Vertical Speed Indicator after Takeoff
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Vertical Speed Indicator after Takeoff
Hello Aviators. Can somebody please clear my doubt:
Why does the VSI show a negative rate of climb on takeoff. It goes from negative rate to zero and then climb. Does it relate to aerodynamics ?
I'm flying the embraer and the static port is near the nose.
Thank you in advance.
Why does the VSI show a negative rate of climb on takeoff. It goes from negative rate to zero and then climb. Does it relate to aerodynamics ?
I'm flying the embraer and the static port is near the nose.
Thank you in advance.
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All static ports are near or just aft of the flight deck. At rotation, wheels still on the runway, looks like a negative to the system. Little to zero altitude gain, zero to minimal vertical increase. But moments latter all has recovered. Does this help?
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Could it have something to do with the IRS position on the aircraft that gives the instrument false acceleration information until lift off after which time the positive rate is sensed by both the ADC and the IRS making the indication accurate?
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Are we talking about a modern Embraer (with IRUs)?
Surely, an IRU would show the V/S more accurately? Does the Embraer integrate the two sources of data poorly? i.e. short term IRU with longer term baro V/S.
Surely, an IRU would show the V/S more accurately? Does the Embraer integrate the two sources of data poorly? i.e. short term IRU with longer term baro V/S.
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I am just wondering if it has something to do with the location of the IRUs. I know the EJet has a number of E&E bays. could the IRUs be located in such a location that it is sensing downward movement as the aircraft is pivoting in the rotation?
Change in pressure field around the aircraft. As the aircraft is rotated the pitot static errors change from on ground errors to those applicable to fairly high Cl.
Assuming steam driven pitot static system you would need the on ground PEC curve to work out what is occuring.
Assuming steam driven pitot static system you would need the on ground PEC curve to work out what is occuring.
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I understand it is due to ground effect. Can you please elaborate what happens to the VSI during ground effect. I understand reduced induced drag during ground effect and working of the VSI with calibrated leak. But can't seem to visualize what happens to the VSI during ground effect.
Hello beinghuman,
I fly helicopters and I've also noticed a tendency to overeact of the more sensitive modern VSI. This is happening apparently when there's a brutal change in static atmospheric pressure; for instance when we cross the edge of an helideck (brutal change from "in ground effect" to "out ground effect" ) or in turbulences. There's an hybridization with a vertical accelerometer to the VSI on this equipment, but it doesn't seems to improve much the indication.
If this assumption is correct, should it mean that the pressure near the static ports in a ground effect air flow, is lower than atmospheric pressure ?
I fly helicopters and I've also noticed a tendency to overeact of the more sensitive modern VSI. This is happening apparently when there's a brutal change in static atmospheric pressure; for instance when we cross the edge of an helideck (brutal change from "in ground effect" to "out ground effect" ) or in turbulences. There's an hybridization with a vertical accelerometer to the VSI on this equipment, but it doesn't seems to improve much the indication.
If this assumption is correct, should it mean that the pressure near the static ports in a ground effect air flow, is lower than atmospheric pressure ?
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In ground effect, shouldn't the air become more compressed under the wing/fuselage, leading to a higher atmospheric pressure (i.e. a reduction in pressure altitude = negative v/s)
Hi NSEU,
What I meant is that, an increase of static pressure will indicate a rate of descend.
I understand then, that when leaving the ground effect, the ambiant static pressure is suddenly "felt" higher than inside the capsule.
It could mean that in ground effect with 0 rate of climb indicated, the ambiant atmospheric pressure sensed by the capsule is lower than the real one.
What I meant is that, an increase of static pressure will indicate a rate of descend.
I understand then, that when leaving the ground effect, the ambiant static pressure is suddenly "felt" higher than inside the capsule.
It could mean that in ground effect with 0 rate of climb indicated, the ambiant atmospheric pressure sensed by the capsule is lower than the real one.
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zzuf, who really does know about these matters, has it.
PEC is a mongrel beast and, apart from taking up a lot of OEM time in flight test, is very sensitive to unsteady airflow around the ports .. any time the aircraft is manoeuvring, PS readings should be taken with a grain of salt.
PEC is a mongrel beast and, apart from taking up a lot of OEM time in flight test, is very sensitive to unsteady airflow around the ports .. any time the aircraft is manoeuvring, PS readings should be taken with a grain of salt.
When I were a lad ... we had an IVSI, the "I" standing for instantaneous, which had a slug in a vertical tube which reacted to the actual first little bit of a climb or descent inertially and pushed a tiny bit of air into a gizmo which made the pointer read the truth for the first few seconds until the mechanism caught up.
Sorry, I'm a pilot not an instrument maker!
Sorry, I'm a pilot not an instrument maker!
