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:

The Wing Portion of the Flap System

Understand the Concept
Before doing anything on the flaps system pull out drawings No. 12 and No. 14. They will give you a good familiarity of how the different parts relate to one another and how they work. Also, study the photos in this section. They will clarify any questions. The flap system is quite simple in that it is nothing but a torque tube coming in from the root with an actuating arm at each end. At the root it is attached to a cable and at the other end a push rod is attached to the middle flap hinge and pushes the flap out. The flaps are held in the up position by the long springs included in the later kits or available from Bearhawk Aircraft for the older kits.
The procedures we’ll use to install the system include:
1. Install torque tube
2. Temporarily slide actuating arms into position on the torque tube
3. Position and drill outboard flap arm.
4. Install inboard flap lever, but don’t drill.
5. Install springs
Install Torque Tube
The torque tube slides through the steel stand-off bushing at the root and through a similar bearing stand-off at the mid-wing cross member. Before sliding the outboard end into the bearing, note that one of the outboard arms has to be slid in place first (see photo).
Because both the torque tube and the bearings have been painted, it’s a good idea to remove the paint from both the inside of the bearings and the area on the torque tube where the bearings will
ride. This not only makes it much easier to slide the tube into position but greasing the metal-to-metal contact makes for much smoother operation.
Drilling the Outboard Actuating Arms
Each torque tube has three actuating arms: one at the root (called the “lever”), and two outboard arms that work together to clamp the pushrod between them (see pictures). A hole needs to be drilled through the base of the arms and through the torque tube to accept AN3 (3/16” bolt) to stop the arms from rotating on the torque tube. Latest kits have the inboard arm welded in place. If this is the case on your kit, the sequence will be slightly different: don’t drill the outboard arms until the wings are in final position and you are able to verify the critical positioning of the inboard arm.
Many planes are flying with holes that were drilled to 3/16, though to give these bolts the tightest fit, you could instead drill with an 11/64” and ream to size to eliminate any possibility of slop in the holes.
For Kits without welded inboard arms:
On the outboard arms, first bolt the short flap push rod between them to hold them in alignment. Then clamp the top end of the push rod where it bolts to the arms down to the crossmember tube to keep it from moving while drilling it. With the outboard actuating arms still clamped against the fore and aft tubing crossmember, position the inboard arm as per Drawing No. 14. The root/inboard actuating levers have to be mounted at a specific angle on the torque tube to give the flap cables the most efficient angle for pulling, as depicted on the plans.
Because there is limited room between the fuselage and the wing root, it is essential that the inboard lever be centered in that gap. For that reason, don’t drill the hole through the inboard lever and torque tube until after the wings are on the airplane to ensure no interference occurs. Plans page 14 depicts the inboard lever in the “flaps up” position.
For all Kits:
When it is time to drill the arms through the tubes, center punch where you’ll drill the hole in the arms. Then drill one arm with a fresh 3/16” bit (make it fresh, so it cuts cleanly and easily). Then put a bolt in place to keep it lined up. Drill one outboard arm first, then install the pushrod bolt and tighten the nut. This will hold the other arm in place to ensure that it doesn’t become misaligned while drilling. If you want, you can install the flap springs now, which will help hold everything under tension and keep the arms and pushrod from moving. After drilling, disassemble and debur the holes. before final reassembly.
The Flap Actuating Cable
Later, after you put the wings back on the airplane semi-permanently and position the actuating arms and drill the mount bolt, you’re ready to attach the actuating cable. The flap arm was delivered with a 3/16” hole (AN3) hole, however you use a 1/4” shackle (AN115-32) rather than a 3/16” shackle (AN115-21) to give a longer distance at the arm, which increases cable clearance from the structure.
A 3/16” (AN3) bolt will be sloppy in the shackle so bush it down with short pieces of 1/4 x .028” tubing. If you can’t find that size tubing, contact Bearhawk Aircraft. Later kits include the bushings, some earlier kits have six inches of the tubing supplied, and you can cut your own bushings from that supply.

This photo shows the outer arms, along with the aileron cable passing by spanwise. Paint must be removed from inside the arms and off the torque tube to ease getting the actuating arms on the tube. Note how the pushrod is sandwiched between two actuating arms. Ensure that the aileron cable is routed above (toward the top of the airplane) the flap pushrod, which is not clear in this picture.

These two photos show the inboard end of the flap torque tube, along with the aileron cable.

Wing Parts Aft of the Rear Spar

Wing Template Use
You received a plywood wing template that is cut in the outline of the upper surface of the wing. This is your guide for establishing the correct profile for everything that will be attached to the rear of the wing. This includes flaps, ailerons and, in this case, the root and tip ribs. If you utilize the template for alignment, you’ll find everything is nicely lined up and the airfoil is accurate.
Root Ribs
Attaching the root ribs is quite straight forward, although there are several possible peculiarities
depending on when your kit was produced. The shortening of the bottom stiffener has been mentioned, but we’ll discuss it again in relation to the root rib. Briefly, in a few airplanes, the bottom flap bay stiffener is 3/4” too long and must be shortened to allow attaching the root ribs. Use the wing template to align the root rib and clamp it against the vertical stiffener in each of the root rib positions. Drill four #40 holes through the rib and the angle that’s riveted to the rear spar. Before drilling, make absolutely the rib is flush against the wing template.
Cleco both ribs to the spar attach angle and slide the pre-bent aluminum skin over the ribs and under the skin and above the flange. Notice on Drawing 2 that the rivets between the two root ribs going through the skins and the spar are AN426-4’s, NOT AN3’s.
On some older kits, if the supplied metal is flushed to the fuselage-side of the root ribs, it hangs into the flap bay by about 1/4” and partially covers one of the holes in the lower rear wing skin. If this happens, slide the sheet metal toward the middle of the airplane enough that it is flush with the flanges of the root rib in the flap bay and clamp it in place in preparation for drilling the rivet holes. Use a rivet spacing fan to layout an even row of rivet holes. After they have been drilled, remove the ribs and the trailing edge skins and debur and dimple all holes.
Trailing Edge Tip Rib
Because it is rather fragile, you can hold off installing the outboard, trailing edge rib until much later, when you’ve riveted down the top skin of the wings and are ready to install the wing tips. The wing tips will protect the trailing edge rib. An alternative is to install it temporarily by clecoing the wing skin down and drilling all of the tip attach holes in the ribs, skin and tip, so the wing tip protects the rib. Then remove it until ready to close up the wing. Regardless of which direction you go, install the tip rib the same way you did the root ribs: use the wing template to guarantee proper alignment and fit the fiberglass wing tip to the tip ribs, not the other way around.
The supplied plywood template is the key to establishing the vertical placement of both the ailerons and the flaps.

Left wing root. Notice how the bottom skin stiffener abuts the flange. You’ll use the plywood template for aligning the ribs.

Aileron Counterbalance Tube


This can be done at any time after the ailerons are hinged to the wings. To balance the ailerons we’re going to pop rivet an aluminum tube weighted with lead. In the early days of the Bearhawk 4-Place, the plans called for a 3/4” O.D. thin wall aluminum tube. This tube diameter was later changed to 1” to improve the flight characteristics of the ailerons. If your ailerons were built to accommodate a ¾” tube, realize that you’ll really need to pack the entire tube full of lead in order to achieve the correct balance. If you are building with ailerons intended for the 1” tube, you will have plenty of air left in the tube at the balance point. Look at the nose ribs of the ailerons to see the hole where the tube goes. It will be positioned spanwise between the two hinges, but there are holes in the rest of the ribs so that you can slide the tube in. Most hardware stores will carry a 6061 aluminum tube with the right dimensions. You’ll want to put 5 pounds, 4 ounces of lead in that tube. You can add a little extra with plans to drill it out before covering, if you prefer.
Although you can go through an entire balancing process in which you suspend the aileron by thread and estimate the fabric and paint weight and then determine how much lead you’ll need (see Russ Erb’s CD), the range will always be between five pounds and five pounds, four ounces. Since overbalancing is better than under balancing, use five pounds four ounces as the target.
Pouring Lead (small tube only)
If you are building with a ¾” tube, the best method is probably to pour molten lead to fill the tube. The lead will cool as it is poured into the tube, which will introduce voids. Mitigate this by having a helper preheat the aluminum tube with a propane torch. This process is much more dangerous than it seems! Use a face shield and respirator, do it out doors, wear welding gloves and make sure no moisture is present as it will turn to steam and blow molten lead all around. Stand the tube up and either make a wood plug for the end or stick it slightly into the ground to seal it. Support the tube with some sort of structure up high, because once you start adding lead it will want to fall over and that will likely set the place on fire. Make sure the can or ladle you’re using has a narrow spout or make a funnel from aluminum flashing.

Because the tube is so long and you want the lead to keep flowing, rather than cool on the way down, carefully warm up the tube with your torch. Remember, it’s aluminum and easy to melt, so don’t get it too hot. Because there is no airspace in poured lead, there will be too much in the tube, so be prepared to drill some out. When the tube is full, slide it in place and pop rivet it with stainless rivets.
Using Lead Birdshot (preferred method for the larger tube)
If your plane uses the larger tube, you won’t want to mess with hot lead and the corresponding safety concerns. Instead, fill the tube with bird shot. Go down to your local gun store that sells reloading supplies and get the smallest lead shot they have. You want nothing bigger than 8 1/2 (the bigger the number the smaller the shot) and finer is better as there will be less air space in it. If you can find number 12 shot, great! make sure it is lead because some places sell steel shot, which isn’t heavy enough.
Although some builders have made up a paste of lead and epoxy, that is difficult to get down the tube and the epoxy takes up space. Instead, we’ll only use the paste on the ends, since the shot itself pours in like sand. First, rough up the inside of both ends of the tube with coarse abrasive, 60 grit or so, to give an epoxy plug something to hang on to later. Tape one end closed. Fill the tube with the lead shot up to about 3/4” from the end. Make sure to lightly pound the tube against the ground, so the shot settles into place. Then, make up a slurry of epoxy (JB Weld is good) and shot that is mostly lead shot (for weight) and fill the remaining space with it as a plug.
Before plugging up the other end, weigh the tube. It should be at least 5.0 pounds and a little heavier is better. Turn the tube over and remove a little shot to give enough room to form another epoxy/shot plug in place and you’re finished with this process Now, slide it in place.


Lead Wool
Yet another way of getting weight in there is stuffing the tube full of lead wool. This looks like steel wool, but it is lead and is available from McMaster-Carr. The method of installation involves nothing more than forming plugs that look like cocktail wienies out of the wool, dropping them in and compacting them with a steel rod. Then an epoxy plug is poured in the end the same as with the lead shot.
Lead wool “wienies” are formed really easily and tamped down are nearly solid.

Trailing Edge Stiffener at Flap Bay

In earlier kits, you’ll need to install the stiffener that lays in the open area behind the rear spar in the flap bay, although it has been done by the factory in later kits.

The goal here is to attach the stiffener and have the back edge of the sheet metal remain perfectly straight. The reason we mention this is because, when a rivet is driven, it expands the hole very slightly and, unless you plan ahead, it’s possible to get distortion in the skin. It will manifest itself as a wavy or slightly curved skin. This can be avoided with just a little planning.
There are actually two stiffeners, one top and one bottom, and they overlap the flange of the rear spar and are flush, or very close to being flush, with the trailing edge of the skin. Wings have been supplied in several different degrees of completion in this area, as the kits were improved.

Drilling the Stiffener
In most of these cases, the stiffener has no holes in it, but both the spar and the skin are drilled and dimpled but an additional line of holes and dimples needs to be made between the spar flange and the edge of the skin. Use the front row of holes as guides to drill the stiffener and hold it in place while drilling the rear holes.
To visualize what you’re trying to do, look at Plans Page 9. You can drill the holes either direction, meaning have the wing right side up and drill from the bottom up (with the edge hanging off the work table) OR turn the wing over and drill down. Most people are more comfortable drilling down, but that’s up to you.

Clamp the Stiffener in Place
What follows is a general instruction of how to drill and install the stiffener. It is assumed the stiffener has no factory-drilled holes in it, nor is the second, rear-most line of rivet holes drilled in the skin. In most later kits the stiffener and all holes in the top skin and spar flange will have been drilled and dimpled. The bottom stiffener may also be finish riveted. If that’s the case, much of this can
be skipped.
The first step is to position the stiffener so it’s flush with the trailing edge (or close to it) but the front edge overlaps the holes in the spar flange enough to give a distance from the center of the holes to the edge of the stiffener of at least 3/16 inch (twice the diameter of the rivet).
Once you have a couple of holes drilled you can hold the stiffener in place with clecos and it won’t move while you drill the other holes. However, getting those first holes in without the stiffener moving takes a little forethought. The stiffener must be clamped in position until you have at least four holes drilled in it to accept clecos. Make one hole at each end and space two through the middle. To clamp the stiffener in place the best solution is about half a dozen side-grip clecos, or small C-clamps padded with masking tape to prevent marking the aluminum as you clamp the stiffener in place.

Drilling the Holes
Make a back-up block out of a six-inch piece of two-by-four or something similar that will be held against the stiffener and drilled into. This will keep the stiffener from flexing while being drilled.
You’ll use the existing holes in the skin and spar flange to drill the front holes in the stiffener. Drill a couple of holes in the middle of the stiffener. Put clecos in the holes, then space out three more holes evenly spaced down the length of the stiffener. Make sure none of the clamps have slipped.
Once you have those clecos in place, the stiffener definitely isn’t going to go anywhere so go ahead and drill the rest of the holes. Don’t start at one end and work to the other end as the stiffener will creep. Start at the middle and work our way out. Once the holes are drilled, debur them and, if they aren’t already dimpled, dimple using a squeezer, but don’t squeeze too hard or you’ll get distortion.

Riveting the Stiffener
While it is entirely possible to simply drop the rivets into the holes and whack away with a squeezer, chances are you won’t be satisfied with the result because it’s hard to keep the trailing edge straight and from curving as the rivets expand and push the aluminum around. However, there is a way to prevent that. Buy a heavy, extruded aluminum angle (1/4” thick, 2” or so wide) and squeeze the rivets using the angle as both a straight edge and as an interface between the squeezer the heads of the rivets. The procedure is as follows:
1. Drop all the rivets into the holes.
2. Position the stiffener over the rivets.
3. Lay the angle down over the rivets.
4. Clamp the angle and stiffener together. Make sure it’s clamped tight in about a dozen places.
5. Adjust your squeezer to properly compress the rivet by squeezing the angle against the
rivets.
6. Don’t rivet in a straight line. Do several in the middle, the end rivets, then every third one starting in the middle and working out. Then come back to the middle and, working your way out, finish the rest of them. Using this technique, you won’t drive the expansion all one direction and will limit distortion.

Mismatched Stiffener/Rib Intersection
A few wings were shipped with the lower stiffener riveted in place but it is about three-quarters of an inch too long and has to be trimmed to let the flap bay root rib fall in place. Just drill out a couple of rivets and cut three-quarters of an inch off the inboard end of the stiffener. A Dremel tool is the easiest way to cut it. Protect the wing skin beneath by inserting a piece of aluminum scrap.

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

Bearhawk 4-Place Door Installation

The doors are one of the features what make the BH a uniquely useful airplane. Besides giving numerous ways of getting in the airplane, the doors let you load some really large, ungainly cargo and carry it with ease. They also hold the key to making the airplane into a flying motorhome.
On your quick-build kit, the doors are easy to mount. Clean the paint out of the hinge holes with a 3/16 drill, and insert either an AN3 bolt or 3/16 Clevis pin, depending on your preference. There’s no need to install cotter pins yet, you’ll be taking the doors off and putting them back on several times.
The Latches
The kit comes with the latches as shown in the plans, and this is the best reference on how to install and tune them. An alternate latch is available from Aircraft Spruce, PN 05-04520/21, which some builders prefer. This latch allows closing and latching the door by just lightly slamming it, which is a great convenience. If using the alternate latch, be sure to provide a thin stainless steel sheet striker plate on the door sill where it will be hitting.

Skinning the doors
Temporarily hang one of the doors in the fuselage to get an idea of what you’re trying to accomplish. The door skins must go out far enough past the frame that they chin themselves on the outside door frames. They then also provide a surface to which weather stripping can be attached. A gap has been purposely left between the door and the frame so it can be sealed properly.
Sealing the gap is necessary to make the airplane weather tight. It also cuts down on the wind noise and increases the airplane’s efficiency. Sealing can be left until the airplane is flying.
.025 2024-T3 is the usual choice for skinning the doors. It is light, tough and easily worked. You’ll also use it for making the outside frame for the top half of the front doors. Windows can be held in place with small “L” shaped strips, or they may be sandwiched between the aluminum skin and steel tube (more detail further down).

To work the aluminum, an inexpensive sheet metal apron break like that available from Harbor Freight will work fine and you’ll find yourself using it for many other applications as well. One of the commonly available shear/break/roller combination tools is slightly more expensive, but makes working all of the aluminum pieces much easier and more exact. It should be noted that all of the cutting can be done with hand shears while two C-clamps and a couple pieces of angle iron can do the bending. Having the brake, however, makes neater bends. The skinning process is the same for all of the doors except the rear cargo door, as that requires several slight bends in the middle to conform to the fuselage/stringer shape.
The skin can be attached to the door frame with common 1/8” “pop” rivets although it is suggested that a filler be put in the rivet head holes to weather proof them and to improve appearance. Also, for appearance sake, some builders have used counter sunk pop rivets by lightly machine-countersinking the skin, which is actually too thin to counter sink, so it cuts slightly into the tubing underneath. This is okay because the doors aren’t primary structure.

Sealing the Door Frames
Some of the earlier kits have open tubing in the door frames and it is suggested that wood or plastic plugs be epoxied into the ends of those tubes to make them weather tight.
Door Sill Protection
Although it isn’t necessary, some builders will fabricate an aluminum or stainless steel scuff panel for the bottom door sills to keep careless feet from wearing down the fabric. This will naturally need to be done after covering.

You’ll want to devise a method for holding the front windows open. Here is one: https://bearhawk.tips/2147, here is another: https://bearhawk.tips/1637, and here is another consideration: https://bearhawk.tips/1742.
The front rear door can be held open with a small gas cylinder, with most builders using one rated for 20 pounds. The rear rear door will stay open thanks to gravity, but you’ll need a short length of cable to keep it from opening too far. A spring will help dampen shocks to that cable.
The Wing Strut “Mouse” Door

The little flap on the bottom of the front doors is necessary to get additional travel in the door for entry. It is nothing more than a piece of .025 aluminum attached to the door with a piano hinge. No spring is necessary as it automatically closes when you close the door. A piano hinge is attached and the mouse door skin is lapped to the inside of the main door skin, so that when the door is closed, the mouse door is automatically sealed shut. Note that there is a slight break at the edges of the door skin to give a better seal.

Note: to protect the paint on the wing strut, put a piece of clear teflon tape where the door flap touches or it’ll eventually scuff the paint. Bonding on a nicely trimmed and polished piece of .016 stainless would look good too.

If you prefer to install decorative indoor trim pieces, they can be screwed or riveted directly to the door frame directly, just as the skin was on the outside.

Installing the Windows
Make the windows out of .080-.125” Acrylic. Allow for expansion and contraction by drilling the holes oversize, using a special drill bit intended for acrylic. When installing them for the last time, run a small bead of caulk at the edge where they contact the door.
If you’ll not be sandwiching the clear panels between the skin and tubing, first make the outside frame cover and rivet it to the frame. Then make up some 3/8” x 3/8” angles using .025 aluminum. You’ll need to cut enough that you can run these angles inside the door window frames all the way around the window. Attach them with small sheet metal screws (PK screws) into the door frame but NOT into the acrylic. The acrylic is just clamped between the L-strips and the door skin.
Before setting the side/rear windows in place for the last time, put some sort of sealer into the channel or where the window will sit. The butyl strip used for sealing corrugated roofing works extremely well. If you’re going to use a caulking material be advised that if you use silicon, it is also a glue and could be a mess to clean up and get a clean edge if you aren’t careful during installation. Mask the windows leaving just a small area for the caulking and it’ll clean up much easier .
Note: There are two primary materials available for the windows, polycarbonate (Lexan is a name brand) or acrylic (Plexiglas is a brand name). Speaking broadly, acrylic is less strong, but more fuel resistant. There will be a fuel quick drain right above the front windows, and some builders have found the Lexan more likely to be damaged by the fuel exposure here. In the original (not model B) Bearhawk, the rear windows are bent slightly, and some builders have found that acrylic crazes at the bend points over time.

Selecting Tires, Wheels, Brakes, and a Tailwheel

Brake Selection
You’ll need to have some brakes and tires fairly early in your build process if you are planning to install the gear legs and keep the plane on its gear. The best strategy is to find a run-out set of any kind of tires that will fit your wheels. Use those until you are ready to fly, which may be years from now, and then purchase a fresh set just before your first flight. Rubber ages unfavorably whether you use it or not. Check at your local flight school for a set of 600×6 tires, which is the size most often used on the main wheels of small Cessna trainers.
Just as with choosing an engine, deciding on your wheels and brakes will require deciding on how you plan to operate the airplane. The financial outlay is not as big as it is with an engine, but it is still significant. The main players for the 4-Place Bearhawk will be Cleveland, Alaskan Bushwheel, and Matco.
Cleveland sells two suitable wheel and brake kits. The 199-62 package will fit large and small tires, and the 199-60 kit will only fit 6.00×6 tires. There are two differences in the kits. The 199-60 has a brake disk that sits ¼” closer to the tire, and the torque plate has shorter lugs. This set is ideal for wheel pants, since the overall width is less. Most Bearhawk builders will be better suited with the 199-62 package, which includes the deeper brake disk and torque plate with longer lugs. See 2016 Q2 Beartracks for more details on the part numbers.
Alaskan Bushwheel makes a wheel and brake package that is interchangeable with the Cleveland 199-62, and sometimes their price is lower. In any case, they are still very expensive.
Grove wheels and brakes are very popular with Bearhawk builders. They are available as single puck brakes (for use with normal aircraft tires up to 8.50’s) or double puck brakes which are required if you ever want to use bigger tires than 8.50’s. Groves are available in aluminum or magnesium.
Matco also offers a package that is suitable for the Bearhawk.

Tire Selection

There is a real tendency to think big tires are necessary to land on grass and dirt runways, which simply isn’t the case. The normal 6.00×6 tires will handle most surfaces 95% of Bearhawk builders will ever see. If the landing surface is called a runway by most people, then the smaller tires are fine. If you’ll be landing on rutted or rocky surfaces, the bigger tires will be necessary. Moving up to 7.00×6 tires will give you added margin and will cost almost nothing in performance. Below is a chart comparing the commonly available tires and their rolling diameter. Notice the big jump from 8.00 to 8.50 x 6.

Tire Size Diameter Width
6.00 17 6.3
7.00 18.25 7
8.00 19.2 7.95
8.50 22.1 8.85
26” Goodyear 26 10

Tailwheel Selection
The Bearhawk is designed with the main wheels pretty far forward, which greatly mitigates the chances of nosing the plane over. The other side of this trait is that there is a lot of weight on the tail. Many tailwheel assemblies that were designed for light taildraggers are simply not up to the task. There are only two tailwheel options that we recommend. One is the assembly designed by Bob and available from BHTailwheels.com. The other candidate is the Scott 3200 (pictured last), though many builders don’t find the Scott to be as cost-effective.

Casting the Elevator Balances

Safety Note: Do not melt lead or otherwise work with it without wearing safety glasses and a respirator and do all lead work in a well ventilated area.
The plans and Beartracks both mention balancing the elevators with lead and, when the word “balance” is used, that means putting enough lead in the balance area (the part sticking ahead of the hinge line) so that, when the surface has paint and fabric on it, it will balance horizontally across the hinge line.
There is a little guess work here because you can’t balance the surface when it has the fabric and paint on it, so you have to make an educated guess as to how much fabric and paint weight will have to be balanced. See Bob’s Bearhawk Book, pg.29 for more detail. This is done by folding up the approximate amount of fabric that will be used to cover the tail and laying it in approximately the center of the elevator surface. At the same time, you’ll have to add a little weight on the fabric to simulate the paint/finish. Fortunately, the tail doesn’t have to be balanced exactly. Casting the weights isn’t as complicated as it would first appear because you are going to actually cast them in position on the tail by making up some crude forms and dams to contain the lead. A word about lead: its fumes are dangerous. Only work outdoors and preferably with enough of a breeze to keep the fumes away from your sensitive nose. Also, don’t underestimate the energy available in molten lead! It will readily start a fire if allowed to contact flammable material like wood or vegetation. You must use a respirator, heavy gloves, and safety goggles, but a full face shield is better.
Some builders have been able to get lead weights from tire shops. If you use tire weights, realize that some are zinc, and you don’t want those in your mix. If you can’t tell the difference from handling them, hit the weight with a hammer, and see how soft it is. The softer weights will be lead. Don’t worry about the steel clips, they will float up to the top once the lead melts. You’ll need a small cast iron pot or ladle to melt them in, although a coffee can and a pair of vice grips will work. A long, feathery flame on a welding or propane torch is all you need to melt them. Just play the flame directly on the lead and keep your face away as all sorts of fumes come up as the oil and dirt on the weights gets cooked. Make sure your weights are dry so they don’t generate steam that can cause the lead to pop.
When the lead melts, the steel attach hooks and all of the impurities will float to the top and you can easily skim them off (it’s called “dross”), then you have lead that is ready to cast with. If this process isn’t going as you’d expect, watch some of the many Youtube videos on the subject. You’re going to cast the lead right in place on the elevator so your mold is going to be built around the tail and it’s really pretty simple. First drill a few holes in the tabs welded into the balance area to give something for the lead to hold onto. You might even put a screw through the tabs but make sure it doesn’t protrude above the surface of the lead. Also, run a few screws into the tubing and let them protrude. You can also run a couple screws through the rib surface. This is all to give the lead something really solid to flow around and lock it in place.
Next, procure your mold pieces. Some builders have used thin plywood, but realize that the plywood is going to leave behind a rough texture that matches the grain, and it is going to scorch and smoke. You’ll probably want to remove this texture before covering. Another option is to use ¼” aluminum plates. Clamp your pieces to the upper and lower part of the area that will receive the lead. That forms the surfaces of your mold.
If you are using aluminum plates, preheat them by playing the flame of the propane torch over the plates just before you pour. If you are heating with an acetylene torch, be careful not to burn a hole in the aluminum. The flame temperature for OA is around 5000 degrees C, for propane it is around 2000 degrees C. The melting point of most aluminum is on the order of 660 degrees C, and lead is 327.
Now, melt your lead and pour it into your makeshift mold. Once it cools, you can rough shape it with a cabinet rasp and 60 grip sand paper. Clean the rasp often as it’ll load up very quickly.
An alternative to casting is to mix a slurry of lead shot and epoxy. This will require a larger volume for the same weight but isn’t hazardous to your health.
Regardless of the particulars, be positive that the lead weight is not going to come loose after you have covered the elevator.
Now, install your elevator on the horizontal stab making certain the hinges are lubricated (light oil) and free. Put your dummy fabric and paint weights on the bare elevator and see if it appears to be balanced.
It’s probably not but it’ll be close and, if you intentionally cast on the heavy side, then you can balance it by gradually drilling weight out.

Pouring lead. Note form is just 1/4” plywood clamed tight to tail. Drill holes in tabs and put screws in edge of tubing before pouring. to give lead attach points USE A FACE MASK, RESPERATOR AND DO IT OUTSIDE OR WITH PLENTY OF VENTLATION. LEAD IS NASTY STUFF


Here are three photos of the Model B version of the process from builder John Reddick:


4-Place Control Stick Assembly


General Considerations
When installing the control stick torque tube and its related items, don’t worry about where the control stick itself is in relation to the seat or in relation to the length of your arms. That is all adjustable by varying the length of the pushrod to the bell crank to make the sticks sit right where you want them. You do, however, need to pay some attention to where the torque tube assembly mounts in relation to the fuselage mounting tabs and in relation to the aileron cable pulley at the bottom of the struts.
Cable/Pulley Alignment
The stick assembly needs to be attached to the metal brackets on the fuselage so that the aileron cables coming out are as closely aligned as possible with the pulleys on the fuselage sides and with those further back in the fuselage in the belly. They can be out of line just a little, but you should strive for perfection.

Bolting the Assembly in Place
Be careful where the bolts that secure the stick assembly to the fuselage tabs fall. If you move the stick assembly too far aft, you will not be able to get nuts on the rear bolts because the T19 tube at station C will interfere. Again, the idea here is to align the cables to relation to one another, e.g. where the torque tube mounts to the fuselage tab, the pulleys at the fuselage sides (at the bottom of the wing strut) and back in the belly.
Bolt the rudder and stick assemblies directly to the tubing structure. Take note that it is standard aircraft procedure that all bolts holding parts that are subject to rotation are drilled and secured with castellated nuts and cotter pins, not nylon/elastic lock nuts. This applies when the bolt is the bearing in a moving part. Where the torque tube mounts to the fuselage tab, elastic lock nuts are acceptable.
Elevator Cable Routing
The stick assembly is connected to the elevator bell crank via a small pushrod with a rod end bearing on either end. Then the elevator cables are routed from the top and bottom of the bell crank and aft through the first pulley bracket towards the tail of the airplane.
Install the three pulleys, as per the drawings. This is a case where it is acceptable to use elastic stop nuts, as long as you tighten the nut fully. The inner race of the pulley bearing should not rotate on the bolt. The cable at the bottom of the elevator bell crank passes through the middle pulley of the three pulleys on the bottom of the airplane. The cable coming from the top of the elevator bell crank runs through the far left pulley (looking forward). Just for future reference, the flap cable goes through the remaining (right-most) pulley.
You need to make spacers to keep the elevator bell crank just aft of the torque tube at the front edge of the seats from moving left and right. To prevent the spacers from rotating, drill a hole through each of the tubes and insert a cotter pin. It is a close fit with the cable coming from the flap handle, so make sure there’s no interference before you finalize the side-to-side location of the elevator bell crank.
When routing the elevator cables through the aft fuselage, only the cable that attaches to the bottom of the elevator horn goes through the fairlead that’s located about half way back. The other cable floats in space.