Wing twist

[n2582d]

I was looking for the correct amount of wing twist for the 170 wing but was unable to find it in the 100 series service manual. Does anybody know where to find this information?

[russfarris]

According to the 1970-71 Jane's All the World's Aircraft, for the 172, 180 and 182 the wing "twist" is 1.5 degrees. Actually, the preferred term is "washout"; the purpose is to insure the inboard section of the wing stalls first, so you have aileron control during the stall. Were you just curious??? You can't do a thing to change it -the angle is built in by the wing jig at the factory (guess that's why it's not mentioned in the maintenance manual.) Russ Farris

[GAHorn]

It's worth noting that all washout occurs outboard of the strut.

[GAHorn]

I found the information regarding "washout" on the 170. The original 170 "ragwing" was actually a 120/140 wing with additional length added to it's inboard section (and why it has 120/140 ailerons which was news to me, and explains why some folks feel it hasn't enough aileron authority). It is a straight wing, and contrary to some writings, it is not supposed to have any washout. (I've read some places where it's wing may be "washed out" by adjusting the rear strut.)
The 170A was the first wing with taper built in, and since it also had it's outboard ends symetrically mfr'd (to allow wingtips to be interchangeable), it's stall handling characteristics weren't as nice as the ragwing, so they made it with a 1-degree of washout.
The increased effectiveness of the B-model's slotted flaps called for still more aileron effectiveness in stalls, so 3-degrees of washout was mfr'd into the 170B wing.
(Russ, I suspect someone has confused dihedral with washout in Jane's.)

[n2582d]

Thanks for the info. I was curious as another local 170B owner is rigging his plane. With the flaps lined up to the trailing edge fairings on the fuselage and the inboard ailerons lined up with the outboard edge of the flaps one aileron tip is about an inch from lining up with the wing tip while the other aileron/wing tip line up. One wing had been rebuilt years ago and I wonder if the rebuilder neglected to put the required washout in the wing.

In the past I've seen a chart in a newer Cessna service manual that gives measurements for washout. I was suprised that I couldn't find it in my manual. Thought I might have been looking in the wrong place.

[GAHorn]

The orginal (factory) blueprints for rigging placed the inboard flap end at the fuselage fairing, and the inboard aileron end even with the outboard flap. The wingtip fairing is symetrically interchangeable left/right, therefore it will trail slightly higher than the outboard end of the aileron. (1/2 inch is nominal). If an airplane has a wing-heaviness to it, then it is adjusted by using the eccentric bushings at the rear spar attach. Such adjustment may move the entire wing trailing edge up or down, but you can see that would also move the wingtip. So the previous relationship at the aileron/wingtip should still exist, although the relationship at the root fairing would change.
The most common error is aileron rigging, followed by flap rigging errors. Start with determining that the flap is coming all the way up, and that the lower surface is flush/parallel with the lower surface of the inboard wing sections. Also be certain to check cable tensions, and control surface movement angles. All these specs are found in the Owner's Manual.