The International Cessna 170 Association

As this has turned into general info on the attachment of rudders I have a shim question:

When shimming, what am I looking for? In other words, what is the angle/dimension/gap/something that I'm trying to set with the shims?

This for:

1. Forward attachment of the horizontal stabilizer
2. Forward attachment of the fin

Thanks.

You're wanting to fill the gap with the shim, so that you don't induce stress in the structure when you tighten the bolts.
The other end of both the horizontal stabilizer and the vertical fin are what sets the location of these subassemblies in the fore-and-aft direction.

sfarringer wrote:You're wanting to fill the gap with the shim, so that you don't induce stress in the structure when you tighten the bolts.
The other end of both the horizontal stabilizer and the vertical fin are what sets the location of these subassemblies in the fore-and-aft direction.

Thanks, that helps!

Unsurprisingly on a 72 year old hull with a donor tail, the gaps on both sides are slightly different and alignment of the original and donor components (new fin and old rudder) is going to be more work than hoped.

gobrien wrote: At this stage the nose of the rudder (counter weight) is touching the top of the fin.

Gareth,
With the vertical fin removed from the aircraft and the rudder attached to the vertical through the top two pivots, does the nose of the rudder still touch the top of the fin? If so, it sounds to me like something is bent.

Hemostats are really useful for many things, in many sizes.

Hey Gary,

Something has to be bent. The hstab and fin are just sitting in place, loosely bolted. With bolts through both Fafnir bearings the rudder nose sits jammed on the top of the fin. The rudder has had a thump on its nose at some stage. There is no visible buckling on the rudder skins (which are painted) and nothing obvious on the fin (stripped) but as you say something has to be bent!

I'm going to disassemble and scope inside both parts. Worst case I'll have to drill rivets along the top of the fin, reposition the top fin rib and shave the skins.

Gareth

Go slow, just got back from a long trip. I’ll update thread asap.

c170b53 wrote:Go slow, just got back from a long trip. I’ll update thread asap.

Nothing urgent happening here! Going to check the fit of the elevators to the Hstab and fabricate empennage fairings, possibly wire in USB power supply and GoPro mount in the cabin overhead. The list of things remaining to do is long and varied!

If the vertical stab was on a bench you could mount the rudder to the vertical stab by the two hinges. Sighting down the vertical gap between the two you should see which way its leaning or see which part is suspect. As for shims with the horizontal stab bolted to the back of the aft fuselage fitting you can measure the HS forward gaps and correct. Once HS and VS assembled to fuselage, you can sight with a straight rod the three hinge points and adjust the shim on the lower hinge on the tail of the fuselage. If need be you can tweak the the top hinge point on the rudder with shims under the rudder attach bearing blocks as long as the rudder top needs to go aft. If it needs to go forward then you’ll have to re-adjust the bottom fuselage attach point.

Lots of fiddling but it should work out

As suggested I mounted the rudder to the bench.

The fin is square (Red line in the photo). The rudder tip is not square to the leading edge rib properly the Support - Bellcrank Assembly - Rudder IPC 1948: 13-26( Hi George!)

Examining the rudder tip it appears that some or all of the rudder has been re-skinned before. There appear to be extra (filled) holes in the rudder tip skin where it attaches to the rudder tip rib (13-6)). A friend (also my inspector) has started work on a recently acquired 170B so I am going to examine his rudder carefully to confirm my suspicions about how square it is supposed to be and check some measurements. I am aware (thanks to searching here) of the differences between 170 and 170B rudders.

Bottom line, it looks like the rudder tip was installed imperfectly and I'm going to take it off, cut new skins, rebuild it and reattached it. If rib is torn up I'll remake that, but hopefully not!

Oh well ... push back first flight by another week or so!

Sorry, I needed to re-open an old post. Where did you get a new bearing and bushing from for the lower rudder hinge point. FYI the lower fuselage hinge bolt is an AN3.

Poncho73 wrote:…. Where did you get a new bearing and bushing from for the lower rudder hinge point. FYI the lower fuselage hinge bolt is an AN3.

It would be so helpful if the part numbers (or at least the IPC Fig and Item numbders) are included in any request for parts…. otherwise requests for parts without that info only increases the task-load for anyone wishing to help out. Additionally, not everyone will recall which model 170 you might have and if you want the correct parts……)

Looks like alot of guys are trying to go fast!

Like the original posters, it’s a 48. S/N 18573, sorry didn’t include that, just replied to the first post. I will post the part number later.