Turbulator tape, dimpletape on tubing
gyrobob
tubing in a 60 to 90 knot airflow?
If so, where should it be placed? I assume it would be 90 degrees
from the relative wind.
Thanks for any info.
F.L. Whiteley
"gyrobob" <rwrom...@yahoo.com> wrote in message
news:481a5b17.02110...@posting.google.com...
Dimple tape, aka golf ball effect, reputedly reduces drag on propellar
leading edges, struts, and landing gear legs. This was discussed a couple
of years ago in rec.aviation.homebuilt. I'd suggest a groups.google.com
search there.
Frank Whiteley
gyrobob
this principle in other google groups, but not much on drag reduction
on tubes/struts.
What I'm hoping is that someone can verify a lot of drag reduction on
exposed struts. I have lots of exposed "strutting" that could really
benefit from some drag reduction.
I need to know if it works at all, and, if so, what works best --
dimpletape, zig-zag, or turbulator tape. For those who have made
their own tape of some sort, what thickness is best?
Anyone got any ideas?
Thanks,
Bob
"F.L. Whiteley" <gre...@greeleynet.com> wrote in message news:<3dc74248$0$184$7586...@news.frii.net>...
tjward
> this principle in other google groups, but not much on drag reduction
> on tubes/struts.
Well, you could paint some dirty oil on the front of the tube, stick it out
a car window, drive down the freeway, and observe where it puddles up on the
back.
Put one of your candidate turbulators a little ahead of the separation point
and do it again.
If you haven't already got the tubes/struts, you might take a look at the
streamlined downtube extrusions available for hang gliders. These are
generally already turbulated, though 60 - 70 mph is probably at the top end
of the speed range they're optimized for.
Take a look at:
http://www.angleofattack.net/html/atmain.html
Tim Ward
Mark Zivley
that's perhaps 1-2mm tall. Since the diameter of the struts are
probably fairly small (0-2 in.), anything wider is possibly wasted
material. In going back to the golf ball scenario that was covered in a
fluid mechanic's textbook, the drag reduction there was to trip from
laminar to turbulent because if you did that, the turbulent flow managed
to stay attached to the backside curvature better. If not tripped (a
smooth ball) the laminar flow would separate from the ball just a bit
past 90 and that left a large area of low pressure over the vast
majority of the back side of the ball. Tripped turbulent, it would
follow back a lot farther before separating and by doing that, the area
that saw the low pressure was a lot smaller and therefore it was a lower
drag configuration.
Pictures always help, so take a look at the sixth and seventh pictures
down that I found at:
http://www.adsources.com/golf/golfinfo/golfpa3.htm
Picture 9 is good two, but I think they are spinning the ball in that
picture.
I'll also suggest that as the airspeed decreases the benefit of the
turbulator will also decrease because at very low airspeeds the flow
won't separate at all.
Good luck.
Mark
Larry Goddard
well hit golf ball just after it leaves on it's trajectory?
Just curious...
Larry
John Wright
http://math.ucr.edu/home/baez/physics/General/golf.html
Which says they leave the tee at about 70 m/s which is 252000 m/h = 252
kph.
This one just says about 200 kph -
http://www.savingsolutions.com/ballinfo4.html may mean once it's moved away
from the head however.
This one says Tiger Wood's swing speed is 125 mph (200+kph)
http://nikegolf.nike.com/nikegolf/gallery/r_082300.shtml
"Larry Goddard" <la...@siriusimages.com> wrote in message
news:3DC87252...@siriusimages.com...
Larry Goddard
So basically about my Uvalde interthermal speed. :-)
Larry
"01" USA
Torben Kristensen
> Thanks, John.
>
> So basically about my Uvalde interthermal speed. :-)
>
Or recommended approach speed on short final for the fairway ;-)
John Wright
"Torben Kristensen" <NOSPA...@aub.dk> wrote in message
news:3dc987dc$0$10681$4d4e...@read-nat.news.dk.uu.net...
I have landed out on a golf club - well their practice putting green. I
spotted that the white things in a larger field next to it were distance
markers for the driving range just in time. They weren't too happy, but not
too bad, as I'd stopped in the top corner and they only lost the use of one
hole while I was there. Interestingly, the golfers totally ignored the
glider and just got on with their practicing, even when the trailer drove
in. They wouldn't let me use the phone or bar in the club house as I wasn't
suitably dressed, I had to use the kitchen entrance and phone. But they do
the same at my gliding club as well...
Martin Gregorie
<johnp...@blueyonder.co.uk> wrote:
>Using google brings up this link
> http://math.ucr.edu/home/baez/physics/General/golf.html
>Which says they leave the tee at about 70 m/s which is 252000 m/h = 252
>kph.
>
>This one just says about 200 kph -
>http://www.savingsolutions.com/ballinfo4.html may mean once it's moved away
>from the head however.
>
>This one says Tiger Wood's swing speed is 125 mph (200+kph)
>http://nikegolf.nike.com/nikegolf/gallery/r_082300.shtml
>
>
The critical thing is the Reynolds number (Re), rather than simple
speed.
A glider wing operates in the 1.0 to 2.5 million Re range.
The golf ball flies at about 200,000 Re.
A 3 inch (75mm) strut at 50 Kts has an Re of about 125,000.
All these are operating essentially in the laminar flow range, so
similar turbulation strategies should be used, i.e. for turbulators
about where the flow breaks away at the rear of the strut.
I think the golf ball is a special case; the whole thing has to be
turbulated simply because it spins in flight and so it has no front or
rear. If it didn't spin a smooth entry with a dimpled rear half would
probably work better.
If the Re was significantly under 100,000 then a turbulent boundary
layer would work better: models that fly in the Re 50,000 region
benefit from textured finishes and boundary layer trips near the
leading edge of the wing on the upper surface.
HTH
--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :
Robert Ehrlich
If I correctly understand what I read at
http://www.bls.fr/amatech/aerotechnique/trainees2/trai2vc1.htm
(sorry, only in French, but anybody should understand the figures),
it should be placed a little ahead of 80 degrees from the
stagnation point, and would not be useful for Reynolds numbers
above 500000. Can't remember the right constant for computing
your Reynolds number for 90 knots and 1" diameter.
Martin Gregorie
Really rough calculation for a 1 inch outside diameter tube:
90 Kts = Re 75,000
60 Kts = Re 50,000
That's pretty much in the turbulent Boundary Layer range, so try a
thread turbulator on each side at 80 - 90 degrees from the stagnation
point and (possibly) one on each side about 25 degrees from the
stagnation point.
You can either glue on strong button thread (nitrate model dope is
good) or use 0.8 mm (1/32") PCB layout tape, layered if needed, to get
the trip about 0.5 mm (1/64") high.
Actual experience: My F1A competition free flight gliders fly at
around 10 Kts and have a 150mm (6") wing chord. That gives them a Re
very close to 50,000. They fly best with a mat finish on the wing and
two thread turbulators on the upper surface. These are placed on the
high point of the wing and 5% of the chord back from the leading edge.
Robert Ehrlich
> ...
> Really rough calculation for a 1 inch outside diameter tube:
>
> 90 Kts = Re 75,000
> 60 Kts = Re 50,000
>
> ...
According to the URL cited in my previous post, the boundary
layer becomes turbulent when Reynolds number reaches 500000,
between 2500 and 500000, the boundary layer is laminar up to
80 degrees from stagnation point, where a separation occurs,
hence the avantage of of a turbulator before this point
forcing the boundary layer to become turbulent and so delaying
the separation, which occurs at 120 degrees in this case.
Martin Gregorie
What I was meaning to say was that turbulation is a big help on low
energy boundary layers in the region Re 25,000 - 75,000 or so but not
much use below 25k or from 100k upward until you reach 1.5M+
Are you sure about turbulent flow above 500k?
I was under the impression that modern sailplane wings were all
laminar sections, hence the neat polished surfaces and general
problems with rain drops and bugs on the LE. The latter disrupt the
nice laminar BL by turbulating it.
In the model world we generally use very smooth wings from 100k
upwards - the laminar region. We reckon that the use of textured
surfaces and trips are beneficial below 50k because they energise
and/or stabilise the turbulent BL found in this region. Of course it
all changes again below 25k as you run into the region where the
curved plate is king and lower still, at 3k or lower where the flat
plate is the berries.
Robert Ehrlich
>
> On Fri, 08 Nov 2002 10:17:48 +0000, Robert Ehrlich
> <Robert....@inria.fr> wrote:
>
> >Martin Gregorie wrote:
> ...
I am sure this is what I read on the Web page I cite
(http://www.bls.fr/amatech/aerotechnique/trainees2/trai2vc1.htm).
Wether it is true or not may be discussed. This value is only
for cylindrical or spherical bodies.