May 2014 Issue
Building the Bearhawk LSA
The start of a long, enjoyable tale.
The Pudding River Bearhawk Gang: Phillip Groelz, Ken Scott and Rion Bourgeois. Our sombreros wouldn't fit under our headsets.
Another Oregon winter was just over the horizon, promising the usual: several months of low ceilings, gray skies and rain. Having lived through 40 of them, I recognized the pitfalls. Without an interesting project to keep me busy, I'd find myself on the couch watching Cleveland play Buffalo…or worse.
Pondering the situation, I glanced through the screen of trees that separates my house from those on either side, and from the grass airstrip that runs through my backyard. On one side, my neighbor Rion Bourgeois was putting the finishing touches on the Taj MaHangar he'd always dreamed about. On the other, neighbor Phillip Groelz was taxiing around in the Christavia he'd just completed.
"Got it!" I told my wife. "I'll build an airplane."
She rolled her eyes.
"No, no," I said. "This one will be different."
"How?" she asked. "Australian?"
Ooof! On a trip to Australia as newlyweds, just after I'd finished my RV-6, we had dinner with a bunch of RV builders. The wives took her aside. "You're sooo lucky," they told her. "You married him after he finished his airplane!" She'd never forgotten it—but on the other hand, she hadn't objected when I built another airplane. And another after that.
"No. It won't be a solo project like the RV-12. Remember the KK-1, where I had a partner? This time I'll have two partners. I'll get Rion and Phillip onboard. They'll need a winter project, too. It'll be great. It will go so much faster with three of us and it'll be fun working with the other guys and I'll learn all kinds of new stuff and I won't get bored…and besides…you already got me the plans for a Bearhawk Patrol last Christmas!"
Remember 27-inch CRT televisions? With the advent of the flat-screen, the boxes they came in are worth more than the TV. This one, with the addition of a screen and small squirrel cage blower, is our priming booth.
Trump card. She'd surprised me completely with those plans, and now, probably to her surprise, they'd made her an accomplice.
And that's how Phillip, Rion, and I came to be sitting in my living room sipping Oregon microbrew in front of the wood stove, Patrol plans spread across the floor. It wasn't the first rodeo for any of us. Besides my all-aluminum projects, Rion had built an RV-4, an airplane that takes a lot more work and problem-solving than current RV kits. Phillip had completed two plansbuilt projects: a Wittman Tailwind and a Christavia MK 1 he'd taken over as a moribund EAA chapter project. Our combined skill sets fit the Bearhawk perfectly—Rion and I had plenty of riveting experience, and the Bearhawk uses a riveted aluminum wing. Phillip had been through two tube-and-rag airplanes, and the Bearhawk uses a steel-tube fuselage.
The first main wingspar going together. We used Stewart Systems water-based primer. It made our lives so much easier.
Bob Barrows' Bearhawk family includes three airplanes. There's the burly four-place Bearhawk that started it all, the two-seat tandem Patrol and his newest, the Patrol LSA. Despite already having the Patrol plans, we found ourselves attracted to the LSA. After all, we're at an age where an LSA makes a lot of sense…
Typical of Bob's designs, the LSA was simple, clean, light and had that "just looks right" quality that some airplanes possess, although nobody can really define it. At first glance the LSA is a reworked Patrol, but actually it's quite a different airplane. It uses a different, no-flap wing and horizontal tail. The structure's lighter, as befits an airplane with lower power and Vne. The result is a handsome tandem two-seat design with plenty of cabin space and decent performance on a small Continental engine. His prototype was the only one flying, but Bob was claiming 120 mph on a C-75. With no electric system the empty weight was in the order of 750 lbs—light enough to provide a decent useful load, even with the 1320-pound gross weight set by LSA standards. Bob's reputation for straight talk and honest numbers gave us hope that we could at least come close to matching his performance and weight.
As a group we had several things going for us, besides our prior experience. I work for a company that would let us buy sheet aluminum and steel tube at favorable prices. Phillip had a collection of small Continental cases, cylinders, and crankshafts that he was pretty sure could produce one good engine. Rion had fallen in love with a lot of cool tools while building his RV-4 and, of course, still had them all. Even better, he could supply an extra set of hands in the person of his college-age son, Elliott, whom he hoped would use the airplane to learn to fly. Split four ways the LSA should provide loads of fun for a very moderate individual cost.
So, we decided to take the plunge and join forces to build a no-frills Bearhawk LSA. Rion, a lawyer by trade, put together a written agreement with four shares and formed an LLC called Pudding River Bearhawk. We all signed on. Once we'd all contributed an equal amount to the Bearhawk bank account, we were in business. Plans for Bearhawks must be ordered from Barrows himself, so the first check on our new account went to Fincastle, Virginia. A few days later, a roll of plans arrived. Twenty-nine 18-inch x 24-inch sheets and one full-size airfoil template were included.
A customer expecting plans similar to those provided with modern kit aircraft like the Sonex, Carbon Cub, or especially the RV series, would be in for something of a shock. No CAD system here—everything is hand-drawn. There are no exploded views or part numbers and limited hardware call-outs. Spelling is, well, approximate. Fuzzy line quality obscures some of the details, and at the bottom of every sheet is the catchall phrase: "scale drawing for dimensions not shown." There is virtually nothing about how to build the airplane—it's expected that the customer knows or will learn how to make the parts shown. It's all understandable in context. Barrows doesn't have an engineering department staffed with CAD draftsmen that can detail every nut and bolt. His job is to present enough information that people with shop skills similar to his can replicate his airplane. Those drawings represent a heck of a lot of work by one man at a drafting board, and they achieve his goal.
At Bob's recommendation, we decided to start by making a set of wingribs. The Bearhawk has a constant-chord wing, so all ribs are the same profile. I decided that modern computer technology could help us here and had the full-size airfoil template scanned at a local print shop. The printed-paper version matched the mylar drawing within a few thousandths of an inch, so we saved the scan as a dxf file, readable by machine tools. There's a steel fabrication shop less than two miles from my house. They had no trouble plugging that dxf file into their laser machine, and after work, I picked up a perfect airfoil template, cut in 3/16-inch steel plate. This became our master template and the source of all subsequent dimensions for the ribs and spars of the wing.
In anticipation of the Patrol, I'd bought a router table and mounted a big Bosch router in it. This turned out to be the workhorse tool of the LSA project, at least in the early, parts-making stages. Using the steel template, we used router bits with bearings on the tips to produce accurate MDF form blocks for the main, nose and rear wingribs.
The master airfoil template was laser-cut from 3/16-inch steel. We used it as a router guide to make form blocks for the various wingribs.
The usual method of producing flat metal parts from Bearhawk plans is to cut out the paper depiction, glue it to the metal with spray adhesive, then cut it out by hand. We did that on some of the parts, where not too many were needed. For larger numbers of identical parts, like wingrib blanks, we used the same scanning technique that produced the airfoil template. We took the resulting dxf files to a local business that makes aluminum parts for computer displays. In 15 minutes, their computer-driven mills and punch presses made enough spar fittings for three airplanes. Wingrib blanks were cut from sheet aluminum, complete with lightening holes, in about two minutes per rib—and accurate to something like two thousandths of an inch.
The Bearhawk uses what seems like miles of thin aluminum angle to reinforce the ribs. Bob specifies 9/16-inch a side. Each main wingrib has four of these and each nose rib one—that's over 200 angles. When I discovered that Van's Aircraft sold 5/8-inch x 5/8-inch angle in four-foot lengths, we declared the extra sixteenth inch meaningless and bought enough to do everything in both wings. It saved a lot of bending!
For the second mainspar, we gained access to a really big squeezer, built for WW-II aircraft production. We should all work so well when we're 70 years old.
The winter months were spent pounding out, shearing out, cutting out parts. Spars front and rear, wings main, nose and trailing edge, aileron spars and ribs, etc., etc., etc. A Bearhawk wing uses a lot of parts. (In hindsight, we could have simplified things considerably with a little more computer work up front. For instance, the main wingspar could have been reduced from over 50 individual parts to five and the assembly work probably halved if we'd had the spar doubler strips and vertical supports punched or milled out of a single piece of 1/8-inch aluminum.)
As things stand today, we've completed all the aluminum parts for both wing skeletons, except the parts for the fuel tanks. We've formed all the ribs, drilled all the spar components and, just last weekend, riveted the first mainspar together. (Finally setting some rivets after making all those parts was a real milestone.) We're having a great time… and, just as I'd hoped, I have no idea who won the Cleveland vs. Buffalo game.
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