The Wag Aero wing plans use spoilers instead of flaps. The spoilers have almost no similarity to flaps. They are very small panels above and below the wing that you deploy upward and downward by pulling a “T” handle just before you flare to land. They are designed to kill the lift of the wing. The Northstar wing kit on the other hand has massive Fowler-like flaps. I decided to use a lever to deploy the flaps manually using a standard Johnson bar flap handle located between the seats. The challenge was how to rout the cables and pulleys from the underside of the belly and back up to the ceiling of the cabin. I bought a used Johnson bar from an old parted out Piper and designed a mount and ratcheting system for the bar to attach. The first set of 3 inch pulleys were welded offset to the centerline of the fuse to avoid competing with the push-pull tube that operates the elevator. I made the cables turn at a right angle behind the baggage panel to keep the turtle deck opening clear and useable. Bringing the cables up and along the side of the fuse allowed for a solid and secure location for a welded pivot point for the bell crank to attach. The Johnson bar had a welded horn centered on the lower bar and the horn had two holes for cable shackles which led me to design a twin cable system all the way to both ends of the bell crank. The theory in my mind was that one of the two cables would always be pulling when raising or lowering the flaps. It was not until I was attaching the wings during the aircraft’s final assembly that I discovered that the travel movement of the bell crank was not sufficient to operate the flap operating range of the wings. To correct this I used only one cable that attaches directly to the cables from both wings and removed the fuse bell crank location entirely. The flaps have a very strong return spring on the rear spar that assure flap retraction as soon as the flap handle is lowered.
The Northstar wing has a very elegant wing tip shape. Instead of the popsicle stick end found on the Piper wing, the Northstar wing tapers down and back into a graceful rake. The wing tip extends the leading edge and maximizes the aspect ratio by increasing the effective wing span, this according to it’s designer. The kit includes a custom shaped fiberglass leading edge element, a tip rib, a wing bow, and a preformed trailing edge sheet metal piece. The fiberglass part is firmly attached with Avex rivets to the end of the leading edge sheet metal and along the top and bottom sides of the wing bow. The trailing edge metal is preformed and temporarily held in place with strapping tape to keep it positioned for drilling rivet holes. The holes are then cleco’d down and a stiffener channel that runs diagonally is placed on top for locating rivet holes. The stiffener channel is then placed inside the trailing edge piece and attached using flush Avex rivets. Northstar also welded the mount on the wing bow for the attaching the standard Whelen nav/strobes light fixture. The design of the wing tip is especially appreciated when fabric is attached making the finished tip an extraordinarily beautiful shape.
The Northstar wing kit includes two custom TIG welded fuel tanks. The tanks hold 52 gallons in total or 312 pounds of fuel. That quantity of fuel will give the aircraft approximately a 6 hour/ 600 mile range. The fuel tanks were crafted to form the airfoil shape of the wing and were held tightly in place with three stainless steel tensioning straps. Inside the tanks were three baffles to reduce sloshing of fuel. After the tanks were installed in the wing a set of “X” braced drag wires were inserted through the fluid tight internal tubes in the tank.
Using the Northstar wing made it unnecessary to use a header tank. Piper aircraft and many Piper replicas require a header tank which is a small fuel tank mounted in the cockpit just above the Pilots feet. The header tank purpose is to ensure consistent fuel flow during climbs, dives and maneuvering. I did not like the idea of highly combustible 100 octane racing/aviation fuel just above my feet. The Northstar wing plumbing and fuel line routing provides positive fuel flow during steep climbs or dives making the header tank unnecessary. The fuel system is gravity fed from a forward port and a rear port that feed together to a central fuel selector. The head pressure is sufficent to also eliminate the need of an electric fuel pump.
One last feature of the Northstar fuel tanks are the fuel sight gauges in the root of each wing. These sight tubes provide the pilot an honest indication of remaining fuel on the ground and in the air.
The Northstar Wing uses the same airfoil shape as the Piper USA 35B as used on a Super Cub but the similarity ends there. For the design of the Northstar wing, Morgan Williams used the heavy duty features of the Piper Pawnee PA-25 Agplane with a higher gross weight. From there he made several more improvements including the alignment of all wing compression struts with the aileron and flap hinges thus directing the airloads in a straight line from the aft spar instead of zig-zagging through the spars. There is also a new raked wing tip to maximize the wing aspect ratio and increasing the effective wing span that allows side-slips even with full flaps. Four sets of stainless steel drag wires including one set that runs through the gas tank extend through the spars and are tightened using a simple nut and block attachment system. Morgan also designed the control cables to stay inside the wing including the upper aileron cable thus maintaining a more aerodynamic and water resistant enclosure.
What was most impressive is the high quality of the parts. The spars came predrilled with reinforcements hard riveted at the factory. The aluminum ribs were preformed and predrilled and when any drilling was required Morgan provided a very detailed video explanation of how to make the set-up, what clamps to use, measurements needed and what type of rivets or AN hardware to complete the assembly with. Also if I ever had a question he was always available to help me work through it.
The ribs were also predrilled for attaching the fabric with fabric rivets which I found to really speed up the fabric covering process. The old method of sewing and tying knots to attach the fabric to the ribs is not needed on the Northstar wings.
Unlike other Experimental Aircraft Plans I had a choice on what wings to build. I could build the Wag Aero 2+2 Sportsman Wings per the plans or select other wing options. The Wag Aero Wings are wood construction with square tips and wing spoilers instead of flaps. At the time I did not have a high confidence level for fabricating wood parts and I really wanted flaps so my attention turned to a wing kit made in Canada and available for use on the Sportsman 2+2.
The Northstar Wings are made by Custom Flight Limited of Perkinsfield Ontario. The Northstars airfoil is the same as the Proven Piper USA 35B and is totally adaptable to fitting my Wag Aero Fuse. Morgan Williams is the owner and Chief Engineer for Custom Flight Limited and is the brightest and most knowledgable person in Aviation that I have ever met. His company (http://www.customflightltd.com) makes the Northstar Bush Plane Kit which is a Super Cub type airframe and they sell the same wings for Sportsman builders like me. In the next several posts I will describe a lot more about this fantastic wing kit and what a joy it was to build such an extraordinary piece of engineering.
However before proceeding I always like to point out misguided ideas I had as a novice homebuilder. Early in the process I read somewhere the need to build an absolutely flat wing table needed to fabricate the wings. That seemed so logical to me that I did not hesitate to build a huge 4 foot wide by 16 foot long wing table. Later on, after purchasing the Northstar wing kit I discovered that they are assembled on a simple pair of saw horses. The Northstar instructions provide all the necessary methods for keeping things square and true. The wing table I built would actually have been a hindrance but it was a nice work bench for other things including the installation of Micro Vortex Generators on the wings during the time of flight testing.
While my main effort was to complete all the welding on the fuselage I had to re-focus my attention to the wood floorboards and seating attachment issues. That’s because metal tabs and seat mounts had to be welded on the fuse to hold them down. I chose 5/16″ exterior grade plywood and carefully cut it out to fit around tube joints and around the control sticks. This was not to be the final finished floorboard. In fact I ended up fabricating three different floorboard patterns until I ended up with a suitable design that evolved with other changes I made along the way.
During this early phase of construction I was reminded of the labor intensive method used for annual inspections for my Cessna Skyhawk. My A&P (Airframe & Powerplant) Mechanic at the time had the complete cockpit interior removed including the seats and carpeting and all the floorboard inspection panels were also off. This close up inspection is to check for airframe corrosion, control cable integrity, pass through wiring integrity, fuel line integrity, etc. But my mechanic also found a large mouse nest which certainly did not belong there!
This led me to think how easy or difficult it would be to inspect my homebuilt when it was finished. The plans specified that all interior sidewall sheet metal panels have a lip or 90 degree edge to be used to attach to the wood floorboards. This would require me to completely remove all the metal sidewalls just to get to the floorboard removal and that would be incredibly difficult and time consuming. The plans also specified a fabric belly and Yes, I could have added several removable inspection rings but they are very small and difficult to get into. Thus I decided in the months ahead to design a system of easily removable full width belly panels and omit the fabric belly altogether.
During this phase of building was the time I also purchased and modified a pair of Cessna 172 seats and removed the upholstery and removed 3 inches of metal frame width and re-welded them back together.
The Wag Aero “2 + 2” model designation refers to the airplanes seating arrangement which means there are two seats in front and two seats in back. However the seats in back are really only suited for children of 12 years old or less or one adult passenger. The fuselage measures only 5 inches wider compared to a Piper Super Cub which makes one wonder why the Sportsman designer thought the extra five inches would allow side by side seating versus the tandem seating arrangement for the Super Cub,
I soon realized this cozy seating arrangement when I jury rigged a couple of front seats using cement blocks and 2 X 6 board seat backs and also placed a fabric sling in position for the back seat. I also made a cardboard template of the instrument panel and for the first time I could sit in the cockpit and feel for myself the interior layout of the aircraft.
I was struck with just how narrow the cockpit was. I immediately rechecked the plans to see if there was any error, but it checked out right. I then measured the interior width of my Cessna 172’s cockpit and was quite surprised to find it was only one inch wider than the Sportman. These measurements were taken at the width of the instrument panel. The major width difference between these two airframes is because the Cessna’s cockpit width remains mostly constant all the way down to the floorboard where as the Sportsmans cockpit width tapers down from 38 inches to 30 inches nominally, thus affecting the seat width. It was now no surprise why Wag Aero specified to remove 3 inches of seat/back width from a Cessna 172 seat and reweld them back together. Using standard Skyhawk seats would never have fit.
My concern for this ergonomic issue was not over and many months later I would develop a solution for this narrow width problem by designing special plexiglas bubble doors that would add 8 inches of interior elbow room to the cockpit without modifying the airframe. In later posts I will describe the tooling and fabrication methods used.
Let’s look a few years ahead at a three minute flight video showing the Aircraft Tail behavior during Cruise, Landing and Side slip maneuvers. A noticeable misalignment of the Elevator and Horizontal Stabilizer occurs in these various flight control movements. An adjustment to the Forward Spar will be needed to realign these surfaces.
After the tail parts were finish welded per the drawings it was time for a trial fit on the fuselage. The rear spars of the horizontal stabilizers were joined together to a rotating sleeve while the front spars were joined together into a moveable and adjustable forward stabilizer mount. This arrangement is different than the traditional jack screw found on the Super Cub. That is because the Sportsman utilizes a cockpit adjustable trim tab on the left elevator very similair to the Cessna 172. The adjustable range on the front spar provides a way to adjust the aircrafts pitch to keep the elevators centered during normal cruise flight and then use the cockpit adjustable trim tab for reducing control pressures. During test flights the pitch angle of the stabilizer was changed several times until an optimal setting was found. Future video posts will show the before and after effects of making these pitch adjustments.
The next trial fit was to attach the elevators to the rear spar hinge points and to my shock and displeasure there was a huge 1″ gap between the left and right elevator horns. These two horns should have had only 1/8″ between them to receive the upper and lower cable attach lugs. What went wrong? Did I make a mistake or were the plans incorrect? It didn’t matter – it had to be corrected and this became my first welding repair. The tubes were cut near the end by the horns. An insert tube was rosette welded between the two and a larger tube doubler was joined over the joint and finger welded over the existing tube.
Flying wires or tail brace wires were attached and a level was used to check tail alignment across the hinge lines of the left and right elevators.
The Sportsman 2+2 plans provide the builder 2 Turtledeck options – A fixed in place Turtledeck or a hinged Turtledeck. I chose the hinged option and I have never regretted it. The hinged turtledeck has its origin from the U.S. Navy Piper HE-1 designed to carry a patient litter. From a practical weight and balance stand point there is only so much you can load behind the passenger compartment, but also from a practical stand point having a hinged deck allows for very easy preflight inspection of all things below and makes sense for easy fabric repair, for access to replace aging rubber fuel lines and for checking elevator cable tension all without ever needing to remove or cut fabric.
Fabricating the thin wall steel channel puts your welding skills to a real test. Most all of the light weight structure is made from .035″ X 3/8″ x 3/8″ Piper mild steel channel, including the stringers and frame channels. Too much heat and you burn right through it!
My styling side got the best of me when I could not resist to change the shape of the window from trapezoids to nautical portholes similar to ones found on one of my favorite STOL aircraft, namely the Helio 295 Super Courier! Granted my Super Sportsman is no Super Courier but why can’t it look like one! I welded small steel rings to the channel structure so the fabric would have something to attach to and used clear plastic lenses from wall clocks for the round bubble windows. Luckily they still make the clock so I have a replacement source for the windows. My next post shows these porthole windows installed.