DH 91 Albatross

With both tail plane halves complete and tested it is time to start the fuselage or rather just the rear section.

8 printed formers and lots of 2mm tapered Depron planks.
Relatively easy planking as it is a straight sided cone but to make things just a bit more difficult it is slightly off vertically!

I imagine keeping it straight would be even harder :evil:

It always amazes me how 'straight' these hollow planked structures turnout. Cutting all the planks to exactly the right length before gluing them in is probably the answer.
The inside of the completed rear fuselage.

370 mm long it is remarkably rigid and weighs 16 g.
Organise extending the elevator and rudder servo wires and the tail planes can be fitted.

Nice work!

After quite a bit of too and fro the tail section is complete - and tested!

Boy! Am i glad I elected to go for individual servos as there is very little room at the tail end of the fuselage.
The biggest issue was almost a 'school boy' error with the rudders.
With individual rudder servos I assumed one would have to be the other way round as you have to for flaps so I installed the LH rudder servo inverted but when I came to test them simultaneously I found they operated as air brakes!
When I sat down and thought about it with twin rudder the horns are on opposite sides so they do operate in unison with both servos mounted the same way. The inverted servo had to be cut out and reinstalled. Doh!
In my defence this was my first twin rudder/twin servo set up.
.

Back to the wing and a start on wiring up the motors.
The LH inner.

The lacquer insulated motor 'magnet' wires run through the nacelle and down the wing.

All four ESCs and the UBEC will be mounted in the wing close to the root to keep the battery to ESC wire length to a minimum.

I connected up the motor to the ESC (not forgetting a separate power for the servo tester) but it did not work - Just beeps!
I had tested the motor before installation so it had to be either the ESC or a bad joint in the wiring.
Not wishing to rip out the wiring I installed another ESC and had the same result suggesting there was a break in the wiring somewhere so out came the knife to cut off the cowling to extract the motor and the wiring.
With only the motor leads it still just beeped suggesting a broken connection in the motor.
Out of desperation I connected the motor to my 'other' test set up that uses a normal BEC ESC and it worked! It then slowly dawned on me that the other test set up also uses its own servo tester - it was actually the servo tester that had failed not the motor or the wiring! :woohoo:
You live and learn.
Not a complete disaster as I was not really happy using solid wiring as it proved very difficult to install. Ordinary 'flex' wire will now be used although this will result in a slight weight penalty.

Shouldn't laugh, but - - :woohoo: [badass]

With the 18 AWG wire delivered the installation of the motors and ESCs can resume.
The LH inboard wiring and its tiny 20A ESC.

4 ESCs and a UBEC will have to be squeezed into the wing under the fuselage.
Although everything will ultimately be permanently 'built in' the motor to ESC wires do have 2 mm bullet connectors so the motor direction can be reversed if required before the top skin finally goes on.
I suppose I could set it all up on the bench to get the desired motor direction but as all the wires have to be threaded through the wing before final soldering it is all to easy to loose track and end up with one motor going the wrong way!

Excellent. Are you spinning motors in opposite directions with props to match?

As the motors were bought as racing drone 'set' I have no choice - two have left hand thread prop nuts! The pair on the RH wing will thus have to turn clockwise while those on the LH wing will turn conventionally counter clockwise.
On the full size all ran the same way but bizarrely it is the 'conventional' props that are not scale as all the Gipsy series engines ran the other way to almost everyone else!

What with car and Tx issues progress is slow but all four motors are now installed in their nacelles.

CW prop nuts black, CCW ones silver giving a conventional "over the top towards fuselage" prop rotation (viewed from the front!).
Slowly wiring them up to their ESCs and trying to make sure I only have to do it once. There are twelve soldered connections to be made for each motor and likely quite a few more when coupling the ESCs and the BEC together but lots of testing to do before that stage.

Thought that might be the case but through choice other than Hobson's. I thought it would aid stability if this was done. :oops: Looks good:

After a bit more thinking and some soldering I have managed to test (and check they were all going the right way!) all four motors with their props on!

Only at 'tick over' as the wing was not restrained in any way but nevertheless remarkably slow, uniform & stable despite it being very much a test 'lash up'.
The next issue is where to mount the rx.
The simplest position is in the wing centre section so the ESCs, aileron and retract servos can be permanently connected leaving only the elevator and rudder servos to be made/undone before the wing is fixed on/removed.
The down side is there is a lot of electrical 'stuff' in the wing centre section already that could interfere with the radio signal. .

Probably the most important test at this stage is a full power run with the intended 1500 mAh 3s battery and a Watt meter to find exactly how much current it took. It proved to be 22A say 240W. The thrust is considerable indeed I was concerned about the strength of its incomplete wing!
My estimate of the final weight is 650 g (23 oz).
At this weight 240W will give it 167 W/lb so not in the 'unlimited vertical' class but not that far short!
More to the point with the Albatross's good streamlining the question is how much (or little) power it will need to cruise.
A Lemon 'stab' Rx is on order for it.