SCEN Puma 3

[Nigel R]

Armed with the Dubro hinge tool, I got the ailerons hinged.

I bought the red handled hinge tool kit. If I'm honest, I think it might be better to buy the blades by themselves, and get a couple of cheap #2 handles. The red plastic handles are not that strong (or straight).

However, the tools do a good job of getting the slots cut, and the resulting slots are just the right size to be a lovely snug fit on the hinges.

With that job out the way, it is starting to look close to a finished wing:

[Nigel R]

Fitted aileron horns and pushrods last night. This was all going smoothly right up to the point where I started. At which point I discover that I've managed to line up the servo output exactly with one of the hinges - whoops! What can I do? Move the hinge? No, there are balsa blocks there for glueing it into, if I move it the hinges will no longer line up with the blocks. Fortunately, the servo hatches are square and the servos are mounted to the hatch - so I rotated them 180 degrees. It now looks a bit odd with the pushrods on the root side of the hatch, but there we go, functionally not a problem.

The pushrods themselves are the usual snaplink at the control horn end, and a Z bend on the servo. The rod has a 45 degree (ish) bend about 3/4" from the Z bend, which means it clears the servo hatch quite neatly at the extremes of movement.

Yet to do - add a few small squares of 1/32 ply, on the surface of the aileron, to prevent the horn from crushing the wood, and as usual, soak a bit of thin CA into the area to stiffen it up a bit.

[Stuart Z]

Still looking good to me!

[Nigel R]

Thanks Stuart!

It's just one of those things; I know it's there, even if no-one else does...

[TIM Shaw]

Looks very nice to me too Nigel.

I've broken threaded rods when I bent them at the end of the threaded bit before now, and I no longer use plastic clevises on any control surfaces after the one I had on the elevator of my second R/C model (KK Student - remember them?) let go at hte bottom of what was supposed to be a square loop.....

Guess that's just me though.

[Nigel R]

Thanks Tim!

Agreed, bending on or near threaded portions is dodgy. I had no option with the gear pushrods (no space to do otherwise) but the aileron rods are dead straight near the clevis.

As for the nylon clevises, I've never had an issue with them failing, but its horses for courses - I would not use them on a highly loaded surface or on anything large. Ailerons need almost no force on something like this (even on a 60 size sport/pattern). Elevator on 40 and up, I would use metal if it is a single connection, but a double pushrod at 40 size I think is ok with nylon. Rudder on 40 upwards, metal every time. I think the nylon benefits from not being opened/closed too often if possible, less bending = less stretching = less breaking.

---

So, some tidy up type jobs during this weekend's building time.

I got the gear hatches fixed in place, using servo screws in the corners. As usual, once I'd drilled the holes, I used thin CA to strengthen the balsa around the hole.

I put some extension cables for the aileron servo in their final resting place. I didn't fit a tube for the cable. I should have done, this was a bit fiddly, I dangled a bit of string with a lump of solder down through the holes and then pulled the extensioon through with the string. All that said, the cables don't come out once they're in, so not something that I need to do again.

Lastly, I started looking at the wingtips. I decided against using the kit supplied blocks, as they were rock solid. Maybe I'll use those as ballast:

I laminated some 1/2" leftover from cutting the ailerons, and several layers of some 1/4", and fretsawed the rough outline before cleaning up with sanding block.

Next job, make a couple of centreline marks, cut the rib profile from the side, and stick it on ready for final shaping. As per LE and TE, I will use some masking tape to protect the existing structure while the tip is shaped.

When the tips are done I'm going to move on to the fuselage, the dowels, bolt plate and glass tape can wait until rigging time. Anyone reading this must be fairly bored of pictures of the wing by now - its time to get the fuse started!

[Jonathan M]

Following this with interest...

Jon

[Nigel R]

Got one of the tips sanded down to rib profile.

Had to fix a mistake before getting them stuck on - I'd cut the tip (looking from the top down) too thin at the rear, which meant I would have been sanding away at the ribs when sanding the rounded profile. I stuck a bit of 1/8" sheet to the tip rib to give me some extra material here.

With that done, tip blocks are stuck on. Masking tape at the ready:

During sanding (just the LE sanded to rib profile):

and one down, one to go:

No idea why that is upside down - looks OK on my phone!

As ever, sand down level with the masking tape, then the final 1/64" is by hand, slowly-slowly-catchy-monkey.

Next shop time should see the other tip sanded to rib profile, and hopefully both tips rounded over.

[Nigel R]

...and the other one:

and I also pared down the tips of the ailerons:

Only the rounding off left on the tips now.

Perhaps unsurprisingly, with a lot of sanding work involved, shaping the tips is turning into one of the longer individual jobs on the wing. I think I've put about 3 hours into the tip blocks so far.

[Nigel R]

Tips again. Photos tell it all. 80 grit block to make the sharp angles then 180 grit paper by hand to smooth it off.

45 deg angles using block

22.5 deg using the same block

Last angles with the block, nearly done

And paper in the hand to finish

[Nigel R]

Not much building done this weekend - thinking time instead. I've been working out the engine / nosegear / FW / layout, and the general fuse construction details.

Before I dive in to the fuse build proper, the plan for the structure is thus:

1/8" balsa sides, top and bottom (I may use 1/16 for the bottom)

1/4" sq longerons top and bottom

1/32" birch doubler, firewall to just rear of wing saddle

1/4" birch firewall F1

1/8" birch F2 at front of wing

3mm liteply F3 at rear of wing

1/2 sq maple blocks for wing bolts

Some 1/4" on the tank / nose gear underside

Soft block cowl

I will have to depart from the plan a bit and give the fuselage some extra height (1/2" or so) in order to get the nose gear in, too. It's looking rather busy in the tank bay, what with the 8oz tank, tank floor, gear, plus 3 lots of control runs all in a tight space. Hence the extra height. So, sadly that means chucking all the formers from the kit and cutting new ones.

I was thinking about using 2mm liteply - with big holes - to do the doublers (with half of the liteply cut away it is about the same weight as 1/32 birch) but space is most definitely at a premium in the tank bay so its birch ply for this build. This also means the kit's "doublers" won't be usable. They were a bit odd (a 1" x 1/8" strip of spruce) anyway so didn't really help reinforce the wing saddle. I suspect their design was mainly for "material availability" reasons.

While I'm busy throwing the plan out the window, I will also have to stretch the tank bay about 1" to fit the retracted nose leg and wheel in (I guess I could cut away the wing root LE - but I'd rather not), and the cowl also needs to be at least 3/4" longer than plan to get the OS SF in there (so there goes the ABS cowl). And while I'm at it, I am going to fit the rudder 1" lower than the plan position, with an underfin, to make control runs simpler, and stretch the tail by 3" to compensate for the longer nose. That kind of means cutting new fuselage sides.

Now, whose idea was it to stick retracts in this thing!?

[TIM Shaw]

Hi Nigel

Beginning to sound like a scratch build would have been easier....

Had a quick look at the Outerzone plan and that fuz top looks more like 1/4" sheet to me, you could maybe build it up from strips to gain the needed internal height without impacting too much on the overall shape, and allowing for plenty shape addition / lightening by rounding the corners off.

Personally, I think your firewall would be fine in 1/8" Birch ply, rather than the 1/4" you suggest, and I'd be looking to fit triangle, rather than square longerons.

I think you're right about the doublers though - 1/32" birch every time.

Can't see a way round the nose leg problem. I'm guessing you're going to be running something like a 10x8" APC on that 46SF?

I suspect that if you fly off grass you won't be happy with tiny wheels either. This problem is a little close to home actually - I reckon to have started on an Aurora 45S (well, I've cut the wing and tail cores and mounted the motor mount to the firewall) but I find myself looking at the nose retract mount / tank bay area and not actually doing anything.... I knew there was a reason I preferred taildraggers.

Sunds like fun anyway, and there really isn't much to a fuz after the work you've put into those wings. Will it be ready for the UKCAA event at Huddersfield, June 10th?

Edited By TIM Shaw on 15/05/2017 13:01:36

[Nigel R]

ha ha - yes, I thought the same myself! I've gone way off-piste now. Regardless, it's all fun.

As designed, the fuse top is 1/4" over the tank (originally to make an access hatch) then 1/8" all the way back. The kit had extra strips glued on top of the fuse sides, which went under the top sheet - that allowed the kit to be built upside down flat on the board.

Intended prop is 11x8 APC - I'm going on about 1.5" clearance - wheels are 2.25". The ones I have right now are very narrow, I will probably replace with something wider. OTOH we are lucky with the grass at my local patch, it is kept very nicely cropped by the committee, so I'm not so concerned on that front.

Original kit FW is 3/8" ! And another five or six formers from 1/8" ply! I'm just intending on the usual 3. I'd normally go with 3/16" on the FW on a 40 size taildragger, but this one takes the nose gear and the engine - the little extra beef won't hurt.

Much as I'd like it to be, I doubt very much if it will be ready in June! I'm expecting to be done more like September at the rate I'm going...

 

"1/32" birch every time."

That's what I thought. It's an expensive choice though; 2mm liteply is dirt cheap by comparison.

Edited By Nigel R on 15/05/2017 13:37:36

Edited By Nigel R on 15/05/2017 13:38:42

[Nigel R]

Last night I got busy on the business end of the fuselage and made a firewall.

FW layout from the side. Things are tighter than a ducks a*** up here. Aiming for prop clearance of around 1.5" - leads to a tank bay of 5.5" (maybe 5.75" by the time I've accounted for F2 thickness) to get the retracted leg in.

Somehow, I have to get the throttle cable through here.

I recessed one of the nose gear's T nuts in order to allow the engine mount to sit flat on the FW. A 12mm auger bit made a neat, quick job of the recess for the M3 T nut.

The gear is stood off from the FW using a couple of washers, so the engine mount nuts do not need cutting or recessing.

That pipe will need a little clearance cut into the corner of the fuselage... On the other hand, I may yet have to open up the bend a little to get a decent clearance between wing and pipe. I haven't finalised the (vertical) wing position yet. The manifold is also closer than I expected to the nose leg when the gear is down, but close isn't touching and everything is nice and clear when the leg retracts and extends.

Note, engine is positioned vertically such that the tank will just fit neatly below the top of the former, and there is just enough space to get a tank floor between it and the nose gear unit.

So as it stands, the tank has dictated where the engine goes relative to top of former, and where the nose gear goes, the engine & prop have determined the nose leg length, which in turn dictates the tank bay length and the position for the wing (so that the main gear is level with the nose leg. And the wing position dictates size of F2 and F3. When I've worked those sizes out I can then layout the fuselage sides. Luckily, with this kind of model the fuselage sides are simplicity itself to layout - no complex shapes and a flat top reference line to work from.

I must admit I would recommend building a different model to anyone who wants to do a trike retract install! Something with more fuselage depth, like a Curare. With hindsight, I'd have made this one a taildragger, it would just work better with the fuselage design (plus I'd now be finished messing around with retracts). Or fixed gear, why didn't I do fixed gear, repeat after me, keep it simple stupid... I keep telling myself it will all be worth it when the wheels go up after takeoff...

 

Edited By Nigel R on 16/05/2017 11:31:19

[TIM Shaw]

All makes perfect sense to me Nigel, although I'm happy with 1/8" birch FWs right up to piped 61s, usually in conjunction with 1/8" birch tank bay floor and a little light internal glassing.

You're right about formers too - never ceases to amaze me how the older kits used so many, each an opportunity to build another bend into your fuselage....... 3 is plenty.

Same issues on the Aurora drawing actually, can see that undergoing a subtle re-design and possibly some foam decks.

[Nigel R]

The Aurora is an ace design. You're a braver man than I for starting it! Piped rear exhaust and a trike is definitely upping the build by a level or two. What are you intending on putting up front in Aurora? YS45FR?

The FW/tank floor/F2 assembly you describe must end up pretty strong by the time you've added some glass. Especially given the birch doublers running from FW past wing TE.

Edited By Nigel R on 16/05/2017 13:03:57

[TIM Shaw]

Hi Nigel

You'll note I specified 45S - this is the one that used a sidewinder mounted, side exhaust 45, with a fully enclosed pipe running underneath, not quite as neat as the original, but, He Ho, not quite as difficult either.

And I'm thinking my nice, new OS 55 AX on a standard muffler will be plenty powerful enough, nice and quiet, and much less bother.

Also frees up the pipe tunnel for retract servos and things.....

But yeah - I downloaded the plan, e-mailed it to a club mate who printed it out, we met at the field, agreed it was very pretty and he admitted he'd done himself a plan too, so I cut him the wing cores and ordered a couple of canopies, and away we went.

Sort of - neither of us are really relishing the challenge and neither of us have got very far.........

[Nigel R]

Yes that would make it a good deal simpler. Still a marathon amount of sanding to make the fuselage shape, it looked quite complex to form especially top deck nose area and the fuselage to fin transition.

Last night I did some more measuring, and a little more cutting. 1/8 ply F2 (front of wing) and 1/8 liteply F3 (rear of wing). F3 will get some big holes somepoint soon. F2 will have most of the top portion cut away for tank access.

All the formers need their corners cut out for longerons, although I expect I will get the fuselage sides cut first, so I can dry fit it in the jig and double check the sizes.

[Nigel R]

Tonight's session saw the sides laid out. scarf joints were needed to make two bits long enough. The sides are 4.5" deep which also meant edge joining another piece to get the final result. The scarf joints will be reinforced by the ply doublers.

Lined up to check everything fits. Wing saddle not cut yet.

And from the other end

Clearance for nose gear looks ok.

Next job is getting the longerons and doublers glued to the sides.

[Nigel R]

A little more done today. Wing saddle carefully marked and cut, tailplane slot marked and cut. Also got the upper longerons ready and cut out the formers to accept them. On to the Doublers next.

[Nigel R]

The last few days I have got the doublers cut and glued on to the sides along with the longerons. Three doublers to be specific. Left side, right side, and the side with the wrong shape. Two of those were useful, the third less so. Whoops.

Tank floor and radio tray to fit up next.

[Nigel R]

1/8 liteply radio tray tonight. Happy with that.

[Nigel R]

Checking tank access and fit. So far so good.

[Nigel R]

Forgot to write this last night.

I use the radio tray to fix the alignment of F3 (the former by the rear of the wing). This works a bit like the slot together crutch assemblies I see being used a lot for firewall/tank floor/former-by-wing-LE in laser cut designs. It provides a known good reference to build the rest of the fuselage from. In this case I will make sure that F2 (wing LE) is square to F3, and that the FW has the correct offset by measuring again from F3. The tank floor will further aid in fixing the front end in place, in the same way as the radio tray.

Note in this design that F3 is slightly narrower than F2, which meant a bit of careful sanding and lining up to get the taper correct. All of that is made much easier in a jig.

Speaking of the jig, I don't know how I managed without one. It makes life so easy, the critical bits of the fuselage can be assembled dry and test fitted as many times as necessary to get proper fit and alignment, radio and motor install can be done before anything is glued in a place where it doesn't work. When all the key parts are fitted then everything comes out, PVA all the joints, and back in the jig to allow glue setting,

Well actually I do know, I used to make everything a parallel box from the wing TE forwards, eyeballed the alignment when drawing in the tail, and just took educated guesses on the radio & motor install. Which sort of works. But not as well as dry fitting in a jig.

[Nigel R]

Not much shop time recently, but I got a few small jobs done.

 

Tank floor cut to size and a small cut out for one of the motor mount T-nuts:

 

Tail end drawn in and sanded down to allow the fuse sides to meet. Still another 1/16" to sand off from the longerons at the tail post. I also have yet to fit the scrap block to give the fin hinge something to bite on.

 

Throttle cable holes drilled in F1 and F2. Cable runs just below tank bay floor. Scrap block yet to be added near throttle servo to support the outer:

I always lean toward bowden cables for throttle. Force of habit more than anything else, I think.

It was quite tight getting the cable through the firewall in an appropriate place. Excuse the terrible photo. Cable comes out right next to one of the nose gear T-nuts:

 

 

Edited By Nigel R on 05/06/2017 10:37:33