# Re: alula

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Philidor11@aol.com wrote:

> In a message dated 6/12/99 1:18:50 PM Eastern Daylight Time,
> sarima@ix.netcom.com writes:
>
> << Some, but not all, leading edge slats function like the avian alula by
> creating a slot at the leading edge of the airfoil.  Air forced through this
> narrow slot increases in velocity over the top of the wing, thereby avoiding
> a stall. That is essentially how an alula works. >>
>
> I'm surprised that a small clump of feathers can divert enough air over the
> top of the wing to make a substantial difference.

If it operated primarily in slot or slat mode, it wouldn't make a substantial
difference in lift.  As an example of slot function, let's make some simplifying
assumptions just for purposes of visualization.  Let's say the wing is uncranked
(unbent) and untapered (constant chord), assume the alula covers 10% of the
span,
assume steady state CLmax without alula is 1.5, and assume steady state CLmax
for
the span directly aft of the alula is arbitrarily increased to 2.0.
Then the effective CL without the alula is the span times the unslatted CLmax or
1.0*1.5 = 1.5
With alula the effective CL is (1.0 - 0.1)*1.5 + 0.1*2.0 = 1.35 + 0.2 = 1.55
So by this scenario, the increase in steady state lift due to a 10% span alula
slot is 1.55/1.5 = 1.033 for a 3.3% increase in lift.  The actual increase would
be expected to be less for several reasons.  An alula can work in this fashion,
but not very effectively, and the slotted scenario doesn't appear to describe
the
actual function of the mechanism.

Best wishes,
JimC

```

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