Canny Canard

As I mentioned in the Cafe I am thinking of building this Canny Canard so I have started a new topic.

 
 

The rear wings are partly in the curved rear section which with the dihedral, no centre section and a curved fuselage makes for a complication.
I am thinking of lowering them into the fuselage. Is the height relationship between the rear and front wings inportant?
On the end of the wings there is a block of balsa before the rudder. Does this bit of weight affect the aerodynamics?

Magpie
I think you will find that the wing tip balsa block is simply to provide a secure mounting for the substantial wingtip "rudders" although strictly they should be called a fins.
It is marked as "soft balsa". Good luck finding any of the truly light weight stuff.
The vertical difference between the canard and the main plane can be important to ensure the down wash from the canard passes under the wing however very small scale aerodynamics behave rather differently to full size so it may be a case of "try and see"
At least the rubber is the full length of the fuselage.   

I'm still looking to keep the height difference so if it makes a diffence the difference will still be there.
Vive la difference!
The rudders & the fin are only 1/32nd on the plan so I don't see them surviving much anyway so I'll at least increase them to 1/16th.
How can I stiffen them without them warping?

Thats a possibility, and there's also the rear fin and a skid underneath.
I could use ply, I'll have to try & work out how much extra weight that would be. If I skipped the wheels that would save quite a bit, 18 grams on a three-wheeler plus the wire, 10 grams.
Flying indoors it would need the wheels but on grass they're superfluous, in fact the forward pointing front wheel is a negative.
How necessary are the wing fins or with having them does it need a tail fin?
I think I can almost build it just using what I have left over from the DH2. With starting from scratch I didn't have any stock of stuff for that and had to buy it all in.
I don't know of anywhere in Durham or Northumberland that really caters for balsa model aircraft so have to buy everything on-line and no single supplier has everything so of course there's the postage which can easily be more than the material.
There is an R/C group somewhere hereabouts, during the foot & mouth they flew on the old steelworks site but I haven't been able to find them.

All of them?

magpie
The balance point is marked on the plan. It about in the middle of the cockpit. That means there is an awful lot of fuselage side a long way ahead of it but very little behind. For "arrow" stability the effective side area behind the balance point must be greater than that ahead of it. A canard has very little fuselage behind so the total fin area has to be large.
Flying wings and delta with little or no rear fuselage have the same problem and have to have big fins as well.

So the wing fins could be an afterthought. They certainly look like it. The central fin is in the lee/shadow of the cockpit so maybe it was ineffectual & the wing fins were added to get it to stabilise it.
The central fin will have to be fitted in a slot arrangment so it could be left out to see if it was necessary,
The builder of the double size R/C version said that the CofG on the plan was too far back & should be further forward & his fin looks larger than the original.

outerzone.co.uk/plan_details.asp?ID=1910
 
 

On the plan the rear section is to be covered in 1/32nd sheet but it has a curve in it so I am looking for an alternative. I have some balsa block but I have been looking at using foam which is a new material to me.
The following two sites stock such stuff, which if either do I want?

www.modelscenerysupplies.co.uk/Build-Mat...raft-foam-white-25mm
modelshop.co.uk/Shop/Raw-Materials/Foam/...ts-300-300mm/ITM4875

Is polystyrene different from craft foam?
Is this polystyrene the same stuff used for packaging?

I've chucked barrowloads away!

And again the postage is likely to be as much as the material!

Magpie
Covered in 1/32 sheet and double? curved.
I could say so what? There is nothing wrong with "planking" even in 1/32 sheet. It does take a bit of perseverance .
I was 22 when I built this.
 
The entire wing and fuselage are just 1/32 sheet. Planked in the curved areas.
I still do planking but now in thin 2 or 3mm moulded sheet polystyrene foam. its called Depron and has quite a dense structure..
Quite a bit of double curvature in a Sea Hawk fuselage. .
 
You do have to use "foam safe" glue using polystyrene. Either a water based wood glue or something like UHU POR.

The problem with block foam is it has a rather open cell structure which makes achieving any sort of a finish almost impossible.. Ready to fly foam planes are moulded which gives a smooth surface 'skin' to the foam.  
If weight is an issue it can be carefully tissue covered and water shrunk. The tissue then "spans" the open foam structure but only use foam safe EZE Dope to seal it and no "rattle can" paints as the propellent eats polystyrene foam.