Stall speed vs wing thicknes & AoA - confused

[Nicke]

Some planes have a thicker root chord than tip chord. never seen the other way around. I thought that was to prevent tip stalls, by having the inner part of the wing stalling first. So I assume thicker airfoils have a higher stall speed.
But on the other hand, isn't it true that thicker airfoils give more lift at slower sppeds; a very fast flying plane has a thinner airfoil, a slow one has a thicker airfoil.

How can this be? does a slow plane stall before a fast one? Seems weird.

I have the same thoughts for AoA. Planes usually have wash out, not wash in. Root AoA larger than tip AoA. So the root stalls before the tip. Which means high AoA stalls before low AoA.
Again, slow planes such as slow- and parkfliers usually have a high AoA wing, and faster planes have a low AoA, if any.

Again, does the slower plane stall before the faster??? Totally confused... Help me clear this out, someone!

[Bruce Abbott]

A tapered wing is more inclined to tip-stall than a straight wing. A straight wing stalls at the root first, but as taper is increased the stall area spreads out towards the tips. Adding just the right amount of taper optimises lift as the whole wing is contributing equally, and the whole wing will also stall at the same AOA (Angle Of Attack - relative to the incoming airflow). Excessive taper causes tip-stalling tendencies.

There is no such thing as 'stall speed' for an airfoil, only stall AOA. Stall speed of the aircraft in level flight is determined by how much lift the wing produces at its stalling AOA. This is why a high-lift airfoil contributes to a slower stall speed, and a heavier plane stalls at a higher speed (more lift is required to hold it up, and any airfoil produces more lift as speed is increased).

High AOA does indeed stall before low AOA. Actually, it is the high AOA that causes the stall. Indoor and parkflyer models often have a high wing incidence (angle relative to the fuselage), to create more lift when flying in a level attitude. However, this does not increase the stall AOA, in fact the plane will stall at a lower climb angle (angle of fuselage relative to horizontal).

Regarding slow plane vs fast; a slow plane has a high-lift airfoil and stalls at a low speed. The airfoil may create more lift by being thicker and/or highly cambered, so it will stall at a higher AOA, but it will have higher drag and is no good for flying fast.

A fast plane usually has a low-drag airfoil that does not need to produce as much lift (all airfoils produce more lift at higher speed). Low drag is achieved by thinning the airfoil, and so stall AOA will be lower.

Another factor to consider is how the wing behaves in stall. Some wing designs produce a soft stall, allowing the pilot to fly at or even beyond the stall point and still have control (eg. delta wing). Other designs stall abruptly, which is great for doing tricky aerobatics, but can cause nasty suprises (eg. elliptical wing on a Spitfire).

[Nicke]

Thanks for taking your time for that long answer. Think it cleared out things a bit. I will have to wait a while and let my brain absorb the info :)

[Andy W]

Any wing will stall at any airspeed if the AOA is sufficient.

A note re: washout, however. The inboard section will indeed stall before the outboard - that's the whole idea - lose lift at the same time as maintaining roll stability (as the outboard sections are still "flying")..
..a

[joao]

Hi Nicke!

Here goes a pictorial info on the effect of taper ratio on the regions of flow separation (wing not working properly) at near-stall conditions.
Info from the great book "Aircraft Performance and Design" by Dr J. Anderson.

Cheers, João

[Nicke]

Thanks for the pic, joao.
Always makes it easier to understand with a good pic.
However I was a bit confused first, didn't know if it was a front view or top view of the wing. Looking at it for a while, it's obvious it is a top view.
What made me confused was that I thought I had asked about varying wing thickness, not chord. But looking at my first post, I see I wrote 'chord' where I meant 'airfoil'. Guess I was VERY confused about a few things... :)

I hope i understand things now... it was a top view, right?