Glass Slipper 2

[Martyn K]

Just before Christmas, I well and truly broke my lovely Glass Slipper Slope Soarer when I clipped a wingtip landing on the edge of a hill in the peak district. The resulting cartwheel with triple solko well and truly finished the fuselage off. My lovely planked fus ended up as a glass fibre bag of planks.

(Glass Slipper Mk 1 - Photo courtesy Ian Jones)

I built a new fuselage, reusing the wing and tailplane which were undamaged and that is waiting for a new maiden. The new fus is much stronger, comprised of thicker balsa sheeting, big triangle section longerons and the curves carved and sanded so it has retained much of its elegance (or at least I think its elegant).

However this did get me thinking that I really need a spare and hopefully improved version.

So Glass Slipper 2 was created. The drawing was started while I was in hospital in the new year and a bit of design discussion on Facebook followed.

The result looks like this:

and

(a bit of a close up). (Hardly a curve in sight)

The wing panels are veneered foam and are currently en route from Bill-Kits (Bill Manley)

The fus layout is similar to the layout I used for the replacement fus mentioned above.

As I am convalescing at the moment, I have been only allowed limited time in the shed but I did manage to make a start on this last weekend.

I have elected not to go for a symmetrical section, the design brief is sporty (hopefully fast) with some aerobatics and Andy Ellison (and others) suggested this wing section.

The fus side (and top/bottom) are 3/16 balsa scarf joined to get the length with 1/16 ply doublers to just behind the wing

1/2" triangle in the corners and tapered in the vertical plane to the front and rear

and

and

The idea is that most of this wood is carved/planed/sanded away leave a nice profile and cross section but quite strong

The snakes need to be added before the fus is puller together at the rear, you will not get them in afterwards.

Today's task was fitting the R/E servos in the nose. This required me to mill out the triangle from the inside. The servos are mounted tandem style but offset slightly so the servo arm would fit. The fus maximum width at the wing root is 40mm. There really isn't much space in there. The servos are midi sized servos, digital metal gear with BB,

The Rx sits under the wing. Those snake outers are 4.5mm wide...

Final job today was to hinge the rudder and elevator and fit and connect the control horns. 3 hours in the shed was the limit of my physical endurance.

Hopefully the wings will arrive tomorrow and I can mark out the ailerons and drag flap and start work there,

More to come

Martyn

[Martyn K]

Wings arrived last Thursday. They are rather thin but usable (I hope).

First job was to mark out the areas to be cut away for the ailerons and flaps

and

Marked top and bottom. A bandsaw was used to cut the cross cuts and a scalpel from both sides for the longitudinal cuts

3/8" square balsa rear to the of the wing along the aileron boundary, 1/4 " Rock hard balsa for the LE of the aiIeron.

The front edge of the flap bay is from 3/8" triangle.

The aileron is very very thin and will need substantial stiffening to prevent flutter

The wing LE is from 1/4" square spruce. This has added an incredible amount of strength.

Gorilla polyurathane glue used for all the wood to foam joints

The TE of the aileron has the last 1/4" replaced with spruce. That, along with the hard balsa LE has stiffened it up sufficiently

Wing tips from 2 laminations of 1/4" sheet balsa. Grain this direction to protect the thin TE of the wing

The flaps were fun. The LE of the flap has triangle section so that when the flap is in the up poistion there is a good air seal between the flap and the wing. The hinge is about 25% of the flap chord, I would have preferred it to be further but the section was too thin.

A 16swg pin runs through the wing and through these bearings - a length of Golden rod inner. The flap and wing carefully measured and drilled and the golden rod glued into place. The pin was then glued (using a thin smear of gorilla glue) into the tube running through the flap.

The flap looks like this in the down position..

and

in the up position.

Done a bit more today but no photos yet,

More to come

Martyn

[Piers Bowlan]

It looks fast and slippery Martyn. Flaps are great and should be really effective. Following with interest .

[Nigel R]

That is one sleek looking machine. Following.

Servos aren't going to move anywhere, that's for sure!

I like the flap setup. Seems a fairly simple way to get a bit of upward airbrake effect as well as the usual downgoing flap area.

How was the flap area / dimensions calculated? Was it based on prior experience, or did you go for a "xyz % of wing area" approach?

[Martyn K]

Thanks both

Nigel, the drag flaps are (as always) a bit of a compromise. Their real purpose is to slow the model up so I can keep the nose down on approach. I don't want them generating lift, the prime purpose is to add lots of drag. Its predecessor was a real pain when it stalled. Always violently..

I have just taken a simple guess at the size, I have no idea how effective they will be. However, I didn't want them blanking off the tailplane with turbulent air, that limited the width. TBH, I wish I had made them another 20mm deeper with the hinge in about the same place. I don't want them to impact on pitch too much and if I had them protracting more along the upper surface, I would have been more comfortable with them. It will be interesting to see how well they work.

The tailplane is a little larger than normal for a glider of this nature. The idea behind that is to move the NP backwards, this means I can move the CG further back (about 35% MAC) and still maintain stability. By moving the CG back, I can fly the wing at a lower angle of decalage which will hopefully keep it fairly neutral across a range of airspeeds. i.e. prevent it from ballooning. Not sure how well that will work, if its too twitchy and I have to move the CG forward, then I'll take about 50mm off the tailplane span. Easier to take away than add.

Martyn

[Martyn K]

A bit more progress. Only able to do an hour or so in the shed at a time... Had another (much milder) heart attack this week

With the wing more or less completed, it's time to set the decalage. I am going for +0.5 degrees but I think I really should have gone a little less than this. I bought this really neat little incidence gauge, it came from Bang Good I think. It seems very accurate. Cost was less that a tenner

So with the model securely fastened and using my home made incidence jig +0.8 for the wing

and the tail

+0.3 = 0.5 degrees decalage. Bang on..

With the wing set, I can then make the upper wing fairing.

Plywood facing and the balsa is 3 pieces of 3/8 sheet sanded to shape

Finally, it looks like this at the moment

This morning I have drilled the access hole to the wing mounting bolt and added a short length of tube to keep the edges nice and neat. Finally added some epoxy and micro balloons to blend in the fairing to wing transition. Just waiting for that to set. Hope to get this finished this weekend.

More to come

Martyn

[john stones 1 - Moderator]

Looks the business Martyn, like it.

[Martyn K]

Thanks John.

Feeling a little better and even managed to get out with the original Glass Slipper (with new fus) at the weekend. This inspired me to crack on.

Had a couple of problems setting the flaps. the two flap torque rods are joined with a short length of brass tube and the idea was to sweat solder into the seam. Which turned out to be a real pain. One half worked the other just turned into a mess.Eventually got it done, mounted a servo in the LE and made a brass torque rod horn. All seems OK now.

Covered the underside of the wing and then slept on it. (I don't mean I actually slept on the wing - its the wing that was bothering me and I called a temporary halt). In the middle of the night I decided that the wing isn't strong enough so added another spar. This meant stripping off the covering, inlaying a 1/4 x 1/8 spruce spar (36" long" with an additional 1/4 x 1.8 doubler (18" long) in the lower surface.Let the glue dry and added a little filler and then recovered it. Still not convinced in will be strong enough though. This model may have a very short shelf life LOL.

Completion was very straightforward, covering the model and hinging and securing the wiggly bits.

It looks like this. A very simple colour scheme. No pint is spending hours doing fancy decoration if its only going to last minutes

and

and underneath

Not bad considering the butchery that went on..

CG set ( alittle on the safe side but still quite a long way back and it weighs this much

Which is a bit light. I'll need to find a way to add ballast/

 

Hope to maiden it this weekend.

 

Not much more to come. I can get back to the the Chippie and Fury and Touche now

 

Martyn

Edited By Martyn K on 20/02/2019 22:24:18

[Nigel R]

It looks the business! Good luck on the maiden.

[Martyn K]

Flew the model for the first time on Saturday. Really pleased on its performance in fairly light airs Quite literally flew hands off from hand launch. In fact, I didn't intend to launch it. I stood back about 30m from the edge of the slope and did a test hand launch. Next thing was that it had cleared the lip and it was away.

Lift was a bit marginal but the model rolls much better than its predecessor. More authority and far more linear. Also did a couple of loops and a stall turn The rudder is very responsive

I think the CG could go back a little but I was happy just to enjoy it Push the nose down and it picks up speed very quickly

Photo shows the model with my Foka 4 which was also successfully maidened on Saturday

Despite being 74" span it's dwarfed by the Foka

No more to come

Martyn

 

Edited By Martyn K on 25/02/2019 13:43:06