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The Sig Hog Bipe

Sig Hog-Bipe
Specifications


  • Wing Span: 54.5 in (138 cm)
  • Wing Area: 966 sq in (6232 cm²)
  • Length: 51.75 in (131 cm)
  • Weight: 7.0 lbs (3.2 kg)
  • Engine: .60 - .65 2 - cycle
    (9.8 - 10.7 cc 2 - cycle)
    .65 - .90 4 - cycle
    (9.8 - 14.7 cc 4 - cycle)
  • 4 Servos required


The Sig Hog-Bipe is loosely based on Sig's popular, Astro-Hog low wing sport model. Building materials are all wood except for the pilot headrest and wheel pants which are of good quality ABS plastic. Wood quality is generally very good with only a couple of wing leading edge sheets found to be a little stiff. These parts were still deemed usable, however. Many of the plywood parts are laser cut, which insures accurate parts fit which is critical in certain phases of construction.

The hardware package was complete and all the provided parts were used except for the push rods. Sullivan Heavy Golden Rods were substituted but this was due more to personal preference than necessity.

The construction manual provides detailed step-by-step instructions with good quality black and white photos of each building phase. No errors were found in the manual.

Sig has done a great job engineering this kit. Construction of the fuselage is of the interlocking type. All structural members are of light ply except for the firewall which is aircraft grade plywood. All parts fit together without need for additional trimming and the basic structure is assembled with rubber bands before any glue is applied. Provided instructions are followed, this self-aligning assembly results in a straight fuselage.

Once the basic fuselage structure is complete, two turtledecks, one fore and one aft, are assembled on the top. Stingers are run between formers and then the whole thing is covered with 3/32" balsa. This actually proved to be more challenging than expected, but is definitely worth the additional effort because it gives the fuselage its pleasing rounded shape.

One of the most difficult steps in building any biplane is getting the top wing aligned correctly. Sig solved this tricky problem through a very ingenious design for the cabane struts. The two preformed sheet aluminum struts are held together in a sandwich with three laser cut plywood parts. Laser cut holes have been pre-cut into the fuselage sides providing exact mounting points for the cabane struts which have themselves been pre-drilled. All this is more difficult to explain than to actually build, but the end result is a self aligning structure which is very easy to assemble and removes any uncertainty regarding the incidence of the top wing .

The tail feathers are of traditional balsa construction. Rudder, elevators and vertical fin are of sheet balsa while the stabilizer is assembled from sticks and sheeted with 1/16" balsa. One nice touch is that the rudder and elevators had the required taper pre- shaped into them saving the builder a lot of tedious sanding. In an effort to give the plane a 1930's military look, the outline of the tailfeathers was changed. This was accomplished by increasing the rake of the vertical fin and rounding the top portion. The fin/rudder area is essentially unchanged although this modification did require the addition of a small piece of vertically grained 1/4" sheet and ended up eliminating the dorsal fin. The stabilizer and elevators were simply rounded to a more pleasing shape.

The wings are of traditional all balsa D-tube construction. Leading and trailing edges are balsa sheeted resulting in a fairly rigid structure even before application of the covering. The top wing, which has no dihedral, is built in one piece which speeds construction considerably. The lower wing halves are joined in the middle by a 1/8" plywood dihedral brace, and this joint is further reinforced with the supplied fiberglass tape. Anyone with some building experience will find nothing hard about wing construction. Care must be taken, however, to insure that the mounting supports for the top wing are accurately positioned to insure proper alignment.

The plane was finished using Cub yellow 21st Century fabric on the wings and stab, while the fuselage was first covered with Super Coverite and then painted with 21st Century silver paint. Some detailing was added with self adhesive lettering and trim sheets while panel lines were drawn using the Top Flite Panel Line Pen.

For power, a well used OS .70 Surpass four-stroke engine was used along with a 12 x 8 APC prop. A break in the weather allowed flight testing to take place in mid-March. The CG had been set at the middle of the range indicated on the plans but this proved to be a mistake, resulting in poor pitch stability. Moving the CG to the forward position settled things down considerably. With the throws at their recommended settings, the Hog-Bipe is a very solid flying airplane. Take-offs are especially fun. With its long tail moment, the plane does not veer much to the left, and once some speed is attained, back pressure on the stick can be released and the plane allowed to run on its mains at half throttle for a while before lifting off at roughly 2/3 power. If allowed to, the Hog-Bipe will almost land itself. With its fully symmetrical airfoil, the plane will do most anything a pilot is willing to perform, limited only by considerable roll coupling of the rudder. Stalls are gentle and straight ahead with no tendency to tip stall. It can be flown at 1/4 throttle with full up elevator without loss of control. The OS .70 4 - stroke proved to be a good match for the plane and with its ample and open-ended front fuselage and slow flying characteristics, the Hog-Bipe is particularly suited to 4 - stroke engines. Those wishing more spirited performance can opt for a .90 4 - stroke for which there is ample room.

Overall, this is an excellent kit for anyone wanting to attempt a first biplane, both because of its almost fool-proof building techniques and forgiving flight characteristics.



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