3.2 Hours -
No reasons to put it off any longer…it’s time to make some longerons!
The longerons are shipped as 16 foot lengths of aluminum angle stock. These pieces of stock must be cut to length and then bent to match the shape of the fuselage. Since these are such critical pieces, I wonder why the factor doesn’t form them, but I do realize that they would be much harder to ship if they were already bent. Oh well, many have been made before me, so it can’t be that bad!
To measure the correct length, I took a tip from several other builders and taped the end of a tape measure to the end of the longeron. Since the metal part of the tape measure end can move a bit, I taped it to the longeron at the one inch mark, and I’ll have to add an inch to the final measurement. The overall length of the longeron is supposed to be 173-7/16″, so I measured to 174-7/16″. After checking the measurement several times, with two different rulers, I cut the longerons using my Dremel with a cut-off disk.
Taping the tape measure to the longeron at the 1" mark seems to be the common method for measuring the longerons.
At least I remembered to add the inch to the other end. The plans call for cutting at 173-7/16" so I measured 174-7/16".
Since a left and a right longeron has to be made, I marked the angles for top, outside, left and right. The next step is to cut a notch out of the horizontal face of the longerons at the aft end. After the notch is cut, there’s no going back, so I made sure I had the longerons marked correctly for left vs. right. The plans, as usual, provide the correct measurements for the notch, and, once the longeron was marked, I made the notch using my Dremel, a few files, and some emery paper.
The aft end of the longerons get trimmed a bit. The flash obscured some of my lines, but you get the idea.
This could still use some smoothing, but here's the trimmed longeron.
Next, I marked the longerons for all the bend locations. This has to be done prior to making any bends since the dimensions provided in the plans are based on a straight piece of angle. The longerons were marked at 28-1/4″ for the downward bend, 38-7/16″ for the start of the shallow curve, and 69-9/32″ for the end of the curve. In addition, I also made marks every inch inside the section that gets curved so that I would know how far to more the longeron dies with each squeeze of the vise.
The longeron bend points are measured on the straight longerons, so all marking must be done before bending. Here's a mark for the downward bend.
The start of the shallow curve is marked. I also ticked off marks every inch, from the start to end of the bend, so that I will know how far to move my longeron dies.
The end of the shallow curve is marked.
Per the instructions that came with the longeron dies, I placed electrical tape on the outside of the vertical face of longeron to prevent the dies from scratching the angle stock. I then inserted the longeron into the dies at my first mark, squeezed the vise closed, moved the dies an inch aft, squeezed the vise…I repeated this, inch by inch, until the curve was complete.
Starting the bend using my longeron bending dies.
About 3/4 through the first bend. Opening and closing the vise is a bit of work, but I think this is easier than the Van's method.
To check the curve, I used both the template in the plans as well as the F-721B aft canopy decks. The bends weren’t perfect, but they were pretty close. A little tweaking and they should be done. I don’t know how much more difficult this would be without the dies, but the nice thing about the dies is that they keep the longerons from twisting as the bend is made. For me, the lack of twist makes them worth the $30 I paid.
The shallow curves are finished. They may still need a little tweaking to make them perfect, but they are pretty close as is.
Since the curves went so well, I decided to not press my luck and I called it quits for the night. I’ll still need to make the downward bend and twist on the forward end of the longerons before they can be called done.
