Wing joiner location

[AdamChambers]

Im converting a design from flat steels to round tube .

The design in question, a airspeed tern has flat steels in between the front and rear spars. Its over engineered and heavy as a result.

Can I locate an alternative single round joiner tube arrangement central in the wing? I will provide suitable reinforcement, although the ribs in question are ply and have incidence pegs.

Should I be placing the joiner over the centre of pressure /cg?

[chris williams]

Adam, there was 3.5 scale Petrel at the last WS scale meet which had a moderately heavy landing on the front of the slope. It had been modified from flat steel to a round joiner. The joiner stayed where it was, while wing re-modified itself around the joiner, resulting in a really difficult-looking repair.
A flat steel joiner would have simply bent forwards, allowing the the rubber bands to do their work. How do I know this? I've had more heavy slopeside landing with my various Petrels than I care to talk about...!

[Cliff Evans]

I really would not change the joiner. You do not need to " save waight" the model is proven as it is. Chris's description is very accurate.

[AdamChambers]

Cliff,

It is mighty heavy . Formers alone are 1kg. Massively over engineered . Ive recut lighter ones .

Both blades are 750mm long and again add a lot of weight.

Barry who built one on here recommended it needs lightening after flying it.

[Barry_Cole]

Im converting a design from flat steels to round tube .

Don't do it........

BC

[chris williams]

What span is the model, and the projected all-up-weight...?

[Trevor]

I'm all in favour of a bit of weight saving but I'd leave the joiners alone and focus on the rear end. Generally the rear fuselage formers are a good target, and I tend to go for balsa skins rather than ply. Tailplane joiner wires often seem rather on the heavy side, unless you are contemplating high speed, high g aerobatics of course.

Each to his own, I suppose,

Trevor

[Cliff Evans]

There is nothing wrong with the weight of the Tern. The models that have been built fly well. I think they have all turned out at around 11-12 lb which is not bad and about average for a 1/4 scale model with a span of 4mtr.

[chris williams]

Next question: which depth of blade; 12mm or 15mm...?

[AdamChambers]

Weight saving operation has already commenced . 5kg is the target , 1 kg below barrys build.

Overall the drafting quality is a 4/10 when it comes to the formers. Ill end commentary there as this isnt the reason for my query.

Chris, 4m span , taper wing . 15mm steel and brass blades x 2.

The rear spar is on the centre of pressure so maybe a tube can go there instead of a blade with a short blade up front ? Barry friend did the opposite way round and seems to be happy with it.