Experiments on Depron (KT) Foam pieces Thermal Forming, Rolling

8 April 2015

Rolling experiment.

Top two are 3mm with skin. Arrows are direction of visible bands. Both creased on concave side, left is better, the creases are smaller. Reduction in thickness in both pieces.
Bottom two are 5mm without skin. Arrows are direction of the longest length. No creases on concave sides, left is better, didn't snap. Resistance to reduction in thickness on the left piece.

Mission Statement

The purpose of conducting thermal forming experiment on Depron (KT) foam pieces is to appreciate its inherent characteristics (readily available from shops in Singapore), identify suitable technique/s to exploit the characteristics to the best advantage and applying them to making components for RC aircraft.

The Iron Experiment

Equipment:

• Normal clothes iron
• Aluminium kitchen foil
• Cotton fabric

Material:

• scrap 5mm Depron (KT) foam pieces

Methodology:

• Set temperature on iron
• Place foil above and below foam piece, shiny side to the foam
• Iron

 

Test 1 (cotton setting)

Result

Observation:

With a hiss, the foam melted and the foil bonded instantly.
On peeling of the foil, creases of foil were replicated on the foam.
Foam has been compressed/melted to paper thin.
The foam piece appears not to be homogeneous in density, resulting in some transparent areas.
Surface is very smooth and not bead-like.
The paper thin foam was rigid but brittle; the resilience of the foam was gone.
Creases were observed on the surface, these creases were the imprint of the aluminium foil.

Conclusion:

"Cotton" temperature setting was too high.

Test 2, 3 (wool and nylon respectively) 

Result

Wool at the bottom, Nylon at the top.

Observation:

Wool is similar to Cotton setting but slower. That's the piece at the bottom.

Nylon is too slow and the 5mm foam piece does not compress further than approximately 2mm. The piece at the top.

In either case, creases can be reduced by moving the aluminium foil, and the compressed surface is shiny.

Conclusion

Somewhere between "Silk" and "Nylon" might be appropriate.
Move the foil on every pass of iron.

 

 

 

 

 

 

 

Test 4 (introducing the cotton cloth)

Result

Observation:

The compressed surface took on the cross texture of the cotton fabric and is matte.
The heat transferred will bond the cloth to the foam.
The cloth may be peeled off.

Conclusion

The temperature of the iron to be at around wool.
Light pressure on the iron is useful for heat transfer and imprintment.

 

 

 

 

 

 

 

 

 

Application of the Iron experiment

This is a slice of the textured foam piece.
The leading edge was sliced with cutter.
This resulted in a flat-bottomed airfoil.










With additional thermal or cold forming (cold forming in this case), the same airfoil foam piece can be made into an under-cambered airfoil.

Further possibilities

It might be possible to iron on tissue by replacing the cotton cloth with coloured tissue and not peeling off the tissue; saves glue too.

Advantages

A 5mm foam is less than half of 1mm balsa. The iron method is quick to produce air-foiled wings that performs well and looks good and by virtue of its thickness has sufficient strength and is light. This method is also relatively clean, compared to the cleaning up of fine static-charged waste particles that resulted from sanding depron (which, is difficult and needs extreme care to avoid the sand paper digging into the foam).

Le Morane Saulnier Type H

6 Apr 2015

I made the pilot from the blister pack of Lipidor and some 3mm foam. The plastic is very thin and can be stretched further using a round pointed tool. The tool which I bought from Banggood which was designed for fingernail painting.

I push fit the propeller, and if I blew on it, it would spin.
The model stalled easily and it crashed a few times.
Then the propeller flew out so I superglued the propeller onto the motor shaft.
However, I couldn't blow the propeller to spin this time, it was binding.
Further test flights ended in spins to the left which I believe is the torque roll. I think the thrust is insufficient to bring the model to flying speed, and the control surfaces has too much throw, each trim click resulted in marked increase of change of incidence. These 2 reasons made the model extremely difficult to trim.

Further test flights were halted because receiver board stop functioning. Now I end up with a static model.

 

1 Apr 2015

Added rigging, step rung, wind shield, oil drain pipe.

In the rigging process I had to take out the wheels because the needle I used to thread the rigging was too long in the limited space between the wheels and the tubing (cotton bud tubing). I also found out that my V-shaped aileron struts is a bit too long and thick.
I did not make a bust of Mr. Roland Garros because of the exposed electronics.

AUW is 30.8 gm. It would be less than 30 grammes if I use smaller/lighter lipo.
This is still a Peanut although the wing span is greater than 13" because the fuselage is 9" long (not really, it'd only be possible if the propeller's depth is discarded) and most importantly, Mr. Fillon said so on the plans.

31 Mar 2015

The cowling was cut loose to expose the battery connector. While the battery connector leads were desoldered, the red wire lead broke at the board. New extension lead (from servo wires) had to be longer and after they were tinned, they were soldered directly to the board after the other ends were soldered to the battery connector. While soldering the red wire to the board, the heat from the soldering iron melted the foam. Next time, I shall be more careful. The board is still working, I had not damaged it.

4 lengths of CF rods of about 1mm diameter were inserted into the tubular undercarriage. The protrusions were superglued: at the front, to the motor mount; at the rear, only to provide keying, were glued to the former. I held the fuselage and undercarriage until initial set of the CA.

2 lengths of the same CF rod were inserted in slits cut in the card decking, the apex was superglued, and then the bases.

CA was applied to the base of the wing panels and each panel was held in placed (in the air again) for the initial set of the CA. I tried to have the wings' incidence glued at slightly different incidence angles to cater for the motor torque, but I think I added incidence to the starboard panel instead.

By now the tubular spreader of the undercarriage took on a bow and the GF axle rod could not be made to spin freely and it was substituted with 1 length of the same 1mm CF rod. The wheels were CA to the CF rod. Last night, it could turn, but this morning it is stuck. I guess it is ok, it was just more fun that the wheels may spin, but there should not be any appreciable difference.

The tubing for the flying elevator and rudder is not strong, last night, it was detached after the wings were glued. I had to apply some CA again and hold the fuselage and tail assembly in the air. Next time, I could secure the tubing with a short length of paper/tissue.

The next step is to glue on 3 short heat shrink tubing and run the rigging through them. I doubt the wing panels will stay in placed without the support from rigging. Shall I make a pilot's head? It is so small.

30 Mar 2015

The tail skid was made of strips from McDonald's plastic coffee stirrer, glued with superglue. The skid is not cut to length, but it would be easy to snip if off with a pair of scissors.

The exiting holes of the control wires were made on the top side of the fuselage.
After the entire tail skid was assembled in the air, it was glued to the tail end of the fuselage. The main strut would be the vertical V strut. The foam was sliced with a cutter and the V strut let in.



And when that's done, the flying elevator and rudder assembly was glued with superglue 2 points at the plastic housing locations.
The fuselage was placed on the cutting mat and sighted using the gridlines to have the tail assembly straight and square to the fuselage.


The left photograph shows the tail end bottom side up.


The 8mm dc motor's wire were swapped for the correct rotation direction. The battery connector extended. After the receiver was superglued to the fuselage's cockpit location, it seems that the battery connector was not long enough. Through some straightening of the wires, the battery could be connected but barely.

The pushrods were linked to the servo horns before the board was glued to the cockpit area.

The control horns are made from clear PVC sheet. The elevator and rudder was slitted and by moving and angling the horns fore and aft, I got the neutral point of the surfaces.

The apple cheeks were drawn on namecard, the namecard curled, the shapes cut out and then covered. Similarly for the cowling.

Exposed edges were coloured with blue marker. Then the cowling and apple cheeks glued to the fuselage with UHU POR and the 'brass' band glued to the entire cowling with glue stick.

I found that the shaft of the 8mm DC motor is too small and short and the propeller's hole is too big.

I could glue the propeller with CA (UHU POR didn't work, I tried), but I want the propeller to be mounted as accurately centred as possible, so I took a short length of heat shrink sleeve of the smallest diameter I have, heat shrink that to the shaft. The shrunk sleeve is easily pulled off, so I took that and slipped a 3030 propeller on it, and force fed the sleeved propeller to the motor shaft.

It was snug enough to spin full power for a few seconds before the propeller flew off with the sleeve. But I think that is acceptable, because I didn't use CA yet and it is very snug to fit in again the sleeved propeller to the motor shaft.

The over long sleeved propeller mounted over the motor shaft looks like a machine gun firing through the hub. One up over Mr. Roland Garros.


I took some cotton buds' plastic tubing and connected them with heat shrink sleeves to make the undercarriage.

Then I realised that if the undercarriage is mounted, I would not be able to complete the battery operation of connecting, slipping battery into the bay and disconnecting. The extended battery connector is still too short.


I shall have to desolder and solder on a longer battery connector that allows practical battery operation.

The undercarriage and propellers were sprayed black.

26 Mar 2015

Made the rotation mechanism for the flying elevator and rudder.
One plastic ear bud, discard cotton buds.
Two short length of fibre glass rod which I picked up at the field many months ago.

And this is how it shall be mounted, with UHU POR on the plastic bearing tube of the flying elevator.









I dropped this option. The servos are too exposed and the mounting weak.

















This option should be robust enough, but it is at the CG location and occupies the cockpit, so I can't put a seat for the pilot.
Photos from the bottom and from the top. The adopted mounting has the board turned 180 degrees with the servo horns at the rear, not as shown in the photographs.

 

25 Mar 2015

Main components from 3mm foam sheet. Cut and marked.

Dummy Rhone (Gnome) 9 cylinder on card. Cowling from card.

Stick on colour paper and fold the fuselage. Internal width of the fuselage box is transferred to make one foam former. Card cowling needs trimming and fixing after I figured out how to mount the radio and motor in photo above. Shall I make a seat for the pilot? How to do the undercarriage, tail skid, bottomV and centre inverted V? Put the battery in the cockpit?

23 Mar 2015

Trace and cutout from 3mm foam sheet. Grain along wing span, fuselage, elevator (with centre piece not cut through), fin, cowling as shown.
Shape wing, elevator, fin.
Draw lines on exposed sides, only fin has lines drawn both sides.

V-cut the inside of the fuselage, then bend and glue with rectangular formers from scrap foam.
Paint on the black lines, blue lines then fill in the yellow on the fuselage.

Roll cowling piece, glue to cowl formers. The MS logo front former is from plastic card. Trim to fit (not glued) fuselage then paint the cowling, inside flat black, outside blue, emblem last.

Cut a plastic tube to width of rear fuselage, notch centre and glue a short length of carbon fibre rod to form a cross, this CF rod is the axle for the flying fin. Ensure that another carbon fibre rod can still rotate freely in the tubing despite the flying fin's axle.
Make up rolled paper tubing. 2 short pieces goes to the end of the plastic tubing to reduce slop. 2 longer pieces covers the flying fin's axle.
Slit and glue the fin to accept the paper tubings.
Cut a longer piece of CF rod to be the flying elevator's axle. Slide it through the paper tubing and centre it.
Slit and glue the elevator halves to the CF rod ends and remove the centre piece.
Reserve the gluing of the flying rudder and elevator till later after the wing is rigged.

Make the inverted V centre struts from short lengths of wood/plastic card, rig and glue it to the top of the fuselage.
Make the V aileron struts and glue it to the bottom of the fuselage.
Make the inverted W front landing gear, join the rear struts and wheel axle and glue it to position.

Roll the wing halves to shape, introduce washout at the tips.
Insert short CF rods to root ends of the wing halves.
Mark position of the rods on the folded fuselage using the drawn lines as guides.
Glue the halves to the fuselage, rigging to the centre struts and centre of the inverted W front landing struts.

Glue the flying elevator and rudder.
Make the tail struts and glue in position.

Fit the RC component and lines.
Glue the painted cowling.
Fit the propeller. If there is space, glue a picture of a blurred radial engine on clear plastic before fitting the propeller.
Make and glue the wire step to port side of fuselage.
Paint the rigging lines black.

Conception

18.5gm in total for the V911 receiver and 8mm motor, GWS 3020 propeller, 150mah battery. I guess that ideal size may be 15-18", but since I have already downloaded a peanut plan, I shall do it peanut sized.