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Kestrel 4500NV Accessories?

 
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Old 03-29-2012, 02:05 PM
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Kestrel 4500NV Accessories?

I just purchased a 4500NV, and I was curious if anyone knows if someone makes a tube that slides in by the impeller to keep wind from coming in from the
side of the impeller (while in use with the vane mount)? Kind of like a little side isolation something...

Thanks. I hope my wording isn't too confusing .
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Old 04-05-2012, 09:34 AM
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Re: Kestrel 4500NV Accessories?

Quote:
Originally Posted by bowhunthard View Post
I just purchased a 4500NV, and I was curious if anyone knows if someone makes a tube that slides in by the impeller to keep wind from coming in from the
side of the impeller (while in use with the vane mount)? Kind of like a little side isolation something...

Thanks. I hope my wording isn't too confusing .
I've talked to a Kestrel engineer with the specific question of whether the Kestrel 4500 gives correct cosine of the velocity values when the unit is pointed at an angle other than directly into the wind. The answer was the because of the structure surrounding the impeller it is considerably different from true cosine values though he did not have a graph or table of what the errors were.

Putting a tube into the impeller housing would induce drag and give low readings. It would still not block side winds as the air flowing though the tube would be a function of the pressure difference at both ends of the tube, which is only zero if the tube is perpendicular th the wind. The whole point of the Kestrel's optional wind vane to keep the kestrel facing into the wind which is the only correct orientation. There can only be one instantaneous wind vector at a point, so when it's pointing into the wind there is no side wind. If there is a sudden change in wind it can momentarily give wrong readings while the vane re-aligns into the wind, but a tube would not help.

I was hoping I could mount the Kestrel with it's wind vane on a tall tripod so it would be at the height of the average of the trajectory above the ground (for flat ground), but the computer interface functions (Bluetooth or USB) don't allow full control of the unit from a laptop. It can download data on command or at selected intervals to a laptop which may be useful to a shooter. if you have a unit with the atrag software the use is mutually exclusive. I was disappointed that the atrag software cannot be operated from a remote laptop.

In a nutshell, anything you put near the impeller of the Kestrel will affect the airflow and give wrong readings. The back of the unit must face into the wind to give correct readings. The engineer said the unit would give correct velocity reading with the unit turned 180 degrees as the impeller is symmetrical, but the magnetic impeller pickup only detects speed and not direction of rotation, so the unit does not know if it's pointed backwards and the magnetic compass will result in wrong direction readings. That's the purpose of the wind vane and it does work. To work properly the wind vane has to be free to turn into the wind. It wont' be free to turn if it has to drag a USB cable. That's the only place I've found the Bluetooth function to be useful. You can gather a few days of wind vector data before the batteries go dead.

Will a Kestrel make you a better shooter? Not without understanding what it does and doesn't measure. If you just blindly believe the wind vector readings you won't get as good of results as someone who is skiled at doping wind just from visual signs. The Kestrel does not know about the wind between the shooter and the target, which for long range shooting can be more important than the wind at the shooter's location.
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Old 04-05-2012, 10:51 AM
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Re: Kestrel 4500NV Accessories?

Thanks for the informative answer!
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