180 Gear vs Lady Legs

[Ryan Smith]

Richard,

I never would have guessed your airplane was on 180 gear. As silly as it sounds, the wheelpants threw me off. I understand Greg's use of the 180 gear as it fit his mission profile of a backcountry airplane, but for someone that spends (has in the past, and will when I start flying again) most of their time on either asphalt or reasonably groomed grass, I was simply curious if 180 gear would be overkill. I don't like the lightweight, stock gear on asphalt.

As I very much respect your opinion on the matter, Richard, I have to say I've had a bit of a change of heart in the matter. Maybe the 180 gear isn't so bad after all.

Now to get back to the P Ponk argument ( ), does the use of heavier gear on the airplane induce a different failure point than lighter-weight gear? Obviously hollow aluminum axles are the Achilles heel in any situation, but assuming solid axles or ski axles, is the gear box the weak link with a more robust gear setup? Is it still the gear leg? Axles?

Maybe I should spend Zenda's money so that I don't have to.

[edbooth]

Thought I would weigh in on this P Ponk thing. All the pictures and speculation do not hold much water for me. I installed the kit on my 53 with the lady legs back in 85. I hate to tell on myself, but within about five years of installing the kit, I had two ground loops. The first one was caused by hitting deep water on the runway taking off after a heavy thunderstorm. I slid off the runway and spun 360 degrees in the grass ("missed the runway lights). The only damage was some fiberglass worn off the bottom edge of the wheel pant and grass between the tire and rim. The second one was landing in a very brisk direct cross wind that was somewhat beyond the capabilities of the plane even though I was landing almost diagonally across the runway to cut down on the x-wind component. Again, off into the grass and spun 180 degrees. This time, no damage. Was it the p-Ponk kit that helped, the severity of the ground loop, the grass ???? Guess we don't really know unless I could duplicate those excursions without the kit. I'm thinking it might have helped.

[hilltop170]

Ed-
That was exactly the point of my earlier post. There is no way to tell whether or not the P-Ponk mod will or will not prevent failure in any given situation. Personally, I believe it does no harm, is a good idea, and most likely IMO will protect the gear from failure beyond the point it would fail with no mod. Whether or not damage would be greater with the mod is a moot point.

It is purely the decision of the owner whether or not they want the mod. If someone does not want them, that's their decision and it's ok with me if they don't. I'm not a betting man so I will reduce the risk by using the mod. If you never hit anything or loose control of the plane, you have nothing to worry about either way but any one of us could be the next one so I choose to install the P-Ponk gear mod.

[hilltop170]

.........Now to get back to the P Ponk argument ( ), does the use of heavier gear on the airplane induce a different failure point than lighter-weight gear? Obviously hollow aluminum axles are the Achilles heel in any situation, but assuming solid axles or ski axles, is the gear box the weak link with a more robust gear setup? Is it still the gear leg?

Ryan-
To answer your question, I don't know but again, I think it depends on the situation. The heavier gear will change the loads imposed on the gearbox but I can't say how or how much. It's the owner's choice and I choose heavy gear, I just like the extra stiffness.

[GAHorn]

...

Now to get back to the P Ponk argument ( ), does the use of heavier gear on the airplane induce a different failure point than lighter-weight gear? Obviously hollow aluminum axles are the Achilles heel in any situation, but assuming solid axles or ski axles, is the gear box the weak link with a more robust gear setup? Is it still the gear leg? Axles?

Maybe I should spend Zenda's money so that I don't have to.

The problem isn't the gear box.... it's the manner in which the gear leg is attached without Pponk.

The problem is Archimedean....the AN7 bolt that so many have installed at the upper attach-end of the gear leg. When that wheel starts hopping in the direction of moving underneath the fuselage...the leverage is so great, it pulls the bolt out of it's nut...or pulls the head off the bolt because of the extreme leverage. (The stronger NAS147-34 bolt is what should be there. And it should have a NAS143-7C washer properly installed with the radius beneath it's head.) However that will indeed make the weak-link the common AN365-720 nut, which can strip off the end of the bolt. Pponk helps prevent that by adding a bracket to physically capture the upper end of the gear leg and to spread the load out on the gear box bulkhead.

[buzzlatka]

I figure I ought to reply to this considering the pics are of my airframe.
I put the 180 gear on the 52 170. I liked the results with stiffer gear and better off airport landing characteristics. On pavement it was very stiff and tended to bounce more and was less forgiving for the super smooth landing.
When we did the 180 gear we also did the pponk gear box mod. At the time we were happy we did it because we found some corrosion in the gear box on what we thought was a corrosion free airframe.
What we did not do at the time was upgrade the axles.
When the accident happened I started a swerve to the right. I was slow and just getting ready to put the tail down. I locked up the left brake and was still on the runway when the left axle failed. I was probably only pointed 30 right of centerline. The gear then folded behind and slightly under the fuse. I came to rest on the right side of the runway pointed about 80 degrees to the right of centerline. If the axle had not failed I am convinced I would have either gone off the runway into the dirt at an angle or looped at a slow speed.

In my opinion the 180 gear is not necessary, just something different if you like it. You sit a little higher and the gear is stiffer. I know of one 170 that has bushwheels and does a lot of backcountry landings with the original gear.
The pponk mod was good at exposing hidden corrosion. It completely ripped the floor of the 170 out. I was surprised at how much damage was done to the fuse. The 180 gear was slightly bent the box was intact. If the old gear was still in I'm convinced there would have been less damage to the fuse.
Moral of the story. UPGRADE AXLES first! That is the part that failed and caused all my problems.

[edbooth]

Now we have the rest of the story! Solid axels are a must for piece of mind. Thanks for the clarification.

[Ryan Smith]

Thanks for chiming in here, Stephen. I'm scared for this airplane to have the same fate as yours, as it's got the recipe for the same outcome with regard to landing gear setup. The airplane is due for a new set of tires soon, so hopefully I can catch their replacement so I can see which axles are currently installed. I'm not even sure my father would know. My fear is that you are an experienced tailwheel driver...the people flying my family's old airplane are just learning. I'm not sure if there is any rush to put the 180 gear on the airplane, but it sounds like the old gear may be more forgiving in the end for the current operation.

To muddle Arash's question, there are two types of hollow (steel) axles, if memory serves. The original hollow axles, and the thicker/reinforced "ski axles". I'm curious as to whether the ski axles are any better or worse than solid axles from the perspective of durability. Also, does the use of wheelpants make any difference, or are wheelpants just not strong enough to act as any form of structural support?

With the L-19 being a military airplane, I would assume that solid axles, or at the very least ski axles would be standard equipment on the L-19s. Blueldr has been conspicuously quiet lately, perhaps he can chime in on the matter?

[edbooth]

Ryan, I have only seen three types of axels. The hollow aluminum, the solid aluminum and the solid steel. I'm thinking the steel were the ski axels...you Alaska folks chime in here. The solid aluminum are very robust also, never heard of one of these breaking. These are what I have on mine. As far as the wheel pants, there is nothing structural about them. If you take the axel nut off, you can very easily tell whether it is solid or hollow

[ptporebski]

As a nose dragger pilot I follow this with an academic interest. But I noted the comment about the main bolt recommendation to be replaced every 500 hrs. My question is - does this main bolt recommendation also apply to 172s? I have never heard of a 172 gear failing so I doubt it, but is it something a straight tail driver with leaf spring gear (similar to the 170s) should be aware of?

Thanks for tolerating us fair-haired stepchildren!!

[Ryan Smith]

Ryan, I have only seen three types of axels. The hollow aluminum, the solid aluminum and the solid steel. I'm thinking the steel were the ski axels...you Alaska folks chime in here. The solid aluminum are very robust also, never heard of one of these breaking. These are what I have on mine. As far as the wheel pants, there is nothing structural about them. If you take the axel nut off, you can very easily tell whether it is solid or hollow

Hi Ed!

I only live three minutes away from the airport where the airplane is based, so I ran over quickly to take some pictures. Please see below the axles that are currently installed on the airplane. They appear to be hollow, but I cannot tell from this perspective (without aid of a flashlight) if they are the standard axles or reinforced hollow axles.

The article that I can recall in the 170 book is not very clear with regard to axle material type. Presumably the hollow axles are steel, and I was always under the impression that ski axles were aluminum since they were solid. I suppose I could dig out my IPC to see when the reinforced axles were introduced, but I could probably take an educated guess that they were introduced with S/N 25373 when the landing gear was changed, but I believe the reinforced tailwheel brackets were introduced in the later 1952 year model. Regardless, the serial number of my family's old airplane is 20408...delivered on March 11, 1952, it most definitely an early B model.

There is a 1949 A model on the field now that has ski fittings. The next time I go up there (and am thinking about it), I'll look at those axles closely to see if there are any differences.

[Blue4]

Please forgive me for steering towards the original question. I recently (within the past 3 years) replaced my "lady leg" gear for 180 gear. The extra ground clearance, strength, and angle of attack outweigh the weight penalty. The Pponk beef-up makes a good deal of sense when putting on longer legs. Both of these mods were done in preparation to operate off airport. In fact, I think that unless you're running larger than 6.00 or even 8.00 tires, you don't need 180 legs. And even then, "need" may be a strong word. Each of these alterations serve a purpose.

And has anyone mentioned -- they look cool!?!

[edbooth]

Ryan, I have only seen three types of axels. The hollow aluminum, the solid aluminum and the solid steel. I'm thinking the steel were the ski axels...you Alaska folks chime in here. The solid aluminum are very robust also, never heard of one of these breaking. These are what I have on mine. As far as the wheel pants, there is nothing structural about them. If you take the axel nut off, you can very easily tell whether it is solid or hollow

Hi Ed!

I only live three minutes away from the airport where the airplane is based, so I ran over quickly to take some pictures. Please see below the axles that are currently installed on the airplane. They appear to be hollow, but I cannot tell from this perspective (without aid of a flashlight) if they are the standard axles or reinforced hollow axles.

The article that I can recall in the 170 book is not very clear with regard to axle material type. Presumably the hollow axles are steel, and I was always under the impression that ski axles were aluminum since they were solid. I suppose I could dig out my IPC to see when the reinforced axles were introduced, but I could probably take an educated guess that they were introduced with S/N 25373 when the landing gear was changed, but I believe the reinforced tailwheel brackets were introduced in the later 1952 year model. Regardless, the serial number of my family's old airplane is 20408...delivered on March 11, 1952, it most definitely an early B model.

There is a 1949 A model on the field now that has ski fittings. The next time I go up there (and am thinking about it), I'll look at those axles closely to see if there are any differences.

Ryan, The number 1 in the illustration is the type I replaced with the number 3 in the illustration. They were both aluminum.

[GAHorn]

The early axles for the 170 series were hollow aluminum. They would develop cracks at the machining-marks and fail, so...
Heavier duty hollow aluminum axles were produced....and they still failed at machining marks, so...
SOLID ALUMINUM "SKI" axles were recommended for all 170 aircraft. While they are much stronger and almost trouble-free ... it is still possible to hear of stories where they have failed in extreme circumstances. (This is what I have in my airplane and have no plans to replace them as I do not operate in the "outback" on 180/185 gear legs with oversized tires. If I did, I'd convert to...
Other, heavier aircraft such as the 180/182/185/205/206 axles are HOLLOW STEEL.... and are the best of all.
FAA-PMA copies of hollow/steel axles are also available on the market.

[gfeher]

My '52 B model has its original legs and I am considering the P-Ponk mod. I don't want to re-open the P-Ponk mod debate as I understand how it is installed and works, and the debate has been thoroughly aired in this thread and others. However, I have a question about the P-Ponk mod that relates to the original legs vs the lady legs vs the 180 legs that was touched on in this thread above but is still not clear (at least to me). Are the lady legs or 180 legs thicker than the original legs in the gear box area? Because the P-Ponk blocks install directly on top of the gear legs in the gear box, it appears (at least to me) that if the mod is installed with original legs, the original legs cannot later be changed out for legs that are thicker in the gear box area (without modifying the P-Ponk blocks). Is this correct? If either the lady legs or 180 legs are thicker, by how much over the original legs? I'm not convinced that I will ever change my gear legs to lady or 180 legs. I just would like to know the facts ahead of time.

Thanks in advance.