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Wiiispa's Tucano


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You certainly seem to have this well thought out. Mine are both fully symmetrical sections with +1 deg. incidence which seems about right so you will not require more than this with a semi.

Making a built up tail just adds too much complication for such a small model and soft 1/4" balsa would be better. Remember that with a heavy i/c motor and a retract unit right up front you may have to add tail weight so no point in trying to make it lighter.

I would stick with a two piece wing since it follows convention and is simpler/lighter.

Try to dispense with the nosewheel steering if you can. It is not necessary. (continued)

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Yes, the nosewheel steering will be fixed. The engine will be angled slightly off from inverted - well that's the idea - allowing access to the plug. The nosewheel will be very slightly offset the opposite way to the inclination of the motor.

The engine will be raised in the fus by 3mm in the vertical plane. I can do this because I'm going with the smaller spinner. The overall fus will be 4mm deeper, with the front end being an extra 29mm deeper than the original plans. It seems a lot I know, but I think it will work, making the fus look like a slightly exaggerated real thing. Taking measurements from photos, it's less than 5% deeper than it should be. The nosewheel won't be quite as far forward as I'd like but it seems accepatable.

According to my plans, there is only about 2-3mm between the nosewheel and the top of the head, so cooling might become an issue. I'm hoping that a generous conventionally placed intake will help with this. If it doesn't look right, then I'll go back to the drawing board.

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Posted by Martin McIntosh on 13/06/2013 19:53:51:

Thought so. Just go for electric and copy what I did! Any help required just ask.

Thinking that way now for this model. Still going with doors for the u/c. The wing design is pretty final now and there are lots of bits already cut for assembly, ribs, tapered spars, false l/e etc. Should get to start assembling the wings in the next 10 days or so.

Spent a lot of today re-doing the front end design for electric. It's a lot easier. Got the modified f2 designed with space for the u/c, front wheel steering if I fit it and cooling exits using the mock turboprop exhausts. The dropped front fuse will be made from 2 x laminated 1/16 balsa, because that should bend relatively easily and save weight. 2 additional lower half formers, either side of f2 will add strength and guide the shape. I'm a little worried about losing the strength of the bottom of the fuse but we'll see how that goes in the build. You'll see what I mean with the altered back half...

The retracts will let the model sit properly when on the ground, it won't be nose up or down.
I'm toying with the idea of fitting a 4 blade prop, have been all along really. More later on that one.

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Wiiispa Obviously not sure which leccy setup your looking at but as most of us have found a 1250kv 42A motor with an 11 / 12" prop will not only pull her of the ground but not get hot in the process so coolings not an issue

my setup is the following (just in case you've not made your mind up yet)

Motor Turnigy 35-42 1250kv (600w)

ESC Turnigy plush 60A

Bty Gens ace 3300Mah 3s1p LiPo

Prop 11x8.5 three blade (yes mines an embraer )

Phil

Flight time with this lot is best part of 12mins and plenty left in the tank (3.7v per cell)

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Thanks Phil, I'll order the 35-42 1250 as it seems the norm, but the plush 60A ESC is out of stock, so I thought about one of these instead. Was thinking of a 9x6 4 blade prop. There's obviously something I'm missing because eCalc says that setup shouldn't work whereas plainly it does.

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Thanks for the link WF. Saving money is good smiley. Fitting the esc could be a problem, I'm glad you brought that up Phil. F2 is already heavily modified for the front u/c ... Time for plan C. I haven't even got a finished plan A yet.

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Encountered a small problem. The wing spars do not form a straight line across the join. The forward pair are close enough to fit a normal dihedral brace, but the rear is too far forward swept. Looks like I'll have to modify the ribs. some to get the required strength. Luckily they're not covered yet.

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Here's my plan for the right wing, ready to start assembly. Hand drawn to scale by me. It's a bit grubby, and some of the stuff should be hidden (dashes as opposed to solid lines), but I understand it so it'll do me. It shows the planned placement of the retract including the doors. Bottom is a front view of the part of the wing that contains the retract at the deepest part of the chord. I'm using a tiny XL-3.7 servo to oopen and close the inner door. Both wing doors will be operated by the same servo.

Hmm picture not working ?

Edited By Wiiispa on 17/06/2013 13:07:11

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Willspa, are you sure you've got a sufficiently robust mounting plate and support for the retracts? Look carefully at Martin's advice on this. The problem you have with the dihedral braces is caused by the fact that you have not drawn the spars parallel to each other. They should give you a straight line across the dihedral join. If you feel that the rear spar is too far forward, you can fit light balsa spars, say 3mmx6mm into the ribs further back and at an angle closer to that of the trailing edge. They would not need any central bracing, that would be provided by 2x3mm ply braces connecting the two parallel main spares.

Personally, I would not be at all happy with it as currently drawn, but it's up to you.

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Thanks Colin. The support for the retracts is pretty much the same as Martins, with 1/8 ply doublers outside ribs 4 and 5 and 1/4 ply beams across these to take the retract mounting plates. On the drawing it shows 1/8 beams across but I changed this.The spars aren't parallel, because I used profili to generate the wing panel and couldn't find a way to ensure they were. Remember I didn't want to cut the spars at all for the retract mounting, because I figured that'd be an unacceptable weakness. I think that using 3 braces at the rear spar, laminated and shaped to the correct angle out to rib 3, will give adequate dihedral bracing. There will be 2 braces at the front upper and lower spars as well. Only time will tell.

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Noted Wiiispa, (did I get that right)? I still do this simple drawing work with old fashioned instruments and to be honest, wouldn't allow any computer programme to compromise basic principles. There is no question of cutting into the spars, they form the front and rear of the "box" that contains the mounting plate, suitably re-inforced.

Laminating the brace in the way you describe looks awfully cumbersome and not the best solution in terms of either strength or weight. Neither do I think that having a single brace on the rear spar is at all a good idea. If you're going to have only one, it would be better on the front spar, but you should be bracing across both. Running out to rib 3 is fine.

You may well get away with this and I hope you do, but it seems to be creating compromises where there don't need to be any really and your brace idea is potentially unsound, I think.

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Ok thanks. I'll have a re-think. I see it being a bit heavy and not having the structural integrity that a parallel brace would have. That said, short of scrapping the wing and starting afresh, I don't see a solution at the moment.

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Look at the pics of my wing joiners and you will see that they are simply pieces of lightply bent to meet the angled spars. They are really only there to assist with the dihedral angle since the strength lies in the gf bandage over the wing sheeting. Note that a veneered foam wing has no spars and totally relies on the bandage.

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I had misread earlier that you had said there will be a brace on the front spar, although even then creating a concentrated bend at the joining point is asking a lot of the ply. My last wish is to be a "wet blanket" after all of the effort that you have clearly put in and maybe we need to hear again from our other pals who have contributed so far. A pause while thinking things through is never a bad idea. You have the prospect here of a really good model, but you have chosen a complicated route and it's so easy to see a huge amount of commitment go down the pan. Believe me, I've been there too often and I'm not the only one.

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Martin's quite right about the wing bandage. I confess I've only ever used that with foam wings. All of the bending moment is at the join and with a built-up wing it's concentrated at where the leading and trailing edges and the spars join. Fitting dihedral braces distributes the load along the length of the spars and minimises the risk of breaking at the join. If you sheet the wing over at the roots, you distribute the load around the whole of the wing area and then the glue join becomes most important, just like in a foam wing. Putting a g/f bandagre around it also distributes the bending stress over a wider area and makes a really strong join. If you are sheeting the centre section and using a bandage as Martin describes, my wittering on becomes meaningless. Good luck, I look forward to seeing the finished job!

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It's more likely my poor explanation that's caused some confusion. Lets hope my bandage is as strong as yours Martin! Colin, the front spar is very close to being parallel wing to wing. I doubt the concentrated bend required would be that weak. The rear spars however are a different kettle of fish. I have some 1/16 ply that'll do a token job there. I'll bow to your combined experience and make the bandage as good as I can when the time comes. How far from the join should the bandage extend?

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  • 2 weeks later...

Pics will follow at the weekend. First wing half is complete but not skinned yet. Built using 12*1/8 ribs at 51mm spacing with a 25mm wing tip. There are 4 spars 1/4 * 3/16. with 1/8 false l/e and t/e. the aileron servo (which is fitted in the wing) and retract are test fitted as is the pair of doors for the retract c/w servo. The wing has 30mm Dihedral only, which was achieved by blocking rib 12 up and using a slec rib jig to fit rib 1 last of all. Some 48mm spacers were used to ensure the correct distance from rib 2, which is critical if the wings are to match. I thought long and hard about the dihedral bracing and have come up with a solution. Custom ply braces. I'm going to make a jig at the correct angles, then soak some 1/16 balsa before bending it into the jig. once dry, the balsa will be laminated together to form a piece of bent balsa ply. That together with the bandage will, I hope, do a good job.

The wingspan will be 1178mm which is more or less 1/10 scale. So the redesigned fuselage will be 978mm long. This is a compromised design, using 3/16 sides that have been drawn more or less to scale. A modified f3 and f4 are fitted at the front and rear of the canopy, using Nigels formers as a template, but extending f3 below the original plan design to accommodate the lowered front fuse. A shortened f3a is fitted just in front of the l/e of the wing for strength. 1/16 ply doublers have been glued between f3 and f4, but they are tapered beyond these formers so that there is no abrupt end to them, they have also been lightened. The rear of the fuse is elevated by 21mm, so the floor is no longer flat from the wing backwards, but closer to scale. this means that the elevator and rudder will sit slightly higher on my model than standard. The nose of the fuse will be made from 5 x 1/8 balsa formers precut and laminated together, the nose ring fitted to this. Hopefully final sanding will bring out the proper shape. the nose will be removable, its mostly decorative in this incarnation as strength is provided elsewhere.

The cockpit will sit at a slightly steeper angle than normal, again hopefully more to scale. The top of the fuselage from the canopy backwards will have custom formers that will take 3 longerons and the fin gusset. These will be skinned with 1/16 balsa sheet, as will the lower font fuse which is similar in its design.

I've pretty much thought it all through and drawn it all up now. Just got to plod on with the build.

Edited By Wiiispa on 27/06/2013 21:07:09

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