Typical ASI variation

skidoo

skidoo

Line Up and Wait
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skidoo
How much variation do you typically see on your airspeed indicator in smooth air and turbulent air. It seems that mine bounces around 2-5 kts in smooth air, and up to about 10kts in turbulent air. So, I am wondering how much is common, or nomal. Yesterday, I had trouble trimming to a good approach speed in turbulent air.
 
In turbulent air set a power setting and pitch attitude that will give you the desired airspeed and don't worry about chasing the airspeed indicator. Works good for landing in smooth air too.
 
skidoo said:
How much variation do you typically see on your airspeed indicator in smooth air and turbulent air. It seems that mine bounces around 2-5 kts in smooth air, and up to about 10kts in turbulent air. So, I am wondering how much is common, or nomal. Yesterday, I had trouble trimming to a good approach speed in turbulent air.
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Depends upon several factors, but the more the mass of the airplane typically the more variation. Kinetic energy comes into play.
 
If you're holding attitude in a light plane, +/- 10 knots seems a lot, even in turbulence. OTOH, if you're chasing the altimeter, it would be a foreseeable result.
 
Ron Levy said:
If you're holding attitude in a light plane, +/- 10 knots seems a lot, even in turbulence. OTOH, if you're chasing the altimeter, it would be a foreseeable result.
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Well, I'm talking about the digital tape bouncing around so rapidly I can see only the 7 for an airspeed of 7X. And then bouncing between 6X and 7X at a little slower pace, probably as I get nearer to 70kts. The X digit is the one bouncing rapidly. It's too rapid to chase!
 
Since this is a G1000 with an Air Data Computer, does it has a setting to slow down the response time, i.e. the sampling rate or an averaging time. I think it would be better to respond over a half second average or so rather than 0.1 sec or less.
 
skidoo said:
Well, I'm talking about the digital tape bouncing around so rapidly I can see only the 7 for an airspeed of 7X. And then bouncing between 6X and 7X at a little slower pace, probably as I get nearer to 70kts. The X digit is the one bouncing rapidly. It's too rapid to chase!
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That does NOT sound normal.

What kind of airplane?
 
skidoo said:
Since this is a G1000 with an Air Data Computer, does it has a setting to slow down the response time, i.e. the sampling rate or an averaging time. I think it would be better to respond over a half second average or so rather than 0.1 sec or less.
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I was thinking direct-reading round gauges. With a G1000 with an ADC, it sounds like there's something needing attention.
 
Ron Levy said:
I was thinking direct-reading round gauges. With a G1000 with an ADC, it sounds like there's something needing attention.
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What Ron said. In the DA40, the G1000 ASI is rock solid in smooth air, varies ±1 knot in light chop, and maybe ±2 in turb. But it's always readable even when it's "bouncy". And the 182 definitely rides the bumps better than the DA40.

If it's changing so fast that you can't read the last digit, something is wrong. Blocked pitot drain, or water (or something else) somewhere in the system maybe?
 
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