Geoff's DB DH60 Moth

[Geoff S]

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.

Geoff

[Woody49]

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

[Former Member]

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[Geoff S]

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

[Former Member]

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[Former Member]

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[Geoff S]

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.

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 S]

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.

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

[cymaz]

Cymaz is overcome with delight Geoff !

[Dwain Dibley.]

D.D. is quite flattered that you thought the idea was good enough to copy.

D.D.

[Geoff S]

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.

 

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.

 

 

 

 

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

[cymaz]

That’s a lot of down force on the engine...

[McG 6969]

I'll agree with Cymaz on this one.

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

Cheers

Chris

[Geoff S]

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 Feather]

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

[Geoff S]

Thanks Simon. I've actually bitten the bullet and 'invested' in a 5 metre roll of Cub Yellow Solartex (just a few days before Solarfilm announced their closing) so that's what I'll be using on this build. However, I seem to have got into building scale models from the so-called golden era (the late 1920s/1930s so not quite as golden as we like to think) so I could well take advantage of your research.

Pretty all I build these days is electric or electric conversions so fuel proofing isn't an issue. However, I have a Hurricane build in the offing which will be Laser 80 powered so fuel proofing will be needed in that case.

thanks again.

Geoff

[Geoff S]

A little more progress. Whist cogitating on the motor mount/battery access modifications I made an effort to reduce the number of parts still in the box by building the tail components. I did bui;ld over the drawing but really with CNC cut parts it's more a matter of assembling and using the drawing as a guide as to which part fits where. I think, apart from waiting for the aliphatic glue to set, it's as quick as solid sheet because the parts just fit neatly together. I added a couple of extra corner pieces cut from left over scrap balsa to the fin post. Probably unnecessary but that fin post carries a big powerful rudder and the extra weight is negligible. The tail is very light which will help the GoG.

Having cogitated, I trimmed the 9mm x 15mm plywood engine plate supports by 5mm each (except where they pass through the former) to give a bit more room for the motor. Then hacked out a motor mount plate from 6mm ply. Once the fuselage is almost complete, I'll decide where it needs to go to put the prop in the right place and then I can determine the offset to bring the prop into the middle with the required right thrust (I think it's around 2 degrees).

Geoff

[Geoff S]

This puzzles me a bit. The instructions state:

"The 3x5mm diagonals 123 are set back from the external surface of the fuselage."

I can't see why that should be unless it's some scale feature but there's lots of scale features that are ignored (closed loops for the rudder and elevator or the tail plane struts for instance). I think I'm going to ignore the instruction and just fit the diagonals pinned to the board.

Actually the next line says little about a lot

"Build the port side in a similar manner"

Not so easy as it involves actually cutting strip to fit accurately rather than simply assembling CNC cut parts as for the tail. Dwain mentions building the port side over the starboard with an intervening sheet of film (I use cling film) to stop joining them together.

The build isn't too difficult for someone with a little experience but I would think it quite difficult for a total beginner. At least I know the end result will be a good flyer.

Geoff

[Geoff S]

I'm trying to fit the cabane but there is a discrepancy between the parts supplied and the drawing. All the drawings I was involved in at work were circuit diagrams but they used the same paper as mechanical ones and all bore the legend in big letters "Do Not Scale". In view of the dimensional uncertainty of those old smelly blueprints perhaps that was sensible but we aeromodellers have no alternative because the drawing we work to are usually undimensioned. We have to scale the prints themselves.

It seems to me that the supplied cabane piano wire supports are 3mm longer than the drawing (which is the thickness of the top wing platform. The platform has cutouts in the corners which have no purpose unless the spruce parts of the cabane extend upwards to glue in them. In fact the front corners have bigger cutouts which I guess are to accommodate the angled front support.

I'm just steeling myself to cut 3mm off the ends of the piano wire before glueing the spruce and wire together so I can fit the top wing.

Another difficulty I'm having is how to ensure the top wing is exactly symetrically positioned wrt to fuselage and in line with the bottom wing (which is now fitted and with tips equi-distant to the tail). I was expecting to fit the platform and cabanes then put the wing in place held at the front by the wooden hooks. It would then be possible to swing the wing slightly to get it exactly right, then drill the holes for the captive T nuts. Unfortunately, the T nut holes are predrilled which means the only method of minor adjustment is to move the whole platform a fraction.

It may be OK assuming my building is accurate to a degree I'm not normally guilty of If not, I'll make another platform and drill the holes after assembly.

In the meantime here's a picture of the fuselage as it is so far:

The rear cabanes are held in place temporarily with cocktail stick dowels, which hold it surprisingly well.

The motor is fitted at the correct down and right thrust. I had to make a new front plywood former but just had to fettle the balsa front a lot for the motor to be far enough forward. When glow engine is used the hole only need to be big enough to allow the prop shaft through but the motor itself needs to be close to the front in this case.

 

 

There were a few adventures earlier which I won't bore you with. Suffice to say progress is being made

Geoff

Edited By Geoff Sleath on 23/02/2018 15:28:31

[Dwain Dibley.]

Geoff,

I think I made a slot for the extra piano wire in the side of the fuselage Mate, as I too was reticent to cut them.I then made the aluclad plates to cover them, to replicate the plates on the full size.

D.D.

[Geoff S]

That's slightly reassuring, Dwayne. I thought you'd had an issue with the cabane fitting but I couldn't find it on your build blog. At least I know I'm not deluded (at least in this respect!). I've just finished cutting mine .

How did you fix the platform? I'm not super keen on the stitching method as it doesn't allow any minor adjustment to get the wing correctly aligned assuming you can't do it by moving the wing on the platform (which you can't with the CNC cut parts). Perhaps it won't be necessary. I'll find out soon.

Geoff

[Geoff S]

Managed to do a trial fit and actually have something that looks a bit like a bi-plane, even a DeHaviland bi-plane.

The bottom wing is properly fitted but the top wing is held with a combination of clamps, elastic bands and will power. Surprisingly, everything seems to be quite square. The top wing is parallel to the bottom one and both are square to the fuselage. The distance between the wing tips is about 4mm different (in 260) but considering the jury rigging I think that will be fine when it's all assembled with inter-plane struts etc.

One item of concern is that the piano wire fixing to the wing platform runs right along one of the lines of holes intended for stitching rather than between them on both front and rear, which means the stitching won't work so it will have to be glued on.

Geoff

[Former Member]

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[Geoff S]

Thanks Percy. As I mentioned, it all turned out to be square anyway but it would have been nice to have a little wiggle room if necessary to get the wing at the correct angle.

I guessed the cutouts were supposed to take the wooden part of the cabane struts (as did DD) but with the supplied piano wire being too long (even by only 3mm) making them too short to fit in the cutouts it threw me for a while. It's not shown - or at least not clear.

The instructions suggest covering the piano wire with masking tape and epoxying to the underside of the platform as an alternative to stitching. Certainly masking tape works well as an interface for glueing things like snakes and it certainly sticks well to the wire on the upright section of the struts. I've no real problems with the stitching except that the ready drilled holes are exactly covered by the piano wire so I'd need to drill 2 more rows which might weaken things too much. I certainly won't try bending the piano wire.

Once I've got the cabane sorted out I'll put it on one side and fit it after I've almost completed the fuselage. Battery hatch and mounting; cockpit openings; cowl etc etc. Still plenty to go at and these problems make the build more of a challenge and add interest.

Geoff

[Former Member]

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