March 25

Build RC Airplane Scratch Progress

Last week I had created the basic fuselage for my new project andHawklett motor installation installed the servos for all of the controls associated with this part of the plane. So let us move on to the next stage and look at how the build rc airplane scratch build progress goes.

Installation of the motor was next on my agenda. Now this model has a very narrow tapered nose profile so I had to be very careful with internal shape of the motor compartment. It needed to offer freedom for the rotating part of the motor without fouling the casing and power wires.

The smooth profile of the nose will involve a spinner of the same diameter as the end of the fuselage. This is exactly 50mm (2″) and, as the front end will be totally hidden behind this spinner, I drilled the centre shaft hole well oversize to allow as much air flow as possible into the motor front end.

Motor & Battery Location

Hawklett Motor Installation

The motor is fastened to a 6mm (1/4″) ply mount to the front of which is a further 6mm (1/4″) Balsa and Ply sandwich to bring the final face plate to within 1.5mm (1/16″) of the spinner back plate.

My choice of motor is an EMP N4250 – 950 KV. This is equivalent to a 50 size glow/nitro engine so there should be plenty of power to perform the aerobatics within my capabilities.

Previously the model was intended for use with a glow/nitro engine and what is now the battery compartment was then the fuel tank location.

The main modification here was to provide a false floor and rear stop plate for the lipo battery above the wing centre section. This meant opening up the cut out in the former F3 ( F1 being the motor mount and F2 just behind the motor) so that the lipo can be moved fore and aft to help with the balance position.

Fairing In The Tail Feathers

The stabilizer is positioned about 40mm (1.625″) belowHawklett Fin Fairings the top of the turtle deck at the leading edge. This means that, once installed,, fairing will be required either side of the fin to continue the shape of the upper fuselage through to the rear.

To create this fairing after the stabilizer and fin have been installed is quite difficult. To avoid this problem I made up a dummy fin/stabilizer ‘T’ section from 7.5mm (5/16″) soft balsa, slightly higher and wider than the tapering turtle deck.

This was ‘tack glued’ to the stabilizer mounting plate to simulate the finished items. I then built up the fairings either side of the dummy fin, ‘tack glued’ them to the dummy and sanded the whole assembly to match the taper of the turtle deck.

Once the profile was correct, I slid a sharp scalpel blade through the ‘tack glue’ and separated everything. I now have two perfectly shaped fairings to fit once the stabilizer and fin are finally installed.

Furnishing A Cockpit

As I explained earlier, the whole of the cockpit assembly needed to beBattery Hatch Cover 2 removable to make for easy access to the Lipo battery compartment.

The base of this assembly is a sheet of hard 3mm (1/8″) balsa to the underside of which are glued 6mm (1/4″) square balsa runners to locate the base flush with the fuselage sides.

The front edge has a hard balsa 6mm (1/4″) cross member that butts up flush with F2. A 3mm dowel set into this cross member centrally locates in a matching hole drilled through the top of F2.

At the rear a balsa plate has two Neodymium disc magnets set into the surface that mate with two similar magnets set into a plate that stretches across the fuselage.

To my mind there is nothing worse than a large cockpit (as this is) without appropriate furniture and at least one pilot. A quick search through my junk box produced a suitable head and shoulders pilot bust. The two in-line seating areas and instrument panels I fabricated from 1.5mm (1/16″) balsa suitably painted in pseudo military colours.

Cockpit

Now, I am nothing if not frugal when it comes to spending my pension so rather then searching on-line for suitable cockpit glazing, I decided to make a plug from scrap balsa and mould my own from a disused soft drinks bottle.

Because of the length of the cockpit this required two bottles. A quick visit to our local grocery store furnished two suitable bottles for the princely sum of 0.56€. Whether or not I drank the contents was irrelevant, the bottles were all important!Hawklett Rear Cockpit Glazing

The rear portion was a simple cut section of curved bottle side to be glued to the rear cockpit former and a balsa laminated support ring over the rear cockpit instrument panel (see picture right). The front section was formed over the balsa plug using scraps of balsa to tension it within the body of the bottle and my trusty heat gun to bring about the necessary re-shaping.

The glazing is attached to the frame using canopy glue. I like this product as it dries totally clear and does not effect the clarity of the cockpit.

Tail End Assembly

Hawklett Tail Assemblies

Now comes a tricky bit! Setting up and fixing the stabilizer and fin into the fuselage rear can be quite challenging as care must taken to obtain correct alignment. The stabilizer must be glued horizontal with relation to the fuselage. Then the fin must be set so that it is vertical with respect to the stabilizer.

The first job was to set the fuselage up with the sides vertical on the flat work bench. I dry fitted the stabilizer to its mounting plate and checked that the tips were equidistant from the bench top. Fortunately my building had given the necessary level but if this had not been the case, I would have gently sanded the mounting plate until correct.Stabilizer Setup

I mixed up a quantity of slow setting Epoxy Glue and applied it to both the mount and the underside of the stabilizer. I then positioned the stabilizer in the correct position and clamped it firmly to allow the glue sufficient setting time.

Whilst this was happening I clamped two previously cut balsa blocks, the same depth as the fuselage, under the stabilizer halves and in line with marked positions on the fuselage sides to keep it horizontal. The slow setting Epoxy allowed me plenty of time to ensure all distances and angles were correct.

Surplus glue that was squeezed out of the joint was wiped away using household rubbing alcohol. This works very well and dries away quickly through evaporation leaving no undesirable residue.

To Be Continued

In my next post I hope to have completed the glazing of the cockpit and have a set of wings built ready  to be mated to the fuselage.

In the meantime, I hope you are enjoying my “build rc airplane from scratch” progress. If you have any questions about this build or there is anything that is not clear to you, please don’t hesitate to ask through the ‘comment’ facility at the end of the post.

please visit my main website: www.rookiercflyer.com if you need any advice or information on getting started in rc model plane flying. Everything you need to know is there.

Thanks for following me, catch you next week.

Colin

 

 

 

 



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Posted March 25, 2016 by Colin Bedson in category "Modelling Skills

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