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s_thatcher(at)bellsouth.n
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 Posted: Sat Jul 01, 2006 9:54 am Post subject: Rear Longerons on 601XL |
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I've run into a problem with the rear longerons (6B2-1). They are identified as 22x22 and slide under the stiffeners and the two back H.T. Frames. My problem is that no matter what I do, I cannot get more than 6-7mm edge distance at the rear of the Longerons due to the H.T. Frames forcing the longerons away from the pre-drilled fuselage. Here is a small text schematic which I sent to Nick but it was on a Friday and I'm hoping to get more work done before he answers.
The following drawing shows the resulting edge distance when all parts are mated.
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+-------------------------------------------------==+========= 6B2-1 width of 21mm inside
+------------------------52mm--------------------+-----------------+ 6B1-2 Rear H.T Frame
+-----------------46mm---------------------------+----+ 6B1-4
+-----------------36mm---------------------------+ Location of pre-drilled rivet hole on 6B1-4
CL
With max width from Center Line of 52mm on the H.T. Frame and a pre-drilled rivet line in Lower skin of 36mm from Center Line, that means the rivet will be placed 16 mm inside of the H.T. Frame. Since the max inside width of the Longeron is 21mm, that leaves an edge distance of 6 mm, which is what I measured after drilling through the pre-drilled holes into the Longeron.
Anyone who has fallen asleep at this point is forgiven as my brain seems to be going mushy just thinking about it!
Has anyone run into this problem (new fuselage design with pre-drilled holes and slightly modified dimensions from the older version) or have a solution for this?
Scott
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Jaybannist(at)cs.com
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| Posted: Sat Jul 01, 2006 10:42 am Post subject: Rear Longerons on 601XL |
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Scott, I remember having the same problem. The line of rivet holes tapers from a 10 mm edge distance (to the inside edge of the longeron) at the forward HT frame to about 6 or 7 mm at the rear HT frame. Since the longeron is .040" and the rivets are so closely spaced, I felt OK with the reduced edge distance. And like you, I could see no other options.
Also, I have seen, in several different sources, that as little as 2 times hole diameter is OK for edge distance. For an A4, that would be 3.2 mm x 2 = 6.4 mm. And that is measured from the center of the hole, not the edge. There are several places in ZAC instructions that call for a 9.5mm edge distance for A5s. That is a 2.375 edge distance.
This is not really authoratative nor a recommendation, but I hope it helps. Maybe someone else could confirm (or dispute) my view.
Jay in Dallas
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p.mulwitz(at)worldnet.att
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| Posted: Sat Jul 01, 2006 11:46 am Post subject: Rear Longerons on 601XL |
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Hi Scott,
I am working on the same area right now. I didn't notice an edge distance problem, but it might be there.
Looking at your little drawing makes me want to ask how you arranged the rear frame. If this is a picture of the bottom of your fuselage then I don't think it should be in the stack-up you drew. According to my interpretation, the angle goes in contact with the longerons on the fuselage bottom and the open end of the HT frame is attached to the angle. That would mean it doesn't appear in the stack-up.
Sorry about not answering your question. I am not at my shop and can't look at the prints or fuselage until I go out there.
Paul
XL Fuselage
do not archive
At 10:52 AM 7/1/2006, you wrote:
| Quote: | I've run into a problem with the rear longerons (6B2-1). They are identified as 22x22 and slide under the stiffeners and the two back H.T. Frames. My problem is that no matter what I do, I cannot get more than 6-7mm edge distance at the rear of the Longerons due to the H.T. Frames forcing the longerons away from the pre-drilled fuselage. Here is a small text schematic which I sent to Nick but it was on a Friday and I'm hoping to get more work done before he answers.
|
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p.mulwitz(at)worldnet.att
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| Posted: Sat Jul 01, 2006 12:45 pm Post subject: Rear Longerons on 601XL |
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Hi Scott,
I went out to my shop and compared your drawing with my prints and actual fuselage. The results are a bit disappointing:
The holes drilled in my bottom rear skin span around 77 mm for the 5 holes. According to your drawing this distance on your plane is 36x2=72mm. When I measure the edge distance from the last rivet hole in the longeron to the flange edge I get around 8mm. This is a good distance for me and a bad one for you.
It seems the folks at ZAC have changed the location of the pre-drilled holes between the time your skin was drilled and mine (mine was shipped a few months ago). It is impossible to tell (at least for me) how this change was done and when because the holes don't show on the drawing 6B1 anyway. I am afraid this is just another case of the poor quality of the drawings at ZAC and the simple fact that the parts are not produced to the drawings we get but to some other (more ethereal, I presume) standard.
I can't give you a solution for your problem. I guess you will have to wait for Nick to respond. It may be a while since he has already missed responding to my latest inquiry for a week now.
When I had to scrap my first wing because of problems created, in part, by the crappy pre-drilled holes in the rear wing skin I decided to reorder new skins without the factory pre-drilled holes. That didn't bother ZAC one bit and the resulting wing came out just fine.
Good luck,
Paul
XL fuselage
At 10:52 AM 7/1/2006, you wrote:
| Quote: | I've run into a problem with the rear longerons (6B2-1). They are identified as 22x22 and slide under the stiffeners and the two back H.T. Frames. My problem is that no matter what I do, I cannot get more than 6-7mm edge distance at the rear of the Longerons due to the H.T. Frames forcing the longerons away from the pre-drilled fuselage. Here is a small text schematic which I sent to Nick but it was on a Friday and I'm hoping to get more work done before he answers.
The following drawing shows the resulting edge distance when all parts are mated.
||
+-------------------------------------------------==+========= 6B2-1 width of 21mm inside
+------------------------52mm--------------------+-----------------+ 6B1-2 Rear H.T Frame
+-----------------46mm---------------------------+----+ 6B1-4
+-----------------36mm---------------------------+ Location of pre-drilled rivet hole on 6B1-4
CL
With max width from Center Line of 52mm on the H.T. Frame and a pre-drilled rivet line in Lower skin of 36mm from Center Line, that means the rivet will be placed 16 mm inside of the H.T. Frame. Since the max inside width of the Longeron is 21mm, that leaves an edge distance of 6 mm, which is what I measured after drilling through the pre-drilled holes into the Longeron.
Anyone who has fallen asleep at this point is forgiven as my brain seems to be going mushy just thinking about it!
Has anyone run into this problem (new fuselage design with pre-drilled holes and slightly modified dimensions from the older version) or have a solution for this?
Scott |
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s_thatcher(at)bellsouth.n
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| Posted: Sun Jul 02, 2006 2:59 am Post subject: Rear Longerons on 601XL |
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Thanks Jay for your confirmation of the edge distance of 6-7mm. I was really wondering what the h... kind of mistake had I made??!!  Answers that confirm that others have had similar problems really help a builder not feel so alone and isolated.
And Paul, thanks for the dimension check you made. BTW, I did have the longeron sandwiched between the bottom skin and the HT Frame. I apparently just casually measured the end of the bottom skin at 92 mm and then made the holes at 72mm center to center. Since it confirmed my actual measurement of edge distance, I was satisfied It appears after actual measurement that the holes are really closer to your measurements of 77mm (I got 76). However, after doing the math, the HT Frame has a width of 104mm or so leaving a non-trig difference of 104-76=28mm or 14mm in from the inside edge of the longeron. With the inside width of the longeron at 21, this leaves 7mm. However, I still wind up with only 6mm when actually measuring the edge distance on the longeron. I love math when it agrees with the facts but it's a real pain when it doesn't!
I'll wait to hear what Nick has to say. He usually responds fairly quickly and I'm sure those guys can't wait for another day of answering questions! I may request that Nick send me some longerons that are 22x26 so that I can get a better edge distance in this area. After all, these tail loads are not insignificant. But I also have a gut feel that due to spacing and thickness of material, the 22x22 should be sufficient (famous last words).
Again, thanks for your responses.
Scott
Working on Fuselage 601XL[url=http://www.graphitech.com][/url]
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Jaybannist(at)cs.com
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| Posted: Sun Jul 02, 2006 5:24 am Post subject: Rear Longerons on 601XL |
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Scott, your point about a wider bottom leg on the longeron is a valid one. ZAC set up an impossible situation by clearly calling for the skin to align with the tangent point of the longeron bend at the tail end of the fuselage and taper to the sharp edge of the extruded front longeron. This makes it impossible to get a 10 mm edge distance on both the longeron and the skin. Since the skin was already drilled with a 10 mm edge distance, the longeron edge distance must suffer. I thought about placing a second row of rivets, offset from the first row, with a 10 mm edge distance on the longeron. Decided that was just overkill.
Jay in Dallas
Do not archive
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