Source: 2022 Q3 Beartracks, summarizing Nev Bailey and others
Over at bearhawkforums.com there has been a great discussion about fuel caps. The New Zealand crew (Nev Bailey, Graham Johnson, and others) went for a deep dive including making a testing rig and trying out different modifications to the fuel caps to improve their function. The goals were to make the caps less likely to come out in flight (which has happened a few times), but still be easy to install after fueling.
It is crucial to lubricate the aluminum threads inside the cap with EZ-turn (fuel lube) to prevent galling, but there was some confusion about lubricating the o-rings on the outside of the cap. Bob has recommended that the external o-rings be lubricated with motor oil, but in some cases folks lubricated the external o-rings with fuel lube. The NZ crew’s test rig enabled force measurements required for cap
removal, and with a very effective lubrication like EZ-Turn, they were finding that the caps could be pulled out by hand. The discussion led to some measurements of the fuel filler necks on the kits, revealing some unexpected variation which has been addressed at the factory. If you aren’t happy with the operation of your fuel caps, I would suggest reading the whole thread, but here are some highlights.
If you would like to reduce the force required to insert the caps, the easiest first step is to try smaller orings. Bob says be sure to use Viton o-rings for their fuel resistance. The o-rings provided with the caps are a –324 size. The next size down is –323. Reports from testing the smaller o-rings have all been positive. Even if you don’t modify the aluminum portion of the caps, the smaller o-rings will slightly reduce the amount of rubber that needs to fit in the gap. A more invasive next step is to chuck up the cap in a lathe and skim off a few thousandths (photo right). If you have to stretch the –323 o-ring on the cap body, remove enough material so that the –323 o-ring just fits. The next key lesson from the NZ experiments was to improve the tightening function of the caps. The bottom portion of the cap was turning during installation, making it harder to get a repeatable torque. Their solution was to drill a hole and install a roll pin as
pictured left. This is something that can be done on a drill press with the caps assembled, just be sure to disassemble them after drilling to debur and remove any chips. I look forward to making this modification also, and am grateful for the time and brain-power that the New Zealand crew invested in these ideas! 
Auxiliary Tanks
Installing the aux tanks is exactly the same as installing the mains with two exceptions:
1. There are no tank bay skin stiffeners to worry about.
2. The tank opening in the bottom of the wing has not been left open, so you’ll have to cut that out and fabricate a cover. You’ll also have to drill out some spar cap rivets for the bolts.
The original Bearhawk uses aux tanks that hold 11 gallons each. The Model B uses tanks that hold 9 gallons each.
Cutting the Bay Open
First, make certain you start working in the right bay: In the original Bearhawk, it is the third bay in from the tip. In the Model B, it is the fourth bay from the tip. Also, there is a right and left tank: the tanks go in so the connections are inboard and the filler caps are outboard. You’re going to cut the skin out of that bay and trim it flush with the rib and spar flanges and leave about 1/8” edge at the rear so you aren’t working too close to the rear spar face (protect it with layers of masking tape anyway). Once you’ve done that, you’re going to make a .025” aluminum cover that overlaps the hole 3/4” on all four sides, drill holes so they fall midway between the existing skin rivets (to give room for nut plates, etc.), dimple the cover, countersink the flanges, install nut plates and you’re done.
Making and installing the straps to hang the tanks follows the exact same procedures we outlined while installing the main tanks. To cut the bay open, start by drilling a 1/4” hole in each corner of the bay from inside the wing. Ideally, when we’re done, we want to have a radius in each corner to reduce the stress concentrations, so drill those first holes far enough from the corners that you can file a radius into the corners by hand. We’ll want to enlarge those holes to 3/8” to get a file in them.
Yes, in theory, you could drill these guide holes right in the corners tangential to the flanges. That, however, requires a steady hand and a mistake can cause headaches. Keep the bit out away from the flanges just a little and file into the corners with a chain saw sharpening file. 5/16” and 3/8” round files are available from Bishop Company, www.bishco.com and are handy for a lot of other uses.
File the corners back so they barely touch the flanges. Then, turn the wings over and draw a guide line from the edge of one hole to the edge of the other. That indicates the edges of the flanges and is the absolute do-not-cross line. Mark another line 3/32”-1/8” in from that first line. This is your cut line. Don’t get the lines confused. Do not try to cut the metal out with snips as it will distort enough that you’ll work your tail off cleaning it up. If you have a steady hand, a die grinder with a cut-off wheel will work, but any mistake will be a big one, so it may not be worth the risk.
Finishing the Edges
You’re going to have 1/16”-1/8” left to trim back and it will work quite quickly with a vixen file, which is available at body shop supply houses. When working aluminum anywhere in the airplane, your goals should always be the same regardless of what you’re working on:
- No scratches of any kind anywhere in the material. This will require you to be careful in how you handle the pieces and where you lay them.
- The edges will be sanded down to at least a 320 grit finish.
- No sharp edges or burrs remain. Sharp edges give fatigue a place to start cracks.
So, when finishing the edges of the hole you just cut in your wing, keep all the above in mind. If you can drag a nylon stocking down the edge and not have it hang up anywhere, you know you’ve done a good job.
The edges of the hole will be defined by the flanges around it. These flanges will receive the nutplates that will hold the cover in place. Complete the straps, cut the filler cap holes, install the tanks, etc., just as you did the mains.
- The aux tank uses two straps on the bottom with tensioners and one over the top. Make sure the top straps don’t touch the skin.
- When the tank bay is cut open, the metal should be smooth and flush with the rib/spar flanges.
Plumbing
The aux tanks are plumbed so that fuel is transferred via a pump from the aux tanks into the mains. The aux fuel then becomes main fuel and feeds to the engine as usual. The connection is run from the bottom boss at the inboard end of the aux tank, through the pump (Facet 40171) and tees into the line that runs between the main tank and the sight gauge.
It’s up to the builder to decide whether to run the flow to the bottom or the top of the sight gauge.
Running it into the top of the sight gauge, even if you don’t have a plastic ball in the sight gauge, when the pump is running and there is fuel in the aux, it fills the sight gauge. When the aux runs dry, bubbles show in the sight gauge. If you have the ball, it forces the ball to the bottom and the ball pops up the top, when the aux tank is empty. Plumbing the Aux tanks into the upper sight glass location is good for keeping the fuel in the main tank from siphoning back to the Aux tank when on slope or if pump check valve leaks.
If you route the line to the bottom of the sight gauge and route the line from the Aux tank to the Main tank high with an anti siphon bend above the upper sight glass port that will usually stop back flow. In this case bubbles will go up the sight glass when transferring fuel and be easily visible that transfer is occurring or stopped.
Place an orifice of .040 at the inlet of the sight glass and an orifice of .030 at the top of the sight glass going back into the tank. The two orifices in series will damp the sight glass much more effectively.
Plumbing Aux to Main
You’ll run an aluminum line off the bottom fitting on the end of the aux tank. The ideal line is 3/8″. Some builders have used 1/4, but the transfer time can be 30-45 minutes with 1/4″ line. To do this, it’ll have to come through a rib. Drill the hole with a stepped drill (Unibit) because it yields a round, clean hole. Make the hole big enough to accept a rubber grommet around the fuel line. Some builders put a reinforcing doubler around the hole using .032 and a number of AN3 rivets. To avoid using a ninety-degree fitting to make the turn aft (there’s no room for it), bring the line out in a large curve and back to an Adel clamp.
There are a few options for mounting the pump.
On the Model B, we recommend putting the transfer pump about mid rib bay opposite of where the tank outlet is in bay 4 from the tip. This is in the bay with the aileron bellcrank and other things.
Some have used a “hat section” of .063 aluminum to mount the transfer pump just opposite of where the aux tank outlet is, with the bottom flanges of the hat section are riveted to the bottom skin.
Another option is to mount the pump on a piece of .050 aluminum that you bolt to the rear spar just inboard of the aileron bellcrank. You’ll have access to it through the large access panel later. Drill out four of the spar attach rivets (use a No. 21 bit) and use AN3 bolts to secure the pump mounting plate. The fittings used on the line are coupling MS20823-4D and nut AN816-4D, 818-4D, MX20819-4D
To get the outgoing line over the aileron actuation rod, you’ll have to use a 45 degree fitting (which gives plenty of arch to clear everything) or bend the line into a gentle “S” turn. You don’t have to worry about supporting the tubing at that point. It will have more than enough strength to support itself.
The feed line comes out of the aux tank and into the pump via the bottom line in the aux tank. Doublers are added to the ribs where the material is removed.
The line will run down the back of the tank bay false spar and you’ll support it with a padded Adel clamp about every ten inches. Where it hits the rib that forms the end of the tank bay, the line needs to make a 90 degree turn forward. Use an AN833 that will allow a tight turn, and also hold the line in place. Use another padded Adel clamp to attach the line to the second rib in from the root. When routing fuel lines (or any line for that matter) it is important to note that everywhere a line goes through aluminum, it is either connected via a bulkhead fitting or, if the line itself goes through the metal, there is a grommet/snap ring pressed into the hole. Fuel line should not be allowed to contact other metal and will be held in position with Adel clamps. It also shouldn’t run long stretches in mid-air with no support. When in doubt, snuggle it up against some structure and throw an Adel clamp around it. If you can easily flex it with your fingers, it needs support. AC43.13 gives guidance about how often fuel lines must be supported.
Aux Tank Quick Drain
There’s a boss on the bottom of the aux tank on the inboard, rear corner. That’s to install a quick drain. Thread it for a 1/8” NPT thread quick drain (Wicks CAV 110). You’ll need to cut a hole in the bottom of the wing large enough for the quick drain. This is yet another place where using a Unibit (the stepped type drill bits) will give much cleaner, perfectly round holes with clean edges and zero distortion.
The aluminum (.025) for the main tank covers is provided, but it is not provided for the aux tanks. Use 2024-T3 aluminum.
The procedures are the same for the aux covers as they were for the main covers.
Model B Note:
Builder Dave points out the following:
The Model B wings have a different configuration and the aux fuel tank goes in the 4th bay rather than the third. This changes the way you need to configure the plumbing. Here’s what I did….
– remove the center rib stiffener on the inboard rib and trim the bottom section. Make a .032″ doubler to fit over the space. This is where you need to make the exit hole for the fuel line. Replace the shorter stiffener.
– make a .063″ doubler plate to take the pump and fit it on the next rib stiffener aft. I drilled out the center 3 rivets and then made extra rivet holes.
– use a 45 nipple on the exit from the pump and route the piping under the aileron bracket and the fuel line along the bottom aft of the ribs
Fuel Tank Mounting Straps
Your kit includes 3/4″ wide steel straps used to support the fuel tanks in the tank bay of the wing. Two straps go over the top of the tank and attach to the bottom of the false spar in the back, and to the bottom of the main spar in the front. Three straps go under the bottom of the tank to support the weight of the tanks. The bottom straps attach to the top of the false spar in the back and the top of the main spar in the front. The bottom straps have tensioners built in to allow you to tighten the straps for nice tight fit. You can also install tensioners in the top straps if you prefer. This will allow for less precision in fabricating the top straps. See the Newsletters or the “Patrol/Bearhawk/LSA Book” that came with the plans for more info on the tank straps.
Note: These instructions apply to the LSA, Patrol, and 4-Place Model B. Original 4-Place kits will use the same concept, but the wings will be inverted, since the top wing skin is riveted by the builder, instead of the bottom as in the other types.
Start with the top straps first. The goal is to set the length of the straps so that they will hold the tank about 1/16″ to 1/8″ off of the hat shaped wing skin stiffeners that are riveted inside the tank bay of the wing. First, remove the tank from the wing. Place it upright on a set of sawhorses and position the strap on top of the tank, with a piece of strap padding temporarily between the strap and the tank. Use a thin padding material- there isn’t much room to spare in the tank bay. Bend the strap into a “Π” shape over the top of the tank, using the upper front and upper rear edges of the tank as your bending die. Now, flip the straps over and lay them inside the wing tank bay, right on top of the hat-shaped stiffeners as shown in the photo above. Trim the length to allow the strap to slide inside the spar flanges, but be careful that you don’t trim it too short. The end of the strap should be against the spar cap strip in the front, and against the false spar web in the rear. Position the bend of the straps to coincide with the front and back upper edges of your tank, as you marked earlier when testing the fit of the filler neck hole in the skin.
Now, make reference marks for the locations of the strap mounting holes. For the front of the strap, make the mark right at the rivet line that secures the main spar cap-strips. For the back of the strap, make a mark at the mounting hole in the false spar. Remove the strap and find the marks. These marks are not where you’ll want to center the holes, since they are based on the strap making contact with the hat section. Make a new set of marks 1/8” up from the first set, and drill a 3/16” hole at each one. The goal is to have a gap of 1/16″ to 1/8” between the top of the strap and the hat section. Round the end of the strap with a file and debur the hole, as pictured below:
In the next picture, both top tank support straps are bolted in place.
These straps will eventually need to be prepped, primed and top coated with paint when we are all finished fitting the tank. In later kits, the strap material comes with a zinc finish and does not necessarily need to be painted.
Now it’s time to test the fit of the tank in the tank bay. Install the top straps with bolts. Check that the bottom of the tank is clear of the bottom wing skin level, and check for a gap of 1/16″ to 1/8″ from the hat stiffeners in top the tank bay. Move the tank fore and aft a little bit and make sure it isn’t rubbing on the hat-shaped stiffeners. Verify that the filler neck on the tank sticks out of the hole in the top skin about 1/8″ to 3/16″.
Bottom Straps
The bottom tank straps are a bit more complicated because of the tensioners. If this gets a bit confusing, study the pictures to get an idea of what we are trying to accomplish here. Also, make sure that you read the “Tank Straps” instructions in the Patrol Book. Then come back here to see how it’s done step-by-step.
The kit comes with these little pre-drilled and pre-tapped steel rod pieces. Half of them are tapped to 10-32 threads and half are just drilled out with no threads. Note: some of the kits have used tensioners tapped to 10-24 and not 10-32. Confirm what you have before ordering the 1.5” long Allen head bolts. The threaded rods will serve as nuts for the screws. As you can see in the photo below, slide two Allen head bolts through the holes in an unthreaded rod, and then thread them into a threaded one. As you tighten the bolts, it pulls the rods closer together, tightening the straps. In the final installation, you’ll want to use screws that are only as long as they need to be to hold the tank in place. If you have trouble getting the screws started without any tension on the straps, you can use much longer screws during the fabrication steps.
You’ll need to make the three short straps (2 1/2″ long) that will attach to the false spar. Start with a piece of strap about 6″ long and one of the steel rods. The rod will serve as a bending die. Hold the rod exactly 90 degrees to the strap and bend the strap around the rod as tight as you can.
Now slide the strap/rod assembly into a vice and start to tighten it while pushing down. Use a scrap aluminum pieces that protect the parts from the steel vice jaws:
As you tighten the vice, lightly tap the strap with a hammer, forming it to the rod, then tighten the vice jaws all the way down. You should end up with a nice tight fit. Remove the assembly from the vice. Place the assembly on your work bench with the shorter tab up, and mark the centerline of the strap. Drill three #30 holes along the center-line using 1/2″ spacing from the end and from each rivet, putting in clecos as you go to keep it lined up. Drill a 3/16″ hole in the longer tab about 2 1/2″ from the tensioner rod. The end result should look something like this:
Now, disassemble the strap, and prep, prime and paint them. Gently bend the strap open to allow for painting the inside of the strap too. After the paint dried for 24 hours, rivet the assemblies together using AN470-4 rivets:
The 3 short tensioners are then bolted in place on the front of the false spar, at the rear of the tank bay. The center tensioner is in the picture below.
Note: the rods that go in these short tensioners are the threaded ones.
Next we need to make the 3 long bottom support straps to the correct length. Start by making one end of the long strap with a tensioner rod just like we made the short ones, bending the strap around the rod, tightening it in the vice, but stop before you set the rivets. For now, just slide the non-threaded rod in the end leaving the assembly un-riveted. Install the fuel tank in the fuel tank bay of the wing. A magnetic screw driver with an Allen tip of the correct size makes it easier to reach the bolts in the tensioner rods, pictured below.
Place the tank back into the bay. Carefully slide the end of the strap with the tensioner rod and Allen bolts in between the aft end of the fuel tank and the false spar. Start the two Allen bolts into the threaded rod in the short tensioner and thread them in a couple of threads. Install the anti-chaffing protection on these straps, at least temporarily, to account for the thickness of the material in the next step. Pull the aft end tight and bend it around the aft edge of the fuel tank, letting the front end just lay across the front spar for now.
See the picture below:
At the front edge of the tank, use a rigid ruler to take a measurement from the front edge of the tank (where the strap will bend) down to the main spar flange, inside corner (where the flange and cap strip meet). In this case, the distance was exactly 8.5″ from the tank edge to inside corner of the main spar flange.
Now make a mark on the strap exactly where it will bend around the front edge of the tank. Measure out from the bend line to the cut line (8 1/2″ for mine) and then cut off the strap at that point. Pull the strap snug against the tank from the rear and bend it over the front edge of the tank.
Slide the front end of the strap down to the corner at the main spar to test the fit. If there is a gap between the strap bend corner and the corner of the tank, as is pictured above, then trim the front end of the strap a little bit more to eliminate the gap.
The goal is to simultaneously get the end of the strap to sit right into the corner main spar flange, and the bent strap snug against the tank corner. When this is the case, remove your tank and put the end of the strap back down into that inside corner of the spar again. Now, make a mark on the strap for where to drill the mounting hole, as pictured below.
Remove the strap, and drill the 3/16″ mounting hole. Debur it as always and round the ends. Repeat this fitting procedure for all three bottom straps.
Attach the bottom tank straps to the main spar, bolting them in place with 3/16” bolts and nuts. On final assembly, these will be AN3 bolts with elastic stop nuts, but it’s best not to use the elastic nuts during fabrication, since they gradually lose their locking function with repeated use. You will recall that the aft end is made up for the tensioner, but it is not yet drilled and riveted.
Now you can test fit the tanks with the straps. Install the tensioner rods and Allen bolts, and then snug the straps down evenly, tightening all three a little at a time to keep from tilting the tank. If you did it correctly, once your bolts are snug and the tank is secure, you should have at least an inch of tightening room left between the threaded and unthreaded rods. Don’t tighten them too much at this point, until the rear strap ends are drilled and riveted.
Now, it is time to take it all apart and prep, prime and paint all of the straps. Once the paint has dried, rivet the aft ends of the long bottom strap tensioners. Then, permanently install your chaffing protection. The photos below show Mylar strips. 1/8” rubber strips are also acceptable.
Routing Fuel Lines from the Tank to the Wing Root
Remove the tank from the wing to start prepping it for the fuel lines.
The fuel feed lines and sight gauge lines must be run from the tank through the root ribs, ribs #1 and 2. This is why in the tank mounting step, we offset the tank to the outboard side of the tank bay to give provide the maximum room to work in.
Start by installing the tank fittings. The threads that go into the tank are NPT threads, which are slightly tapered. NPT threads require a sealer to prevent leakage, as detailed here. We recommend “Fuel Lube,” which is sold at Aircraft Spruce as “EZ Turn.” A small tube will likely provide all you’ll need for your project. This product is impervious to fuel and water, and also helps prevent thread galling. Use this only on the NPT threads, never on any part of a flared fitting. Use it sparingly and wipe off any globs of it once the fitting is secured in place.
Warning: Do NOT use Teflon tape for the fuel system connections. Little pieces could be cut off by the threads and contaminate the fuel system.
The inboard side of the tank receives the finger strainers and AN fittings pictured above. Front fuel feed fitting: AN816-6D. Sight gauge fittings: AN816-4D. Rear feed line fitting: AN824-6D.
One note of caution: The finger strainers (ACS PN 05-17700) are made of relatively soft brass, and they can collapse if they are tightened without support. Before you tighten them with a wrench, install the AN fitting inside the finger strainer to support it against the pressures of the wrench. Use the box end of a wrench instead of the open end.
With the fittings installed, you can position the fuel tank back in the tank bay. The next step will require tank removal again, so there is no need to tighten the straps, other than an optional test fit. Make sure the tank is offset to the outboard side of the tank bay to allow maximum room for the fittings.
The AN824-6D tank fitting at the aft end of the tank is a 45 degree elbow because its location lines up with the edge of a rib lightening hole. Notice how drawing #2 in the plans shows how the tank is offset to the outboard side, and how the aft fuel line is angled aft before finally passing through the root ribs.
The next step is to locate the fuel line clearance holes in ribs #1 and #2. With the tank in the bay, there is no room to get a drill motor in place to drill the holes. We’ll use reference lines and measurements instead, which will allow for removing the tank to drill the holes. Place a straight edge or ruler on the skin over the rivet line for the rib flange, and align it by eye with the centerline of the flared end of the aft fuel tank fitting. Draw a line with a Sharpie marker onto the wing skin that depicts this extended center line:
Next, measure the depth from the wing skin to the center of the fitting, measuring perpendicular to the skin. In this case, the center of the fitting was 1″ below the wing skin. Note the measurement somewhere. In the photos, the measurement is conveniently written next to the line that we drew in the last step.
Repeat this for all four tank fittings:
Remove the fuel tank and use a small square make vertical lines on the outboard side of the number 2 rib that correspond with the lines from the last step. Measure vertically on that line to mark where the center of the fuel line hole should go. Cut the holes in the rib with a step drill, using 1” holes for the feed lines and ¾” holes for the sight gauge lines. If you find that you need to remove more material than that, you’ll want to consider adding a doubler to the rib.
To mark the hole locations on rib #1, rest one edge of a square on the inboard side of the wing skin, and make span-wise lines that intersect the lines made in the last step. Use these marks to locate and drill the holes in rib #1. Use ¾” holes for the feed lines and ½” holes for the sight gauges. Use AN931-4-7 grommets for the sight gauges and AN931-6-10 grommets for the feed lines.
Here is a diagram provided by one builder of his fuel system in the wings:
Builder Bruce Case suggests the following edits to the above diagram for his Patrol, and also provided the fuel tank drawing:
Fuel Diagram With Errors
LEFT WING TANK ASSEMBLY
If you draw a diagram for your system, send it over and we’ll add it here too!
Locating the Filler Neck in the Top Wing Skin
Source: 2017 Q2 Beartracks, Mark Richardson
Well, in keeping with a lot of tasks on my scratchbuilt Bearhawk, I had been dreading the whole process of cutting the fuel tank filler neck holes in my wing skins. I was really worried that I would mess something up and cut the holes in the wrong spot (like that NEVER happens, right?) and wind up trashing some expensive sheets of aluminum. Well, turns out it was really easy and I did both holes in my left wing (I have an Aux tank) in a little over an hour and they both turned out perfect. I figured since I bored you in the last issue with some building tips, I might as well do it again since this actually worked out.
I was a little leery about using some of the methods I had read about, including the one about smearing some kind of liquid/putty/whatever on the rim of the filler neck and then pressing that against the inside of the skin. I didn’t think that would be very accurate.
This is what I did (your mileage may vary, batteries not included, objects in mirror are closer than they appear…)
1. I took a square of paper and drew a 2″ circle on it.
2. With spray contact cement, I attached the paper perfectly centered on the filler neck. I then put duct tape on paper facing up (towards the inside of the wing skin) along the side closest to the edge of the tank.
3. I then positioned the tank where it needed to be (vertically and horizontally) and then used a long wooden coffee stir stick to reach through a lightening hole and press the tape to the skin.
4. The tank was then removed. The duct tape easy overcame the stickiness of the contact cement, so the square paper template was now stuck EXACTLY where I needed to drill the hole. I drilled a #40 hole through the center so I could mark the hole on the top side of the skin.
5. Using a #40 drill, I worked my way around the hole and then used a Dremel tool and file bit to remove the waste in the center.
6. I used a spiral bit in an air die grinder to round out the hole and make it 2 1/4″ in diameter (1/8″ all the way around the hole). Why not go straight to 2 1/4″ at first? In case I buggered something up; you can’t put material back in :-)
That’s it. Quite easy actually. And nobody is more surprised than me …..
Fuel Tank Ideas
Source: 2000 Beartracks, Bob Barrows
In the 1996 newsletters you will find reference to Optional Outboard Fuel Tanks. We have given them a little more thought and come up with a couple of ideas to make them more useful and practical. With 55 gallons available in the main tanks it would be hard to imagine a trip leg that could burn that much fuel without at least one stop (I’m not talking Ocean crossing here). It may be better NOT to plumb these tanks into the main tanks and NOT to run a separate fuel line to a selector valve – let’s keep this all simple and light.
The Tanker Tanks offer two 11 gallon tanks of whatever you need, be it water, fuel oil, or gasoline to your back woods camp. Mostly we use them to haul 100LL fuel back to our grass strip where it is drained into containers until it is needed. When we find a good deal on fuel, we can stock up! Carry a 5 gallon can and some hose with you and you can refill the main tanks from the Tanker Tanks without much difficulty while on your trip.
Several problems are eliminated with this system such as not having another set of fuel gauges, cross feeding while parked on an uneven surface, the complexities of plumbing and check valves and vent lines and fuel leaks at fitting locations etc.
Bob’s Vented Fuel Cap Design
Source: 2000 Beartracks, Bob Barrows
Show below and on the next page are detail drawings and photos of the fuel caps that I made some years ago for Bearhawk N6890R. The same cap design is used on Bearhawk N33RB (Proto II). I like these caps because they seal well and have ram air venting. Leakage out the vent hole has not been a problem, even when parked on somewhat unlevel terrain.
If you have or can use a small lathe, making these cap assemblies can be a fun project and can save you $50 – 100 in cost.
Be sure to lubricate the threads during use (use fuel lube), and do not unscrew too far when removing from tank. Also verify that the vent hole is pointing forward when installed.
2000 Beartracks Mailbag: Q&A with Bob
Bob, Enclosed is a check for Bear-Tracks for another year. I do have a few questions:
1 – What is a good method to use to transfer the airfoil shape to the wood to be used for the form block for the wing ribs?
2 – What is the recommended radius for the wing rib form blocks? I believe that 1/8″ would be about right for both .025 and .032.
3 – Do you have an e-mail address and if so do you answer e-mail correspondence?
I have a piece of 1″ thick hard maple for the form block. I just need to transfer the airfoil shape to the wood and cut it out. I am ready to start with the ribs. Is Proto II in the air? I bet the performance is really great – Thanks for your time.
Paul Foster – #289 – Monte Vista, CO
Paul, Thanks for your questions and newsletter renewal. As for your questions
1) The best method to use is to glue drawing #7 to your form block with contact cement or Plyobond.
2) a 1/16″ radius will work best for both thicknesses of the aluminum.
3) I do not have an e-mail account. Proto II is flying great -look for a flying report in this issue of Bear-Tracks. -Bob
This letter was pulled from the Bearhawk E-group. For more information on the Bearhawk E-group see page 7.
Well, after several days of non-stop building, 023 is on the main gear. I stumbled across a new Scott 3200 tailwheel in some stuff my Dad purchased from someone’s attic. He got a bunch of stuff (including a 65 hp engine, prop, landing gear, etc) for less than the price of a new Scott! What a deal.
Anyway, related to tail leaf springs, after much discussion and some consulting with Bob, I have decided on purchasing a PA25 tail spring from Univair (part number PA25TWS1) for approximately $90. 1 decided on the PA25 because Bob recommended two leafs all the way to the tail wheel bolt. Taper rod was attractive but with the Scott tailwheel, side loads should not be a big problem – it will go to full swivel if a major side load occurs.
My plan on putting a Continental 0470 on my Bearhawk has been changed. Finding an engine mount damaged or not – is not easy. Any found, even damaged, seem to run between $500 & $700. The Lycoming 0540 seems easier to make an engine mount following Bob’s newsletter. Also, Bingelis only talks about Lycomings!
Compressing the landing gear shock strut took some thought. I used a bar clamp – very long – and it worked fine. Later Bob told me he used his drill press with the table moved off center – I wish I thought of that! Oh well, some days I make things harder than necessary.
Piper TriPacer Seats also took some work to find. I ended up paying $60 each – frames in very good condition and but they need covering. Seemed like allot but finding seats was not as easy as hoped. Salvage dealers did not have any. My source has a couple more sets if anyone is interested.
Well, that’s my story for now. If anyone is near Cincinnati (actually Florence, KY) or Elkton, Ky, let me know. I build my parts in Florence and assemble in Elkton. It would be great to have some other builders close to discuss building, etc.
Bill Johnson – #023 – Florence, KY
Hi Bob, So glad to hear that you are ready (perhaps already have) to fly #2. Our second wing is going together quickly. Should have both sides, including control surfaces before the end of the year. Looking forward to starting on the fuselage.
The photo is my left wing with control surfaces installed. I am starting to look for a wind damaged Maule or C180/182 to scavenge for the engine and other needed parts. Still having a ball with the whole project.
Pat Fagan – #232 – Pearblossom, CA
Also from the Internet -I have most of the systems hooked up or at least roughed in. All the flight controls are working. I am finishing up the fuel system now. #75 is being powered by a (1996) Ford Taurus 3.0 24 valve engine that I modified with a polybelt GT. The engine has run with no propeller but hasn’t been run to RPM or load yet. Items needing to be finished are the fuel system, engine control linkages, a few things left on the cowl, and trimming everything. I am installing a removable interior for complete inspections in the future. I know that a lot of little details need to be worked out yet.
I am in the process of moving again. This time I am going to build a house and hanger at an air park. I hope to continue working on the Bear hawk through out the house project and get it in the air by at least late summer. How is everyone else doing on progress?
I will be happy to answer any questions the group has and give my opinion of what I may have done different. I will say as far as the plans I have followed them to the line and had very good results, The project gets more interesting when you start to improvise beyond the main part of the plane, i.e. engine controls and all the other goodies. Enough for now. Happy building.
Tom Yeoman – #075 – Apache Junction, AZ
Hi, Bob,
Things are moving along, not on schedule, but forward.
I was saddened to hear of Ray Thurston’s passing – It was like hearing about a family member.
The enclosed picture shows the flanging tool I used for the rib “holes” – it was made from a standard flycutter and worked great! The wood handle was used to exert pressure on the bearing. Steel washers were glued to the form bloc to serve as bearings for the center pin. This might be helpful to other builders so I am passing it along. All the Best,
Walt Draxler – #082 – Arlington Heights, IL
Bob, I hope this letter finds you and Mike in good health and fun flying in your Bearhawks. Enclosed is a check for my newsletter renewal – I have been so busy that I forgot to send it in. I’ve finally got a good start on my Bearhawk. I have all my small steel parts cut out. I am just finishing all my ribs and I am about to start on the wing spars. My goal is to have the wings done by the beginning of winter. I am enclosing some long overdue pictures of my project. I will be looking forward to seeing you and Mike at EAA again this year. If you need a place to stay for a couple of nights you can stay at my place. I am about 40 miles from Oshkosh. Maybe that is too far, let me know. I sure would like to hear your comments about my project. I can take criticism. I hope to have the wings framed up by then. I have a question about the fuel tanks. I noticed in one of the newsletters that you weld and rivet them. Is the riveting necessary? Can I just weld them? Is the riveting for added strength or just to hold them together for welding?
Ray Gabriel – # 334 – Greenleaf, WI
Ray, thanks for the nice letter and your newsletter renewal. Your parts look very good in the photos that you sent. Mike and I might be able to stay over at your place for one night while at Oshkosh, check with us at Oshkosh. It would be interesting to look over your project. The rivets in the fuel tanks are only to hold the sheets in place for welding. ~ Bob.
Ray Gabriel using a Liebert Hole Cutting Machine. Ray reports that a user can cut all the holes in all the ribs in about 3 hours with this machine. Also pictured are all the 4130 steel and a few of the aluminum parts ready for bending and drilling.
Bob, I have been meaning to write for sometime to thank you for the information in your newsletter. I have been working on my seating arrangement. The front seats incorporate a “captain’s table” arrangement for the mounting. Adjustments are made by pulling a side lever to the right and sliding the seats back and forth. The back of the front seats fold forward to allow entry to the rear passenger area. The back of the rear seat is adjustable. I used 3/4″ x .035 square tubing for the windows and door frames. I know that it costs a little more but it sure is easy to work with. I’ve got to relocate the rear window frame 2″ higher.
The engine is a Lycoming 0-540 of 235 HP. It will be pulling a fixed pitch McCauley 8452 Prop. I hope to have it up and running by October 2000.
George Anderson – #153 – Daphne, AL
Hello Bob, Just got the Jan 2000 Bear-Tracks. I am always looking forward to receiving the next issue. Sorry that we didn’t make it to the fly-in in Oct. We were planning on coming down to the fly-in and visit relatives but I came down with the flu – so maybe next time.
Thanks for the information in the newsletter – It must be nice to have two Bearhawks!
Thank you for coming to our cook-out last summer and I hope you can make it to our next one sometime in June this year. Since the cook-out there have been 4 of my neighbors talking about building Bearhawks. My daughter and son-in-law are planning on building one as soon as they finish their Cessna 140. We might have to change the name of the airport from Hale’s Landing to Bearhawk Landing!
I have been busy working on the 1959 Cessna 172 that I am restoring – it’s almost done. The Koala 202 is almost ready to cover and I have most of the 4130 steel hardware for my Bearhawk wings made. I have too many projects and not enough time or money to finish them all.
Do you have plans for any future modifications for the Bearhawk? If so what? How about plans in the newsletter for seat frames and tracks. I have found that the Tri-Pacer seats are hard to find.
Dan Riffee – #267 – Hale’s Landing, WV
Dan, Sorry to hear that you were sick and couldn’t make it to the fly-in. Like you say maybe next year. Mike and I really enjoyed our trip to Hale’s Landing last year and are looking forward to it again this year. When you firm up a date – let us know.
Currently I have no more modifications to the Bearhawk design planned. Your idea for seat drawings is a good one and I will work on that for a future newsletter. -Bob
Bob, Enclosed is a check for the 2000 newsletter, also I have a few questions:
1) The part of the nose ribs that form the leading edge, have you noticed on the prototype or do you forsee a problem with fretting because the metal is not secured together at the leading edge tip?
2) On the plans it calls out a 1.25″ flange on the main spar and a 1″ on the rear. The newsletter has instructions for laying out spar blanks : Width = web finished height PLUS 2 x flange width PLUS 1/16″. This will give a larger flange than calls out in the plans, the same also with the 9/16″ and 1/2″ marker for the rib flanges. I wonder if it makes a difference or would I have clearance problems later?
3) Are the spar webs square on both ends or do the root ends have the shape of the wing attach fittings to fill the gap between the fittings?
I have started slowly on the wings, having trouble getting consistently sized ribs but getting there, I have all my tools and shop set up so far and having a lot of fun.
Mark Skiba – #349 – Camarillo, CA
Mark, Looks like you are really getting into the drawings and giving them a good going over. As for your questions: 1) Fretting has not shown to be a problem on the prototype and I don’t see any indication that it would start. 2) Slightly larger or smaller flanges will not cause a problem. 3) The spar blanks have the shape of the wing attach fittings.
Your ribs should be consistent within about 1/32″, let me know if you are still having trouble with the ribs. Maybe I can give you some more pointers for rib construction. ~ Bob
Mike and I received notice that Ray Thurston’s #005 BEARHAWK project has been purchased from his estate by John H. Dugdale. Ray had completed a tremendous amount of work on his BEARHAWK and it would have been a shame to see it go to waste.
Hi Bob,
I’m making good progress on the BEARHAWK. I’m on the wheels and rudder hook up to the pedals (I had to move the rudder pedals back from the firewall for brake cylinder clearance). I have a 0-470 and Prop and a good lead for the mount.
The seats are installed and I’m rigging up the rest of the tail. I have included a few photos of me forming the T25 ribs 1/8″ bend with a steel mandrel on the anvil.
Do you have a date for the fall BEARHAWK Cookout?
Will Graft – #365 – Wadsworth, OH
Wil, good to hear from you. I mention the distance used on my rudder pedal setback on page 5 of this issue. As for the cook out – we are still working out the best date as October has suddenly become very busy. We will have a firm date by Sept 1. ~Bob
The following post is from the BEARHAWK e-group.
Today I had to go see the IA who helped my brother restore his Citabria and I mentioned the e-mail list discussion of reverse engineering a set of EDO floats. The one hassle which he could see, would be forming the “hoop” stiffeners which give the rounded top of the floats their shape. He showed me an old partially torn up EDO and it looked like they were formed in a brake and then formed into their rounded shape, similar to how the fuel bay wing skin stiffeners are made for the BEARHAWK wings, only with a LOT more curve. So it would be a lot of trial and error compensating for springback, and it would have to be redone for each size hoop due to the taper of the floats. Not an insurmountable challenge, but probably easier to copy a float with flat top and sides.
He did mention that in the EDO line the model 2425 is not rounded like the others, and might make a good candidate for duplication. If the model number is also the displacement, that might be a bit on the small side, but may be close enough if you don’t increase the gross weight above what is specified for the landplane version.
Other than the hoops the rest of the float looked pretty straightforward and ought to be easy to copy if you could get the right extrusions. The one thing I noticed was LOTS and LOTS of closely spaced rivets. I think I would prefer to build my floats in fiberglass if a set of suitable plans become available. Matter of fact, my friend the IA asked “why don’t you just design your own?”
Del Rawlings – #316 – Cordova, AK
#232 is really coming along well now. I bent the top frame as you suggested and was pleased to find everything lined up! I almost have the entire frame tacked together.
I was wondering, do you call for any special bolts, like close tolerance or high strength in the wing struts or landing gear?
I am planning on an 0-540 for a powerplant, will any 0-540 core serve for setting up my motor mount or do I need the actual engine?
Pat Fagan – #232 – Pearblossom, CA
Pat, good to hear that the process worked, as for the special bolts question, the answer is no. The airplane was designed to use standard AN hardware. The actual engine would be best – short of that, make sure that the engine that you use is set up the same as your core and that it has the same mounting bosses that match your motor mount ~ Bob
Another note from the e-Group:
Has anyone perfected the “Barrows Method” of flanging the @#$% lightening holes?
Mike’s book as well as “BearTracks” makes this look real simple.
“Barrows” Method:
1. Wax it up.
2. Using the flange tool, lift the hole 30 degrees by smoothly going around it about 2-3 times.
3. Flip the rib over and push it down with the back of your flanging tool to lock in the 30 degrees and tame any bends.
4. Sit back, admire your work, and realize that you’re God’s Gift to the Bearhawk community and builders world over.
“Romanko” method:
1. Wax it up. (Even I couldn’t screw up this step)
2. Fail at smoothly taking the flanging tool around the @#$% hole. Instead, use the flanging tool like a soda pop opener and go around the @#$% hole lifting it up in increments equal to the width of the flanging tool.
3. Admire all waves you just put in the @#$% hole.
4. Wax it again, and go around the @#$% hole with the flanging tool, realizing the waves will never come out.
5. Flip the rib over and push the waves with the back of the flanging tool until you realize you really are having a hard time judging 30 degrees with your eye at 0400 in the morning. Induce more waves.
6. Sit back in amazement as you realize what was once a straight rib has turned into an oil can. Go outside. Look up. If you see stars, leave for the airport and get in some quick flying before work.
I know that some of you have built elaborate dies for forming your holes, but I really hate the thought of spending time doing that. Frankly, I’d prefer to keep everything “Barrows Simple”. I keep looking at Bob Barrows as my example. If he built THREE sets of wings using this method, it’s good enough for me. I think it’s just an issue of practice, but I really thought I’d have it down by now. Until I do, I will continue to refer to them as the @#$% lightening holes.
Bob Romanko – #399-Charlottesville, VA
Bob, Bob and I have agreed to conduct a personal workshop with you to perfect the “Barrows Method” of rib flanging. I got it on my first try. ~Mike
I found some rod ends at Sun & Fun for $12.00 each. Talked to the surplus dealer (Russell). He has about 1000 more of these jewels. The part number on the rod end is RE4H6-2 made by Fafnir (look at the Spruce catalog and you will see these are the right ones). If you would like to purchase, fax an order to Russell AT2 Surplus (847-432-6847). He said it takes time for him to fill orders so be patient.
Bill Johnson – #023 – Florence. KY
Bill, you look good sitting in that fuselage. I was able to confirm the rod end information with Russell – Order what you need builders! ~Mike
Bob, I’m enclosing some photos of my Bearhawk. I have completed the fuselage, both wings, wing-tips, fuel tanks (installed), nose bowl, and the seats. All cables are hooked up and operational.
I constructed the seats myself with 4130 tubing and
zig-zag springs for the seat bottoms and backs. They are fully adjustable front and back with a hinged back for access to the rear seat compartment.
I’m getting ready to mount my engine on the Bearhawk.
It is a Continental 0-470. I hope to have my Bearhawk in the air by next fall – God willing.
Things seem to be going very well building from your plans. I cut my first tube three years ago.
Sorry I missed seeing you and the prototype in May when I was on the east coast. Maybe it will work out better on my next visit. God Speed,
Boyd Newgen – 264 – Ontario, OR
Boyd, What a great letter to receive the day I return from Oshkosh! Thanks for all the great photos and keep them coming. I am glad to hear that you are making such good progress, ~Mike
Hi Bob & Mike, I have had the Bearhawk plans 5 years and I am only now just starting. I have done a Kitfox and a Thorp T-18 (which took People’s Choice at Oshkosh) in the early 80’s. I want my Bearhawk to do the same.
You mentioned that you stayed at Blackhawk Field in WI during your trip to Alaska. I hangared there for two years prior to coming to Oregon.
I am a steadfast promoter of the Bearhawk. Why someone didn’t think of it the 30 years proceeding Bob remains one of life’s mysteries!
Don Schindler – 068 – Springfield, OR
Dear Bob, Please send me a copy of the Utility Door Plans ($25 M.O. enclosed).
I have been studying the plans at great length, trying to create and assemble the aircraft in my mind. In this way I feel I will have an understanding of the aircraft as a complete idea and not just some parts to make and slap together. This activity alone has been a source of great entertainment for me.
I expect to be full bore into parts construction by the end of December.
I have a couple of questions for you concerning the plans – At the root end of the spars you show the .032 web is to be continued all the way under the spar end plates and the spar end inside plates. Also you show the web flange ending at the top and bottom of the spar slightly short of the corner angle of the end plates. this creates and inside right angle cut at the top and the bottom of the web material at the end of the flanges. Is this inside right angle cut a possible source of future web cracking from stress? Should I radius it or continue it as a gentle curve up to the flange?
Do the line diagrams of the fuselage tubing depict the inside, centerline, or outside of the tubes?
And finally are there any unusual cluster arrangements in the fuselage tubing joints?
Bion T. Rodgers – 436 – Mount Royal, NJ
Bion, You should have your utility door drawings by now – let me know what you think. As for your questions: You make a good point about the spar flange. There should be no sharp inside corners on ANY aircraft metal part. Use a 1/8″ radius or larger. The fuselage line drawings depict the CENTERLINE of each tube. And there are no unusual cluster joints used in the Bearhawk frame as designed. ~ Bob
Dear Bob, I was pleased to have made your acquaintance on the telephone the other day. As indicated I have purchased Ray Thurston’s Bearhawk project but have not yet collected it from Blenheim. I will collect it soon, in the meantime Mrs. Thurston has sent me the plans and I am studying these.
Ray has done a lot of work on his project and it is a tragedy that he was not able to complete it. I hope to be able to pick up where he left off and continue the quality of workmanship. I am not a trained engineer, but enjoy a challenge and have always had a “hands on” practical tendency to make and fix things – boats, engines, travelling irrigators amongst others.
We live on a small block (14 acres) about 14 miles from Christchurch. While we are within the Christchurch International Airport Control Zone, there is a possibility we could fly off the block (it is 515 meters long (that’s 1690 feet to you and me)). The big thing will be to not annoy the neighbors as the area is in the process of being divided into smaller and smaller blocks with people moving here from the city.
So far as the Bearhawk is concerned, I have not decided what engine to use yet. Personally I am not keen on air cooled engines, but there is considerably less work and less uncertainty involved in sticking with the Lycoming. I am also not keen on reduction drives as many of these seem to have some problems. I quite like the idea of an inverted, direct drive, alloy V8, such as Steve Whitman used in his Tailwind. No doubt this would take some development too. A Rover 3500cc can be stoked and resleaved to give over 5000cc and this would give enough HP, but this too would take some development.
I would appreciate if you could provide me with a bit more specific performance data re: the Bearhawk than is contained on the websites. If this has been published in the newsletters do not bother to repeat it (I am awaiting receipt of the back issues from Mrs. Thurston). I am interested in the specific performance of the prototypes – e.g. estimated HP of the engines and the cruise speed at 2400 RPM for each, climb rate, fuel burn at cruse. Do your take off and landing figures represent literally lifting off the ground or are they the traditional 50 foot obstacle clearance? Also can you supply some data on the Bearhawk’s ability to handle cross winds. I look forward to meeting you someday in the U.S. or in New Zealand
John Dugdale – 005 – Canterbury, NEW ZEALAND
John, Thank you for the introduction and I hope that you find the Bearhawk to be to your satisfaction once you begin construction. I considered Ray to be a very good friend even though he was on the other side of the planet and I am pleased to learn that all his hard work will not go to waste. I think that you will find the answers to most of your questions in the back issues of the newsletters. My performance figures represent actually lifting off the ground. I personally think that the Bearhawk handles crosswinds quite well. The nearest production airplanes that would be close in crosswind competence would be the Husky, Super Cub or Citabria. ~Bob
Fuel System
The Fuel System
The fuel system used in the Bearhawk is simple and a proven layout. I would NOT recommend any basic deviation from this design. Those builders using the extra range tanks as described in the October 1996 should contact me (by mail) with the hook-up that they plan to use.
All tubing used in the fuel system is 5052 aluminum 3/8″ OD. All hose is -6 size and all pipe threads are 1/4″ NPT or larger. NEVER use teflon tape to seal fittings in an aircraft fuel system.
The four way fuel valve needs to be ported with 1/4″ – 5/16″ passage ways to insure adequate flow to the engine.
As shown in the sketches and photos, the fuel valve and gascolator are mounted on the floor near the flap control handle. This location allows the gascolator to to be at the lowest point in the system as required to remove any water that may contaminate the fuel.
The fuel lines upstream of the gascolator should not have any swags that could collect water and freeze while the aircraft is sitting.
If you consider another fuel system consider the above points.
I do not like the inline filter for aircraft – use a gascolator.
A fuel flow test should be performed to insure that enough fuel is reaching the engine. Using the hose that hooks up to the carburetor. The flow should be:
This is based on .5 lbs. fuel per hp per hour with a 1.5 safety factor. A 1.25 safety factor can be used with a fuel pump (check the flow at the inlet of the fuel pump).
See the complete article of fuel flow test in Sport Aviation July 1998 page 121 for more information.
The gascolator shown in the photo is one that I machined from round aluminum bar stock. You can use a standard type gascolator and make up a mounting bracket to fit using T25 channel material. This will also work for mounting the 4 way fuel selector valve. If the gascolator is a little too deep and protrudes below the belly skin tunnel you will need to add an aluminum blister.
This fuel system information is not complete in all the related details. I believe the necessary basics are pointed out and you can work out the details as related to the hardware that you use.
Optional Outboard Fuel Tanks
Source: 1996 Beartracks, Bob Barrows
As requested by a number of Bearhawk builders here is another builder option – extra fuel tanks. The current configuration of the Bearhawk allows for over 6 hours endurance at a cruise setting with the O-360. You however may need the extra fuel if you have a really thirsty engine. I have found 55 gallons to be a more than enough fuel. I do not like to go for much more than 4 – 5 hours a time on a trip leg. I like to stop a different airports and meet new people, see new places and interesting aircraft.
The tanks are located in each wing, between ribs #10 and #11, using the space between the main spar and the rear spar. The tanks are held in place with straps attached to the main and rear spar cap strips. A .032 aluminum access panel is employed on the underside wing skin….
Reference April “96” Bear-Tracks “fuel tank” for related information.
Use two straps on bottom of tank with tightening links, and two straps on top of tank. No baffles are needed in this size tank. Each tank is 13 1/4 ” wide and 29″ long and at the deepest point 7 1/4″ deep, following the contour of wing rib: the tanks will hold about 11 gallons each. Locate the fill cap at the top front outboard corner. The quick drain is at the bottom rear inboard corner. Locate the 1/4″ vent and 3/8″ supply line as shown on the sketch. With four tanks, two mains and two outboard, it is difficult to control leakage of fuel out of the tank vents unless the aircraft is parked with the wings level, or the vent location is higher than any connected tank. Installing these tanks is not recommended unless you have a real need for more than the standard 55 gallon fuel capacity, they add weight, approximately 18 pounds, and air drag (bottom access panel & fill cap), and also increase your chance of fuel leaks.