,



Thanks for your input and questions...answers indented below.



 -> Europa-List message posted by: "Duncan & Ami McFadyean" <ami(at)mcfadyean.freeserve.co.uk>



Fred,

Nice execution of a good idea.

CSA-VLA provides little guidance:



http://www.easa.eu.int/doc/Agency_Mesures/Certification_Spec/decision_ED_2003_18_RM.pdf

See pdf page 100 (or pages 2-8 and 2-9 at the back.



It merely advises for "..adequate separation of ...straps to minimise... chafing of wearer's neck...."  but recommends a maximum separation of 8" and maximum included angle of 60 degrees.



        I really didn't want to re-invent the wheel here, so one of the starting points was to not alter the attach point of the shoulder straps...and to secure the "riser" to the same hard point used for the straps. If our shoulder straps had had individual bolts to the hard point(s), I would have maintained them; since they go back to a single point, that's what this design works from. The key to "minimise...chafing of wearer's neck" is the location of where the shoulder straps connect to the seat belt; in my opinion, there is no cause for concern here.



 Was your load testing applied to the straps as fitted to the device in the aircraft or merely to the device sat on a strong surface? 



        I've done no testing with this "riser" bolted to the CM. The photo below shows the test rig I used. The riser is mounted on a piece of 4 x 10 wood with an angled face, set to duplicate the angle between the back and top of the head rest. Unseen beneath the strapping are two AN3 bolts which correspond to those bolts which penetrate the hard point on the back of the headrest and flank the AN4 bolt which secures the typical shoulder straps; see other photos. Note that I've substituted 2" wide cargo straps for the standard issue shoulder harness straps; since I'm testing this little "riser" and not the shoulder harness, I thought this would have no effect. Note also that the straps are clamped beyond the edge of the "flap"; the riser is held in place solely by the two AN3 bolts (under the straps). 



        Also visable in the photo is a gauge resting on a loop in the straps with a pressure plate beneath a 2 x 2 steel tube which receives the force from a 20 ton hydraulic press.



        The test rig presumes that tension forces on the shoulder straps will be transmitted to the "riser" at its apex which has a radius of 3/8"...so the big question was...Would the "riser" be crushed?  Well, I really didn't want to destroy it, so I stopped at 1500#; this load was reached incrementally...it was not an instantaneous load.



        Full Disclosure: My buddy with the hydraulic press uses this gauge to measure the tongue weight on trailers he uses w/ his business...he swears that it measures weight in pounds. However, as you can see in the next photo, the gauge is labeled in psi. You can note the size of the pressure plate in relation to the 2 x 2 steel tube...it appears to be about 2.5 inches in diameter...which means its area is just under 4.9 sq. in. This then implies (to this non-engineer) that the force on the straps would be more like 7359# rather than just 1500#. Could this be so? Help! 



 And would it be better to wrap the forward edge of the device around the front edge of the headrest, to reduce the eccentricity of loading on that corner? thereby maximising the resistant of the front face of the headrest



        Though it appears greater in the photos, the front face of the riser is only about 1/4" back from the face of the head rest...the intersection between the top and the front faces of the head rest has a radius...I sized the "riser" so as to not extend beyond the start of the radius. Personally, I'm unclear as to what portions of the loads are transmitted to the front face and what portions are distributed over the top head rest surface. The head rest construction appears to me to be the same on all faces, so I didn't think aligning the front faces would be significant. 



 Would prefer to see the guides at the top made as part of (or recessed in to) the moulding, with broad rounded edges.



        The beauty of homebuilt aircraft is the latitude (at least here in the US) it gives to allow for personal preferences. The design I developed was intended to both satisfy the functional requirement and be sympathetic to the tapered forms of the head rests...guess I could live with the "ears"!



        Ron Pagoris has suggested I do some load tests of side loads such as those which might be encountered in a ground loop...so notwithstanding the pixs of these puppies on my CM, I guess it's back to the lab for a bit.



Fred

A194



[b]

fklein(at)orcasonline.com
Guest

Posted: Wed Dec 05, 2007 9:49 am Post subject: Shoulder harness restraint

On Wednesday, Dec 5, 2007, at 06:30 US/Pacific, Karl Heindl wrote:



 	  Quote: 	
		    I would hope that the Europa Club mods people will take this on as a 

 standard mod with PFA approval.


	




Interesting thought Karl...I'd be happy to assist in any way if someone 

in UK wants to pursue this.



Fred



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