Andy's Drak

Andy Sayle · February 09, 2016, 11:47:37 AM

Rather than jump all over Mutley's thread on his Drak build, I thought I'd do my own. I ordered a nice pair of Draks (Draken? not sure what the plural of Drak is.) last year after seeing the kickstarter that Chris of Ritewing did. It looked like it would fit my needs perfectly.

I wanted something bigger than a fun jet, but a similar layout. Something that can cruise fast, and carry a decent payload. Something that is robust and can handle rough landing sites. The Drak will do all this, it looks a bit like a funjet if I take my glasses off. And squint. Quite a bit of squinting actually. Its the right layout anyway, pusher, eleven controlled, pointy nose. And it has a vast fuselage. Really big. And if that wasn't enough, there are two saddle bays in the wing roots too! Just the ticket.

Feeling flush, and after selling a few multirotor kits, I ordered two. The idea was to build one up for fast FPV action, and another to have a foray into mapping, with a down facing CSC camera in the fuselage. There should be plenty of room for my Sony A6000 to mount nicely.

The kits came, and I have cleared my workbench for the build. Sort of. The workshop is like a bombsite. Organised chaos you could call it. The quality of the kit is outstanding. The EPP foam mouldings are all great, a silvery grey colour and quite high density too. The foam is very sturdy, but with a little bit of give. It should take an impact very nicely indeed. The downside to this is a bit of extra weight, the foam components don't feel as light as they perhaps could be. You can't have everything though, and as this is never intended to be a lightweight floater of a model, Mr Ritewing made a good choice. The accessories are great too, some cleanly cut Correx fins and compartment lids, a bundle of spars, a bag of thumb screws and some threaded inserts, a formed ally motor mount and a roll of laminate. So, on with the build! Oh, have a look here: http://www.fpvhub.com/index.php/topic,48115.0.html for some nice pictures of the Drak components, along with Mutley's choice of equipment that he is putting in his... I'll decide the stuff to go in mine, as I go along I think...

First up was the elevons. These are foam, and are designed to have some 1mm glass spars bonded in with Goop. Before this can be done, some EPP lumps need trimming off, these are presumably part of the moulding process. I used a new snapoff knife blade to cut the lumps off cleanly, and accidentally cut a bit of my finger too. Blood all over the place, which has to be a good omen right? Any model that draws blood is going to be good...

The moulded grooves for the spars stop just short of the end of the elevons, so I melted the slot out on one end to extend it. This will allow me to leave the spars too long, but have something to hold on to whilst manipulating them in the slots (and not getting myself covered with Goop!). I taped the elevons down to the workbench to hold them flat, ran a bead of goop in the slot and pressed the spar in with a rolling action. This should make sure the spar is evenly bonded in the moulded EPP slot. I had to press it down a little to get it to the bottom of the slot, using a little pokey stick. I then ran another small bead of goop over the top, and smoothed it out using a wet fingertip. This is being left to dry for a day whilst work gets in the way of things...

I also did the top side of the wings whilst I had the fans on (did I mention Goop stinks!), these have two spars in the top, and two in the bottom. No pictures yet, phone battery had died....

I'll do the other sides when they are properly dry, although the wings need to have the spar tubes bonded in first.

More later.....

Andy Sayle · February 09, 2016, 11:50:28 AM

Oh, did I mention I ordered one of the motors and ESC's that Mr Ritewing sells specifically for the Drak? Well I did. Very nice quality motor, and the ESC looks like an ESC. We shall see how that works later, as that is getting installed in the mapping machine. This will be built reasonably lightly. The FPV machine though, I am debating whether to put an "adequate" powertrain in it. Roughly translated, that means stupidly overpowered....

We shall see....

Coyote · February 09, 2016, 12:56:36 PM

Cool another build ! Like a bit of variety :)

Cockney Boy · February 09, 2016, 02:30:03 PM

Proper tempted to buy one but it would be packaged in Divorce papers :(

Billy_boy_2010 · February 09, 2016, 11:38:46 PM

Looking good so far.

Please tell me you're running it on 6s. Seems the perfect plane for a fast 6s setup but with the potential for a semi sensible cruise current?

Andy Sayle · February 10, 2016, 12:23:46 AM

I'm in a dilemma with the power setup. On the one hand I have the ritewing motor and esc, optimised for 5s. On the other hand I could ditch those, and fit a setup for 6s. Or even 8s. I use a fair few 4s packs on other stuff, so doubling up in series would be an option... I think I may stick with the ritewing setup on the mapping plane, and have some fun with the other...

wgt40w · February 10, 2016, 10:28:33 AM

Quote from: Andy Sayle on February 10, 2016, 12:23:46 AM
I'm in a dilemma with the power setup. On the one hand I have the ritewing motor and esc, optimised for 5s. On the other hand I could ditch those, and fit a setup for 6s. Or even 8s. I use a fair few 4s packs on other stuff, so doubling up in series would be an option... I think I may stick with the ritewing setup on the mapping plane, and have some fun with the other...

If a mapping plane is flown too fast, at an unsuitable low altitude, might that mean:-

1) You get insufficient image overlap?

2) Images are slightly blurred?

Andy Sayle · February 10, 2016, 10:33:59 AM

That's what I'm thinking too. I've slept on it (not literally) and I think I'll use the Ritewing setup for the mapping beastie, mainly because I already have it. And as for the FPV ship, that shall be treated to a monster of a powertrain. I'm going to have a look at ecalc now, and run some numbers to see what sort of motor I should be aiming at for a big power 4 or 8s setup. I'm leaning towards running a pair of 4s in series, and getting the power from voltage, rather than high currents. That way I can use a lighter ESC, cables, connectors etc.

Oh, and bragging rights ;)

Andy

Andy Sayle · February 10, 2016, 01:06:57 PM

This build is great. It's been a while since my building mojo has been in attendance, but this kit is going together really nicely. It seems to be really well thought out. Anyway, here's some more pictures too, of things like the moulded in spar grooves, and where I melted the ends away a bit so I can keep the spars too long, which makes them easier to manipulate when covered in Goop. Which, incidentally, is possibly the second most sticky substance known to man. The first being snot from a 2 year old. The glued finish is pretty good. It seems that most of Goop is solvent that disappears overnight, leaving about 50% of the stuff behind as a tough rubbery layer. As a result, the finish is not nice and smooth like when it was applied, but it leaves behind a little trench. I may fill these in. Then again, I may not. I'll probably laminate the fast FPV ship wings, so it's not essential there I reckon.

There should be some pictures of the motor mount. This is an ally plate glued to the fuselage, and with a covering foam moulding over the top, to make a sandwich. There is then an adjustable folded ally part that motor bolts to, and this can be positioned fore/aft to suit on the plate when it is glued in. This was a bit of a pain to get lined up when bonding, as the parts tended to slide about a fair bit. I used plenty of Goop here, and a bit of pressure from some clamps to squeeze the excess out. You can't see, but I put a few pins in to hold it in the right place overnight.

The end result is a really strong motor mount, with a tiny bit of give in the foam. Perfect for absorbing knocks on landing. Oh, the formed motor mount bit, can also be orientated so the motor doesn't scrape on the ground on landing. Clever stuff from Mr Ritewing. Surprisingly light too!

Next job, is spar tubes. Measure these to length, and cut using my trusty razor saw. A new blade would have helped here, but who wants to wait around for a delivery of new blades?! Make doubly, no triply sure that you remove the actual spar from inside the spar tubes here! They are shipped one inside the other, and the last thing you want to do is cut the spar at the same time as the tube! I wrapped a bit of tape around the tubes before cutting. It helps stop splintering of carbon tubes I find...

Once they are cut to size, I took the shine off the tubes with a bit of 120 grit sandpaper, used very lightly. This should help get the best bond, not many adhesives like shiny surfaces. Wipe down with alcohol to get the dust off, and they are ready to be installed in the wings/fuselage. I did an alignment check on the dining room table (Shhh, don't tell SWMBO), and the alignment is pretty good with no adjustment needed. The tubes were bonded in along the bottom with Goop, and left to cure overnight. I'll glue the foam caps in place when this is set, so not to risk them moving about too much.

That was it for last night, the Goop fumes were making me dizzy.

Andy Sayle · February 11, 2016, 10:52:45 AM

Another couple of hours spent on the Draks last night. As the spar tubes are nicely bonded in place, I couldn't resist a quick assemble to see what it looked like. A decent size is probably the words I would use to describe it. I did notice that the Goop drying had pulled one of the spar tubes slightly off centre. Not so much to cause any major issues when assembling, but enough to be noticeable. It might be worth pinning the spar tubes in place to stop this happening if I ever build another.

Now spar tube caps. These are more EPP foam mouldings, but they are quite a loose fit in the slots. Apparently this is so that a foaming adhesive can be used, and allow the spar tubes to be positioned perfectly. Given the fact that accurate airfoils can be made in EPP, I'd like to think that a nice fitting spar tube recess could also be made Ah well, out with the foaming polyurethane glue. I'm going to mix this with some quality American wood glue, to make sure it foams up nicely. The PU glue basically reacts with moisture, which it gets from the wood glue. Any pva, or white glue would do the trick. Even using a small bit of water would probably work too.

I followed Mr Ritewing's build video for gluing these caps in. A smnall amount of foaming PU glue on the spar, a bit of goop on the EPP-EPP bit, and a bead of hot glue around the top, to ensure the small bit of foam doesn't move, whilst the other glues foam up, and move around to fill the gaps up. A good tip is to not put a massive amount of the foamy glue on here. After a few minutes it all starts to get a bit messy.

Once all the spar caps for the wings were in place, I did the fuselage spar caps too. These are much bigger chunks of foam, so it takes a bit of preparation, and speedy work with the hot glue gun to get them held in place before the foamy PU glue starts expanding.

Whilst I had the hot glue gun powered up, I also did the bottom of the fuselage stringers. These are done in a similar way to the wings, with the exception of the slots not being straight. I used a bead of goop on the straight bits, and hot glue on the bendy bits, and a number of T pins to hold the spar in place whilst everything sets. I'll do the top sides on the next building session, as well as trim excess glue and fill any gaps left on the spar caps.

After that, I think most of the gluey stuff, is done, and it is on to painting/laminating/making stuff look pretty. Oh, I better route some wiring before the laminating too.

mutley2 · February 11, 2016, 11:49:22 AM

Coming on a treat, my capping's were a little short, good to see your are the right length.

Andy Sayle · February 11, 2016, 12:30:00 PM

I was quite glad too. They are far too long for the wings, but about 10mm longer than the slots in the fuselage. I'll trim them back with some side cutters when the glue is cured/dried/glued.

I forgot to mention above, that the spar cap mouldings in my kits, were about 5mm too short too. I whipped out SWMBO hairdryer, warmed them up, and stretched them by hand. It worked a treat.

Billy_boy_2010 · February 11, 2016, 08:12:13 PM

Looking good so far.

It's a really quick build by the looks of things.

Really must resist!

Andy Sayle · February 12, 2016, 11:46:54 AM

Yeah, it is going together quickly. So far, I'm impressed with the kits. There are a couple of little niggles but that is just me being really picky, like the spar tube foam caps being a little distorted or on the small side, but I can see my Mr Ritewing has done it that way. Including the control horns and links would have been a nice touch too, instead of having to buy them separately (guess which bits I forgot to order!).

Oh, and, Resistance is Futile. Apparently....

Andy Sayle · February 12, 2016, 11:47:57 AM

Here's another build update too. It was just a quick building session last night. First up was to inspect the foamey PU glued in spar caps, and see if they have distorted or gone wrong at all. Other than me putting a bit too much glue mix in, and it foaming out of the ends, it seems to have worked really well. I had a few little puddles of cured foam on the floor of my little workshop, but luckily I put a sheet of plastic down to catch them! These trimmed off fairly easily with a sharp knife (that bit me. Another Drak related injury). On a few of them, there was a little bit of glue that had crept into the spar tube. Again, this trimmed off nicely with a sharp scalpel, and a little bit of sanding.

Once these were cleaned up, I installed the remaining little fibreglass spars on the underside of the wings, and top of the fuselage. Exactly the same methods were used as before, so no pictures. I also filled a few of the gaps in the spar caps with some Goop whilst I had a fresh tube open.

Once that lot is dry, I'll glue a couple of blocks of foam inside the fuselage to make a few equipment bays and that is pretty much it for big gluey type jobs. So I'll start thinking about wiring, and cutting some channels for that. Once that is done, I'll get some laminating done. I'm definitely doing the elevons, and the wings for the fast FPV ship. As for the wings on the mapping type one, I'm tempted to leave as is for now, to save a bit of weight. I'm undecided on whether to lam the fuselage too. On the one hand it will add even more strength, and impact/wear resistance to the underside. On the other hand, there are compound curves all over the place, which will make it a pain to do. I'd welcome opinions on this!

I've been having a think about colour schemes too. I'm toying with the idea of getting a bit creative with some black sharpie markers and maybe a bit of brush applied plastidip in either bright green or bright orange applied direct to the EPP, underneath the laminate. This should last nicely. The alternative, is some lightweight printed vinyl (or applique type Profilm) applied over the laminate. I've done that on wings before, and whilst it adds a bit of weight, it looks amazing. The advantage of that is that it can easily be replaced, or changed at a later date too. Although, anything under the laminate can just be covered over too I suppose!

Cheers
Andy