Wing Incidence Isssue

szicree · #1 01-26-2007, 01:50 PM

Several months ago I fit the wings to the fuse and drilled the rear spar. Today I rechecked all the measurements and found that one wing is 0.1 degree too high, and the other is 0.1 degree too low. The only fix I can think of is to find a way to drill the rear spar attach slightly oversize while shifting the hole a bit. I figure each hole would have to move about 3/64 inch. Obviously this is a delicate operation and could easily make the situation worse. Is a 0.2 degree difference between wings significant? Will I only be able to fly in circles? Boy this really sucks right now.

Radomir · #2 01-26-2007, 02:04 PM

I wouldn't mess with it... just my opinion, though. there's a chance of making things worse and it's a fairly critical area... Also, doesn't Vans say something like "if it's within 1/4" it's good..." I believe their tolerances are far bigger than 0.1 deg. Remember, setting wing incidence was done before this kind of accuracy was possible and those planes fly fine too.

Ironflight · #3 01-26-2007, 02:33 PM

Steve,

I think this is one where I'd consult Van's (and it is very rare that I say that)....fairly critical area, and I'd at least want their opinion to back up any others you'd get here.

Paul

pierre smith · #4 01-26-2007, 02:36 PM

Steve,
Are you absolutely sure of the difference? How did you measure the incidence this time? Radomir has a very good point. Leave it alone 'til you talk to Van's. .1 degree sure is small.

Regards,

beattiema · #5 01-26-2007, 02:56 PM

Geez, I know we strive for perfection but .1 degree - 3/64ths of an inch. If that ends up being critical I may have to start over.

Mel · #6 01-26-2007, 03:01 PM

Many, many airplanes, including RVs, have been built over the years with a "bubble" level. There is no way you can achieve 0.1 degree accuracy with a bubble. While it never hurts to check with the designer, I can assure you that this kind of accuracy is not necessary on this type of aircraft.

Steve Sampson · #7 01-26-2007, 03:12 PM

Steve - talk to VANS but I would not worry. The good news about a single engined aeroplane is that there is NO symetry about it since the prop is rotating in one direction with a resultant cork screw airflow at least on the inner part of the wing. It will probably make it the best coordinated -4 ever!

I would also add that mine is sitting there with pilot holes in the rear spars ready to be drilled. I cant get the same set of readings off the level two days in a row! they are always + or - 0.1 deg.

Dont loose sleep!

szicree · #8 01-26-2007, 03:17 PM

I sure do appreciate all the quick responses. I've been out in the yard checking and rechecking (mostly sobbing really). I'm using a smart level and the mysterious 2.8 inch block. As near as I can tell it really is off by 0.1 degree on each side. Unfortunately, the left wing has too much and the left too little, so that I guess I'll only be able to fly at airports with a right-hand pattern

. The thing that bothers me the most is that this is exactly the same method I used when I originally mated them and I must've checked it a gazillion times. I'm very puzzled to see that it is now different

.

I was hoping that there was some specific allowable difference, but I guess only Van's will know. I've also measured everything in terms of edge distances and I think redrilling is out of the question.

Any additional ideas about this would be greatly appreciated and probably prevent some serious drinking.

David-aviator · #9 01-26-2007, 03:17 PM

Steve,

My Smart Level is cool, but I wouldn't bet my life on a tenth of a degree with it. Pick it up and shake it, turn it around and measure the other way, it will easily vary that much. There was a time when incidence was set with a bubble level.

I wouldn't sweat it.

Kevin Horton · #10 01-26-2007, 03:18 PM

How many different places on each wing have you measured the incidence at? I found that on my wings, depending on exactly where I put the level, I could get very small differences. I ended up going with the average.

Personally, I wouldn't try to fix this now. The only way to fix it without compromising the strength would be to replace the rear spar, which is a huge job. Messing around trying to redrill the holes in the existing spar might allow you to get the incidence sorted out, but with less strength than needed.

You can trim the aircraft laterally after you get flying by tweaking the flap angles on each wing, playing with the vertical location of the ailerons, and tweaking the aileron trailing edges. It is possible you might have a bit more roll off at the stall than some other RVs. If the stall proves too scary, then I would add an AOA system with aural stall warning.