Archive for category Longerons
Longeron Bending Finished (2/4/12)
Posted by Ethan Jacoby in Construction, Fuselage, Longerons on February 4, 2012
1.1 Hours -
Today, I finished bending the main longerons. To make the downward bend, I simply clamped each longeron in my vise, measured the angle, pushed the forward end down a bit, and whacked the apex of the bend with a rubber mallet. The bend only needed to be 5.6 degrees (according to the plans), so it didn’t take long to get the right amount of bend. The hardest part of this was checking the bend against the fuselage skin. Since the longeron has a bend in it, and the skin does not, it was hard to hold the longeron in place against the skin. However, I think my bends are good enough, and they can always be adjusted a bit if needed.
The downward bend is supposed to be 5.6 degrees...close enough!
After the downward bends were done, I had to put 17 degrees of twist on the end of the longeron. Again, no subtlety is needed. You simply grab the end of the longeron with a crescent wrench and twist the appropriate direction. To get the 17 degrees of twist, you have to twist way past 17. The first longeron took me a few tries, but I got the second on my first attempt!
17 degrees of twist...
With the downward bend and twist in place, the longeron bending is complete. Assuming everything is correct, this wasn’t nearly as difficult as I was expecting it to be. I’m sure the longeron dies made the shallow curve easier to make, but I still don’t see why longeron bending receives so many complaints.
With the main longerons out-of-the-way, I located the J-channel stock. Six J-channels (two each of three different lengths) have to be cut from the provided stock. Cutting them to the correct length was easy, but I came to a roadblock when it was time to trim the end of each channel. The plans seem really vague on the dimensions for the trimming (unless I’m reading them wrong), so I decided to call it a day in order to do a little research.
I cut the J-channels to length, but I'm confused about how to trim the ends.
Aft Canopy Decks Drilled and Trimmed (1/29/12)
Posted by Ethan Jacoby in Construction, Fuselage, Longerons on January 29, 2012
2.5 Hours -
When I went back into the garage today, the first thing I did was to double-check the curve in the longerons against both the paper template and the F-721B aft canopy decks. Both longerons needed a little tweaking, but not much. In both cases, the longerons had too much curve. To reduce the curve, I used the paper template to see where the curve started to become too much. I then clamped the longeron in my vise just forward of the section that had too much curve, and pulled the aft end of the longeron a bit by hand. It only took me a couple of attempts to get both longerons close to perfect.
After the curve is finished, the plans call for the F-721B aft canopy decks to be drilled to the longerons. The canopy decks need to overhang the longerons by .032″ so that they make a flush surface with the fuselage skin. To mimic the skin, I clamped a scrap strip of .032″ aluminum to the vertical side of the longeron. I then positioned the canopy deck, keeping it flush with my aluminum shim, and started to back-drill the longeron through the F-721B.
The F-721B aft canopy decks overhang the longerons by .032" so they sit flush with the skin. A .032" piece of aluminum acts as a shim while the canopy decks are positioned and drilled.
I wasn’t sure of the best way to drill the canopy deck. Usually, I start at one end of the part and work my way to the other end, drilling and clecoing each hole along the way. However, with the curve in the longeron and F-721B needing to be perfectly aligned, I decided to drill the forward hole, check alignment, drill the aft hole, check alignment, drill the middle hole, and then start drilling the holes in between. Apparently this worked ok, because the canopy decks and the longerons and aligned exactly as they need to be.
The F-721B aft canopy decks have been drilled and clecoed to the longerons.
Once the canopy decks were drilled to the longerons, they had to be removed so that I could trim the aft end of the decks per plans. You have to pay attention here because there are two drawings detailing the trim dimensions. One has dimensions for slider and tip-up, and the other has some additional area that needs to be removed for the tip-up. As usual, the drawings are well labeled, and it really didn’t take much time to mark the decks for trimming.
To do the actual trimming of the F-721B decks, I made rough cuts with my bandsaw and Dremel. Then, I had to do a lot of filing/smoothing to get a descent finish. Files, emery cloth, Scotchbrite…you name it, I probably used it!
The aft end of the canopy gets a little trimming. The cutting was easy, but smoothing out slot wasn't much fun.
Now that the canopy decks are drilled/clecoed to the longerons, the next step is to put the downward bend and twist on the forward end of the longerons. More fun longeron bending!
Longerons Started (1/28/12)
Posted by Ethan Jacoby in Construction, Fuselage, Longerons on January 28, 2012
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.
Bulkheads Finished (1/22/12)
Posted by Ethan Jacoby in Bulkheads, Construction, Fuselage, Longerons on January 22, 2012
1.0 Hours -
With a Penguins hockey game and two NFL playoff games on TV today, I only planned for short work session. Priorities, right!
Since I had already primed my F-711 and F-712 bulkhead parts, all that was left was to rivet them. The F-711 needed the bulkhead halves, as well as the F-711C bars riveted together at this time. The F-711D angle won’t get riveted until later in assembly after the skins are on. All of the bulkhead rivets could be reached with the squeezer, so I was a happy camper.
The completed F-711 bulkhead. The F-711D angle doesn't get riveted until after the skins are on.
A side view of the F-711 bulkhead.
The F-712 bulkhead was even easier than the F-711. For the F-712, just the bulkhead halves are riveted together (it’s a bit more complicated if you’re building a tri-gear model). As with the F-711, the squeezer could reach everything, making my short work session that much easier.
The F-712 bulkhead is riveted together with flush rivets on the aft side.
A side view of the F-712 bulkhead.
With these two bulkheads done, all of the bulkheads are finished (for now), and it’s time to move on to something new. Unfortunately, the next step in the plans is to cut and bend the longerons. This seems to be an area where a lot of builders get stressed out, but end up with satisfactory results. To make this a bit easier (I hope), I bought some longeron bending dies off a Vansairforce.net member some time ago. The dies are milled out of a relatively hefty chunk of aluminum, and the idea is to squeeze the longeron in the dies using a vise to make the gentle bend. I’m sure it will be a fun process.
Up next is longeron bending. I bought these dies a long time ago to assist with making the shallow curve.
The longeron dies bend the longerons by squeezing the dies together in a vise.
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