Fly Aeroplane: Kirby Cadet

7 March 2016

I went to Bedok Reservoir last month. It is still the North-East monsoon, the wind was gusty, fairly strong.

I clipped on a strong 10mm square hardwood strip to the wing's leading edge. I inserted a piece of blue foam in between the hardwood and the wing's leading edge, creating a bow to the wing's leading edge and steamed that over a hot kettle. Then the blue foam and hardwood was removed and the wing has some dihedral. I also moved the CG back to around 50% so that

It glides but I couldn't get it to soar. I moved the CG back to around 50% by removing the hefty pilot and it got better but it still didn't soar. This is strange when the loading is already so low. Perhaps the wing's chord is too small.

It looks good, but it doesn't fly good, so this model is retired.

14 October 2015

I have bound the F929 939 receiver with the Flysky transmitter that Ming gave me.
I did a mix on the Flysky trans, so that the rudder stick and the aileron stick both control the rudder servo. It felt so much better. it was quite awkward flying with left thumb.
I am looking forward to the North-East monsoon which should come in November.

14 September 2015

Building

I started with the wing.
The oversized wing blank was curved, the convex side would be the top side and a strip of 1/8" x 3/8" balsa strip was glued to the leading edge.
The wing was trimmed to planform. The balsa leading edge was planed and sanded. The bottom of the trailing edge sliced to form a taper. The trailing edge and the tip edges were then rubbed with a AAA battery to compress the edges.

The pdf plan was converted to jpeg and the jpeg made reverse so I get both starboard and port views. The fuselage template was the left and right fuselage panels with the topview in-between.

Oversized templates were cut out from the plan.

These templates were stuck to the 3mm KT/Depron with glue stick.

The parts were cut out and the templates peeled.

The cut-out in the fuselage was for the damaged WLToys' F929 F939 receiver board.

V-groove was cut on the insides of the main fuselage piece, the underside of the stabiliser elevator and the starboard side of the fin rudder.

All the sheet foam pieces only amounted 2.6gm.

The fuselage was assembled and the receiver board glued in.

The bottom sheet foam was curled and let into the fuselage. Then the craft foam nosepiece was trimmed, and an additional piece of sheet foam fitted in-situ.

Now it weighs 12gm with battery.

The keel piece with a monowheel assembly was glued to the bottom of the fuselage.

The bottom Vee-panels were glued to the keel edge and trimmed to the fuselage sides, followed by the top inverted Vee decking.

Without battery, it weighed 10.2gm. If without fin and elevator, it weighed 9.6gm.

The templates fit in one A4 page.

To join the two halves of the elevators, I used a piece of CF strip. I think it was 0.5mm x 3mm

The fin and elevators were trimmed and compressed with an AAA battery to form the airfoil section.

The fin was glued to the stern. A bit of Blenderm tape completes the elevator and rudder hinges. The tape for the rudder is to the port side and went all the way from the top of the fin to the bottom of the fuselage's stern. A bit of plastic represents the tailskid, I forego the wire.

Every open cockpit must have a pilot.

The polymer was wrapped around a short length of drinking straw. Drinking straw was used to hollow the bust, so that less polymer is used and it shall be lighter.

The black eyes and brows were drawn and the goggles cut from plastic sheet. It weighed 2.4 gm.

I cut out 2 pieces from the leftover plans and glued it to the fuselage rear deck. From 9.6gm, it increased to 10gm.

Combined weight of the different components was 21.2gm.

Spraying was over very quickly.

I made the mistake of spraying too thick a coat: some areas were attacked by the spray can solvent.

Sprayed-finished Weight (include battery and pilot): 21.7gm. This weight comprised of Fuselage (including fin rudder which was already glued on): 10.2gm, Wing: 5.5gm, Elevator: 0.6g, Battery: 3.1gm, Pilot: 2.4gm. The spray finish increased the weight from 21.2gm to 21.7gm.

The hingelines were re-drawn, roundels and vertical stripes completed before final assembly of gluing the elevators and wings.

Hinglines: pen.
Roundels: Blue tissue discs glued on then white paint marker was used to paint within the circles drawn with circle template followed by red paint marker for the little red dot.
Stripes: Blue tissue, white and red paint markers.
Headrest: Craft foam.
Goggle strap: Brown thread.

The two CF pushrods from the Yak 3 weighed 1.1gm. The 2 pushrods required for this model were made from 1 such pushrod. The slight weight over pull spring was the deciding factor.

The horns were cut from PVC plastic after the holes were pierced by a hot wire. The installation of these horns were very simple, the horizontal tabs ensured correct height placement and only slits are required on the control surfaces. The pushrods were connected.

A length of string was glued to the wing tips. The string was folded at the centre and a tubing passed through.

The parquet floor is accurate enough.

The wing was placed inverted on a raised flat surface and the two plastic bottles held the fuselage while the epoxy cured on the pylon mount. A set square was used to check that the elevator shall be parallel to the wing.

I did not glue the wings on centrally, but it didn't look too bad.

The struts of the wings and elevators were added. They were made from plastic strips, painted with silver paint marker.

The main skid (and towline hook) was made from doubling similarly pre-finished plastic strip and a bit of craft foam for the rubber tube.

AUW: 23.3gm
Span: 20"
Area: approx. 40 sq in.
Loading: approx. 3 oz/sq ft.

CG was aft of that indicated on plan. One bar forward elevator on the V911 transmitter and it glided (sank) ok. A starboard turnaround also showed that the absence of wing dihedral was still ok for this model.

Now to wait for NE monsoon.

10 September 2015

This is the damaged F929 F939 receiver board I shall use. There is no output to the motor, but the 2 servos are working, so I am using this for the glider. Unfortunately the servos are rudder and elevator, so the right stick would be practically un-touched.

I cannot transfer the almost 6gm of receiver ahead of the CG and I think the nose can be constructed heavier. Shall I use PVC plastic sheet, craft foam sheet, cardboard?

Last night I made the 10mm diameter monowheel from craft foam sheet (2mm?). Nope, I couldn't find anything suitably sized and appropriate to use as a cutter. So I used a pen's plastic cap, and of course it doesn't cut through. So I had to use a scissors to cut it out. But at least the edges are compressed by the pen's cap, and this would, eh, 'streamline' and slice through the air? I then inserted a short piece of small plastic tubing, maybe around 4mm long, through the foam disc and voila! It is off-centred. Nevermind, I tell myself, the reason it appears off-centered is because I am working on a very small scale which would appear fine in the air. More than half of it would be enclosed and I don't really expect the wheel to be functional, even though I had made a functional although off-centred wheel? Afterall, who cares? Really?

If there is a next time when I can be bothered to, in order to make a better wheel, I would use my drill/dremel and sand a nice disc after the bushing is glued.

9 September 2015

I have already noted that there is no space to mount the receiver except in a vertical orientation because of the depth of the receiver. It didn't seem feasible to have pushrods. Last night I check the placement of the receiver board again. This time round, I found how tight it would be if the receiver is within the cavity of the fuselage. The servo horns would be rubbing against the inside of the fuselage sheet.

Perhaps I can let out the horns? Perhaps I can have the horns above the fuselage datum line, in the space where it tapers to the wing mount? I could position the receiver with the servo horns above the fuselage sheet and use tissue/paper for the upper fuselage section, which I would have to anyway because of the twists?

I could visualise it working like a charm, so I took the receiver, some scrap pieces of the foam sheet material and play it out on the plan. Turns out that the servo horns are too short. I would have ended up with servo horns rubbing against the outside of the fuselage sheet.

Now, if I weren't set on using 3mm foam sheet either method might still have worked. If I would use 1/16" balsa sheet for fuselage sides, there ought to be sufficient clearance.

I have ruled out placing the receiver at the cockpit because although the cockpit is wider, it is not as deep, and some part of the receiver would be exposed beyond the outline. The main reason however is because I want to have a pilot at the cockpit. How could there be no pilot in an open cockpit?

Another option is to recess the 3mm foam fuselage side. I could accommodate the bottom of the receiver with many small recesses (servo horns inside the fuselage) or to accommodate the servos so that only one larger recess is required (or to cut a single rectangular opening) and have the servos sit flush to the fuselage's external with servo horns on the outside.

Having exposed horns mean I can thread the strings after the fuselage is completed, but it also mean visible protrusions.

7 September 2015

20" wingspan.
Using damaged WLToys F939 receiver.

From outerzone, a plan for 30" wingspan.
I print it on an A3 paper, reducing it to 20" wingspan.
Then comes the difficulty of fitting in the RC gears.

with a 3/8x1/8 balsa leading edge, 3mm laminated KT board

Follow the curvature of the 3mm laminated KT board. No appreciable camber because I want this to be a slope soarer and I think drag is to be minimised as much as possible if I want better penetration.