Archive for the ‘Longerons’ Category

Drilled Longerons – 7 hrs

July 16, 2011 Leave a comment

Saturday Jul 16, 2011

Based on the photos alone it doesn’t look like I spent that much time on the project today but in fact it took hours to drill all the holes for the longerons. First I had to trim the forward end of both longerons to be 3/4  inch back from the end of the F-770 skins. That took longer than expected because I had to do it in place on the fuselage using a rotary tool and a file. That was about 1/8 inch of material removed. Once cut and cleaned up it looked like this.

Then after double checking that everything was in alignment and everthing was cleco’d and clamped up tight  I started drilling from the aft end working forward on the left side. Since the longerons are 1/8 thick and not pre-drilled each hole took longer to drill than normal. It took about an hour and a half to work my way up to the F-704 bulkhead. At that point I made the two F-704-L straps that overlap the joint on the inside. My method to do this was to drill through the longeron first, then drill a #40 hole 1/4 inch from one end of the strap stock, cleco the strap to the longeron, align it vertically and match drill the other two holes through the skin. Then I trimmed off the excess length from the strap. In this photo you can see one of the two straps on this side.

Then I continued drilling forward along the longeron. I used a vice grip clamp to hold the skin in alignment four or five holes ahead of where I was drilling . That way I could adjust the position of the longeron to make sure it was flush with the edge of the skin. The last seven holes are #30.

Then I moved to the other side and did it all over again.

With both longerons drilled I started the installation of the firewall. Initially you simply place it in the two longerons and clamp it in place. Then the instructions say to draw a line down the center of the flange of the bottom aluminum firewall angle which I did. Then you put the F-772 bottom skin on and cleco it to the center section and side skins. The instructions for alignment are somewhat contradictory they say to align the second row of holes on the F-772 skin to the line drawn on the flange but also to align the forward face of the firewall 5/8″ aft of the forward edge of the F-770 skin. Turns out those are not the same position by about 1/32 inch. Other builders have reported the same thing. I chose to go with the 5/8 rule because the instructions seem to  emphasize it more plus I can use the same method to check the alignment of the firewall along the sides to the F-770 side skins. With that set I drilled two holes through the bottom skin and the flange of the firewall angle to set the distance of the firewall from the F-704 bulkhead. Here is where I stopped for the day.

Categories: Fuselage, Longerons

Finished Longeron Bends – 1.5 hrs

May 23, 2011 Leave a comment

Monday May 23, 2011

Feeling mentally prepared tonight, I dove into bending the sharp downward bends on the longerons. I started by using the Orndorff method (search the Vans Airforce site on Orndorff) where both longerons are clamped back to back in the vice and you simply pull one from the end sideways until it is 2.75 inches from the other longeron. Then you pull the other the other way until its 5.5 inches from the first. The problem was after the first bend on the left longeron I found that the curve was spread out over about 3 inches instead of being localized at the 28 1/4 inch line. As a result when I put the longeron up against the skin the bend did not track the edge of the skin as well as I wanted. The skin line is completely straight right up to the 28 1/4 line where it jogs 5.6 degrees. So I used the Vans method to bend the right longeron with better results. By applying preload to the longeron and whacking it with a mallet the bend is more localized at the point where the longeron is clamped in the vice. In other words, the bend is sharper.

Sharp downward bend on right longeron

So after getting better results on the right longeron I went back and partially unbent the left longeron and rebent it with the Vans method to localize the bend at the 28 1/4 line. So it turned out fine in the end. Then I used a large crescent wrench to put the 17 degree twist into the first 28 inches of each longeron. As a check, I clamped both longerons back to back and placed them on the floor to see how well the two profiles matched. The curvature upward from the floor is due to the shallow bend, then the Y-split is due to the sharp downward bends. They match as mirror images surprisingly well.

Both longerons back to back

Then I marked and trimmed the F-721B aft deck extrusions for trimming as illustrated on the drawing. Be careful here because the tip-up and slider required different trimming.

F-721 B aft deck marked for trimming

Here is the right F-721B after trimming. It matches the picture on the lower right. I also trimmed the left F-721B.

After trimming

Last but not least was cutting the j-channels to length as shown on the drawing. This is in preparation for starting to assemble the tail cone of the aft fuselage.

J-channels cut to length

Drilled F-721 B Aft Deck – 2 hrs

May 22, 2011 Leave a comment

Sunday May 22, 2011

After a good long day on the project yesterday, today was comparatively brief. I had tickets to the Angels game today so Scott and I went to see them beat the Atlanta Braves 4 to 1. Seats were directly behind home base, 2nd row up from the field. Sweet! Thanks Desi!

But on the project I aligned and match drilled the F-21B aft deck parts to the longerons. Most of the time was clamping a couple of scrap pieces of .032 aluminum sheet to the outboard edge of the longeron to simulate the skin and aligning the F-721B to be flush with that and 28 1/4 inches back from the front edge. Then I just drilled through the F-721-B holes. Here you can see the set up.

Match drilling F-721 B aft deck to the right longeron

And here is the completed set. I did the same thing on the left longeron as well.

Match drilled and cleco'd

Categories: Fuselage, Longerons

Priming Parts and Bending Longerons – 9 hrs

May 21, 2011 Leave a comment

Saturday May 21, 2011

I was planning to start priming parts first thing thins morning but it was overcast and humid so I decided to wait for better conditions. So next in order is the longerons. Like others, I was a little anxious about bending the longerons. Vans says you need to get this right and it can be “maddening”. So I started preparing by marking the bend lines, top, left, right and overall length. Then after double checking measurements I cut the end to the final length plus about 1/8 inch which i will trim later. I clamped both longerons back to back in my vise and found that there is already a bow to the parts. That will make it more interesting.

Marking and cutting longerons to length

Then the real fun began. I started at the aft most bend line for the shallow curve and began using the Vans method. I applied pressure to the end of the angle and whacked it several times near the vice. Then moved down two inches and repeated. After stepping all the way to the forward bend line I checked the result. It was bent, but not enough. So I repeated, checking the shape of the bend with the drawing template frequently. When it was close to the final shape I checked the twist and it was. So I used a crescent wrench to twist it back. That worked pretty well.

Making the long bend

Then I checked the straightness in the other axis and it was curved downward. So I unbent it using the Vans method. That caused the original bend to relax a bit so I spent the next half hour iterating the shape in each axis until the so called “shallow curve” was “to spec”.

One down and one to go

By this time the sky is clearing and the sun is coming out but I am on a roll so I continued with the second longeron. I think it took about 45 minutes to bend the second longeron shallow curve to final shape. Here are both parts laid back to back.

Big bends complete!

With the shallow curves done I feel confident i can do the other two bends but with the weather now bright and sunny I shifted back to  priming so I can finish the bulkheads.

Given my limited priming space it took almost three hours to get the spray gun loaded and prime all the bulkhead parts. That includes tacking time and multiple light coats.

Lotta parts primed

After lunch and a break for a haircut I started assembling the bulkheads. The F-706 is the most complicated. The vertical channel is partially riveted to the angle. The instructions are unclear but  I may have to drill those rivets out to all the vertical channel to be drilled to the bulkhead later.

F-706 bulkhead assembled

The F-70 and F-708 bulkheads go together easily.

F-707 and F-708 bulkhead assembled

The F-711 and F-712 bulkheads are also pretty straightforward to rivet.

F-711 and F-712 bulkheads completed

Altogether a very good day of progress.

Categories: Bulkheads, Fuselage, Longerons