Hangar, Truss, and Bi-fold Door

The building is a 40'x 30' x 14' tall "pole barn" with steel siding and polycarbonate skylights around the north and south walls. It's basically a $6000 kit comprised of everything you need to make the building (except the front door), delivered on a trailer and assembled in place for another $2000. I made it tall so I could add a second story in the back for storage. There's plenty of room for a 10' deep mezanine thing that will let me put a bunch of my car and airplane junk on. The extra height worked out nicely for a 79" passage door in the bottom section of the door. It was built on 2' of clay, replacing the organic material that had been a plowed field 50-60 years ago. Trusses are "chicken house" trusses, good for 10,500 lb load each. I have about 800 pounds of load on each one, except the front and rear ones have half that, 400 pounds. These trusses are overkill, since it basically doesn't snow here anymore. The one thing you might notice about these trusses is that it leaves me nothing to hinge a door from.

Concrete is 3500 psi commercial grade. The work was done by the best guy in the business around here, and has recieved rave reviews by the local airport gang. First we did the interior floor...

....and a few weeks later did the "apron". But now the concrete sticks up 4-5" on the sides, so we need some topsoil.

Nothing that 28 yards couldn't take care of.

Back to the door situation, I needed a truss in the shape of an A that would have a straight bottom edge to fasten the door hinges to. I studied hangar doors for months, and finally decided to design my own (no question about that, I guess) using the best of everything I'd seen. Jim Hill's Erect-a-tube bi-fold door was my primary guide. It's well thought out, but commercial overkill for what I need. Jim's hangar is where my plane has been for the last two years, and is right next door to my next hangar. He sold me part of his land to put my hangar on, which I really appreciate. He's been letting me keep my plane in his hangar for free, but now it's time to put the wings on his Sportman 2+2, so N56ML needed a home of its own!

First order of business was to design a lightweight truss. Although I'm a mechanical engineer and am theoretically capable of designing a truss, I took the easy way out and found a trial version of some truss software to do the job for me. After inputing the cross sectional area, moment of inertia, and modulus of elasticity for the material (A500 steel), it drew some nice FEM type images showing stress, strain, deflection, and buckling factor of safety (which turned out to be 1500 on mine). Positive numbers are tension, negative numbers are compression. I played games with various wall thickness and sizes, and settled on a 2 x 2 x .84 square tubing truss and door frame, with 1.5 x 1.5 x .084 bracing and stringers, except for the two red ones in the shape of an A, which I made 2 x 2. This also made a nice point to mount the winch. The stress levels are shown in PSI, so you can see that even my version of the truss is overkill, but this is an overhead door, so the factor of safety needs to be something like 5, and more importantly, I don't want the thing to sag. Deflection is just about miniscule fully loaded, in the order of a sixteenth of an inch out in the middle.

The truss weighs a grand total of 320 pounds. The door will be the traditional bi-fold type, which to me is the most efficient type. I'll have less than $1500 in my door when it's finished, compared to $6000-$8000 for a "real" hangar door.

Motivation is an AC powered 1500 pound Superwinch AC 1500, which comes complete with up and down button. A 1500 lb winch may not sound like enough to raise an 800 pound door with a 5x safety factor, but the truss is holding half the weight, and when you double the cables around a pulley on the door bottom, the remaining 400 is cut in half again, so the winch is only lifting 200 pounds. At 200 pounds, the winch is drawing a quarter of the full load current, so it can lift the door in about a minute, and without overheating. Full 1500 pound lift capacity is only sustainable for 20 seconds, and the door wouldn't be fully open by then. The cable between winch and control buttons is only 6', so I ordered 25 more feet of 5 conductor 18 gauge wire from McMaster Carr and spliced in an extension to get the 31 feet of cable I need to mount the control buttons 4' off the ground on one of the posts.

Here's the eventual goal. You can see where the new truss fits with respect to the original "Warren" chickenhouse truss. The black line is the cabling from the winch, around the pullies, and back up to the truss again. I'm using aircraft grade .125" 7x19, good for 2000 pounds, which is a 16:1 safety factor for 125 pounds of tension. Pullies are MS20220-3.

James Mitchell from work came out and helped me cut, fit, and tack up the truss frame, since he had a 110V Miller MIG welder he was willing to let me borrow for a while. Then my wife and son came out one Saturday and helped cut and weld-prep the steel for the doors. Once it was all laid out, I enlisted the help of Curly Scrimsher from TBE to finish welding the whole thing up for me. He was going to bring his generator powered MIG out, but it turned out that he was able to make-do with James' little Miller. I don't have power in the building yet, so I can't power my 220V TIG welder. TIG is pretty slow anyway. This MIG welder was pretty quick, and although it had a duty cycle of only 20%, Curly pushed it to about 60% and got all of the welding on the truss and doors in just two sessions, about 11 hours total. The welding is gorgeous, but what would you expect from a guy who's certified to weld on Space Shuttle main engine nozzles, among other things? Again, the locals are jealous. I have a little more welding to do to attach the cable pullies and the door locking mechanism, but I can handle that, whether MIG or TIG (I may have 220V in it shortly, weather permitting). In the picture above you can see Jim Hill's bifold door next door. We were getting the MIG power from an extension cord run to Jim's hangar.

How will I get the truss up there? I'll mount the winch to it's final mounting position, hook the cable hook to the existing chicken house truss, and let it pull itself up! Then once mounted on top of the 6 x 6 posts, I'll use the winch to pull the door up into position, and reinstall the hinge pins. I think two guys can do this, one to push the button, and one to guide the truss (while standing on scaffolding).

And it worked just fine. Other than some interference with 2x4 bracing, the winch pulled it right up into place on top of the posts, where it was bolted to the existing truss to make it stay there. This is my son Jordan shoehorning the truss between the chicken house truss and the outer siding.

And here it is installed.

I'll have to experiment a little, but I'm starting to think that I can counterweight the door and delete the winch altogether. Then I could open it in about 5 seconds, and power failures would not be a problem (not that I've ever seen the power out at the airport anyway).

After pressure washing away the preservative, grinding away the rust with a flapper wheel on my right angle grinder, treatment with phosphate etchant, and a coat of paint, the top half of the door was ready to go into place. Once again, the winch lifted up it right up there. A little alignment and the pins slid in without much fanfare. This picture shows the bottom of the door being pressure washed. It's amazing how much preservative was on the 3" tubing. I had to use Gunk to get it all off, which is what I was doing in this picture.

Here's the door frame hanging, operable with the winch (but not the pullies yet), and the personnel entry door installed and working. Doors are rolling up and down on commerical grade garage door tracks countersunk into the 6x6's.

Here are the center pullies. I used 4" aircraft pullies, which are bolted to a 4130 steel strap which is welded to half of a 4" hinge, which has it's other half welded to the bottom door member.

The hinges mentioned above are what the door hangs from the truss on, and what the center join is comprised of.

The siding's pretty much done, except for an 8" tall strip at the very top.

There are three standoffs that push the center of the door (the fold line) out at the beginning of the lift process. This one is in the middle, and there is also one at each side of the door where the cables go back up to the truss. They align with the lift cables, so the first thing that happens when the lift cables are tightened is the door center is pushed outwards. Otherwise the door might just try to pull up, or worse, inward. It's hinged to allow the doors to fold up without it binding.

I lock the doors with two of these dirt simple clamps, made from concrete foundation anchors, a piece of bed frame angle, and a knob from McMaster Carr. The catch is a piece of angle I welded to the door, and really need to paint before it rusts away.

Here's N56ML in its new home. I built a 24'x3' work bench with a huge shelf to put boxes of airplane stuff on. Now all that's left is some decent lights. I eventually installed twelve 4-bulb x 48" fluorescent fixtures that I rescued from the scrap pile at work. They were headed to the dump, but I intalled new electronic ballasts and T-8 bulbs and hung them from the trusses. I got the ballasts off of ebay for about $8 each, the bulbs for about $4 each, so each light cost me $24 and twenty minutes to convert them for a high-quality commerical grade fixture. The lighting is perfect, and way better than I had in Jim's hangar.

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