English Electric Canberra - in Depron of course

your best to cover it with 6 micron Mylar first then tissue, you'll use far less dope sealing the tissue, it works out lighter than tissue and dope on there own and it's incredibly strong and puncture resistant, it's what I'm going to use on my latest effort.
I've got a roll of it on its way to me if you have trouble getting any.
For paint the indoor free flight guys swear by humbrol enamel thinned with cellulose as the lightest way to add colour, apparently the trick is not to stir the enamel but just use the thick stuff at the bottom of the tin.
www.ffscale.co.uk/ have a look at this guys site...he knows a thing or 2 about building light!!

Tissue completed.

Top and bottom it added 9g exactly.
With ailerons the all up weight is now 144.5 g.
So dope and silver for 5.5 g?

You could have (should have?) used silver tissue.
Presumably your using eze dope rather than real dope? I quite like the stuff but I apply it diluted 50/50 rather than the recommended 70/30 I also found it best applied with a sponge rather than brush .

Paul
Unfortunately silver tissue would not be the full answer as the tissue only covers the open panels. The rest of the Depron would still have to be painted. I am not sure using silver tissue 'all over' to avoid paint would actually end up lighter.
The original used real lightweight Modelspan tissue whereas the stuff I am using is actually slightly lighter but it is not truly water proof so although it water shrinks well enough the Eze dope makes it go very 'saggy' which does not fully disappear as it dries.
I will certainly try applying it with a sponge although I suspect the ultimate answer is to invest in some model spray kit.

In truth I am not too bothered if the B57D comes out a few grams over the limit as I still want to see the effect of the extra wing area.
In the original build I was not trying to reach a 'target' so it was given a particularly 'solid' colour finish (two coats) and a polyurethane gloss top coat as well so the bits of the original structure are relatively heavy.
I am sure if I started again from scratch a B57D of this size could be below 250 g.

I need not have worried the Eze dope has pulled all the tissue tight.
The all up weight is now calculated at 148.5 g.
Unless I can find a way to spray the silver I expect it will end up at 152 g.

Looking good Q, but don't you mean 252 g not 152 g ?

Affirmative!

To be exactly legal I will finish fitting the ailerons and fly it unpainted at 248.5 g.

Now complete and in a flyable state.

With is 950 mAh 2s it weighs 249.4 g

I should really fly it now (almost no wind) but the battery is not charged and by the time it is it will be too dark.

Virtually flat calm this morning after the mist lifted and it flies.
Sorry no video the battery in the camera is dead.
Very gentle and as expected really slow for an EDF and no trim change required from the previous Canberra setting either which means I must have built the new wing straight or at least 'aerodynamically equal'.

Flying slow is not ideal for an EDF as their efficiency, particularly tiny ones, falls away below a certain optimum air speed so overall its potential max duration is likely a bit lower bearing in mind it was not that good to start with as a Canberra.

Never mind it is below 250g and flies. Its glide performance is 'interesting' and landing is easy with a dramatic ground effect. Unlike the full size I have the advantage I can switch power truly off. I believe on the full size when in ground effect it could maintain level flight even at idle thrust. You had to use the air brakes to actually 'land'. Even taxiing worked the brakes rather hard.

Congratulations! you just need to fly the Antonov now....

I did wonder about that but it did not take much to convince myself "no" so I did the maiden of the Gnat instead!