Using different airfoils from root to tip on glider wing.

[HaiDang]

hello everyone at rcgroup.

maybe someone can answer my question?

i want to build multi taper glider wing and use 4 different airfoils in wing.

airfoils are hq series and all airfoils are exactly same with respect to camber etc. differing only in thickness. thickness starts at 9% at root and then 8.5% then 8% and at tip 7.5% it is 3 taper wing

my question is, do i need to use any washout in wing?

my thinking is since airfoils are exactly same except for thickness then if i design wing with proper lift distribution wing should not need washout.

but i not sure so any one can comment i appreciate it.


Hai Dang

[Ollie]

The wing washout can be zero and if the planfrom doesn't too tapered so the tip stall is not severe. If the taper is too severe there is a tip stall problem. Then the washout must be used to avoiding tip stall. For efficient lift distribution and at small angular attack, washout must be avoided.

See:
http://aero.stanford.edu/WingCalc.html

[HaiDang]

thanks ollie

please excuse my confusion but i just want to make sure.

as long as i design wing with good aspect ratio and not to much taper and good lift distribution then i can use different airfoils accross the span of wing?

all airfoils i want to use have same camber and are only different in thickness.


Thanks for more informaton.



Hai Dang

[biber]

To achieve good handling I would recommend to slightly increase the camber towards the tip, just as much as it needs to maintain at least the same CLmax inspite of the lower RE and thickness towards the tip. Then add as much washout as it needs to compensate the eventually changed zero lift angle (due to higher camber) of the airfoils. From an aerodynamical point of view even that is still no washout since therefor only the zero lift angles are counting wich schould be aligned refering to the methode described above. If done so, you will get ever the same lift distribution independent to the actual angle of attack, only dependent to the chosen wing planform. So essentially i guess the tip section maybe should have an about 0.5% higher camber than the root section. Hope that helps.

Biber