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1planeguy(at)kilocharlie.
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 Posted: Mon Jun 29, 2009 12:26 pm Post subject: VG test done on GA airplane, and "Slow flight" with VGS] |
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John, the VG's don't really increase the "lift" of the wing at normal
angles of attack (i.e. less than the normal stall angle of attack of a
VG-less wing)...the difference would have been past that...The VG's
allow the wing to produce lift to a higher AOA before stalling (VG's
energize the boundary layer to keep the airflow attached). So up until
the VG-less wing started to stall the plane probably wouldn't have
handled TOO strangely. If pushed to the point of allowing the VG-less
wing to stall you would have then had asymmetric stalling which is
essentially a spin entry...possibly unrecoverable. Steve Wittman used to
do empirical testing like this...he was also an extremely good pilot who
knew the edges of the envelope not to push too much. The clipped
triangle wingtip of the W10 Tailwind was added like that...on 1 wing
first then some test hops down the runway. From what was written about
it years ago I never understood if he flew it around the pattern or just
a crow-hop, but whatever...he realized the improvement and went and
modified the second wing to match.
The argument about a higher stall speed not being entirely bad does have
some validity. Talked to Randy Schlitter at SnF years ago. He was
looking over my RANS S7 and asked about my VGs...I told him the
improvement they made and he agreed that they helped a good bit, and
like John H., said "I don't like them..." I give him a puzzled look and
he added, "In the land of eternal wind, Kansas...at some point you WANT
it to stall..." Makes sense for him... The majority of the world though
they are going to be an improvement.
Jeremy Casey
John Hauck wrote:
| Quote: | Nick:
Your GA pilot friend seems to have less than good judgement.
You forgot to mention a few things in your post:
1-If it took full aileron to keep the VG-less wing up in ground
effect, it probably took full aileron to keep the wing up in any part
of the flight. How did he do when he climbed up to stall the airplane?
2-Requiring full aileron to fly in ground effect, the pilot would have
become aware of this soon as he broke ground, or most likely soon as
the mains started getting light. Seems like at this point of the
flight, he would have been running out of rudder and cajones.
For what it is worth,
john h
mkIII
….A GA pilot friend of my Tested VG’s on his Scout…Don’t do this
yourself………. He taped the VG’s on only one wing. His wings where
well balance prior to test. He tested stalling his plane at
altitude. The wing *without* VGs always stalled first.
Next that he came in low over the runway, in ground effect, and
had to use full aileron to keep the wing without VG’s up. Not sure
what he would have done if he ran out of aileron? He now flies
with VG’s.
For what is worth.
Nick Cassara
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Mon Jun 29, 2009 12:43 pm Post subject: VG test done on GA airplane, and "Slow flight" with VGS] |
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> John, the VG's don't really increase the "lift" of the wing at normal
| Quote: | angles of attack (i.e. less than the normal stall angle of attack of a
VG-less wing)...the difference would have been past that...The VG's allow
the wing to produce lift to a higher AOA before stalling (VG's energize
the boundary layer to keep the airflow attached). So up until the VG-less
wing started to stall the plane probably wouldn't have handled TOO
strangely.
>
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Thanks, Jeremy:
That's why I ask questions, to learn.
Seems like many of my questions go unanswered though.
John Williamson tested his forward and aft cg limits in flight. Wish I had
those numbers. They don't agree with the paper weight and balance by any
means. One of the reasons I can fly with a 12 lb tail wheel, 150 lbs of
fuel behind the cg, and 125 lbs of cargo back there too. 
john h
mkIII
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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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