Build your first flying scale Jet - Chapter 2 - Stringers and motor tube
Before we have too many of the stringers on, it would seem sensible to make and install the tube for the Rapier motor,
and this is what you need to make one. So, a piece of notepaper, steel rule, paper masking tape (a wide roll), knife and a Rapier L2 motor.
The masking tape is wrapped three times round the motor to act as a spacer. When the motors burn, they expand slightly, so you need
some clearance in the paper tube. The notepaper is cut so that the motor tube length matches the plan (or slightly longer to allow for trimming) and so that there is enough
paper to wrap round the motor approximately three times. The pencil line equals once round the motor.
Apply wood glue as shown, to the paper on the far side of the marked line, and spread out with your finger.
Now wrap the paper round the motor and carefully roll along to wrap up the tube. Because the glue only started after the pencil line, it should not stick to the
motor or masking tape. You can leave the motor inside the tube once you know it has not stuck to it, to hold the shape as the wood glue dries.
We need a plug in the back of the motor tube, which is simply a disc of balsa glued inside
the end with wood glue (best to use non inflammable glue for this,
rather than balsa cement!) The disc was cut out using an Olfa Compass Cutter, and sanded until it was snug fit.
The tube is now glued into the fuselage. You can also see here that four stringers
have been attached each side, two above and two below the side keels.
You can see from this photo that I have been a bit generous in the space between the keels,
so when the tube is glued to the bottom keel, there is a gap at the top. This could be bridged
with scrap balsa if you are feeling keen, but I confess I just left it.
Make sure you line up the tube carefully so it is parallel to the direction of flight.
One possibly confusing area is the trough sides, where the stringers are doubled.
The first stage is to glue in two short
lengths of 1/16” square between formers 6 and 8. Make sure the stringers are pushed to the bottom of the slots.
Now lay the full length stringers down the fuselage, gluing these to the strips you just added between formers
6 and 8. The double thickness alongside the trough is useful in adding strength, and gives something solid
for the notepaper trough to be attached to.
These two small parts are to support the front of the paper trough, and in hindsight would have been
easier to fit before the motor tube!
You need to add a spring clip from thin wire to stop the motor falling out of the tube as you launch the model.
This is very embarrassing, and makes you look silly, never mind wasting the cost of a motor.
There are many ways to arrange this, but this is the shape I usually use. The curve at the left hand end should match the radius of the
paper motor tube.
Here is the clip placed on the mounting tube to show how it fits. Note a notch has been cut in the bottom of the former
to clear the wire. You need to place a Rapier L2 motor in the tube
to position the clip correctly. Best to leave a bit of a gap between the wire step and the motor as there can be a small
variation in motor length from batch to batch.
Here the wire has been glued to the tube, using a wood glue soaked patch of paper at the front,
and a strip of balsa next to the keel. As shown here, there is only a small length of wire that can deflect, so it is fairly stiff.
To make it more flexible, a longer movable length could easily be facilitated by cutting a slot in the balsa on top of the wire.
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