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.
- What are the FLAP SPEEDS?
- What is the MAXIMUM MANEUVERING SPEED?
- Do you know the approximate GLIDE RATIO?
- Do you have a maximum “G” operating figure?
- 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?
- What is the range of the C of G and where is the datum?
- Do you have a sample C of G calculation at M.A.U.W. (Max Load) and with only the pilot and minimal fuel?
- Do you have a rough idea of the material costs for the fuselage and wings without engine, instruments, seating and cabin finishing?
- 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:
- 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.
- Maneuvering speed is 110 M.P. H. at 5 g’s.
- Glide ratio is approximately 9 to 1.
- Maximum “G” allowed 4-1/2 @ 2400 lb. and 5 @ 2300 lb.
- Rudder control vs. torque looks OK for 260 hp.
- C of G range 9″ to 22″ of leading edge of wing. (Note: later changed to 10.5″ to 22.5″)
- See weight and balance sheet (upcoming, January 1997).
- Estimated cost (U.S.) for the fuselage and tail tubing is $1200.00 and for the aluminum is $1500.00.
- 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.
- See weight and balance sheet (upcoming, January 1997).
I hope that answers most of your questions and please stay in touch.
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.
- 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?
- What welding technique do you use on the steel tube components, gas, heliarc, etc.?
- 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
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
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
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
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



