I have a rough idea about why $C_{{l}_{max}}$ increases with increase in camber. But I can't explain why the stall angle decreases simultaneously.
5
-
1$\begingroup$ Related (maybe duplicate since extending flaps increases camber): Why does stall speed decrease when flaps are deployed?. $\endgroup$– BianfableCommented Oct 6, 2019 at 19:53
-
$\begingroup$ You may reread your question. You can at least delete the "enter image description here" $\endgroup$– Manu HCommented Oct 6, 2019 at 20:12
-
1$\begingroup$ Possible duplicate of Why does stall speed decrease when flaps are deployed? $\endgroup$– Manu HCommented Oct 6, 2019 at 20:13
-
1$\begingroup$ @Bianfable I don't think that is a duplicate since flaps not only increase camber, but often chord as well; but it is definitely related. $\endgroup$– AEhere supports MonicaCommented Oct 7, 2019 at 11:02
-
1$\begingroup$ @AEhere Yeah, I wasn't quite sure, that's why I also did not vote to close as duplicate. $\endgroup$– BianfableCommented Oct 7, 2019 at 15:52
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
4
At the same angle of attack, a cambered airfoil has a larger suction peak on the upper side (toward the leading edge), and a larger associated pressure recovery (toward the trailing edge).
Larger pressure recovery is equivalent to larger adverse pressure gradient, which leads to easier onset of boundary layer separation and stall.
-
$\begingroup$ Now, decrease aspect ratio and check the AOA curve again. This is why the thick Gottingen airfoils of a century ago were so revolutionary, giving the slow flying, maneuvering dogfighters of that day many advantages over the thinner undercambered wing design. Ironicly, the thinner airfoils proved superior years later as Mach numbers increased towards one. $\endgroup$ Commented Oct 7, 2019 at 6:20
-
$\begingroup$ @Robert DiGiovanni aspect ratio? I think you meant something else, there is no aspect ratio in 2D analysis. $\endgroup$ Commented Oct 7, 2019 at 10:41
-
$\begingroup$ @AEhere That's why we add the 3rd one. Thick Hershey wings make excellent recreational airfoils, and present the other side of the spectrum from thin supercritical wings (for some strange reason I keep writing about this). $\endgroup$ Commented Oct 7, 2019 at 12:02
-
1$\begingroup$ @RobertDiGiovanni the question is about airfoils, not wings, though, so bringing in the complexity of 3D flow doesn't seem like a good idea for something that can be explained in 2D. $\endgroup$ Commented Oct 7, 2019 at 13:12