Forward wing sweep OK?

alpinelakespilot2000 · #1 03-02-2007, 10:21 PM

After fitting the wings a couple times, my wing tip triangulation to aft-fuse is absolutely perfect but I have 3/16" forward sweep remaining in each wing. Van's indicates within 1/2" is OK on both the triangulation and sweep, but do they care whether the sweep is forward or aft? It's just the fuselage fork causing the sweep and I can certainly file it down some more to get a more neutral sweep. I'm certainly happy to aim for perfection, but I'm just wondering if I'm getting too greedy and tempting fate for the future drilling of the rear spar.

Since Van's is closed for the weekend I though I'd see what others have learned. I'm kind of wondering if I leave a small bit of forward sweep will my RV-9 require fifty supercomputers just for straight and level flight. (Remember the X-29, or whatever it was from about 20 years ago that had forward swept wings?)

szicree · #2 03-02-2007, 11:05 PM

I don't have a direct answer to your question, and have never even seen a -9, but before you finalize the sweep, you might wanna check flap fit. Specifically, the clearance between flap and fuse. I had some problems in this area on my 4.

db1yg · #3 03-03-2007, 05:56 AM

Steve,

I can't tell you what the result would be if you leave the sweep in but I can tell you that I had a similar issue on my 9a. I did a little filing and got the sweep to 0.0. It really does not take much filing inboard to make a significant difference outboard!! I would file a little at a time until I had it nailed--however I have been accused of being a little of a "fanatic" on issues such as this!!??

Cheers,

db

Mel · #4 03-03-2007, 06:19 AM

If you can correct the problem easily, then do it. If not, don't worry about it. As long as both wings are the same, it's not a problem.

Steve · #5 03-03-2007, 06:49 AM

Steve,
The prints allow you to remove stock from the outboard ends of the aft spar fitting on the fuselage. This would allow more aft sweep. Can't recall the dwg number.

Putting in a few hours at the day job on Saturday morn,
Steve Fabiszak

Kevin Horton · #6 03-03-2007, 10:37 AM

3/16" forward sweep will have negligible effect on handling or structural strength. It could possibly affect the fit of other components, but I really doubt it, as it represents a miniscule amount of error at the wing root.

But, it should be possible to sort this out before you drill the rear spar. Decreasing the sweep should give you more edge distance margin, so I don't think you will have a problem there.

I would try to fix it if possible, but it isn't critical if you leave it with 3/16" forward sweep.

frankh · #7 03-03-2007, 11:16 AM

Vans told me there are a few flying around with 3 INCHES of forward sweep and they fly just fine!

I called em up after I had about the same and they just laughed and told me to "move on"..

Frank

Rosie · #8 03-03-2007, 11:20 AM

Quote:

Originally Posted by alpinelakespilot2000

After fitting the wings a couple times, my wing tip triangulation to aft-fuse is absolutely perfect but I have 3/16" forward sweep remaining in each wing. Van's indicates within 1/2" is OK on both the triangulation and sweep, but do they care whether the sweep is forward or aft? It's just the fuselage fork causing the sweep and I can certainly file it down some more to get a more neutral sweep. I'm certainly happy to aim for perfection, but I'm just wondering if I'm getting too greedy and tempting fate for the future drilling of the rear spar.

Since Van's is closed for the weekend I though I'd see what others have learned. I'm kind of wondering if I leave a small bit of forward sweep will my RV-9 require fifty supercomputers just for straight and level flight. (Remember the X-29, or whatever it was from about 20 years ago that had forward swept wings?)

I checked with one of our Lockheed Technical Fellows (& private pilot) and here is his reply:

3/16=0.1875?/12?per foot / 14ft and take the inverse arc tangent = sweep assuming the measurements are for the right location but close enough for this opinion and you get 0.06 degrees. I would think is no big deal. What fwd sweep would give you is a greater tendency to roll off in a spin because of the more forward the sweep the less roll stability a wing has...

Rosie

alpinelakespilot2000 · #9 03-03-2007, 11:27 AM

Thanks for the thoughtful replies all. I'll work on filing it down a little at a time to get it a little closer to neutral sweep... just because I can. Besides, who wants 0.06 degrees of sweep! (I didn't actually expect anyone to do math on a Saturday for me. Thanks Rosie!)

I guess you know what I'll be doing multiple times for the rest of today: "Wings on... wings off, Daniel-san."

Thanks again.

Stephen Lindberg · #10 03-03-2007, 11:36 AM

Steve: I had the same issue with my 7A. It was easy to fix. I removed 1/16" (I just measured it) from the front fuselage forks and that relieved the interference. BTW, drilling the rear spar can be made less stressful by making drill blocks, starting with 1/8" and increasing by increments to the final size. I used blocks of aluminum I had on hand but steel would be easier to find. Buy some 1/2" bar and cut it into 1" lengths. Drill the desired size hole in the drill block and clamp the drill block to the rear spar/fork assembly. This will keep your hole square to the fork. Clamp the bejeebers out of it and remeasure everything. It wants to creep. Don't just freehand the hole. I know of an airplane that needed new fuselage forks and rear spars after a freehand job. (The builder must have been real discouraged because he hired someone else to fix it for him. I don't know the builder but I know the guy who fixed it.) Edge distance was easy to maintain in my case; I had plenty, on the order of 1/8" or so. Steve Lindberg, Olywa, 7A panel/FWF