ORIGINAL: ptulmer
What would blending a Clark YH to a blunt symmetrical airfoil do for things like stall. What other things should I be looking for? (root clark yh to tip symmetrical)
I have recently done this on a delta and ended up with a perfect airplane. It had no bad characteristics at all.
You can get away with a lot when it comes to delta wings. The are not very sensitive to stalling problems and can operate at very high AOA.
The wing planform you have choosen compensated for the negative effects of using the blended airfoils in the way you described. If on the other hand you had chosen a high aspect ratio planform (e.g. glider wing) you might have had some problems.
ORIGINAL: davidfee
Or if he leaves it the way it is, he doesn't need to add washout because the wing already has aerodynamic washout due to the change in zero lift angle between the cambered root and symmetrical tip.
-David
David, IMHO the result will not be the desired one.
Assuming a Clark-Y profile with a zero lift AOA of -2 deg. and an uncambered symmetrical airfoil (NACA009) with zero lift at 0 deg AOA:
If the cambered airfoil is placed at the tip and the symmetrical airfoil at the root, the wing need to be twisted geometrically by 2 deg (washout) so that there is no aerodynamic twist, i.e. maintaining a constant lift coefficient along the wing. The more cambered airfoil will stall at a higher lift coefficient than the uncambered airfoil and the result will be a safe stalling behaviour where the wing root will tend to stall before the wing tip.
If, as you suggest David, the cambered airfoil is placed at the root, the uncambered section at the tip and the wing is built without twist a problem occurs. If one looks at the polar curves (lift coefficient versus AOA) it becomes apparent that both airfoils will stall at roughly the same AOA (approx. 10 deg at Re=100000). This will not give the wing a safe stall behavior as it will be hard to tell which part of the wing that will stall first.
Furthermore, because the wing is built without twist, at high speed (at low angle of attack) different portions of the wing will operate at different lifting coefficients which is bad from an efficiency point-of-view, especially at high speeds where the lift coefficient of the wing as a whole is small (let's assume 0.1 as a typical example).
With an untwisted wing at 0 deg AOA, the lift coefficient is approx 0.4 for the Clark-Y and 0 for the NACA 009. To achieve an average of 0.1 (for the high speed flight example) the wing will need to operate at a slightly negative AOA. The Clark-Y will be producing an upward lifting force at a lift coefficient that is positive but less than 0.4. The NACA 009 however will produce a downward force with a NEGATIVE lift coefficient. This adds to the induced drag of the wing and is highly inefficient.
Summary: In general, a wing with a cambered root and an uncamberd (symmetrical) tip airfoil will not produce a safe stalling behaviour and is inefficent at high speed.
/Red B.