My engineer mate came over the other day and although he has no interest in gliders he raved on about beams and box structures and confirmed that the FLRS’s are the right way to go. Narrow vertical plates will laterally deflect under load, even if you make them quite big but a small top and bottom plate increases rigidity and resists deforming, enormously.
I mixed lightweight filler with PU glue for spackling. I don’t have a particular ratio – I think it was about 3 parts filler to 1 part PU.
This was a bit stronger than I’d previously used. I put gloves on (I keep a box of disposable food gloves handy) and started to spatula it on, then smearing it on by hand. But it was getting sticky and clumpy, tending to pull away in chewy strings rather than plastering on. I got a bit worried and thought I’d used too much PU. But I tried adding some water and this solved it perfectly – it was then really easy to smear on.
It’s very different putting spackle on a molded wing like the Bat, as compared to a wire cut wing. The Bat and Bee have a skin on the surface, so the spackle doesn’t really soak in much but with a cut wing, the porous surface takes a lot of filler.
A couple of hours later it was really easy to sand.
But it looked pretty scrappy, so I mixed up some more, with less PU this time, and hand rubbed it all over then later sanded again. But I noticed in some spots where I hadn’t sanded the Bat’s “skin” and it was still shiny, the spackle came away to leave the original shiny skin showing! So I think for a good spackle job, it’s best to give it more of a roughing up than I did.
After Sean said that you need a bit of reflex in the fixed elevons I cut each one close to the subspar and smeared with Shoe-Goo, and re-set them at the correct angle.
Then sprayed it all over one side, and taped it with bi-di tape. I put a full length 50mm strip along the spar line, then criss-crossed diagonals. I rub each piece down with sandpaper after putting it on, to remove the anti-stick coating. On the outer wing I used 38mm strips to save weight. I don’t overlap them to the other side. Then the other side with exactly the same pattern, then one strip along the LE. When finished I ironed all over the tape to press it in and activate the glue more.
This thing is really, really stiff! I held one side on the bench and sat my drill on it ... no bend!
A few days later, I misted the elevons with Super 77 and wrapped them in bi-di tape. (I can hear the howls of disagreement here!)
Then hinged them the conventional way, using 38mm tape. Normally I use 25mm but this thing needs to be strong.
I didn’t do much during the week but sprayed the area around the LE and tips with 3M90. It’s a bit of an experiment but I have a mental block against the whole “Gooping” thing and I like the way you can spray the 90 on and it sets so dry rubbery. I think it will add bounce factor. I took photos but it didn't show up clearly.
Then I covered the wing with Monokote. That sounds so easy to write but it takes many hours! After a lull in building, I started on the top last night. But I had a drama since my new replacement iron (first one died in 3 months) suddenly went berserk and went smokin’ hot … it would melt the film instantly. I found that a stopper was slipping on the dial shaft so it was turned way past its normal operating range. It took me hours to figure out a bush remedy to get it back under control again. Also this iron has a really dangerous habit … it keeps turning its own dial up! When I keep picking it up and putting it down, the dial rotates clockwise by itself! Pretty scary!
I started working on the top first because it’s the light colour, and cut one piece for the right half, and one piece for the left with overlap all round. Sprayed the wing with 77, let it dry 5 mins or so till tacky, then lay the Monokote on & squeegee it with fingers till it’s nearly perfect, then start ironing it on, not hot enough to shrink it. Then once it was all on, I turned the iron up and pulled/ shrunk the film over the tip. But it would have been smarter to put a piece over the tip first, coz I couldn’t avoid tiny wrinkles, but it’s not an issue to me since I’ll stretch a piece of electrical tape all around the LE and tip anyway. Top side done before bed.
After work today I got stuck into the Bat again, worked frenetically and got it into the air! To cover the bottom side with the elevon hinge gap, the first thing was to cut a long rectangular strip of red Monokote to fit in the V of each gap and I ironed it in, with 5mm of overlap onto the wing and elevon. For the main red bottom pieces, I pre-cut the line for the LE perfectly, but left the TE and tip with some overhanging. I laid it on so the LE was perfectly lined up then flattened the whole sheet out towards the back. Otherwise same as the top.
Then quickly designed a fin shape and made up a fin. This time I laminated 1.6mm balsa with a sheet of 1mm either side, with the grain at right angles. I then tried a supersimple bonding method by just spraying them with Super 77, sticking them and pressing them flat for a while. It seems really good.
Then cut a piece of 5.2mm carbon spar tube to length, cut a slot in the fin and glued it with 5min epoxy, plus smeared some of the epoxy on the bottom edge, which cops a beating.
Sanded a foil on the edges, then sprayed with 77, and covered with Monokote. I made up a mount plate for the fin using 5mm coreflute. I cut the outer flutes to allow the edge to be squashed flatter.
Sprayed the corflute plate and the underside of the wing with 77 and carefully stuck it on.
I do this with the fin in the coreflute and I stick the back lip of it down lightly, then look down the centre line from the front, to make sure the fin is straight, then press the plate on hard. Then I cut a piece of signwriting vinyl and stick it over the top as a fairing.
At this point I turned on the radio gear, cut holes over the servo arms, and fitted the big Dubro elevon horns and made up control rods using thin stainless bike spokes, attached short on the servo arms. It now looked finished!
I did a radio range test and was a bit perturbed by the funny whiney-buzzing sound that the digital servos make! But they are very strong, and the resolution is really fine, and they seem fast.
Time to get the balance right! Sean and I had some intense communication about this and he got me a little program which can calculate the CG of a multi-panel wing. We thought 20%MAC would be good (= CG 140mm from nose), but then he had problems with his test flights and suggested I go for 18% (=CG 133mm from nose). I marked that and perched it on the thingy, and stacked lead on the nose, and found that it needed 245 grams of lead!
I hacked into the newly covered nose (finding surprisingly that the bi-di tape peeled cleanly off the EPP skin!) and cut a hole between the batteries.
I pushed several layers of alfoil in there to make a rough mould, and Nick and his mate delighted in melting the lead and pouring it in! (Wow, Cool!). First time I’ve done that for a plane – it was a tip from “Karl the Predator” from RCGroups in the US) and it’s easy and effective.
I put it in and stuck another 20gm of lead on top for good measure. By this time it was nearly dark so I piled all the kids in the car and raced down to the kite field at Pelican Park, Clontarf. Not ideal, with a swirly northerly, short turf and very hard ground to hit! Having guessed at the elevon position I picked a spot in front of the thickest clover, tossed it and it plunged down but when I gave full up, it came up to skim the ground for a couple of metres. I gave it more up, and it flew a bit better, but a bit like a brick. I decided it must be too nose heavy so I pulled the big nugget out from the nose hole and piled in lots of bits of lead. Then when launched again it pitched up steeply and I kept lowering the elevons and finally got it so it was able to glide!
When I got home I found that it had 210 grams of lead in the nose (so I’d taken out 55gms to get it to fly), and the CG was at 143mm (about 22% MAC). The all-up weight was 880gms.
Now I’m waiting to get it to the slope!
). I reckon it's gonna be very fast in strong lift but in light lift it's a real handful!!! The Reaper was the complete opposite, banging incredibly tight turns with full elev and not a hint of stall/spin.