RE: Bounce on Landing >.<
sdavied, has brought up some very good points. But 5-10 knots above stall in full scale, would be around 1-2 knots in RC. Not very good thing to be flying an RC airplane that close to stall. I agree with what you have said to some extent sdavied! I fly full scale airplanes as well. 80% of all places teach full stall landing as the correct approach, but this is not always correct.
An example of this is in the Fairchild Metro III that I fly. The stall speed is around 85 knots with full flaps, but our "ref" speed used for touchdown varies with our weight, and is generally around 110 knots! The reason that "ref' speed is sued in large category full scale planes is that "ref" is generally 1-5 knots on the "backside" of the power curve.
In simple terms the power curve is a 2 sided beast, and is simply the power needed to keep the airplane in the air. On the "front" side of the curve, power equals speed and pitch equals lift. An example is that if you have an airplane in cruise flight if you pitch up, you gain more altitude than you lose speed, and exact opposite for power.
On the "backside" of the power curve (slower than maximum lift to drag speed) you will have an excess in angle of attack and little forward airspeed. This means, that the wings are pitched up to the point that anymore pitch results in increassing more induced drag (remember that lift is 90 degrees to the angle of attack.) Imagine this for a momment to get a picture. The airplane is pitched up at a very high angle of attack but is traveling forward across the ground. Due to the wings being pointed upward, lift is actually pointing rearward to the realative motion of the airplane, instead of skyward like normal. Now in this area of flight, increasing pitch generally results in an ever DECREASING amount of speed, with little loss of altitude. This "region of reverse command" as I was taught it's name, it is CRITICAL to remember that POWER keeps you airborne, and PITCH keeps airspeed!!
Why does all this matter, easy if in a level attitude while doing an approach, it can be VERY easy to pitch up only to find that the airplane SLOWS down MORE. This can be VERY dangerous if low to the ground and with the resultling loss of airspeed! Stalling an airplane close to the ground, if not INTENDED for landing, can be VERY dangerous! Remember that when the wings stall, spins can occur!! This is why "ref" speed is important for large full scale airplanes, pitching up more say for a flare, does nothing below this point but to slow you further!
This is why I teach having a slight nose down approach, and only to raise the nose enough to keep it from hitting first! The approach I teach may result in longer landing distance required, but generally it is slightly safer. If you have an airspeed indicator that you could see the realative airspeed of the air passing over airplaneat all times, I would say yes, a nose level / slightly nose up approach would be fine! But for RC where that isn't possible, a nose low attitude for an approach would be much safer in keeping a plane from stalling at to low an altitude.
Don't get me wrong, sdavied! Your technique is perfectly acceptable! I just find the technique I use and teach to be slightly safer for RC use.
Carlos Murphy, THAT IS A GREAT TECHNIQUE!!! I never thought about whispering that to someone!! If you don't mind I am goona try that one too!!!
Thanks,
Reg