Three Landing Gear/ Gear Box Questions

[EZFlap]

Possibly wrong but, the wedges are in contact and hold the gear firmly in place in the vertical plane as the ground loads would be transmitted through the vertical plane. Any movement here would cause fretting, wear, and ultimately dissimilar corrosion which can ruin an aluminum extrusion in short order. Would firmly fixing the fore and aft sides of the gear subject the fitting to cyclical expansion loads as the steel cross section at its widest point would expand and contract at a greater rate than the relatively narrow aluminum extrusion?

Thank you for your insight. The fretting, multiplied by a factor of hundreds, is called "Brinelling", which to the rest of us means it was hammered and beaten all to s**t. It is exactly this type of failure that is evident on one of the used unairworthy sample parts I purchased to begin my research. it looks a LOT like the failed outboard bulkhead on the PPONK website. This type of failure is one of the things my version of the part will address.

[4517C]

Give me a call or email. ( 207 924 5905 jakemorrel@yahoo.com ). I hold a couple of STSs for the 170B, including one that required an evaluation of the gearbox. Jake

[EZFlap]

A buddy of mine, whose 1952 C-170B I instruct in, is contemplating a C-175 taildragger project, using the Stoots STC. He would specify it be built with the PPONK gear box parts and 180 gear legs from the start.

If using new Cessna parts adds a significant value to the project in the mind of the aircraft owner, then the Stoots kit is probably a very a good choice. If I am successful in offering improved and/or lower cost parts than the Cessna parts, then my "market position" would be simply to offer another option for potential customers to choose from.

The four applicable PPONK gear box parts can indeed be used on my STC, because they are STC-PMA replacements for the Cessna parts called out. I cannot comment on whether the PPONK parts can or cannot be used on someone else's STC. There will still be several additional parts that will be needed (inboard bulkhead, sheet metal angle parts, two large formed steel parts, etc. etc. etc.

Your friend might want to proceed immediately with the Stoots 175 conversion, or he may want to see what I come up with in the 175 department within a few months. Once again, if the use of genuine stamped Cessna parts is a high value item for him, the Stoots kit may be the most desirable option.

[EZFlap]

I can't even begin to immagine that there will EVER be a market for anywhere near the number of C-170 landing gear leg units that would have to be sold in order for production to be economically viable. What with owners of C-170s converting to C-180 legs and all of the C-180s in the registry, why not build C-180 stuff instead? More commonality. You might as well go broke with a product with a larger market!

This is one of the main decision points I need to finalize before anything goes into production. Part of the difficult decision is that I've read George's posts on the subject, making it reasonably clear that the late "Lady Leg" is probably the best choice for most 170 operators. However, it is also likely that anyone who is a customer for a 172 conversion is looking more for a low cost bushplane than a sport flyer classic or antique. A higher number of them would be interested in the heavier duty gear.

If I can make both without too much waste and excess cost, I'd make both.

[GAHorn]

[...4) This is why there is a PMA approval process in the first place... so that anyone, regardless of their funding or 3 piece suit or engineering or facility can be guaranteed to produce a good part your family can fly with. ...

That's a nice, heartfelt response in favor of your own dream/efforts...but it's (to enable cheap sole-owner garage operations) certainly NOT why "... there is a PMA approval process in the first place..."

The reason there is such a process is to ascertain the capability of, and enforce the quality of production of, an aftermarket supplier/manufacturer of IDENTICAL replacement parts.... Not "similar"...not "alike'... but IDENTICAL. If your product is not IDENTICAL...in form, fit, function, performance.... then it is not likely to receive FAA-PMA.

And it doesn't sound as if you are trying to DUPLICATE Cessna's product... bu that you are attempting to produce an improved product at lower cost. If so, then I believe you will need to obtain, not an FAA-PMA, ...but OEM or STC status.

I'm afraid I don't follow the Lucas/MG auto correlations. Or the relevance of your use of a British engineer to meet FAA requirements. (But I agree the Brits have some excellent capabilities.... I just don't think your example of Lucas engineering is the best one you could have chosen.)

[GAHorn]

[...This is one of the main decision points I need to finalize before anything goes into production. Part of the difficult decision is that I've read George's posts on the subject, making it reasonably clear that the late "Lady Leg" is probably the best choice for most 170 operators. However, it is also likely that anyone who is a customer for a 172 conversion is looking more for a low cost bushplane than a sport flyer classic or antique. A higher number of them would be interested in the heavier duty gear.

If I can make both without too much waste and excess cost, I'd make both.

THAT is a fair analysis of the situation, I'd say.

Still... it's difficult to imagine you're likely to make any profit on this venture, but good luck! It'd be great to have another source of parts. (Unfortunately, these old, classic airplanes are being wrecked sufficiently regular to provide plenty of spares for the diminishing fleet.)

[EZFlap]

The reason there is such a process is to ascertain the capability of, and enforce the quality of production of, an aftermarket supplier/manufacturer of IDENTICAL replacement parts.... Not "similar"...not "alike'... but IDENTICAL. If your product is not IDENTICAL...in form, fit, function, performance.... then it is not likely to receive FAA-PMA.

No, not exactly. PMA is simply an authorization to produce acceptable parts. PMA is required for either an identical replacement part, or a new drop-in replacement part that is improved. The PPONK parts are PMA and none of them are identical to Cessna parts. This is how PPONK can say their part is a drop-in replacement for a Cessna p/n.

And it doesn't sound as if you are trying to DUPLICATE Cessna's product... bu that you are attempting to produce an improved product at lower cost. If so, then I believe you will need to obtain, not an FAA-PMA, ...but OEM or STC status.

Yes, the parts I plan on making will be PMA replacements, but they will not be identical. There will be an approved STC amendment, which makes them STC parts.

I'm afraid I don't follow the Lucas/MG auto correlations. Or the relevance of your use of a British engineer to meet FAA requirements. (But I agree the Brits have some excellent capabilities.... I just don't think your example of Lucas engineering is the best one you could have chosen.)

The Lucas Electric brand name has become synonymous with marginal quality, yet their products were original factory equipment on a large number of British cars. Ask anyone in the sportscar world about "Lucas, The Prince of Darkness" . The point I was making is that not all OEM parts are first rate, and that there are plenty of aftermarket parts that are as good or better than OEM. Cessna Royalite plastic interior parts come to mind, Cessna OEM radios come to mind, and the difference between the Cessna and McFarlane seat rails comes to mind.

My old beer-swilling English engineer was mentioned only to illustrate the caliber of help I am lucky enough to have on this. Sorry to have confused anyone You can ask any serious student of aviation history about the old engineer apprentice system at British aircraft companies during and following WW2. They started as kids sweeping the floor, then they built airplanes with the construction crews on the factory floor, then they apprenticed under the older engineers while taking advanced metallurgy classes... an education of unmatched breadth and depth. My guy was famous for showing up at JPL and Rocketdyne as a troubleshooter whenever the young rocket propulsion engineers could not solve a problem, and open a 50 year old wooden case with a slide rule... and solve their problem.

[blueldr]

Trying to produce C-170 landing gear legs is about the dumbest idea i've seen, so far.

[GAHorn]

I took a "shortcut" in my previous discussion regarding FAA-PMA, in that I wasn't trying to re-define "PMA".... I was pointing out that you are not discussing a "replacement" part...you are discussing making parts for a modification...an STC item. For that reason it still didn't make sense (to my thinking) to not spend the money to have genuine engineering drawings. I'll bet your British engineer would also endorse that ... over making designs based on ad hoc field measurements.

The Lucas reference is an old one, and I wasn't confused about that old-saw. What I didn't find relevant about that illustration was the relationship between an electrical part and the design of a fixed landing gear. It didn't follow (at least for me) that better, more modern electrical designs which happily replace bad ones....is somehow is analagous to re-manufacturing an already simple, durable, and successful landing gear design.

A better example might be the Cleveland/McCauley brakes which replaced the orginal Goodyear system, perhaps?

But no matter.... You aren't talking about exact replacements which most of us might find interesting. You are talking about modified designs which won't likely interest many 170 owners. (And is why this discussion might seem pointless to more than just bluEldr.)

Good luck with it.

[EZFlap]

I don't want to overstay my welcome or get too wrapped up on one point. I've received several informative replies and learned things I didn't know. Mission accomplished. I may be able to make a Lady Leg that is close enough to interest 170 owners, or I may only be able to make a gear leg for the 172 conversion customers. So unless people want to discuss this particular point further, I will let this subject rest.

Thank you George and the others who have participated in this thread and helped to inform/educate me.

[jatkins]

One questiuon, ?
Are the C-170 "lady Legs" stiff enough for skis , or wheel skis ??
( I was told they probably are not ?? ) Which is why I switched to 180 gear on my 170B.

[blueldr]

Having had some ski flying experience in Alaska and having flown my '52 C-170 on both the original gear legs and the later "Lady Legs" models, I believe that the "Lady Legs" have adequate stiffnes for ski opeations. There was a world of difference in the two types of gear legs.

[jatkins]

Where you on straight skis , ? or wheel skis ?
Was the differance a positive differance ?

[GAHorn]

I don't want to overstay my welcome ....

You're not overstaying your welcome... I'm just not certain we're going to be of much help in your new enterprise...And courtesy demands that we all treat each other respectfully even if we don't find the topic to hold much personal interest, and you've been courteous. Thank you.
In any case, the Forums are, in part, for the purpose of discussion anything of interest regarding these airplanes, and perhaps your topic is interesting to more than just those that responded.

[c170b53]

Absolutely correct George