Tails and Tales.
Hi Dave. When I was testing V.G.'s on the wing, it was clear that the wing efficiency was improved to the point that the tail (horizontal/elevator) no longer had the authority to stall the wing. The problem had to be corrected before further testing could proceed. I am currently using a PA-20/22 balanced tail. The fix according to Mr. Dodge, and a requirement on one of his STC's was to install the 6" longer PA-18 tail. I rejected this because of the additional weight and the increased twisting moment on the fuselage. Cost was also a factor. It was only logical that the V.G.'s caused the problem (with the wings) that they should be able to fix the problem (with the tail). I installed them under the horizontal and the problem went away. Later when the wing testing was complete, I revisited the tail and removed all of the V.G.'s that were not necessary, leaving only enough V.G.'s to completely stall the wing for 3 point landings. (with power). The weight of the additional V.G.'s was 1.6 oz. I believe that 95% of the stock engine/wing PA-18's will get along fine with a stock tail if flown using the techniques outlined in the { Landing Short Over A 50 Or 100 ft. Obstacle } thread. I don't believe that power off or ( 0-thrust ) landings have any place in the STOL world. In addition to giving the tail more authority on approach, using power makes it less likely that the engine will falter (fart) when a burst of power is needed for a power flare. For the other 5% or those with modified wings, the large squared tail with V.G.'s is about the limit for a practical application. An all flying tail (stableator ) is probably the best, but it and it's mounts are heavy. The real problem to deal with at high AOA is that the stabilizer acts like a Delta Fin and tends to push the tail up (you can see Delta Fins under the tail of the new Lears) as the elevator is trying to push it down. At some point they just cancell each other out. The easiest way to solve this is to reduce the size of the stabilizer. (( For those that have BLR kits and have installed the plates on the fuselage that effectively INCREASE the size of the stabilizer, please don't ask me for ways to increase the elevator effectiveness. You have created your own problem )). A simple/light method would to add an airfoil to the bottom leading edge of the elevator. A slat if you will. They were used on Polish built Storches. They would be simple to add to the existing structure. The inverted airfoil that some STOL types use, are hard to adapt to the Cub. They have to be both large and light and on a Cub STRONG. The Cub tube and fabric is about as sturdy and simple as you can get. If I had elevator problems, I would probably test the elevator slat first. Wayne is involved in this problem on his STOLMASTER Slat kit. And he will probably have a lot to add to my simple musings.
Jerry.
