Hinges with 360 degrees of freedom

 

Nothing worse than having your pilot in the hanger all day because his aircraft is grounded. Especially if you broke it yourself getting it out of the car. This elevator got a good bump one day - we stuffed it full of glue and went flying the next day anyway. Lasted for about ten minutes. Then the pilot was forced to bring it in quickly because half the elevator was flapping freely behind the plane. Time for a rebuild.

My son was given this plane by someone at the field when we first started flying. People in this sport are like that. Our doner was a scratch builder with years of experience, not much for store-bought parts. Upon examining the now defunct part he built, we noted that his hinge had been made out of pieces of covering material cleverly fitted to create a hing that swings a full 360 degrees.

I'm sure some of you more advanced builders will recognize this but it was brand new to me. I also have never seen it written up anywhere so we decided to document our efforts. What follows is how we replicated that hinge.

 First step was to create a drawing from the busted parts. Then we created the individual pieces fitted dry for testing.

 

Then the glue-up. The elevator flap shown here has two important facets: Firstly, it is not attached to the rest of the assembly at all. It is simply lined up to keep everything straight and true. Secondly, where the hinged piece meets the elevator proper, it is beveled approximately 45 degrees for clearance.

Both pieces will be covered separately after drying and sanding. The only thing holding them together will be the hinge.

This is what we are going for as demonstrated in the old part. Note the first silver piece wraps from the upper piece and is tacked onto the top of the hinged piece above my thumb. The second silver piece does the opposite, wrapping from the bottom. Where both pieces meet in the joint, they are free to move, not adhering to the parts.

The really interesting part is that as you swing this hinge, the pivot point changes from the top edge to the bottom edge. This is what allows the full swing from top to bottom. It's also why you cannot allow any gluing inside the hinge.

To replicate, we are first going to cut a uniform one inch strip of covering material.

Then we are going to take of one-quarter of the backing off to expose some the tacky side.

 

We cut the strip in half and reversed one side so that the two exposed tacky sections met up with each other. You will note how the backing for the material that remains are on opposite sides.

We used the pointed end of our iron to heat JUST the area where the two overlaps meet. You just want to heat it enough to get the glue flowing. You don't want to start shrinking the material. I used a Hobby King iron at medium setting.

Now that we have a connected strip, we cut it into uniform one inch pieces. The actual width you select here is more of a design consideration than anything else. These will be the individual parts that make the final hinge mechanism.

To apply these, we started on the outside edge. We had also taped the two pieces together with some blue painter's tape so we would have good alignment to start with. After those first two outer edge pieces were on, it was a just a matter of repeating the process.

• Place one piece on either part. Aligning the center section ( that has no glue) so that it sets within the hing area. That is, from the top edge of one piece to the bottom edge of the other. Tack that piece down to secure the alignment.
• Flip over the part and peel off the backing of the opposite end. Check your part alignment to insure the hinge line is straight (you only need enough gap between the pieces to slip in the hinge). Then tack in this second side.
• As we were working from outside edge in, we also did the same on the opposite end.
• At this point, we could fold the hing completely to one side and more securely set the exposed hinge, along with giving the hinge center more heat. Remember, the place where these two covering materials meet in the center were only tacked in place when we made the hinge part. You want to make it a secure bond now.
• Swing the hinge to the opposite end and repeat the glue setting process.

Repeat for the next set. Just make sure that they go the opposite way, If you started the last one on the top, the next one goes on the bottom. For example, you will note that the first (outermost) and third covering piece in the photo above start from the top left, and thread their way down underneath the part on the right. Between them, you can see the covering is on the top right and it flows down to the lower side on the left. Interweaving them in this way is what really tightens it up like a single unit. You will notice that after you get the second set of covering strips in place.

 

 

Here is the hinge, fully turned up (to the right).

 

And here it is again, fully down (left). You can see the hinge points change from top to bottom. Very handy stuff.

I chose to use a contrasting color for the hinge knowing that as a result I would have a distinctive design for my effort. One could just as easily use the same color covering and effectively hide the hinge from most people's view. At least everyone further than five feet away.

Only thing left to do was reassemble the aircraft and attach the control rod.

The hinge makes a fairly tight fit - no serious gap to disturb airflow. It's also tough as nails. Heat two pieces of covering together and try to pull the apart. Unless you can tear it, you won't have much luck.

There's  a lot of design variations one can use with this also. As it is two separate pieces of covering, one could have different colors top and bottom. You could hide the hinge using clear covering, or the same color covering. You could vary the width of the pieces. You could even extend them so that they continued to the leading and trailing edges so they looked as though they were purely decorative and not a hinge at all.

I learned a lot. Glad I wrecked that thing ...