SCEN Puma 3

[Stuart Z]

I've managed with a blow lamp as Bob has done. Worked on a Calypso ,and helped me get the header into the exhaust tunnel.

S

[Nigel R]

Thanks gents. Some points to ponder. I think I need about 1/2" so I might be able to do it with a spacer but may be a bit much for a bend. I guess I could always get weston or je to do a custom job if all else fails.

Meanwhile, to avoid having to make a decision I got on with opening the nose gear hatch. Paper template first, transfer to the hatch and progressively open up until its just large enough to sneak the wheel through:

I'll probably retain the hatch with a couple of screws gong into the bottom of the ply formers.

[Nigel R]

Some internal fettling this week.

The last pre-covering trial fit of rudder/elevator pushrods revealed a major whoops, I had (1) raised the rudders servo by 1/4" to help the pushrods clear each other and (2) built the RX battery box too deep. Result, the box fouled the rudder pushrod. So that had to be remade about 1/2" shallower. There I was, trying to be clever getting the battery back to help balance...

I started sorting out the nosegear steering link. I have precisely just too much distance to cover with a 12" threaded control rod, so this will mean making up a balsa pushrod in the usual way. It will also need some bowden cable outer stuck to the fuselage side to keep the rod located in the steering arm. More on that later.

I decided to go the spacer route for the exhaust. In a box of old exhaust bits I found a likely looking lump of 1/2" square aluminium, which had at some point in its life been attached between a dustbin silencer and an exhaust port. It already had the slot cut for an exhaust. The slow was too narrow and the lump was filed to something of a a wedge shape, full 1/2" at one end and about 3/8" at the other. A bit of filing later I have a reshaped spacer, with less of a wedge shape:

Edited By Nigel R on 21/07/2017 09:03:06

[TIM Shaw]

Nice....

[Nigel R]

Some odd jobs today.

Got the first layer of wing cloth on. This is glass tissue stuck with pva. This layer is about 9" wide and I'll out a second on at half that width.

I cut some hardwood blocks to take the wing bolts. These need some hard balsa triangle stock out on to reinforce the joint so still a work in progress. They will need tapping for m5 when that's all done.

Lastly I made the nose gear steering pushrod which ended up being tremendously fiddly job. This needs a small guide to be glued in close to the gear unit itself but is finished to all intents and purposes.

Thinned pva soaks into this stuff easily.

Clamps while the pva dries.

The steering is the straight pushrod at the top. Ball link on servo end to avoid any problems with binding on the arm.

[Nigel R]

Minor disaster.

That's the centre section wing sheeting after I removed it. Note it has buckled in completely the opposite direction to the wing section.

My fault completely - schoolboy error - I didn't seal (pva) the sheeting before applying the glass with lightly thinned pva. Coupled to which, the weather was quite humid and this didn't dry out as quickly as it could have done. As a result it soaked up a lot of water and lifted. Luckily the D box is fine, as is the trailing edge sheet, so the wing is structurally intact. It seems the wood I had for the centre section absorbed more water, and two individual sheets have lifted. I have made good one sheet and have one more to go. Of course these now also need some more glass on them...

Lesson learned, seal the wood, and get it indoors to dry quicker.

 

On the fuselage, the exhaust extension now looks about right, I have a good amount of clearance under the nose now, and the pipe will fit nicely.

 

However, I may have to file a slight angle to shift the manifold and pipe away from the nose gear a bit.

 

Edited By Nigel R on 24/07/2017 08:36:59

[Nigel R]

I didn't manage to get any photos (yet - to follow) but I've been busy getting a couple of installation & rigging jobs done:

Throttle linkage - that meant cutting the bowden cable inner (dremel cut wheel), soldering (100W iron) one end to an M2 extender, to use with a quicklink (engine end of cable), and sealing the other end of the cable with some solder to prevent it unravelling. The servo end uses a nipplelink - pin removed, and bolted (M2 hardware) to the servo arm to allow completely free movement.

Centre section glass - second layer now done, the same surface tissue as before, but a narrow (4" wide) strip this time.

Wing bolts - I rigged the wing carefully measuring wing tip to tail post alignment, and marked bolt hole position, then drilled through into the hardwood blocks. I used a block of MDF to keep the drill aligned. I then tapped the wing holes for the M5 bolts. The blocks have also been reinforced with some scrap block balsa so these should be good and secure now. 1/16" ply plate now needs adding to centre section and that's the wing completed.

Edited By Nigel R on 31/07/2017 08:38:31

[Nigel R]

Tapped blocks for wing bolts:

 

Butchered nipplelink.

The pin on these things never seems to engage with anything very well, but the screw clamp is a useful way to hook onto a bowden cable. If someone made those quick attachment widgets with a proper threaded connection to the servo arm, I'd use one of them.

 

Wing bolt plate, 1/16" ply, nothing complicated here:

 

Edited By Nigel R on 01/08/2017 09:25:31

[Nigel R]

Got the fin on. Also the stake. So I'm about here:

[Nigel R]

Quick update to the log, I've not been slacking off, but nothing worthy of photos has been done...

I've been:

• fuelproofing the tank, nose gear & engine bays
• making a hatch for the RX battery
• sanding to smooth off the airframe
• doing a bit of filling/sanding on the cowl
• fettling the wing set to get the wings nicely aligned

With just a little more sanding & filling, it will be time to cover. Closing straights, finally!

[Nigel R]

Getting there!

[Jonathan M]

Sexy and interesting!

[Nigel R]

Thanks!

To add some detail.

It's entirely covered with Solarfilm. I used the stuff many moons ago and got fairly comfortable with it, more so than with tissue & paint finishes. It's all to-the-letter standard process - Clearcoat around the messy bits, and some awkward corners and inside spaces. Start with small bits of film into the nooks & crannies (corner of aileron, that kind of thing) before doing the big panels. As said all standard stuff straight out of the instructions. Perhaps the only unusual point is that I didn't use a heat gun - just the iron - I don't find that the gun speeds up the job very much (the shrinking bit is a tiny portion of the covering job and easily done with the iron anyway).

While we're at the covering stage, does anyone know how to get nice straight clean edges when overlapping solarfilm? All my overlapping edges come out looking like I cut them with a breadknife. It's far too late for this build, everything is done, but for future stuff I'd like to know. It's a massive thorn in my side when it comes to covering. I can get a reasonable job done on the big panels and the compound curves but cannot for the life of me get good straight edges. Even with nice fresh blades.

I have some trim to stick on the top side, I'm going to leave the underneath plain blue.

[Nigel R]

Not much visible progress since the covering was put on, but I've been re-fitting all the radio, U/C & engine kit and I'm nearly done now.

Somewhat annoyingly, the hatch behind the wing is not going to be needed, as balance comes out about right with the battery at the front of the wing saddle.

The RX is buried in a block made of 3/8" thick black open cell foam, . I cut out a couple of layers so the RX sits nicely in the middle of it. Plenty safe from vibration. Battery is wrapped in the white closed cell foam, taped up, and popped in front of the RX. All very standard for a glow power installation. A couple of flat bits of scrap balsa retain the kit.

I'm going to put a fore/aft piece in, so that all the servo wires can sit on the right side of the fuse, leaving space for the nose gear pushrods on the left.

Switches will go by the throttle servo, I'll make something from liteply to hold them in place. I just dangle several bits of thin string out the wing saddle to move the switches with.

Beyond that, there's not much to do. Some fettling of U/C legs (cut to final length, file some flats), and the tuned pipe mount and the canopy to stick on.

Edited By Nigel R on 13/09/2017 10:28:59

[TIM Shaw]

Looking good Nigel.

Re covering - I hate covering. I filmed my little Challenger and my KF4 / 40, and was frequently heard to mutter "wish I'd glassed the b*&*^^^& thing" along the way.

I have glassed my Bullet, and am really wishing I'd filmed it....

Straight edges on overlapping film joints are very difficult, I can usually get a decent cut with a new scalpel bade, and have had some success using a rotary wallpaper trimming knife too, but it all goes pear shaped when I try to iron it on, bits shrink and pull away etc etc, so i usually end up cheating and covering the join with auto trim tape.....

Sticking the canopy on is another job I rarely do well.....

[extra slim]

fresh blade, and then I turn the iron down to do the "first fit", the film doesn't distort at low heat and goes on straight, and then after it is "tacked on" I increase the heat and go over it again... works for me..

[Nigel R]

Thanks chaps

"Fresh blades" sounds like a common theme when cutting film, so I have to assume that mine weren't quite sharp enough - I'll try getting a pack of razors next time around.

I'm with you on the low iron temperature, I set the thermostat to the point where the film only just does the 'wrinkle' thing and then leave it right there throughout. I've never found the need to have the iron any hotter, at least, not with regular solarfilm.

[extra slim]

a ha.. for straight line or trim application I go "cooler than the wrinkle".. (now thats a phrase!) to iron it on in position with no distortion, then once on and straight, up the temp a little and iron over it again..

[Nigel R]

gotcha - thanks slim

[Nigel R]

Time for a proper update!

[Nigel R]

Things done recently

Canopy - stuck on with Pacer canopy glue. I copied a technique I'd found on rcgroups - draw the canopy outline on the deck, make a lot of pinholes along the outline, and make a fillet of the canopy glue, on the outside of the canopy. It's come out quite well.

Finally covered the nose gear hatch, another film & clearcoat job, like the rest of the model.

Got the pipe clip on the wing. Nothing complex here; it's a standard terry clip (I need to put some heatshrink over it) mounted on a 1/8 ply plate, which is epoxied onto the wing.

Filed some flats on the UC legs to stop the axles rotating.

[Nigel R]

Lastly, I managed to get the motor running. Only slightly hampered by forgetting to bring my hex drivers to the field (can't connect up the retracts properly), and, the plug blowing the first time I started the motor, yet continuing to draw 3A and give the odd promising fire when I spun it.

Anyway, before I ran out of time I popped the old spare from the box in and got it peaked, just to make sure it's broadly ok. Second needle is a bit out (way rich) but even with the old plug the peak is just under 11k on the 11x8.

Things yet to do;

Trim

Get a new plug in

Get the pipe length set (might need to be 1/4 or 1/2 longer I think, just going on needle sensitivity).

[Nigel R]

Final post (!)

A few stats on the model;

Scen Puma 3

OS46SF, Macs 1250, APC 11x8

Span 55in, Length 52in, Wing area 570sqin

Weight 5 1/4 lb

Wing loading 21 oz sq ft, Wing cube loading 10.6

Build time approx 130 hrs

[Jonathan M]

Looks excellent Nigel, and the stats are good to know.

Do you intend to add colour to the white airframe and any other detail?

[Nigel R]

Indeed I do, it's the last major job left.