Therapy Project

RVBottomly said:

That red tube makes sense to me. You said it was smaller. What size did you use?

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3/8" tube

Here are those 3/8" tubes on a late model Super Cub.

skywagon8a said:

Gordon, I was only going by Tom's pictures in #175 where there are two tubes with a column buckle. His X brace reinforcement cuts the column length of four tubes by half. By welding the X in the center there is additional stiffening. The damage is caused by torsion on the entire aft end of the fuselage but when you narrow your focus to one tube at a time you can see the column failure.

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I don't think that's a compression buckling failure, I think it's plain ol' bending from torque imposed by the tailwheel.

Nonetheless, I certainly see how the additional bracing makes sense, and I'm glad I did it on mine.

Thanks to all for the pics and thoughts - - -

3/8 tubes

3 Inch Extended Gear

Switching gears, so to speak. I'm starting to fabricate the landing gear. What exactly is extension of 3 inches in the 3" extended gear?

Is the axle attachment 3" farther from the pivot points, or is the 3" measured vertically?

I can't seem to find actual dimensions.

Thanks,
Vic

Gear Issues

So I researched what I could find on extending the landing gear--not sure it's something I want to do, but I ran across something that caused my first real concern with the Wag Aero plans.

First, stock gear for a PA 18, latest iteration on the Northland plans, is 1 3/8 x .058 4130 for the front tube and 1 1/4 x .058 4130 for the rear tube on each leg.

The Wag plans have the same diameter of tubes, except they call for .049 thickness. As drawn, they are not even as stout as the L-21 plans. And the 2+2 is supposed to have a GW of 2200 pounds as opposed to the 1750 of the Northland plans. (Add to that a story I can't find anymore of a 2+2 breaking its gear on a gravel strip).

Then I ran across a reference to heavy duty PA 18 gear: 1 1/2 X .058 for the front and 1 3/8 X .058 for the rear.

I already ordered and have the .049 tubes, but now I think that not only should they not be used for extended gear, I'm not inclined to use them at all.

Any thoughts on this?

Thanks,
Vic

My thoughts on extended gear differs from what most here seem to like. I believe that a stout standard size gear is more robust. The extended sized gear will have greater leverage on the fuselage attach fittings making their margin of safety less. The leverage component on the fittings is the distance from the axle to the fittings. If you want to increase the three point angle of attack you install larger diameter tires to standard gear from which you get two advantages. Increased wing angle and better rolling on unimproved ground. If you combine the long gear legs with the large diameter tires your low speed drag component for take off can actually retard performance. If your only purpose is to increase the angle of attack then use the long gear with small tires.

From a flight perspective if you use extended gear with large tires rather than standard gear with large tires your drag component will be higher due to the requirement for more nose up trim to compensate.

Also if your airplane is heavily loaded, acceleration for take off will be slower with the extended gear due to the increased drag from the down elevator requirement while accelerating. Seems to me that a 2+2 has the cabin volume for "heavy" loads. Enough so that standard gear would be preferable under certain conditions. When a plane is lightly loaded these differences may not be very noticeable to most pilots. But, when you are heavily loaded the differences could make the difference of whether the take off is successful or not.

RVBottomly said:

Switching gears, so to speak. I'm starting to fabricate the landing gear. What exactly is extension of 3 inches in the 3" extended gear?

Is the axle attachment 3" farther from the pivot points, or is the 3" measured vertically?

I can't seem to find actual dimensions.

Thanks,
Vic

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I believe the 3” longer is in the tubes so the installed gear adds approx 1-1/2” in height and width. The taller gear was a necessity for legal prop clearance with Borer props on straight skis. Then we all wanted to maximize AOA, and 3” extended became the norm. Now some guys with 35s use standard length gear and on the flip side, Mackey built airplanes use something like 10” extended gear. One size does not fit all. The available new gas shocks negate most of the stress on gear. The difference is amazing.

As we all know anything you change will be a trade-off of some sort. The thicker wall thickness will make it heavier, depends where you plan on taking them. Heavy-duty is a must on skis. Can be the most punishment your airplane will take, you'll hear all kinds of interesting noises. The extended gear also gives you a wider stance. They make it harder to grab the struts at the wing attachments and raise your ski. For my 5'7" frame 3" extended gear and Bushwheels is about maximum height for putting on wing covers. In addition the higher you go your three-point CG changes making the tail heavier.

Thanks everyone for the insights. I ordered .058 tubes with a step up in diameter. Now I have the chance to compare weights.

One thing I'm considering is my fuselage has the gear attach points 4" wider than on a super cub, so it has a wider stance already.

So, I'm not sure if I will go with extended gear. It is unlikely I'll do much ski work here, given that we have snow on the ground, at most, about a week each winter. Lot's of snow 30 miles east of me, though.

But I'm pretty sure I want the stouter tubes.

The stouter tubes can be a good thing. One thing to consider is how many tubes fail. In heavy compression the tube is prone to bend or buckle mid tube. The heavier wall helps a bunch in these loads.
In a hard landing where the is extreme tension or side loads in a tube, a cuff, or doubler at the ends of the tube even with a lighter wall thickness offers a substantial increase in strength. This doubler can be a length of say the next size larger tube with say a 0.065 wall welded over the ends. This can even be a section of 0.049 tube slit along it's length so it can be wrapped snug over the parent tube.
I use allot of doublers in what I build.

Back at it

I left off working on the cabane vee. Here is the finger strap and bushing for it.



Then it was time to lay out and bend up the u-fittings that weld to the gear legs.






The tubes in previous picture are 9/16 x .065. 7/16 x .028 bushings are supposed to fit inside. I had 7/16 x .049 for some reason, so I drilled them out.



And tacked things together


I ordered my larger tubes from Wicks last Friday, taking advantage of a 15% ebay sale. They came the following Monday, 12/24, which surprised me. I started cutting things up and tried a tack.



Then came a Christmas diversion. I had promised my wife a coat rack. There was a dead poplar I had cut down last summer. OK, time to get to those overdue promises.



My little lathe did some wood duty for the pegs



By noon I had a rustic rack. I later varnished it up and now it does its work de-cluttering our entry way.



Then it was back to the landing gear. Main tubes are tacked and aligned. I still need to fabricate some finger straps, and then a jig to put it all together with axles, etc.



So I've gotten a fair dose of therapy these past few days. A good thing, I think. I have to store some of this playtime against the crush of work that is lurking over the next 4 weeks.

Continuing with the landing gear

I suddenly found myself with a spare 4 hours, so I jumped in to see what I could do on fitting the gear legs.


First I leveled up a temporary cross brace to establish the angle of the legs at the point where the axles are level.





Then followed some free-hand profiling and trial and error fitting with the help of some 1X4 homemade clamps.





Eyeballing the rear angles.





Then tacked it together and did the same on the other side.



Now comes the slow part, making finger straps and welding everything up, adding bushings, and reaming.

And of course, layout of the axle. I ran out of time as I was marking out some finger straps.



So I remain happily engaged at the pace of plod.

Happy New Year! Nice to have a quiet day in the shop. I spent some time on axles.

For some reason, I couldn't find a 1 5/8 hole saw in my collection. So I tried the lathe to make the axle hole for the brake plate. Glad I had a 4-jaw chuck.



I needed a thin tool to start the hole. My regular tools caused too much chatter and would catch the work. I didn't really want to grind down 5/16 tool stock. A worn out Phillips impact driver bit ground to size seemed to work just fine.



Then it was just a matter of machining the hole outward with a side cutting tool until I reached the 1 5/8 diameter.





They fit....



I'm expecting a set of Grove brakes to arrive tomorrow. I'll wait on drilling mounting holes until I can line things up.
Meanwhile, there was work on finger straps to be done.






Then the supper bell called.

Nice looking project!! I am getting ready to build my axels as well. Any pictures you can put up on how you cut and flatten the cabane slot in the axel would be a great help to me. Thanks!


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Beaverpilot said:

Nice looking project!! I am getting ready to build my axels as well. Any pictures you can put up on how you cut and flatten the cabane slot in the axel would be a great help to me. Thanks!


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Providentially, I got more done with more pictures.

I should have waited to get my brakes before making the torque plates last week. Even though I looked at the specs, I didn't make the connection that the torque plate on the Grove brakes I purchased were based on a 2 1/2 diameter instead of the smaller square of the cub design. So I'm glad I waited to tack the plates on until the brakes came.

New plates marked out.



Then I marked out the slots for cutting.



I used a hand-held cut-off wheel to start the slots. I made notches at the end of longitudinal cuts and then used pliers to bend up and down the tabs to break them off.



Then I was going to grind to the lines, but I remembered I had a mill. Ding-Ding-Ding. It was easy using that.



An aside--before I cut the notches, I tacked the axle tube to the doubler so it wouldn't shift.

After milling the notches it was time to tack the torque plates. Didn't take a picture, but I found I could use a square piece of 1 1/2 angle iron as a guide to make the plate square to the tube in a vise.



Then the plans called for edge welding on the end.



Then welded up the torque plates on the inside only and drilled 3/8 holes.





The Wag Aero plans say nothing about flattening the end with the holes. The Northland drawings specify that it be flattened. I'm confident that heating up the end with a torch and squeezing with a vise would do a good job flattening it. But I am still contemplating a beefed-up filler there, as I saw on the carbon cub, so I'm waiting on that task.

Next step was to come up with a way to align the axles. I cut a 6 foot length of angle iron and used hose clamps to clamp the axles to the angle iron. It seems pretty solid and aligned up pretty well. I'll need to make a scaffold of some sort to hold it all in place for welding the axles in. That will be for another day.

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this is what I have on the sport trainer drawings. About heating and flattening the tabs

Beaverpilot said:

this is what I have on the sport trainer drawings. About heating and flattening the tabs

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Well, that's interesting. The 2+2 plans have a note for edge welding, but no detail on flattening the ends. What size axle are you using?

I’ve been debating— I have some 1.25 axels that came with my project and I have plenty of 1.5 stock that I could make some. I’m leaning towards the 1.25 as I plan on having it on skis part of the year and have read that it is difficult to find skis for 1.5 axels


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I think the 1.25 works best for a sport trainer. Plenty of options for brakes, and skies, etc. I went with 1.5 because that was on the plans and it's a heavier airplane at gross weight.

Actually I’m building an 18/l-21 clone. I do refer to wag’s drawings along with the Northland and the Supercub project website. There is also the plethora of advice and info on this site that makes sense of things that need clarification. Thanks for the pictures of your axels


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Tacking the Axles

I finished up welding on finger straps, but didn't take any more photos of that. I decided to take the plunge on tacking up the axle assemblies.

First there was fitting with a hand grinder to profile the tubes. The axles were aligned by strapping them to a straight piece of angle iron.





After measuring various reference points twice, it was time to tack things in place.



Then I flipped it over again and drove through the axle centers a long piece of 1.25 tubing I had laying around. I'm hoping it will keep things stiff while I finish weld the axles and add gussets.



This stretch took a fairly long time, around 5 hours. It's funny how time flies when you aren't paying attention to it.

More plodding

Continued working on the landing gear. I had to wait for an order fix from Wicks. I had ordered 3/8 square tubing for the upper cross-member of the gear but instead I had gotten 3/4 round. But the new tube came in a nice box complete with a few goodies. Wicks has been good to me.



I used a wooden spacer to try to get it aligned properly.



Welded that in place and then cuts some gussets from .090 sheet.



Tacked and later welded the gussets in place.



Then used a hand reamer to clean out holes.



Then I wanted to test fit things to see how they would hang. I used some scrap 3/4 tube for in place of the shock assembly.





I was thinking of cutting some logs thin and drilling 1 1/2 holes through them for wheels, but decided I had more productive things to do....

I ended up with 3" extended gear patterned after heavy-duty designs I've seen elsewhere. I'm still not sure that was the best thing, but it is what I have for now.

you probably want to replace those gussets, with newer style/stronger, if someone could post a picture of an Atlee's or airframes, ??

https://www.univair.com/piper/piper...007hd-piper-pa-18-hd-landing-gear-right-hand/

compare the 2 gussets... much longer... atlee's even has a larger tube onto of gear leg to spread out the force

mike mcs repair said:

https://www.univair.com/piper/piper...007hd-piper-pa-18-hd-landing-gear-right-hand/

compare the 2 gussets... much longer... atlee's even has a larger tube onto of gear leg to spread out the force

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Yes. I like that. About a month ago I was thinking I should do that, but I didn't write it down on the plans. Thanks for the heads up.

I followed Mike's suggestion and redid the gussets. I spent a little time looking over my various books and came up with this version:







In other efforts, I have been looking over shock absorbing options. I'm trying to get a handle on the geometry and forces involved. First thing I did was simply measure vertical travel of an axle compared to the travel of the shock strut at the cabane Vee. Here is a chart of what I measured:


Unfortunately, I tried to make x-axis of the Excel sheet linear, but it kept coming out logarithmic. Here is the original hand drawn chart that shows the linear units.



Anyway, I was surprised at how linear the travel was. Ratio is around 0.54 to 1 for shock travel to axle travel within the ranged measured. Invert that to 1.85 and you have 185 pounds force for every 100 pounds pushing down on the axle. A starting point for figuring spring rates, etc.

I wonder if anyone else have played with numbers like this. I'm tempted to get creative in some kind of shock absorbing system.

What you are seeing in your graph is what we call a rising rate, this is a good thing. As you get deeper into the travel the shock starts traveling further which increases both the spring rate as well as damping force.
What this gives you is a softer suspension when taxiing yet firms up when you get into it hard such as arresting vertical loads or absorbing rough terrain.

Why did I miss your post? I just ran to my hangar to take some pics of my 6'' certified 1.250'' gear. Looks kind of similar to what you've built.

Olibuilt said:

Why did I miss your post? I just ran to my hangar to take some pics of my 6'' certified 1.250'' gear. Looks kind of similar to what you've built.







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Nice looking gear Olivier! That is also really close to what I have drawn up in AutoCAD.
Question though, how did you avoid the creases in your axels where you flattened out for the shock strut to attach.


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