The P-733

     Now knowing what it is to fly an unstable plane, I knew what my primary goal was in my second plane; stability. I essentially wanted to make a powered glider, something that just hangs in the air and leisurely strolls across the sky.

     The first idea to achieve high lift was large wings, specifically long thin wings. With a high wing aspect ratio, you can reduce the amount of drag produced from the lift (Induced Drag). The biggest restriction for wing size was the size of the poster board sheets at Wal-Mart. With a 30"x20" sheets, we could achieve a total wingspan of 60" using 2 sheet per wing, any more sheets would involve excess structure (and therefore weight) and weak points. Next up was to find a suitable airfoil. It was off to the internet to research wing cross-sections. We looked a many wings, comparing those from slower planes such as the C-130, the Cessna, and un-powered gliders. What we were able to pull from it was the camber to put in the airfoil, and the placement of the maximum camber.  Luckily Brent already drew up some basic plans for his plane, but there still changes to be made.

      Brent wanted a faster flying, more maneuverable plane, so he built his with significantly swept back wings. While wing sweep reduces drag at higher speeds (most noticeably at mach 0.8-1.2), this was not a luxury I could afford. Swept wings tend to start their stall at the wingtips, where the ailerons provide the most roll control, while rectangular wings stall at their root near the fuselage. Since I was planning on flying as slow as possible, the possibility of a stall was high and I needed to maintain full control at all times. A rectangular wing also allows me to utilize the entire sheet of poster board, minimizing waste.

     Unfortunately, I forgot to take a picture of the airfoil shape, but there are pictures of it later in the build. As seen here, the wingspan in 60" long, a chord length of 10", and a maximum thickness of 1.25". At first, I thought that was a monster of a camber seeing that the foam board was merely 0.2". but compared to lighter, smaller planes/gliders, that level of camber isn't unheard of for the amount of lift needed with little airspeed. Also seen here is the structural spar. In a normal wing, the spar would take most of the loading, but here we can treat the entire wing as a beam. So here, the spar is taking the shear load, while the wing skin takes the axial forces. So in all actuality, the spar is just being used as a spacer. For additional strength,  I uses regular printer paper and spray adhesive to 'tape' the panels together, and take advantage paper's high tensile strength. I felt this solution was both ligher and stronger than balsa spars.

     Next up was the fuselage. I chose to go with a light weight pink insulating foam that can bought in large panels, so the fuselage can be constructed without discontinuities.

With stability in mind, I used the entire length of the foam, 48", to move my tail as far back as possible. To bind the 2 sheets of 1" thick panels together, foam safe spray on adhesive worked quite well. I cut a long taper at the aft to conserve weight and keep the CG forward.

With only 2 sheets of foam, the fuselage was quite weak to twisting along it's length. The simplest solution was to add another thin strip to either side of the fuselage, to increase the area moment of inertia. This was an added bonus as it also widened the area that the wing would sit on.

The tail sizes were taken from various Cessna personal aircraft.  I scaled it down, based on the wingspans. The shapes of the stabilizers were eyeballed, but inspired by various slow aircraft (below mach .6). Cut the control surfaces at 1.5" wide,

The Horizontal stabilizer was simply hot glued onto the fuselage. The vertical stabilizer would then fit into the slot previously cut.

Here I added more pink foam to help re-enforce the vertical stabilizer. This was also a good opportunity to set in the servos close to the tail.

Now that the tail was mostly finished, the heavy components could be set in place, and the center of gravity could be estimated, and thus the placement of the wing. Note the notch cut out at the nose for the battery motor and other electronics. Also note the "Bloody Wonder" in the background, awaiting to be stripped of it's useful components.

 After cutting a small notch in the foam fuselage for the wing to sit in and drilling a few holes for some wooden pins, it was completed.







Finally seeing it completed for the fist time, It had a striking resemblance to the P-3 Orion. So as a tribute to the sub hunting plane, I named my craft:
The P-733

Here I am before the initial test flight, and after a long night trying to finalize the plane. Deadlines are always a pain. Also note my skepticism, the plane turned out a lot heavier than I was planing.