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  #11  
Old 11-10-2018, 11:35 PM
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az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
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Quote:
Originally Posted by arffguy View Post
The notch on the rear spar that Gil refers to is on plan sheet fourteen, revision ten, dated 7/1994.
Yes, good spotting.

But you would think Sheet 46 labeled "Wing/Fuselage Attach" would be a better location for that optional notch picture.
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  #12  
Old 11-11-2018, 08:46 AM
6 Gun 6 Gun is offline
 
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Cool Wing Incidence

Not sure how this is going to be received but if your going to have a light engine you might want the wings just a hair forward and if you are going to have a heavy firewall forward to wings back some make a big difference in tail weight.
Bob
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  #13  
Old 11-13-2018, 10:23 PM
WenEng WenEng is offline
 
Join Date: Aug 2008
Location: Jacksonville, FL
Posts: 515
Default An example of incorrect and correct clearance.

Vans has instructions to set correct wing sweep. They give you a little variance to play with, but when you go for zero sweep you may run into challenges. I originally could not get zero sweep and still have 5/8 clearance to drill the rear spar hole. I had to replace the rear spar doubler with a longer one because the original wing builder made a mistake. In this picture I superimposed two red lines. The left line marks 5/8 clearance on the two fuselage bars from the end of those bars. The right red line (draw it all the way up the rear wing spar) marks 5/8 inch clearance from the end of the rear wing spar. Your goal is to have space between the two red lines to start a drill hole. You'll do the same with horizontal lines to measure 5/8 inch from the top and from the bottom of the same pieces.



The picture below, shows the same wing with the old rear spar extension in it. Notice that when I set the wing to zero sweep, the wing spar line is LEFT of the fuselage bar line. That means its impossible to drill a 5/8 clearance hole.
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  #14  
Old 11-14-2018, 06:02 AM
WingsOnWheels WingsOnWheels is offline
 
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Quote:
Originally Posted by 6 Gun View Post
Not sure how this is going to be received but if your going to have a light engine you might want the wings just a hair forward and if you are going to have a heavy firewall forward to wings back some make a big difference in tail weight.
Bob
That change would have to be made during the fuselage construction to shift the bulkheads. At this point in the build it is way to late. Here the sweep and AOI are being set. A forward swept wing would reduce dynamic stability and could significantly increase wing torsional load. Think X-29.
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  #15  
Old 11-14-2018, 04:54 PM
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JonJay JonJay is offline
 
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Vans allows a certain amount of sweep tolerance. It used to be 1/2. Check your plans. I have one of the first QB fuselages whereby I built the wings and sent them the Center section. They built it with the Center Section out of square. So, the best I could do was one wing 1/2 forward sweep, the other 0.
It flew perfectly.
Do your best, but Vans allows a tolerance for a reason.
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  #16  
Old 11-15-2018, 12:27 PM
scsmith scsmith is offline
 
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I would like to see if I can add some clarity here for the OP and others.

First point, for the OP:
You are correct that it is not necessary to worry about "edge clearance" to the inside of the part, since there is no edge there - the material keeps going.

BUT.....and this is a a BIG BUT......

The other part that mates WILL have an edge at about that location, or perhaps even a small distance away from that. So you surely can not drill a hole closer than 5/8" on the "inside" edge, because it will be at the outside edge of the other part.

This is what Larry was saying in post #8. I'm just trying to say it a little different way, hope it makes sense.

Second point, remember that the 5/8" dimension is from the center of the hole to the edge.

It should not be difficult to achieve zero sweep and maintain 5/8" edge clearance on both parts. Imagine for a moment that the rear spar stub was 1.25" long, and the fuselage rear-spar attach bars were 1.25" long, and you set the wing so that the end of the rear spar was inserted all the way, touching the spacer block in the fuselage rear spar attach-bar assembly, and at the same time the attach bars were touching the root rib of the wing. This would certainly result in either zero sweep or some aft sweep, and it would still be possible to locate the hole at the center of the 1.25" length, leaving 5/8" in both directions.

However, please don't just trim both parts to 1.25" because if zero sweep results in less than complete insertion- in other words a gap at the end of the bars to the root rib or a gap at the end of the rear spar at the spacer block between the bars, then you are out of luck, you will not be able to maintain proper edge clearance in that case.

So, here is what I would do:
If either the bars touch the root rib or the spar touches the spacer block and you have forward sweep, then trim off the one that is touching by just enough so that after trimming, BOTH parts touch. By that I mean that the rear spar is touching the spacer block and the fuselage bars are touching the root rib. If you still have forward sweep, you now need to trim an equal amount off both the rear spar and the fuselage bars.

But no case trim either the spar or the fuselage bars to be less than 1.25" long.

You can calculate how much needs to be trimmed. If you need to move the wing tip aft 1", then you need to trim off (26/112) or 0.23". These numbers apply to the RV-8, so other models will have different numbers. Where did I get these numbers? 26" is the spacing between the main spar and the rear spar. 112" is the length of the wing from the side of body to the tip (126" - 14"=112" for the RV-8) The side of body is approximately the point that the wing pivots about when you change sweep, since that is where the main spar is constrained.

But no case trim either the spar or the fuselage bars to be less than 1.25" long.
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Last edited by scsmith : 11-15-2018 at 12:45 PM.
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  #17  
Old 11-16-2018, 01:05 PM
Zazoos Zazoos is offline
 
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Thank you all for the great responses. I know it takes time our of your day but it is really appreciated. I ended up only needing to shave 1/8 from one forward clevis and 3/16 from the other forward clevis, leaving a bit more than enough to manage 5/8 edge distance in all directions for all pieces. I ended up with a 1/8 inch forward sweep but felt like that was well with in the plus minus tolerance.

Thought I would show my angle of incidence tool that I made. Super easy to make and set to the correct height. The small clamp on it is to help balance it.



Thank you again!
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  #18  
Old 11-16-2018, 01:18 PM
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JonJay JonJay is offline
 
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Good job Trent!
I like your tool.
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