Blow holes vs turbulaator tape.

On Monday, October 24, 2016 at 3:26:10 PM UTC+1, Jonathan St. Cloud wrote:
Thanks for the reply. I seem to remember that Dick Butler had throttled the blow holes on his ETA biter, not sure how he did that. seems like tape would have more drag but the manufacturing must be very time consuming (expensive).

On Sunday, October 23, 2016 at 5:45:04 PM UTC-7, Michael Opitz wrote:
At 23:54 23 October 2016, Jonathan St. Cloud wrote:
Just curious if there is research that compares blow holes versus
tabulator
tape as to effectiveness and drag? i.e., are the bow holes worth
the
maintenance or is tape effectively just as good? Does the new
Ventus have
tape or blow holes?

That subject goes back over 30 years. As I recall, the blowholes
would be better performance-wise if they could be regulated to blow
really strongly at low speeds, and then blow only a little at higher
speeds. To do this, one needs a large inlet to supply enough air to
the ducts at thermalling speeds. Then, you have to shut that
supply down to a trickle when cruising at higher speeds. This goes
backwards to just having a fixed size inlet that is not adjustable in
flight. One would have to have an extendable scoop on each wing
that the pilot could extend and retract depending on airspeed to
achieve this.

Anyway, the Z-tape works pretty well, is cheap to install, and is
easy to maintain. The blowholes are labor intensive both in
construction ($) and in maintenance.

I had DG-300 serial number 2, which was one of the first gliders
with this technology. Back in 1983-1985, I did side by side
comparison tests with the blowhole system working on the regular
fixed size inlets. Then, I repeated the (side by side) tests with the
inlets removed (to nullify the blowholes), and used Z-tape for the
turbulation instead.

I could not see any measurable performance difference between
blowholes (with fixed size inlet) and Z-tape. There were arguments
about the Standard Class rules to the point that there would have
been protests filed if I had come up with and used a variable inlet
scoop, so I left it alone.

So, long story short. The Z-tape is a lot cheaper and easier, and
yields good results. If you are in a class which would allow inlet
size adjustment in flight, and you have lots of money to pay for the
installation, and lots of time to spend maintaining all of of those tiny
holes, then you might see a marginal improvement over Z-tape.

That's how I remember it, although it was a long time ago, and the
blowhole technology may have gotten better.....FWIW

RO

Other than a little care during polishing blowholes don't need much attention but zig-zag tape keeps catching on grass, clothing, under finger-nails and on rigging trestle tops resulting in little sharp and draggy lifted corners that won't stick back down easily.

On 10/24/2016 9:12 AM, wrote:
snip
Other than a little care during polishing blowholes don't need much attention but zig-zag tape keeps catching on grass, clothing, under finger-nails and on rigging trestle tops resulting in little sharp and draggy lifted corners that won't stick back down easily.
And lots of triangle shaped divots in your finger tips...
--
Dan, 5J

Herr Waibel has been quoted as saying of the ASW27 that "there is a 50/50
chance that the blow holes improve performance by 1/2 point". Possibly
apocryphal. Easy to clean with a piece of copper wire and a vacuum cleaner
but tedious beyond belief. jim

At 16:50 24 October 2016, Jim White wrote:
Herr Waibel has been quoted as saying of the ASW27 that "there is a 50/5
chance that the blow holes improve performance by 1/2 point". Possibl
apocryphal. Easy to clean with a piece of copper wire and a vacuum cleane
but tedious beyond belief. jim

I once got a DG300 in for insp and found that the blow holes on one wing
were inop (apparently the seal of the internal blow hole channel had
failed). The factory said a fix was problematic and to go ahead and
install dimple tape as it works just as well. No telling how many years
the glider flew with one wing turbulated and the other not. The owner was
oblivious to any degradation in handling or performance before and after
installing the dimple tape.

ME

One would think if the blow holes did not add much a pencil pusher at the factory would realize they could have lots of man hours ($) by just using dimple tape.

On Monday, October 24, 2016 at 11:30:06 AM UTC-7, soarin wrote:
At 16:50 24 October 2016, Jim White wrote:
Herr Waibel has been quoted as saying of the ASW27 that "there is a 50/5
chance that the blow holes improve performance by 1/2 point". Possibl
apocryphal. Easy to clean with a piece of copper wire and a vacuum cleane
but tedious beyond belief. jim

I once got a DG300 in for insp and found that the blow holes on one wing
were inop (apparently the seal of the internal blow hole channel had
failed). The factory said a fix was problematic and to go ahead and
install dimple tape as it works just as well. No telling how many years
the glider flew with one wing turbulated and the other not. The owner was
oblivious to any degradation in handling or performance before and after
installing the dimple tape.

ME

On Monday, October 24, 2016 at 1:49:18 PM UTC-5, Jonathan St. Cloud wrote:
One would think if the blow holes did not add much a pencil pusher at the factory would realize they could have lots of man hours ($) by just using dimple tape.

Another claimed, but I don't know if it was ever proven, benefit of the blow holes is that even if they are behind the leading edge of the laminar bubble, they can still "blow out far enough to burst the bubble and get the advantage of not having the high drag, laminar bubble" whereas, turbulator tape inside the bubble does nothing at all for you.

It is all about how much are you willing to do to get that last half percent.

On Monday, October 24, 2016 at 10:14:25 PM UTC+3, Steve Leonard wrote:
On Monday, October 24, 2016 at 1:49:18 PM UTC-5, Jonathan St. Cloud wrote:
One would think if the blow holes did not add much a pencil pusher at the factory would realize they could have lots of man hours ($) by just using dimple tape.

Another claimed, but I don't know if it was ever proven, benefit of the blow holes is that even if they are behind the leading edge of the laminar bubble, they can still "blow out far enough to burst the bubble and get the advantage of not having the high drag, laminar bubble" whereas, turbulator tape inside the bubble does nothing at all for you.

It is all about how much are you willing to do to get that last half percent.

Half a percent? One minute on a three hour race? Plenty are won and lost by less than that.

It won't make any meaningful difference to whether you can stay up, or even whether you can complete a task.

On Monday, October 24, 2016 at 3:14:25 PM UTC-4, Steve Leonard wrote:
On Monday, October 24, 2016 at 1:49:18 PM UTC-5, Jonathan St. Cloud wrote:
One would think if the blow holes did not add much a pencil pusher at the factory would realize they could have lots of man hours ($) by just using dimple tape.

Another claimed, but I don't know if it was ever proven, benefit of the blow holes is that even if they are behind the leading edge of the laminar bubble, they can still "blow out far enough to burst the bubble and get the advantage of not having the high drag, laminar bubble" whereas, turbulator tape inside the bubble does nothing at all for you.

It is all about how much are you willing to do to get that last half percent.

If the airfoil is designed to use blowing, the gains may well be more than that.
Listen to the noise on a '27 when in the wrong flap position and you know
something is going on.
UH

Thanks Steve, I do remember now reading about that. Makes sitting down with a tiny drill bit and a six pack seem worth it.

On Monday, October 24, 2016 at 12:14:25 PM UTC-7, Steve Leonard wrote:
On Monday, October 24, 2016 at 1:49:18 PM UTC-5, Jonathan St. Cloud wrote:
One would think if the blow holes did not add much a pencil pusher at the factory would realize they could have lots of man hours ($) by just using dimple tape.

Another claimed, but I don't know if it was ever proven, benefit of the blow holes is that even if they are behind the leading edge of the laminar bubble, they can still "blow out far enough to burst the bubble and get the advantage of not having the high drag, laminar bubble" whereas, turbulator tape inside the bubble does nothing at all for you.

It is all about how much are you willing to do to get that last half percent.

Jonathan St. Cloud wrote on 10/24/2016 11:49 AM:
One would think if the blow holes did not add much a pencil pusher at
the factory would realize they could have lots of man hours ($) by
just using dimple tape.

Schleicher has used blow holes from at least 1984 on the ASW20C and B.
The holes were thin metal tubes on the wing bottom, and looked like they
might be costly. My ASH 26 E does not use the tubes on the wings;
instead, the blow holes are drilled into the the bottom of the flaps and
ailerons. That's not on the wing, but on the control surface!

My guess is the boundary layer is too thick on the control surfaces for
zig zag tape to work, unless it was stacked two or three high.

Drilled holes are probably cheap enough, and installing the tiny NACA
scoops is easy, too.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf