During the last post we attached the ply motor mount to the spine of the pod frame. In this post we will prepare and assemble the wing clamp.
The clamp is used, via a clamp screw to hold the wing spar in place whilst flying thus allowing for easy dis-assembly during transport. The images below detail the end result of this post:
To complete the clamp you will need the following key pieces. In addition, you will require the two 14 mm self tap screws and the washer for the clamp screw.
Start by dry fitting all of the ply pieces and insert the Delrin tube. Take particular note of the direction of the Clamp Rib. The Clamb Rib fits properly only in one direction, see how the bottom tab of the rib fits neatly into a recess in pod foam. Once you feel comfortable with how the pieces fit together, remove the ply spine. Now squeeze the clamp by hand and test resistance of the Delrin tube being pushed out sideways.
You will likely note that the pressure of the two clamps is restricted which hinders their ability to grip the delrin tube. This is due to the extra ply layer at the top of the rib not aligning correctly. Inspect the rectangular slots where one layer is higher than the other. Using a flat file or sand paper, sand down this excess until you get similar movement in both clamps. The image below identifies the latitude of movement you are seeking. Mark each of the clamps with a pencil as to their fitting location, ie. T(op) and B(ottom).
The clamp mechanism uses two self tap screws as additional protection should the clamp not grip securely during flight. Drill two 2 mm pilot holes in the top clamp for the tap screw. Dry fit and remove the screws.
As the clamps perform the challenging work, we will add extra strength by dousing both clamps, on both sides, liberally with thin CA. Once the CA has hardened, add the hidden nut with a hammer to the lower side of the bottom clamp. You will need to drill out the existing pilot hole to around 4-5 mm before installing.
Dry fit the clamp and Delrin tubing again but this time use the clamp bolt to hold the clamp in place. The kit includes a washer which should be installed at the top (head) of the bolt. Apply just enough pressure to observe the Delrin tube deform slightly. However, you will likely observe that the movement of clamps is now limiting by the Clamp Guide preventing the Delrin tube from being firmly clamped (refer red arrows in image below).
Using a flat file or sand paper, progressively remove enough of the clamp guide slots to allow the clamp to squeeze further to a point where the Delrin tube starts to deform slightly. You will want around 1 mm of additional gap in the clamp guide slots. Do not remove too much as you will risk the clamp being over tightened and potentially snapping a clamp
Dry fit all of the clamp parts again, this time with the ply spine attached. You will likely observe that the clamp bolt tip collides with the ply spine. Use a file to remove a little allowing the screw to extend as required. Ensure that the removed area does not interfere with the recess that holds the Clamp Guide in position.
In the next part of the post we will modify the Delrin tube to function. Join the two wings together with the delrin tube as the joiner. Don’t stress the joint as we do not have the internal carbon rod installed. The objective of this exercise is to ensure the Delrin tube is not to long. In our case, the length was perfect or we would be required to trim any excess. Note the front of the wing join is flush whilst the back maintains a gap of several millimeters. Once you are comfortable with the length, cut the Delrin tube into two equal halves. Clean up any burr from the cut with sandpaper or file.
Once cut, dry install the Delrin tube on each wing spar and then slot the spars into the clamp. Ensure the tap screws are well raised with the tip not exposed on the underneath side of the top clamp. Push the wings firmly together and tighten the clamp to a gentle holding pressure (as the carbon rod is not installed). Gently tighten the tap screw until the screw tip cuts a small mark in the Delrin tube. Disassemble and use these marks to drill a hole of 3.5 mm in the Delrin halves.
At this stage, the tap screws are too long and will extend through the Delrin tube wall (3 mm) into the carbon wing spar. If the screws were to strike the spar, the result could be severe. Accordingly, the tap screws will be shortened where they protrude only 2mm through the clamp giving a 1 mm buffer.
After grinding the screws down, this completes the clamp mechanism. In our next post we will start to assemble the various pod components together.