Making Aux Tank Covers

This section is provided by builder David Pearson on 4/18/2023.
Disclaimer: This is my first build. I am not a professional builder. Use at your own risk.

Aux Tank Cover Installation Steps

Here is the method I developed to locate the screws for the aux tank cover and install the associated nut plates. It’s an alternative to the published approach of putting the cover retaining screws and nut plates between the existing rivets that surround the bay. This process worked well on my A-model Quick Build wings, which arrived with the bottom skin already riveted in place and the top skin loose. The resulting screw pattern was evenly spaced, had screws at the corners of the cover, and matches both the surrounding rivet patterns and the screw pattern of the main tank.
“Less common” tools required:
• #40 strap duplicator (Aircraft Spruce 12-01497 or similar)
• Reverse Counterbore/Spotfacer tool with 1/8” Pilot (Brown Tool BAT4005-105 + BAT4006-2 is what I used)
Steps:
1. Remove aux tank and tank straps from bay
2. Drill out the rivets around the perimeter of the bay. Use a #40 bit for the AN426AD-3 rivets and remove them completely. If you encounter any AN426AD-4 rivets (I found one at the front outboard corner of the bay) center-drill them with a #40 bit (they will be fully removed later) to leave a hole that will work well with the #40 strap duplicator when match-drilling the cover. I found it helpful to temporarily leave a couple of rivets in place on each rib to keep the rib and skin aligned while drilling out the majority of the rivets. Then I put silver Clecos in the holes next to the remaining rivets to keep things stable as I drilled the last few rivets out.
3. Center the cover on the opening (should overlap the edges ¾” on all sides according to the builders manual), and tape it securely in place.
4. Lift one corner of the cover just enough to slide the strap duplicator in, and drill a #40 hole aligned with the corner hole of the bay (which until Step 2 had a rivet in it). Note: I ended up putting a layer of tape on the skin around the perimeter of the bay to keep the pin on the strap duplicator from scratching the skin.

5. Put a silver Cleco in the hole you just drilled, locking that corner of the cover into the existing hole in the skin and spar cap.
6. Repeat steps 4 & 5 on the diagonally opposite corner of the cover.
7. Continue to use the strap duplicator to match drill the other two corners, then the remainder of the holes, strategically positioning enough Clecos to ensure the cover doesn’t shift but can still be pulled away from the skin to insert the strap duplicator.
8. If there are any AN426AD-4 rivets remaining, remove the cover and drill those out so they don’t interfere with the next step. Then Cleco the cover back into place.
9. With the cover Clecoed in place, updrill the screw holes to #27 (through the cover, skin and rib/spar flanges in one pass). Use some copper Clecos in the enlarged holes to keep things stable.
10. Remove cover and set aside
11. You will notice that each #27 hole in the rib and spar flanges has the remnants of the dimple that accommodated the AN426 rivet head which forms residual “volcano” on the inner surface:

Left untreated, these will keep the nut plates from sitting flush and flat on the surface of the flange:

I used a back spotfacer to bring these protrusions down to an acceptable height. Be careful to keep the spotfacer pilot perpendicular to the skin, and don’t cut too much material or the outer diameter of the spotfacer can scrape the surface of the material surrounding the hole. I clamped a drill chuck to the spotfacer pilot to use as a handle, and then turned it by hand:

12. Use nutplate jig and drill rivet holes to #40. Note: Watch for interfering flutes on rib flanges – “One armed” MS21051L06 nut plates can be used to avoid these. For the four corner locations I used three MS21051L06 and one MS21073-06 due to a hole-to-edge spacing issue.
13. Countersink each screw hole (I used a #27 pilot bit with a simple centering tool to keep Microstop from wandering)

14. Deburr all holes
15. Dimple or countersink (Depending on access and material stack thickness) the nut plate rivet holes
16. Clean between skin and flange layers at all nut plate locations
17. Rivet nut plates in place
18. Deburr cover
19. Edge roll cover
20. Dimple cover
21. Test fit

22. Re-install straps and tank
23. Mark and drill quick drain hole in the cover. The instructions in https://bearhawk.tips/2770 worked well for me.

Rudder Cable Attachment Detail for Tandem Seating

Patrol builder Stefan Hechenberger made this fantastic detailed diagram of how the rudder cables attach to the rudder pedals.

The BOM for one side is:
Front rudder pedal
1x AN3-13 bolt
1x AN393-13 clevis pin
1x AN960-10 washer
2x AN960-10L thin washer
1x short bushing
1x long bushing
2x cable link
1x AN310-3 castle nut
2x MS24665-151 cotter pin
Connection front to rear pedal
42″ of 1/8″, 7×19 galvanized cable
2x AN100-C4 cable thimble
2x MS51844-44 nicopress sleeve. 1/8″
Rear rudder pedal
1x AN3-13 bolt
2x AN393-13 clevis pin
1x AN960-10 washer
3x AN960-10L thin washer
1x short bushing
2x long bushing
2x cable link
1x AN310-3 castle nut
3x MS24665-151 cotter pin
Connection Rear pedal to rudder horn
turnbuckle (clip version)
1x MS21251-B5S turnbuckle barrel
1x MS21255-5RS right turnbuckle eye
1x MS21255-5LS left turnbuckle eye
2x MS21256-1 locking clips
190″ of 1/8″, 7×19 galvanized cable
4x AN100-C4 cable thimble
4x MS51844-44 nicopress sleeve. 1/8″
Rudder horn
1x AN115-21 shackle
1x AN393-13 clevis pin
1x AN960-10 washer
1x MS24665-151 cotter pin

Some notes about assembly:
I made sure the cable links rotate freely on the bushings. I reduced the diameter slightly and adjusted the length to just prevent the bolt from squeezing the links.
The rudder horn is slightly thicker than the shackle allows. Slightly bending the shackle open is necessary.

Bob prefers to not run turnbuckles in the rudder system, because the rudder system is an open loop that doesn’t need to be tensioned. If you are not using turnbuckles, make the cables one piece from the rear seat rudder pedals back to the horn. If you do add turnbuckles, they are best positioned aft of the baggage area.

Using Clip-Lock Turnbuckles

Source: 2020 Q3 Beartracks, Rob Caldwell
Turnbuckle Conversion Table
Builder Rob Caldwell has been making fast progress on his Bearhawk 4-Place. He’s installing MS Clip Lock turnbuckles instead of the older style AN turnbuckles that are secured with safety wire. This table shows the part number conversions for folks who might like to do the
same. The center column shows the traditional safety wire turnbuckle parts, and the right column shows the MS Clip-Locking style.

Type Safety Wire Clip Lock
Outer Ailerons (AN130-32L) 2 ea.
Barrel AN155 MS21251-B5L
Fork Eye AN161 MS21252-5LS
Cable Eye AN170 MS21255-5RS
Cabin Center Aileron (AN130-16S) 1 ea.
Barrel AN155 MS21251-B5S
Cable Eye AN170 MS21255-5RS
Cable Eye AN170 MS21255-5LS
Flaps (AN130-16S) 2 ea. (same as outer ailerons)
Barrel AN155 MS21251-B5L
Fork Eye AN161 MS21252-5LS
Cable Eye AN170 MS21255-5RS
Elevator (AN135-32S) 2 ea.
Barrel AN155 MS21251-B5S
Pin Eye AN165 MS21254-5RS
Pin Eye AN170 MS21255-5LS

Installing a Lycoming type Engine

Some builders have found it challenging to get the engine onto the mount for the first time. The good news is that these steps are pretty universal, so rather than re-invent the wheel, we’ll provide a few resources that you may want to consider.

Here’s a link to a great article on Doug’s site, targeted to RV builders but applicable for us too.

Similarly, Doug hosts this very good discussion thread with some common questions.

Helpful books, available at the EAA Bookstore:
Firewall Forward: Engine Installation Methods by Tony Bingelis
Tony Bingelis on Engines by Tony Bingelis
Sky Ranch Engine Manual, by John Schwaner

2019 Kit Upgrades, Skylight Detail

Source: 2019 Q4 Beartracks, Mark Goldberg
Over the last year and a half, we have made a number of changes to the kits. The purpose of this write up is to detail the most recent changes we have made in the Quick Build kits.
But first, let me go back to May 2018 to begin. Bob Barrows made the trip to the kit factory with me back then. We successfully showed the workers some new tricks. Really three things:
1) Bob showed the guys how to drill the wings to the fuselage and drill the wing struts.
2) Bob showed the workers how to make up the fuel tank straps and install the fuel tanks in the wings with the filler neck sticking out.
3) Bob calculated the lead weight needed for the elevator’s counter weights when the elevators are covered with the lightest fabric, Oratex. The lead is melted and installed on the elevators. Room is left for more lead/epoxy slurry if a builder uses a heavier fabric process or sprays a lot of paint.
More recently, we made two additional changes to the kits. Ever since kit production began in 2001, many builders have modified the ceiling for a skylight instead of a fabric ceiling as Bob intended. Our intention was to come up with a ceiling modification where a skylight could be installed with no modification but fabric could continue to be used for those of us suffering through the heat of summer down South. Bob designed a system using 5052 aluminum of .050 as used on the fuel tanks.
As you see in the pictures, the very easy installation is to slide the Lexan in from the side for the two outer panels. The Lexan is captured on three sides by the channels made from the aluminum. This ceiling retains some of the “hump” in the middle so the fabric will behave if an all-fabric ceiling is installed. The aluminum channels are held by three “stand offs” welded to the tubing as opposed to the two that previously connected the ceiling to the tubing. After sliding the Lexan into place, it is screwed down to the square tubing above the upper longeron that follows the shape of the upper wing skin. It is recommended to use bigger holes (like 3/16”), then bush a #6 screw with nylon or rubber line. This helps prevent cracking as the Lexan expands and contracts differently from heat and cold than the steel or aluminum around it.
It should be possible and easy to install a Lexan panel on the center section also. A builder would use two additional pieces of the channel but facing the opposite direction of the existing channels running front to back.
At the factory in December, per Bob’s instructions – I showed the workers how to final drill the aileron and flap hinges to their spars after placing the ailerons & flaps in their correct positions.
Detailed photos of the new skylight accomodations:

Patrol: Installing the Flap Handle, Cables and Pulleys

The first thing to do is assemble the flap handle actuating tube, it is a simple matter of inserting the spring and tube inside the larger flap handle tube,(A). Builders often start with a spring that is too long and snip the spring off until the desired button pressure is achieved. Then you take the curved and detented flap position part (B), and insert it through the slot in the handle, and the tube that you put inside. Then the assembly gets sandwiched in between two tubes, (C), and a bushing, (D), is slid in place to hold it. You then bolt the detented flap position part at the top and bottom. The bushing gets drilled in place with the tube, and a cotter pin inserted, just like the rudder pedal bushings. Please note that in the following pictures, some fasteners are just temporary, or have temporary nuts on them.


Cables for the flap system are galvanized or stainless steel 1/8 7×19. The first cable is made up and connected to the bottom arm of the flap handle using a cable shackle, (E). It then runs through the lower two fairleads, around the first pulley and then under and around the second pulley. Make your cable so that you have approx 10 inches of cable after the second pulley, this is when the flap handle is in it’s lowest position (flaps 0). This cable then gets attached to the bottom of a triangular plate with a cable shackle. Remember to make the cable guards for the pulleys. What you are looking for in the final installation is to have the steel triangle as close to the pulley as possible when the flaps are in the full down position. This assures max travel of the flaps.



You will then need to make up two more cables that run from the triangle plate to the flap control horn on each wing. A turnbuckle on each cable end gets attached to the upper holes in the triangle plate, this will be for adjusting the cables later after you connect to the flaps, so make sure you leave adjustment in the right direction. The cables then run up to their respective pulley’s at the rear baggage station, go forward through two more fairleads before running under the final pulley just aft up of each flap control horn.




The final attachment is connecting the cable to the flap horn with another cable shackle. Here is a place that at times a larger cable shackle is used (1/4″) to help avoid interference with the wing rear spar end. This space is very tight. So be sure your cable, the flap control horn, or any of the attach hardware do not rub on the wing rear spar end as the flap moves through its travel range.
Remember to make sure the flap control horn (at the wing) is in the flaps up position, and the flap control handle is in it’s lowest position (closest to the floor), when making up your cable lengths. The position (angle) of the flap control horn is shown on the plans with the flaps all the way UP. Measure that angle and position it as shown on the plans.

These two drawings show the flap handle assembly, courtesy of builder Bruce Case:
Flap Handle Drawing A
Flap Handle Drawing B

Installing the Round Tail Spring

by Steve Busby, Aerolite Flight Services
The tail spring for the Bearhawk Patrol and Model B Bearhawk 4-Place has two pre-drilled holes, one at each end, to accept AN4 bolts. The socket for the spring, on the fuselage, has a hole pre drilled as well, so its a simple matter of lining up and bolting. The tail wheel has two holes so you will need to drill the second one once the spring is inserted. Make sure the tailwheel is properly standing vertical with no leaning to a side before drilling. And confirm the final hole sizes/bolts required by referring the the plans.
The spring is made of 17-4 Stainless Steel hardened to approx 44 Rc. Though it is tough, it can still be drilled. Use a new HSS drill bit, turning slow with steady pressure and some form of cutting fluid. A cobalt drill bit is preferable (NOT carbide) as it handles the hard, tempered material better.

Builder video from Ken:

Builder Bruce Case drew this nice diagram of Bob’s tailwheel assembly:
Bearhawk Tailwheel Exploded Diagram

Selecting Engine for the Bearhawk Patrol

by Steve Busby, Aerolite Flight Services

The Patrol can accept engines from 115hp to 210hp. The prototype is powered by an O-360 Lycoming 180hp engine, and this is the standard choice among most builders. It is up to the builder to decide on accessories and engine configuration, e.g. carburated vs fuel injected, standard mags vs electronic ignition. The kit is supplied with a Lycoming O-360 Type 1 dynafocal mount. This mount will work on all four cylinder Lycomings except the engines that have conical mounts.

If a builder wants to use a smaller engine, e.g. Lyc O-320, then you will want to keep weight in mind when building. 180hp is very adequate for the patrol, though, as the horsepower rating is stated, you can go higher. As an experiment on an early Patrol kit, we had a 210hp IO-390 in the shop, so we test fitted it to the kit. It bolted right on to the engine mount, but being an angled valve motor, was wider than a 360. To make the cowls look right, it was decided a wider firewall would be needed. We decided right then that the required mods were not worth the extra expense, complications and weight penalty.
The same kit as mentioned above, was fitted with a 195hp IO-375 Lycoming, with dual Pmags for electronic ignition. The accompanied pictures here show that installation, but a 180hp O-360 would be very similar, the large oil cooler being the biggest change. Though the performance with the 375 is amazing, a standard 360 will meet most everyone’s needs and will provide performance beyond most builders expectations.

Fairings

The wing root fairings are nothing more than flat strips shaped to follow and lap the wing root rib and slightly overlap the cabin structure on the top and not-quite-touch the fuselage on the bottom. The top fairing will be attached to the wing and to the steel fuselage tube. The bottom fairings are attached to the wing but not the fuselage.

Fairing Shape
The easiest way to work out the shape of the fairings is with posterboard available in the school supply section of your local grocery store. The fairings will be in three pieces: one in the front and one top and bottom. The front piece will run back almost to the spar and the top and bottom pieces will run off the trailing edge where they can be screwed together. Or, if you want to eliminate the unsightly joint at the back, you can make them out of four pieces with the fourth piece being a folded trailing edge piece that goes about a foot up the back of the joint, top and bottom.
The fairings will be joined to the wings with #6 PK screws and Tinnerman nuts, or machine screws and nutplates. The edge that bears against the airplane will have rubber “J” molding glued on the edges to protect the fabric.

Use grocery store poster paper to make patterns for the wing root fairings. Once you have the shape worked out, make the fairings out of .025 aluminum and fasten them to the wing root with Tinnerman nuts and PK screws, or nutplates at every third rivet. Where the windshield hits the wing, there will be some funky intersect angles, so don’t plan on putting screws all the way around he leading edge, as there will be gaps under the fairing.

Strut Fairings
The lower strut fairings aren’t screwed to anything. Their shape holds them in place. The gear fairing is screwed to the gear leg only Looking up at the bottom of the aileron hinge cut-out on the aileron. Tail of airplane is at top of the picture. A flat fairing is made with an inspection hole for the bolts.



The latest kits include upper and lower fiberglass strut fairings. If you will be making your own, the upper end of the strut can be nothing more than flat wrap aluminum. Neither of the fairings, top or bottom, are fastened to the strut in any way. The shape and strut-attach bolts locate them. These fairings are just one of many places in the Bearhawk where giving some thought to streamlining will net out free speed. Small details like those exposed bolt heads create drag and can add up.