Rudder needed

[collin]

Hello,

I need a rudder for a B model. Do rudders from earlier models fit?

Thanks

Collin

McMinnville Or

[Lopez]

Nope, I learned that the hard way after being told by one or more of the "experts" that they were all the same.

To be fair, they are the same from the middle hinge up, and an A model rudder will fit a B if some parts are changed below the middle hinge.

[Bruce Fenstermacher]

Collin,

Popular belief among experts is they are all interchangeable. If fact add the L-19 to the list.

However Lopez has added some doubt so I've investigated as far as I can at my desk and here is what I found.

I have compared the part numbers of all three models. The '48 and the 170A are the same part number for part number. Comparing the 170-170A and the B IPC the first thing you will note is the part number for the rudder assembly is different. The 170-170A is 0533000 and the B model assembly has a -3 added to it. This means something is different but what.

When comparing the parts list 170-170A is the same as the B with three exceptions. The first the main skins. On the 170-170A the main skin assembly is 0333000-12. The individual skins are not listed. On the B model the skins are listed as an assembly 0533000-35 and the skins listed individually as 0533000-20 and -21. I believe we will find the skins on all the rudders to be the same and this just a part number change to accommodate the assembly listing. But we will have to study this further.

The second difference is the part numbers of the lower skins have changed from 0533000-4 and -5 to 0533000-14 and -15. This indicates a change but what? I think I might know and will explain with the third change.

The third change might prove to be the most important and that setting the rudders apart. The bell crank assembly has a different part with the 170-170A being 0533000-11 and the B model being 0533000-30. Looking at the list of the parts of each assembly we will see one difference, the bell crank support channel. In the 170-170A it is 0533000-7 and in the B model 0533000-13. While not always correct, looking at the IPC drawings of each part you will see a difference.

170A rudder bellcrank support.PNG

Notice the channel flanges of the 170-170A are folded towards the front of the rudder and the 170B channel edges are folded toward the rear.

170B rudder bellcrank support.PNG

Remember that one of the main differences between the 170-170A and the B model is the B has a different balanced elevator. The elevators have different hinges and connecting between them and the rudder must clear this. I'll bet we find that the 170-170A rudders with the channel facing aft and then a shorter skin, have a larger opening than the B model (and L-19). And there is where you might find the difference.

But does it matter? It will matter if I'm correct and one put a B model (or L-19) rudder on a 170-170A AND with the rudder at each extreme, it interfered with the elevator connection. But if it doesn't then the difference shouldn't matter in my opinion.

I've heard of L-19 rudders being swapped on to many 170s of all years. In fact my own 170A is suppose to have an L-19 rudder. I have the original rudder which substantiates that my rudder has at least been changed. If there was an interference between early planes and later rudders you would think we would know about it by now.

So Collin, I know I haven't exactly answered your question but am glad you asked so we can get to the bottom of this.

I guess we will all be looking closely at our rudders with a tape measure now.

More to follow I'm sure.

[minton]

"B" and l-19 fit. If you find a repairable one www.airrepair.com has L-19 parts, many are available.

[Lopez]

Bruce got it, the B model elevator hinge line is approximately 1" further aft than the A model. The "notch" on the front of the rudder for the elevator torque tube to pass through is smaller (by 1") on the A model rudder. You can put a B model rudder on an A model, but not vice versa.

I learned this after I purchased a 170 rudder without doing the research myself. A rudder is a rudder (or so I was told) so I found an A model rudder on ebay for reasonable money. I reskinned it and balanced it (turned out beautiful, I was proud of myself since I'd never skinned a rudder before). several months later I bolted it on the airframe for test fitting and it fit, then I bolted on the freshly reskinned elevators and now we have problems. I ended up making a new bell crank support channel using my old one from the damaged rudder as a template. Then I cut the skins on both sides to the proper size and then, A rudder to B rudder...

I still have the form I used to make the support channel, so if you find an A rudder and want to change it, let me know and maybe I can help.