I don't think I ever posted a picture of my finished Kingcobra (P63) here on my blog. It's been flown at the last Borah Festival since this picture.

Jim.

I've have some more insights into why my servos stalled in the plank "Circa" and totalled it.
The reflexed wing section (airfoil) on a plank flies straight and level when trimmed correctly. The reflex trailing edge part of the section provided negative lift to counteract the normal forward pitching moment of the aifoil as it generates lift.
So it follows that the control surfaces (and the servos) will have a load on them in normal, level flight, to provide this self stabilising force.
Which means that as the speed increases, the demand on the servos to maintain the level flight, reflexed inclination, will increase. As in a dive!
Then, if additional demand load is required of the servo to pull the control surfaces up, it might be pushed beyond it's limit. This will happen earlier in the case of a reflexed plank airfoil, than in a tailed aircraft with a conventional airfoil. (all other factors taken into consideration.).

All the more reason for the servos to stall!

Comments, corrections and additions invited, as usual.

Jim.

Sadly, my very good performing Circa crashed on the last day of flying after the slope fest had finished. It was a late afternoon flight, and I think that was a contributing factor. The batteries were a bit run down, but not enough to trigger the low voltage alarm on the telemetry.
I've written up a full report here: https://www.rcgroups.com/forums/show...36870&page=167

After some discussion, we have drawn the conclusion that the servos stalled. They were Corona939MG and were most likely not strong enough for the task. I'll use stronger ones next time, most likely MKS6100 or better.

Jim.

I've decided on a good method ( I think) for fixing the batteries into the nose of a plank (or any other fuse for that matter), which the nose is long with no canopy or nose cone.
I first determined the position to obtain the required CG position by taping them externally. Then I cut a strip of coreflute to the length that would support them and extend aft far enough to fix that. I fixed the batteries to the coreflute strip with hot glue and cable ties. Then slid them in, checked the CG and when right, I hot glued the after end of the strip where it was accessible.
The only thing remaining was to push up a cube of foam rubber between the batteries and the top of the fuse to prevent them bouncing up and down.

They can be removed easily if and when required.

Jim.

I started the hinges on the new foam plank "Harlequin", but ran out of tape. The hinges are tension hinges. I used the tape and method recommended by my brother John.
It is a HobbyKing product described as :
"Ultra thin prismatic sticker sheet" and can be found here:
https://www.hobbyking.com/hobbyking/s...dProduct=11338

It comes in a sheet 180mm wide. I sliced stips off this 22mm wide. (180 long). Then removed the backing sheet from each piece and replaced it with 6 - 8 mm exposed. Then I took 2 of these and flipped one of them over so that the exposed sticky parts stuck to each other. This was then cut into 12mm wide strips. The stips were slid between the control surface and the drag spar, one of the backing strips removed and the strip stuck to the top of the wing. I had placed a strip of masking tape along the wing and control surface and the elevon to create a line to position each of these hinge pieces in a straight line. The second hinge piece was then slid in and stuck to the elevon, ie: alternating. When I had a set of four stuck on top, I turned the plane over and tensioned up each one in turn and stuck to its corresponding wing/elevon, as the case may be. I did four at each end like this to hold the elevon in position before continuing on the complete the entire hinge length.
The reason that I ran out of material is that I stuck the backing paper back on some of the film the wrong way up. It has a shiny side! I've ordered more from HobbyKing so I expect it will arrive within a short time. I want this plane flying in time for the slope fest in September at Mt. Borah, Manilla NSW Australia.

Jim.

I now have everything that I need to complete my new foam plank.
Next is to fit the control horns and the rx. into the wing. The batteries and the switch is in the fuselage (well forward) and the rx. in the wing.
Hope to get onto it in the next couple of days.

Jim.

I did managed to get some of the colour on the Cobra during our very brief dry spell. I noticed a couple of delamination spots that I missed, so I fixed them by injecting under the skin with a syringe etc. Now I just have to touch up the paint again. I used very narrow plastic spray painters masking tape to do the curve around the spinner. It worked really well, but pulled a bit of paint off. So now I have to touch that up as well.
I have the Soviet star decals from HobbyKing to put on after that and a flying buddy is sending me some vinyl window stickers. I don't know about panel lines, maybe I will do them, maybe just clear coat without.

Meanwhile, I have been building a foam plank for flying at festivals with crowded air space (Mt. Borah for instance). I've been a bit slack with my blog entries, but here's a pic of it in the jig with the fin socket gluing up. I made a socket out of some glass/epoxy by vac bagging it onto the bottom of the fin after covering it with cling wrap for a release. After trimming, I glued it in place in my old jig as per the picture.

The plank is 1500mm span, PW51 airfoil and looks like it will be AUW of around 1200 grams. That will equate to around 40 g/sdm, which will be fine for the good lift we most often get out at Mt. Borah, NSW Australia.
This one will have 2 servos only.

Jim.

I've been working on my cobra. Repairing the damage from last year's mid-air collision. The repairs were not too much work, and I was supplied with a new canopy for it personally delivered to Steve Wenban by TFLG, who then posted it on to me. It was lost after the collision. This has made me think about fixing some sort of strap out of kevlar string, or fishing line, to it next time.
I have stripped the old paint ready for a complete re-decorated. I will be doing it in Soviet colours of "number 31".

Jim.

I have now set up the bench with accurately positioned MDF panes at the dihedral with a 110mm wide flat section in the middle to position the centre part of the wing that will be fixed to the fuselage.
The joiner tube can be seen in the accompanying picture. The incidence pin cut out is next.
I discovered an easy way to make the tubes for the incidence pins. I have some 3mm carbon rod that I will use for the pins. Just by chance I had some nylon tube that fits it quite snuggly. I will wrap some glass cloth around that and bind it with carbon tow. The nylon tube will stay in there.

Jim.

edit: I just realised that I meant to post this on the Wompoo build thread. So, this is a double post!

I have cut the foam cores for the wing plugs. The cores are in 5 panels with one panel parrallel for the centre section. The plan is to glue ply or fibreglass laminate ribs to each end of this centre section and to the mating ends of the wings prior to joining. A piece of wing joiner tube will be in place also, embedded in the foam cores so that joiner rods can be inserted in the finished plugs to set up the mould accurately. I will glue them together with a thin cardboard spacer so that they can be easily and accurately cut apart with a thin kerf hacksaw after the complete wing is fibreglassed and vac bagged.
The joiner rods then become the alignment jig for the final wing and fuselage tubes.

I am about to layup a fuselage out of the old mould to build on to make the final plug. The centre section (above) has to be incorporated with their tubes etc. The "V" tail joiners have to be included in the plug. Then a "final" mould will be made from that.

The challenge as I see it, is the "V" tail joiners........

More soon.

Jim.

I have posted a report of some RF problems I've had here:
https://www.rcgroups.com/forums/show....php?t=1572618
and also on the FlyDream thread here:
https://www.rcgroups.com/forums/show....php?t=1207547

The short story is that I have resorted to 36 mhz equipment for my Wompoo. I tried two brands of 2.4 ghz in it unsuccessfully.

Jim.

Some of the bubbles that occured in more than one of my vac bagged wings has developed into a significant delamination. This one is on my 1.8mtr. homebrew "Endorphin". The bubble had spread to an actual compression ripple due to inflight stress's. There is no spar in this wing.
I repaired it very successfully using vacuum applied under the skin on one end of the ripple. I used a sports inflation needle (used to inflate footballs I think), inserted through a drilled hole. Then in another hole at the other end, I applied low viscosity epoxy using a syringe untill I could visually see the epoxy bubbling out the needle through the clear vinyl tubing.
I have previously tried repairing these by just syringing the epoxy under the skin with very limited success: the epoxy simply will not spread enough to cover the affected area.
This worked very well and emboldened by this success, I went and repaired several other bubbles.
I have since identified what is the cause of this phenomenon. I used to mix "Q" cells with the spackle that I filled slight dings on the foam cores before vac bagging. The "Q" cells caused slight dust which repelled the epoxy slightly, sufficiently so to reduce adhesion. Any offgassing of the foam with heat (during hot box post curing or simply in the hot sun), would then cause a bubble or more.

Jim.

I have completed the fit out and ballance. It took 300 grams of nose weight. And the AUW is 2 kg.! Much heavier than I anticipated, but it will be ok in "big air" conditions. The sort of conditions we get out at Mt. Borah NSW where our annual slope festival is held.

That work out at close to 70 g./sq.Dm wing loading, the highest loaded plane that I have. My Cobra flies very nicely at 65 g./sq.Dm, so this should be fine. I still have the provision for ballast, two cast lead slugs totalling 650 grams, but.......................

Jim.

I have got the paint job done. No clear coat yet, I will wait untill I give it the maiden flight and any necessary trimming before I do that.
I'm quite pleased with the job, the fuse came out with an almost "gloss off the gun" while the wings are a bit flat. No problem though, a wet sand with 600 - 800 grit to level off the masking ridges etc. and then a clear coat will make it look ok.
It seems the trick with acrylic lacquer is to use a high dilution rate, almost 2:1, and apply several coats, preferrably many. But of course, the danger of runs is high, so care must be taken. Any pro's reading this? I would appreciate any tips.
I just need to fit the cast nose lead (200grams), the batteries and final fitting etc. The servos and pushrods are already in, and the tx. program sorted out to suit.
Then ready for that maiden flight out at one of the beach headlands.

Jim.

p.s. The model now has a name. "Circa" latin for, well, you know what!

The wipers are formed with the mylar tucked under the wing skin. Curing as I write. All surfaces are bottom hinged.

The wipers are being made using Joe Manor's description on his thread.
https://www.rcgroups.com/forums/show...wipers&page=76
I have hung the plane like shown in the picture to ensure the "Q" cells splooge slumps onto the mylar to form the wiper surface but not onto the hinge line.
When the epoxy starts to kick and become jelly like consistency, I will slide the mylar strips under the wing top skin to form the required curve.

I have glued in pine servo mounting blocks front and back of the servo position. These also bridge the top and bottom skins, so provide a bit of support for them in a vulnerable area.
The servos will be slid in between these blocks and then hot glued to the blocks. For subsequent removal if necessary, a piece of wire is heated and used to melt the hot glue.
I just need to monitor just how soft the hot glue becomes in when the plane is in the hot summer sun!
This is another reason for painting composite planes light colours. Apart from the HTD (high temperature distortion) concern.

Jim.

I cut a template for the control surface cut outs. This is to minimise mistakes and ensure both wings are cut the same!

I fitted the wing/joiner/pin set to a previous fuselage. I used an aluminium root rib as a template to locate and cut the holes in the fuse. It all fits well, especially considering this was "reversed engineered". The original plug and mould was not meant to be for a moulded, two part wing aeroplane.
It started life as the simplest fuselage shape I could imagine to learn how to do fuse moulding with and inflation bladder. It progressed to included fin and fillets. And finally, this moulded version. So the alignment had to be done after the fact, which is not to be recommended for obvious reasons.

Jim.

These are the wings trimmed and fitted together with the joiner and pin. Alignment is correct! I will now make a root alignment rib out of 2 mm aluminium to act as set out guide for cutting the holes in the fuselage. Then I can do a full test assembly!