Back to modelling youth: Druine Turbulent

5-7 November 2024 (Overthinking?)

Overthink then Simplify. The key to successful model building is often in simplicity, especially in unexperienced areas. Overcomplication can lead to frustration and delays. I can achieve good results by focusing on the core principles and using practical techniques.

The curved slanted root

The next step is to make the pair of wing panels. The plan of the left and right wing panels show the root ribs are to be slanted (for dihedral) but are otherwise straight. The top view plan of the fuselage is clearly curve at the junction and the fuselage box structure has been completed. 

1. These curved root ribs are to be installed without extending the leading and trailing edges.
2. Two oversized piece of balsa are wetted and curved to match the fuselage curve.
3. Tape these curved root ribs to the fuselage.
4. Jig the fuselage and wing panel so that they have the correct dihedral angle relationship. The incidence is only tweaked when gluing the wing panels to the fuselage. I am probably overthinking if it is possible, to make a single re-usable jig that can be used for both panels for this temporary set up process and the final gluing process.  
5. Superglue the wing panel to the curved root rib, add gussets.
6. Remove the wing panel by unpeeling the tapes and sand the bottom of the curved root rib first, follow by the top of the curved root rib.

Point 4, a beam type of jig for dihedral and a cradle type for root incidence may be easiest.

I am probably overthinking about the curved root ribs. In order to get the oversized curved root ribs to have the airfoil shape in Step 6:

1. Superglue 2 pieces of balsa template that mimics the dihedral on the curved blanks.
2. Sand the bottom of the curved blanks until the base is flush with the balsa templates.
3. Measure the height of the normal straight ribs at the points where the balsa templates are and transfer this to the curved blanks.
4. Cut roughly to shape and proceed to Step 4, the markings will guide the final sanding to airfoil shape matching the normal rib airfoil in Step 6. 

The simplest method being to draw and cut a rectangular piece of 1/16" balsa sheet. The rectangle is longer than the path of the curved rib and wider than double the height of the intended airfoil height with a centre line drawn in. On the other side, parallel lines are drawn across the width of the rectangle piece, these lines mark the positions along the airfoil which will be used to determine the top curvature later. Wet and curl this piece until it matches visually with the curve on the fuselage top view. After the blank is dry, check against the top view again. Re-wet and tweak the curvature as necessary and let dry again. Repeat the tweak until the dried blank matches the curvature, or, when I get bored and decide it is good enough. The high line of this curvature will need trimming since there is the dihedral angle to consider. Sand to match the dihedral angle. Do the same for the other long edge. Cut along the centreline and we have a pair of root ribs. Mark the height at the vertical lines previously drawn on the inside of the curved blanks and cut approximately. The 2 root ribs can now be used for the wing panels. They cap the root end of the wing panels.

Propeller shaft

The following instruction is when viewed downwards. For the simple hook, 1) use a vice and grip the short end of the wire across the shank of a vertically placed drill bit, the wire being near side 2) pull the free end around the shank clockwise beyond 180 degrees, 3) relax the vice and remove drill bit and the single coiled wire, 4) adjust the coiled wire so that the coiled wire appears to have a straight entry and straight exit, 5) grip with round nose plier and bend the longer end, adjust until it appears to bisect the loop, 6) cut off the other end of the wire leaving a gap for the rubber to pass through. 

Over thinking? This is almost as complicated as doing the reverse S hook.

Maybe a pair of round nose pliers bend in the air is enough.

For diamond hook, similarly, a pair of round nose plier to get the 2 critical points correct, the lowest point and the highest bend that is the shaft. Whether the other bends are perfectly right angled or round loop shouldn't matter.

I think I'll do the propeller shaft after the full model is trimmed as a glider. I'll have enough time to think if I should use a plastic tube as a bearing or I can use the aluminum from a beverage can to face the removable nose block as a bearing surface.

Modelling weight

I discovered that in the past, modelers used plasticene to balance the model. Plasticene has inherent disadvantage which I dislike. It appears oil is present in the product, I had to wash my hand with soap or it won't be cleaned. I noticed also that it stains balsa wood, and dropped off easily on my chuck gliders. Sand and small particles are attracted to plasticene. Therefore, it does not appeal to me.

Blu-Tack is a relatively modern product that is cleaner and stickier, although it is more expensive.

I'll use Blu-Tack when balancing my model. I can use it on tissued surfaces, I can use it to attach small metal objects like nuts, bolts, coins.

Balsa Cement

I read that balsa cement was a favorite with modelers when gluing on the horizontal stabilisers for free flight model. When more or less tail incidence is required, the modelers dissolved the joints with solvent and re-glue. So smart, I thought, I didn't know that.

Disappointingly, balsa cement is not readily available anymore. Superglue, a relatively new product, is readily available. I think I can use superglue in lieu of balsa cement and use acetone/alcohol/nail polish remover to dissolve the joints.  

 

Wheels

This is overthinking. To make 1" wheels from extruded foam.

Yes, I can make true spinning wheels using a drill and sandpaper, but this method does not appeal to me.

Method A

1. Make a 90 degrees perpendicular cut on the extruded foam sheet.
2. Using double side tape, stick two Singapore $1 coins to both sides of the foam sheet, the coins being directly on the 90 degrees perpendicular cut.
3. Cut or sand away the rest of the foam around the coin.
4. One advantage of using coins is that it is metallic and you can hot-wire cut perpendicularly the foam.
5. To save effort, you can stack 2 pieces of extruded foam sheet after step 1, aligning the foam sheet 90 degrees perpendicular edges.
6. Remove both coins and use a circle template to locate the centre of the foam discs.
7. Pierce the foam discs with thin wire, ream with drill bit, glue the axle bearing. 
8. Axle bearings may be short sections of plastic tubing or rolled paper tubing.
9. The coin's diameter is less than 25mm, glue paper strip around the discs until it is 1" in diameter.
10. Sand the wheels to shape.

Method B

1. Rough cut 1.5" square 6mm foam pieces. Make more, if you need 2 make 4.
2. Pierce the foam pieces with bamboo skewers.
3. Make a jig from corrugated cardboard, it has a 1" slot that is about 30mm wide.
4. Bend 2 spindle saddles to allow the bamboo spindle to rotate freely within.
5. Position the saddles so that they are 13mm from the edge of the jig slot. 
6. Place the hot wire bow cutter at the entrance of the slot and by rotating the skewer, the hot wire will cut the 4 discs of foam pieces.
7. Cut a pair of disc from thin aluminum or transparency sheet for each wheel.
8. Pierce each disc with a sharp pin for the axle.
9. Remove the foam discs from skewer and glue the thin axle bearing discs against each face.
10. Sand the wheels to shape.

I think I will choose method B because I have a small bow hot wire cutter and I can use the jig for many wheel diameters by adapting the jig. This method is also suitable for straight simple cones and an adaptation of this method can hot wire cut straight transitory cones using base and tip templates.  

Method C

This is the simplified method B and is without the jig board, steps 1, 2, 7-10 are identical.

1. Rough cut 1.5" square 6mm foam pieces. If you need 2, make 2.
2. Pierce the foam pieces with bamboo skewers.
3. Insert a circular cardboard template to each end of the foam. Simply draw the circles. pierce the centres and cut with a pair of scissors. 
4. Hold the skewer in non-master-hand and the hot-wire bow cutter with the master hand, slice against the templates.
5. Cut a pair of disc from thin aluminum or transparency sheet for each wheel.
6. Pierce each disc with a sharp pin for the axle.
7. Remove the foam discs from skewer and glue the thin axle bearing discs against each face.
8. Sand the wheels to shape.

I think I will choose method C now because I have a small bow hot wire cutter and everything is literary done by hand.  

4 November 2024 (12 hours?)

Decades later, the wizened youth rediscovered his creative spark. Now that I know what I know now and have what I did not then, it becomes easy.

I made a few photocopies of the plan  Oz : Druine Turbulent plan - free download and pasted them on some corrugated cardboard. Covered with transparent packing tape, these are my small, light, cheap and fast building boards. The packing tape and corrugated cardboard provides a surface where I can superglue balsa components and if necessary, to cut, for these reasons, I call them my jig boards.

Here, the fuselage side frames is superglued on the jig board and the spacers added, start with the longest and end at the tail and nose.

I deviated from the plan and tried laminated tips. Each tip is a single balsa strip with a few slits. The strip was wetted and superglued on the jig board. Nudging the strip with my fingers and a 10 cents coin (the 5 cents coin is a bit too thin), I spot glue the slitted slip to hold the curvature. Progress until the other end is reached.

The glass of water was not for drinking. It's for wetting balsa strips.

Here, the left handed wing tip will be discarded, it is not long enough.

This jig board is to build the right wing, I pasted the wing tip of the left wing over it. This way, the same jig board can be used for both wing panels.

The slightly rusty carbon steel guitar string is 0.38mm diameter (PL015).

A masking tape was laid on the cutting mat and drawn as shown. 

Lift one edge of the tape to slip in the guitar string, then fold over, and the small marks show where to bend. 

Here, the string is bent but not cut, and the masking tape has to be removed. 

Try to bend it symmetrically. It probably won't happen, but you can tweak it after the tape is removed.

Tweak the wire against the plan. The wire is so small that I can tweak it without pliers.

When satisfied, or in my case, when I gave up, I taped the wheel axles with masking tape onto the plan. The balsa piece below the wire has been test fitted to the fuselage. 

  

Later, I tissued over the wire and balsa and soaked it in superglue. I didn't feel like searching for cotton strings.