Hi! All.
Still talking about TRIKE I'm afraid!
Further to my previous messages re :- Bungee problem.
An alternative reason for the breaks is the fact that the top plate on the
actual "bumper" being light gauge material (though not particularly sharp)
has in fact sawn through the rear most centre "falls" of bungee rope since
on fully exercised travel the plate has to pass through these falls of
bungee?
My safety strap is quite a lot in excess of the 2" mentioned in the manual,
infact 2 + 5/8th",even so I can see that with only the specified 2" the thin
plate collides with the rear falls of bungee and whether it passes through
or not the sawing action is quite possible.
I have reported this to Roger Bull at Europa Factory who initially suggested
to trim the bump plate to the supporting tube diameter and file rounded
edges on the top .On further discussion he will be taking the matter up with
Andy Draper on his return from
America. IMHO the only solution (which means the engine AND frame out) is to
weld the bump stop to the frame and cut it from the nose leg pivot letting
it bump at the OTHER END, since the bungee is already parted at that end
going each side of the nose leg, then if the item conflicts with the line of
the bungee it doesn't have to part it or collide with it.?
In the meantime my Brazil /Savannah trip has been put back a month
(Clients!!???) and now I can't fly since the job is on hold. I guess the
damn garden is next in line!!!
Regards to all.
Bob Harrison G-PTAG grounded waiting !
-----Original Message-----
From: owner-europa@post.aviators.net
Sent: 01 August 2001 06:19
Subject: RE: Trike Nose Leg Bungee Breaking.
Hi! Rob.
Thanks for the assurances that the safety strap is really safe. I would much
rather replace a nose gear leg AGAIN than have a "buggered" propeller !
However 0.6" isn't a lot of suspension is it ? So the suspension is really
provided by the bungee on anything but the most "greasy" of landings ?
At least a better understanding has evolved over how to achieve the correct
bungee tension/down load figure WITH ENGINE FITTED . (no pain no gain!)
I used mountain climbing gear to pull down on one side and push up on the
other with both loose ends fastened to my car tow bar and the plane
anchored to a "dead man". Then I clamped it in place whilst I let the loose
end tension off to do the "tie offs". I will still make some arrangement to
hold the loop of slack safety cable away from the bungee and so keep it
under it.
Incidentally I will be absent from Saturday through 27th August. Going on
business to Brazil via a week in Savannah.
Regards
Bob Harrison G-PTAG
-----Original Message-----
Sent: 31 July 2001 22:42
Subject: Re: Trike Nose Leg Bungee Breaking.
Now it's getting more interesting, and I've answered my own question.
The gear leg is 4130 rather than an aluminum alloy because the yield
strength of 4130 (80 ksi) is reached at a mere at 700 lb force (up) on the
nose wheel, and deflection at the nose wheel end of the leg for this force
is about 0.6 inch. These values are based on the measured values of 1.25 in
diameter and 0.125 in wall thickness, for a 20 in long cantilever beam (the
gear leg) fixed at one end (which isn't literally true but this assumption
is good enough for now). 7075 would come close with yield strength of 73
ksi but it would deflect three times as much at the same load for the same
cross section.
So, if the leg will take a permanent set at not much more than 700 lb (and
fail at less than 1000 lb), how can the safety cable break without damage to
the gear leg?
Something isn't right here and I can't see what it is, but these
calculations say that it takes a lot more force on the nose wheel to break
the safety cable than it takes to bend (or break) the nose gear leg.
Best regards,
Rob Housman
A070
----- Original Message -----
From: "Rob Housman" <robh@hyperion-ef.com>
<fillinger@ameritech.net>; <europa@avnet.co.uk>
Subject: RE: Trike Nose Leg Bungee Breaking.
> Agreed, on all points, and especially on the manual's pretense regarding
> flexing of the gear leg, which seems a bit unlikely. Not knowing either
the
> force to stretch the bungee enough to load the 2.5mm (3/32 inch) diameter
> safety cable, or the cable's tensile strength (and not having the nose
gear
> leg handy to make measurements) I'll make a guess that the breaking force
> for a single length of the cable is 1200lbs and the pivot point on the
gear
> leg is located at around 1/4 of the overall length (for a 3:1 mechanical
> advantage), which computes to 1600lbs at the wheel to break the cable with
> none of the load taken by the bungee (for a load shared by four parallel
> cables - but the calculated value is an approximation because it is
actually
> a single cable wrapped over the assembly). I'll go out on a limb here
> (because I'd rather guess than calculate) and say that a mere 1600lbs is
not
> going to flex that beefy gear leg by much, and definitely not enough for
the
> eye to perceive. Later I'll get out my (ancient) Mechanics of Materials
> textbook and do the calculation for the deflection of the gear leg under
> load.
>
> Now that I see how little it takes to break the safety cable it makes me
> wonder why the nose heavy Europa has a steel assembly instead of one
> fabricated from aluminum.
>
>
> Best regards,
>
> Rob Housman
> A070
>
> -----Original Message-----
> From: owner-europa@post.aviators.net
> Subject: RE: Trike Nose Leg Bungee Breaking.
>
> Hi! Rob.
> IMHO The main item to protect is the propeller and its attendant parent
> attaching point !
> In my case thank the Lord for the safety strap/cable. IMHO I would like to
> know the load at which the nose leg tube provides "flexing" ? and then
next
> I would like to know its yield load? Having bent mine DOWN with a
> "wheelbarrow" bounced landing! All these questions because I don't believe
> the theory that the leg is ACTUALLY providing sufficient "FLEXING" on its
> own even with moderately heavy landings.
> When a) and b) bounced it , it was with such force that the TAIL of the
nose
> wheel spat got a bash and also gravel rash from the runway ! { a) and b)
> shall remain nameless! But that's where I believe the rot started with my
> bungee}
> Regards
> Bob Harrison G-PTAG
>
>
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