Thoughts on Upcoming Annual

[rnealon1]

On upcoming Annual thinking about:

1. Replacing aluminum axles with steel; I want to remove wheel fairing brackets that are not in use anyway.

2. Overhauling Scott 3200 tailwheel (no issues but has not been done in a very long time).

Thoughts on risk/reward/cost benefit?

Bob

[GAHorn]

Hollow $teel axles are certainly stronger than any aluminum axles…including the solid aluminum, so-called “ski” axles (which EveryOne should have at the very minimum. If anyone has hollow Aluminum axles they should replace them with either solid aluminum or hollow $teel.)

However, Bob, I would not replace solid aluminum axles with $teel unless I were given a set.

[rnealon1]

Thanks George,

I know mine are aluminum but I do not know if they are solid or hollow...will find out.

Bob

[Bruce Fenstermacher]

Bob, take your hub cap off and look behind the cotter pin. If you are still running the wheel pant axle nut you will have to remove the cotter and remove the nut. If you see a shallow dish rather that the entire axle behind the cotter being hollow, and the axle is made of aluminum, you have solid aluminum axles. I doubt if I would replace solid aluminum axles with solid steel even if they were given to me. I just wouldn't get around to it.

Understand that to remove the wheel fairing brackets you will need new bolts of different grip length. Also if you do this make sure to mark any axle shims and replace them exactly has they were or else you will be doing a wheel alignment procedure.

[rnealon1]

Hi Bruce,

Thank you, I will look into this and make sure I don't end up making something worse. I do have the wheel pant axle nuts.

Bob

[GAHorn]

Bob, here are pics of three types of aluminum axles…. several views of them.

In the Top pic, you can see the two different styles of hollow on the right…versus the solid axle on the left.

The very FIRST type of hollow axle issued (not pictured) had only AN5 bolts on all Four attach points….(all 4 holes same size)…but otherwise identical to the axle pictured on the right. (I erroneously have that one on the right with the AN6 holes positioned at top when I snapped the pic.)

On the SECOND type hollow axle, there were two AN5 bolts on the top holes…but two AN6 bolts on the lower holes…this axle is pictured on the right.

The third type hollow axle axle also as not bored-all-the-way-through same-size….it was “stepped”, or slightly small I.D. at the base of the axle. This is evident by the smaller hole at the base-end…but larger at the outboard “axle-nut” end. (This axle actually introduced yet another failure-mode…it could develop a crack and snap at the machined-part internally where that smaller tube opened up to the larger hollow area.)

The best aluminum axle (4th type) was finally settled on by Cessna when they created the SOLID axle…AKA the “ski axle”…. which is what we recommend for All models. (Later Cessna airplanes utilized a hollow-steel axle…which is also fine to use if you want to be “spendy”.)

If you have the Earliest axle with four AN5 bolts ( SN19218 and Previous) …it is advisable to drill out the lower landing gear axle attach holes to 3/8” AN6 size (and slightly radius the edges of the newly-cut holes to avoid stress-cracks)… to increase the strength of the axle attachments and to accommodate the Solid Aluminum Ski Axle installations.

All airplanes subsequent to SN19219 had the lower axles fitted with AN6 bolts. BUT CAUTION: It is not possible to predict that these 70-year old airplanes have their original landing gear legs/axles/etc. Many airplanes of this vintage have UN-RECORDED modifications and substitutions. Only a close inspection can determine this.

Addt’l Note: The AN 5 and AN6 bolts may also be substituted with NAS bolts, which were often used on ski-equipped airplanes. See the B-model IPC pgs 50/51….and for some reason the B-model reversed the axle attach bolts such that the nuts were placed Inside the landing leg spring gear (lowest illustration)

170 and 170A installation

B-model installation

[rnealon1]

George,

Thank you so much, this helps visualize Bruce's description. I look forward to seeing exactly what is installed.

Bob

[DaveF]

I disassemble, clean, and lube my Scott tailwheel assembly every annual. In addition to general grit and filth, the most common problem I’ve found is the pins broken off the pressure plate.

Keep careful track of parts during disassembly. Considering how few there are, it can be surprisingly confusing putting them back together.

[Bruce Fenstermacher]

George mentioned the bottom holes in the axle could be drilled out. All aircraft that ever had Goodyear crosswind gear installed would have had this done as it was required for the installation. That ups the number of axles and gear legs you might find drilled that where not originally. So the size of the bottom hole is not a good indicator what axle you might be looking at. As important when considering replacing the axle bolts is to visual confirm what size bolt you have. Don't just follow the IPC.

[rnealon1]

Thanks Bruce and all. As always nothing is simple. Early in it's life 37C had Geiss crosswind gear installed and later removed.

I will come back to the forum when I have more info.

Bob

[rnealon1]

Looks like solid aluminum...