Kestrel Density Alt Readings

[TrickPony29]

Hello all, I have a question about my Kestrel 4500. What are you guys getting for deviation in density altitude. I took it out for the first time to the range and had readings bouncing from -50 up to 1700, after about 15min it settled down but was still bouncing around +-50. I know the D Alt is set from the factory but is this normal?
Thanks in advance,
Drew

 

[treebasher]

Re: Kestrel Density Alt Readings

It is normal for the Kestrel to take around 15 minutes to stabilize. And the +-50' is not uncommon, at least with my unit it is not.

 

[Lindy]

Re: Kestrel Density Alt Readings

Sit and watch the barometric pressure reading sometime. It changes. So does the temperature. And that's what's affecting the reading.

A DA change of +/- 50 feet is insignificant. To see that for yourself, experiment by changing that in a ballistic program.

 

[TrickPony29]

Re: Kestrel Density Alt Readings

Thanks a lot for the replies guys. Was getting worried I might have gotten a bad one.

Thanks again,
Drew

 

[BFD711]

Re: Kestrel Density Alt Readings

My Kestrel 4500 does the same thing. I used to wonder the same thing but these posts explain the reason for it well.

 

[rmfield]

Re: Kestrel Density Alt Readings

I think most of the wandering DA you are seeing is due to temperature. The Kestral is very accurate, but you need to understand that it is only measuring that little tiny parcel of air surrounding its sensor. Lots of things can effect that little parcel of air including the temperature of the instrument housing, your nearby truck, and your body. To work best, the instrument needs to be at ambient temperature, not near anything radiating heat, and having the air moving over the sensor.

 

[Lindy]

Re: Kestrel Density Alt Readings

For an illustration of the magnitude of minor changes in DA, I set up my load in a ballistics program, and varied the DA by 250 feet. The difference on a 1000 yard shot is 3.1 inches. That's less than a tenth of a mil.

A ballistic program is a handy tool for experimention to determine the magnitude of changes.

And since we're discussing that, perhaps this reference is appropriate:

Sources of Ballistic Program Inaccuracies