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  #11  
Old 11-21-2017, 05:27 PM
Bevan Bevan is offline
 
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I seem to recall a Van's approved fix for when the longeron holes are too close to the edge. I cannot find it now but it involved replacing the small spacer under the two bolts with one which was much bigger to include four rivets along the longeron forward and aft of the attach bolts. Can anyone find this thread/diagram/picture?

Might be something worth adding to this thread for future reference.

Bevan
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  #12  
Old 11-21-2017, 06:14 PM
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jcarne jcarne is offline
 
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Quote:
Originally Posted by Bevan View Post
I seem to recall a Van's approved fix for when the longeron holes are too close to the edge. I cannot find it now but it involved replacing the small spacer under the two bolts with one which was much bigger to include four rivets along the longeron forward and aft of the attach bolts. Can anyone find this thread/diagram/picture?

Might be something worth adding to this thread for future reference.

Bevan
Was it post #39 on this thread?

http://www.vansairforce.com/communit...=140972&page=4
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  #13  
Old 12-19-2017, 03:17 PM
keitht keitht is offline
 
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Default Re: post #39 gusset

I am working through the HS front spar fuselage attach issues. Have come to the conclusion that the fundamental issue is that the F710 and F711 frames that came punched and formed from Vans are slightly wider than the design limits. This puts the longerons spacing wider than the design limits. The F 710 B angle is built exactly to spec but comes up short of nesting inside the longerons. This causes a problem with edge distances on the HS 714 , longerons and F710B angle bracket.
I called Vans and talked to Eric about the gusset design in post #39 sent him pictures of my construction project and the issues. Got the reply that Vans could not find any supporting engineering for the post #39 gusset, which wasn't a big surprise. So, if like me, you have a fundemental problem as a result of parts shipped out from Vans that were outside tolerance that in combination with some less than stellar design engineering results in the inability to meet 2D edge margins then as far as I can tell you are on your own to figure out a solution other than to take it all apart and start over.

Looking at the different load situations in that tail area there are the following load conditions.
1. Normal flight where the loads are down and aft on the front spar attach.
2. Inverted flight where the loads are trying to separate the HS from the fuselage and aft from drag.
3. Torsional and transient rotational loads on the HS due to propellor airflow mostly at start of take off and high power low airspeed situations.

I would expect that static strength issues are not of concern given the number of flying aircraft are out there but cracking and crack propagation would be something to be concerned about. Since the vertical stab is also attached in the same area there is a lot going on in that part of the design.
I try and look at these situation in terms of the probability/ consequences chart. The consequences of it coming apart are fatal so the probability has to be be really low to be in an acceptable area of the chart.
I have designed a " bow tie" doubler in T6 0.072 sheet that spans the longerons ahead of and behind the front spar attach. I propose to maintain 2D to the end of the HS714 angle which will result in not centering the outboard attach holes in the longerons. I have already drilled #40 holes to confirm my measurements. I designed another small gusset in T6 0.072 sheet for the rear spar attach area to spread the load in that area and to make it position neutral in terms of incidence. I plan on getting some my former structural engineer colleagues at the local kite factory to comment on this design addition.
Any comments and suggestions would be welcome - even if it's to tell me I am over thinking this issue.
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  #14  
Old 12-19-2017, 03:43 PM
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wirejock wirejock is online now
 
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Just an FYI. I knew this was an issue early on so I made the angle fit like it was poured between the longerons.
I spent a ton of time measuring, marking, earasing, measuring and re-marking. My Mentor Dave Paule came over and we measured again. He is far more precise and happily confirmed my markings. I bailed several afternoons so I wouldn't be tempted to blow a hole. I called Van and asked lots of questions. After a big cup of coconfidence,I drilled. Specifics are in my blog but every hole hit exactly in the center of the longeron. Bolts, washers and nuts fit perfect.
Note: there is an OP drawing on the RV8 that shows the two outboard holes located 1/4" from the inboard edge of the longeron. Not specifically applicable to the RV7 but worth mentioning.
So what I'm saying is don't be in a rush. Take time. Measure, mark, walk away. Come back and check. Ask a friend to confirm.
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  #15  
Old 12-19-2017, 03:58 PM
keitht keitht is offline
 
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Default Mounting HS

Thanks Larry,

I have only drilled #40 holes so I have wiggle room to move the holes over to favor the longerons rather than the HS 714 edge distance depending on the advice I get from former colleagues. My main concern is that I not move loads into places that are not set up to take them. I have been working this problem for a couple of weeks now- working a bit on this problem, giving it a break, working on something else, thinking about it ( 3:00 am) remeasuring, thinking about alternate solutions etc. This is one area not to screw up.
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  #16  
Old 12-19-2017, 04:14 PM
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wirejock wirejock is online now
 
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Quote:
Originally Posted by keitht View Post
Thanks Larry,

I have only drilled #40 holes so I have wiggle room to move the holes over to favor the longerons rather than the HS 714 edge distance depending on the advice I get from former colleagues. My main concern is that I not move loads into places that are not set up to take them. I have been working this problem for a couple of weeks now- working a bit on this problem, giving it a break, working on something else, thinking about it ( 3:00 am) remeasuring, thinking about alternate solutions etc. This is one area not to screw up.
Keith,
Vans has a fix for the mounting should a hole fall too close to an edge. It sounds like you have already discussed it with them but it's worth mentioning. Keep us posted.
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Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 12/01/2017. Plus a little extra.
RV-7A #73391, N511RV reserved (1,800+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #17  
Old 12-19-2017, 05:14 PM
keitht keitht is offline
 
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Location: coupeville wa
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Default Mounting HS

Larry,

I can make 9/32 from hole center to edge on both of the longerons (inboard edge to hole center) if I keep to 2D to the outboard edge of the HS714. I have already drilled out rivets and removed the top deck to get to the F710B angle ( which I have already remade longer to nest tightly into the longerons). Just no margins in this part of the design. I'll take a look at the RV8 OP drawing as well. Thanks for the info
KT
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  #18  
Old 12-19-2017, 05:37 PM
Aggie78 Aggie78 is offline
 
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Quote:
Originally Posted by jcarne View Post


I had a post on that thread also (#2) and updated the links from my old Photo Bucket account to Google Photos where they reside now...haven't figured out a way to post them, but it appears the links work if you want to take a look.

Upshot was, we put a bigger spacer under the affected area and put 2 more bolts in upon guidance from Van's. Beefy fix I feel good about.
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  #19  
Old 12-19-2017, 06:40 PM
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wirejock wirejock is online now
 
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Default Edge distance

Quote:
Originally Posted by keitht View Post
Larry,

I can make 9/32 from hole center to edge on both of the longerons (inboard edge to hole center) if I keep to 2D to the outboard edge of the HS714. I have already drilled out rivets and removed the top deck to get to the F710B angle ( which I have already remade longer to nest tightly into the longerons). Just no margins in this part of the design. I'll take a look at the RV8 OP drawing as well. Thanks for the info
KT
There's no way to get 2D on the longeron either. Ideally it should be 3/8". Best you can get at dead center is 5/16". I was told to aim for dead center and the resulting edge distance on the angle was ok. Since my angle is nested pretty close, that edge distance ended up about the same. We did discuss the RV8 OP drawing which actually moves the hole closer to the inboard edge of the longeron but they preffered aiming for dead center on the longeron rather than allowing the hole to creep inboard.
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Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 12/01/2017. Plus a little extra.
RV-7A #73391, N511RV reserved (1,800+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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