25 November 2015
Alternative to CF cabanes, struts and undercarriage is to use plastic sheet by cutting the plastic sheet (pvc clear?) to shape with glue tabs and then bend and glue to model. This seems more accurate, simpler and easier to do then CF rods and there are no need for blue foam blocks. If some parts need to be stronger (compression), then glue some CF rods to the inside of the plastic parts.
21 November 2015
Cowling can be made from blue foam. It can be halved so that the top half can be removed for battery access and replaced before flight. The top and bottom halves can have magnets to hold them together. The bottom half to have a slot to glue on the geared motor. The bottom half is glued to the fuselage.
Fuselage can be made from 3mm foam sheet to a U-channel, open at the bottom. Some formers are glued to the trough and some to the top and sides. The top decking can be a piece of paper glued to 3 top formers: behind the cowling, at the instrument panel and at the back of the cockpit. It should be rolled to a curve and has the cockpit cutout removed last. The rear turtle deck can be a piece of paper, bent to resemble the stringer lines, and glued to the former at the back of the cockpit and the former at the front of the horizontal stabilizer. The rear turtle deck should be glued before the front decking. The side cheeks an be 2 pieces of paper, scored to resemble the stringer lines, and glued to formers behind the cowling.
To have the servos exposed on the starboard sides is an attractive proposition. Another attractive proposition is to have the servos hidden in the fuselage trough with the pushrods running internally.
For ease of cabane set up, simple blue foam blocks can be glued at those locations where the struts will be anchored. The completed fuselage, i.e. painted, finished, controls in placed etc, can be drilled at the oblique angle for CF rods. The CF rods are passed through the top wing's centre section and into the drilled holes. When the top wing, painted, finished, etc, is at the correct position, CA will lock all in place.
A similar approach can be used to strengthen the fuselage at the bottom wing's position. A bit of blue foam to fit in the U-channel, thus making that section a box, and with 2 CF rods grooved in, the lower wings' inboard sections rest on the protruding CF rods. The wing struts are also CF rods and passes through both top and lower wings. When the lower wings are in the correct position, use jig if necessary, the CF rods are CA'd, at the wing struts and at the inboard sections of the lower wings. Add two more pieces of blue foam behind the cowling where the landing gear is and the undercarriage can be assembled similarly.
Obviously the exposed CF rods has to be then dressed up, either as cabane or wing struts, or as undercarriage. This can be simply folded pieces of printed/painted paper.
If I prepare the blanks for the foam sheet fuselage and paper coverings, it would be easy to make another fuselage and use that for a Sopwith Triplane model, which as I understand having read it somewhere, that the real Sopwith Triplane uses the Sopwith Pup's fuselage.
11 November 2015
Mount it this way?
5 November 2015
To improve the odds, I think it should have a lifting tail. When the CG can be moved back, the items in front of the CG will have a bigger moment arm and less noseweight is required.
My modelling experience started with chuck gliders. Wings and tails were mounted with zero incidence in order to have higher launch height. Otherwise the gliders would be looping and would transitioned to glide attitude around knee level! Those tails were from sheet balsa, the airfoil might have been lifting but I doubt I did that. My CG were mostly around the 25% mark except for tailless which was something like 10-15%.
Then I progressed to control line planes. Again the wings and tails were at zero incidence. CG was less important and level flight is achieved with the control line system.
I started RC with simple trainer planes. This time with some incidence in the wing and the thrustline had to be offset. But my RC planes/gliders had sheet tails or built up flat tails and this continued to present day because I didn't think of it and even if I did, I wouldn't have done a lifting tail from foam sheet.
My flying experience was incomplete because I did not do free flight models. And because my experience has always been with flat tails, I always considered that tails should no purpose apart from correcting the attitude, i.e. be set trailing without up or down force (like in aerobatic planes) or when I need more stability, provide downwards moment.
I think I should use a lifting tail for this model. On closer examination of the dimensions of the material indicated on the plan, it seems that was intended too.
I would probably still use foam sheet for the tail, and I would not sand any airfoil, but I would make sure that it shall be set at a positive angle to the thrust line, and set the elevators down slightly so it may be a cambered/cranked airfoil. This would of course mean that the wings should be set at an even higher positive angle. The aim of this combination would hopefully result in a model with a rearwards CG and therefore a lighter one, and the fuselage set head-on to the direction of flying, i.e. not the usual pitched up attitude.
I could do a simpler model that uses a 'lifting' tail before doing this Pup.
3 November 2015 (review of 6 July 2015 entry)
Won't be so lucky to find a suitable plastic bottle for cowling. They would be close but not exact. Also, with such a short nose, it might need noseweight but plastic is light although resilient. How about making a blue foam male mould and make a paper mache cowl?
How about making the fuselage and rear deck stringers in one piece? A rectangular piece cut out for servos will fit from the cockpit forwards. The front and side deckings (including stringered portion) can be paper/card. WLToys 8.5mm motor can be glued to a slotted (with side thrust) piee of balsa, and the balsa glued with slight downthrust. The WLToys receiver fits infront of the rear cabane, with the servos in an upright position. This would mean running the pushrods within the paper/card front decking, passing through the cockpit and pilot, under the rear stringered portion of the fuselage and exiting to the tail.
But it ought to be quite troublesome to do all that, maybe something simpler like letting in the receiver/servo block to the starboard side of the model? Like what was done on the Kirby Cadet? The starboard side decking may just be enough to cover/camouflage the exposed servo horns, and maybe the pushrod should just be left exposed, i.e., outside on the starboard side. Within the fuselage box, the port side should have enough space for the battery. I still think battery should be dropped in from below, this way a paper rotary engine can be glued on the propeller shaft. Maybe the battery could be slide in from the bottom, just behind the cowling, at an angle and retained by what-else but those velcro spots? Angle = weight forward and avoid cutting of lower wing.
The wings, tails and interplane struts seems ok, but I think the rear cabane struts should extend to anchor at the base of the fuselage, in the middle between the rear legs of the undercarriable. The front cabane struts would not be able to extend through because the motor would be in the way. For the anchor point of the rear cabane, rear legs of the undercarriage, might as well make it the support point of the lower wings.
Should the undercarriage be made removable or hinged so that the battery may be placed there? I would prefer a one piece lower wing. If I can bend wires precisely, maybe the front cabane should be tied to the front legs of the undercarriage.
I shall study some photos of the Sopwith Pup.
6 July 2015, Shall I?
The plan fits nicely on 2 pieces of A3 paper.
The fuselage may be built from a piece of plastic bottle for cowling, creased and lined paper for front and side decking including rear stringers, over a basic structure of 3mm laminated foam folded all the way to the front of the cowl.
Wings and tails are cut from 3mm laminated foam. Stick on paper reinforcing rings to the underside of top wings and upperside of the bottom rings to spread the loading points of the interplane struts and cabane struts. Draw lines for the ribs and ailerons. Silver for riblines on the upper surface. Black for the undersides and aileron hinge lines (both upper and lower). Spray green khaki for upper surfaces and cream for lower surfaces. To the upper wing, cut two slits past the centre section, crease the upper wing and insert CF strips, when dihedral is correct, drop in some superglue and touch up.
Interplane struts are from 1/16" balsa, pre-painted brown before inserting through the pair of wings. Snipped off when the wings are at the correct position and touched up after installation.
The cabane struts from 1/16" CF rods, pierced from the top surface of the top wing, all the way to the fuselage. Snip off and touched up after installation. The struts shall be faired with pre-printed paper.
