I need to know what profiles did the De Havilland Chipmunk use at wing-root and wing-tip.
From : Don Stackhouse
Ah, yes, the Chipmunk, one of my all-time favorite airplanes! I had the
privilege of taking my aerobatics training in a stock DHC-1 Chipmunk. It
was probably the best behaved, most delightfully honest airplanes I've ever
flown.
As you might guess, it's on my "to-do" list of planes I'd like to model one
of these days. Fortunately I made some friends at DeHavilland Canada in my
previous career, so I happen to have some good documentation for it,
including airfoils.
As far as I've investigated they were NACA 1415 at root and USA 35B at
tips. But despite an extensive search I've been unable to find the NACA
1415 Coordinates.
That's because it was not a NACA 1415 at the root. It was a NACA 2412 at
the root. The tip was a USA 35B, same as the airfoil for the Piper J-3 Cub.
The NACA 2412 has a really benign stall, but still has a well defined stall
break. The USA 35B has an even more gentle stall with almost no definable
break. Between that, and the 2 degrees of washout, the ailerons never
actually quit flying.
Meanwhile, the 18" stall strips about a foot out from the fuselage on each
side plus the natural characteristics of the NACA 2412 cause flow to start
to separate at the root starting at about 8 knots above the stall. That
hits the elevators, causing a little "nibble" in the stick. As you
decelerate further, the nibble turns into a wiggle and then a shake, till
about 4 knots above the stall the stick is shaking quite hard. At that
point there's a little vibration starting up in the seat, which continues
to grow, until by the time you actually get to the stall, the whole
airplane is vibrating unmistakably. When it finally does let go, the nose
drops straight ahead, no significant wing drop, and with very strong
aileron authority available throughout the stall. Just ease off on the back
pressure on the stick and it's flying again. Delightfully honest, doesn't
do anything without practically phoning ahead for a reservation first, and
does it that same way whether it's pulling half a "G" at the top of a loop
or 3 G's at the bottom of one. Truly one of the most viceless airplanes
I've ever had the honor to fly!
Don Stackhouse
DJ Aerotech
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May 17, 2012
