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BuiltByNOF

R&R

A "How-I-Did-It" Article

February 2000

For some, R&R means Rest and Recreation. But, for my Comanche, R&R means Raise and Retract... using my homemade jacks.

Several years ago I had my first encounter with AD 77-13-21, the one that requires a gear inspection every 1000 hours and a change of bungee cords every 500 hours or three years. I had just read an article in the Comanche Flyer that told about making a tool for the bungee change and, being an avid do-it-yourselfer, I became intrigued with the idea of making my own tool and trying the bungee changing procedure myself. I built the tool and learned from an old pro at my airport about how to stretch the bungee cord for positioning on the tool (it's described in Tips Special). Then, with the blessing of my IA, using a set of borrowed jacks, and following the procedure prescribed in the maintenance manual, I did the bungee change myself. It was a real accomplishment, I thought, and quite satisfying to learn how it could be done, plus getting to know my airplane more intimately.

Then, the jacks went back to their owner, and I knew I would again have to locate a set and beg to borrow them for next year's annual. It would be so convenient to have my own... but I knew they were costly (at least in those days). The idea of having my own jacks became almost an obsession. Then, one day I was in a tool store and saw some long stroke hydraulic jacks that looked like ones I'd seen in advertisements for aircraft jacks. The price of the ones in the store was reasonable; they looked like they'd fit under a Comanche wing; and I thought, "Why couldn't I build my own?" So, I bought a pair and conjured up a simple way (for me) to construct an aircraft jack using materials I was familiar with (calling on my carpentry mentality). I started with a plywood base and figured I'd brace the jack with four legs made of 3/4" electrical conduit fastened to a collar around the jack. The collar would be fashioned from a steel fence part I found at a building supply store while buying the plywood and conduit I needed.

(Warning: The next part is dry technical stuff. Skip the next four paragraphs if making your own jacks is not your cup of tea.)

I took the jacks to a machine shop and had the tops cut flush and machined with a recess to fit the jack points under the wings. Now I was ready to see if my concoction would go together. I cut the plywood into two 22" squares and drilled 1/4" holes in the corners 17 3/4" apart. Then, I cut the conduit into 24 1/2" lengths (8 pieces) and flattened each end in a vise. The ends were then drilled with 1/4" holes and bent to fit between the base and the collar. Each collar was drilled with four 1/4" holes spaced 90 degrees apart.

For each jack, the conduit legs were fastened to the base using flat head 1/4" bolts through large washers on the bottom. Next, the jack was placed in position with the base of the jack in the center of the plywood base. Flat head 1/4" bolts were inserted in the collar with the threads sticking out and the collar was slipped over the jack. The legs were fastened to the collar; the collar was secured with a 3/8" bolt and all nuts were tightened.

For the next step, the plywood base was placed on a level surface. The jack was then tapped into position making sure it was plumb vertically. The base was then held in place by a frame of wood around the bottom of the jack, using pieces of door trim 1 5/8" wide, glued and nailed into position. See... I told you I was using my carpentry skills.

Now for the finishing touches, I gave the base a coat of paint, and screwed a pair of tension clips (broom holders) to each base for storing the jack handle. The black glossy base is a nice contrast with the red jacks and silvery colored braces. The jacks have proven invaluable, and they work as well for a twin Comanche as they do for a single. Maintenance which requires having my airplane's wheels off the ground can now be done anytime I want.

    Homemade Jack with all components assembled

acftjack 

(Okay, non-do-it-yourselfers can join in again here)

If the challenge of building your own jacks doesn't turn you on, at least the idea of owning your own should. The advantages are incalculable and prices are reasonable. While you'd spend only about $100 to build your own, you can purchase a pair ready-made for just a little over $300 with shipping. If you are a determined do-it-yourselfer, J.C. Whitney lists long stroke ram jacks in its catalog, Stock No. 07ND1507W for $39.99. Capacity is 3 tons; range is 24.9" to 44.6"; the same specifications as the ready-made jacks described below. Many have said these jacks are available from Harbor Freight as well.

Air Sea, Inc., Auburn, WA, 1-888-939-7340 or (253) 939-7340 offers a 3-legged jack with a steel angle base for $149.00 each, plus shipping.

The Jack House, Inc., North Little Rock, AR, (501) 835-6033 offers a 4-legged jack with a steel channel base for $154.00 each, plus shipping. The brace legs are round, similar to my homebuilt jacks. For stability, it's your choice, but I lean toward having four legs.

Okay, you've decided that owning your own jacks is right for you, but wait, that's not all. You'll need a tail anchor, too. For me, I put an anchor in the hangar floor with a 3/8" eyebolt and have a chain which I hook to the tail skid. If a permanent anchor is not feasible, a portable one could be used. Others have said it requires about 200 lbs to hold the tail of a PA-24 down. I'd prefer a safety margin of at least 50% and would use more like 300 pounds. Two cubic feet of concrete in a roll around box or barrel should be enough. That'd be five 60 lb. bags of sack-mix concrete with an eyebolt anchored in the center. I'm sure there's other ingenious ways you can think of to secure the tail, too. Hey, it's an opportunity to be creative

With your own jacks, either homemade or store bought, you can participate in as much landing gear maintenance as you want; change tires, lube bearings, replace bungees, adjust gear doors, practice manual gear extensions to your heart's content, reconnect your gear transmission... even do a 1000 hour inspection... under the watchful eye of a supervising IA, of course.

If you really want to know your airplane up close and personal, a set of jacks can help!

Glenn Plymate ex-ICS # 02658

Click here for the: HOMEMADE JACK DWG

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