Vibrating plane wings may delay stalling

[VectorLine]

"Making aircraft wings buzz.........the panels would be able to tilt its wing by up to 5° more, equating to 22% more lift at the same speed."

Article Here (http://www.abc.net.au/science/news/stories/s1439827.htm)

[Mad (Flt) Scientist]

I wonder if the delay in stall onset is based purely on wind tunnel data; I suspect so. In which case one question would be:

is the stall angle in a tunnel with sound effects higher or lower than that for the same aerofoil at full scale?

I'm wondering if it's a Reynolds number dependent phenomenom. (Im never sure how to stop spelling that word!). In which case it could be akin to transition strips, which help on a tunnel model sometimes but don't get the chance to be effective at full scale.

[Thridle Op Des]

I am wondering if this is connected to a phenomena observed in helicopters in forward flight, where the airflow remains attached to the top of the rotor blade a lot longer than expected during the retreating blade phase. I seem to recollect that the aerodynamicists believed that during the rapid pitch change to alpha max created a leading edge vortex that helped keep the boundry layer adhered to the top of the aerofoil.

[barit1]

Posted here too (http://www.newscientist.com/article.ns?id=dn7867&feedId=online-news_rss20)

Did I see a related pprune thread back in August? If so, can't find it now.

My uncle was a jazz trombonist and also a pretty "hot" pilot. Maybe this explains a lot.

[john_tullamarine]

Thridle Op Des,

The phenomenon to which you refer is a "superstall" (not to be confused with a deep stall situation) or "accelerated stall" and is described in the literature.

The driving factor is the aerofoil pitch rate and, as one would expect, it is seen more in the rotary side of the house. If the pitch rate exceeds a critical value (rusty memory seems to flash 70-plus deg/sec in the cortex), then a vortex arises which causes the flow to reattach and the alpha can go somewhat above "normal" values.

There was a very readable article on this subject in the RAeS Journal several years ago. If I recall correctly, the subject has been touched on in PPRuNe before and there may be a reference to the AeroSoc article ?

[Cron]

We do this for reverse purposes on hang gliders when the air is laminar, you are about 20 feet too high for a hill top landing at about 15kts and don't fancy the overshoot.

We call it 'shaking it down' - you rattle the 'A' frame forward and back using about the same frequency and amplitude which you would apply to a stuck door.

The effect seems to degrade the performance but controllability is retained and a shorter landing achieved.

We don't have a clue why it works and have often discussed it.

[Blacksheep]

This must explain the bee's famed defiance of aerodynamic theory. ;)

[john_tullamarine]

.. perhaps not .. but it could certainly explain my unique style of swimming ...