Wiiispa

Sorry Martyn, not yet. It's one of my busy times of year at work, covering holidays etc 78 hours last week. That and I've just had to re-felt the garage roof. As soon as I've finished the second wing, I'll put up the photo's so far. Thanks for the continued interest.

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

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?

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.

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.

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

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.

Thanks for the link WF. Saving money is good . 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.

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.

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.

Apologies to Martin, engine just turned up, laid it all out - measuring error it won't fit. Somehow I'd lost 30mm in my drawing. Oh well re-think necessary.

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.

Finally started the build. The NACA 0016 upper / NACA 0010 lower wing section would actually be too narrow to hold the retracts. I've gone for an NACA 0016 upper / NACA 0012 lower, which still retains the semi symmetrical profile but is wide enough to contain the retracts. It'll be slightly larger than 45" span, there are 12 ribs with 51 mm equal spacing for each wing, the retract hinging end being mounted between ribs 3 and 4 which are to be reinforced. The wing section ends at the fuselage, where I'm using a similar system to Phil Winks to join both wings. (Thanks for the idea Phil.) 4 x 1/4" spars in each wing, spaced so that the retracts fit comfortably between the lower 2 spars without having to hack them about. Having thought long and hard about the doors, I've decided to go with servo operated inner doors on an adjustable retract door sequencer. The outer doors are simply attached to the landing gear itself. Today I've started manually cutting and shaping the ribs. The fuselage itself has undergone significant deviation from the plans, being 2mm wider at the widest point and 4mm taller all along it's length. Use of a 1.75" spinner has enabled the engine to mount 3mm higher than the line on the plan, The extra curve at the front end as a result doesn't look out of place on my drawings. That combined with a 27mm lowered front fuselage which tapers to the trailing edge of the wing gives enough room for the inverted SC .25 engine, the retractable nosewheel and the servo operated doors. Photo's to follow shortly.

Thanks for the input Martin. The 'Rubber Band' as you term it isn't going to be used like that. I'm using part of a wide elastic band as a stop to prevent slap in the door closing by acting as a shock absorbing cushion. The small magnet is there to hold the door in both the open and closed position so that it doesn't move around too much if at all during flight or taxing/Takeoff/landing. The magnet and catches will be hidden within the wing itself. The Main wheels have a two piece door that looks basically like the two peice door on the real thing. The Inner wheel door will unfortunately not operate independently, so I can't close it at will. It could, if I designed it that way, but that's a step too far for this attempt. I hear what you say about the front wheel, and indeed the measurements I have taken make it a very tight fit. But fit it will, I'm quite sure of that. Hopefully my mock-up will be completed within a couple of weeks and we can discuss it further then. You might be surprised, or you might be right we will have to wait and see. Edited By Wiiispa on 05/06/2013 19:52:40

The DSR-D retracts turned up today, so I can get measuring for wing thickness and rib spacing. The instructions that came with them are fantastic - not. There aren't any. Never mind, did I say I like a challenge? A question for the technical amongst you. The built up wing profile is a mix of NACA 0016 upper and NACA 0010 lower. I assume this will need a small amount of + incidence. How much? 1-2 degrees? Also if I go for a built-up tail, I assume a symmetrical section with no + incidence would be needed, because no lift in straight flight is wanted at the back end? Noob questions, but got to ask.