DH87B Hornet Moth

[Tomtom39]

Thanks Martyn. Really enjoying reading up your thread build .

[Martyn K]

Thanks. Glad you are enjoying it. Its nice to get feedback

Appreciated

Martyn

[john stones 1 - Moderator]

Would be a nervous wreck attempting this myself, it looks great Martyn, shame about Geoffrey seemed a nice enough fella.

John

[Martyn K]

LOL. When a BMFA scale judge reviews my work and strongly suggests that I think of a way of removing a pilot before static judging, you have to take the hint seriously.

Geoffrey is not sat on a shelf in my shed supervising me. All is not lost for him

Martyn

[Martyn K]

Its been a few days since I updated this - work has progressed = albeit slowly but other personal issues have taken a big chunk of my time.

I started covering the tailplane, fin and rudder - something I had been dreading as tissue covering is definitely not a strength. A quick and careful sand down to make sure all bumps and dings had been removed and the silver esaki jap tissue from free flight supplies was carefully applied to the rudder and tailplane.

After covering one surface of the tailplane, I added the riblets - glued to the LE and the tissue

I was quite pleased - it was tight and wrinkle free - but 30 minutes later they looked like this.

 

It took me quite a while to work out what was going on - basically, I think the problem was that the tissue had been stored in a tube and was absorbing moisture from the air. I could dry and shrink it with a heat gun but as soon as it cooled it went floppy again. Didn't improve with water shrinking either.

Same problem with the tailplane. So both stripped and recovered but this time with the tissue applied wet and then doped

The toll of recovering now shows with lots of minor wrinkles which don't look quite so bad in more flattering light

(edit - in the above photo, they have both been airbrushed with silver paint on top of the silver esaki tissue). A week later and the dope has continued to work although not blemish free, its about as good as I can get it)

While this was going on and I am trying to cure my depression, I covered the upper wings (with wet tissue) and they appear to have covered OK but the wings have bowed very sightly. Nothing I can do about that - but its not excessive fortunately.

Started work on the lower wing aileron linkages.

Aileron servo fitted

and aileron bellcrank assemblies fabricated. 1/32 ply base, 24g ali bellcranks and 10BA bolt

< 1g each

and fitted - which was a bit of a faff.. The pushrod is 1mm carbon with stainless steel linkages attached with a slither of epoxy and heat shrink tubing

The aileron horns have been cut from 1/32 ply

and fitted.

I have hinged the ailerons using 2 small strips of kevlar cloth. It looks rough but this is about a x5 magnification

The gusset adds a bit of support and also a contact surface for the tissue

and then ailerons were covered

More to come but running out of time

 

Edited By Martyn K on 20/02/2017 12:09:22

[onetenor]

Very nice but to save a bit more weight cut a triangle out of the bellcrank leaving an L shape .A bellcrank does not need to be a triangle./Not a big saving but some which at this size every little helps

[Martyn K]

Thanks

I did actually consider drilling a lightning hole in the bellcrank but was worried about causing a bit of distortion.. I am actually more concerned that it doesn't bind TBH, (Lack of) Time is getting to be a problem. All these little bits are eating away into the number of days I have left to get this finished.

Martyn

Edited By Martyn K on 20/02/2017 13:18:48

[Martyn K]

A bit of an update. Its a little while but have been very busy at work and progress has actually been rather slow.

The ailerons have been fitted and tested

The lower wing covered - and covered again - see below

The tail components have been fitted. Originally managed to fit the tailplane with about +4 incidence which would have done nothing for its ability to take off. Now corrected. Hinges are tiny strips of kevlar cloth in the rudder and thread on the tailplane. Because I had to assemble the elevator in situ, I couldnt get the kevlar to fit - shame really as its much neater

I have had a nightmare trying to get the model covered. I think the problem is that the damp weather kept causing the tissue to slacken. Additionally, the use of thinned shrinking dope was causing the fus to buckle and generate even more unwanted creases

Eventually and with help from Andy Sephton and Facebook Stick and Tissue group I eventually decided that the fus was best covered with the tissue grain lateral, applied wet and then as soon as it had dried and watershrunk, sealed with with (very) thinned gloss Flair clear fuel proofer. I still had to redo several areas but its getting there.

The orange cellophane roof came from the wrapper of a packet of Jaffa Cakes - which heat shrunk very nicely indeed.

With the majority of the model covered, I added the side cheeks to the cowl from sanded down 1/32 balsa

and started fitting the Micron radio gear

Pushrods are 1mm carbon with a join (heatshrink and epoxied) where they neded to change direction

Small 1/32 balsa guides have been placed down the fus as well

The servos don/t move far enough to cause snagging.. You can also see a little of the covering problems I was having in this photo - now redone.

At the tail, the carbon transitions back to wire and is joined to a carbon horn with a length of heat shrink. No adjustments anywhere - except on sub-trims.. Soon find out if that was a good idea..

With the model mainly covered I had my fist full dry assembly. Its always nice to get this far

and

The struts were much easier than I expected. There are tiny loops fitted to the wing surfaces (which you can see on the photo above) and the struts have a small hoot at the top and a bent wire at the base that simply slide into the loop. If I have got everything right then the flying wires will hold it all together. That will be the last job after painting though

Finally, last night I started work on the undercarriage. The main and front wires had been in for a while, I couldn't fit the rear wires as I needed the wing in place. The rear wire V at the centre locates in a wire loop under the wing - allowing me to remove the wing for maintenance if necessary. It stops the undercarriage bending backwards.By the way, the wing isn't bowed - just a wide angle distortion he says convincingly,,

All smoke, mirrors and bent pins

The wheels were turned from 6mm balsa blanks - and sanded while in the Dremel. As Danny said, sand away everything that doesn't look like a wheel. Not perfect and a bit wobbly when spinning. The fairings are from 1/32 balsa with a 1/32 balsa back with a slot for the wire. Epoxied in place last night and allowed to dry overnight. They will get covered tonight then a final inspection and the fus will be airbrushed in very thin red enamel to even up the covering colours.

Then I can start on the final detail. There is still a lot to do.

More to come

Martyn

[Colin Leighfield]

It looks amazing, what a huge amount of work. It does look though that very small section balsa in a well-designed structure and light tissue is the only guarantee of getting the super light weight needed for a top class indoor flyer. The closest I've been in recent years is to build a KeilKraft Cadet from Replikit! (I built my last one in 1957, talk about deja vu)! Are you still on for 120 gms? It looks as if you will be.

[Martyn K]

I haven't weighed it for a while Colin. The CG without battery is about 50% of the lower wing chord at the moment and I still have to paint and trim at the rear. Its going to need quite a bit of noseweight. Being a bipe, I don't think I need to worry too much about wing loading but the weight is creeping up..

2 weeks to get it finished.. Getting worried now.

Martyn

[Chris Freeman 3]

Great build so far, I find my building ability reduces as the size reduces.

[Martyn K]

Progress has been ongoing but so busy I haven't had much time for updating the blog. Facebook updates happen on the fly and I can do those from the phone..

The fuselage has been airbrushed with a thin coat of red enamel and the wing airbrushed in silver. Both have added a nice colour depth which has evened out the edges on the underlying structure.

Firstly, a shot of the tail wheel.

Photos like this are really useful. They show areas that need to be tidied up which I would have missed as this is about 3x lifesize.. The tailwheel is manufactured from 1 side of the 'frame' being 1/32 ply and the rest balsa. The spring is cut from a cocktail stick with grooves cut into it (not very well).

The big challenge was to get the glazing and frames done.

Glazing was cut from the clear plastic from the base of a cake tray. Much thinner than LMS stuff.

The frames were cut from the base of an aluminium 33p baking tray. So thin that I would never dream of using them for cooking but they cut easily with a scalpel. You can also see the exhaust in this shot. Cut from a length of thin walled plastic tube, painted matt black and then flecked with silver paint (dry brushed) to add a bit of life to it.

Excess glue was peeled off the frames after it had dried

The camera isn't doing this any favours...

With that lot done, I started on the artwork. Rather I have been working on the artwork for a while.. Basically, the lettering was lifted from a photo and dropped into Draftsight where it was all cleaned up and borders added. Doing it this way, I could check it was the right size against the model. Things like the Flag were drawn from scratch and the colour lifted using a pen dropper in Photoshop

All moved around and placed onto a single sheet of A4. I needed 2 sheets as the wing lettering was too large to fit on one sheet

Two sizes of flag as the first one was too small and I couldnt be bothered to delete it.

The idea was to send these off to a commercial printer who wanted £144 for 3 sheets. I was expecting about £10 sheet max and I thought that was too expensive.. So Plan B - DIY. An eBay supplied supplied my 5 sheets of white transfer paper for £4.99 and my ink jet printer did the rest. A spray over with clear lacquer to seal and waterproof it then carefully cutting out all the shapes using a scalpel and cutting mat.

Carefully applied and it looks like this..

and

and

and

The wheel trims were printed on photo paper. I am not happy with those as the retaining nut needs to be on the inside so I'll redo those.

Just need to do some final tidying and rig it than its just about ready to crash.

Not much more to come

Martyn

[Colin Leighfield]

It looks great Martyn. Will you hit your target 120 gms? It certainly looks light.

[Martyn K]

Thanks Colin

I'll weigh it later. I think its got a bit porky due to the amount of rework I had to do, but it will be what it will be..

Martyn

Edited By Martyn K on 15/03/2017 14:14:27

[Colin Leighfield]

I understand exactly what you mean! 140 gms for mine was an optimistic guesstimate, although I'm trying very hard to keep it within the limit, which appears to be 186! It is pretty clear that if I started again I could reduce the fuselage by a few gms, but I doubt if by more than 20 and I don't think the wing could be any lighter. That is nearly all 2mmDepron, with 1/32" balsa stiffeners in leading edge and spars and a small amount of 1/16 balsa to provide strength around the large sky light in the centre section. Crucially, with a servo weighing 3.5 gms and aileron set-up that weighs about 2, the wing weighs 40 gms. That of course is only about 1.4 ozs and it feels as light as a feather, but it does put into perspective just how seriously light these indoor aces know how to build. Quite chastening really when I look at my efforts! I don't think that using this building technique I could it get light enough at this size to fly on the P51 geared motor unit.

[Martyn K]

Hi Colin

I have just been out to weigh it.

Lower wing 17g (including servo)

Upper wing 8g

Fus = 72g including radio gear but no LiPo

So far it weighs 97g but I haven't set the CG yet and I think it need nose weight.

Still got the rigging to do and some general tidying up. 120g may still be achievable

Martyn

[Colin Leighfield]

It certainly sounds as if it is. If I use the 320 mah 2S Lipo, that alone adds 23 gms, without it at the moment I am around 157. The 240 mah battery saves me 6gms and will probably give enough duration, as long as there are no c of g issues. I have to fit glazing and paint it though, so I reckon the rudder servo is most likely to come out.

It is all down to having limited time to sort things out and "trial and error" doesn't improve things. Still, hope springs eternal. By the time I finish with it tonight the picture should be getting clearer. A good sanding will offset some of the paint weight. There won't be much in the way of internal detail or a pilot though. I'm not expecting to achieve anything with it at Shawbury, but at least I hope to get it there. After that, if it survives, I will put the rudder servo back in and fly it outside, because it is looking quite good. I will have a more serious go at a proper indoor version later. I will see what I can learn on 26 March.

 

Edited By Colin Leighfield on 15/03/2017 16:45:35

[McG 6969]

Amazing what you are achieving, Martyn.

Even if you can't beat Danny this time, it's well worth trying...

Cheers

Chris

[Martyn K]

Thanks Chris

Much appreciated.. Its been very different to what I normally do and I have thoroughly enjoyed the build.. I am definitely going to build another indoor scale model.

Martyn

[Nev]

Nice one Martyn.

I've followed your build all along. I did think you were going a bit over the top with the lightness but obviously not.

I'm intrigued to give this a go myself but maybe not under the same time pressures. I will have to have a think about suitable types.

Good luck with the comp, hope you enjoy it.

Nev.

[Martyn K]

And all of a sudden....

It was finished

and

and

and

AUW less battery = just 100g.

Still need to set the CG but its not far out and of course test crash it..

Finito

Martyn

[john stones 1 - Moderator]

Very nice

[McG 6969]

Congratulations, Martyn.

Remarkable achievement... and thumbs up for the maiden.

Cheers

Chris

[Dwain Dibley.]

Beautiful Martin, Well Done.

Ditto Re :- the maiden

I hope that rug is rubber backed.....could be a health and safety issue.....

D.D.

[David Davis]

That looks absolutely lovely Martin, well done!