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DH87B Hornet Moth

Indoor Scale Candidate

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Danny Fenton24/01/2017 12:57:41
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You will do it Martyn, I have every faith. Personally I would dump the wing fold idea unless it is part of crash resiliency wing attachment.

I know I have gone against the grain by fixing my Cub wings with no give. But my reasoning is don't crash!

Cheers

Danny

Martyn K24/01/2017 15:04:38
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LOL,

I am not actually going to fold the wings but I want to delimit the Wing fold panels. I'll only kick myself if I don't do it now.

I have a plan.

I am still scratching my head on the ailerons. I am going to use torque rods - probably thin ali tube as I can easily crimp bend and glue these to a central servo in the wing root. Lower wing will be in one piece and will be removable for access. Probably held in place with a pair of 10BA bolts and central pegs. As the lower wings need to come off then so will the uppers. These are simply plug ins using thin short stubby 20g piano wire joiners. The idea is that the lower wing carries all the flight loads and the upper wing is supported using struts and wires.

You can see why I am worried...

Martyn

Danny Fenton24/01/2017 15:19:37
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Sounds good to me Martyn, if you haven't a visible cockpit ceiling then piano wire and tubes is a good springy solution, put a slight kink in the piano wire and you will get a nice friction fit.

If I was doing ailerons in my Cub I would use fishing line and spring load the aileron down, then one line to each aileron to pull and lift it. Getting the spring rate right might be interesting, rubber band perhaps? it would need to be very soft.

Will be good to see how you crack it, torsion rods will work but the mechanics may be tough to keep light?

Cheers

Danny

Martyn K24/01/2017 15:28:11
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its the weight that is bothering me. Fortunately, the ailerons are quite long so the rods will be short but at least I can bend them up to make the horns etc.

The upper wing joiners are a bit tricky as the full size has a perspex roof. My idea is to use a square 'U shaped joiner linked to the front and rear spar on each wing and then simply bind these to the upper longeron. It will be just over half the weight of 2 separate joiners because the fus is so wide

The upper wing will mate to a small faired in to the fuselage top rail that extends about 6mm in front of the cross member, It should give me a nice junction if my building skills are up to it. Also handy as there is a colour change here

Do I need a pilot?

Martyn

Paul H24/01/2017 15:40:10
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47 photos

Hang in there Martin, I suspect you might share the feelings I have occasionally of desperation and a strong desire to chuck it in the bin but once I push through confidence starts to build again. My learning curve on this project is very steep not least because time is against me. Definitely a case of if I was going there I wouldn't start from here but you live and learn and the challenge is (sort of) enjoyable

Martyn K24/01/2017 15:49:26
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Cheers Paul

I have no intention of binning this unless the cat sits on it. However its now a balance of what I can reasonably achieve in the time I have available. I'll start work on the lower wings tonight. I thin I know what needs to be done. I will be happy when experience proves me wrong

Colin Leighfield24/01/2017 15:49:51
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5965 forum posts
2494 photos

I'm looking at the details of my (much less ambitious!) Wicko project while I'm away. The wing is also complicated by a considerable glazed area in the roof, I'm pretty certain now that I will make the wing in two halves, they and the struts will be attached together and to the fuselage by tiny neodymium magnets. The model will therefore comprise seven parts:- fuselage with tail surfaces in one piece, two wing panels and four struts. That makes everything completely accessible and those magnets are strong so there's no way that it will come apart in the air. I've got quite a few in different sizes I bought through EBay. I attached the very large under cowling to the Super Marauder using only these things and it takes some shifting. No sign of it moving on the first two flights last week.

I only mention this because it simplifies the design and adds a lot of convenience. I just need to think about how I set up the ailerons doing it this way, I think I can do it.

Martyn K24/01/2017 15:52:22
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4998 forum posts
3658 photos

Cheers Colin. The risk with something that needs a lot of force to separate it, is that there is an increased risk you'll break it in the process. I was going to use a magnet to secure the lower wing but have since decided against in..

I cant wait to see how you progress..

Martyn

Colin Leighfield24/01/2017 16:02:38
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5965 forum posts
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I did think about that Martyn, it's certainly a risk if you give it a direct pull! Sadly I can't do anything to test the idea until I get home on 11 February, but this is a pretty simple project so hopefully I can quickly resolve what works and what doesn't.

Martyn K24/01/2017 17:18:44
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4998 forum posts
3658 photos

Just found this cracking YouTube video of a Hornet Moth. Lots of scale detail that I wasn't aware of

Watch it in HD - Full screen. Very worthwhile
Colin Leighfield24/01/2017 21:12:29
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I enjoyed that. Something about these thirties and forties flying machines that doesn't seem to date when it comes to actually flying in them. It's an element of character and personality that can't be improved on. A timeless quality that can't be substituted. When I flew the Auster AOP6, in spite of it's tube and fabric construction, it had an air of solidity and smoothness in the air that I never felt in any Cessna. It might have been more fiddly to operate and less convenient, but once it was airborne I greatly preferred it. Hard to explain really, but our wish to model these things might be some reflection of that perception.

Martyn K26/01/2017 14:45:41
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4998 forum posts
3658 photos

Still working on this. 24 days into the project, 30 days left to complete...surprise

Wing 3 is now on the board and ready to lift and add the wingtip

The ailerons on the DH87B were lower wing only, and quite long.

The plan is to use aluminium torque rods which I can also bend and crimp and make into horns. I only need about 100mm per wing - a 300mm length weighs this much:

wing9.jpg

< 1.5 grams. about 1 gram for both halves plus glue

The ailerons look like this at the moment

wing10.jpg

and

wing11.jpg

the spar and the aileron LE will be carefully built up so they are flush with the upper and lower wing ribs.Mainly 1/32 sheet balsa. I can then separate them..

With that well underway and the glue drying, I decided to tackle the upper wing mounting.

My plan - it may be a bad one - is for the lower wing to carry all the flying loads. The upper wing will essentially be a cantilever supported by pins at the root and the struts and the landing and flying wires.

So using very short pins epoxied into the wing root and short ali tubes in the fuselage root the first mounted wing looks like this.

fus18.jpg

Gently jigged into place with the correct dihedral angle set (by tilting the fuselage.

You can also see where I have had to extend the upper stringers. Its amazing how everything starts to click when you see it as an object.

There is also a soft balsa upper fairing above the cockpit that has been added and sanded to shape. The root ribs are balsa on both sides - hope it will be rugged enough.

I have spotted one 'major' error in my drafting though. The side windows should have been inclined slightly (about 3mm) - mine are vertical.. (They looked vertical in the photos - except 1. It means that the curved fairing is totally inboard of the root ribs - it should have been partly outside the root as well. Hey-oh.

fus17.jpg

A close up showing the pins and tubes.I still have to make the wing fold panels but at least they will be in the right place..

The rear cross member will also need to be reinforced slightly to carry the additional load

It's coming along though. Wing no 4 will be started tonight and probably completed over the weekend then I can think about the aileron servo and the rest of the flight gear

More to come.

Danny Fenton26/01/2017 16:45:32
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9280 forum posts
4112 photos

Looking good Martyn, you do seem to be enjoying the challenge

Cheers

Danny

Martyn K26/01/2017 16:55:13
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4998 forum posts
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Its very different. I am quite pleased with it, mainly with the engineering challenges I am facing. I could quite happily not build a 4th wing though,, A bit like pulling teeth. Still once done, then its done and I can concentrate on some of the more interesting bits, Wing fitting was fun last night.

Still dreading covering and painting though

Martyn

Colin Leighfield27/01/2017 17:15:11
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5965 forum posts
2494 photos

The structure detail is getting close to full-size. Achieving strength by structure design rather than material mass. You really need incredible patience to do something like this.

Timo Starkloff30/01/2017 17:34:30
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352 forum posts
787 photos

Very interesting building thread, Martyn! And a good video, too!

I also thought about building a small scale indoor rc model, but it is hard to find information on the web (and finding the time for drawing/building + deciding what to build). Many from my new club fly indoor over the winter. My personal experience is from 1999/2000 with a self built 80cm Depron Cirrus Moth. Todays technique has improved a lot and I would also prefer wood for better looks.

Could you please provide pictures of the indoor scale event your building the Hornet Moth for?

Best regards,
Timo

Martyn K30/01/2017 17:38:59
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4998 forum posts
3658 photos

Thanks Timo

The event is going to be held at in a hanger at RAF Shawbury at the end of March

I think this is fairly recent
best wishes
Martyn
Martyn K30/01/2017 17:42:47
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Posted by Colin Leighfield on 27/01/2017 17:15:11:

The structure detail is getting close to full-size. Achieving strength by structure design rather than material mass. You really need incredible patience to do something like this.

Thanks Colin

Basically, I enlarged the 3v and drew my structure directly on top of the 3v. Even the wing ribs are not evenly spaced. Obviously some compromises, the inner fus isn't a plywood box like the full size.

Doing it this way has helped identify some of the traps I would have otherwise walked into. Sadly the (lack of) detail on the 3v hasn't stopped me making a few mistakes though..

Martyn

Danny Fenton30/01/2017 17:56:47
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9280 forum posts
4112 photos

Just to clarify that video above is showing the smaller free flight area at Shawbury. The larger area behind the cameraman, is where the R/C competition will take place.

Malcolm's models fly well, but as they are profile depron would not do so well in the "scale" competition, they would lose heavily in the static judging, especially when viewed head on etc. But they would be very suitable for the "scale flying only" cattegory.

This video gives an idea of the other end of the hall....

Having designed and flown a model for indoor my oppinion is to work out the largest wing area you can go to and stay under the 200g weight limit. I think a 50" Cub is doable, and the wing loading would be very low indeed.
Cheers
Danny

Colin Leighfield30/01/2017 19:50:39
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5965 forum posts
2494 photos

Martyn, it's going to be an impressive scale model regardless.

Danny, the Cub is looking well sorted now, you should be in good shape for the event. I can see your point about maximising the wing area combined with lightness. You've got me interested, I want to get home and see if mine will be viable or not. If it isn't I haven't got the time to dream up a bigger lighter one!

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