Accurately, Inverted U Channel fuselage, Upright U Channel fuselage, Paper Covering

1 August 2017

Displacing a vertical keel to a horizontal orientation has several advantages, mainly:

• receiver board mounted horizontally;
• accurate wing and horizontal mounting;
• motor mounted horizontally.

After the horizontal planform piece is cut out and centre lines drawn top and bottom and former lines drawn as well, glue the top and bottom formers. Cut a vertical profile into sections, discarding the cross structure and formers, insert between formers. Then the whole can be sanded and covered with sections of tissue or curled paper sections to complete the look. Stringers can become optional if curled paper sections are used inbecause the basic structure should be strong enough for the model already. Lots of 3D flat fuselage has diagonal braces to stiffen the horizontal and vertical pieces, this method substitute the diagonal braces with formers.

12 July 2017 Stick and Tissue

Central keel method is sometimes used for stick and tissue models. This is usually a vertical keel to the profile of the fuselage, and/or a horizontal clutch frame to the planform of the fuselage, with formers are added and then the stringers on the outside. The 'good' thing about this is that 'round' or 'compound curved' fuselages can be represented by segmented panels. There are many rubber scale plans that uses this type of construction since mid last century so most of the hard work have already been done. I think that adopting this method to use foam sheets to replace the keel and formers is easy.

I could use foam sheet cut to the side profile of fuselage and mark out the position of the formers on one side. Then the formers are cut from foam in pairs, forming left and right formers. Side formers are glued to the marked locations at the profile blank. Then a jig is prepared to position the other side formers. This jig can be as simple as a foam piece with a slot cut out to the width of the foam profile. The slot will ensure that the pair of side formers are in the same level with each other. The current stage of construction will look like a single pole ladder when viewed in planform.

Reinforcement bits such as noseblock, motor mounting block, wing cut out etc, receiver board and motor are installed and then the stringers are added along with pieces of reinforcement that can only be added at this stage, such as pushrod exit holes, wing or tail mounting plates etc.

Advantages over traditional central keel:
Dimensionally stable.
There is no need for precise joints. The joints in the segmented balsa keel needs to be precise and there being no joints in foam since it is a single piece.
Bigger gluing surface, and the keel has surface to mount gears and reinforcement bits.
Easy and fast to cut foam

Accurately, Inverted U Channel fuselage, Upright U Channel fuselage, Paper Covering

5 February 2016

Many things are easy to learn but difficult to master, so is aero-modelling.
There are many good concepts in older plans and articles, I enjoy reading about them. Many times, I will come to realise that there is nothing new under the sun.

Turning to building model airplanes. My slab-sided foam fuselages are constructed 'in-the-air'. They turned out accurate because I folded the fuselage to an inverted U section and therefore it is quite fool proof. Here is a method if I don't want to start fuselage construction with an inverted U section, simply, using a building board:

1. Cut 2 slab sides to the fuselage's lower profile (a datum line below the curved sections of a fuselage). If the fuselage is square bottomed, the bottom edge of the slab sides is raised (reduced in height) by the thickness of the bottom's foam thickness. If the fuselage is complex bottomed, have generous allowance to the bottom edge of the slab sides for trimming later.
2. Lay them inverted over the top view on the building board and glue square (for simple square bottomed fuselage) foam formers in between the slab sides. This gives a basic box structure.
3. If the fuselage is square bottomed, glue the bottom foam piece. If the fuselage is complex bottomed, a central spar to be let into the shaped former and then having the slab sides trimmed to fit.
4. Make cutouts from the completed lower fuselage. For example, on bottom winged aircraft, prop templates against the fuselage sides and hot-wire cut. If the wing has a curved or cranked airfoil or even a proper airfoil, start with the bottom profile and then the top profile of the wing. The bonus is having an accurate bottom cover for the wing's centre section.
5. Landing gear, tail skid/wheel, underfins, horizontal tail etc should be installed before removing from building board.

 Continuiing from above, it is time to install the motor, radio etc.

1. Formers/blocks of foam may be added to the nose to mount the motor and radio.
2. If using F929 939 receiver block, it is more convenient if the run of the push-rods are at the top edge of the slab sides.
3. The tail surfaces should be fixed to the fuselage box before the pushrod runs. If the horizontal tail is let into the slab sides, then it should be attached when the fuselage lower profile is still inverted on the building board.
4. The rear decking is usually non-removable and so it can be made from rolled/creased paper with cutouts for tail and pushrods. Incase
5. The front decking is usually removable and it can be made from foam block with magnetic attachments.
6. The nosepiece can be made from harder or heavier material.

Paper covering is similar to tissue covering with some major differences. It can be printed or painted easily and in good colour, it is much stronger although heavier, and it will not be as easy to mask the edges or conform to compound curves. Below is about covering the fuselage with printed paper and it is trimmed 'in-the-air'; it is glued on after the lower fuselage is formed but before other protruding pieces like stabiliser etc.:

1. The printed sides will be much larger than the side profile to cater for the fuselage top and bottom surfaces.
2. The printed paper is positioned and glued to the slab sides of the fuselage.
3. Slits are cut above and below the slab sides for the top and bottom covering. Roll and glue the starboard flaps, trim, glue, then do the port side (my favourite side). Start at the tail end and progress forward (don't we all want to progress forward?). Before gluiing, pre-colour the edges of the slits if they will be conspicuous because of the printed surface.
4. For a neat look, the slits at the conical decking can not be perpendicular to the slab sides, instead it has to be at an angle, the same angle left and right side, so that the slit can appear to be perpendicular or straight when the whole fuselage is viewed sideways or from the top. It can only be perpendicular to the slab sides if the sides are parallel.