Aggregate A9 (A4b)

The new nose glued in place.

Install the ESC and battery box next.

ESC installed and the battery box built in.

The battery is now as far forward as it can possibly go. It touches the nose skin top and bottom.

Just the skin to make good.

All back together.

CofG moved forward by 1/4" (6mm)
I think I will wait for the mud to harden a bit (and the grass to grow!) before I try again.

Really looking forward to the test flights a great thread so far

I was never entirely happy with the inlet geometry of the cheat holes.
As the rear end has proved to be much more rigid than I had expected I have decided to 'open them out'.
Before

After

I am not sure it will make a huge difference but with the much reduced thrust resulting from the move to a 55 mm EDF I wanted its 'breathing' to be as good as possible.

Virtually no wind this morning just mud so here you go!

I make no apologies for keeping high most of the time but it glides remarkably well, which of course it was intended to do!
Quite controllable but absolutely no natural roll stability. The gyro was 'on'.
I am too much out of practice and the field is still very water logged and muddy so only one short flight.

You have to be very pleased with that a fantastic conclusion to an enthralling thread many thanks.

looks good in the air

Another success Q, well done.

I had always intended to explore the possibility of it doing a 'scale' vertical take off but at the moment its thrust is only 85% of its weight.
My original thought was to use a 4s battery however neither the fan nor the motor are rated for it. To make matters worse the balance its EDF is rather poor so I fear it would destroy itself in pretty short order at a higher power.
The original 70 mm I used is not only considerably more powerful to start with but can run on a 4s for short periods. This leads to the logical conclusion of making another A4b but bigger.
The construction of the 'small' A4b has proved to be plenty strong and rigid enough suggesting the same thickness materials could be used on the bigger one with the result that its airframe weight would rise approximately as the square of the size rather than the cube.
So instead of 48" we go to 72" (1.5 times).
Airframe weight would increase by 2.25 times (1.5x1.5) to about 12 oz. The EDF, battery and electrics should come to about the same giving a 24 oz all up weight.
According to HK the 70 mm EDF produces 34 oz thrust on a 4s which gives a 'theoretical' thrust to weight of 1.4:1.
Whilst a vertical lift off would be possible the acceleration would be quite slow. No doubt very impressive to watch but I am sure it would require positive stabilizing until sufficient air speed had be achieved for conventional control. A switch-able 'heading hold' 3 axis gyro with vanes in the exhaust slip stream? A bit like the full size!
This could get rather complicated! :woohoo:
This is the sort of thing you might end up with.

Before spending the time building such a big Depron structure I have to consider whether it would be prudent to build a much simpler test rig to prove that a gyro controlled EDF 'slow' vertical lift off is actually likely to work!

It seems to me that the 'vertical lift off' bit needs to be proved with something much simpler and quicker to build than a 6 foot long scale A4b! The chances of it working first time must be small and its survivability in a take off accident would be little better than it was in full size! :woohoo:
So what could be made that would emulate the dynamics of a 6 foot long A4b but be quick and simple to make (relatively! ) yet be strong enough and no heavier or preferably even lighter?
The best idea so far is.

A simple square box fuselage with a pyramid nose (so just 8 pieces) but with a cone rear leading to the EDF. The fin and control surfaces would be the same as the A4b but with a simple 'plank' wing of equal area and requiring the same CofG.
If this could be made to lift off vertically and fly then subject to weight limitations the scale A4b should as well.

One further benefit is that by using the same tail whatever launch arrangements ended up being required would also work on the scale one.

Still an awful lots of ifs and buts!

I like the idea Q, but beware of the different lift generating characteristics of straight wings when compared to swept. You may need a different C of G.

Agreed but the 'flying' bit is the least of my worries.
If it ever achieves a controlled vertical lift off but crashes during the "flight" due to a CofG problem I will still be mighty pleased!

Fair comment Q, I shall watch the experiment with interest.

Good Luck, BTW. Having hovered several marks of Harrier/ABV8B, both with and without stabs, I can say from experience that it's a whole different ball-game to hovering a helicopter and/or conventional flight...

When I came to printout the simple A4b plan I realised the EDF scale was all wrong when compared to the rest of the airframe. A 70 mm EDF of a 72" long airframe looks like this.

I have left the wings off simply because I am not sure they will be necessary! :woohoo:
The 'lift off' test plane will be so light it should manage a satisfactory belly landing using just fuselage lift alone. The fuselage ahead of the fins is after all over 48" long and 7" wide (2 sq ft)! :ohmy:
Of course simple wings can always be added later if required.
I am still undecided whether to keep the fuselage square or put in the effort and make it circular which would be that bit lighter.
No immediate rush to decide as some of the 'electrics' required are coming from China. Expected delivery 8 March!!