Jim asked:
> In reading it I noticed the comment that the reason
> the wing does not stall at the tips is because of a
> small ridge along the leading dge of the wing
> where it attaches to the fusalage.
Jim,
The outer part of the wing doesn't stall because the aircraft is configured
to limit the angle of attack such that most of the wing never gets to its
stalling angle of attack.
The wing root does get some stalling action because the shape of the
wing/fuselage fairing and the wing root leading edge ridge were designed to
allow the wing root to stall.
This wing root stall cuts down on lift, somewhat, and causes burbled air to
flow over the empennage. The burbling air over the empennage gives you
feedback of a "stall" AND, combined with the elevator up travel limit,
helps limit the elevator's ability to push down the tail (which could have
allowed a more developed stall).
If you can get a copy of Stan Thomas's book "The Ercoupe," you'll see a
diagram showing a fan shaped stall that starts at the wing root and
develops out to be a 45˚ fan shape from the wing root leading edge and
encompassing the first yard or two of the wing root trailing edge.
/|
//|
///|
////|
/////|
//////|
///////|
Many planes are designed so the outer panels of the wing stay UN-stalled
when the wing roots stall. (Did Fred Weick originate this or was it a
design feature before the Ercoupe??) Some use a bit of wing twist so the
outer panel has a lower angle of attack, others use other methods.
Key for the Ercoupe is that a fully developed stall, involving most of the
wing, cannot develop. For sure (as long as the rigging is correct and the
plane is within the CG), the majority of the Ercoupe wing cannot be kept
stalled and so autorotation cannot be maintained. (A spin is often defined
as autorotation due to one wing being more stalled than the other wing.)
Even an Ercoupe can be forced into a temporary full stall and maybe the
start of a spin, i.e. with a hammerhead stall. But, due to its design, the
Ercoupe cannot be held in a stall/spin with any application of its controls.
While they don't apply for the "characteristically incapable of spinning"
label, it seems that many new aircraft designs are so spin resistant that
some may actually match the Ercoupe's spin resistance. Designers aren't
all stupid, after all.
Ed
Ed Burkhead
http://edburkhead/Ercoupe/index.htm
ed -at- edburkh???ead . com (change -at- to @ and remove ??? and
spaces)
