Installing Bungee Cord/s

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tonyp51
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Joined: Sun Mar 05, 2017 8:36 pm
Location: Mojave CA

Installing Bungee Cord/s

Post by tonyp51 »

Hello,
I'm in of instruction on how to properly put the Bungee cord/s on my solid axle wood gear Piet. Also the correct size. I have both 1/2" and 3/8" diameter cord from Aircraft Spruce. I'm thinking the 1/2" is what I need. Also the length of each cord before use. I have researched uncle Tony's books. Also the FAA AC 43.13.2. [not specific to Piets} Thanks!

Tony
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KenBickers
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Re: Installing Bungee Cord/s

Post by KenBickers »

TonyP, I now have a split gear with the wire wheels on my Piet. Previously I had the solid axle, wood gear on it. I used 1/2" shock cord, with three wraps over the axle in-board and outboard of the wooden gear leg horizontal member. If memory serves, that took something like 5 feet of shock cord, when everything was tied off and trimmed. You'll need an extra few feet per side, however, during the wrapping process in order to get adequate purchase on the cord while you stretch with all your might. I'd recommend buying, say, 9 feet per side to be safe. I used a pair of clamps so that I could "walk" them out as I bent each stretched wrap around the axle. Use one clamp to hold things in place, while you stretch the cord over the other side and hold that in place with the other clamp. Repeat until done. Cheers, Ken
PoconoJohn
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Re: Installing Bungee Cord/s

Post by PoconoJohn »

I'm getting ready to order parts for the gear. I'm going with the split axle as shown on sheet 3. I'm trying to figure out what bungee cord to buy at Aircraft Spruce. Plans say six feet of 5/8", but looks like I have to buy a couple of small pieces.

John C
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KenBickers
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Re: Installing Bungee Cord/s

Post by KenBickers »

Here's what I found when I checked the invoice for the shock cord that I bought when I installed the split axle gear on my Piet. The invoice from Aircraft Spruce shows "06-12600 TYPE I 5/8" SHOCK CORD." I bought 24 feet. I'm sure that was too much, but I tend to prefer to have a bit too much than have to order more because I bought too little. I made four shock cord rings by whipping the ends together with safety wire.

Somewhere I have some pics and a description if you are interested.

Cheers, Ken
PoconoJohn
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Re: Installing Bungee Cord/s

Post by PoconoJohn »

Thanks Ken! I'll check that. I like the spring in a can set-up (like WW shows on his site), but I need plans, so sticking to sheet 3 and that means bungees. Photos are always helpful as are explanations of the work. My project is here: https://imageevent.com/hatz/piet

John C
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KenBickers
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Re: Installing Bungee Cord/s

Post by KenBickers »

John,

The spring in a can has become popular in recent years. I'm not sure why. It's heavy. It's nearly impossible to tune to get the right amount of tension (technically compression). And it seems like a great place for corrosion to develop without a good way to know. The original design by Mr. Pietenpol is pretty straightforward, light, looks period, and simple to maintain long-term.

[I'm copying here something I posted on the facebook site not too long ago]. If you stick to the plans, you can make shock rings yourself by whipping the ends of a section of bungee with safety wire. This may take some experimentation to get the ring to the size you need. Then, assuming the horizontal tubes on the telescoping gear tubes are built according to the plans, the rest is straightforward. Drill a block of wood with a couple short sections of tubes the same distance apart as the horizontal pieces of the telescoping gear tubes. You'll want tubes with I.D. that is just barely larger than the horizontal pieces of the telescoping gear tube. Chock that block into your bench vise, take a long piece of scrap tubing to use to gain leverage to stretch the homemade shock ring over the short sections of tubing. When everything is nice and tight, slide the horizontal pieces just inside the short tubes in the block of wood and skootch the bungee onto the telescoping gear legs. When the shock ring is in place, Insert the wooden plugs called out in the plans into the horizontal tube of the telescoping gear tube and secure with a set screws Do that four times, and your done. Takes about an hour to make the shock rings and another hour to wrap them on the telescoping tubes.

Cheers, Ken
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PoconoJohn
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Re: Installing Bungee Cord/s

Post by PoconoJohn »

Awesome Ken! The photo of the gear sure helps. As long as sheet three is accurate, there's a descent chance I can build it. With the one telescoping pole crossing the other, do I need to adjust brackets or axles, or will the plans work? Thank you again. :)

John C
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KenBickers
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Re: Installing Bungee Cord/s

Post by KenBickers »

John,

Look very closely at the plans (i.e., before welding). You'll see that the attachment at the forward fuselage bracket for the telescoping legs is offset a bit on the left side to the right side (not the brackets themselves, but the doo dads to which the telescoping legs attach). That's what gives the legs clearance to pass by one another.

Also, I suspect that I may still have the section of the 5/8" shock cord that I didn't use in a bin somewhere in my hangar. I'll try to find that. By subtracting that length from the 24' that I bought, we'll know how much I actually used.

And one more thing while I'm thinking about the gear, you'll want to use inserts just as the plans show to cap off the horizontal tubes on the telescoping legs. I've seen that some people weld big washers there. What a pain that would be for installing and replacing the shock cords?! Done to the plans, you can do all the tightening of the shock ring hoops on a jig and slide the stretched shock cords easily into place. Then the inserts go in and are held in place with a set screw.

Good luck with this. Ken
PoconoJohn
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Re: Installing Bungee Cord/s

Post by PoconoJohn »

Thank you for the photos, advice and your time writing all that. Nothing to do now but order supplies and get 'er done!

John C
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KenBickers
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Re: Installing Bungee Cord/s

Post by KenBickers »

John,

I located the remaining portion of the 5/8" shock cord. It appears that I used slightly more than 14' to test a few prototypes and make the shock rings that are currently on my Piet. Now that I have examples of shock rings that work just fine, I'd be able to get by ordering about 8' of the 5/8" cord.

Cheers, Ken
PoconoJohn
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Re: Installing Bungee Cord/s

Post by PoconoJohn »

Great! I ordered 12' since I'm new to this.

John C
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rightforlineup
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Location: St Louie

Re: Installing Bungee Cord/s

Post by rightforlineup »

Ken Bickers,
Thanks for making me feel better about keeping my bungees. I was contemplating the die spring solution as an "improvement" that wouldn't need the occasional maintenance.
Bob Miller
Bob Miller EAA64
GN-1 Aircamper
Based 1IL4 Millstadt, IL
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KenBickers
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Re: Installing Bungee Cord/s

Post by KenBickers »

Bob,

That's great. Newer isn't always better.

Cheers, Ken
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