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Author Topic: Vortex Generators:  (Read 3706 times)
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Glen
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« Reply #15 on: December 12, 2016, 08:25:53 PM »

Some have said it gives clean air for the pilot chute to catch the air better and help pull out the main canopy.
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Jim Phelps
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« Reply #16 on: December 12, 2016, 09:07:51 PM »

The Nish family has used and promoted the generators for years.  Have 'em on the van, the race cars (as allowed, I presume) and so on.  I'd say they'd be a reasonable source for information - maybe even data.

I wonder if Layne and Tom*, at Darko wind tunnel, have ever tried to quantify the things?

*Or anyone at any wind tunnel, or even you, Woody.

Twenty years ago,  we tested patented vortex generator strips an inventor contacted us about.  We let him guide the location on a couple of cars we had.  Most of the trials were unsuccessful.  Then we evaluated the vortex strips on a notch-back vehicle like the one shown in the Mitsubishi paper.  They were located just below the back glass header.  We measured a significant drop in drag in that application, more than double the small amount (CD=0.004) stated in this paper.
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deucemac
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« Reply #17 on: December 13, 2016, 03:08:23 AM »

Oh bbarn, if production  aircraft  don't use vortex generators,  than B-52  A through E models never existed. There were long rows do v/g on the back of each wing ahead of the ailerons  to promote better airflow  to them. Boeing  made around 500 or so of them. On the G and H models, ailerons  were eliminated  and roll control  was done by spoiler  action. I worked  flight test for several  of the large aircraft  manufacturers  and many of their aircraft used vortex generators. One funny thing we used to  do to new airman just out of  tech  school  was to send them to the tool crib for a special  voltmeter  to check the vortex generators. It never failed to amuse  us and make the  tool crib attendant  unhappy  when the kid went over there dutifully  intending  to get that special  meter. In flight test we often tufted a surface  to record laminar  airflow. Depending  on the camera results, we might add  a row of vortex  generators  to see if airflow  to the surface was improved  and how much. If it worked  out, than production  was notified and a modification  was authorized. Depending on the  shape of a vehicle on the ground or in the air, vortex generators  may be great or something  to bang into tear up your body or really  add to stability, but is all  case by case as I see it?
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bbarn
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« Reply #18 on: December 13, 2016, 07:36:08 AM »

Oh bbarn, if production  aircraft  don't use vortex generators,  than B-52  A through E models never existed. There were long rows do v/g on the back of each wing ahead of the ailerons  to promote better airflow  to them. Boeing  made around 500 or so of them. On the G and H models, ailerons  were eliminated  and roll control  was done by spoiler  action. I worked  flight test for several  of the large aircraft  manufacturers  and many of their aircraft used vortex generators. One funny thing we used to  do to new airman just out of  tech  school  was to send them to the tool crib for a special  voltmeter  to check the vortex generators. It never failed to amuse  us and make the  tool crib attendant  unhappy  when the kid went over there dutifully  intending  to get that special  meter. In flight test we often tufted a surface  to record laminar  airflow. Depending  on the camera results, we might add  a row of vortex  generators  to see if airflow  to the surface was improved  and how much. If it worked  out, than production  was notified and a modification  was authorized. Depending on the  shape of a vehicle on the ground or in the air, vortex generators  may be great or something  to bang into tear up your body or really  add to stability, but is all  case by case as I see it?

I would agree with your case by case assessment. VG's do exist on many aircraft, there are even aircraft that have been issued a certificate of waiver for their use. Back in the 90's we looked at putting them on our Navajo Chieftain. They did increase payload and reduce fuel burn so I would say they do work - of course I never said they didn't either.

GENERALLY, they are not installed onto GA aircraft at the factory. Some of it is cost, some of it is paperwork, some of it is they aren't effective for a particular model. On a B52, I could see them as highly beneficial. A B52 has a specific mission and that has to do with carrying weight. A VG CAN lower the stall speed as well as increase lifting capacity. On the B52 I would imagine that the VG's installed on both the wing and the ailerons were never at the trailing edge of the structure but rather at or forward of the recovery point of the wing.

You will also find VG's on production aircraft in specific locations, not strewn out in a line on the wing. They are judiciously placed on various areas of the fuselage other areas to correct or control specific areas of concern.

Keep in mind when I see the term VG I immediately think of the early applications in the general aviation market. These devices were installed in-line on each wing at the point of recovery along the entire length of the wing. The purpose of those was to promote particular characteristics of a wing within a give flight envelope. I am not counting the ones installed on the nose of an Super MD-88 that control the airflow into the engines 100' behind them. That is a particular application designed to shape a small segment of airflow and not induce lift/drag properties on a wing shape.

I could certainly see them in the pictures earlier in the thread having some influence on the pilot chute. Would be interesting to see video of deployment both with and without them and how much effect they may have.

Here are two examples of their employment that I am referring to. Notice they are installed in a line and in front of the recovery point of the wing. Their purpose here is to promote laminar flow. By that definition if you install them on the trailing edge of the wing they cannot promote laminar flow as there is nothing to attach the air too.



I'll add this picture too. This is a flap on a Malibu, you can see they installed them forward of the recovery point. Again, their intended/purported use is to promote laminar flow so location, location, location!! lol


« Last Edit: December 13, 2016, 07:44:43 AM by bbarn » Logged

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« Reply #19 on: December 13, 2016, 12:16:21 PM »

Has anyone tried air injection into the separated airflow region to reduce drag? The air to inject could be redirected from the front of the vehicle to small holes in the skin where vortex generators would normally be installed.

I have been reading where large ships are now using a similar concept called micro-bubbles that are injected onto the hull surface underwater. The air reduces drag up to 20% in the case of Quantum of the Seas cruise ship.

Don

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« Reply #20 on: December 14, 2016, 10:23:45 PM »

The air reduces drag up to 20% in the case of Quantum of the Seas cruise ship.

Don



the oxygen contained in that air will nurture barnacles to grow up to 40%  faster  grin
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