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>
Date: Tue, 4 Dec 2007 22:13:00 -0800Subject: Europa-List: Shoulder harness
restraintFrom: fklein@orcasonline.comTo: europa-list@matronics.com
Duncan,Thanks for your input and questions...answers indented below.
reeserve.co.uk>Fred,Nice execution of a good idea.CSA-VLA provides little g
uidance:http://www.easa.eu.int/doc/Agency_Mesures/Certification_Spec/decisi
on_ED_2003_18_RM.pdfSee pdf page 100 (or pages 2-8 and 2-9 at the back.It m
erely advises for "..adequate separation of ...straps to minimise... chafin
g of wearer's neck...." but recommends a maximum separation of 8" and maxi
mum 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 p
oint of the shoulder straps...and to secure the "riser" to the same hard po
int 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 s
ingle point, that's what this design works from. The key to "minimise...cha
fing 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 t
est rig I used. The riser is mounted on a piece of 4 x 10 wood with an angl
ed face, set to duplicate the angle between the back and top of the head re
st. Unseen beneath the strapping are two AN3 bolts which correspond to thos
e bolts which penetrate the hard point on the back of the headrest and flan
k 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 sho
ulder harness straps; since I'm testing this little "riser" and not the sho
ulder harness, I thought this would have no effect. Note also that the stra
ps are clamped beyond the edge of the "flap"; the riser is held in place so
lely by the two AN3 bolts (under the straps). Also visable in the p
hoto is a gauge resting on a loop in the straps with a pressure plate benea
th a 2 x 2 steel tube which receives the force from a 20 ton hydraulic pres
s. 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 di
dn't want to destroy it, so I stopped at 1500#; this load was reached incre
mentally...it was not an instantaneous load. Full Disclosure: My bud
dy 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 po
unds. However, as you can see in the next photo, the gauge is labeled in ps
i. You can note the size of the pressure plate in relation to the 2 x 2 ste
el tube...it appears to be about 2.5 inches in diameter...which means its a
rea 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#. C
ould this be so? Help!
And would it be better to wrap the forward edge of the device around the fr
ont edge of the headrest, to reduce the eccentricity of loading on that cor
ner? 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 bet
ween the top and the front faces of the head rest has a radius...I sized th
e "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 fa
ce and what portions are distributed over the top head rest surface. The he
ad 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 t
o) the moulding, with broad rounded edges. The beauty of homebuilt a
ircraft is the latitude (at least here in the US) it gives to allow for per
sonal 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 suggeste
d I do some load tests of side loads such as those which might be encounter
ed 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.FredA194
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