A

apatti

Well Known Member
All,
The instructions for fitting F891 state in bold letters that the tabs on the skin MUST be even with the vertex of the lower longeron. When I do this I find the skin doesn't align just right with the upper longeron. Forward of the 802 bulkhead the skin is even with the upper longeron. Aft of the 802 the skin protrudes beyond (below as jigged) the upper longeron by 3/16" +/-1/16. I was thinking it should be even all along the upper longeron.

Since you later trim those tabs off, wouldn't it be better to make the skin align with the upper longeron and let the line along the lower longeron vary?

Any thoughts would be greatly appreciated.
 
Will get back

Tony

I am sorry, it has been a while and I will have to look at the plans and get back to you, unless someone else chimes in first.

Off the top of my head, I would think the bottom edge would be more critical, since the top seams will be covered (If I have the question right). After many calls to Mark Fredericks for help, I have contemplated calling my
-8, "1/16 OFF" , he said I should be so lucky!
 
Tony, I read your post last night but to be honest I'm having a hard time visulizing what you are asking. That's not unusual for me so it's probably not your question causing it.

I didn't have a problem with the area you are asking about but I'll look at mine when I go to the hangar tomorrow to try to get a better idea of what you are asking.

I agree with Wade though, a 16th here and there doesn't seem to matter that much.

I'm helping a friend with a Sonex and they call out down to 64th of an inch all over there plans. It's enough to drive you crazy.
 
Wade, John,

Thanks for the replies. I have heard the comment Van sometimes makes "you aren't building a watch". But it is hard for someone without experience to judge what is too picky or not.

I worked on this all day Sunday and now have it down to between 2 and 3 32nds. I tried the other side (right side) and it appears to fit fine. It is very perplexing. I suspect it has something to do with the twist in the upper longerons. That is by far the most imprecise "adjustment" the builder has to make in this area. Unfortunately, my twistometer is out for calibration. :)

Once again, thanks for the replies. However, don't go to any major effort to investigate. Now that it is Monday, I can call Van's. I sure wish they had builder support on the weekends. That is when most builders are working on their planes and could use the help. Oh well, then the they would have to charge more for the kits.
 
I had a similar issue.

I believe that I know what you are talking about. I lined up the tabs per the directions and am glad that I did. I can't remember the specifics, but it seemed to make more sense later on. I had a similar issue as you so I ended up bending the upper (lower as jigged) longerons down (as jigged) to match flush with the skins. Before drilling, I used several small C-clamps to hold it in place. Of course, you don't want to bend them excessively, but a little adjustment on the fly is fine. Hope that helps.
 
I took a look today and both sides of mine line up fine BUT I think I persuaded them a bit when I drilled the holes. It's been a couple of months ago and I don't remember exactly how much but it couldn't have been much of a problem or I would definitely remember.

I agree that the twist/bend is about the most precise thing you could do with a hammer and vice. I just got very lucky when I did it.

Let us know what Vans said, I'm sure others will have the same question.
 
Eric,

I am trying to visualize what you are saying. The lower (as jigged) longerons go straight from the 804 center section bulkhead to the weldements on the firewall. Are you saying you made an extra bend in the longeron so that it was not in a straight line any more?

BTW, I called Van's about this today. The one valuable piece of information I received is that 2-3 32nds will probably cause me trouble later on. Thus, I need to resolve this issue. However, when I asked for suggestions as to what areas to check (I have already spent a lot of time looking for the problem), the guy at Van's bluntly said he had no idea. Too many variables... I know he isn't here where he can measure things for himself. However, I at least expected something like, "other builders have had trouble with ...". But, I got nothing... Oh, well. That's why these forums are so valuable!
 
Tony, is it possible for you to post a picture so we can make sure we are talking about the same thing?
 
RatMan said:
Tony, is it possible for you to post a picture so we can make sure we are talking about the same thing?
Click to expand...

I second that, a picture would be worth a whole bunch of words. :)
 
Yes, I will post a pic. However, I am going out of town for the next two days. I will have to post it after I get back. Thanks for the help.
 
Flex, no bending

apatti said:
I am trying to visualize what you are saying. The lower (as jigged) longerons go straight from the 804 center section bulkhead to the weldements on the firewall. Are you saying you made an extra bend in the longeron so that it was not in a straight line any more?
Click to expand...
Sorry if I wasn't very clear. I didn't make an extra bend, but rather I flexed them downward towards the floor and C-clamped them to the skin. In other words, if I would unscrew the C-clamps, the longerons would spring back upward. I was able to clamp the longeron to the skin because I had already drilled the lower longerons and center section at that point, so the skin was fairly rigid.

I believe that my longerons were not perfectly straight between the 804 center section and the firewall. Maybe yours are not either. It isn't obvious if they are straight or not because of the twisting. If I remember correctly, the upper longerons did line up fairly well at each end of the skin, but the middle required the longeron to be flexed downward.

Once you post pictures, we can help you more. This may be frustrating, but the rest of the skinning process should go easier once this is solved. And whatever you do, don't think about how much easier it would be with the new matched hole kit, it will drive you nuts. :D
 
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Sounds like Eric and I had about the same experience with it. I just looked at mine again and it isn't perfect either but is very close.

ericwolf said:
And whatever you do, don't think about how much easier it would be with the new matched hole kit, it will drive you nuts. :D
Click to expand...

Couldn't agree more!
 
Same Problem: F-820 Skins

I just found this post, and I'm glad to see I'm not alone. I am having a very hard time fitting my F-820 skins, the RV-8's version of the 8A's F-891 skins. I got the tabs lined up on the lower longerons so I have an even 1/4" distance between the edge of the skin and the vertex of the longeron. The pre-punched holes line up with the centerline of my firewall flange, and the bottom (as jigged) edge of the skin lines up with most of the main longeron, but not near the F-804 bulkhead. The skin protrudes below the longeron (as jigged) there. I've measured the bends in my longerons, and they seem fine. I can't figure out what I've done wrong in the jigging process that is keeping these skins from fitting properly. :confused:
 
I pulled the longerons off the jig today and noticed that the bend at the F-804 bulkead isn't sharp. It has too much curve in it. How did you all get a crisp bend without having it spread out over too great a distance?
 
I just followed the manual, put it in a vice and wapped it with a rubber mallet close to the bend. You have to be firm with it, really let it know you mean business.
 
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