DIHEDRAL????

[EDMO 1078]

Just spent the day rigging the wings on a J3 - Came home thinking about Dihedral on Kitfox/Avid - Been thru 4 builders manuals and cant find a thing on it, except Avid Magnum says, "Dihedral is set at the factory"..,..Duh....Anyone got any answers?

ED in MO

[dholly 718]

I've never seen a reference to dihedral in my Avid (Mk-IV and Plus) or KF manuals (model 3 and 4-1200) either. This snip from a another forum in response to a KF5 rigging issue may provide a clue. Dunno if it's specific to KF5 only or dihedral the same thru all models. I believe twist is consistent thru all KF 4-7 models.

Re: Trying to correct left roll in cruise flight.

You are entering the "Test Pilot" stage. Be sure you are qualified and comfortable with making changes and test flying your aircraft.

Knowing that you are not the builder... I would suggest a reset... assume nothing.

Check the horizontal stabilizer for correct installation..

Set the wings back to the standard known condition and start from there.

Refer to your manual. 1 degree twist and 1 degree dihedral. Check length of the rod end thread.

From that point you can adjust either side.. we will typically decrease the angle of incidence first then increase on the opposite wing if needed. try to make changes equal.

For example.. We have a slight left turn.. or a heavy left wing as they say.

We have determined that we do not have a yaw issue that is causing the left turn.

We adjust the right wing rear lift strut rod end out 1 turn... record our change and pre-flight for a test flight. Decreased Twist (wash-out)

Not enough.. so now we'll adjust the left wing rear lift strut rod end in one turn.. record our change and pre-flight for a test flight. Increased Twist (wash-out)

Still not enough.. adjust the right wing front lift strut rod end in 1 turn... record our change and pre-flight for a test flight. Decreased Twist (wash-out)

Still not enough.. adjust the left wing front lift strut rod end out 1 turn... record our change and pre-flight for a test flight. Increased Twist (wash-out)

You may need to make a 1/2 turn or maybe a 1 1/2 turn all depends on the severity of the roll rate...

__________________

John McBean

www.kitfoxaircraft.com

208.337.5111

"The Sky is not the Limit... It's a Playground"

[EDMO 1078]

Thanks again for the info Doug.

John probably is the best source of info on the Kitfox, as Brett or someone from Avid or Airdale would be for that model.

The Magnum photos look like it has more dihedral than others, but could just be in the photos.

We got 4 different dihedrals quoted for the J3, we compared one in inches to one in degrees, and they were about the same.

AS it turned out, the J3 shows front wing spar nearly perfectly level when the quoted measurements for dihedral are met.

If you look at a Cessna 172 compared to the L-19 Birddog, the L-19 has a lot more dihedral than its predecessor.

Dihedral is supposed to make a plane more stabil - but someone says it could make it slower - got to go back to books to check that statement.

Going to my toolmaker background - One degree equals .017" (actually .0166666") per inch, or about .5 sillymeters per inch, so can calculate what height of wingtips and height about center the dihedral will be. More important, is to make sure everything checks out with a level and that both wings match.

The one degree dihedral would be about .816, or 13/16" on the end of a 48 inch level (3/4" block would probably be enough, IMO)

Cant do anything about washout at this stage, except to make the wings match - too much washout WILL slow it down in cruise.

The J3 only has 3/8th inch washout on a 30 inch level - lots less than what was built into the KF/Avid wings.

Again, thanks for the info.

ED in MO

Edited 18 Aug 2012 by Ed In Missouri

[EDMO 1078]

Went back to J3 yesterday and checked the dihedral with a level and shims - turns out to be .86 degrees - slightly less than the one degree our Kitfoxes (John McBean) called for. Not enough to make any difference, IMO.

ED in MO