DH90 Dragonfly after-build - Page 2 - RC Groups
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Feb 26, 2012, 04:19 PM
Big gov never Works
St. Martin's Avatar
I stand corrected, Robin. Thank you!

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Feb 28, 2012, 05:29 AM
eye4wings's Avatar
I rather like the next stage of the fuselage because you can start to see the ultimate shape starting to emerge...

It is a very long tail and takes a dozen formers to support the skin - and not one of them is the same as any other - except that they are repeated later along the top of the fuselage, which has to be left open for the installation of the pull-pull wires which will be the control method for both elevators and rudder.

The first stage however is to attach the two tailplane bearers to the underside stringers. Then the underside formers are added. These I rough cut, glued on and then sanded to their final shape by eye and the 2' steel straight edge you will spot (among many other things too numerous (and some too awful!) to mention) on the bench or around. Then to make sure the formers stay straight a length of 1/8" x 1/14" cut from medium sheet is cut into each one down the centre line - or as near the centre line as I get in my usual haste! This will also act as a fixing for sheet joints.

I have to say you are honoured (though I very much doubt that is the correct word to use!) to be the first to see the interior of my workshop. It is not the most decorative of places... even my wife is not allowed in for fear she will be tempted to attack it with vacuum cleaner and mop ... and all sorts of small items lurking in dusty corners pending their being put to use become lost for ever. Fortunately the workshop is at the end of the garden, which is long enough for me to pat most of the dust and balsa shavings off my clothing before I get to the house!

Where was I?... oh yes! Good bit next - take a whole sheet of 1/16" soft balsa and glue one edge onto the junction with the side sheet. Pin in place and leave to dry.
After a good night's sleep it's really rather nice to go out to the workshop and glue the faces of all the formers and the centre stringer and gently bend the sheet round the curve and fit it in place.
Normally I don't advocate wetting the sheet (or steaming) because that is the best way to get that dreaded starved horse effect as it dries out again and shrinks.
On this occasion though I did wet a small part of the sheet at the trailing edge end because the bend is quite sharp there. The way I have found that helps avoid the ribs showing through for ever after is to apply a bit of pressure across the grain so that the sheet pulls away from the glued ribs a little, pin it onto the stringer, then pull it down back onto the ribs with the rubber bands you can see. (Thanks for the freebies Post Office!) A quick burst from the heat gun can speed the drying of the wetted sheet.
An hour or so later that should all be dry and can be unbanded, unpinned, and the excess sheet cut away on the centre line. Stand back, enjoy the effect, then do the same the other side of the centre line. Very satisfying!
Feb 28, 2012, 05:39 AM
eye4wings's Avatar
Supporting evidence for my over-hasty and disorganised nature is all too easily seen in this last post and the previous one. This time I omitted to mark the third picture to appear as number 3 in the correct time sequence - so still being marked 0 it appeared first.
On the previous post, having spent some time composing captions for the photos I forgot to press the 'save changes' box so the system ignored the captions altogether.

So my apologies to all - I should know the system's foibles by now!
Mar 01, 2012, 03:10 AM
eye4wings's Avatar
Having said that I don't build some part until I can actually build it onto the model it should come as no surprise that now is the time to be cutting out the 1/16" soft sheet for the under surface of the tailplane.
We already have the bearers for it sticking out rearwards from the fuselage, so a check with straight edge and eyeball confirms (or otherwise) that the bearers are level with the trailing edge of the wing centre section (and adjustments made if not) then the sheet can be fitted and glued to the bearers. The main spar (at elevator hinge line) and front spar (at the last fus former) are then added, after which the leading edge can be laminated from soft sheet and the ribs cut and fitted in place.
This is allowed to dry before adding the top sheet.

You will see that there is a cut-out in the main spar to allow operation of the elevator horn. This is off-centre so as to avoid conflict with the rudder horn. Both assemblies have horns cut from sheet brass silver soldered to piano wire and tube guides slipped on before making the bends that will form the connecting levers that will be glued into their control surfaces.
To avoid any possible chafing of the wire from my brass horns I bend up small connecting hooks from piano wire with loops to which I can connect the wires. To the completed connections I add a drop of adhesive so that they cannot move then loop them through the horns. The wire are of course cut over length for the servo positions and dangled through the fuselage with the fuselage nose down in vertical position.

Before inserting the rudder control assembly (from below) a length of 1/4" sheet is cut to connect to the last former and the curved underside sheet of the fuselage and is drilled to take the tailwheel assembly. Slip this onto the assembly and drill through the tailplane so as to pass the rudder horn up through it and into place. Once glued in we can add the rudder post and build the fin onto the top of the tailplane in a similar way to the building of the tailplane. The elevator horn is easily added after this. Then I fitted the foam tailwheel for the photos.
And of course it is easier to instal the servos as they are required to connect the control wires and prevent these getting tangled - although having left the top of the fuselage open it would be no great problem if they did... it just seems tidier to connect the wires as we go.
Mar 01, 2012, 06:24 AM
eye4wings's Avatar
I'm noticing a clear pattern in the number of views for the photos I post, which displays an unsettling characteristic that we blokes are not so far different from our womenfolk (whom we often castigate for their being prone to pry and gossip) in that the most interest is being shown in those photos in which the muck and general tut is to be seen.

Of course I must therefore swallow what little is left of my pride and recognise that it is not so much the model itself that excites interest but whatsoever else might be revealed lurking in the background!

Okay then - if you want to register your guesses as to what other models are represented in the various glimpses offered, that's fine with me.
Of course some are immediately obvious, and some not perhaps so clear though at least capable of being deduced following a visit to my blog. A few however have not been published and just two (so far) of these are not scale models either and therefore not likely to be guessed without access to esoteric divination methods. (If you get those - top points!)

Fire away then dust-delvers!
Mar 01, 2012, 10:50 PM
William from Windham NH USA
saltydog56's Avatar
Awsome Great !! keep up the good work, enjoyed the reading while I recover!!

I too would like to see the lurkers at least make some short coment as to encourage the author to keep going!!

So keep going!!!

Mar 02, 2012, 04:39 AM
eye4wings's Avatar
Thanks for looking in William.

Did you have the op?
Is the recovery going any better yet?

I expect you're starting to see how different my approach to putting a model together is from the conventional.

Thanks for the encouragement too... another installment coming up...
Mar 02, 2012, 05:16 AM
eye4wings's Avatar
Having got all the tail control runs installed and working the top of the fuselage can have its formers added. I did this just the same as the underside, but found that I only had one sheet of really soft 1/16" sheet suitable for bending round the formers left in my stock box. I therefore cut it down the middle, stuck one side of each to the fuselage and then bent them over as before.
The long triangle could be filled in later with some of the medium stuff that didn't have to be bent - because that area is dead flat.

I'm one of those who cannot resist the urge to see what the end affect is going to be as soon as possible. I find the long haul difficult to sustain and need to see results to spur me on for the next step. Consequently I cannot resist getting some covering ironed on as soon as possible. When there is also the excuse that it is necessary to permanently hinge the control surfaces after they and the bits they attach to are covered...

So the fin and tailplane were covered in silver Solarfilm while waiting for glue to dry on the rudder and elevators.
These are of such simple construction that I didn't even think to photograph them! Next morning they too were covered in silver and promptly attached to the airframe.

Now I could complete the tail cone - which was a complete bodge-up! Softest bits of scrap balsa I could find and all sorts of odd shapes that could get stuck together to make it were stuck together. I probably added more weight in glue than balsa in the process, but here it is anyway...
Mar 02, 2012, 08:57 PM
Registered User
destrat's Avatar

I'm one of those "lurkers" you are refering to and to let you know that ordered Robins plans for the DH90 and just picked up th wood for it. At the moment I will be in the process of cutting out all the parts. Robin has asked me to post into his thread whenever I might have something that would be of interest to any of you guys as I proceed with my build hopefully drumming up more enthusiasm.

Stay tuned....

Mar 03, 2012, 03:02 AM
eye4wings's Avatar
Welcome Dan!

In case anyone hasn't realised, this thread was born out of William's DH89 thread on which Dan asked me to post more detail of the DH90 as he had bought my plan. I felt that although the two types were closely related it would be a bit 'off topic' to post there and that it would perhaps also be a pain for anyone who wanted to follow either model to skip over the other. So I started this thread so everyone knew what they were getting from the outset.

There are in any case distinct differences between the two models in that the DH89 William (and a friend of mine over here) is building was designed some time ago for I.C. power while mine was designed at the outset for electric power, which makes quite a difference in the design strategies employed.

In the DH90 DeHavilland were using a revolutionary new rolled ply technology for the first time and producing in effect a 'stressed skin' aircraft - although in wood - and I attempted to reflect that in the design. Thus the only stringers I include in the tail end of the fuselage are actually only there to provide enough wood to provide purchase for pinning on the skins while the glue dries - although they do obviously also provide added strength as well.
Mar 03, 2012, 04:40 AM
eye4wings's Avatar
Just to tidy up matters around the tail end before progressing to the wing, I'll post a picture taken after the wings were completed...

In fact the top of the fuselage is best left without the top skin for a while because it will mean far easier access while the connections of the top wings are installed. These are fixed in place by hook levers pivoted on a cross member that will give added support to the roof skin and hook over wire loops left projecting from the top wing root. In fact, having done it that way, in practice, largely because of my lack of metalwork skills (and tooling) I think the same job could be done easier with the same loop and pin system that is employed in the nacelles for the lower wings.

Anyway, the tail and control surfaces are better shown in this later photo taken after that glossy red had been given to the fuselage...
Mar 04, 2012, 04:04 AM
eye4wings's Avatar
In the process of drawing up the wings I had counted up that there were about 138 ribs required - and because of the taper and the fact that lower and upper wings were different lengths VERY few of them repeated and I was therefore facing the prospect of cutting out every one individually and only being able to use any one of them as a template for its opposite number once each.
As I mulled this over it seemed to me an ideal opportunity to enjoy what many of you scratch builders enjoy - simply putting my wings together from a kit of laser-cut parts. This I have never done before, all my drawings being hand drawn the old-fashioned way and once the prototype has been successfully test flown transferred to CAD for publication.

The deal was that I would pay a modest sum for the wing kit and the cutter would have the right to sell the kit of my whole design. Fair enough I thought, but by the time I got my kit of parts the supplier's computer had crashed, losing all his data, and it seemed the deal was off. I tried to use the parts but it dawned on me (perhaps I should have noticed earlier?) that not only had he taken upon himself the right to slim the wings down to what he thought was more scale but he had ignored my means (shown on the drawing I sent) of achieving tip washout and I would have to make some tricky adjustments such as inverting the part spar at the aileron junction.

Now I design and build light, but although I do take a certain amount of pride in the lightness of my building I allow enough meat in the various parts so that someone with perhaps thicker fingers than my own can have a reasonable hope of making a decent job without breaking bits left right and centre.
As my design called for the insertion of two tapered spars through slots in the ribs I could see from the outset that even I was going to be hard put to doing it successfully... and in the event I broke many of the ribs and had to glue them back together.
But even though some of the parts were cut from the wrong thickness sheet and sheet that was clearly rescued from the scrap bin I put the wings together as well as I was able, replacing only the Bass spars with Cyparis in one length in stead of the spliced ones supplied.

So here is the photographic record of that stage - but do please bear in mind that what you see here is not what you would get if you purchase the kit of parts from Traplet... there is more of the story to come!
Mar 04, 2012, 05:54 AM
eye4wings's Avatar
Once the wings were made up it was time to instal and connect the aileron servos.
I simply fitted a piece of 3/32" medium balsa flush with the underside of the wing, cut a slot in it for the servo output arm to go through and glued the servo to it. In the event of having to replace the servo I would have to cut through the covering on top of the wing and iron a new piece on afterwards... no big deal.
I cut the lead off the servos leaving only a couple of inches of wire, which I bared and tinned ready for the extension wires.

Now for several models I have been using audio DIN plugs and sockets to connect wiring at all the junctions where parts detach. These are much more robust than the D9 or D15 plugs that many others use and are more able to tolerate the inaccuracies of my construction, so I have standardised on them now and, even though I was not planning any fancy lighting on the model and only had one servo only requiring three pins, I used them anyway - just for their ruggedness.

The pins are in the wings and sockets in the fuselage. Could be the other way around I expect - that just seemed the 'natural' way round at the time.
The fuselage sockets were installed first and the plugs glued in position with the wings in position on the fuselage. Make sure they are as true as possible to the line of the horizontal and not the dihedral angle of the wings as the piano wires cause the wings to move in towards the fuselage in the horizontal.
Mar 06, 2012, 05:59 AM
eye4wings's Avatar
During the covering process it is possible for light-weight wings like these to become distorted out of shape but one problem I didn't think one should expect occurred as I tightened the top sheeting - the trailing edge broke all those flimsy connections with the ribs and cocked up several degrees. I hastily tightened the underside too and guided the T.E. back into level position with horrified visions of having to rip it all off and strengthen the joints, but feeling the resulting wing I felt it was at least good enough for a first flight and left it well alone.

The final rigging of the wings is by 7-strand 'Pike wire' from the local fishing shop. They also sell (at considerable outlay) ferrules, but I have found these to be very difficult to feed three wires through and have gone back to cutting short lengths of brass tube to do the job. The fixing positions are achieved by drilling fine holes in the tops and bottoms of the struts and feeding the wire through these, using the brass tube ferrules for wire ends only.
This means that it it still possible to adjust the AofA of the wings a little before running superglue in to fix the wires permanently in position.

Now back to the fuselage to finish off the top sheeting and at last get the covering on.

I see that the first construction shots were take at the end of Nov 2009 and the ones below are dated 9 Feb 2010 so that makes about 14 weeks for construction so far. Not out of the ordinary for a medium-sized model like this. At least I wasn't thinking 'will it ever be finished?' by this stage!

The registration letters were printed out in greyscale on my ordinary printer paper, a thin coating of Balsaloc applied, cut out from the sheet, ironed onto the airframe and finally sprayed over with clear finish lacquer to give a measure of weather-proofing.
Mar 06, 2012, 11:30 AM
Registered User
yel914's Avatar
Enthusiastically lurking...and enjoying every bit of it! Can't wait to see the completed project.

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