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Geoff's DB DH60 Moth

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Dwain Dibley.21/01/2018 22:46:54
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Looking Good Geoff, I did the same with one leading edge.....lets blame the instructions Eh?? wink

D.D.

Geoff Sleath24/01/2018 11:39:06
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Yes, let's, Dwain I'll be studying your build for the servo mounting soon.

OK, nothing very interesting to report. The top wing is just about complete there's just a few reinforcing soft balsa bits to add to make sure the ribs are secure where they've been cut to accept the plywood dihedral braces and to the interplane strut mounts (don't want them to shift after the wing's covered).

One or two things I've found that might help other builders.

1: Rather than attack the completed wing or centre section after it's completed. I cut the ribs for the top wing centre section before building. My new scroll saw was very useful for that. I'm pretty clumsy with fragile soft balsa at the best of times and had to do a few repairs when my razor slipped cutting the wing ribs on the completed structure. I intend to cut the ribs for the braces before building the bottom wing.

2. I drilled the holes for the top wing fixing bolts in the centre section before attaching the wings in my pillar drill to make sure they were vertical. Despite that, on of them was about 1mm out. I hadn't been super careful to get them exactly as the drawing because I assumed I'd be drilling through them into the mount to fix the T nuts! Wrong! The holes for the T nuts are already burnt into the platform so I should have used that as jig. Not too difficult to bodge but I'd rather not have done it.

3: Bottom wing next, which means ailerons and individual servo mounts. Again the instructions suggest building the wing before cutting out the aileron. That's a recipe for disaster for me - something will break. I intend cutting the ribs to length before building the structure. I also intend to slot the pieces which form the leading edge of the aileron and the t/e of the wing which takes the hinges to accept the ribs - I don't trust my glueing of 1.5mm rib end grain without extra support.

Pictures later to see how well I succeed.

Geoff

Geoff Sleath24/01/2018 21:32:34
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Well pre-cutting the wing ribs rather than building the wing then using a razor saw to fit the dihedral braces and separate the aileron seems to have worked OK. I find building wings quite stressful (as well as interesting!) because get them wrong and the model never flies well. I also notched the aileron leading edge and the false t/e to take the cut ribs. I chamfered the aileron l/e ready for the hinges.

Here are the pre-cut ribs.

wing build - cut ribs.jpg

And here is the lower stbd wing with the main components dry fitted ready for glueing:

wing build - dry fit cut ribs.jpg

A bit more fettling of the ready cut ribs was needed but not much and less of a problem than trying to get them the right length on an already assembled wing.

So far so good.

I was originally going to go for the cheap option of using HK film rather than 'tex but I ordered 5 metres of Cub yellow 'tex this afternoon on the basis of not spoiling the plane for a ha'porth of tar. I think I'd regret not going down the Solartex route. The black parts on the fuselage will be painted with Warbirds paint, probably brushed.

Geoff

cymaz25/01/2018 06:51:32
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Geoff ...will you be adding LE ribblets?

Geoff Sleath25/01/2018 12:01:20
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Not real ones, Cymaz. Unlike the full size, the l/e is sheeted at the top only so I'll be fitting cheat riblets like Dwain did on his. Once covered they'll show through as if they were real, I hope. I'm also intending to eschew rib stitching but will add rib tape as if the stitching was there. At this scale I don't think it matters. I also intend scale-like closed loop control to the rudder and elevators.

The kit provides parts for the early type undercarriage but the Moth I'm modelling (G-AAMY) because of its yellow/black scheme has the later type like the Tiger Moth so I've got to make one. I'm wondering about trying to make it sprung (the DB one is absolutely rigid and unforgiving). I'm sure there's a design somewhere for a 1/6 scale one.

Geoff

Geoff Sleath29/01/2018 20:03:19
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This is the scheme I'm going for and as you can see it has the Tiger Moth/Gypsy Moth later undercarriage. There was a post a few months (Gordon Whitehead?) with a design for a sprung version but I can't find it. Can anyone remember which thread it was posted on. There are some suggested designs in Gordin's book 'Radio Control Scale Aircraft' which I can use to design and make my own but it would help to see the one posted here.

g-aamy 1.jpg

Geoff

Woody4903/02/2018 09:30:47
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Hi Geoff, you will find Gordon's u/c design in the Stampe 1/4 scale thread on here - page 119. Thanks for posting your build thread - I have the 80 inch version of the kit in my loft! Regards Steve

Percy Verance03/02/2018 09:59:27
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And so have I..... smiley   Geoff, it's a while ago now - 1990 in fact - but I used the bolt holes (and the bolts themselves) as a jig to align the holes up for the wing centre section. As I recall, there were some small sections of brass tube built into the rear part of the centre section structure to take the bolts. These also functioned as anti-crush bushes when the bolts were tightened. I built the centre section up with the bolts and tubes in place, to ensure it all lined up ok. Worked out well. My only regret was not having a servo in each wing panel. But back then it was still pretty much the thing to go with bellcranks. I found I couldn't quite get as much movement as I'd have liked, although there was enough to control the model safely, a slightly improved roll rate would have been tidier.

 

Edited By Percy Verance on 03/02/2018 10:13:28

Geoff Sleath03/02/2018 13:42:50
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Thanks, Woody. That's exactly the drawing I was thinking of. I have Gordon's book which illustrates some u/c designs but not this one. I think that's the one he has on his 1/5th scale Tiggie I drooled over when he brought it to Ashbourne for our scale day a couple of years ago so it should adapt quite well to my Cirrus/Gypsy Moth at sixth.

Percy: Those brass bushes are still part of the kit. I'm going to have separate servos for the ailerons as most do these days. Back in 1990 small servos were presumably quite rare and costly. It was before my aeromodelling days but I built a Flair SE5a in 1995/6 with a central aileron servo - it was my 3rd model after my trainer and a Precedent Electrafly which was my first (so you see even then I started in electric flight )

I'm plodding on with the lower wings. Just the starboard panel to go and I'm well on with that. My method of cutting the ribs etc before the build has worked really well and a a lot easier than cutting slots for the dihedral braces and sawing off for the ailerons from the completed wing almost as an afterthought.

Geoff

Percy Verance04/02/2018 09:22:44
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6012 forum posts
109 photos

You're right Geoff, not too many mini style servos around back in 1990. There were Futaba and Multiplex ones available, but they were twice the cost (or more!) of standard jobs. They were (I assume) mostly used by glider flyers in their slim fuselaged jobs. It's funny how times change. I don't imagine anyone would consider going with a central servo and bellcranks on a model such as this these days.

I do like the way you've slotted the ribs. It surely must be a bit easier than the method normally used. I'll pinch that idea if I may.

I assumed the little brass bushes might still be in the current kit Geoff. I've yet to get as far as looking into the little bag of accessories. So far I've looked at the quality of the wood in the kit, which is - as I'd expect - excellent, as is the lazer cutting. A far cry from the 1990 kit I built first time around. Similarly, the Tiger Moth kit (which I also have) is very good too.

 

 

Edited By Percy Verance on 04/02/2018 09:41:31

Percy Verance04/02/2018 10:30:14
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6012 forum posts
109 photos

Here's what I'm going with for the ailerons in mine Geoff. Little Multiplex jobs. Not produced anymore, so I bought a slack handful while I could.... That's a HiTec 322 standard job for size comparison Geoff.

p1000232 mod.jpg

Geoff Sleath11/02/2018 12:22:04
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2273 forum posts
174 photos

Here's how the aileron fits with notched leading edge and notched false t/e for the wing. The notches were done before assembly. I use short triangular stock (not supplied by DB) as supports rather than triangular parts cut from sheet as the instructions specify - easier and better IMO.

wing build 4.jpg

I use those homemade saws to cut the hinge slots. Just bits of Junior hacksaw blades glued into short lengths of dowel and set to cut in opposite directions. They work really well and are really cheap (which is why I like them so much )

Geoff

Edited By Geoff Sleath on 11/02/2018 12:23:58

Geoff Sleath13/02/2018 14:45:26
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Well the wings are now complete and I can get on with the bit I like best - the fuselage. Whereas the wings have been built more or less as the instructions and plan, apart from choosing separate servos, the fuselage will need some redesign to allow easy battery changing as well as the motor fitting.

wing build 5.jpg

Cymaz will be pleased to see that simulated ribs and riblets have been added to the sheeted l/e. I hope Dwain will forgive me fro blatently copying his idea. I did wonder if I'd need to cut the 'ribs' with grain across so that they conform to the l/e but I found that provided I damped the part that went over the sharper curve at the front they usually glued on OK with a few breakages that were discarded. I don't use a lot of cyano but in this case quick bonding made the job easier.

The other thing to watch out for is the fixings for the interplane struts which uses split cotters glued into 6x6 hardwood supports. I drilled and glued in the cotters before building the wing. That was OK for all but the 2 on the lower wing l/e when the pin eye has to extend through both the covering and the 1.5mm sheet. In that case I glued in the hardwood support with a 1.5mm hole ready drilled abd then drilled through before glueing in the cotter.

Geoff

cymaz13/02/2018 17:18:26
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Cymaz is overcome with delight Geoff !

Dwain Dibley.13/02/2018 20:41:31
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D.D. is quite flattered that you thought the idea was good enough to copy. wink

D.D.

Geoff Sleath14/02/2018 17:17:06
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Some modifications will be needed to fit my motor. It's the same as the one in my DB Tiger Moth except for having a lower kv so I can turn a slightly bigger prop so should fit.

 

fuselage 1.jpg

A dummy dry assembly illustrates the problem. (those old 12v batteries come in useful!) The space available is only 45mm wide and the motor is 45mm diameter.

 

 

fuselage 2.jpg

 

fuselage 3.jpg

 

The 15mm wide plywood supports intended to carry the paxolin engine plate are far too beefy anyway so I'll trim them by at least 3mm each. They pass right through the firewall to the next former and also make the intended battery space more restricted than necessary. The structure is designed to cope with the vibration associated with a glow engine which won't be the case with an outrunner electric motor. I'm going to be quite generous with the motor mount because I'm anticipating the need for weight up front because the motor is lighter than an engine. I had to fit lead in the Tiggie to get the CoG right.

I like to solve motor mounting and battery hatches etc as early as possible with an electric conversion when I can easily modify or change the structure before it's all glued together.

Geoff

PS the motor is an Emax GT3526/05  and  the kv is 710 rpm/volt. The maximum quoted thrust is 3.3kg and it weighs 265 grams.  It will comfortably turn a 13x6 prop at around 8k rpm I think.  There'll be stacks of power with a 4S LiPo pack

Edited By Geoff Sleath on 14/02/2018 17:28:50

cymaz14/02/2018 17:41:42
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7330 forum posts
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That’s a lot of down force on the engine...wink

McG 696914/02/2018 19:30:41
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I'll agree with Cymaz on this one. yes

Don't you think about 30° of down thrust is a bit OTT, Geoff? indecision

Cheers

Chris

Geoff Sleath14/02/2018 20:32:24
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2273 forum posts
174 photos

Naah, it'll be rate, youth (as they say round here ) It's just to counter the enormous lift generated by having more wings than absolutely necessary. Actually there is quite a lot of downthrust, which surprises me as well as around 2 degrees of side thrust which doesn't. The side thrust means I need even more clearance between what were the glow engine bearers because of the motor's angle.

I'm thinking a lot more than building at the moment (always a danger with me because that's when I make mistakes!). I think I may be able to insert battery through a hatch under the engine and have the esc in the tank bay cooled through the abs 'engine' cover/cowl and connecting to the battery via a safety plug fitting in the front cockpit dash board. I don't normally bother with so-called safety plug/battery isolator because in my previous conversions it's been very easy to access the actual battery connection but in this case it won't be so easy with the battery hatch either in the front or underneath (as Dwain has in his conversion).

At least doing a dry assembly like this has meant I've had to locate the components and checked the fit well before any glueing apart from the doublers.

Geoff

Simon Feather14/02/2018 20:57:45
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177 forum posts
150 photos

Geoff - I may have a possible solution to your "matting down" quandary of shiny film earlier in this thread - I had some success recently matting down the very shiny finish on an ARTF Seagull Zero - see my posting in this thread here: **LINK**. Rustoleum Polyurethane Clear Matt Finish Varnish is the stuff - reasonably fuel resistant if you need that, and seems to stick well to film whether or not you have keyed the surface. £9 from B&Q or less than half the price online. Well worth doing your own test in my opinion!

regards

Simon

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