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teamgrumman(at)YAHOO.COM
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 Posted: Thu Sep 09, 2010 10:12 am Post subject: air flow |
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This is just a sample of the hundreds of tests I've done trying to get rid of airframe drag.
The first pic, 612, is the bottom of the plane without the fairing. Notice the cross flow. There is a significant amount of drag in this photo. Here's something I'll bet you didn't know: that cross flow makes noise. If you can make the right frequency, you can enhance the flow attachment. That's extremely rare.
The next pic, 400, is using the first style fairing. There is still a small recirculation zone adjacent to the fairing behind the PFS pipe. If you can see the little black dots in the 612 pic, those are rivnuts. I moved the fairing around a bit to see if I could affect the strength of the recirculation zone.
The major cross flow you see coming across from the sides is due to air flow during climb out. I've toyed with the idea if drilling a series of small holes in the cowling and bleeding oil from the inside after I level off.
The second style fairing was an attempt to keep the airflow attached to the bottom of the muffler as it exits the pipe. The fairing gets sooty but it does help some.
The third style fairing, the short one, was an attempt to affect the recirculation zone.
The recirculation zone, as it happens, was due to the nose strut faring I had on the original cowling. After I got rid of the fairing, CHTs went up about 15 degrees, but the plane was 2-4 knots faster.
I have another 'mod' in the works as I write this. Trying to keep the speed and improve the cooling. It's a very fine tightrope.
Gary
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haveblue1(at)mac.com
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| Posted: Thu Sep 09, 2010 5:06 pm Post subject: air flow |
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Gary,
So, if I understand this, at the correct frequency of sound, you can achieve a drag reduction?
Bruce Smith
On Sep 9, 2010, at 2:09 PM, Gary Vogt wrote:
| Quote: | This is just a sample of the hundreds of tests I've done trying to get rid of airframe drag.
The first pic, 612, is the bottom of the plane without the fairing. Notice the cross flow. There is a significant amount of drag in this photo. Here's something I'll bet you didn't know: that cross flow makes noise. If you can make the right frequency, you can enhance the flow attachment. That's extremely rare.
<IMG_0612.JPG><PICT0400.JPG>
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teamgrumman(at)YAHOO.COM
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| Posted: Thu Sep 09, 2010 5:58 pm Post subject: air flow |
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Yes. In the 70's and 80's there was a significant amount of research using sound generation (speakers) that blasted sound onto the wing. What it did was energize the boundary layer (up to .1 inches above the surface of the wing). The airflow would reattach. This was based on research done in the early 1900's by Prandtl, Helmholts, and Blasius.
From: Bruce Smith <haveblue1(at)mac.com>
To: teamgrumman-list(at)matronics.com
Sent: Thu, September 9, 2010 6:03:35 PM
Subject: Re: air flow
Gary,
So, if I understand this, at the correct frequency of sound, you can achieve a drag reduction?
Bruce Smith
On Sep 9, 2010, at 2:09 PM, Gary Vogt wrote:
| Quote: | This is just a sample of the hundreds of tests I've done trying to get rid of airframe drag.
The first pic, 612, is the bottom of the plane without the fairing. Notice the cross flow. There is a significant amount of drag in this photo. Here's something I'll bet you didn't know: that cross flow makes noise. If you can make the right frequency, you can enhance the flow attachment. That's extremely rare.
<IMG_0612.JPG><PICT0400.JPG>
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[quote][b]
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