Do you know what the main problem is building biplanes and triplanes? Simple, you get to build more wings!! So I'm sorry if this post is comparable to the last but the lower wing needs sanding to shape too...I bet you're glad I'm not building a triplane!!
I first cut to length the spars, leading and trailing edges that ran past both root ribs and sanded everything flush.
Before trimming and sending.
After, trimmed and sanded flush.
I then sanded the bottom of each wing panel using my plate glass sheet with abrasive paper fixed to it, sanding in a circular motion until flat, (I used this method on the top wing panels too but, forgot to mention it, sorry). After sanding the bottom of the 2 wing panels I applied masking tape to each of the 2 wing ribs inboard of the root ribs. The root ribs were then sanded to follow the exact shape of the inboard ribs.
Masking tape used to protect the other ribs whilst sanding root rib.
After the preliminary sanding was complete the lower wing panels were marked up in the same way as the top wing panels. All the lines were drawn on using a ball point pen, then the planing and sanding began.
Leading edge marked and being planed to shape.
Trailing edge marked and ready for shaping.
The leading edge sanded to the correct profile.
A sanding block was used to sand the leading edge top and bottom until the correct profile was obtained. When sanding the top of the leading edge care should be taken so as not to catch the wing ribs and riblets with the sanding block. It is best to just pull the sanding block over the ribs keeping it parallel to the leading edge.
Keep sanding block parallel whilst pulling towards the leading edge.
Then finish off by sanding with fine abrasive paper wrapped around a wooden block. The block should always be kept at a slight angle and overhang the leading edge slightly so as not to catch and damage the ribs. If you sand parallel to the leading edge the front of the block will almost certainly hit the edge of a rib, causing it to split or break away from the structure.
Sanding block held at an angle and overhanging leading edge during sanding.
Sanding direction from left to right.
Sanding direction from left to right.
Using the sanding block like this will result in catching and breaking the ribs.
Sanding direction from left to right.
Sanding direction from left to right.
When you sand down tailing and leading edges (other items too) you can check the progress of the shape by holding the object to be checked up against a light source. This light source should be from above and behind the item you are checking. For this reason the lights in my workshop are placed at 90 degrees to the workbench. There is one strip light to the left and one to the right. The lights can be switched on individually, thus casting shadows from the left or from the right. I have tried to show this in the picture below.
Back light used to cast a shadow on the sanded trailing edge.
The shadow is fairly straight, indicating that the sanding is consistent.
Finally the wingtips were sanded to shape. As you can see they are far easier to create then the top wing wingtips.
Lower wingtip sanded to shape, top.
Lower wingtip sanded to shape, underside.
Finished lower wingtip, end view.
After the 2 lower wing panels had been sanded to shape they were put aside whilst I made the rigging brackets and control horns. Wow, I'm glad all that sanding is over!!
Workshop Tip No. 5
When you are sanding down strip and block wood, leading edges or block wood wingtips (other items too) you can monitor the progress of the shape by holding the object to be checked up against a light source.
The light source should be from above and behind the item you are checking thus casting a shadow onto the shape being created. If you are sanding and shaping a trailing edge for instance when you hold it up to the light source a shadow will be cast along its length. If the shadow is true and symmetrical then you know your work is finished. It not, then keep sanding, a little at a time until a symmetrical shadow is created.
The light source should be from above and behind the item you are checking thus casting a shadow onto the shape being created. If you are sanding and shaping a trailing edge for instance when you hold it up to the light source a shadow will be cast along its length. If the shadow is true and symmetrical then you know your work is finished. It not, then keep sanding, a little at a time until a symmetrical shadow is created.
To be continued...
No comments:
Post a Comment