Bearhawk Model B
Design engineer Bob Barrows had long wanted to try the Riblett airfoil used on the Patrol to improve the flight characteristics of the original four place Bearhawk. In addition, there were several design features Bob tried on the Patrol and Bearhawk LSA which he believed would benefit the four place Bearhawk. Here is a list of the changes made to the original Bearhawk to turn it into the Model B which is now the kit we are manufacturing.
1) The major modification was changing the original 4412 airfoil to the Riblett GA30-4135. If you would like to learn a little about Harry Riblett (without reading his entire book), click here. This change also resulted in the flap area increasing as the flap now goes all the way inboard to the fuselage.
2) The original Bearhawk had flat ribs for the horizontal stabilizers and vertical stab. In discussions with Harry Riblett, Bob learned that replacing the flat ribs with airfoil shaped ribs would have the effect of acting like an increase in area of these control surfaces by 20%. This translates into increased stability and control authority. In addition, this change allows the down deflection of the hor stabs to be decreased from 4 degrees (original design) to 3 degrees Model B). We found that the corresponding reduction in drag gave a few MPH speed increase.
3) The tail spring was changed from a set of three leaf type flat springs to a round spring of 6150 steel heat treated to a Rc hardness of 49-50. Bob believes the round spring has some advantages over the flat springs. He felt this way after flying his Patrol and LSA with round tail springs for many years.
4) On the original four place, the side formers, window and door sills were bent 4130 sheet steel parts welded in place to the fuselage tubing. On the Patrol, Bob designed these parts in 5052 aluminum (.050). The door sill is 6061T6 (.063) as this is harder than 5052 for where people are getting in and out of the plane. These aluminum parts are pop riveted to tabs welded to the fuselage tubing. There are two advantages to this change. When these parts were made of steel, getting paint coverage into every little corner and preventing long term corrosion was more difficult. This is not an issue when aluminum is used. 5052 is referred to as “marine” aluminum for its corrosion resistance. Secondly, there is a minor weight savings of a few pounds when changing these to aluminum.
5) The lower tubing of the shock struts was always streamlined 4130 tubing for drag resistance. Over the years, a few pilots flying their Bearhawks got into severe swerving and ground loops resulting in the streamlined tubing failure in compression. This was not a surprise to Bob as it was what he expected. The original shock strut was extremely strong and reliable if the Bearhawk was kept going straight down the runway. This has been proven by some off airport landings in very rough conditions where zero damage occurred. But enough Bearhawk pilots were ground looping that Bob felt beefing up this part to round 1 1/8” x .065 was called for. This doubled the compression strength but does increase the chance of fuselage damage instead of limiting the damage to the L/G, shock struts, and outboard wing (in a ground loop). With our kits, pieces of streamline tubing of PVC are provided to be epoxied in place over the round tubing so there is little increase in drag.
6) On the Patrol and LSA, Bob designed aluminum window frames for the aft fuselage windows. On the Model B – Bob incorporated the same window frames into the side windows replacing the steel frames as used originally.
7) The aileron and flap hinge mounts were redesigned for standard spherical bearings. It is a fixed fixed design for easier assembly to the wing.