bigal126

My Feedback: (18)

I am building a kit. It is a goldberg extra 300. Fully symetrical wing. 68" wingspan. The plane will weigh about 9 lbs AUW when done.

The plan shows 0 incidence for both the wing and the horizontal stab off of the datum line. I am about to glue in the wing bolting platform. As it stands, the wing shows a -1 degree incidence when the horizontal stab is set at zero. In other words the wing and stab have a 1 degree difference between them. The trailing edge of the wing is higher than the leading edge. I think that means it has a negative incidence.

My question is whether I should try to correct the difference or is -1 degree no big deal? It'll be a little extra work to get the wing set at zero, but if it isn't going to make any difference in how the plane flies, then I won't do it.

Another question would be: Would it be better if the wing incidence was a little positive, or a little negative? I'm not sure if I can get it dead on, but I'll err on the better side if there is such a thing.

Thanks!

CrateCruncher

My Feedback: (1)

A degree doesn't sound like much but it will make a noticeable difference. The symmetric airfoil I fly daily only needs 1/64th degree positive AOA for level flight at full throttle! For level flight with -1 deg wing you'll have to trim in some up elevator. This in turn will change your downthrust and cause other performance robbing flight characteristics and trimming hassles.

If it were mine I'd want to get as close to zero as possible and err toward slightly positive. I've found it easier and more accurate to convert to inches or millimeters when setting up my planes than using degrees. Incidence meters have a habit of giving inconsistent readings. From the forethought implied in your question this probably isn't your first rodeo. But let me know if you need the trig overview for getting to inches etc.

gadix

My Feedback: (2)

i had a H9 ext 260 with a +1 on the LT wing and -1.5 on the RT wing whicj make a diff of 2.5dgree
i had to use a lot of trim for the plane to fly stait

i used TH laser incidence JIG for stariten them up!

fusealge at "0", than horizental stab at "0"
than to check the RT stab in relevence to RT wing-> the same for the LT side

in order to "rotate" the wing to the "0" i had to drill the hole of the "anti rotation pin" in an ovale shape so i can "play" with the wing on the boom axis to get to the "0" dgree.
when done for both wings i made a new wooden plate with new hole for the pin , glue it to the fusealge at the "0" per the wing new place

set all trims back to ziro at my TX and went up in the air...

the ext was leveld with all trims at ziro

bigal126

My Feedback: (18)

Thanks for the reply. I will make the adjustment. I spent about an hour on it and I'm almost there.

What would the negative incidence have done with respect to roll coupling? Will this change affect the ability to hold knife edge in any way good or negative? Theoretically speaking of course.

CrateCruncher

My Feedback: (1)

Theoretically, the -1 deg wouldn't cause roll couple or knife problems once trimmed for level flight and assuming you didn't change the throttle setting. But I always give it the juice when I knife which would cause the plane to go out of trim and quite possibly become a handful of fish. Just for grins, once you feel comfortable with the plane, stick some washers under the front wingbolts so you get -1(If thats even possible on your wing). Then you'll really know how it would have flown.

bigal126

My Feedback: (18)

That is possible with my wing and maybe I'll do just that.

Anyways, thank you for the info. I just spent another half an hour on the project, and guess what? I'm now just on the heavy side (+) of zero. Not only that, it seems that once the high parts of the wing saddle were sanded down, the wing seats very nicely now (not before). I killed two birds with one stone. Still have to drop the wing mounting plate holding cut outs, but that will be a breeze.

Thanks again.

Al

Luftwaffe Oberst

Keep it 0* on both LW and RW. It will make things easier on your maiden flight with the trim.

gadix

My Feedback: (2)

this 120% true
especilay for IMAC and 3D