Making Bending Dies to Bend a Radius to Fit Around a Tube

Source: 2025 Q4 Beartracks, George Huntington
MAKING BENDING DIES TO BEND A RADIUS TO FIT AROUND A TUBE: This trick is great for matching a bend radius to a tube, such as aluminum panels that might be installed under the cabin doors and wrapping around the longerons. First, find a thick tube whose inside diameter matches the outside radius you want.
-use the procedure from the this tip to get a straight line on each side off the tube, then cut the tube in half lengthwise. Clean up the edges and cover them with masking tape, so as not to mark the aluminum sheet when bending.
-now using a tube that fits into the half tube with some clearance for the sheet aluminum you are using, place it into a vise or use “C” clamps to form the sheet aluminum into a nice radius. This works good for the elevator cable attach access at the tail, and the kick panel at the entrance. It also makes a nice large radius like I used for my gear fairings.




Duplicating Fitted Tube Ends with Paper Templates

Source: 2025 Q4 Beartracks, George Huntington
DUPLICATING FITTED TUBE ENDS: For example, if you have fit a tube for one side of the fuselage, and want to make a second tube for the other side:
-Stick a small piece of 2-sided tape place between the two tubes at each end, then wrap masking tape around both tubes near the ends (leave a space for marking). This helps to hold the 2 pieces of tubing secure without either one turning.


-Next take a new box cutter blade and using the back side, draw it across the sides of the tube. This makes a perfect straight line down the tubes, as you just remove the manufacturing scale. Be careful not to press too hard, as you only want a nice fine line. A small fine file works good for this step also.
-While the two tubes are taped together, the other side can be marked also, giving you a nice center line on both sides. This can be useful in drilling a straight hole, by drilling from each side.
-Take a piece of paper and wrap it around both ends of the fitted tube, slightly overhanging the coped ends. Tape the paper to itself, but not too tight as you’ll want to slide it off of one tube and onto the new one. You can also use a rubber band to hold the paper in place while still being able to move it around.
– Use a half round file on each end of the tube to remove the excess paper from the fitted ends. The file is cutting the paper where it is rubbing the paper between the tube end and the file. When done, the paper will have the exact shape of the fitted tube.
-Next take a sharp pencil and mark the other end of the paper, corresponding to the center line that you scribed on the tube. Measure and record the distance between the 2 pieces of paper, or the total length of the tube.
–Slide each paper off of that first tube, and onto the next tube you want to cut to fit. Set the length and align the pencil marks with the scribe mark along the length of the tube. Using a felt marker, trace the paper’s outline on the ends of the tube. Now the tube can be trimmed to make a duplicate tube.
If you want to make the same tube but mirror it for the opposite side of the fuselage, untape the paper templates and roll them up opposite way around the tube, making sure you can still see the pencil marks for the centerline. Install them as above, mark and cut the tube. Now you have made a left and right tube.

Welding – Kit Builders Introduction

Quick-build kits are completely welded and painted. If for some reason you need to weld anything on your fuselage, it is important to find a welder with the right kind of experience. “Welding” is like “painting” when it comes to terminology. You wouldn’t hire a house painter to paint your portrait and vice versa, even though they are both correctly described as painters. If you can’t find someone with tube and fabric airplane experience, look for one who uses a TIG or Oxy-Acetylene process and can handle the very thin tubing in your parts (.028 inches, for example). Avoid other welding processes, such as MIG and stick welding, even if the welder says it should be fine. If that happens, perhaps it is best to avoid that welder, because he doesn’t know what he doesn’t know. We know of experienced welders in a few parts of the country, so feel free to ask if you have trouble finding a good one.
It is important that the 4130 steel not cool too quickly after welding. Ensure that the shop temperature is comfortably warm and that the air is not moving around the cooling weld. If the weld cools too quickly, it may crack now, or later in service.
After welding, remove all contaminants. This is best done by media blasting. Your steel parts from Bearhawk Aircraft have been painted with a yellow primer (MIL-P-23377E epoxy Strotium Chromate) and a top coat (MIL-C-22750D) in gray. Select a primer and paint system that provides similar performance, and most importantly, that will be compatible with your final covering process. Polyfiber offers EP-420 epoxy primer, for example. We do not recommend powder coating.

Tool for Holding Tabs in Place While Welding

Source: 2017 Q3 Beartracks, Shawn Burns
Shawn Burns made this handy jig for attaching tabs to steel tubes. It’s similar to the design published by Eric Newton, but some builders might find Shawn’s arrangement slightly easier to use and make. In the photos, the cleco is holding on the tab that is to be welded. The middle photo shows how the jig holds the tab in place for tacking.


Bob’s Preference for Oxy-Acetylene Welding

Source: 1997 Beartracks, Bob Barrows

~ The two welding samples of 4130 tubing to the left were provided to us by Carl Adams.

The sample on the far left was TIG welded and was worked back and forth twice – then it broke! As you can see the tube became brittle just above the weld.

The near side tube was welded with OXY-ACETYLENE. Carl worked it back and forth SIX times and gave up.

We have always recommended gas welding because it is a proven way to join aircraft tubing. It is also one of the cheapest outfits you can buy and get started welding with.

Welding Distortion Mitigation

Source: 1997 Beartracks, Bob Barrows

After welding the tail feathers together be sure that frame is flat and not twisted. Also check to see that all tubes are contoured properly and not warped by welding. Heat structure as required to properly flatten and straighten.

Tubes in all welded areas can be straightened as shown below.

Heat red hot about 1″ long and on opposite side of welded area.



After cooling



This photo shows one of the horizontal stabilizers in the jig after welding. This is the best way to check to see that all dimensions have been held after welding.

1995 Beartracks Mailbag

This is a combined list of mail Q&A from the 1995 Beartracks issues.

Dear Bob,

You have mentioned that you have the drawings for the wings of the BEARHAWK ready and had sent some out to builders in the U.S., at first I thought that I would leave it until you had the fuselage drawings ready as well, but on second thought I too would like a set to study and perhaps organize materials and you could forward the remaining drawings later. Bob, I have a few questions which I may need to give our Civil Aviation Authority some answers to when talking to them about the BEARHAWK.


  1. What are the FLAP SPEEDS?
  2. What is the MAXIMUM MANEUVERING SPEED?
  3. Do you know the approximate GLIDE RATIO?
  4. Do you have a maximum “G” operating figure?
  5. Based on your experience so far with the BEARHAWK do you consider there will be sufficient fin and rudder area to control the thrust and torque with a 260 hp. engine?
  6. What is the range of the C of G and where is the datum?
  7. Do you have a sample C of G calculation at M.A.U.W. (Max Load) and with only the pilot and minimal fuel?
  8. Do you have a rough idea of the material costs for the fuselage and wings without engine, instruments, seating and cabin finishing?
  9. Did you give any consideration to fitting Wittman type spring steel undercarriage as fitted to Cessnas as opposed to to the bungee type? If you ruled it out for a particular reason could you tell me why. I noticed that some aircraft have treated alloy 7075 I believe in their undercarriage, I don’t know how good it is.

Regards and best wishes.

Ray Thurston – Blenheim – New Zealand

Ray,

I sent your wing drawing by air post on Jan. 19, 1995. Please mark in on drawing #1 your serial number 005. Listed below are answers to most of you questions:


  1. Flaps can be dropped at 90 M.P.H. @ 1.5 g’s. I am still experimenting with different flap settings. Currently the BEARHAWK has 5 flap settings at 10 – 15 – 25 – 35 – 40 degrees respectively.
  2. Maneuvering speed is 110 M.P. H. at 5 g’s.
  3. Glide ratio is approximately 9 to 1.
  4. Maximum “G” allowed 4-1/2 @ 2400 lb. and 5 @ 2300 lb.
  5. Rudder control vs. torque looks OK for 260 hp.
  6. C of G range 9″ to 22″ of leading edge of wing. (Note: later changed to 10.5″ to 22.5″)
  7. See weight and balance sheet (upcoming, January 1997).
  8. Estimated cost (U.S.) for the fuselage and tail tubing is $1200.00 and for the aluminum is $1500.00.
  9. The BEARHAWK has a homebuilt spring / oil system of a simple design, similar to that used on a Maule. This gear is lighter than spring type and offers far less rebound.

I hope that answers most of your questions and please stay in touch.

Bob

Bob:

Enclosed please find a check for the second half of the BEARHAWK plans. As for my progress, I do not plan on starting until June. I have however, spent considerable time studying the first half of the plans. This has naturally generated several questions which I would greatly appreciate getting your input on.


  1. On aluminum sheets, how do I determine the grain orientation of the metal and what should that grain orientation be on the spar web, ribs and wing skins?
  2. What welding technique do you use on the steel tube components, gas, heliarc, etc.?
  3. A recent article in SPORT AVIATION concerning the merits of various types of welding rod has left me overwhelmed with concerns. I have been welding for over 10 years using classic gas welding techniques and mild steel rod- I have never had any problems with my welds. I would like to know your opinion on the issue raised in this article and what type of welding rod you use.

Gordon Champion – Deep River – Ct. – serial #004

Gordon,

Grain is determined by the direction of the printing on the sheet aluminum; however, grain orientation is not a problem while your aircraft is under construction. Stress levels are within limits for either direction. Be sure to use proper bend radii to insure crack free parts.

As for my preferred welding technique I use gas welding (Oxy. – Acetylene), Tig should be OK as well.

The article you mention has raised concern with other builders also. I am recommending that you stick with mild steel welding rod. Airplanes built with 4130 tubing have used mild steel welding rod for years with almost perfect results. Alloy rod can be a big problem with cracking and brittle failure.

I hope that answers you questions. Let me know when you start construction.

Bob

Dear Bob,

The remainder of the Bearhawk drawings arrived so I have now worked out the quantities for the 4130 and other pieces on the fuselage, and have been in touch with Dillsburg Aeroplane Works.
I have ordered all the aluminum from Airparts in Kansas and that is due here in a container ship later on this month.

Meantime, I have constructed a long level work table the same as I had when I built my Tailwind, it is somewhat longer at 20′. I have also located a pair of Lift Struts, something I thought would not be available here.

Following your instructions in the newsletter I have made up a rib former and made up an end rib with some scrap to check it out complete with lightening holes, the wooden tool for flanging worked perfectly. I have a pair of fluting pliers which I made some years ago, everything else I need I either have or can obtain the use of.

I am retired so I have plenty of time, fortunately my wife likes gardening so that lets me off the hook there, although I do help by cutting lawns etc., perhaps I am a little spoilt, but it’s a nice setup. I don’t know if I told you but I was a mechanical engineer all my life and have had good experience with welding, machining and sheet metal work but have never had anything to do with aircraft sheet metal.

A few questions I want to ask you as you are a qualified in aircraft engineering.

When I built the Tailwind I constructed the the fuselage sides on the table, then stood them up in a jig and tackwelded in all the braces and crosspieces. I get the impression from your plans that you made up the top and the bottom and then fitted the side pieces, it probably doesn’t matter either way but as you are well into designing and building your methods would be useful to know.

I used oxy-acetylene with the Tailwind, I had thought of using a MIG welder this time and normalizing the welds after, what are your thoughts? Another question I have is regarding the weight and balance calculations, drawing No. 1 gives the C of G limitations also gross and empty weights etc., could you give me the length of arm for the engine, fuel, front and rear passengers and luggage if a locker were fitted beyond the rear seat I would like to know what numbers you used and when you weighed the aircraft what weights were on the mains and on the tailwheel. Could you give me your engine weight, the only Lycoming weights I can find give it at 256-265 lb. and I am unsure if this includes the mags. I note that you do not have an alternator or starter, but you have a constant speed prop, I believe they are quite chunky.

Looking at a Lycoming I0-540, they seem to weigh about 400 lb., once again I am unsure what this includes, so adding on a constant speed prop could put the total weight up to 500 lb., so is the C of G still within limits with this weight?

Regarding wing construction, there seems to be different ideas on attaching the skin, do you favour mounting the assembled spars and ribs on a vertical stand for skinning or packed up level on a flat surface?

Some of these things you may cover in future newsletters, so let me know.

Regards and Best Wishes, RAY THURSTON – NEW ZEALAND

DearRay,

We just got back from a great trip to SUN N’FUN with the BEARHAWK (1400mi.), plus another trip delivering a Lycoming engine to the Northeastern USA (1100 mi.). That’s a total of 160 hrs. on the BEARHAWK now. Good to read that you are a B.S.M.E. and past builder of a Tailwind.

Regarding the questions in your letter of April 1. 1995:

1. I built the fuselage as per plans due to the rounded nature of the sides of the fuselage. It is best to build the top and bottom frames, then jig in place and tack and weld the sides. This system seems to work best. This method will be covered in an upcoming issue of BEAR-TRACKS.

2. We use only OXY-ACETYLENE. MIG welding would not be my recommendation.

3. The length of engine arm will vary with engine used. Distance from wing leading edge to engine prop flange is approximately 56 inches. We are planing a complete weight and balance write-up in the near future. You can scale drawing #1, and reference construction drawings for other information.

Prototype: Mains = 1064 Tail = 78
  Arm = -3.75 Arm = + 195

4. The list of engines in the first newsletter should fit the C. of G. limits. The prototype 0-360 weighs 293 lb. dry (Dry is with mags and fuel system – carb or injection and without a starter or alternator). The heavier models (Lyc. 0-540) (396 lb. w/starter and alternator) will require battery mounting in the rear of the fuselage.

Sincerely,

Bob

Dear Bob,

I enjoyed talking with you at Oshkosh very much. You have a super design so I am enclosing a check for $200 for a set of plans. I think I will go with the Ford V6 engine as I can’t afford to start development work on a V8 right now. The V6 appears to be a proven powerplant and it is economical and well suited to the Bearhawk airframe.

At this time I do have a few questions for you:

1. Do you recommend that I only tack weld the sides and join them together before finish welding all, or do I finish each side while it is flat on the bench and join the finished sides together?

2. Can I use used 180 struts or should I buy new ones?

3. What parts can be purchased for the airframe that would speed up the assembly?

4. What used parts cart be substituted for new to keep the cost down?

Thanks again for a great design!

Mike Holcomb

Mike,

Your Bearhawk plans are on the way!! I hope you enjoy building the Bearhawk as much as I know you will enjoy flying it. Regarding your questions:

1. You will only need to tack weld the top and bottom of the fuselage separate, then join the two halves together by tack welding in the side tubes. The Bearhawk is different from
most other plans-built projects as you construct the top & bottom of the fuselage first and then tack weld in the side tubes. Look for more details in upcoming issues of BEAR-TRACKS.

2. You may use used 180 struts with broken ends as you will be installing your own end fittings anyway.

3. As this is a plans-built you will be building most of the parts. You may be able to ‘farm-out’ some of the work. Keep an eye on our suppliers’ section for possible sources.

4. There are a lot of used parts you can use in your Bearhawk to keep cost down. Instruments, wheels & brakes, hardware, etc. Again, look for a write-up on keeping cost low in an upcoming issue.

Best Wishes – Bob

Dear Bob,

Good news! BEARHAWK 009 is underway, with my first order for aluminum sheet for the ribs placed today from Dillsburg! Meanwhile I have been busy for two weeks building the assembly table, buying some used tools (metal band saw, floor drill press, welding clamps, air shears, bench grinder, acetylene welder) and studying the plans. My “airplane factory” is now set up on our screened back porch, once unused, with all tools under lock and key, good light and ceiling fans overhead (this is Florida, don’t forget). I’m also awaiting arrival of the four Tony Bingelis books from EAA (the fourth one is Engines). Until the aluminum arrives, I’ll be working on the rib form block, marking took and fluting pliers. I’m very excited and look forward now to each few hours I’ll get to work on the BEARHAWK. Beth is being a good sport even though she thinks I’m crazy and has to explain that I don’t even know how to fly. But not for long!

Below is a small idea that has worked out very well in case you want to pass it along. Thanks for making this dream possible with such a fine and affordable airplane. Hope you had a great time at Oshkosh, with lots of admiring interest in the BARROWS BEARHAWK.

Roy Nash

Dear Bob,

I am making up another order for raw material and I thought I would order a windshield, not that I will need it for sometime, but with freight cost to New Zealand, it pays to get a reasonable amount of material when making an order. Can you give me the suggested model of the Cessna 170 windshield I need. I also need the approximate lengths of control cable required for rudder, elevator, ailerons and trim.

There was also the matter of an increase to the VNE. I would like to have it increased to about 185 mph, your comment was about the prototype wings which were skinned with .020″ and the drawings were showing .025″ and that this would probably be OK, if this correct could you make the higher VNE official? I suppose when you have fitted the new wings to the Bearhawk you will be testing this aspect.

My final question is in relation to the wing to fuselage spar plates, do you drill and ream if required the 3/8″ and 5/16″ bolt holes out to full size at the time of assembly onto the spars or do you pilot drill only at that stage?

Regards,

Ray Thurston – New Zealand

Dear Ray,

Always good to hear from you. I just read an interesting article in the September ’95 issue of PRIVATE PILOT about flying the South Island of New Zealand. I must say I was very impressed. I think the Bearhawk will be right at home in your area! Regarding your questions:

The best looking and fitting windshield for the Bearhawk I have found is the Cessna 170B model made by L.P. Aero Plastic. The part number is #312 or #312.187 The 312 is 1/8″ thick the 312.187 is 3/16″ thick. 3/16″ would be best if you want a 185 VNE. Bearhawk.tips 2015 Note: LP now carries a Bearhawk-specific windshield that is a pre-trimmmed Cessna 170 model that will save considerable time

I will do the testing for the 185 VNE when the new wings are installed.

Control cable needed is 150 ft. of 1/8″ (7×19) and 30 ft. of 1/16″ (7×7). Scale your drawings for individual lengths needed, and leave a little extra for fitting on assembly.

When fitting the wings, I used a smaller 3/16″ pilot holes in the fuselage fittings and wing root fittings, then drilled to size on assembly.

Best Wishes – Bob

Welding Safety Tip– Use a Thermometer to Prevent Burns

Source: 2015 Q2 Beartracks, Russ Erb
15q2ziI’m working on rebuilding the rear seat after its sacrificial catch of the plunging Bearhawk wing. I’ve done very little welding since building whatever the last welded thing was that went into the airplane back before covering and painting lo those many years ago. As a result, I’m having to relearn all those little techniques I picked up back when I was proficient. One problem I always had was knowing how long to leave a freshly welded part sitting to cool before picking it up. I have a few scars from when I guessed wrong. Today I realized a simple, cheap, fool-resistant solution. Non-contact digital infrared thermometers are available for dirt cheap now. So cheap you’ll have to order a bunch of other stuff to qualify for free shipping at Amazon. These look sort of like a pistol. When you pull the trigger, a laser beam shows the measurement spot and an IR sensor measures the surface temperature. I bought one to measure pan temperature for cooking, but I just tried it and found it works great on welds. If the temperature is below about 100 degrees F it is safe to handle.

Proper Procedure for Welding AA 5052 Aluminum Fuel Tanks

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

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