Jeremy,
I have been away on business and so have not been around to join the
discussion about MOD 70 but I have to say I am very unhappy about the Mod
and its possible implications. I appreciate that being a non current
engineer makes my opinion of little value to Europa 2004 or Francis
Donaldson, but that never stopped me before.
Firstly, the installation of the cables on the Mass Balance arm during the
build struck me as very much hit or miss procedure at best. Page 20-2 of the
builders manual- quote- " Make the cable as tight as possible before swaging
the sleeve. This operation is almost certainly a two person job, holding the
cable and swaging tool at the same time." When I came to that, it seemed to
me that obtaining a reasonable cable tension and getting the the mass
balance arm normal to the tailplane torque tube was almost mutually
exclusive. It was for that reason that I installed a turnbuckle in each
cable - this enabled precise measurement of the mass balance arm and
allowed for a predictable tension to be set. I don't know how many builders
adopted the same approach, but I know I am not alone with this idea.
The requirement for a stronger mass balance arm was decided following the
failure of one classic that had suffered ' a number of landing incidents'.
OK, I can accept that without a problem.
Last monday I drove up to Kirbymoorside to speak to Andy about the Mod and
my misgivings about it. Andy has done a lot of testing on the setup and he
showed me the new balance arm. It is made of thicker wall tubing and has a
considerably more substantial adjuster assembly replacing the original TP18A
adjuster. Andy also conducted some load tests on the original arm (in the
vertical plane) he found that the test arm initialy twisted and then the
lower tube buckled - he showed me the failed item. I am not sure whether
the arm was installed in the aircraft, with cables attached, or whether it
was just a straightforward bench test - if it was a bench test I doubt
whether any cables were installed - perhaps if cables had been attached the
inital twist prior to failure might have been delayed. However, the new arm
is much stronger and should do the job nicely - but there are no cable
attachment lugs.
I asked Andy why he had discarded the cables? His reason was purely to make
the installation easier for owners. I explained my turnbuckle arrangement.
to which he replied that it was not a problem and Europa could easily put
the cable attachment lugs on the new arm. Remember that the identified
weakness is in the vertical plane of the mass balance arm not in the cable
system. I asked if he would contact Francis Donaldson, but he said that he
would be happy for me to do it - as the new arm would be fitted with the
existing, proven engineering - it should require no flight testing. As it
happens my aircraft is in the workshop for its' permit renewal so I removed
the D panel and the fuselage access panels and had a good look around. The
fitting of the turnbuckles to install the new balance arm would actually be
quite easy. After carefully measuring and marking the cables so that the
end of the turnbuckle can be fitted in the correct place, the cables can be
cut as far forward as possible, that is just short of the cable lugs. Now
if the fuselage access panel, on the right side by the tail is in the
standard position, the cut end of the cables can be brought outside the
fuselage and the turnbuckle end swaged in comfort. The other end of the
turnbuckle can be fitted to the attachment lug on the arm using a standard
fork fitting, cotter pin and split pin. The new arm is then installed onto
the torque tube and with minimal time in the rear fuselage, the barrels of
the turnbuckle are fitted, the arm is adjusted to the centre of the pushrod
containment assembly, the tension set on the cables and finally locking
wires fitted to the turnbuckles. It may be necessary to drill a little out
of the mass balance weights to reset the balance.
Now the point is that if some europas, because arranging the mass balance
arm normal to the torque shaft is not a given, and the containment assemble
was built around the already installed mass balance arm. It is quite likely
that the resting place of the new uncabled arm is not going to be in the
same place. This means that the pitch tube containment attachment brackets
will have to be moved, and quite likely the fit of the ply around the pitch
tube itself may need adjusting. How much time will be required down the
black hole to do that!!! Using the existing cables would avoid all those
problems. I asked Andy why he hadn't considered using turnbuckles, his
comment - - "Well people might not have any turnbuckles."
What worries me is that this big lump of steel is going to be free to move
left and right at will, perhaps hundreds of times in an hour in opposition
to the slightest yaw of the aircraft. How much could it move? I noted that
a value of 4mm was mentioned on this forum. In fact, Para 5 of step 3 of
the modification leaflet states - "The diameter of the mass balance weights
is 50mm, and the nominal clearance is 2mm each side - check that the
clearance achieved is between 1mm and 4mm each side". I interpret that to
mean that the lateral movement of the arm could be 8 mm. Such a movement
does not take into account the flexing of the plywood of the pitch
containment assembly - not the sturdiest of structures. In real terms this
new arrangement could have these not insignificant balance weights
'clonking' left and right by maybe 12mm. Is this movement likely to cause
any fatigue problems at the attachment points on the torque shaft - perhaps
one of the forum metallurgists could advise.
I discussed this movement with Andy and he said that the weight moves even
with the cables. If they are fitted in the manner described in the build
manual I can see that there might be some movement. With properly tensioned
cables, there is negligible movement.
Actually, it is not outside the realms of possibility that a fracture of
the original TP18A could be accellerated because of lateral movement caused
by slack cables.
The bottom line is that, the history of why the cables were originally
fitted to the mass balance arm is irrelevant. Many Europas have done may
thousands of hours flying with he current mass balance arm configuration
without a problem. Now following the fracture of one TP18A on an aircraft
that has suffered 1 or more landing incidents we are all to fit stronger
mass balance arms. Changing the arm is the right thing to do. But I
totally disagree that discarding the cables is the right thing to do. It is
one aircraft modified and tested at the factory for a few hours against the
experience of the whole fleet.
I understand from Bob Harrison that since I spoke to Andy Draper he has been
told by his boss that he cannot put the lugs on the new arms as he promised
me. It seems that the only way we can incorporate this modified component
is the way Europa 2004 say, because that is what they have worked out and
tested. I smell commercial pressure here.
I fear we are in danger of throwing the baby out with the bath water!!!!
I have sent this email to the forum in the hope that someone can allay my
fears about MOD 70 - perhaps it might generate some positive comment.
regards,
Mike Parkin (G-JULZ - hiding in the corner of the workshop with cables a
quivering.)
----- Original Message -----
From: "Jeremy Davey" <EuropaFlyer_3@msn.com>
Subject: RE: Europa-List: Mod 70
>
> Fred,
>
> It wasn't stripped threads - the threaded portion sheared in two.
>
> Tim,
>
> I offered and you declined. OK, I'm 6' and 220lbs, but I still contend
> you're being fussy! :-)
>
> Cheers,
> 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)
> 1390 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 Fred
> Fillinger
> To: europa-list@matronics.com
> Subject: Re: Europa-List: Mod 70
>
>
> "R.C.Harrison" <ptag.dev@tiscali.co.uk> wrote:
>> ...
>> I understand that the part that broke ( Having been previously under
>> extraneous circumstances!) was actually the adjuster screw thread,
>
> I think I'm beginning to understand. There is considerable inertia in
> the counterweight, and a few good whacks to the tail in occasional
> hard landings would put the lower arm components in compression once
> too often, stripping threads? The rebound may not help either. I
> know this is amateur engineering, but perhaps the trigear doesn't
> suffer as badly in ungraceful handling, because the force exerted on
> the counterweight will be less abrupt. Hope so.
>
> Reg,
> Fred F.
>
>
>
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