Aggregate A9 (A4b)

The wing complete.

It has a 1 mm balsa leading edge to give a bit of 'ding' resistance.
The symmetrical section.

The thin trailing edge will be very prone to hanger rash but then so will the rest of it!
With no aileron servos required it is pretty light at 34 g (1.2 oz) but can easily carry the A4b's predicted full weight supported just at the wing tips. My '4g equivalent' test!

Eric
Agree about a sharp(ish) leading edge but then at the Reynold's number this will be working at air is more like treacle so stall characteristics are a bit different which is part of the reason that flat plate wing 'shockies' manage so well. In addition I am expecting a significant lift contribution from the fuselage and that won't have a stall as such.
In fact the balsa leading edge itself is rounded but:

In the words of Paul Daniels - not a lot!

Very interesting, I never realised that much work went into depron models, following the build, boz

The centre section of the fuselage is a bit tricky.
It requires 8 formers all of nearly the same size so there is no chance of using the centres of the ring formers for anything else so it could waste a lot of Depron.
On the sharply tapered nose cone all but two of the nine formers could be cut from the centre of a larger one.
The best solution is to 'build up' each ring former from 4 quadrants as the outline of each quadrant can be 'nested' quite efficiently in a sheet.

However although all the formers are similar they have slightly different diameters of 136, 138, 140, 142, 140, 138, 136 and 134 mm.
I am not at all sure I could build up a ring former to that level of accuracy. The problem is any variation in diameter on such a gentle curve is likely to be pretty obvious when the skin is in place.
My intended solution is to build all the formers to the largest diameter, mark the appropriate outline on each and sand down to shape.
I let you know how it works out!

Rather slow going but the 8 formers are now complete and finished to the correct size.

The small difference in former diameter along the centre section's length should allow fewer broader planks to be used, maybe as low as 16, instead of the 28 that were used on the nose section.

Using broader planks it is important that each has a radius to match the formers.

The first planks go on.

Not visible but each plank is very slight tapered towards each end to match the final 'barrel' shape of the centre section.
The 'bottom' former is solid as it is only temporary and will be almost completely removed as the skin will be supported by the corresponding former in the nose section when the two are glued together.

Progress with the centre section.

Just 12 planks this time.
The really tricky bit is cutting slots in it to slide the wing through but after many trial fits and sanding got there in the end.

Of course everything so far has been 'dumb' with nothing in it.
The nose will have a large cut out to fit the battery, radio and ESC once the rest in complete.
In contrast the tail section is not only a much more complex shape but also has quite a bit of hardware and cables to build in.

A start on the tail section.

Built in the same way as the rest.
Along side is the 'stack' of 8 fin skins.
The extreme change in diameter from full fuselage to the 28 mm of the EDF hub requires a considerable progressive taper on each plank which make progress much slower and results in a bigger pile of off cuts and sanding dust!

After two days of solid planking the tail section 'cone' is complete.

It looks very much like a Depron wine bottle!
Next step in to construct the fins as these will locate the EDF.

As the elevon and rudderon servos will be flush with both skin surfaces they will be installed once the fin is glued in place.

At last I have been able to run the 'test' duct at full power.
Using a 2200mAh 3s it draws:

giving:

and generating 26oz (737 g) of thrust.
It looks like it might have been designed for those kitchen scales!

The A4b should come out quite close to my 20 oz all up target so there should be more than enough oomph! but enough control is another matter.

Just because I made one here is a video of the test duct running on a 3s. No movement - just noise!

An interesting point about that video is the the test duct was not restrained in any way indicating that the EDF creates only modest torque despite the substantial 420W going in.

Satisfied that the EDF and duct layout would provide sufficient thrust a start can be made to install it in the 'flight' rear body section.

At this stage the EDF is held in position just by the fins although additional support will be provided when the inlet ducting is installed.

The first 'long slot' inlet duct completed.

The object is to maintain approximately a constant width across the duct as it gradually gets deeper and at the same time developing the cross section into a true quadrant.

The duct dividers also stop some 15 mm before the fan blades to reduce the 'siren' effect and hopefully improve the efficiency a bit.
Now I just have to repeat what is a pretty fiddly fitting job on the other 3 inlets!

With all the ducts complete it could be tested.
44A, 431W on a 'storage' level charge 3s which is pretty much the same as it was with the 'test' duct.
A trial assembly to get an idea of what it will look like.

Its not actually that big. I now think I Should have made it 25% bigger.
Servos (when they eventually arrive!) and control surfaces next.