Aquila

[Martyn K]

A bit more progress and that is as well getting a cracking evenings flying in yesterday.

The next job on the wing was to fit the leading edge sheeting and upper cap strips

My usual method is to glue the sheet to the spar (after it has been cut slightly oversize), pin and let the glue start to set. Glue the top of the ribs and le and pull down - I usually spray a little water on the sheeting to help it set - just a little - just slightly damp so it doesn't swell too much.

The excess wood for the spoilers is removed between the upper front and rear spars. The spoiler is simply a length of 1" x 1/4" TE section. Note the cap strips have been added except those to the rear of the spoiler.

I was tempted to go down the micro servo route to activate the spoilers but chose to stick with the original method of a string pull system. A couple of hooks were made that will be recessed into the lower edge of the spoiler. These are capped with 1/32 ply pieces as shown

Like this. the arm needs a cutaway between the spars so a small section of web is removed (and then cleaned up).

A small piece of hardwood with a piano wire loop is glued under the rear spar - using epoxy.

The spoiler is hinged on the upper surface using Oracover. The string (sea ranger fishing line) is looped as shown and then routed to the servo in the fuselage down the PTFE tube. The knot is glued up using a drop of PVA.

And with the final pieces of cap strip fitted.

 

Next the wing tip blocks. These are laminated from a piece of 3/8" balsa and a piece if 1/4" balsa. and cut oversize and glued to the tips. The original design used reverse Hoerner tips. These are complex to carve and I have never been convinced of the benefit. They are meant to reduce the drag at the tips by reducing the vortices but at model aircraft speeds I am not sure that they are that efficient. I am settling on simple block tips of the same planform.

Glued into place and then attacked with a razor plane. Don't try and get too close to the final shape - finish it with a sanding block

The lower surface. By leaving it too big you can safely carve/plane away with some confidence of a safety margin.

20 minutes later with a perma-grit block - ready for a final polish.

Finally, I couldn't resist a first full assembly

and

Yep - very pleased with that..

A bit more to come..

Martyn

 

Edited By Martyn K on 18/07/2014 23:00:43

[john stones 1 - Moderator]

It looks a beauty Martyn

John

[john stones 1 - Moderator]

duplicate

Edited By john stones 1 on 18/07/2014 23:06:55

[Colin Leighfield]

When it looks right, it generally is. (Except for the Depron Barnstormer, which has really got me scratching my head).

I've still got my Multiplex Alpha from the eighties, which I put on one side after flying it through some electricity cables and dinking the leading edge. I used to love it, seeing this makes me think about resurrection.

[Martyn K]

Ok - I managed to get it covered this weekend..

taa-daa

and

Underneath - contrasting - so I can tell which way up it is.

I haven't covered the spruce skid - just given it a couple of coats of clearkote - it looks very nice - brought the grain up beautifully.

I now need to make a canopy - which also means that I have to make a vacuum box.. I may do a separate blog on that.

The main spar is 6mm carbon rod - which is a nice fit in the wing tube. Still a bit loose though so I may need to think of a way of clamping the wings on - I don't want them falling off.

The other problem that I have is that the spoilers aren't closing cleanly so I will have to redo the hinges I think. Got some time to sort it - there is no rush

Martyn

[Tony Bennett]

looking beautiful now martyn

[Erfolg]

Martyn

I assume that the spoilers are typical (for the period) letter box type. On that basis I assume that they are similar to the Sagitta ( although an earlier design) and that they are Bowden cable pull type.

I always found there were two issues with these, the first, was for the wing to move during the tow, just enough that the air-brakes would crack up a bit, unless i had some slack in the system. Even then I would have to often knock them flush.

To solve this problem I found that either high strength magnets would hold them down, pretty much under any sensible circumstances. The other method was to use a very light piano wire torsion bar. Although the wire used is ridiculously thin, the closing torque is high.

I found that the traditional elastic band, had a strong closing action when the brakes were out, but pretty poor at keeping them closed.

I thing that my last gliders all used fishing wire, as the opening mechanism, less sticktion than cable (non to talk off), does not stretch,

The one big glider I resurrected when re starting, I bit the bullet, cut the wing open and used a direct acting servo, with magnet to keep positively closed.

The nose looks a lot shorter than a Sagitta, which needed lead in the nose to get the right CG, although I think from your photos, the Aquilla is a little lighter in construction, although I can see how and from where the design was developed. It was from knowing that I needed lead, I had no issue with a pine sandwiched nose block, the weight did not matter there.

So the next post will be about thermal hunting!

Edited By Erfolg on 21/07/2014 16:57:06

[Martyn K]

Thanks Erfolg

That is very useful. You are correct with your functional description, it uses a pull line to lift them from a single servo in the fuselage. The plan shows a 10g weight on the spoiler to close it - if you look at the photos, you can see they are slightly open. However, a 10g weight doesn't close them properly so I am investigating other methods. I have looked at and eliminated elastic bands - I do like the idea of a piano wire torsion bar though. I think it should be quite easy to fit.

To be honest, I wish that I had been less puritanical about this and fitted a 9g servo in each wing. It would have been lighter and as you say would work independently of wing position.

It will need nose weight - there is a ballast box in the nose in the pine noseblock. I am using a 4AA NiMh Rx battery but it needs considerably more weight than that. It will soon be time to start melting lead..

Martyn

[Martyn K]

Getting very close to completion.

To recap, I have 3 challenges remaining:

1. Canopy

2. Stop the wings falling off

3. Make the Spoilers shut properly

4. Fit the radio gear

5. Get the CG correct

(OK that's 5 challenges)

The canopy. Plan A was to make a plug and then vac form a canopy from Acetate.

Here is the plug

Here is my vacuum box. Driven by the shack vac. My first attempt was an unmitigated disaster and I ended up melting my plug.

Plan 'B; - make one out of balsa.

A frame was glued up in situ and then capped with two laminations of 1/2" sheet.

Note the doubling up where I will be carving through the base layer. The sandwich was then planed carved and sanded to shape and covered in silver solarfilm. Not exactly what I wanted but it will do until I get the vac moulding process sorted.

Radio gear installation was fairly straightforward. I use my standard method of 3mm liteply tray with 3mm liteply doublers to hold the servo screws. It has proved to be reliable and rugged for small to medium sized low stress models.

and with the radio gear installed:

The servos are for (front to back) - tug tow release, elevator, rudder and spoilers. The spoiler arm is a 10BA bolt - the cords to the spoilers have loops that hook over the arm. It is driven by a simply on/off switch on the Tx.

You can also see the tinplate bands that latch onto a pair of magnets in the base of the 'canopy'. The rear of the canopy is retained by a pin located into the rear canopy bulkhead.

The Rx is the new FrSky X8R with a variometer telemetry module located just behind the canopy. The Rx has the new PCB aerials - one is visible adjacent to the rudder servo.

I forgot to take and photos of this, but the spoilers are pulled down be a weak elastic band with about 20 turns wound on. The idea is that as the band looses tension, the turns cause light knotting which add a little extra pull and do not put an undue load on the servo when they are pulled up. The MG90 servo seems to cope OK with them.

The last major challenge was to stop the wings falling off. The carbon wing joiner is a little too slippery in the joiner tube for comfort so I needed a method of holding the wings together.

A 7mm hole was drilled through the fus, just behind the joiner tube - carefully aligned with the joiner.

This gives me a 6mm hole when the tube is fittted - each wing root has small hook installed. This is bent from 18swg piano wire, basically a 'L' shape with a small hook at the end. A small washer is soldered at the bend of the 'L'. Keyhole slots are then cut into the root ribs and the hooks are slotted in and epoxied into place. As there is vey little scope for error here, the wing was offered up to the fuselage in the correct position, then a little dayglo paint sprayed down the tube. This provides a perfect target for the hook position.

A bit blurry - sorry about that.

Finally, the model was ballasted to get the CG correct. Basically, this involve filling the ballast box with folded lead strip.

Now ready for a maiden, hopefully one evening this week.

I'll do some more detail photos as well this week.

Martyn

[PatMc]

Martyn, have you considered making the canopy from a pop bottle ?
All that would be needed is a piece of scrap pine to make the plug a 2 litre bottle (green, brown or clear) & a heat gun or paint stripper gun.

[Martyn K]

Hi Pat

I bought a large bottle of R Whites Lemonade for that purpose (the bottle has no ridges or mouldings). I have never had much success moulding pop bottles, sometimes I can get them to fit quite easily without heat but I really want to master the art of vac forming so I'll proceed down that path. The vac form failed mainly because I didn't get the acetate hot or floppy enough. I need to rethink the process.

I am happy with the balsa canopy for the short term.. It looks OK.

Martyn

[Martyn K]

A couple of points. In case it is not obvious, the wings will be pulled together using a small number of small elastic bands. Basically, the bands are hooked over one hook on the wing, pulled through to the other side and then hooked onto the second wing as it is offered up.

The missing photos:

The balsa canopy..

A shot in the fus looking towards the nose showing the tug tow release. You can see the flight battery and lead in the ballast compartment.

Finally, the aileron return system. Twisted elastic bands between 2 glass headed pins doubling as hooks.

Maiden tonight if I get a pass out

Martyn

Edited By Martyn K on 28/07/2014 17:34:56

[Martyn K]

Fantastic... I maidened the Aquila this evening. I used an old bungee launch that I made up nearly 30 years ago. I would have thought that the rubber would have perished but it seemed OK. It may have lost little of its elasticity though. 50m of bungee plus 150m of monofilament. Lack of wind prevented a really high launch, but high enough to check the glide and telemetry. A little under elevated but a quick check shows the CG a Little too far forward. Apart from that a lovely flat glide and one weak lift flight of a few minutes. Perfect..

I'll see if I can get some photos next time.

Martyn