SPAD Building Techniques
There are many other SPAD Web sites with detailed construction videos and so forth. The intention is to detail only things I have not seen anywhere else, or ones I use myself and are useful.
Areas covered are ;
a) Gluing (No "Flashing" please !) Correx.
b) Aileron Warp.
c) Elastic Bands.
d) Hinge Tool.
1) Gluing Correx
Many plans include details on "flashing" Correx due to the surface oils issue preventing a good bond. I tried this and found the method far too random and the results even more arbitrary. It melts too ! So I resolved to find an easier, better, stronger way.
After a lot of joint testing, including field testing, I came to the conclusion that the joint had to be ;
a) as much area involved as possible.
b) mating surfaces had to be treated to ensure a better joint.
c) Thin CA was by far the best for spreading purposes.
The technique I ended up with is as follows ;
1) Roughen both mating surfaces with course sandpaper.
2) Use enough CA to lightly coat both surfaces.
3) Spread the CA thinly over both surface areas using a piece of wire or a length of solder. Do not use too much CA !
4) Clamp the surfaces to be mated together using some "yardstick" strips for at least 2 hours - these need to be as wide as the mating surfaces. CA takes a while to cure on Correx, as it cannot soak into the plastic.
I suggest you try this on two off-cuts. Testing the joint now obtained will rip the plastic apart, but the CA joint will stay intact.
As proof of the joints strength, when optimising the CG for Dracula, the plane hit the ground left wing tip first, then pancaked at full throttle twice. The glue broke for 3 " at the wing tip but the elevons stayed intact - the engine mount however and prop. were not so lucky !
Aileron Warp
Many plans for SPADS have a single servo moving both ailerons and using the standard flute method of hinging. 4mm Correx is pretty stiff and resists flexing, but will warp easily under these conditions, especially where the horn is at one end of the aileron. Once warped, it is impossible to straighten out.
First of all, reduce the (rates) movement. Secondly, use two flutes instead of one if the Correx is really stiff (correx varies in stiffness) - the servo will have an easier time too ! Bear in mind you may induce flutter though if the ailerons are too large ! Thirdly, if the ailerons are large in area, use a servo for each aileron.
Elastic Bands
Elastic bands are great - allows easy transportation and re-assembly - flexible in an unplanned meeting with terra firma - cheap fixing method.
However, they suffer from one 2 major problems where Correx is concerned ;
1) Compression Squash.
2) Cutting through the hinge, when the wing shifts from it's mounted position.
Compression Squash
Compression squash can be alleviated by Bamboo sticks or dowel in the flutes or using larger size elastic bands. Alternatively, using the top web in the opposite flute direction also works well.
Bands Cutting Hinges
This happens upon wing tip impact - the wing slews around and the band slides off the dowel peg and is propelled down the hinge flute, making a nice job of cutting it in two.
The answer is to use two pieces of dowel inserted into the wing at the TE, the opposite way round to the wing holding dowels (pointing towards the tail). The bands have to be threaded around both the vertical and horizontal dowels.
When the inevitable happens, usually a not quite straight arrival, and the wing tip hits first, the bands will be held by the vertical dowels and not allowed to move towards the aileron hinges. This way your hinges will last a very long time, without having to split the wing to accomodate new ailerons.
Cutting Hinges
There is a DIY tool which makes this job so much easier - available on the www.spadtothebone.com web site - an essential as far as I am concerned.
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