John,
I appreciate the time and expense for your service to the Europa community.
In the States, I have used a 6 inch access hole in the rear fuselage for ye
ars. It is using a reverse of the flange layup in chapter 23 which ties th
e two skins together with a flox corner then 4 plies of bid on the inside.
One can use the hole cutout for the cover in this method, by reinforcing t
he edge with a fill of flox to stabilize the skin and support the screws.
Of course I use a 4 ply inner skin reinforcement of 8 oz bid and a tie betw
een the inner and outer skin as Flight Crafters initially did. (Bob used a
common sense approach used by Rutan that ties the skins together at the ho
le perimeter and add a flange of the same number of plies as used in the sa
ndwich in that area plus two for nutplate attachments if required.) These
are the techniques used in the Eze, Quickie and by Ken Rand in the KR clams
hell wings skins.) No problem with the flow of stress around the hole in a
ny of these aircraft either.
I did calculations on it years ago. My calculations were simply based on t
he 45 ply orientation with a 2 inch overlap on the inner skin. I worked up
the vertical (tail plane) force on a round cylinder of 1.5 foot diameter
with a six inch hole. I just evaluated the shear loads (as all the strands
are at a 45 back there and very light glass). I use 4 AN screws on the c
over/flange and found the load to be acceptable with over a safety margin o
f two provided there were at least 4 layers to support the countersunk nutp
late rivets. Many years of mild aerobatics and flying at 1370 pounds doing
advanced handling with no cracks wrinkles or problems after 10 years and 3
00 hours in my old Classic. This sized hole has been put in about 16 aircr
aft without incident using this method. It only opens the hole from 5 inch
to 6 so a man can get an arm in and ties the inner skin to the outer. For
normal flight I fly at 1450 lbs. nearly all the time as the guys I fly are
not the 170 pound FAA specimens. Again, no problem. (Also fly XC with th
e wife at 1450 pounds of mandatory wifely needed items)
I am very sorry that all that was on an old computer that I can no longer f
ind the file with the calculations. I used the shear load of a cylinder us
ing an example from =93Aircraft Structures=94 (Perry I think) used by Boein
g. They have a very good metal structure analysis of monocoque tube struct
ure, then applied the stress sandwich load of Michael Niu who wrote Composi
te Airframe Structures. Assuming the tailplane load at 1750 pounds and the
hole at about the 11 O,clock position. Enlarging the hole to a size that
is appropriate for a normal mans arm can be done without need for a stringe
r and rib in that area. Again, I am just an aero guy and not a structural
guy. I found the exercise to be challenging using only the Rutan documenta
tion, but I was introduced to Niu back in the late 90=92s and he has a grea
t analytical book on molding and the use of fasteners in composite material
as well as and structural repairs and how the stresses flow around access
holes and damage. Pretty neat for the early 90s.
Keep us posted on your results. Todays structural analysis programs are aw
esome and I envy you having access to such wonderful computing aids.
Best Regards,
Bud Yerly
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s 10
From: John Wighton<mailto:john@wighton.net>
Sent: Thursday, January 25, 2018 4:02 AM
Subject: Europa-List: Re: Tank access hole at bottom of fuselage
As per David Joyce's response, this area of the fuselage is load bearing an
d is fairly highly stressed for symmetric and asymmetric lifting loads (fro
m the empennage). A large hole with a cover will likely pass load via the
flange/fasteners - this is not good practice. Without the cover the corner
stresses will be very high, potentially leading to damage. The aircraft de
sign philosophy for damage tolerance is 'no growth', requiring there to be
sufficient strength for inherent damages (incurred during factory build and
by individual users completion processes, plus in-service accumulation of
damage) - so as not to compromise the original MS/RF calculated.
The two 'standard' access holes are small for a reason.
I continue to progress the loads and stressing work on the Europa, this is
being done as a R&D side project in my business. The aim is to fully under
stand the structural margins that exist in the XS structure and, if possibl
e, show a modest MAUW increase (possibly aligned with the US commonly used
MTOW). The project is being conducted as per a clean sheet design. I inten
d to write some articles for the Club Mag.
--------
John Wighton
Europa XS trigear G-IPOD
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