The International Cessna^® 170 Association

Mark,

I installed this kit over 20 years ago with a set of threaded bits that I haven't used since. I completed this without cutting any new access holes in the floor of the airplane. If you need the tools just let me know.

One additional note. I am not sure that this kit really buys you very much. From what I understand the attachment bolt for the gear leg is stronger then the gear box. From one accident that I have seen I believe that the inner bulkhead will detach from the gearbox before the bolt fails in a severe side load. Would welcome any other comments on this topic.

Steve Grimsley #3204

Steve, your opinions are always well-received because you do your homework and are not prone to emotional conclusion. (It's the engineer in you.)

However, in this case, I believe the examples of failed bolts prove otherwise. While it's true that the bolt is stronger than the surrounding bulkhead en masse ... it is not the expected common shear-type of bolt failure that the Pponk kit prevents. The three failures I've inspected consisted of two cases of the nut stripping off the bottom of the bolt allowing the bolt to pull up/out of the original attachment, and one case of the bolt-head snapping off at the juncture at the shank. In all three cases the bulkheads appeared to be undamaged by the bolt failure, however they were damaged by the subsequent collapse of the airplane.

Certainly, as you infer, the original set-up is adequate for well-executed, normal landings and also for most of the types landings we all commonly perform....provided the aircraft is inspected and maintained in-depth, including the inspection and regular replacement using proper assembly techniques and regular replacements of that bolt, etc. But most of these airplanes truly meet the definition of "aging aircraft" , their landing gears have been in-place for 50-plus years, and those bolts have seen just about as much abuse as even the most cavalier engineers could have imagined. (Just imagining what a "cavalier engineer" might be like is an excersize in itself.)

The Pponk mod definitely strengthens the gearleg bolt-attachment (by capturing it against failure) to the point that it takes a lot more than just a bad landing to rip it out, and that's what I wanted in my airplane. (That bridge in Minnesota held up just fine for 60 years until it's seemingly-adequate structure gave way. The comfort of knowing that structure exceeds the demands of operations is well worth the effort, in my opinion.)

George, any truth to the rumor that the p-ponk mod may add some strength to the gearbox, but if a landing is severe enough to damage the mod that it will most likely do substantially more damage than had the mod not been installed?

If you tell me how hard you intend to hit that brick wall.... I'll tell you if a 5-mph bumper will save your car.

The problem with those that decry Pponk as contributing to gearbox damage is...... there's no standard or "control group" with which to make a comparison.

Either way, by the time Pponk is ripped out... things are going to be expensive. (They would have been by that time anyway, however.) Hopefully tho', Pponk will keep you from finding out.

gahorn wrote:If you tell me how hard you intend to hit that brick wall.... I'll tell you if a 5-mph bumper will save your car.

The problem with those that decry Pponk as contributing to gearbox damage is...... there's no standard or "control group" with which to make a comparison.

Either way, by the time Pponk is ripped out... things are going to be expensive. (They would have been by that time anyway, however.) Hopefully tho', Pponk will keep you from finding out.

From my perspective.......enough said......

Someone pointed out that a non-Pponk airplane is like having seat belts, and Pponk is like adding shoulder harnesses. Your face is the gearbox.

I look at it this way: If Cessna had originally designed the gear attach to be like the PPonk, would someone have come up with an STC to remove it? Would we then be debating the merits of the "breakaway gear" mod?

DaveF wrote:I look at it this way: If Cessna had originally designed the gear attach to be like the PPonk, would someone have come up with an STC to remove it? Would we then be debating the merits of the "breakaway gear" mod?

Why as a matter of fact Dave we would be debating it and it would sound something like this.

George of course wouldn't touch the original pieces to the point that replacing original rivets would be questionable. BluLeader of course might ripe them out as not being necessary as they didn't have them in the first aircraft he flew and they just take of weight his MOGAS requires. Besides you can't maintain them with anything found at Pep Boys. The west coast guys, well who knows what mod they might want to do but it will probably be close to what is commonly found in Alaska and in any case a certian Texas FSDO won't allow it requiring extra paperwork proving Cessna actuall put it there. Mean while half of us would be pouring MMO on it to preserve and keep them working in top notch order. The NASCAR guys will secretly only be using the right side because they only make left turns of the runway. I could go on.

sgrimsley2717 wrote:From what I understand the attachment bolt for the gear leg is stronger then the gear box. From one accident that I have seen I believe that the inner bulkhead will detach from the gearbox before the bolt fails in a severe side load. Would welcome any other comments on this topic.

Steve Grimsley #3204

I would have thought this aircraft had the P-Ponk reinforcement as the entire gear was ripped out. Looking at the pictures further down though it appears it did not have the reinforced gear. Doubt it would have helped. NTSB report on N2929N

Pponk seems like cheap insurance. Seems like the direction of the force on the gear box or bolt effects the usefullness of the mod. I did it because I will be flying on skis, but think it is a good mod for all. I found a right angle drill on ebay last year when I did the pponk. It was perfect for the job. Used by Boeing. If any one needs to use it let me know. Mark

In my view P-Ponk is the only way to go, So is a right angle drill to install...........Brad

Mark, I have installed a set in my 48 with the help of Eric at Sandhill, since the he has installed 4 or 5 more. Yes the shortened bits were a help and a nice angle drill was used. The small holes were needed at first to feed the hardware in, later installs were acomplished with the help of Sandhill Aviations secret weapon, a young female asistant with rubber hands, she is able to get her hands thru inspection panels and then thru lightening holes up to her shoulder. took us 6 hours for each side the first time, after that we halved the time pending no other issuse. The last one he did had severe corrosion of the attach fittings, so CHECK for corrosion when you get the gear legs out. will post some pictures