ORIGINAL: speedracerntrixie
ORIGINAL: Rotaryphile
Old text "Airplane Design" by Warner shows effect of three different leading edge radii for the NACA 0012 symmetrical section.
A knife-edged leading edge reduced peak lift coefficient from 1.4 to 1.03, but produced a very gentle stall. Minimum profile drag was reduced only by a percent or so, and was increased at lift coefficients over 0.2 - definitely a poor trade-off, apart from its friendly stall characteristics.
A very blunt leading edge with radius of about 5% of chord increased maximum lift coefficient to about 1.5, increased minimum profile drag by about 10%, and produced a far more abrupt stall.
<span style="color: rgb(255,0,0)">The blunt section, with its higher lift and abrupt stall is good for maximum possible lift, clean snap-roll entry, at the cost of tendency to stall and snap-roll. This probably explains the popularity of the so-called ice cream cone sections used on Extras, Edges, and Sukois for all-out aerobatics. Just don't let your airspeed get too low during a landing approach.</span>
For our IMAC type Extras, Edges, Caps and Sukois with the low wing loading we have the exact opposite is true. This is why one just can't use full scale data on our models and have it work the same.
SRT hit it on the head regards to model aerobatics. In fact, blunt wing LE takes so much elevator and rudder to partially stall one panel during a snap roll, thatsnaps are often "buried" which makes recovery very difficult and unpredictable. Also, many times initiation suffers since we just can't get enough throw into ele and rud fast enough in radio controlled aerobatic flying. Radios are just too slow compared with a guy sitting in the cockpit.
One can easily do an experiment on thick winged, blunt LE'd aerobats. Add a strip of balsa to the outside 12-15" of wing LE, near the tip. 1/8" thick X 1/2" wide strip is fine. Results will be immediate...