>the Europa would not be cleared in the UK,
>as I understood, because of differences in construction from the
>demonstrator
Pete - at the May 1998 Europa Club Seminar at The Mill on the Soar,
Francis Donaldson gave us the impression that aerobatic clearance
could be granted to the XS Europa, at reduced weight. Here are the
notes I made at the time of his presentation. I apologise for the
size of this posting, but I think most of it is probably relevant to
this topic:
>Francis Donaldson (PFA Engineering): Wing/spar ultimate load testing
>
>Europa weight = total lift = 1300 lbs (or 650 lb per wing)
>
>If 4G max allowed during operation, then lift per wing = 1300 * 4 /
>2 = 2600 lb
>
>Tail adds extra stress as its "lift" acts downwards, adding 5% to give 2730 lb
>
>Lift distributed across wings & fuselage, which is 44" out of 300",
>so wing load can be reduced by (300 - 44) / 300, giving 2329 lb
>
>Load can be reduced by the 80 lb weight of the wing itself (as each
>element of the wing has its own share of weight & lift). At 4G, this
>reduces loading required by 320 lb to 2009 lb.
>
>50% extra strength to be available for gusts, mistakes, overloads,
>etc - but entering this region will lead to permanent damage even if
>it gets you home. At ultimate load wing carries 1.5 * 2009 lb = 3013
>lb (or equivalent to 6G).
>
>Strength of composite structures more difficult to predict than
>conventional engineering materials, particularly as homebuilder's
>output will have more variability than a lab sample made under
>controlled conditions. Tests on composites require an extra factor
>of 1.3 to allow for this. Also the degradation of composite strength
>with temperature requires a total "composite" factor of 1.5, or that
>all tests be done at an elevated temperature of 54C. This comes to
>2009 * 2.25 = 4520.25 lb.
>
>Full load tests were required for the XS wing because its
>thin-section sandwich was more likely to buckle.
>
>In the Europa, the high angle-of-attack case is the critical one. In
>this situation the resultant force can actually be forward relative
>to neutral axis. To simulate this "anti-drag" force, the wing, when
>tested upside-down, had it s leading edge tilted down by about 12
>degrees.
>
>Some failures led to various modifications to the rear wing attach
>point. The final solution was a tie-rod across the rear fuselage (to
>carry tension loads), attached to the rear wing pins by a hinge (to
>allow flexing). This arrangement was taken to 9G without failure.
>
>(1) There is a potential for increase to 1370 lb gross weight
>clearance (but not for 912 80hp with fixed pitch prop).
>
>(2) Potential aerobatic clearance at reduced max gross weight (eg 1050 lb).
>
>(3) Safety margin increased from 1.5 to over 2.25 at normal ambient
>temperature.
>
>(4) Improved fatigue life of root pins (previously was maybe 3000 hours).
>
>Recommended that whole Europa fleet be modified to this standard,
>not urgently, but by next permit renewal.
I remember that Francis said that he'd done some back-of-an-envelope
calculations about the aerobatic clearance just before the seminar,
in anticipation of that very question, but hadn't done a formal
analysis.
It's my impression at present that he is still trying to get out from
under a big pile of work, and I believe his wife Kay may be unwell
again, plus of course he is involved in moving house from the south
coast. Thus, I suspect this is probably not the optimum time to
harangue him about aerobatic clearance for Europas. It's certainly
something I'd like to see, but of course I'm in no position to press
for it just yet!
Incidentally, I note that in the Kitplanes magazine (Dec 03) listing
of available kits, the Europa is listed with a gross weight of 1450
lbs. I wonder where that figure comes from? The only test results
I've ever seen published relate to the old 1300 lbs or the later 1370
lbs. Perhaps Europas built in USA are just stronger :-) Mind, you,
the Kitplanes list also shows the empty weight of the Europa tri-gear
as 750 lbs, so I guess you can't believe everything you read in the
papers! (Only G-BVGF comes close to that at 758 lbs and there are
only 2 other tri-gears under 800 lbs.)
regards
Rowland
--
| Rowland Carson PFA #16532 <http://home.clara.net/rowil/aviation/>
| 670 hours building Europa #435 G-ROWI e-mail <rowil@clara.net>
|