DeHavilland DH90 Dragonfly

[Steve Rickett 2333]

Hi Pete,

I'm working really hard to try and reduce the amount of lead needed but I'm sure it's going to be more than the 5lbs I've estimated. I'm sure the airframe will be able to carry the extra weight.

The plug will have two heavy duty female mould halves taken from it, and then the final cowls will be laid up inside these moulds. They'll be in at least 3 sections...but I won't confuse you by try to explain just yet.....once the weather has warmed up a bit then I'll post the process!

[Steve Rickett 2333]

A ply battery tray has been installed to take the load of 6x A123 batteries (3lbs) and 2 x Jeti Max BEC battery backers and regulators. Onto this plate I've made a battery box from 1/8" ply to keep the batteries secure during my wild flying schedule.

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I'll add a keeper to the front of this box to hold the batteries firmly in place.

I've also added the last of the rear 1/4sq stringers. I'll let the photos describe the process, but thats a 1/4" wide permagrit file doing the hard work....

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[Steve Rickett 2333]

I've also added a bit of sheeting around the windows....1/8" balsa adds some strength to the 1/64" ply outer skin. Note that the 1/8" balsa has been cut undersize so I now have a lip to glue my acetate windows to....

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Cutting the main longeron out to make way for the door was a little bit scary!

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[Steve Rickett 2333]

The compound curves of the nose are going to be planked in balsa so I started off by cutting out the base of the cockpit framing from 1/8" ply.

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I added a few formers in the void...but forgot to take a photo! So the finished nose is up next....

I cut 1/4" wide, 1/8" balsa planks and glued them with aliphatic...

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[Steve Rickett 2333]

The next job to complete was the rest of the fuselage sheeting. 1/64" ply cut into manageable sized sections and glued with aliphatic again.

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[DAVE JOHNSON]

Steve--another stunning job---really looking forward to seeing this on the circuit-----DAVE

[Steve Rickett 2333]

Thanks Dave,

Hopefully I'll be able to persuade my Dad to bring his Dh86 to a few more events once the Dragonfly is done!

[DAVE JOHNSON]

All we need then is to convince Ted to bring his and what a slot that would be

[Peter Siggins]

Stunning build Steve - I looked on rcsc and wondered how you had supported the nose planking.What brand of aliphatic do you use for planking?
Better put some guns on it to keep Phil happy

Pete

[Stuart Solomon]

Blimey Siggy, don't tell me you've opened your wallet lately and paid your leccy bill ?
Never seen so many moths

[Peter Siggins]

Careful Solly or I'll post you some anobium punctatum

Sorry Steve needed an answer

Pete

[Steve Rickett 2333]

No problems Pete, I'm afraid I didn't take a photo before I planked the nose. I added just one former that sits at the front of the battery box...

I use Deluxe Materials Aliphatic glue. Been using it for years and really like how quickly it 'grabs' and that it is really easy to sand once cured.

I got the fuselage lifted off the jig yesterday...thanks for the lift Phil! I'm really pleased with how rigid the structure currently is, once the final sheeting goes on the undersides then it'll be rock solid.

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I also separated the rear fuselage section for the first time. I'll re-attach this before I do anymore sheeting...

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[Steve Rickett 2333]

I've flipped the fuselage over to work on the undersides of the nose. First off was to think of a way that I can get the last of the ballast onboard. I've built a box out of 1/8" ply and opened up a slot underneath the battery tray. I should be able to get upto 6lbs in here (though I hope I'll only need 3). This box has been epoxied together and bonded to the strong battery tray. I've wrapped one of the formers around it too so it will be held firmly in place. That access hole will have a hatch cover screwed over the top when complete.

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[Steve Rickett 2333]

Before I seal up the nose for good, I need to install some of the wiring. I'm using two completely separate RC systems. Each system has 2x 2500mAh A123 batteries feeding into a Jeti Max BEC unit and then into a Futaba 7008SB Rx.

I needed to make up some extension leads/adaptors for the connection between the Jeti and the Rx. I have decided that, seeing as the Rx's don't weigh anything, I'm going to fit them inside the cabin (by the door so I can get my big chunky hands inside!). I like to have as much redundancy as I can with power connections.....so I'll show you how I like to do it....

The Jeti comes with a female Multiplex connector as standard, I quite like these as it means three pins for Negative and three for positive.

I bend the solder tags slightly together....

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then solder 2 x 20 AWG silicon wires to each terminal.

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Secure the solder joints with Heat shrink tubing and then get plaiting!

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The other end terminates in two self crimped Futaba female plugs which both plug into the same Rx.

Why? You ask!

This provides a 'ring main' system. Sever any part of the power supply line and everything will still have power. This caters for broken wires, disconnected plugs as well as spreading the current load through two cables.

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This is one whole power system connected for testing...

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And both of them.....

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The cables were then installed into the awkward-to-reach areas before sheeting and planking began!

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Width ways grain across the flat section and then length ways 1/4" x 1/8th strip wood for the planking.

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[Steve Rickett 2333]

I got the planking finished off this morning...

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[Steve Rickett 2333]

Back at the tail end the past few days.....

I've mounted the Rudder servo inside the removable section of fuselage

Thats just a 1/8" ply plate and a 1/4" sq cyparis beam to support the plate. I'll add some local reinforcing around the edges once dry....but not too much as every ounce here needs about 4 ounces to compensate in the nose....

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I am using one 3mm bolt to hold on each tailplane half. Access to the bolts is just a length of nylon tube that exits underneath the tailplane and the other end stops just short of the bolt. There is not enough of a gap to allow the bolt to fall out and the flexible nature of the tubing makes it all self align very easily. I wrapped a bit of carbon tow as a lazy way of making a bracket....think it might be lighter this way...at least, that is my excuse!

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Before the bottom sheeting could be applied, I made some strengtheners to support an access hatch on the bottom. This hatch allows me to get to the rear fuselage mounting bolts...

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The remainder of the 1/64" ply skinning was added while the fuselage was held straight and true with some simple jigs.

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[Steve Rickett 2333]

The cover for the access hatch was built out of Lithoplate and balsa. Two magnets glued to the hatch and...

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...two glued to a balsa support inside the hatch.

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A small lip was bent into the Litho to allow the hatch to be 'picked' off.

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I've also shaped the nose and tail plugs and first coat of resin applied....thought I'd glass the fin while I had some resin mixed!

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[Steven Weir]

All that weight up the front is very good...but I am 100% certain that it won't be enough to get the balance point in the right location. With such a short nose, and a loooong sheeted tail I can admit defeat right now and accept the inevitable 1/2 a church roof of lead. With this in mind, I set out a very rough sketch of the airplane and the weights of key assemblies and used my rather no existant Maths skills to produce some moments. (head scratching moments mainly).

I won't bore you with the gory details but suffice to say that I estimate a whopping 5lbs of lead up the front to get the correct CG. Clearly this is only a guesstimate, but it gives me a rough idea and means I'm not so shocked later on! Securing such a large chunk of 'hardware' to a sharp and pointy nose is never going to be easy so I've elected to build some of the lead permanently into the structure. This way, it'll not take up any space, can't break loose and will give them impression that I've built this thing with only a tiny bit of ballast required (shhhh, don't tell anyone.)

So, that's two ounces shy of 3lbs epoxied into the void between the fuselage skins. It won't be enough...but it's a good start.

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While fettling the fit of the formers I had to pre-assemble the two formers that make up the fuselage join. These are made from hard 1/4"balsa with 45 degree joins so that the grain is always traveling across the 'span'. 1/8" ply load spreaders were cut out by tack gluing four bits of ply together and then cutting them all out at once......

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M4 blind nuts installed to the rear of the pair of formers and then installed in the fuselage. I've added some 1/16" packing between the formers to allow for some ply facing and also the thickness of the fiberglass and paint. It also gives me a bit of clearance for a hand saw when it comes time to chop the tail section off.....but I won't do that until the sheeting is in place.

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Hello Steve Just had to comment on this build, first look at your impressive dragonfly beautifull model, my uncle used to fly one of these in the early 60s lovely aircraft, will keep an eye open for more photo's and good luck with the build.

[Steve Rickett 2333]

Thanks Steven, I hope to get a little bit more done in a couple of days and will post some updates soon!

Thanks for looking in.

[Philip Goff]

Steve,
I must admit I enjoy reading your build threads,
they really are a joy to behold.

DeHavilland certainly made some beautiful aircraft.

Regards Phil G.