gear legs

H. Mark Smith · Post by **H. Mark Smith** » Tue Mar 04, 2003 4:23 am

I read on "Vector" New Zealand CAA website about main landing gear leg failures on 180's adn c-206's in N.Z. The article said that Cessna shotpeened the main gear legs on the inside of the gear leg to increase the fatigue resistance of the gear legs. The 180 gear legs are made of 6150 steel, heat treated, then shot peened because the gear legs is "notch sensitive", meaning they are prone to brittle fracture(not good). The shot peening helps reduce the likely hood of this happening. The NTSB wanted the FAA to issue an AD on Cessna gear legs becasue of this but the failure rate is not that high so no AD was issued. Still this might be potential problem worth looking at. Rust pits and nicks can make stress riseres leading to a crack. Dye penetrant may not work if the crack is subsurface so magnaflux might find a crack if one is present. Has anyone had thier gear elgs re-shotpeened after repair????

ak2711c · Post by **ak2711c** » Tue Mar 04, 2003 7:15 am

Magnaflux will not find a subsurface crack ether. You would have to use something like eddy current or ultrasonic to find them. Haven't heard of anybody reshotpeening.
Shawn

N3243A · Post by **N3243A** » Tue Mar 04, 2003 6:55 pm

Are C-170 "lady" legs made of the same steel (6150) and go thru the same fabrication processes as the C-180 legs? I think somebody on an old post said they were different steel, and therefore not as prone to cracking out as 180 legs. Any truth to this?

Bruce

funseventy · Post by **funseventy** » Tue Mar 04, 2003 7:08 pm

I know its hard to find a ragwing that doesn't have bowed legs. But my '54 B sits nice. What is the difference between those airplanes? I would not go to 180 legs because of the weight and the good condition of the originals. I like some additional infor between different years of 170 legs. I am not familiar with "lady legs". Is that a generic term for 170 gear legs? I think Bruce's are good like mine.

I think I'm looking for George on this one.

Kelly

N3243A · Post by **N3243A** » Tue Mar 04, 2003 7:39 pm

Kelly, since Gahorn has been a little scarce, allow me to assist:

There are two types of original gear legs found on 170's. The early type found on '48 thru early '52B models had the "wobble" legs that are concave or bowed down looking (from front). These legs are interchangeable from left to right.

The latter and more desireable gear legs are found on '53 and newer 170's had what are commonly called "lady legs". The narrow ankle just above the axle is contoured so that the legs are left-right specific and are why the term "lady legs" came about. These legs are a little stiffer and the airplane doesn't suffer the wobbles like with the early gear. The aircraft serial number change for the lady legs was around 255xx. Can't recall offhand exactly what it is.

Bruce

lowNslow · Post by **lowNslow** » Tue Mar 04, 2003 8:57 pm

The gear change occured in the middle of the '53 production year starting with serial number 25612. The early gear was produced with 4xxx steel, the newer lady legs used 6xxx steel, same as the 180.

H. Mark Smith · Post by **H. Mark Smith** » Wed Mar 05, 2003 4:12 am

As best I can tell, the original , flat(un-arched)gear legs on the 170 are made from 4000 series steel, heat treated, shot peened. If you strip the paint and inspect with a 5x or 10x glasss, you can see the shot peened surface.
The later 180 gear legs and probably the "lady legs' on the 170 are of 6000s eries steel, arched, heat treated, then shot peened to increase the fatigue resistance to surface cracks.
What I wanted to know is this. Since there is a recommendatoin from the NTSB to the FAA to issue an AD note on the gear legs, what can we do out in the "field" to inspect and help prevent gear leg failures... I have seen what it can do to a 170 or 180./ My uncle had the gear leg break across the top two bolt hole where the axle connects to the gear leg in 1971. The c180 had a total time of 3100 hrs, and was equipped with wheel skis from day one and used in Alaska. tamarack air had another fail in 1999 I think it was on a c-`185. Almost totaled the airplane.
Ill continue with next post

H. Mark Smith · Post by **H. Mark Smith** » Wed Mar 05, 2003 4:19 am

so it appears to me that it is feasible to stirp the gear legs, bead blast, then have the legs re-shot peened if there is corrosion or dents in the gear legs that go thru the .006" think shot -peened surface. I'll try to see if I can get some info on this from Cessna. It might take me a few days as I am away from phones, computers etc the next few days, but if i find out any ifo , I'll tyr ot post it here. I think it is possible to strip,bead blast, blend out damaged areas,then re-shot peen the gear legs as required.
The NTSB report says the gear legs are prone to fail due to stress riseres created by corrosion pits in and around the bolt holes that hold hte axles to the gear legs. The wheel ski stub axle puts a bending load on the gear leg opposite that the wheel does. Cessna heavily shot peened the inside of the gear leg,but lightly shot peened the outside so I am wondering if this may be a contributing factor in the brittle fracture that occasionally occurs. In fact, most allthe gear legs that failes were from aircraft that had been used on wheel skis. Just some to think about.

lowNslow · Post by **lowNslow** » Wed Mar 05, 2003 4:42 pm

I believe it was determined that the majority of cracked gear (normally through the upper axle attach holes) occurred with aircraft that had been on skis. This was the reason the FAA decided not to go with a general AD notice, there were overall a small number of aircraft affected.

H. Mark Smith · Post by **H. Mark Smith** » Fri Mar 07, 2003 3:51 am

The FAA Aircraft Certification Office (ACE-115W) in Wichita, Kansas published an article in August of 2001 and it says in part,"Whenver repairs are made, the underside of the strut(gear leg) must be shot-peened."I think the repairs they are talking about are blending out of dents, gouges, corrosion(rust pits).
I obtained some info from Cessna. CHapt 32-10-00 of the C-206 maintenace manual .
IT says the 206 and I think the 180 gear legs are:
made from 6150A alloy spring steel
the bottom ofthe gear leg has a 0.012 inch compressive distance to prevent stress risers and to extend the spring fatigue life.
the gear legs is shot peened to an Almen intensity of 0.012A to 0.016A with 330 steel shot. So now to find out what all this means....

Post by **GAHorn** » Sat Mar 15, 2003 5:39 pm

The legs were shot peened to relieve stress from manufacturing, to prevent stress-crack propagation, and to harden the surface to avoid corrosion from rock/debris strikes. The change from the flat springs to arched, narrow-ankle (or "lady-leg") springs occured at SN:25612.

zero.one.victor · Post by **zero.one.victor** » Sat Mar 15, 2003 11:06 pm

I have 180 gear on my ragwing,the 337 sez they are "later model" gear legs,p/n 0741001-5 & 0741001-6. I just recently did a new weight & balance,the arm for the MLG wheels is 18.5" aft of firewall,the arm for the MLG wheels was 22" with the stock ragwing gear legs.
Is the later model 170 gear (lady legs) raked the same as the earlier model 170 gear,resulting in the same arm for the MLG wheels? You can probably look on the W&B sheets & see what arm was used. Like I said before,the lady legs might be a better choice than the 180 legs because of the wheels-forward aspect of the 180 legs. I have some information in my 180 notes that sez the pre-1955 gear legs postioned the wheels 3" farther aft,which would give them an arm of 21.5". Not too much different than the stock early 170 gear legs. So if a change is made to 180 gear,maybe a set of the 1953-54 legs would be the way to go.

Eric

zero.one.victor · Post by **zero.one.victor** » Mon Mar 17, 2003 4:56 pm

So,how about it,you guys with "lady leg" main gear? (Bela,George,Kelly) Please check your W&B sheets and post what the arm is for your MLG wheels. Bela,maybe you could check the W&B sheets for Gnarly Dude,to verify what the arm of the early 180 gear is.

early 170 gear: 22"
lady leg 170 gear: ???
early (pre-55) 180 gear: 21.5" ?
late 180 gear: 18.5"

The 180 information I have sez that in 1955 the wheels were moved forward 3",in 1957 the gear leg thickness was increased from .650" to .700",and in 1964 they changed to 185 gear. So that is 3 versions of 180 gear,plus the 185 gear. I recall reading someone's posts about "wheels forward" and "wheels aft" 180 gear,but I can't recall what the whole story was. Anybody remember that?
Some people will say this belongs on a 180 site,not here,but I think that it's pertinent because of how many 170 owners have (or plan to have) 180 gear legs on their 170's.

Eric

zero.one.victor · Post by **zero.one.victor** » Mon Mar 17, 2003 6:31 pm

I just checked the 170-A-B TCDS sheet,it includes the arm of various parts for W&B purposes. The arm listed for the MLG wheels is the same ( +22") for all three models. So I assume that the rake is the same on the lady legs as on the early legs.
I recall that at least one of us here owns a 180,maybe you could look on the TCDS and see what it sez for MLG wheel arm. When you post the info,please include what year 180.
Thanks,

Eric

zero.one.victor · Post by **zero.one.victor** » Wed Mar 26, 2003 6:21 pm

Who can do me a favor & post the part numbers for the later lady legs? I'd also like the part number for the 53-54 180 legs,if someone has that info. Bela??-- If you don't have the 180 p/n info,Jeff or somebody probably does.

Eric

The International Cessna 170 Association

gear legs

gear legs

gear legs

gear legs

170/180 gear legs and shot peening