1948 Tail Leaf Spring

[melcessna]

Since everyone has been so helpful, I have another question. My 170 experience has been the "B" model which has a more stout spring. The restoration I'm doing is extensive and I am trying to be somewhat true to originality except in cases where it just makes no sense, like having ADSB. What has been the thinking regarding the original 48 design or beefing up the spring. Both will be new if that influences anyone's comments. Appreciate the input, Mike.

[Bruce Fenstermacher]

The tail wheel leaf spring(s) are exactly the same on a '48 as all later models. Fact is the ''48 uses one more spring perhaps making it stiffer.

Maybe you are thinking of the tail spring fuselage mount. The '48, A model and the first B models had that steel mount. It was prone to cracking. So the second and current design was created which we refer to as the fish mouth bracket. There are still lots of steel brackets being used. And you can get brand new steel brackets from Univair.

Most tail wheel brackets I've had knowledge of being replaced for cracking have been the later fish mouth bracket. Sometimes I wonder if the fish mouth and its parts might even crack at a higher rate than the steel version it replaced.

One thing for sure. The fish mouth version is mounted differently with the load spread over more formers. But that was not the failure of the the original steel mount.

[hilltop170]

My opinion is Cessna designed the tailwheel bracket/spring assembly correctly whether the original or “fishmouth” version. It is also my opinion the best way to keep any tailwheel bracket from cracking, spring leaves from breaking, and hard bounces on the tailwheel is simply to make wheel landings and lower the tailwheel gently once the plane has slowed down almost to taxi speed.

[melcessna]

Great answers. My 48 has less than 2000 hours so I will replace the leaves and go with the original. The bracket has been inspected. As always, many thanks.

[GAHorn]

It’s my understanding the early “box” (steel) tailwheel mounting bracket was replaced in a re-design resulting in the larger aluminum “fish-mouth” bracket because the early steel bracket had two problems: 1- Frequent cracking issues of the aircraft fuselage in that area due to the small “purchase” area of the bracke, and 2- Corrosion due to the dissimilarities of materials of steel on aluminum.

Certainly the larger area of the aluminum bracket ended the fuselage cracking issues and the bracket was successful with the L-10/O-1 “Birddog” series.

The only cracking issues of the aluminum mount I’m aware of has been in the area where the leaf-springs are fitted to the bracket. There are minor differences which exist in that area due to the fitment of the thicker L-19 main leafspring, and the L-19 IPC shows different “dash” numbers to notate a small change in that design.

Unless one has an early steel “box” bracket that has caused cracks in the fuselage, I see no reason to arbitrarily change to the aluminum bracket, but the Service Kit can be accomplished with the later design if desired or necessary.

The REAL concern, IMO is that older main leafsprings be changed/replaced with new springs before the old ones break, which they WILL after a stress riser develops from abrasion with the spring above it. A few years ago we (the assoc’n) queried Members who’ve had issues with that and came to the unofficial conclusion that 500 hours/cycles is the safe life-span of that lower main spring. There was ample suspicion that around 700 hours those springs tend to “snap” and usually result in significant damage to the rudder as the tailwheel, captive of it’s steering-chains, “beat” the rudder to death. The main spring is the only one which needs to be changed and is generally less than $100 and lot’s cheaper than rudder repairs.

[melcessna]

Appreciate your thought. New leaves will be coming.