Glass Slipper

[Andy Meade]

Very pretty, and some lovely woodwork to boot. I'd say I'd love to have a go at building one, but my planking is not as neat as what maybe required for such a taper - boxes and simple curves are more my level!

Looking forward to the wings, but have a nice holiday in the meantime

[Martyn K]

Hi Andy

the planking isn't too difficult. The hardest bit was getting round the sharp curve on the lower side from the backbone. After that it wasn't too bad. All the planks are 3mm balsa, 6mm wide except the ones round the sharp bend (3mm wide) and of course the last 2 that were cut to fit. Its slow because (the way I do it), I fit one plank then let the PVA glue dry, otherwise its like stacking a house of cards.

Its the sort of project you need to have in the background while you are building something more important.

The wings will be fun though

Martyn

[Bob Cotsford]

There's something even more satisfying about planking than there is carving - achieving beautiful flowing lines with an absolute minimum of wood. (but lots of frustration!) Lovely job Martyn.

I assume you will preform your spars with steam or ammonia? That should minimise the stresses you need to fight when sheeting the wing.

[Martyn K]

Hi Bob

The bends aren't too aggressive and I find spruce is OK to bend and laminate in this manner. I have got an idea for assembling the wing so it remains straight which I will try and then share with you in due course.

I am still thinking it through though - hence the (unusual) lack of urgency

M

[Martyn K]

I have spent quite a bit of time on this model in the past week although I don't seem to have much to show for my efforts. I have just spotted that I have a couple of photos missing so I'll upload those later

I have started work on the fin and tailplane.

The required section of the plan was produced by Tile Printing, joined and the 1/2" sheet outline pinned down. The LE is harder wood than the fin post as this will carry most of the load

Additional gussets have also been added above the 1/2" cross member (rib) - this will support the tailplane. As usual (for me), I am using Kevlar cloth hinge for the rudder. The fin post is laminated from 2 x 1/4" balsa

The outline (when dry) is then sanded down from 1/2" wide at the base to 1/8" wide at the tip

The frame was glued into position, checking that it is vertical - use the joiner as a reference and then I have sheeted with 1/8" balsa - grain vertical. Need to leave a gap for the tailplane

The front of the fin is blocked in with soft balsa, slotted to support the fin.

Another layer has been subsequently added, When dry, this will be carved and blended, the lines will flow seamlessly (I hope!) from the fuselage into the fin. That's the plan anyway

More to come

Martyn

[Martyn K]

The two missing photos..

The canopy has a subframe and it is fitted. Unfortunately, being a bear of very little brain, the subframe sits perfectly inside the fuselage, the canopy sits on the outside..

 

The tailplane - laminated from 2 x 3/16 sheet balsa

Quite high aspect ratio. It looks quite thick, but it will be carved to a NACA0008 section (or thereabouts). I don't really like flat plates for any aerofoil section..

More to come

 

Martyn

Edited By Martyn K on 28/07/2015 13:31:07

[Paul Nazaroff]

Why did you use a solid horizontal stab? I don't like flat plates either but ribs and spars would require a lot less sanding and be lighter. Any weight saving back there is amplified by fore/aft aspect ratio to a greater saving up front.

Paul

[Martyn K]

Hi Paul

I did think about that.

Basically, it was to try and keep it simple, lots of curves and quite a high taper, I was struggling to visualise just how I would get this assembled. I have selected quite light wood, I don't think weight will be too much of an issue, in fact I may incorporate a spruce spar yet (over the centre 1/3rd) but I don't think it will be necessary.

M

[Martyn K]

A bit of progress last night.

I carved the block that links the fuselage to the fin and blended it in.

and

It actually feels better than it looks. Needs a tiny bit of filler on the other side. I haven't quite got the curves quite as I wanted, but it's near enough

I also sanded and fitted the tailplane.

The tailplane was aligned by visually comparing that it is horizontal with the wing joining tube and also using triangulation to the centre of the fuselage, just behind the canopy.

The tailplane is sandwiched between the two 1/2" sheet balsa blocks. This is the lower block.There will be a gusset linking the lower block to the fin post, the elevator push rod needs to be fitted next then 1/8" balsa sheet to fill the gap.

Starting to look more like an aeroplane now and less like a boat

More to come

Martyn

[Martyn K]

A little more progress last night

The lower fin skin added to the left side

and a supporting gusset added. Note the grain is the wrong direction.. it should have been diagonal (ideally) or vertical - however, its quite thick wood so I should get away with it. .

Really not sure how I missed something so fundamental.

a bit of filler required but its looking OK

Slot cut and the elevator push rod added - before the lower right skin is fitted..

Just a couple of small balsa in-fills required and then sand it down ready for covering.

Wing next, I need to clear some space on the main build board which is currently occupied by the Aurora or see if I find another board which will fit

More to come.

Martyn

[Martyn K]

Back from my hols and getting back into build mode again. Its taken a few days - I must be getting old.

After lots of pondering, I have started work on the wing. One of the problems that I had to get round was how to keep the false TE straight while the LE and spars were trying to spring straight. The only way I could think of getting round this was to add a vertical 'board' to my horizontal board and build the wing with the ribs etc pushed back against it. The wing upper surface will need to be sheeted while the wing is still pinned down.

So

The vertical part was made from 2 strips of 10mm square pine from B&Q.

False TE parts assembled using Kevlar cloth as the hinge material.

I then realised that I couldn't use this as the cloth was preventing the false TE from sitting flush.

I have now decided to use a strip of 1/16 spruce as a false/false TE.. The false LE is a 1/8" balsa taper that sits on the board. this will be trimmed back when the sheeting on the underside is added.

One set of wing ribs prepared - laser cut by Lasercraft. The 3 root ribs have 1/16 ply doublers to carry the wing joining tube.

Starting from the root, add the wing ribs, butted up against the false LE and TE. Pins and weights hold it in place

Junction with the false TE

The wing rib positions were simply drawn onto the board using a soft pencil.

After an hour of fitting the ribs are all in place and left to dry overnight

This morning, the upper spar was added. This comprises of 4 laminations of 1/8 sq spruce at the root tapering to 2 laminations at the tip. The tip rib is very thin and inevitably got cracked while fitting the spar.

This shows the first taper point where the 4 laminations are reduced to 3 laminations. The plan shows a full taper from 1/2" to 1/4", the reality was that it was too difficult to do this so the slots needs to be opened slightly (and chamfered at the tip because of the angle of the spar to the rib).

And it now looks like this. I need to add gussets to support the ribs to the false TE, then add the upper sheeting.

More to come

Martyn

[Martyn K]

A little bit more progress last night and this morning

The upper sheeting was applied.

Due to a bit of bad planning, the two 4" wide balsa sheets were exactly 1/8" too narrow at the root so a 3rd strip needed to be added for the inner 3 or 4 inches

Flipping this over, the lower spar has been added - again laminated from strips of 1/8 sq spruce

Not very sharp for some reason..

The end of each sub strip - i.e the two that are not full length have slight tapers on them, but more importantly, they are staggered top and bottom to avoid stress discontinuities.

Next job is to fit the webs then the wing joining tube and then the bottom skin. At the moment is back on the board, sheet side up and carefully weighted down to make sure that the wing stays flat. Getting a bit paranoid about this but there are a lot of strange stresses in this wing and I am not sure how it will behave/settle.

More to come

Martyn

[Martyn K]

I nearly forgot to fit the servos. Now that would have been embarrassing

Lite ply trays sitting on 10mm wide pine beams glued directly to the lower skin. I was a bit nervous about this, but they seem quite sturdy. The servos are Corona Thin wing metal gear units bought from Giant Shark. I wish I had bought a lot more, they seem very good, very fast and centre well.

Wing joining tube fitted and thoroughly epoxied to the webs - helps transfer the load as smoothly as possible from the joiner into the wing. You can see the servo trays and how the pine has been tapered to get the servo at the correct angle

The end of the tube has been capped with a 3mm wide length of joiner epoxied into place.

Now with the servos fitted and almost ready for the lower skins to be fitted

Finally, a small ply plate to support the screw that will be used to lock the wings into place.

The false LE and TE have been trimmed back and building tabs removed. So far the wing seems to have stayed flat.

Last night, I started the skinning and the other wing is also well under way. Top skins fitted and lower spar fitted this morning

Cracking on now

More to come.

Martyn

[Andy Meade]

Very neat work. I use those Coronas in some builds too - I've got them from Hobbyking in the past.

[Martyn K]

Thanks Andy - that is useful to know.

Martyn

[Andy Meade]

No problems - here is a direct link to them

[MattyB]

Very very nice work Martyn - I particularly like the shape and craftsmanship in the fuselage, and the classic "Foss-ish" tail feathers. This is going to be a lovely looking model when it is finished!

Two QQs...

• In the 3 view on page one it looks like you have very long flaps and quite small ailerons; have you stuck with the original proportions, or made the ailerons longer and the flaps shorter? In my experience 60:40 works best on the slope for a model like this, though obviously you may be intending to set the wing up with Quattro flap meaning the proportions are much less critical.
• It looks like you glued the horizontal tailplane already, before the wing was built and attached. Is there a reason for doing it this way? I have only built a couple of wood models, but have always understood it is easier to set the decalage once the wing is in position, "fudging" the tailplane incidence until you get the right AoA relative to the wing.

[Martyn K]

Hi Matty

Thanks

No - that was a draughting error and now been corrected. The flaps go out 3 bays, the ailerons then out to the tip, but tapering as the chord narrows, There are 11 bays so a little less that 60:40, but better than 75:25

The tailplane is set at 0 degreed to the datum - which is the horizontal spruce crutch and was quite easy to measure from. As you will see when I set up the wing (+1.5), this will be adjusted by positioning of two very thick root ribs that the wing will plug into (I hope its as easy as it sounds)..

The rear end - certainly the fin - is very unfashionable. It's deliberately short and squat - the area is OK, but most modern gliders have quite high aspect ratio fin and rudders. The reason for the disparity - personally, I like my shape but it also has less torque moment for when the model gets flipped or when it lands upside down

I needed to get the tailplane assembled so I could get the fin finished.- I think it will be OK.

Fingers crossed

Martyn

[Martyn K]

Done quite a bit of work on this in the past few days, but not really much to show for it..

The LE has been added, comprising of a balsa laminate capped with a spruce laminate

held in place with elastic bands while the glue dried..

and then sanded to shape.. Much easier than I thought it was going to be. I'll use this method again - even on a straight LE wing

The wing tips were assembled from 2 x 3/16" with a 1/32" ply core

Then glued in place, then ripped out again because the shape was wrong.. Hey Ho. Note the spruce LE is continued into the wing tip.

Replacements cut and glued back in - same type of laminate

and this morning reinforced with a new hi-tech material known as Nylon, well impregnated with PVA - just like we used to do back in the 70's

The ailerons have been very problematic. They are only 3/16" at the thickest tapering to a sharp edge at the TE. My first attempt was OK, but the ailerons were far too flexible, had 'flutter' written all over them

The remedy (hopefully was to strip off the last 1/8" and replace with 1/8" sq spruce strip, but not tapered to a point. They are much stiffer although now not quite conforming to the planned wing section

They are tapered to about 1/16" wide at the TE

The root has also been beefed up with 2 x 1/8" sq laminations of spruce - being a clumsy person, I know these will be problematic

Still WIP, but getting there. Both wing panels are now at the same state, Next job will be to get the wings lined up and fitted to the fuselage.

Martyn

[Martyn K]

Good grief - 2 weeks since the last update. Usual excuses, been working maintaining the fleet etc..

But progress has been ongoing

There are 2 x 12.5mm thick wing ribs that are used to fair the fair the wing into the fuselage. These need to be carved and sanded to meet the complex double curve on the fuselage while still maintaining the correct facing angle to the wing. I almost got it right.  

These ribs are faced with 1/16" ply which were glued into place before the carving started.

Top

Bottom - with a little filler required.

To add to the complexity, the wing has to be mounted at the correct angle of incidence - +1.5 degrees relative to the Datum and tailplane (0 degrees). I used my home made incidence jig - see the Kwik Fli build for more info.

The fairings were added one half at a time, jigged and allowed to dry overnight.

+1.4 was near enough..

This is how it was jigged in the workshop, - basically strategically placed blocks of wood and tools and then carefully walking out the shed without slamming the door.

As the fuselage joining tube was already in place, this ensured that the wing was flat - or horizontal - whichever you prefer.

Then repeated for the other half. This was probably the most difficult building task so far on the model.

The nose has been added, laminated from 2 x 3.5mm ply plus 2 x 12mm balsa and then carved to shape.

Very beak like

The elevator has been added. A 14g wire joined holds the halves together.

Looks a bit rough but it all gets filled with epoxy

Kevlar hinges again and lots of pegs while the glue dries. The rudder will be added after the fuselage has been glassed, the elevator is assembled in one piece and will be cut away where the rudder will go - if that makes sense.

Finally, an assembled shot taken in the garden this morning.

 

More to come

Martyn

Edited By Martyn K on 06/10/2015 10:13:04

[Andy Meade]

Oooh that looks nice in the garden!

[Martyn K]

Thanks Andy

I have to admit that there are probably much quicker ways to get back into Slope Soaring..

M

[Andy Meade]

But surely none so satisfying as designing and building your own work of art like this!

[Martyn K]

Yes - very true .. I have to admit I am feeling quite chuffed with this, I have done a few O/D models in the past but none as structurally complex as this and its gone together much better than expected.

I just hope it flies OK. I have a feeling it will need to be flown quite fast to get the best out of it - or in other words it will be a pig at slow speeds.

[Andy Meade]

Hmmm, maybe. Perhaps a bit of reflexed aileron would make things a bit less frightening in low speed turns? Any indication of the final weight / wing loading yet?