Scale Soaring UK

Here's a photo of the prototype . . .

and here's how I received it . . .

Apparently Caproni were quite prolific builders of two seater gliders and the A-14 was the only single seater they ever made. Going by the photo, it looks like it flew OK.

I liked the look of the A-14 as soon as I saw it - even though it was quite broken.

The first thing to do was re-glass the inside of the cockpit and then begin the restoration by using 1 mm carbon fibre rods and spruce spars.

Then I commenced rebuilding the control devices, including an inverted servo for the cable release and a pull/pull servo for the fully flying rear stabiliser. I also added a retractable undercarriage and a servo for that.

The doors were made from the centre of a toilet roll which was fibreglassed. Hat elastic is the spring which closes the doors as the wheel retracts.

In the crash, the wings tore out of the fuselage, so more glass and epoxy were required to rebuild that area.

A bit more work on the cockpit innards.


There is a bellcrank inside the fin root and a push rod powering the T bar which operates the full flying stabiliser.
The pull/pull servo in the centre of the cockpit (see above), operates the bell crank.
That took some micro fiddling and faffing to find the hole in the top of the push rod and insert the cross pin.



A 15mm carbon fibre rod was used to replace the flat spring steel wing joiner which was twisted into a pretzel in the crash. A piece of plastic 20mm conduit was then inserted where the old carriers had been and epoxied in.
This further strengthened the fuselage at the wing roots, tying the whole section together.


The old reliable Bosch laser level was used to check the alignment of the fin, fuselage and wing joiner.

Next - rebuilding the cockpit base and canopy.

The cockpit base and canopy were both smashed - although I had the major pieces which I taped together to get an idea of how it looked.

I first made cardboard templates of the three parts of the cockpit base, and then cut two sets of plywood copies - one of which I set up on the fuselage and glued braces into them so they would retain their angles.

Once the glue had set, I made a single rib based on the remnants of the canopy and having regard to the height of the pilot figure.
I filled the interior with polystyrene foam and then cut seven notches in the rib and drilled seven corresponding holes in each of the end plates. Seven 1mm carbon rods were inserted which gave the shape.

Then I plastered it with drywall putty which was sanded to shape and then painted with putty paint undercoat.

This made the buck for pulling a canopy of 1mm PET G sheet.

Now I returned to the second set of plates I cut for the canopy base.

A small dam was glued around the edge and the 5/8" magnets were epoxied in.

Then I set about recreating the environment shapes of the cockpit and loosely placed the pilot.


Some puttying later, the whole thing was painted.
However, I wasn't happy with the angle of the pilot, so I angled the base on the disc sander.
I had previously glued a block on the bottom, which took the angle.

Then I pulled the canopy on my vacuum forming machine.

I installed the 3mm LED which will become the power ON indicator, trimmed the canopy and glued it in place.

I used 9mm automotive pin striping tape to simulate the canopy frame.

In the next episode, I turn my attention to the wings.

OK Wings

The spoilers are well made plastic jobbies, but the torque drive from a servo mounted in the fuselage was beset with problems.

So I decided to mount thin servos in the wings and close couple them to the ends of the torque rods.

Late last century, when this model was made, thin wing servos apparently weren't around.

First, I have cut out a pit in the wings.

After cleaning out the foam, I epoxied a 2mm ply doubler inside the 1mm skin of the wing.

Then I placed a special tool designed for the purpose, inside the pit to force the 24 hour epoxy to its thinnest.

As the epoxy oozed out of the gaps around the side, it was scraped away with a pointed stick.

The residue was wiped away with isopropyl alcohol.

Tomorrow I will continue with boxing in.

Cheers

I rather liked the way you set up the canopy form with 1mm carbon rods Max. I must remember that the next time I need to do a canopy.
Brian.

Thanks, Brian.

Now that the space has been boxed in by epoxy and ply, I turn my attention to the mechanism . . .

I removed the aluminium torque tube from the spoiler box and cut it to length.

Then I took a piece of 1mm piano wire and bent it into a U and passed it through holes drilled in the tube.

Then I wrapped a piece of copper wire around the piano wire and soldered it together, pushing the spare end into the tube.

I took a cross type control horn and reamed it out so that it was an interference fit on the servo spline and then screwed it into place.

The cross horn and the piano wire form a universal joint.

So, the box has been fitted out and the servo has been attached to the torque rod.

I've made a 2mm styrene cover plate and soldered in an extension for the spoiler servo.

. . . and I've crimped on a lead for the aileron servo cable.

I'm waiting for the glue to set up (and for the countersunk head screws to arrive).

Test fit the wings with only the anti-rotation pins in . . .

Just noticed that the wings are swept back.

That should be interesting.

OK I'm still waiting for my magnets to arrive so I can start my first proper build.

It's been nearly a month now. The Covid 19 has really played havoc with deliveries.

Anyway, I've still got this fellow to play with . . .


This is where the old Graupner box used to be. My router made short work of that.

I had to put in a side panel next to where the cables run. It's 2mm ply and will help support the spar.


This is the tube which takes the 15mm carbon fibre wing joiner. It will be the same length as the old Graupner system, extending 300mm into each wing.

I'm using the root ribs and the moulded part of the fuselage as a guide to set the dihedral. The wings are polyhedral, with the tips carrying the ailerons.

Once the wings are set up correctly with the laser on blocks, I'll pour epoxy into the spaces. Then I'll fabricate the rest of the bottom of the wing and cover it with 0.6mm Finnish Birch ply.

Well, that's the plan anyway.

This is going to be a much more sophisticated craft than the original Aviomodelli.

Cheers

This is how it's looking after the epoxy has been poured around the wing tubes . . .


Once the epoxy had set up, I cut a piece of 2 mm ply, 22 mm wide and 320 mm long and epoxied it in to replace the lower wing skin. Then the filling and sanding began.


The three hatches in each wing have been covered with masking tape in readiness for the putty paint.

The left wing is done!

Finally. Both wings done!

You are getting there Max. By the way, I am very envious of the size of your workshop.
Brian.

Thanks, Brian.

When we bought the house a couple of years ago, I was attracted by the 8m x 7m garage with 5m high walls.

I never actually gave the house a second look.

I built a mezzanine floor in the garage for my man cave and went on from there.

The walls are still not flushed and painted, but the insulation and airconditioner are in.

Cheers

Max Wright wrote: ↑23 Oct 2020, 22:03 Thanks, Brian.
I was attracted by the 8m x 7m garage with 5m high walls.

Brian,
That's not a garage, that's a warehouse.....



BC

When I lifted the assembled model, it seemed extra heavy. So I stepped on to the scales, deducted my 90 kg and the residue was 4.5 kg. The wings together have an area of 0.570 m² = wing loading of 126 grams/m².

I have a South African friend who lives in Hungary; who guided me through the calculations.

He also showed me his calculator for GC which indicates that the swept back wings will take the CG forward rather than back - which was the direction my intuition was taking me.

I'm not experienced enough yet to know if a wing loading of 126 grams/m² is good; or not.

Preliminary balance tests are pointing towards having to add weight to bring the CG forward, so it looks like I have some wriggle room.

I have heard that nose heavy models can fly poorly, but tail heavy models fly once.

Cheers

Full assembly shot?

Max Wright wrote: ↑24 Oct 2020, 22:08 When I lifted the assembled model, it seemed extra heavy. So I stepped on to the scales, deducted my 90 kg and the residue was 4.5 kg. The wings together have an area of 0.570 m² = wing loading of 126 grams/m².

Max, I think your calcs are a bit out. 4.5kg & 0.57m square, gives 9.7kg/m square.
This equates to nearly 26oz/sq ft in old imperial money - which is a bit heavier than the 16oz/sq ft area I would expect. If that is correct then it might need a good blow to stay up!

My advice was 0.570 m² ÷ 4.5 kg = 0.126 kg/m² Peter.

Are you doing 0.570 m² x 4.5 kg = 2.56 ?

No. That's not 9.7 kg/m²

Sorry. How did you arrive at 9.7?

4.5 ÷ .570 = 7.89

4.5 x .570 = 2.56

Sorry for being thick. What are we missing?

Cheers

1/0.57= 1.754385964912281

1.754385964912281 x 4.5 = 7.89

So 7.89 Kg/SqMtr
or 23.59 Oz/Sqft

I could be wrong though.



BC

Max, as Barry shows - you have to divide your weight by your wing area (in sq m), thus you increase your weight per m sq. as you say you have less than 1 sq m.
(Wing loading = weight / wing area)

But this is in upside down land.......................

RobbieB wrote: ↑25 Oct 2020, 10:19 But this is in upside down land.......................

I would like it noted that I did not say that....

BC

Barry_Cole wrote: ↑25 Oct 2020, 11:18

RobbieB wrote: ↑25 Oct 2020, 10:19 But this is in upside down land.......................

I would like it noted that I did not say that....

BC

But I bet you thought it

My long and well thought out reply has disappeared.

The precis is "What is my wing loading in grams per square decimetre?"

That's the yard stick.

Max,
Google says multiply by 10, so that makes 78.9grams/decimetre squared.

Thanks, Peter.

Hi Max,

I've loved following your rebuild - good effort!

Just to make sure we are confused, I'm pretty sure your wing area is significantly more than 0.57m².

Even if Aviomodelli stuck with the high aspect ratio of the original (25), you would have 0.68m². But it's much more likely they widened the wing chord a little, so you probably have nearer 0.75m². The 4m Alpina has over 0.80, by comparison.

The effect of this will be to reduce your wing loading significantly.

Assuming your 4.5kg mass is correct, I'd expect your wing loading to be about 60g/dm². This is 19.7oz/ft², in old money.

Oooh, I do love a spot of arithmetic.

Good luck with the test fly.

Rog

Hi Rog

Thanks for that. The maiden will be delayed as I've discovered that the aileron in the right wing has developed a twist over time, which has resulted in wash IN . . .


So I have cut it free and I'm going to re-set it using ammonia/water. Shouldn't take long.

But today I'm hoping to meet the Scouts blokes at Blanchetown so I can photograph the prototype of the Motor Falke.

The calculation of the wing area were done by taking the span and then drawing two triangles, and subtracting one. The span is 2.00 metres. The root chord is 195mm and the tip chord is 90mm. Hopefully your arithmetic will give us a better result.

Cheers

Oh dear - wash-in is not a good thing. Hope it comes out ok.

Thanks for the chord numbers Max. Based on the wing platform, that gives an area of 0.7186m². If the mass is 4.5kg that’s a wing loading of 62.6g/dm², or 20.5 oz/ft². Anyway, I’m sure it will fly well.

Thanks, Rog.

62.6g/dm² is better than 78.9g/dm²

OK Sorry about the delay. I've stopped work on the Falke build to concentrate on getting this model ready for Bordertown aero-tow on 27- 29th of this month. We are ready for a hand launch tomorrow. Fingers crossed.

I've filled the nose with lead shot and covered it with PVA to keep it in place, and glued the original lead plug in with silicone.


Then I assembled my VicRC large model CG machine.


Because of the swept back wings, I balanced it with the CG at 25% of the root chord.

I can always add some stick on wheel weights if I need to.


Here are some random shots of it sitting on the balancer . . .


When the retro fitted retract goes up and down there is a slight deflection on the balance pointer.

Hardly noticeable.

Don't know why I have an extra copy of the photo.

Before we could start hand launching, my friend who was helping me, suggested we try lifting the model at the wingtips to confirm where the CG should be.

As the fuselage lifted clear of the table, a dimple about 50 mm across appeared in the middle of the upper sheeting of the wing; about 1/3rd the way out from the root.

It is clear that some internal damage has occurred to the spar at that location. A similar, smaller dimple also appeared in the other wing at about the same spot.

We decided that it would be necessary to insert a strip of 1 mm carbon fibre on its edge, into the wing.

Unfortunately I won't be able to do it before Bordertown, so the A-14 will become a hangar queen for the time being.

I will turn my attention in what free time I have, to starting the Motor Falke build.

Max

Unless you intend to do violent aerobatics it is a bit extream to try lifting a model like your Calif by the wingtips. A much more realistic test of the strength of the wings would be achieved by lifting at around 1/2 span.
I do accept however that if you have a localised deformation in the wing skin, it needs investigation.

AEB

Yes. We did it very carefully, John.

But it doesn't look good.

Cheers