What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Wing Attach 5/8 Distance

Zazoos

Well Known Member
Working on the right wing. Per the plumb bob it is swept forward 1 inch.

The wing rear spar is fully seated and touching the fuselage. The fuselage rear spar forward piece of the fork is touching the wing rib.

I marked my 5/8 distance grid on both pieces. The inside 5/8 distance on the fuselage is measured from where the two forks mate an become a solid spar.
The inside 5/8 on the wing rear spar is measured from the root rib flange.

Questions:
1. Since the both spars obviously continue in there respective directions can the inside 5/8 distance be somewhat ignored? Otherwise as you can see in my grid layout I really do not have the room to remove any materials (especially on the wing rear spar).
2. If I'm correct that the inside edge distance can be ignored, is there a good ratio as to how much material to remove to get close to a 1 inch movement at the wing tip?

fuse_rear_spar.jpg


wing_rear_spar.jpg


Thank you,
 
Also applies to the wing spar

The short answer is the inside clearance matters as well. The rear wing spar sits between the plates and drives the inside edge distance needed.

Brian
 
Some of us had to trim the top web of the rear spar a bit to keep it clear of the top of the fuselage slot. This lets the spar slip a bit further into the fuselage.

o7Z.jpg
 
The short answer is the inside clearance matters as well. The rear wing spar sits between the plates and drives the inside edge distance needed.

Brian

Just to make sure I'm on the same page about what I am calling the inside.

wing_rear_spar1.jpg


fuse_rear_spar1.jpg


The way I see it the spar material continues either towards the center of the fuselage or towards the wing tip. Hence the edge distance there doesn't seem as important. With that said, I can certainly could have a flawed thought process. That is why I want to be as clear as possible, because I do not want to foul this up.

Thank you again,
 
5/8 distance

I'm at this point on my RV-7 as well. Looking at Gil's diagram, it looks like it applies to the outside of the spars coming out of the fuselage. Bottom line, if you have at least 5/8" of real estate all around your hole, I think you're good.

Doug
RV-7
Mounting the wings
 
From http://vansaircraft.com/pdf/Wing_ Incidence.pdf

(search for "incidence" on Van's web site)

"3: If there is a sweep or triangulation problem STOP. The common reasons are:
A: The rear spar structure that sticks out of the fuselage is comprised of
two pieces of 1/8? aluminum bar. One piece ends up on the front side of the wing rear spar stub and one is on the back side (where you can see it). The forward piece OFTEN is too long and hits the wing root rib flange and prevents sufficient
insertion of the rear spar stub into the ?hand? of the fuselage (thus producing
forward sweep). If so, then remove the wing and cut off the minimum amount
required to correct for the sweep error. In general, if the tip of the wing is swept
forward 1? then trim 1/8? to ?? from the end of the bar.
B: Sometimes the culprit is the wing rear spar stub! If it is running into the
spacer block in the ?hand? of the fuselage, and that is all that is wrong, then
remove the wing and trim off as in ?A? above."

The only issue I can think of is hole-to-hole clearance between the hole you are trying to drill and and hole further inboard. Is there a bolt through the spacer mentioned above in the RV-6?

Finn
 
Just to make sure I'm on the same page about what I am calling the inside.

wing_rear_spar1.jpg


fuse_rear_spar1.jpg


The way I see it the spar material continues either towards the center of the fuselage or towards the wing tip. Hence the edge distance there doesn't seem as important. With that said, I can certainly could have a flawed thought process. That is why I want to be as clear as possible, because I do not want to foul this up.

Thank you again,

I think I understand what you are saying, and yes, if there is no edge you don't have edge distance to be concerned with on the "inside" as you reference. However, you need enough clearance to get a socket/wrench on the bolt and nut clear of the fuselage skin, so be mindful of that.
 
Edge distance is the distance from the holes center to the edge of the material. If there is no edge, as in what you call the "inside," then by definition there is no edge distance to account for. However, in this case, two pieces of material are mating with the edges opposite one another and therefore the holes location is constrained on both sides. Your placed hole must provide the appropriate edge distance for both pieces.

Larry
 
Last edited:
I'm at this point on my RV-7 as well. Looking at Gil's diagram, it looks like it applies to the outside of the spars coming out of the fuselage. Bottom line, if you have at least 5/8" of real estate all around your hole, I think you're good.

Doug
RV-7
Mounting the wings

I'm not sure if my description was clear, so I added red to the OP's picture -

o7X.jpg


Finn also mentioned this relative to incidence, but it also affects the sweep. -

B: Sometimes the culprit is the wing rear spar stub! If it is running into the
spacer block in the “hand” of the fuselage, and that is all that is wrong, then
remove the wing and trim off as in “A” above."


The spacer block, shown as a rivet hole on sheet 26, but becomes a AN3 bolt on sheet 33, can certainly affect how far the wing rear spar penetrates the fuselage.

The bolt can be removed and the spacer - fabricated from 1/4 inch stock - can be trimmed down a bit on the outer side or flipped for more clearance..
 
Last edited:
The notch on the rear spar that Gil refers to is on plan sheet fourteen, revision ten, dated 7/1994.
 
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. :)
 
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
 
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.

45870793271_dcbfb45540_c.jpg


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.
44054080570_9a3e339729_c.jpg
 
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.
 
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.
 
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.
 
Last edited:
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.

IncidenceTool.jpg


Thank you again!
 
Back
Top