I probably am overpropped at static and low speed. I told Clark Lydick to build me a speed prop. I figured that being overpropped on take-off doesnt matter if you have lots of HP and can get off the ground in 1200 ft and climb like a banshee anyway. I'll be sending the prop back for adjustment once I get solid numbers, but I don't think I'll want him to cut it back much.
john Slade
What sort of top speed, and cruise speed do you expect? What would be common for an O-360 powered plane?
Cheers,
Rusty (wishing the RV airfoil wasn't so draggy over 220 mph)
I used to think the same thing (draggy airfoil) but I think the problem with RVs over 220 is related to wing / tail / fuselage incidence. At 220 I get the visual impression that I am in a dive during level flight.
The early Citation jets used the same airfoil as the lowly RV.
Tracy
Tracy,
As you known, the airflow over the horizontal tail is such as to exert down force on the tail (Nose up) to overcome the forward pitching movement of the CL of the wing airfoil. I suspect that at the higher airspeeds the airflow over the wing could be changed sufficiently that the tail surface might be providing less downforce (nose up ) than required. In otherwords the downforce on the horizontal stab is sufficiently lessened that the nose lowers until the horizontal stab finds a new equilibrium point at your higher airspeed. As nose goes down, more of the upper surface of the horiz stab is exposed to the airflow causing more down force/nose up until the new equilibrium is reached. Just a thought.
Ed
Hi Ed,
I thought the major reason for down force on H stab was to resist the force due to CG being ahead of CL. Or maybe that's saying the same thing you said? CL does not move much on the 23013 series airfoil in normal flight envelope.
In my limited understanding of the aerodynamics (in non canard aircraft), it is always "all about the wing" and what it requires to do what is asked of it
At any given speed, the pitch requirement for level flight is X, end of story The hor. stab and elevator delivers the amount of down force required to make it thus. If this happen to be at an angle where the H. Stab & elevator are shaped like a shallow inverted V and the fuse is plowing through the air in a nose down attitude, it's going to make drag. The fix is to lower the incidence of the wing relative to the fuselage and to lower the incidence of the H stab relative to the wing. This is what all the serious RV racers are doing.
The only reason I don't do this is that it increases drag at more normal flight speeds. Everything is a compromise.
Tracy