Owen Smith’s Patrol First Flight

Source: 2013 Q3 Beartracks, Owen Smith

Photo by Harless Brand

Photo by Harless Brand

Construction was mostly according to Bob’s plans. The major difference was that I used a wet wing instead of fabricated fuel tanks. This increased the fuel capacity and reduced the weight slightly. Three additional access plates are required in each lower wing skin, and of course you must use ribs without lightening holes at each end of the tank and seal the ribs and skins with Pro-Seal. I also substituted 0.030 skins on the tank bottoms.
The aircraft was built from plans, with the following exceptions. I bought the hydroformed rib package from Avipro and the CNC profiled fuselage tubing from Cartesian Tube in Canada. Construction time was about 3-1/2 years. I expect purchasing the ribs and profiled tubing saved about a year. I used TIG welding throughout and flame stress relieved the welds when completed. The landing gear struts and the engine mount were heat treated up to about RC35 after stress relieving.
I installed an ECI O-375A1A engine and a Hartzell constant speed propeller removed from a Husky. The engine was built with low compression pistons and without any fuel pump. After the engine is broken in I should be able to use 91 octane auto gas, which (out here) contains up to 10% ethanol. The engine is rated at 195 hp, but no doubt makes slightly less with the lower compression ratio. I used a large oil cooler, the one Vans sells for the RV-10. It is mounted on the firewall. In spite of this I did see higher than desired oil temperature on the first flight, about 225-230 F with a 75-80 F OAT.
The aircraft empty weight is 1190 pounds with an empty CG of 15% MAC; just forward of the forward limit. I used an Odyssey battery installed just aft of the baggage bulkhead. The engine mount was fabricated to put the engine as close to the firewall as possible. The limiting factor is the clearance necessary to remove the spin-on oil filter, which places the engine about half an inch forward of the aft-most location specified in the plans. If you do this using a constant speed prop and an aft mounted prop governor, you will have to make a recess in the firewall in order to install or remove the governor. Either that or install a sealed, removable access plate in the firewall. I did the latter. I used a PCU 5000 governor, which requires slightly less clearance than a Woodward, and much less than a Hartzell.
My wing root fairings are a little different than others I’ve seen. They are one piece, flat wraparounds which incorporate the filler box between the flap ends and the fuselage. They look nice and are plenty strong enough for any air loads. The only change you need to use the design is to weld in a couple of threaded bosses into the top longeron aft of the rear spar fitting. I can provide pictures for anyone that is interested. I also have Autocad drawings for virtually all the bits and pieces made from aluminum or steel plate. If you have access to a waterjet cutter, these could save you a lot of time. I would be happy to provide them to builders as long as it’s OK with Bob. I also have paper patterns for the engine baffling adapted from the plans Vans sells for the RV-4. Mine are for an ECI engine but should work with Lycoming O-320s or O-360s with very minor modification. If someone wants to organize these into a blueprint such as Vans sells for the RVs, I would be happy to provide them. I could not find a suitable airbox, so I fabricated one of my own design.
I have only one flight on the aircraft as this is written. I did the first flight with only myself and about 20 gallons of fuel aboard. That put me at 18% MAC; near the forward limit. I had only 28 degrees up elevator available, slightly less than the plans call for. It flew nicely, but needed more up elevator when using flaps. Power off stall speed was 41 KIAS clean. With 4 notches of flaps I ran out of elevator at 34 K IAS. I did try a landing with 4 notches just to see what would happen. I ran out of elevator about a foot from the ground, resulting in a small bounce. Likely with a reasonable amount of fuel the CG will move back enough so that it will stall with full flaps, at least I hope so. If not, I’ll either have to use less flap or change something on the aircraft. The only changes I’m making for the second flight are moving the pushrod attach point on the trim tabs so as to minimize the tab movement and adding some more fuel.

Proper Procedure for Welding AA 5052 Aluminum Fuel Tanks

Source: 2010 Beartracks, Bob Smith #727
As bearhawkers we are primarily interested in making sound crack free welds on our gas tanks.
The information in this article is gleamed from the CSA standards as well as ASTM.
The cracking of aluminum alloys is primarily due to the hot shortness of the alloy. Hot shortness is that characteristic of a metal that results in complete loss of ductility while the alloy is solidifying (contracting). Cracking is caused by the chemistry of the weld bead and the shrinkage stress due to cooling.
There is two ways to prevent hot shortness. When they are used together they produce a sound crack free weld ( no pinhole leaks either).
1. Change the alloy
2. Reduce the dilution of the base metal
AA5356 was designed to weld AA5052. By moving the alloy out of the crack sensitive area however you must make sure that your weld bead consists of at least 50 percent filler metal (5356). This is accomplished in two ways.
1. Weld procedure – full fusion but low penetration and lots of filler metal
2. Joint design – a strait but joint has the most amount of parent metal dilution (85% not good) A V groove equals 45% base metal dilution and will give an acceptable weld. A lap or a T joint is best because there is only 10% parent metal dilution, so this joint design is best. So how do we put this information to use while welding our gas tanks?
1. We use 5356 filler rod
2. All joints are lap joints so use only enough heat to allow full fusion and add lots of filler metal
When I welded my first gas tank I had 6 rivets with small leaks from trying to make small welds with too little filler metal. On the second tank I realized my mistake and added the proper amount of filler metal on each rivet. The second tank had no leaks. I hope this helps. If you need any help or advice with 4130 or 5052 please don’t hesitate to contact me at smith727@drytel.net. Bob Smith #727

Note: Bob Smith is a Red Seal inter provincial Journeyman welder, qualified to weld pressure vessels and boiler tubing in both Stainless steel and mild steel. He has held these tickets for the last 31 years consecutivetly.

Wing Skin Stiffeners for the Fuel Tank Bay

Source: 2008 Q2 Beartracks, Glenn Patterson
Here is a simple method to make wing skin stiffeners without any buckling and with flat flanges that will lay tight to the wing skin. The process is a modified version of the previous Beartracks method & will give excellent stiffener ribs. The stiffener ribs turned out great.
This assumes that a full size MDF wing pattern template was made earlier in the project. Our original wing drawing was accurately traced onto mylar and glued on MDF. The working MDF pattern was invaluable in making jigs and parts for the project. A flush cut router bit in the router table made accurate MDF copies of the working template for the rib flanging form & another was cut up for small pattern blocks used to aid in bending the spars for checking the angles, shape and fit. The original MDF working pattern still remains in good condition.
Essentially this method is to build a jig with two MDF ribs longer than the fuel tank bay. The forms are spaced so that both stiffener rib flanges can lie on the form boards with the belly of the rib lying between the boards. The flanges are formed accurately to the exact wing profile with ease. A little care in layout and a couple of spacers make the form. The wood rib forms can be cut & recycled as the substitute ribs in the fuel bay for fitting the wing skins which is described at the end of this article. This work produces all the wing skin stiffener ribs & the missing rib stand-ins for the fuel bay in 2 hours.
In the following the rib form is a 5/8 – 3/4” thick MDF. You can use what ever is available and stable. Work efficiently & try to keep the time diverted on the side projects to a minimum.
08q1wingle4
STEP 1. Cut two boards 35” long x 9” wide. Make sure the lengths match and there is one long straight edge on each board. Stack the two boards so that the ends are even and the straight long edges are even.
Set the wood wing template on top of the stacked boards so that the lines for the false spar and main spar are close to equal from both ends and the template is centered up. The underside of the wing template should be on the side where the boards are aligned. Drill square and vertical through the stack at one jig pin hole near a spar with the same diameter drill used in the master template, drop in a screw to keep the alignment and secure with a wing nut. Drill through the second jig pin hole near the second spar. Mark the two boards so that you know how they were stacked.
Step 2. Take one board and lay the master template on top. Tighten the assembly together with screws & wing nuts. Countersink the screw heads into the board to be profiled so that the router base or table will be flat against the wood. Set up a router with a flush cut bearing type router bit so that the bearing follower will run against the master template & it will cut the MDF board flush to the master pattern. This will make the rib bending forms the exact wing profile for the fuel tank bay stiffener location. Carry the main spar and false spar centerlines across the top & bottom of the routered board. This will allow the ribs to be marked and cut at the correct references and to be used for future trimming. Repeat the process for the second board. Now there is a board for each flange of the wing skin stiffener. It is recommended to router one board at a time to work safe.
Cut three spacer blocks that are wide enough to let the flanges sit flat on the form boards as shown below.
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Install the spacer blocks on one board with screws. Then stand the two boards on edge, line the spar reference lines up with a square. Square the entire assembly, check that the edges are properly aligned across the form and then secure the second form board to complete the jig assembly. One inch holes were drilled at the ends of the forms so that C clamps could be used to clamp a board across the jig.
Forming the Stiffener Rib
Use two C clamps and a board as shown to secure the tail end of the rib. Eye down the form & center the preformed rib material between the form boards to ensure it will lay straight down the middle.
08q1joggle3
Remember this is a gentle process so let the heat do most of the work. Use a propane torch and heat the rib starting at the clamps & the rib will begin to lay down with its own weight as the heat soaks in. Keep going back and forth with the heat.
Have an assistant put gentle pressure with a board to keep the rib tight to the crown so that it does not spring back as you work to the front spar. Use a wood board with gentle pressure and keep warming the rib and working it down until it is snug against the form full length, have an assistant help to keep the front end down with a 2nd board as well when you have the rib formed to the jig.
Go back to the beginning and warm up the flanges. Lay a board across the two flanges then press the flanges flat to the form with firm pressure. Continue this process back and forth to the end of the rib. Keep massaging the rib with the board until the flanges are flat to the form on both sides of the rib.
Hold the rib down to the form while the rib is cooling. The wood holds the heat and it takes time to dissipate. Do not use water. A fan may speed up the cooling. Once it is cool to the touch, mark the main and false spar lines on the stiffener rib. Remove the rib and dampen the top of the forms before starting the next rib. A little moisture on the form helps reduce the wood from toasting. All that remains is to cut the ribs to length and work with them to get their final fit.
The joggle was of concern because the material is soft. Put the trimmed rib into the forms so that just
the end to be joggled sticks out past the end of the form. Put a board across and clamp it tight to hold the rib from distorting when pressing in the joggles.
08q1joggle4This is a picture of the joggle vise grips made by Bob for forming the rib joggles. The joggle vise grips work great and it is easy to dial in the right amount of joggle setting. Fabricate with vise grips if you are making your own tools. The vise grips can be dialed in, the repeatability is excellent and the mechanical advantage is easy on the hands.
It is suggested to have two wood wing rib forms to substitute for the two missing ribs when fitting the wing skins over the fuel tank bay. Tear apart the stiffer rib jig form and use the spar reference lines to cut the rib boards to length. You will have to cut the front spar end shorter to fit inside the spar capstrips. It may take a couple of trial fits to get the rib forms to fit snug between the false spar and main spar. Do not force the fit as it may distort the wing structure. Mark the wood ribs where the edges of the main and false spar flanges cross the wood ribs. Remove the wood ribs and glue .025 aluminum strips with 3M 77 spray glue between the lines to bring the wood rib profile flush with the aluminum ribs. Reposition in your wing. Only one set is necessary.
Hope this helps.
Bearhawk 727
Bob Smith, Jim Reid & Glenn Patterson