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Undercarriage wire choice, 8 or 7 swg?

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martin collins 102/04/2020 21:14:08
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I am modifying my second Priory models Silhouette to make it look similar to some of Peter Millers Pursuit type aircraft, giving it a radial cowl, modified cockpit and fuselage mounted undercarriage. The wing mounted u/c on the Silhouette is 8swg but the fuselage mounted conversion will be a bit longer is 8 swg sufficient or would i be better with 7?, wingspan on it is 55", it may be used with upt o a 6s batt pack so it may weigh a bit more than the original. Also i have some lengths of 8 and 7 here, i think they are u/c (piano) wire but how can i tell?

img_20200402_093937_resized_20200402_094142062.jpg

Edited By martin collins 1 on 02/04/2020 21:15:10

Edited By martin collins 1 on 02/04/2020 21:15:30

john stones 103/04/2020 00:19:02
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No help ?

Will bump it, someone will have an answer. wink

Denis Watkins03/04/2020 09:17:29
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Martin, use the wire that you have for a number of reasons.

As you already have the wire with you, then you can crack on with the job. If you mess up, then you have not just forked out for it.

The thinner of the two wires is totally suitable for the Silhouette, and don't forget that you are only using the wire under load for a few seconds.

For as long as I can remember, I doubt that we are buying Piano wire

Piano Wire is high carbon, tempered steel, and much of our purchases are bright steel, but this will do.

Tempered steel is Matt blue in colour, and literally becomes spring steel.

martin collins 103/04/2020 09:33:07
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368 forum posts
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Ok, thanks for the answer, i will go with the thinner wire then as i want to enlarge Peter Miller`s Miss Lizzy plan and put a petrol engine in it so the larger wire i have will go into that one..........

Nigel R03/04/2020 09:38:17
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At 55" and I guess around 5 or 6lb, that 8swg will be plenty.

Are you doing a torque rod U/C? Or one made from two 'U' shaped pieces soldered near the axle?

martin collins 103/04/2020 09:44:08
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Hi Nigel just a single length of wire in a large inverted V shape bound and epoxied into a ply former that comprises of 2 1/4" pieces epoxied together, sound ok?

Nigel R03/04/2020 10:00:11
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3750 forum posts
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This gives you a stress point where the wire exits the ply sandwich. You might want to add a light gauge spreader bar near the axles.

I'd recommend using a torque rod approach if you still can, they're very robust and the torque bit of it provides extra spring to protect that bend.

This sort of thing (scaled up a bit):

20-size-torque-uc.jpg

As for structure, you need a flat ply plate, 3/16 or 1/4 on this sort of size, on the fuselage underside to clamp the horizontal length to, and a couple of support blocks (hardwood) or plates (3/16 ply) for the upright.

I do any fuselage mounted gear this way, if I can.

Wing mounted gear works in the same way, but instead of the diagonal leg it has a vertical leg.

Edited By Nigel R on 03/04/2020 10:01:44

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