The International Cessna 170 Association

Guys. Someone made an observation of my plane. The left outboard wing it tilted up and the right wing is tilted down. In checking with another B model it was the same. Can anybody explain accurately why this is?

Any chance of a photo ? I am lost on this one

Doug,
I assume you are not talking about the slight change to the angle of incidence one can make by adjusting the eccentrics at the rear spar attach fittings. Three accidents with “substantial” damage might explain some of the lack of symmetry. Two groundloops and a Stearman hitting the left wing. Probably quite typical for our 65 year old planes. How straight does it fly? On the B model both wings should have the same twist from the strut outboard and no twist from the strut inboard.Starting on page 601 here shows how to check wing twist. Use C-172 numbers.
Edit: These twist numbers are for later model 172's which have 3º37' twist. They are NOT correct for the 170.

n2582d wrote:Doug,
I assume you are not talking about the slight change to the angle of incidence one can make by adjusting the eccentrics at the rear spar attach fittings. Three accidents with “substantial” damage might explain some of the lack of symmetry. Probably quite typical for our 65 year old planes. How straight does it fly? On the B model both wings should have the same twist from the strut outboard and no twist from the strut inboard.

F835262E-86FD-468E-9AC1-059D625E2946.jpeg

Starting on page 601 here shows how to check wing twist. Use C-172 numbers.

Gary no It is not the wing itself rather the outboard approx. 18 inches of the wing. It is exactly the same on both airplanes. I will try to get pictures in the next few days. I would not have believed it till my hangar neighbor came over to ask about this. I thought he was crazy till he looked at mine and mine was exactly the same. I would have lost the bet if he didn’t have a straight edge. The aircraft flies hands free and no ground loop history in the logbooks although wing replacement has occurred. Doug

I was told that outboard section of each wing was to be a "break-away section" that would fail without damaging the rest of the wing in a hangar rash situation. I don't know how true that is. I would suspect the difference was a production line issue since you have observed another one exactly the same.

Doug, What does the NTSB show on your friend’s 170B? I still think the most plausible explanation is a field repair without using a jig. Checking twist is pretty easy using the steps outlined in the link of my earlier post. As far as a “break-away section”, the leading edge and the top and bottom skin from station 190 to station 208 - the most outboard bay- are separate from the skins further inboard. Replacing them was designed to be relatively straightforward. But there is no break in the main or aux. spar at station 190. Cessna did produce several Service Kits for splicing the spars but I believe they are all further inboard. I’ll try and download those to the Maintenance Library. However it does not take a bent spar to mess up the wing twist. One would only have to incorrectly rivet on new outboard skins to change the twist. I doubt it’s something that can just be “eyeballed” as the airfoil is transitioning from the asymmetrical profile inboard of station 190 to the symmetrical outboard rib.

What I find puzzling - and something that may give credence to the outboard twist being asymmetrical from the factory - is that the aileron twist table that I have shows that the twist at the most outboard station is different between the left and right aileron. This looks like a Cessna blueprint to me.

That's an interesting table. However, it's also interesting to note that WD Thompson wrote that it was very common for production test pilots to grab the ailerons at their outboard ends and give them a twist of their own design to make the individual airplanes fly hands-off. So much for blueprint specs.