Dave,
I'm sure that PFA Engineering did an analysis of all the stress and strain
cases. Mod 70 has certainly taken up a chunk of their time, and some have
even commented that in their opinion Engineering have OVER-analysed it!
The cables were eliminated as fitting them correctly to the previous design
with the lid on would have been virtually impossibly. In fact, I think the
only successful approach would have been to cut them off at the forward end
and fit turnbuckles to the shortened ends with fork-ends onto the TP18 lugs.
Also, they were there because the original design had no pitch-stop support
as we know it. The design of the TP18 lateral retention was never
re-addressed after the support was added - that has now happened and it has
been recognised that the cables can be disposed of (some have already done
this anyway).
Regarding weight: it's my understanding that replacing the cables with
Tufnol just about balances out the heavier TP18.
Above all, let's not forget that the maximum lateral movement now allowed is
4mm! Even a lateral acceleration of 1g is only the equivalent of dropping
the weights 4mm onto the Tufnol+ply+layup. As an admitted non-Engineer, this
seems to me not to be an issue. 4mm at the end of 1m is a rotation of about
1/4 of a degree!
Regards,
Jeremy
Jeremy Davey
Europa Monowheel 537M G-EZZA
Europa Club Vice-Chairman, Webmaster, PFA NC Representative
PFA EC Member
If you can keep your head when all about you are losing theirs, then it is
possible you haven't grasped the severity of the situation.
Tail done
Standard XS wings with mods underway
CM installed in fuse (with airbrakes fittings)
1380 build hours to date
Intended fit:
Rotax 914 turbo, Airmaster CS fully-feathering prop
Lots of lights, buttons, switches, gizmos, and alarms
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Moore, Dave
Subject: Re: Europa-List: Mod 70 and the PFA letter
May I ask the following via the forum, because I don't want to add to
Andy Draper's bulging electronic in-tray or list of telephone calls...
I've just had a look at the Mod 70 description (Thank you, Steve D) and
wondered whether any of you have discussed, with Andy or PFA
Engineering, the possibility of fatigue of the new unrestrained mass
balance arm.?
The new design, without the bracing cables, looks a recipe for a fatigue
failure at or near to the TP18B fitting. (From vibration in the
horizontal plane).
It would make for some peace of mind to know that a fatigue analysis or
tests have been conducted to demonstrate that the thicker wall tubing of
the arm will be sufficient, in itself, not to suffer fatigue as it
oscillates between the rubbing strips.
Why didn't the new design retain the cables? It is a minor weight
penalty, would its retention be overkill/over-engineering.?
Regards,
Dave Moore
Monowheel 550
Aberdeen UK
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