Thursday, 4 August 2016

Cheshire Cat - 100S Glider

The glider bug is quite infective. After not building a Glider for several years, this is my 3rd in fairly rapid succession.

This is a 100S contest glider, the class rules dictate that Rudder Elevator and Spoilers are the only flight controls permitted, i.e. no ailerons and wing span restricted to 100". This class of model is also eligible for the 'OPEN' class events as well - F3J and F5J if electric powered.

There are very few 'modern' designs around that are suitable for home scratch building, so this is my own design with a great deal of help from Jef Ott on the BARCS forum.

The full build blog is available here on BARCS:

To add a little extra, this model will be an 'E' version with an electric motor, height limiter etc. so that it will qualify for the Bartlett's league - if I ever manage to get down there.

Our local field isn't particularly brilliant for tow or bungee launching so I need to have an alternative method of launching models.

There have been several iterations of the design, starting from a simple 'Vee' dihedral aircraft in imperial units and ending up as 6 panel wing in metric units... Wing section is Mark Drela's AG35 at the root tapering to AG37 at the tip.

I used a spreadsheet to calculate the various stability values, that in itself was a very interesting exercise..

These are the 3 key stability values, I need a model that can fly by itself if I ever need to rest my eyes momentarily.

The latest iteration looks a little like this:

The construction follows that of a 'Bubble Dancer' that I built late last year, in fact the tailplane is scaled directly from the BC plan. Boom, tail mount and spars are all Carbon Fibre or CF Composite - again following the same type of construction method used on the BD.

Tailplane - a little heavier than hoped for at 16gms

 The covered tail assembly showing the Carbon boom and Vladimir tail mount - from Hyperflight

Wing construction (inner right panel) in progress. Lasercraft produced the wing ribs for me - beautifully cut as usual.

Updated: 2016-08-04

The wing went together in a similar manner to the Bubble Dancer, the spars are actually thick soft balsa webs capped with carbon fibre caps that go down the length of the panel. Thinner caps are used in the tip sections to reduce moments of inertia (weight!)

This shows the spar (web), lower carbon cap and a carbon strip reinforcement that goes over the dihedral break

The top cap is added (and in the centre panels) bound with Kevlar. Probably not needed for an Electric model, but I'll be able to use these wings on a winch launched towline glider version if needed

The spoilers were a bit tricky. I originally wanted to use wing mounted direct drive servos but I couldn't get them to fit so resorted to a bell-crank and fuselage mounted servo driving snakes through the holes originally intended for the servo lead.

 Like this.. The horn was bent (downwards - this is upside down) to clear the push-rod.

Next job was to get the fuselage pod made.

 Manufactured from Lite-ply with balsa triangle section corners, it looks very uninspiring

 But with a bit of work it can be made to look quite attractive

 I can never resist a dry assembly shot :)

The Front end - a 40mm Aluminium spinner and a reasonable fit, 5 degrees of downthrust, no side thrust

Servo's are mounted at 45 degrees so that the arms don't interfere with each other (the spindles are on the fuselage centre line. The 3mm Carbon wing alignment rod passes through the fuselage as you can see

A bit of work finishing the fuselage, making some nice curved hatches and covering the wing

And it weighs this much with batteries.

And a shot of the Cheshire Cat modelled by my beautiful No. 2 daughter :)

Just a maiden to come..