Source: 2025 Q4 Beartracks, Bob Barrows
I have made and installed lighter weight door skins and floor sheets. Instead of using aluminum, I used carbon fiber and Kevlar. For the floor, use Kevlar layup, to about the same thickness as the aluminum call out. For the door skins, use carbon fiber about .025 thick, 2-3 layers. Lay up by using a sheet of .032 aluminum, about 2” larger all around than the panel needed. Apply three coats of wax to the face. Apply epoxy resin, lay first layer of cloth on wet resin, then apply a little more resin. Apply the next layer of cloth and poke it with a stiff brush until the cloth is a little wet from the underlying resin. Scrape the extra resin off to the sides with a plastic Bondo spreader. These panels will be about 1/2 the weight of aluminum.
I use the West System resins, selecting the slower variant (206) if I’m going to be working in hot temperatures, or the faster variant (205) for colder temperatures. A good starting point for these materials is Aircraft Spruce Part Number 01-01665 for the Aramid (Kevlar), or Part Number 01-01232 for the carbon fiber.
The West Systems epoxies are sold in various kit combinations starting with Part Number 01-08100 through 01-08400, depending on the size of the can and the hardener type.
The photo below shows the Kevlar hinge on the mouse door. This is a scrap piece of the same material in the floorboards. I start with a rectangle, then bend it in a brake to about 90 degrees. This breaks the plastic resin but the Kevlar fibers remain. It has a natural spring-back action and is good use for what would otherwise be waste.
Carbon Fiber Door Construction Using 3D-Printed Joints
Source: 2025Q2 Beartracks, Matt Clark
I wanted one-piece gull-wing style doors similar to what Virgil did on his BH5. I considered welding the window and door sections together or building from scratch out of steel, aluminum, or carbon fiber. I wanted to use square tubing to make attaching the plexiglass and sealing the edges easier. I’m better with composites than I am with TIG but my initial problem with the carbon fiber idea was how to make the corners strong.
When looking at carbon fiber tubing online I found some manufacturers sold corner inserts at normal angles like 45 and 90 to make strong epoxied joints. So, I figured I could 3D print corner inserts like those at whatever angles I needed and then wrap the corners with another layer of carbon fiber to make a very strong joint. I used 3/4 square 0.045 wall thickness CF tubing (Dragonplate from Allred co.) and 3D printed corner inserts using ASA-CF filament. The ASA is good with epoxy and the CF infusion makes it stiff and dimensionally stable. I created a 3D model in Solidworks for the corner insert and printed a few (many!) prototypes in cheap PLA or PETG. The top two corners are the easiest because those 3 pieces (top, upper front, and rear) are in the same plane. I measured each corner angle and printed those top 2 prototypes first. I had to print a few versions to get the angles just right. To get the angles perfect on the CF tubes I cut with an abrasive wheel and then sanded to fit.
1. Prototype Corner Insert:
2. Checking Fit
3. Fits Good
Once I was happy with the fit, I printed the corners out of the ASA-CF. I had to adjust the dimensions of the CAD drawings to get the ASA-CF part to fit snugly compared to the PLA or PETG. I epoxied those top 2 corners in place by clamping them into the door openings with approximately a 3/16 gap all around.
Top 3 Pieces and Hinges Tacked:
With those 2 corners secure I next worked on the hinges using 3/8” long sections of 3/16”ID stainless tubing on either side of the fuselage hinge tube very similar to the window hinge design. The stainless barrels were epoxy tacked in place. I used a clear 3/16 PETG plastic rod through all the stainless to keep them aligned during the glue up. I did have to adjust the hinges on the frame to provide more standoff to clear the square tubing and reinforcement CF (two photos below). I cut the outer welds, bent the barrels down slightly and then re-welded. I used a 3/16 solid brass rod through both hinges to keep them aligned while adjusting.
Hinge Outer Welds Cut:
Hinges Adjusted and Welded:
Once the SS hinge pieces were tacked in place on the top CF tube, I used epoxy with micro bubble filler to smooth the hinges out before wrapping them with carbon fiber.
7. Micro filler epoxy:
8. Sanded Smooth and Painted:
9. Unwrapping Hinges:
To wrap the hinges, I used 3 wraps of 3k carbon fiber, peel ply, and flow material. I then tightly wrapped the whole joint with electrical tape working from the middle out and let it set for the whole curing process under a heat blanket. The electrical tape wrap is a good way squeeze the excess resin out into the peel ply and flow material for a part that is difficult to vacuum bag. And the vinyl tape doesn’t stick to epoxy. The lower doors are a little more complicated as the front lower piece is curved and creates a compound angle at the 2 lower joints. For the curved lower pieces I clecoed a piece of .025 aluminum to the lower front door former and used that to trace the curve onto a piece of ¾” MDF. I cut kerfs into the inside of that piece without cutting through the 4th wall and bent it around the MDF form to glue the kerfs shut. Then I wrapped and vacuum bagged those pieces.
10. Lower front piece bent around form. The cuts are on the gold lines through only 3 walls:
11. Vacuum bagged lower pieces:
The lower corners have to allow for a slight twist to allow the square tube to be parallel and flush to the bottom former, so one leg of the bottom corner inserts is round to allow the bottom tube to be on a slightly different plane than the lower front. The round section isn’t as strong because it’s less surface area to epoxy, but that lower front corner will get a lot more reinforcement to mount the door handles there.
12. Final corner inserts for the lower 3 joints in ASA-CF:
13. Epoxy for lower corners
Once I had it all aligned perfectly in the door opening, I epoxied all the corners with the doors clamped into the openings just like I had done the top three pieces.
14. Curing in place within door formers:
15. Corners reinforced:
After the inserts cured, I reinforced each corner with an external wrap of carbon fiber using the same technique as the hinges, with the electrical tape compression. Once I figure out where exactly to mount the gas strut to the front upper tube, I’ll add 1 more wrap from the front hinge all the way to the gas strut attachment. To seal the front, bottom, and rear edges I’ll wet layup carbon and Kevlar around the edges just like Virgil did. Those pieces will extend ½” inside the frame to provide the lip for securing the window pane. This will also strengthen and stiffen the whole assemblies. To seal the top, weatherstrip will get squeezed between the top tube of the door and the fuselage tube as it closes. The lower front corners will get reinforced further to mount the door handles which will be the same as Virgil’s with the Z linkage to pin the front and rear. I’m planning to use a single pane of 3/32 Lexan for the windows. My door frames weigh 0lb 13oz compared to 4lb 14oz for the steel frames. Yes, there is more weight to add with the handles, windows, seals etc, but all those things get added to the steel frames too.
Summer 2024 Updates from Bob Barrows
Source: 2024 Q2 Beartracks
Work continues on Bob’s Companion project. As of press time he did a preliminary installation of the wings and has mostly completed the cowling. There is a mock-up engine that has no cylinders in place, and he has validated alignment and positioning of the engine, and is quite pleased with the kit’s conformation to the plans. The ailerons, flaps, rudder are covered, and the elevators and horizontal stabilizer are in progress. With the mock-up engine in place, the weight was 767 pounds. Bob feels like he is on track to meet the target empty weight of 1050 pounds. This build uses carbon fiber door panels instead of aluminum. Bob says it saves a little weight, and he’s pleased with how the carbon panels flex, drill, and otherwise behave much like aluminum would. To make them, he starts with a flat sheet of aluminum. He says you can also bend the aluminum if you want the part to also be bent. He applies lots of wax to the aluminum, draws out an outline of the rough shape of the panel, and paints resin onto the panel. Then he lays 2-3 layers of carbon onto the panel, and the next day, it’s ready for cutting to shape and installing. He made similar floor boards out of Kevlar, and figures those are 2/3 to 1/2 the weight of aluminum in the same application.
Bob and Diana recently flew the Patrol to Pence Springs, West Virginia for a get-together that included around 30 airplanes. They have a nice long grass strip there. Diana’s improved mobility and health are great news. She’s always eager to ride along whenever Bob flies. He says he alternates between flying his Patrol and LSA, just to keep both active, and enjoys both equally.
He has not been working much on his electric Ultralight project. It is still pending a new motor controller to up the motor output from 230 to 300 amps. Bob did design and build a new full-castering tailwheel for it, to improve taxi handling. The new tailwheel doesn’t attach to the rudder for steering but is easier to maneuver than the original skid. Bob says back when he flew his RV3 the tailwheel could either be swiveling or steerable, so he usually left the chains off and allowed it to swivel so that he could turn around more readily at the end of the runway.
Bob has been working on a solution for the Brake master cylinders that uses an EDM (electrical discharge machining) machine to make very precise fluid passageways inside of the bore. The EDM machine is well-suited for this kind of work and yields very smooth and precise shapes down inside the bore, based on the shape of a custom electrode.
Save the date for Bob’s Picnic on 10/19/2024 at VA04!
Carbon Fiber Gull Wing Doors
Source: 2023Q3 Beartracks, Rod Smith
I completed these several months ago. The latching system and gas strut installation was another task that took way too much time. I built the frames from 20mm square carbon tubes. The frames by themselves weigh 3 pounds each. That is a 6-pound savings each compared to building them from 3/4″ steel tubing. I used the hinges that would have been used for the windows. To reinforce the attach points in the carbon fiber, I inserted 1″ pieces of 5/8″ square steel tube into the upper tube before connecting the tubes. The lower door opening is raised 1-3/4” leaving 1/2” for overlap. I purchased Suspa gas tubes from Amazon to support the doors. The struts are 17″ extended, 10 3/4″ compressed. I initially used 20-pound struts that provided marginal support. One tube by itself would slowly collapse. Went with 28-pound struts that securely support the door. Hopefully will be able to taxi with the doors open. I used the Hendricks latches which are expensive but very well made. Figuring out the arrangement of the locking rods and levers took me a long time. I initially tried to locate the hole for the forward rod too high on the sheet metal former. It interfered with the vertical tube. My goal was to have the rods at 90 deg to the structure so the bushings would sit flat. It took me quite a while to realize that I could accomplish that by slightly bending the rods. Hendricks sells pre made rods and links. You need to make your own. I found the best price for the 3/8th aluminum rod and 1/2 x 1/8 aluminum bar at Wicks. For closing the door I think a handle separate from the latch handle is needed. I couldn’t find a suitable one so welded one from 3/8th steel tube. For the door trim, I laid up carbon fiber in place. It is one piece. It attaches with #8 screws through the trim, Plexiglas and into drilled and tapped holes in the carbon fiber tubes. I learned that was possible from Mike Patey, initially thought I would need long screws through the tubes. Plexiglas is .100, think that will work with the cross tube providing additional support. Total weight of the doors is 9 pounds. Would I recommend others build their windows or doors with carbon tubes? That’s a definite no. While it was nice to save 12 pounds, the extra time and expense was not worth it. I am going to love the view out of the full Plexiglas doors.
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.
Details of Bob’s Door Catch for the Upper Front Windows
I have had several request for a detail photo of the door catch used on the two Bearhawks. .032 2024-T3 is used to fabricated this catch – lightweight, simple and effective.
Utility Door System Photos & C.G. Testing Information
Load testing was done with 50 lb salt bags lashed to the floor of the cargo area. Photo 1 shows the doors closed and the cargo area empty. Photo 2 illustrates how 300 lbs of salt was secured for the C.G. testing of N33RB. Photos 3 and 4 show the Utility Door System closed and open.
1999 Engineering Notice Regarding Upper Front Door Hinge Positioning (416 and below)
Engineering Notices
Source: 1999 Beartracks, Bob Barrows
Reference plans number 416 and below, Drawing #16. As shown in the drawing below change the 5 1/2″ dimension to 5 3/4″ to increase clearance between door frame and bottom of the wing in the open position. If the fuselage is already welded up, adjust hinge location for needed clearance.
Bob’s Methods for the Cabin Doors
Source: 1998 Beartracks, Bob Barrows
The door system used on the the prototype and on the BEARHAWK currently under construction uses a two piece door on both the left and the right sides of the aircraft. This design has many benefits such as light weight, durability, ease of construction and the ability to fly with the windows open. There are no detailed drawings available for the door so this area is open up to the builders needs and ingenuity.
Using the two piece design the top section can be opened easily on the ground or when flying up to 120 mph.
As shown in the photos the frame of the lower door half is made from 3/4″ x .035 4130.
The tubing at the front of the lower section is curved to match the fuselage contour (see photo). The diagonal tube shown in the photo can be omitted to save weight. The latch mechanism used is by far the simplest, lightest and most durable that we could design. The details are illustrated below. The hinges on the front of the door are made from .100 4130 plate as are the hinges that are welded to the front fuselage door frame. The door should be built on the fuselage using heavy tack welds to hold it together. A 1/8″ gap should be maintained around the perimeter of the door. The outside portion of the door should be sheeted in .025 2024 aluminum with a 1/4″ overlap at the door/fuselage area.
The top section of the two piece door system also utilizes a frame of welded 3/4″ x .035 4130 tubing. The door is hinged at the top and a clip will hold it in the open position while on the ground. An aluminum skin of .025 2024 is attached to the tubing and is used to hold the side windows in place. The photos and the drawings show the needed details. As with the lower door a 1/8″ spacing is used around the perimeter and the aluminum skin overhangs the tubing (except at the very top) to act as a stop and a seal.
The latch used on the two piece door system is quite sturdy, light and easy to build. The hook gives you something to hold onto while opening the window in flight. The door really wants to get sucked up and bang against the bottom of the wing. Air pressure will keep it in the up position while flying. A small clip is recommended on the bottom of the wing to hold the door up while parked.
Updated Door Information
If you are planning on covering the interior of your doors with fabric you will need to add the vertical tube shown in the photo. This will keep the fabric from distorting the top tube.
1998 Beartracks Mailbag, Q&A with Bob Barrows
Source: 1998 Beartracks, Bob Barrows
Dear Bob,
This is a formal invitation to come visit us in this area on your trip to Alaska. It is sure to be an exciting adventure and I am envious of you actually planning it. I often talk about going to see my old flying instructor (Ray Krumrey) in Old Harbor, Kodiak Island but haven’t got there yet. It is one of my flights of fancy to fly there in the Bearhawk and do a big impression on him. Ray is a great guy and we became good friends as a result of flying.
David Giles (#222) wants to meet you. He is an SDA Minister who flies an RV-6 he built and is barely started on the Bearhawk his son and he are doing. He is a really nice fellow – one of your fellow Countrymen originally – and he visits me fairly often. I’m sure that there are others who would like to meet you too. Another reason for coming is that you will be right on course for the “Rocky Mountain Trench” which will take you right to your destinations in Alaska. It will be a comfort to you to know that you will be flying over a lot of paved road (emergency landing strip). Be advised that GPS is definitely a good idea as there are very few other Nav aids in this North Country once you get 300 miles North of the Border. I haven’t actually been over but I am told it is great!
Progress on the Bearhawk is slow and steady. My Son has already dubbed it with the moniker “Times Two” since I have made so many things twice! I keep telling him that those were “test pieces”! However, the fuselage is largely done and I am working on the little bits and pieces necessary before I move it off the reference plane of the dead level and flat workbench I built from three 16ft TGI floor truss crops. Used 4×4 legs with adjustment bolts in bottoms. Covered top with 4×8 plywood with one foot overhang. Using other shipping plywood, I made shelves between the truss ledges. This works well as they slide out and is a handy place to store pieces of tube right under the bench top. Simple, strong and flat and it can be disassembled as I put the legs on with lag bolts and left about 4″ edge overhang!
Have all the wing pieces built but have not done any skinning of them. I got tired of pounding aluminum and switched to building the fuselage. This winter I hope to make the tanks and a lot of the hardware pieces like seats, controls, levers and such. The main idea for me was to have a project to keep me out of mischief! It has worked but I have also derived a great deal of enjoyment and satisfaction from building (to this point).
Bill and his wife spend their winters in Arizona. He got me onto this design of yours and has been a great resource with all his experience. He and another of his friends are building an RV-6 each. He likes to get upside down once in a while, he says! He sold his Stearman. The Airline driver who bought it had to get some old timer to fly it back East because he couldn’t handle it. After getting it home, the nerd wrecked it within a week! Wheel landed on wet grass area and hit some puddles of water. End of story! $50,000 later … ??? All the best,
Rod Dressell – *190 – Creston, B.C.
Dear Bob,
Do we need to consider increasing the vertical stabilizer/rudder size, or add a dorsal (ventral) fin for use with floats?
Thanks,
Bob Thomasson – #280 – Santa Rosa, CA
Bob,
The rudder will not have to be altered in size to accommodate floats. The vertical fin area may have to be increased to counter the side area of the floats. A dorsal fin bolted to the bottom of the fuselage will accomplish this. Weld in a bushing for a 5/16″ bolt at station G-K and use the tail spring attach fitting to bolt on the dorsal fin. I am not sure as to how much fin area is needed – you will need to experiment, and talk to other float pilots. Bob
Bob,
Keep up the good work, your newsletter is invaluable! … Still working on the wings.
Thanks
Brad Young – #229 – Spearfish, SD
Dear Bob,
Just a reminder that we wanted to be put on the list as one of those who would order struts from you. Fritz and I put the wings on last weekend. We had the fuselage setting sideways in my garage with one wing in and one wing outside of the garage. The door was covered with plastic sheet so we could heat the place. It took a day or so to get things squared up and the wings are off now and tucked away in their rack until next spring when we can paint them.
We hope to be done by the first of April ’98 if things go well.
Tom Lee – *98 – Winona, MN
Dear Bob,
Well, I’ve had your Bearhawk in the back of my mind since I read the Sport Aviation article 2 years ago. I poked around the airplane a OSH last year but never got to meet you or talk to you about it.
My RV-6 is almost rebuilt – after being run over by a Chevy, believe it or not – and I am contemplating a project where I can learn some new skills.
I work for Dick VanGrunsven and can get almost all the materials needed very reasonably along with access to all the metal forming equipment you could ever want.
So – what I’m thinking about is a minimal, light airplane – but with a battery and starter, hooked to the lightest six cylinder engine I can find. Say an 0-470? Do you think this is practical for a guy with minimal welding skills but good teachers?
Enclosed is a check for your flyer & – I hope – a collection of past newsletters. I write the one for Van’s, so I like to read other peoples! Addresses of Western OR or WA builders would be appreciated too. Thanks.
Ken Scutt – Hillsboro, OR
Ken,
Thank you for your letter and the request for information on the Bearhawk. It is interesting to hear that you work for Van’s Aircraft and write his newsletter.
Many builders of the Bearhawk are doing this airplane as a first time project and learning the skills as needed, from knowledgeable EAA members.
Please find enclosed a data sheet, photo, a selection of newsletters and a list of builders in your area.
Thank You – BOB
Dear Mr. R. Barrows,
I have received the drawings for the Bearhawk: The drawings are beautiful!
For your super excellent work – I send my graduation!
Yours Faithfully,
#209 Stefan Kjorcev-#308-Oberglatt SWITZERLAND
Tim Neal #209 sent in this photo of his project.
A few questions as my fuselage is well on and I will need some answers to keep going.
1) For the rear door modification – you specify .032 alloy, would .025 be too light?
2) Will you be supplying a detail of the main doors in the newsletter?
3) What weight of alloy do you use for engine cowling – .020 or .025?
4) Routing of fuel lines from tanks and do you run separate line from the front and rear draw off points on tank and join to one in cabin or how do you do it?
5) Your method of attaching plastic sight tubes for fuel to alloy tank tubing?
6) Have you a fore and aft adjustable for front seats to seat long and short legs?
7) Some friends of mine at Oshkosh talked to you and took some good photos, a question on your exhaust system, by the photo: you appear to have 4 separate pipes, are they straight out and what is the noise like?
8) The trim system on your drawing #22; Do you need a friction disk or is there enough friction in the system? Is the trim chain a 1/4″ with a 12 tooth sprocket?
9) Positioning of wing attachment fittings on fuselage, the 32″ dimension is OK but the parallel dimension for both sides in relation to the spar fittings and lining everything up, my spar fittings are pilot drilled 3/16″, presumably the fuselage fittings should only be pilot drilled at this stage? These wings are quiet large compared to my Tailwind, so will you be giving a rundown on the fitting, lining up and setting dihedral, drilling and reaming holes to size, etc.?
10) Lift strut fittings, I have made up the wing end channel fittings, the double joggle in the fuselage end is somewhat more complex. What was your method of shaping? Also do you square cut the ends of the struts or angle cut to angle of wing and fuselage?
11) 1 know from a previous comment that you prefer a control stick and my Tailwind has a stick but I really want to have a yoke system with the Bearhawk. Much easier for females with a dress on and the floor remains relatively free of obstruction. Could I copy something?
12) Finally, the need for a fixed step up into the cabin like many aircraft have, my wife is not that tall.
Regards,
Ray Thurston – #5 – Blenheim NEW ZEALAND
Ray,
Good to hear from you again.
Regarding your questions:
1: .025 should be OK. 032 is better for the wear and tear resistance.
2: We will cover door construction in a upcoming issue of Bear-Tracks.
3: .025 is used. You may use .032 for the top.
4: The tubing is joined below lower front door frame with T section. (Upcoming newsletter)
5: Below is a sketch of what I recommend:
6: Yes – the same as a Piper Tri-Pacer. This system is nice in that as the seat moves forward it also rises lifting the shorter pilot up to see over the instrument panel, as it goes back the seat lowers giving the taller pilot more headroom.
7: I have 4 straight stacks out of the bottom of the cowling. I am told that they are loud but not unpleasant. I do wear earplugs.
8: No there is enough friction in the system.
9: See here.
10: I’ll cover the correct method for bending the end fittings in the next newsletter. Cut the strut ends square.
11: We do not plan to design such a system but you could copy the Tri-Pacer or a Cessna design.
12: A step is a builders option – check as designed on other tube fuselage aircraft.
Thanks for your letter and send us some photos of your project! ~ BOB
Bob,
I want to thank you again for your time and sharing techniques. I made another set of fluting pliers and they make a nicer crimp. I am also doing my rib lightning hole flanges a lot better, no warped ribs.
The idea of putting tape on the fluting pliers to keep from marking the aluminum really works. Thanks.
J.T. Newbegin – #284 – McAlpin, FL
Hi Bob & Mike,
Just got your newsletter, sounds like a lot of great activity with the builders. It also looks like you are getting close with Proto II.
I have enclosed a check for $250 for a pair of wing struts. I will be looking forward to getting them.
BEARHAWK 075 has fabric on it now. I am taping at this time and hope to have everything in silver in a couple of weeks.
The engine has not been installed yet, it will be a Ford Dura Tech 24 Valve 3.0 V6. I am converting the engine myself and have had to do a lot of searching to find an ignition/fuel injection computer system that I felt comfortable with. The original Ford system has too many extra input requirements and no adequate wiring diagrams.
After the engine is roughed in and the fuselage is on the gear I will send you some photos.
Have a great day!
Tom Yeomans – 075 – Richland, MI
Tom,
Sounds like you have made quite a bit of progress on your project. A lot of the builders may have an interest in more information about your Ford conversion. Keep us updated. ~ Mike
Chuck Frasier called the shop a few weeks back and had a question about the tail feathers. He was fitting up the elevator and found that the trim tab arm is rubbing the T-14 spar tubes on the horizontal stabilizer and the elevator.
To fix this you put a 10° – 15° bend in the trim tab arm under the elevator T-14 tube. You should clear the spars by a bit more than 1/4″.
Reference drawing #20.
Enclosed is a check for one pair of struts. I have finished a full review of the plans and worked out a material list. I bought all the .025 aluminum I’ll need and I am accumulating the other material.
Still trying to get my garage finished and other projects I had already started so I can start pounding out ribs. Is there enough strength requirement for using the 1/2″ X 1/2″ rib attach angles or can I make more than one forming block and bend up the end of ribs for attachment? I would rather make more forming blocks and save some weight unless the attach angles are required.
I have not seen in the October Sport Aviation article or in Bear-Tracks or in the plans any information on testing. Has the plane been flutter tested? Has the plane gone through flight testing such as dives to Vne, stalls at both ends of the envelope, light weight to gross?
Thanks for the help. Would sure like to see N6890R if you stop near Seattle on your way to Alaska this year. A visit to the Arlington fly-in would sure be nice for the west coast builders who can’t make it to Oshkosh but would like to see the BEARHAWK!
Wayne Hallburg – 266 – Centralia, WA
Wayne,
Thank you for the strut order – we will be shipping the struts (hopefully) before you read this. About your questions: Yes you can eliminate the angles if you wish but you must take into account the varying widths of the spars at different locations. The flutter testing was done during dives to Vne speed at 180 mph and stalls have been done at 1500 lb and 2400 lb gross with no unusual characteristics shown.
We are planning on attending the Arlington fly-in this year and hope to see you there. -Bob
Bob responds to a fax from Ray Thurston :
Ray,
In reference to your fax of 01/16/98 about the flap control assembly drawing #28: In checking the fit up on the BEARHAWK now under construction in my shop I did use the arm length as shown on drawing #28 but I offset it as shown below. In addition I moved the shock strut attach fitting (see drawing #24) up as high as I could and still have room for the rod ends HMX-76. This all gave me the clearance that I needed. ~Bob
Dear Bob,
Enclosed is a check for a pair of wing struts. I am also enclosing a photo for the newsletter. It is a picture of a die, made by Doug Jasper, for bending the flat plate pieces for the wing hardware.
It worked quite well and I think it is obvious how it works. He spaced the bars so that one side will bend .063 and the other side .080. I filed a radius on the edge of the male die, which is 3/4″ key stock, so one side does .063 and the other .080.
I just finished my steel wing hardware. I brought my flap and aileron mechanism to my EAA Chapter meeting last night and everyone commented on how nice they looked. Even had one person praise you for the engineering and how smoothly the mechanisms worked. I am now finally beginning to assemble my first wing. Slow but sure.
Pat Fagan – #232 – Pearblossorn CA
Dear Bob,
I am confused about the turnbuckles for the elevator where connecting to the bellcrank.
Drawing #26 says AN 135-32S Turnbuckle. I just ordered as specified and find on arrival when I was doing a trial fit that the pin eye is .25″ and yet the bellcrank says 3/16″.
The Cable eye likewise seems larger than required at .281″.
All parts are stamped and the turnbuckle is definitely AN135-32S. Would AN135-16S be more appropriate? Could you let me know?
Ray Thurston – #005 – New Zealand
Ray,
The AN 135-32S as called for in the plans is correct. You will need to make a bushing from 1/4 ” x .028 4130 tube, and use (2) AN960-416 washers as shown. ~Bob
While at Sun N’ Fun several builders brought pictures of their progress. Below is a photo of Larry Williams #184 project. Larry is using a Continental 0-470 for power. ~Bob
Bob,
I received the wing struts Saturday and the plans for the struts a few days later. Thank you. I received the cap strip material I ordered from Wicks last week and I bought some rivets to practice with over at the fly-in and flea market at Hampton Airfield on the coast of New Hampshire. I am a little nervous about starting the spars but I am sure that it will all go fine.
A friend of mine has landing gear and the gear shock struts that go on a 1947 108-2 and we were wondering if it would work on the Bearhawk. If so is it as strong as your design. What are your thoughts.
Sonny Cilley – #234 – Royalton, VT
Sonny,
I am sure that your spars will come out fine. It is just a matter of following the directions on the plans and in the newsletters.
The 108-2 landing gear system that you have is strong enough for the Bearhawk – but doing the engineering work to install them would be quite involved and time consuming. The time spent adapting the Bearhawk to accept the Stintson landing gear would be greater that just building the gear shown in the drawings. ~Bob
Bob & Mike,
It was great meeting both of you at Palmer, Alaska and I immediately dived into the plans and newsletters. Wish I had had the chance to study before going to Palmer but that is life in the frozen North.
As stated at Palmer, here is my check for a set of struts and drawings. I also want your wing construction and photo log, which will answer many procedural questions, I’m sure. May as well get the Disogrin ring set as I don’t want any delays for parts. While I have not yet ordered my 4130 and Aluminum, I have sent for all the books and catalogs recommended, made up a material list, made the wing rib form and acquired jig material (table) and a good shop to build in. All this since getting back from Alaska on August 12th. Being retired has its advantages.
I was in Alaska for about two months installing the water wheel power project for my friend. We are still evaluating the project, though the initial data
is quite favorable and slightly exceeds expectations after some modifications.
Hope all is well in Fincastle, do you think you might do Arlington again next year? I would like to have a list of Washington builders list and when available. In the meantime I will be attending the local EAA chapter meetings which I understand is loaded with talent.
Is there a drawing for the float hard points?
Just so I don’t miss any bets, please let me know your pricing for an 0-360. Thanks and looking forward to building.
Jack Piggott – #347 – Sequin, WA
Jack,
Thanks for the photos and letter. The struts have been mailed out along with the drawings and the o-ring seal kit. You should unwrap and oil down the struts when you receive them before putting them in storage. Mike has sent you a photo log that you should receive soon.
It sounds like you have really been chugging along on your project. Keep up a good head of steam because it is a long haul.
Regarding the float attach points, see the 1996 issue for rear float attach location, and use the front landing gear fitting for the forward attachment point. The fitting at the rear can be made just like the landing gear fitting if you like. We will work more with you on this area as needed. Do you have any idea what kind of floats you will be using? ~Bob
Mr Barrows,
Just a letter of introduction that is long over-due. I recently purchased plans s/n 188 from Mr Serge Valin the package also included the photo log and newsletters to October 1996. Enclosed is a check for all the back issue that I am missing and a subscription for 1999.
With any luck this winter will see me pounding out ribs. If there are any builders that are close to Detroit, I have access to a 10′ shear and brake for spars.
Mark Deacon- *188 – Brownstown, MI 734/789-1196
Mark
Your newsletters are on the way. I’ve included your phone number for builders in your area that may want to get in touch with you regarding the 10′ shear and brake. ~Bob