PPonk / 180 gear

[fishdoc]

Greetings from the proud new (and first time aircraft) owner of 1264D, a 1951 170A.
Love the differences between this plane and the 172's I've been flying the past few years.

It's probably been covered somewhere already but I would value the opinion of some other 170 owners on the value and importance of beefing up the gear box with the PPonk kit. My aircraft is equipped with 8.50's and 180 gear legs.
After reading through pages of NTSB files on C-170 accidents over the years, it seems they have a tendency to fold the gear under on one side if one is unfortunate to experience enough of a ground loop to put a severe side load on it.
It seems like relatively cheap insurance but would like to hear from some other owners on the necessity of it.
I don't plan to go off road just yet but most of the gear failures I read about happened at paved strips.
Any comments would be appreciated.

[Jr.CubBuilder]

The P-Ponk beef up is one I've been mulling over for a couple of years. For what it's worth I've decided to put it on the front burner along with a fairly extensive examination of my gear boxes.

I've got early 180 gear legs on my 52, and I've been into some unpaved strips some of which haven't been to smooth.

Here's my $.50 worth. I'll be putting the P-Ponk beef up kit on, but I'll be doing it because of the extra weight of the heavier gear and eventually I'd like to put some bushwheels on (which equals more weight). That sort of a setup will undoubtedly put more strain on that bolt on the inboard end of the gear leg as the plane wallows around on rough fields. If you look at the way the gear box setup on your 170 works you'll notice that the gear is bolted on the inboard side down to a bracket by one bolt. It's that single point of failure that the P-Ponk kit addresses, it puts a second bracket over the top of the inboard end of the gear leg with two more bolts.

If you ground loop hard enough the gear box will get ripped completely out with the P-Ponk kit. There are some who believe that without the P-Ponk kit damage will be limited to the floor pan and wing. With the extra piece of bracing the entire assembly will get ripped out damaging bulkheads etc. I think that sentiment is probably correct, but in the case of my old airframe either scenario would be the end of the plane. So I'll be adding the extra bracket to solve that single point of failure, but I won't have any illusions that it will do me any good in the case of a bad ground loop.

Personally I think that if you fly these planes on the stock gear with light tires, and land at smooth airstrips where you know you aren't going to run into a rut or chuckhole then the P-Ponk kit is only going to add weight.

[N2865C]

Personally I think that if you fly these planes on the stock gear with light tires, and land at smooth airstrips where you know you aren't going to run into a rut or chuckhole then the P-Ponk kit is only going to add weight.

I agree with that.... up until the plane decides to swap ends. It's the side load on the gear box during a moderate ground loop or incipient ground loop where the P-ponk MIGHT save the day IMHO.

[GAHorn]

Anti- ponk folks frequently point to the extensive damage they've seen that occured to such aircraft subsequent to a wreck. The problem is.... it's like asking if a 5 mph bumper on a car is a good thing. If you'll tell me how hard you intend to crash into the brick wall....I'll tell you if it'll help you. If you intend to hit the wall at 10 mph it'll probably help. If you intend to hit the wall at 100 mph it probably won't, and the repair bill will be larger than the 10 mph hit.

P-ponk is an excellent mod. It is not difficult or expensive yet it may save you a bunch of grief. Key word: may.

Adding a longer gear ( such as 180/185 gearlegs) also adds stress to the gearbox and leafspring attachments, because it increases the length of the "lever" that stresses that one bolt that holds the inner end of the gear leg.. P-ponk helps prevent failures of that area by capturing the inboard end of the gearleg.

I have it on my 170 and if I didn't have it... it would be one of the first mods I spent spare money on. If I had a new-to-me 170, in order of importance I'd be disabling the parking brake, getting rid of hollow aluminum axles, and installing shoulder harnesses, and seeing to the engine and exhaust system. If I were shopping for a 170, it'd be worth $2,000 more to me when comparing to other airplanes.

All other mods would take a back seat to those.

[denalipilot]

This thread has got me thinking about side-loading and torqueing the gear-box as relates to skiplane operations. My '53 B has 180 gear legs and the original gear box (No P-Ponk conversion). Even if I never ground-loop it on wheels, I am wondering now about the extra forces generated by attaching skis and wallowing around in snow. Skis add so much longer of an arm than wheels that torsional forces on the gear are said to be much greater; I don't know how quantifiable the differnece is, but it must be quite significant. Would this increase the justification for the P-Ponk upgrade? For what it's worth, I am on Aero 3000 skis, which are nice in my opinion because they are somewhat wider and shorter than other models, reducing the arm and improving turning. BTW, My axles have been upgraded twice, from hollow aluminum, to solid aluminum, to hollow steel. The mechanic insisted on going to the latter when installing the skis.

Interested in anyone's opinions on this, and experience of any other ski-flyers out there.

Thanks, -DP

[blueldr]

It seems that a lot of people worry about hollow aluminum axles. I have a couple of friends who are in the business of recovering wrecked aircraft for insurance companies. Neither of them has ever seen a broken hollow aluminum axle from a recovered wreck. They frequently recover ripped off landing gear legs, but no broken axles.

I ripped a gear leg off , gear box and all, and the hollow axle was OK.
On another one I tore up the wheel and bent the gear ankle and the hollow axle but it didn't break.

( I apparently have been selected by a much higher authority to test C-170s almost to complete destruction)

Broken hollow aluminum axles seem to be a problem only on ski equipped airplanes.

[GAHorn]

No disrespect meant, .... but just because two friends you have haven't seen broken hollow aluminum axles does not mean that hollow alum. axles aren't a weakness in need of replacement. Hollow aluminum axles have a bad reputation in this regard, albeit largely from machining marks inside them from mfr'g that left stress risers. (I'm not certain that all alum. hollow axles suffer the same degree of such marks, and the safe bet is to get rid of them.)
I strongly urge all C-170 owners to check their axles and replace all versions of hollow aluminum axles. (Hollow steel axles are fine.)

[blueldr]

George,

I'm led to believe that you've had some experience or exposure to failed hollow aluminum axles.

Do you have any specifics or incident examples?

I've heard of them only on ski applications and am curious about other
cases.

[GAHorn]

I have not personally witnessed a failed axle. I am relying upon the good words passed on to us by previous owners accounts as related in this association's "The 170 Book" which includes even the later, improved hollow aluminum axle which also failed.

Cessna did indeed refer to their solid, aluminum axle as a ski axle. It was doubtless produced specifically to address hollow aluminum axle frailties in ski-operations. The solid axle is much sturdier and a good investment. The hollow steel axle is even better.

(Hollow steel axles were used on later/larger Cessna's and an approved aftermarket axle AF1441003-1 is also produced by Airframes, Inc.
P.O. Box 521795
Big Lake, AK 99652
PH: 907-892-8244

They are also a supporter of our association, having donated a complete engine cooling baffle set up for the Kelowna convention.

[denalipilot]

Since this thread started out addressing the P-Ponk Beef Up kit, I'd still like to know if that is a recommended upgrade for skiplane ops specifically. Any takers?

Thanks,

DP

[cessna170bdriver]

I have not personally witnessed a failed axle. I am relying upon the good words passed on to us by previous owners accounts as related in this association's "The 170 Book" which includes even the later, improved hollow aluminum axle which also failed.

The "light" axles are the same thickness (I'd guess about 1/8") tube all the way in to the mounting block. These are the ones that are prone to failure, especially on heavier airplanes (C170's included).

There is another hollow axle that is only thin on the end where the nut threads on. Further in, the thickness steps up another 1/4" or so (just guessing here). I am not aware of any documented failures on these "heavy duty" hollow axles, although I do seem to remember that TIC170A publications recommend solid axles just to be on the safe side. It's probably still a good idea to NDI (non-destructive inspect) ANY axle periodically.

Miles

[Jr.CubBuilder]

Since this thread started out addressing the P-Ponk Beef Up kit, I'd still like to know if that is a recommended upgrade for skiplane ops specifically. Any takers?

Thanks,

DP

Don't have any experience with ski's, but it seems like it sure wouldn't hurt. I was talking with a fellow who had the P-Ponk beefup kit done on his 170, and it wasn't that expensive (seems like $500) pretty cheap for the piece of mind and pretty light to.

[Joe Moilanen]

When I replaced my hollow (light) axles with solid ones back when the problem was first brought to light, I discovered that one of the hollow ones had a crack around about 1/3 of its radius. Glad I changed when I did.

Joe

[ak2711c]

Skis do put alot of additional stress on that gear bolt. It is a common failure point with the twisting action that gets put on it while on skis. For the type of flying I do, which is a lot of off airport on rough unimproved strips and then ski flying the rest of the year, its a must. It is cheap insurance. They only take about 3 hours to install and are not that expensive.
Shawn