Paul:
I meant to send that previous message to the whole list and not just
reply to you.
Sorry
Steve
Steve Hagar
hagargs@earthlink.net
> [Original Message]
> From: Paul Boulet <possibletodo@yahoo.com>
> To: <europa-list@matronics.com>
> Date: 11/1/2005 10:51:20 AM
> Subject: RE: Europa-List: Nose Gear Springs
>
>
> I'm willing to be point man for U.S. collection/distribution if needed
>
> Paul Boulet, N914PB
> Malibu, CA
>
> G-IANI <g-iani@ntlworld.com> wrote:
>
>
> Thanks to all those who have declared an interest in the Trigear bungee
> replacement springs. At this moment 13 builders have said they are
> interested.
>
> Here is some background so you know where we have got to.
>
> Two springs have been used to replace the nose wheel bungee and this has
> been done on at least five aircraft (on the Dutch register). The spring
> specification was done by Nico Groot and it took three attempts to get a
> suitable spec. Andy Draper was aware that the work was being done and had
> some reservation as to how successful it might be. Those who have them are
> very happy with the result.
>
> I have produced a drawing of the spring (complete with English translation
> of the specification) and calculated forces "on the stop" and at the
extreme
> of the spring travel (hitting the wire stop).
>
> Andy's reservation was that the spring rate (Young's modulus) of the
spring
> is much higher than that of the bungee. The modulus of a steel spring is
> linear whereas that of the bungee is highly non linear. This is because a)
> The Young's modulus of rubber is non linear, b) the bungee is multi
strand,
> c) the sheath probably plays a significant role, d) the bungee may have a
> safety thread, e) the installation may have anything from 12 to 20 working
> strands and f) these may be of two lengths. So the Young's modulus of your
> bungee might anything. Based on some very crude measurements I think mine
> may be about 25N/mm. The spring rate of the two springs is 65N/mm. While
> this arithmetic is interesting it is somewhat academic as only about half
> the load on the nose wheel is known (the weight of the aircraft). The
> remaining loads are dynamic loads caused by bumps so they are almost
> impossible to quantify.
>
> I have talked this through with Andy and reached the following
conclusion:-
>
> a) The initial springing is done by the nose leg, just as with the bungee.
> b) Once the nose leg is bounced off the stop the spring will give a
"harder"
> ride but this may prevent the wire stop being reached. In fact the higher
> spring rate may actually reduce the chance of a bent leg or prop strike.
> c) Once the nose leg hits the stop, and if sufficient further force is
> applied, the nose leg is going to bend.
>
> Following this logic, as long as the spring tension at full extension to
the
> stop (wire loop) is less than the strain at which the nose leg will bend
> then there is no disadvantage to using the springs. Andy has offered to do
> the calculations on the strain needed to bend the nose leg. Andy does not
> wish to see the protection, against bending the nose wheel leg lost.
>
> The disadvantage of using the spring is a weight increase of about 1KG.
The
> advantage is "fit and forget" and less blood on the floor.
>
> Assuming Andy is satisfied that the springs do not significantly increase
> the danger of bending the nose leg then I will get a modification
> application off to the PFA as soon as possible (the paperwork is already
> prepared). If Andy's calculations suggest these springs could be a problem
> then we may have to look at the spring design again.
>
> Everyone should be aware that the details on my drawing are more a
> requirement than a complete specification. They do not specify the
material,
> heat treatment etc so my remarks apply to only those springs made by the
> Dutch manufacturer. It will be perfectly possible for others to
manufacture
> suitable springs but it will require some development work and may not be
> cost effective.
>
> As Tim Weert has clearly explained (his posting dated 31/10/2005) the
> manufacturing cost of the springs has a high fixed overhead. To offset
this
> it will be of great benefit to order in bulk. My preference would be for
> Europa(2004) to handle this but I am prepared, if necessary, to act as
> co-ordinator.
>
> I will keep you all informed as to progress.
>
> Ian Rickard #505 G-IANI XS Trigear
> Europa Club Mods Rep (Trigear)
> e-mail mods@europaclub.org.uk
> or direct g-iani@ntlworld.com
>
>
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