Blow holes vs turbulaator tape.

[Jonathan St. Cloud]

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?

[[email protected]]

On Sunday, October 23, 2016 at 4:54:27 PM UTC-7, 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?

Blow holes don't involve much extra maintenance. When I was polishing the wings on my DG-303, I'd just put a piece of wing tape over them. I only checked whether any holes were clogged once, as I decided it was unnecessary. Hook a low pressure air source to the intake (I used a vacuum cleaner exhaust port). Hold a lit stick of incense over each one, if it failed to brighten up, run an appropriate size needle through the hole (carefully, so as not to push out the brass tube insert). It took longer to replace old turbulator tape on my other gliders.

DG offered a DG-300/303 Club with (among other things) dimple tape replacing the blow holes, I guess they decided the blow holes were worth a premium for that particular airfoil.

Marc

[Michael Opitz]

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

[Jonathan St. Cloud]

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

[[email protected]]

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.

[Steve Leonard[_2_]]

On Monday, October 24, 2016 at 9:26:10 AM UTC-5, 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.

Model airplane servos to open or close the supply. I think there were two sets of holes. One set further forward for lower speed, and another further back for higher speed. I think the aft set was always open, but the forward set could be closed off to not trip the flow before it needed to be tripped. Tape is only set for one C/L. With multiple sets of holes, you can transition based on C/L with different hole locations.

[Dan Marotta]

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

[Jim White[_3_]]

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

[Jonathan St. Cloud]

I think the JS-1 has two sets of blow holes, as per their web site.


On Monday, October 24, 2016 at 8:23:15 AM UTC-7, Steve Leonard wrote:
> On Monday, October 24, 2016 at 9:26:10 AM UTC-5, 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.
>
> Model airplane servos to open or close the supply. I think there were two sets of holes. One set further forward for lower speed, and another further back for higher speed. I think the aft set was always open, but the forward set could be closed off to not trip the flow before it needed to be tripped. Tape is only set for one C/L. With multiple sets of holes, you can transition based on C/L with different hole locations.

[Soarin Again[_2_]]

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

[Jonathan St. Cloud]

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

[Steve Leonard[_2_]]

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.

[Bruce Hoult]

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.

[[email protected]]

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

[Jonathan St. Cloud]

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.

[Tom Kelley #711]

On Monday, October 24, 2016 at 2:16:19 PM UTC-6, Jonathan St. Cloud wrote:
> 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.

I get these on Ebay. Works good on my 29. I find that inflight dust and bugs do get in and I do clean them several times a year. If you drop them, they do break rather easily.

..024" 0.60mm #73 - Five Carbide Drill Bits -

Best. Tom #711.

[Eric Greenwell[_4_]]

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/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[krasw]

On Wednesday, 26 October 2016 03:26:21 UTC+3, Eric Greenwell wrote:
> 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.
>

If the function of blowholes is to trip laminar flow into turbulent, how can laminar flow be "thick"?

[Eric Greenwell[_4_]]

krasw wrote on 10/26/2016 12:33 AM:
> On Wednesday, 26 October 2016 03:26:21 UTC+3, Eric Greenwell wrote:
>> 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.
>>
>
> If the function of blowholes is to trip laminar flow into turbulent, how can laminar flow be "thick"?

I'm not sure what you are asking, but in general, laminar flow has a
thicker boundary layer than turbulent flow, and when it grows too thick,
it separates from the airfoil into a "laminar separation bubble" that is
high drag. The cure is to trip the laminar flow into turbulent flow,
which "sticks" better to the airflow.

Schleicher uses two layers of zig-zag tape just in front of the NACA
inlets that pressurize the control surface blowholes. A single layer is
not thick enough to trip the laminar flow that far back on the airfoil.
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

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

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[ND]

i'll tell you everything i know based on my time with eta-biter, concordia, and talking to butler.

The blow holes on eta biter are driven by a naca duct. the naca duct has been modified to be closed via a switch in the cockpit that drives a servo. at a certain airspeed, the blowing is swithced of and the boundry layer is turbulated further back by....zig sag tape. there is a presentation by butler about this "blowing articulation" out there on the web. Due to manufacturing and maintainance complexity, concordia doesn't have blowholes. neither does the V3. that's kinda a schleicher thing.

When we refinished my 20C two years ago, the question was this: can we fill in the blowholes, and just put zig zag over the blow-hole location? the idea was to reduce the maintainance/not worry about filling them with wax/ no cracking of the paint over the longer term.
we wanted to make sure that the turbulator tape would provide the same benefits though, and not actually harm the performance. butler and waibel both said zig zig in the same location would offer the same performance benefits..

I personally wanted to keep the blowholes, and fantazised about installing blowhole articulation for a club class ringer. I was outvoted though, so we did zig zag tape. the glider flies really well. Ask erik nelson and his V2XA... ;)

On Sunday, October 23, 2016 at 7:54:27 PM UTC-4, 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?

[Ed Downham[_3_]]

We’ve gone from a NACA duct with an airspeed-sensing servo to turbulator tape on our ASH-25 EB28 and it seems fine. I think the Binder factory did a lot of comparison testing and the extra weight and complexity of the blown wing didn’t make it worthwhile, as long as you got the tape in the right place...

[krasw]

On Wednesday, 26 October 2016 21:20:09 UTC+3, Eric Greenwell wrote:
> Schleicher uses two layers of zig-zag tape just in front of the NACA
> inlets that pressurize the control surface blowholes. A single layer is
> not thick enough to trip the laminar flow that far back on the airfoil.

Ok. Blow holes seems amazingly expensive and complicated construction when compared to simple tape. I have very hard time believing that Waibel, Heide et al. did this without any benefits. I have to confess that I have more believe in their collective aerodynamic wisdom than this groups', no doubt impressive it might also be.