That little nylon thrust button

6 February 2025

I saw this on an Outerzone plan, 9" wingspan I think, and it depicts a balsa dowel and a fibre washer to create a thrust button.

I wondered what's a fibre washer and I put it to Gemini Flash 2, after that it came to me:

"Ah, then I can also use a thick card. I could glue a card disk (with a hole that fits the propeller shaft) to a balsa dowel (with a slightly larger hole) and then I will get a thrust button that can be removable."

Gemini responded:

"That's a clever and practical solution for creating a removable thrust button! Using thick card for the disk is a good idea, as it's lightweight and readily available. Combining it with a balsa dowel gives you a sturdy and easily workable component. Here's a breakdown of your approach and some additional tips:

Your Approach:

• Card Disk: The card provides a lightweight and easily shaped surface for the thrust force to be applied.
• Balsa Dowel: The balsa dowel provides a strong and lightweight core for the button, allowing it to be easily gripped and removed.
• Removable: This design allows you to easily remove and replace the thrust button if needed, which is a handy feature.

Additional Tips and Considerations:

• Card Thickness: Choose a thick, stiff card. Poster board, heavy card stock, or even layers of thinner card laminated together would work well. The thicker the card, the more durable the button will be.
• Dowel Size: The balsa dowel should be thick enough to provide a good grip but not so thick that it adds unnecessary weight. A diameter slightly larger than the propeller shaft is a good starting point.
• Hole Sizes: Ensure the hole in the card disk is a snug fit for the propeller shaft, and the hole in the balsa dowel is slightly larger, allowing the shaft to rotate freely. Accurate drilling is important for smooth operation.
• Gluing: Use a strong and lightweight glue (like CA glue or epoxy) to attach the card disk to the balsa dowel. Make sure the bond is strong and that the disk is centered on the dowel.
• Reinforcement: Consider reinforcing the card disk by laminating it with thin tissue paper or covering it with a thin layer of clear tape. This will make it more resistant to wear and tear.
• Shape of the Disk: A circular disk is the simplest shape, but you could also experiment with other shapes, such as a square or a polygon, to see if it affects performance.
• Smoothness: Sand the edges of the card disk and the balsa dowel to ensure they are smooth. This will reduce friction and improve the efficiency of the thrust button.
• Lubrication: A tiny amount of graphite powder or dry lubricant on the contact surfaces can further reduce friction.

Alternative Materials:

• Plastic: You could also use a stiff plastic sheet (like from blister packaging) instead of card for the disk. This would be more durable.
• Hardwood Dowel: If you need extra strength, you could use a hardwood dowel instead of balsa. However, balsa is usually sufficient for small rubber-powered models.

Your idea is excellent in its simplicity and effectiveness. By following these tips, you can create a durable, lightweight, and easily removable thrust button for your model. It's a great example of creative problem-solving in model aircraft design!"

17 January 2025

All the Veron's rubber powered model plane's plans I have seen uses a tiny nylon thrust bottom. This little nylon thrust button shaped like a mushroom has a hole in which the propeller wire shaft can spin. The dome-top or the mushroom-head, not only spaces the propeller away from the bulkhead in which it is mounted, it also ensure that it won't pull through under tension of tightly wound rubber motor.

I only have various plastic tubes (from pen's tubes) but they are simply tubes without the dome-head which doesn't offer mechanical advantage to resist pulling it through the bulkhead. Sure, given sufficient area of the tube in contact with the bulkhead, the tube can be glued securely, but that is relying solely on the glue strength. 

Ways to creating the flange to the tube

1. It might be possible to use 2 sizes of plastic tube. The larger tube will be over the smaller tube, the propeller shaft passes within the inner tube. The gap between the inner and outer tubes can be occupied by rolled paper (or stuffed with cotton wool) and later superglued, the outer tube will be the flange and the inner tube unhindered for the wire shaft to spin. Cut thin (like 1.5-2 mm) rings from the bigger tube, any thicker is just weight, which is fine in most cases especially when it is at the nose of the aircraft.
2. Superglue a ring of rolled paper to a tubing?
3. Glue the tubing to the bulkhead and superglue cotton thread coiled at the nose?
4. Superglue the tubing through a small piece of ply and shape the ply (doesn't have to be round), this removable unit fits (without gluing) to the final bulkhead/nosepiece but allows shimming?

Come to that, do we really need tubing? Perhaps a small piece from an aluminum to bear the axial load and another piece at the other end of the bulkhead for adjustability and withstanding lateral forces?