Wiiispa's Tucano

[Wiiispa]

OK it's decided then. This will be my first ever build. Like I said elsewhere, I like doing things the hard way. So I'll order the kit next week. What I'd like to do is make it an IC build, with built up wings and retracts. A lot for a first build, I know and I will make mistakes, but it'll be interesting and entertaining I hope.

[Concorde Speedbird]

Sounds good, have a good look at Martyn's build.

CS

[Wiiispa]

Thanks CS, yes I've had a good read of Martyn's build already. Good inspiration. I'll probably make the wings semi symmetrical due to my lack of flying experience.

[WolstonFlyer]

This sounds interesting Wiiispa, especially as a first build.

I am watching with interest!

[Ian Jones]

Posted by Wiiispa on 22/05/2013 18:54:03:

Thanks CS, yes I've had a good read of Martyn's build already. Good inspiration. I'll probably make the wings semi symmetrical due to my lack of flying experience.

Don't quite follow that. If you can explain your reasoning I think you may get some useful advice in return.

One of mine will be IC but with a sheet wing.

Good luck with the build.

Ian

Edited By Ian Jones on 22/05/2013 20:55:37

[Wiiispa]

Don't quite follow that. If you can explain your reasoning I think you may get some useful advice in return.

Ian

Edited By Ian Jones on 22/05/2013 20:55:37

Well I was hoping that a semi symmetrical wing would mean less AoA in the build, resulting in slightly less drag at lower speeds and making it more of a pussy regarding landing but I stand to be corrected.

[GrahamC]

My Tuccano has the sheet wing and flies really well and lands a treat. Not quite a first model, but I would subscribe to the "if it aint broke; don't fix it" school, and a Hawes Tuccano built as per the plan certainly isn't broke!

[Wiiispa]

It's not that it's broke, I dont think that the sheet wing will take retracts as it stands, and I'd like retracts. The challenge of getting them to fit and work is something I'll enjoy.

[GrahamC]

Fair point. Do you have a wing section in mind?

[Ian Jones]

Posted by Wiiispa on 22/05/2013 21:22:41:

Don't quite follow that. If you can explain your reasoning I think you may get some useful advice in return.

Ian

Edited By Ian Jones on 22/05/2013 20:55:37

Well I was hoping that a semi symmetrical wing would mean less AoA in the build, resulting in slightly less drag at lower speeds and making it more of a pussy regarding landing but I stand to be corrected.

Oh dear that's what I was bothered about.

The thing is Wiispa, the sheet wing has a flat bottom and a fair dihedral endowing the model with the "pussy" characteristics you refer to. You can make a fully built up flat bottomed wing which can take retracts and it would be more suitable for someone with the lack of flying experience you eluded to. The AoA for the sheet wing is zero and the same would apply to a built up version of this type of wing section.

It's true that some of the best trainers have semi-symetrical wing sections but the flat bottomed wing will give you the more benign qualities that this model is known for and I think you would be thankful for that pretty quickly.

I hope this is helpful

[Wiiispa]

All information is helpful Ian, many thanks. As for a section, there is still much for me to learn before I make that decision. Back to the retracts, it'd be nice if they could have closing doors, similar to the real thing. I've been pondering over how this might be achieved mechanically, without adding too much weight. Once I have the retracts in my hands, there'l be some experimenting going on. I realise that there will be implications for the handling of the aircraft with the wheels down. So it might just be a case of suck it and see.

[Codename-John]

Sounds like a lot of work and expense to me for something that wont last very long, why not just do it the recognised best, cheapest way with a proper trainer and help while you build a model with retracts, gear doors etc which might have at least a chance of lasting more than a few seconds, you sound keen to get into the hobby, but why o why would you want your first experiences to be filled with misery ?

[Martyn K]

Posted by Wiiispa on 22/05/2013 18:54:03:

Thanks CS, yes I've had a good read of Martyn's build already. Good inspiration. I'll probably make the wings semi symmetrical due to my lack of flying experience.

If you want me to do you a set of DXF files to send to a laser cutter let me know. I can modify my original with no problems at all. I would suggest a NACA 0016 upper and a NACA 0010 lower will give a nice predictable semi symmetrical wing section. Give me a shout if you need help

Martyn

[Wiiispa]

Thanks for the kind offer Martyn. I'll give it careful consideration. If you don't mind me asking, how did you arrive at your choice of wing section?

[Martyn K]

How do I choose? The NACA 4 series symmetrical range are a nice reliable and predictable suite of airfoils - although a little dated now, They are not particularly good at low Re, but most people dont seem to notice. The standard symmetrical suite have maximum thickness at 30% chord and it is very easy to merge them. For sports models, I try to keep to a thickness of between 12 to 18%. This lets you build a nice rigid wing with the least amount of wood.

Not really rocket science - mainly experience.

Martyn

[Wiiispa]

Thanks again Martyn. Because I'm thinking of fitting either a 25 or 32 IC engine - inverted, there won't be enough room for the front retract with the fuselage at the depth it is on the plan. However, as stated in another thread, the fuselage depth has been compromised to allow for use of stock 4" sides. I'm thinking of increasing the depth of fuselage nearer to scale to accomodate the front nosewheel.

By my calculations, I can get an extra 1/2" at the front end this way which should suffice. How it will fly is another question altogether.

[Wiiispa]

I've mocked up a drawing to scale of the modified front end design. There's an extra 20mm of fuselage depth at the critical point where an SC .25 engine will fit inverted. The fuselage will taper back to the t/e of the wings just as it does on the real thing. I think that with careful positioning, the front retracting nosewheel will fit, and be in the forward position it needs to be. The curve of the lower fuselage will be taken by copying f2 and inverting it to make an extended version. It'll need a grp cowel, so hopefully I'll be able to come up with a mount strong enough to take the nosewheel.

[Wiiispa]

Tools ordered. UC ordered. Some wood ordered. Should start building by the weekend. Wings first.

[Wiiispa]

UC hasn't turned up in time for the w/e, so makes it difficult to determine rib spacing for the wings It's critical that the ribs around the u/c are spaced to fit, otherwise there might be some weakness.

On the positive side, I think I've come up with a mechanical, lightweight way to have 2 peice doors on the retracts. It involves a small magnet and part of an elastic band. Watch this space

I'm going to go with Martyn's idea for the semi-symetric wing design, using two different profiles for the top and bottom surfaces. Whether it be the NACA 0016 top surface or not I've yet to decide. It depends on how thick the wing needs to be to hold the u/c, something I won't know till I have the u/c in my hands.

Edited By Wiiispa on 01/06/2013 09:02:04

[Wiiispa]

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.

[Colin Leighfield]

At this size Willspa the precise detail of the section is probably not too critical, but the semi- symmetrical section suggested by Martyn is probably as good as you'll get. Personally, I'd set it up zero/zero, although others might see it differently? The section has positive upper surface camber, so it is bordering on being a lifting section anyway. Any slight imbalance will be sorted out with cg position and elevator trim. I guess the cg will finish up between 25/30% of mean chord. Again, there may be other experiences, but there is my preferred starting point.

[Martin McIntosh]

Hi, I expect that you have looked at my built up wing retract version.

The noseleg was a squeeze even with an extended fus and electric power.

Considering that this is your first build I would strongly suggest that you put the retracts away until you have very much more experience since there are many pitfalls even on a much larger model. Just trying to fit and get the legs to remain in the correct place can be mind boggling even to an experienced modeller.

If you think that you really must go ahead with this then a single door fixed to each mainleg oleo will give you enough to think about. Forget magnets and rubber bands. It is not done like this. The slightest impediment to an electric unit will cause it to shut down and stop.

[Martin McIntosh]

Continued.

Sorry to sound so negative but I fear that this would only end up as a tale of woe.

Remember that I have nearly fifty years experience of fitting every type of these and whilst electric units require no complex linkages or air valves the rest of the pitfalls are still present.

Martin

[Wiiispa]

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

[Wiiispa]

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.