SCEN Puma 3

[Nigel R]

One £20 engine, the aforementioned ringed 46 SF.

Its a bit discoloured, but the carbon and castor cleaned off no problem with a few minutes of boiling in water with some dishwasher powder. It's been run since and oiled of course. Note non-standard old Irvine 40 plastic carb. The manifold is from an Irvine 40, too. The old mk1 Irvines had the same width (quite narrow) bolt on exhaust as the OS FSRs, and the OS SFs kept that bolt drilling (as well as adding the now fairly standard 37mm bolt through).

Starts easiest with a backflip, somewhat unusually. Starter & the normal forwards flip, it does not like.

Edited By Nigel R on 24/02/2017 08:53:56

[Nigel R]

I made a start on the carve & sand exercise, that is the trailing edge and ailerons.

From this

to this:

A slow business. Anyway, that's the first side nearly complete.

The masking tape is there to protect the ribs from an errant swipe with the sanding block. And, when you get close to complete with the TE sanding, the masking tape will start rubbing away. At that point, tape off, and proceed very carefully with the last 1/32". This is where I'm at now, with the pictured aileron.

And then, just the other side to do!

[Nigel R]

I got the retract units lined up and drilled some holes in the bearers. These will have some m3 blind nuts on but right now they're taped into the maple, so as I have some way of boring the units on while I get the legs set up correctly and the pushrods in place and that sort of stuff. First job was to cut the legs down a little and to cut a clearance slot in the rib with the razor saw.

 

The units are mounted just below the level of the wing skins. They'll be covered up by a 1/8 balsa plate to beautify things a bit. 

Just for completeness here's a picture of the top side if the unit. You can sort of make out the cam mechanism at the front of the unit. Also visible at the front is the slot to clear the pushrod.

 

 

 

 

 

Edited By Nigel R on 27/02/2017 09:46:14

[Nigel R]

On the subject of the motor, I need to add a pressure tap to the exhaust. I'm thinking it could go on the manifold, right by the engine on the nice flat surface. Any periods or cons to this location?

[Bill Michie]

Best place was said to be on the first high-point of the pipe (for max pressure), though I've found (& have used) several manifolds where the nipple is on the straight part of the manifold after the bend (on the inside of the bend or angled outwards slightly). Fitting the nipple to the pipe results in a long pressure line to the tank also.

Hope this helps! Main thing I think, is consistency & simplicity/reliability.

Regards,

Bill

[Nigel R]

Thanks Bill, I think I may go for the point you suggest, just after the bend.

Ok, not much happened over the past couple of weeks, but I have managed to fettle the retracts a bit, this included:

Making the leg sit at 90deg downward, and hence in line with the underside of wing when retracted; I also made both the legs sit at the same horizontal level when retracted, one was a bit higher than the other. This was basically a good hour or so, in and out of a vice, a little bend here, checking, another little bend there, checking...

Bending some 2mm pushrods to the right shape, in order to clear the maple bearers.

Making a few small notches in the ribs to allow the pushrods to move without rubbing on the woodwork.

Putting in some scrap braces around where the retract servo will fit, so that I can easily form the well when the wings are joined.

That lot took what seemed like an absolute age, and nothing looks very much different for it! Still, all necessary jobs.

I have a final bit of tickling to do to the angle of the retract legs (I'm a degree or so low when retracted) and then its back to the woodwork proper.

[Nigel R]

Did a bit more shaping of ailerons. Also added the top centre sheeting, after checking that the retract pushrods would actually go back into place after it was on.

Time to get wheel wells in next.

[Nigel R]

On with the U/C.

Trimmed the axle a bit, formed some wheel wells from 1/16", and got one side in place.

Remaining jobs in this area; tidy up the U/C leg on both retract units, and duplicate the axle & wheel well work to the other wing.

[Nigel R]

I don't think I'm going to bother sinking M3 blind nuts into the back of the retract bearers. If those M3 bolts are pulled out of the maple, then I've got bigger problems than just a stripped thread. They seem plenty secure as they are.

I'll stick to my usual method for threads in hardwood; tap the wood, soak in some thin CA, leave a day or so, then run the tap through again. I do that for all threads in wood; it's particularly good with that lovely soggy liteply and transforms the solidity of the thread in the wood; CA can even get a coarse thread to stay in balsa (light models and small servos, hatch screws, that kind of thing).

I'm starting to feel like the wing is in the closing stages now. If I get the other wheel well done, the big jobs left are joining the panels, hinging the ailerons and shaping some tip blocks. Then I can move onto the fuselage, which I like better than wings - hence getting the wing done first!

Edited By Nigel R on 15/03/2017 09:47:09

[Nigel R]

This arrived today. Seems quite nicely made.

[Nigel R]

Small update - the second wheel well is in and gear cut down. The struts will be cut to its final length and the axles solder later on I think, when the whole thing is rigged and near ready to go.

After doing that, I realise my mistake, I've made both of the wells perpendicular with the top wing skin. However I'm not going to remove them to fix that. The wheels fit just fine as is.

Underside centre section sheeting to go on next.

[Nigel R]

Got the lower sheeting on last night, and the wheel wells cut out. Made a start on cutting the gear servo well out, too.

Remembered at the last minute before getting glue on the sheeting that I still needed to make some holes for a servo cable tube (phew). This will be some rolled paper. Somewhat awkwardly, the servo leads do not make it all the way to the wing root, so I now need some short extensions.

Forgot to take any pictures, but the next update should cover these bits.

[Nigel R]

A little progress this week, I got the retract hatches cut from some 1/16 sheet, and stuck in some scrap block bearers to hold on to them. Hatches are doubled up around the gear leg cutout. I also got cap strips on (not in the photo!)

It's around this point I start wondering what I was thinking when I decided to use retracts, I probably could have had the wing wrapped up by now if I had used fixed gear!

[Stuart Z]

Looking good!

[Nigel R]

Thanks Stuart!

Last nights shed time got the ailerons carefully cut & sawed free. I could really have used a deeper blade on the razor saw to get through the aileron stock at the root - one to add to my tools wishlist. I then put enough bevel on the aileron leading edge to get just over 1/2" throw either direction.

Next job is to hinge the ailerons and get the pushrods and horns set up. After that, wing LE proper, and then time to join the panels. Beyond that point, it is just wingtips and the gear servo to go.

Dowels and 1/16 ply wing bolt plate can wait until its time to rig the whole airframe.

Edited By Nigel R on 04/04/2017 08:56:27

[Nigel R]

Decided to do the leading edges next, rather than getting the ailerons hinged and pushrods set up. It's surprised me just how long shaping the leading and trailing edge stock takes. I should probably know, but you forget a lot in twenty years...

[Nigel R]

This is half a stanley blade, snapped (in a vice with a hammer) to about the width of a hinge. At some point I really must grind the back of the blade so that the knife handle can attach nicely, instead of clinging on to the edge.

Makes a brilliant job of a mylar hinge slot. The stanley blade is stiff enough to stay straight as you plunge it into a surface, it doesn't wander like the thinner blades I have on my #1 craft knife.

However, it makes an awful job for the pinned hinges I'm using. I caved in and ordered a dubro slotter.

Anyway, that's one aileron done now, with a nice tight gap. I try and recess the centre part of the pinned hinge into the bevelled edge of the aileron as much as possible; the centre part sits proud of the wings trailing edge. No need to use tape or film to seal the hinge gaps that way.

[Nigel R]

As the hinge slotter hasn't dropped through my letterbox yet, this weekends shed time saw the wing halves joined at the root.

There we go, joined with about 1" dihedral. The root was sanded to angle using some scrap ply to block up the tip to the right height, and using a sanding block held vertical using my makeshift MDF sanding jig. All this rather highlighted the need for me to make some proper sanding tools soon, a 12" x 3" x 3" right angle block is definitely needed for this kind of job, and I know I could use some slot sanders as well, 1/8, 3/16, 1/4, etc etc, and a couple of different sized circular sanders (i.e. some dowell with paper glued round it) and a decent length sanding bar (24" ?). Right now I only have a few 9" blocks.

Panels were joined using a spirit level to set the tips flat, with a couple of wedges to hold things the alignment while the root was glued up. Then I opened up this well for the retract servo:

The liteply bearers have to be fitted next. Also a liteply plate at the root LE to reinforce around where the dowels will be stuck into the wing, and a plate to reinforce the wing bolt area at the TE.

I also need to locate the aileron servo lead location and make several holes to get the cables through. After that the wing bandage will go on.

[Stuart Z]

Nigel,

Coming along nicely and yes, waiting for things through the post is very frustrating but at least you are making progress elsewhere.

S

[Nigel R]

Thanks Stuart, yes it is slow and steady wins the race, and at this stage in the build that sort of thing isn't holding me up much.

Got the retract servo mounted, and made up the basic pushrods:

Bearers are the usual 3mm liteply on some scrap balsa block.

As you can see the pushrods are not finished yet. I have to get them bent in such a way as they clear all the woodwork and the centre of the servo disk when it moves through the complete 170 deg arc. It's quite tight in that servo bay so this needs so careful adjusting. It's nearly there, just tweaking the bends a bit, then I'll cut them off to length.

The trick (hopefully) is that with some 2mm collets to retain the pushrods, I can then use a ball link attachment to drive the nose gear, as it will wind up being above the level of the collets allowing the third pushrod to move freely. More to follow.

[Nigel R]

Small progress. I tweaked the gear pushrods and got the bends at the servo end, and the length right. I then proceeded to mismeasure and cut off the end (where the collet retains them) too short - whoops. So now I need another pair of rods. Measure twice, measure twice, measure twice...

However I can use these as patterns to make the second set, so all is not lost. And the hinge slotting tool has arrived, so now I can get the ailerons on and connected to their servos.

This terrible photo shows the current state of the gear install, and should illustrate how I'm going to handle the nose gear rod (however because I've taken it from directly above the servo, what you can't see is that the ball link is higher than the collets).

[Martyn K]

That is looking lovely Nigel

beautiful woodwork

Martyn

[Nigel R]

That's very kind Martyn

I should admit - there are a few rough bits hidden by the photos!

[Nigel R]

A couple of hours flew by last night, while I got the main gear pushrods sorted.

First off, bend up a replacement pair of pushrods, using the last ones as templates.

Next, I changed the connection on the gear unit - removing the ball link, replacing it with a cut down snaplink, with a 2mm hole drill through it. A 2mm bolt then threads through the snaplink and into the gear unit's cam block.

A bit awkward to attach/detach/adjust - the unit has to come out - but I don't see that being a problem. These won't come loose, and now they're set to the right length they needn't be touched. If all goes well they will never come out the wing again...

Now if I can just figure out how to embed video from youtube, watch this space.

[Nigel R]

 

 

Edited By Nigel R on 28/04/2017 16:28:11