Rib Plotting by Computer

[Jeffrey Cottrell 2]

Hi guys

Started on my Chilli Wind build, using templates supplied by Harry, and they really are excellent.

Basic wing structure is built, and I'm pleased with it, but run into a stumbling block with u/c mounting.

The plan shows a foam wing, and even then only shows the position of the u/c wire, without any detail as to how to mount it. With my built up wing I have even more of an issue.

So, any suggestions as to how to go about it would be most welcome.

Asked the same question on the Built up wing thread, here, so ideas on either thread would be most welcome.

Thanks

Jeff

[Andy Stephenson]

When I built the Breeze I mounted the U/C on the fuselage just in front of the wing using the usual cross-over wire type, I prefer this method because it removes the landing stresses from the wing.

[Nigel R]

1/16" ply doublers, you'll need them on two ribs, probably the one about 3" outboard of fuse side, and the next one out. These occupy the area from LE to spar. Also needed, a 1" wide bit of 1/4" ply, this needs to be about 1" longer than the rib gap, say 5" (ish).  The 1/16" doublers are rebated to take the 1/4" ply plate, such that the 1/4" ply sits level with wing surface. Wing sheeting is cut out for said 1/4" ply plate. "Securely fasten" the plate to the doublers, a job for epoxy.

 

I would put a second bit of 1/4" ply on the inside doubler - this would be notched to take the 8g (?) U/C torque arm, i.e. the short bit that sticks upward.

 

Here's one I made earlier:

 

 

Left is inboard. Short torque arm goes from under the big plate up into the small notched squarish piece of 1/4 ply.

 

This was for a trike, so it is all behind the spar, but, same principles applies.

 

Detail of the small squarish pieces:

 

 

I've no idea why I felt the need to label the top of a symmetrical part!

Edited October 11, 2021 by Nigel R

[Jeffrey Cottrell 2]

Hi Nigel

Thanks for the quick reply and the details. Pretty much what I had in mind, although I'd probably use 1/8 liteply to reinforce the ribs.

However, what's exercising my noggin at the moment is this:

Your example was from a tricycle u/c, which puts the blocks behind the spar where the aerofoil is relatively flat. On the Wind, it's anything but.

Blocks are fitted in front of the spar where the rib curvature is at its highest, and given the tapered wing this gets even greater as you go outboard.

So, fitting the blocks level with the top of the ribs is a non-starter.  That's my issue, any ideas?

Jeff

[Nigel R]

I think you've identified a bit of a non-problem, to be honest.

 

Knock down the bits of ply that stick out, with a sanding block. Only the front tip corner that will need adjusting, the other three can be got level with the doublers.

 

Or you can recess the block a bit and use some 1/8 (ish) balsa to form the shape of wing surface, obviously need to make the balsa doesn't foul the clamps or wire.

[Jeffrey Cottrell 2]

On 12/10/2021 at 07:52, Nigel R said:

I think you've identified a bit of a non-problem, to be honest.

Hi Nigel

You could well be right on that. Didn't like the idea of cutting chunks out of the ribs without a plan, but no-one else has come up with anything better, so that's the way to go. Thanks.

Andy

Sticking with the wing mounted u/c, for the old fashioned look. Even considering a central servo and torque rods for the ailerons. Can't get more 'old school' than that.

We'll see

Jeff

[Martin McIntosh]

Nasty floppy torque rods?

I went as far as fitting analogue servos to my Curare for authenticity but no more than that.

[Jeffrey Cottrell 2]

Thanks Martin but I don't do nasty floppy anything, apart from when I've spent too long in the pub!

Jeff

[Nigel R]

I don't get the anti torque rod thing either. They're just a way to get the horns inside the fuselage. Also means just one servo to mount. Swings and roundabouts...

[Martin McIntosh]

Torque rods were a 1960`s way of operating strip ailerons rather than using snakes or bellcranks. Nowadays we all(?) use two servos. Assuming that they are piano wire running in a brass tube from the servo then they are likely to seize up with rust and the wire must twist a bit. All of my own linkages are directly from the servos with ball links at each end, as short as possible, and have zero slop.

[Peter Miller]

I have used torque rods on smaller fast models (My Macchi 202 Folgore and Kawasaki Hien)amd never had any trouble with them but I mainly used pushrods and bellcranks from a central servo out into the wing on all my designs up until I went electric.

[Nigel R]

9 hours ago, Martin McIntosh said:

Assuming that they are piano wire running in a brass tube from the servo then they are likely to seize up with rust and the wire must twist a bit

 

I use the commercial offerings (life's too short, etc) that come with two separate nylon bearings. My experience, this type has very little slop and don't suffer rust. Thus:

 

https://www.ebay.co.uk/itm/254628197157?epid=2043053526&hash=item3b4905f325:g:KKoAAOSwQP5e6qcC

 

I found the type with wire-in-nylon tube tend to have a slightly sloppy fit in the tube, which leads to a little play in the whole mechanism.

 

That said, servos can be had cheap these days, for sure.

 

But I can see why Pete used bellcranks. They cost buttons and are not tricky to install or setup.

 

No method is wrong.

[Jeffrey Cottrell 2]

Hi Nigel

Thanks for that link, very interesting. Mind you, in my box labelled 'useful one day' I found a piece of 12g piano wire and some plastic tubing that is a nice snug fit.

Might roll my own, haven't decided yet.

Jeff

[Sam Longley]

To calculate ribs at any point in a wing try this.

Download a copy of Freecad CAD software. Takes a little while to learn the basics, but there are loads of vids on it & you do not have to learn everything.

Draw the ribs at the root & tip, along with the holes & spar slots.

Set them at the correct distance for wing half span & loft between the two.

Cut the loft with planes at each rib & you will get a perfect cross section at each rib.

I do have Alibre Atom which I paid for but  I had spent some time with Freecad which is pretty easy & fun to learn whilst between TV programs.

Edited March 1 by Sam Longley

[Sam Longley]

I can no longer edit my last post but here is a link to an alibre video

wing

freecad is not much different

Edited March 1 by Sam Longley