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calibrating airspeeds, revisited


207WF

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The Dynon Skyview calculates the TAS with use of the OAT and barometer setting in my CTLS ,the skyview only allows a calibration to zero.

On the Dynon forum any one with to high than true airspeed readings gets pointed to look at position of the static vent.

I can see that with the CTLS ground affect at rotation could affect air pressure at the static vent in that area.

 

The Altimeter and Airspeed readings to the Skyview got tested only 3 months ago as part of the transponder registration and found to be very accurate . However the test is done in a work shop and no allowance is made for a static vent that could be positioned in a higher or lower than ambient air pressure area of the aircraft.

 

If I'm the only one with this problem I have to start looking elsewhere than static vent position.

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It has not eliminated the static vent as an issue though, you have only proven that the instrument itself is not the problem. Installation of the static port, or installation of the ram air port on the pitot tube, can both contribute to problematic readings. Even OAT placement can cause issues.

This is why aircraft in flight testing may have complex sensor arrays mounted on booms ahead of the aircraft airstream. It allows data collection of undisturbed air as a control reference.

Try checking your gps with waas altitude. It will not be perfect either, but it can definately help to see if your instrumentation is favoring a high or low bias. Just make several comparisons, as gps altitude can very a bit (waas helps a lot!) EDIT: GPS altitude and MSL are not the same, as pointed out later in this thread! See www.esri.com/news/arcuser/0703/geoid1of3.html

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If you look at the right pitot tube on the CT (as you face the prop) you will see a small hole on a small bevel on near the tip.  That is where the wind indicator gets its primary wind force reading.  

 

Maybe that small hole is for AOA info?

 

The plane flies in the relative wind and cannot sense wind, only shear.  Winds shown on your EFIS are calculated by comparing TAS and GS for headwind / tailwind component and comparing your heading to ground track to compute the crosswind component.  When these are both known the winds direction and velocity are then known but will include error if you are not pointed into the relative wind.

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Maybe that small hole is for AOA info?

 

The plane flies in the relative wind and cannot sense wind, only shear.  Winds shown on your EFIS are calculated by comparing TAS and GS for headwind / tailwind component and comparing your heading to ground track to compute the crosswind component.  When these are both known the winds direction and velocity are then known but will include error if you are not pointed into the relative wind.

 

Agreed, the wind is calculated from airspeed, temp, and GPS ground speed.  The second hole in the pitot is AoA.  If it was a wind indicator, how could it sense a wind from the side or behind?    ;)

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Andy & CT, according to the Dynon info that is exactly what the second hole provides. It is referred to a the AOA/Boom Pitot by Dynon.

My LS has two pitots, is that only redundancy, or could that provided cross wind info? Does crosswind show on the SWs EFIS?

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Andy & CT, according to the Dynon info that is exactly what the second hole provides. It is referred to a the AOA/Boom Pitot by Dynon.

My LS has two pitots, is that only redundancy, or could that provided cross wind info? Does crosswind show on the SWs EFIS?

 

I have a simple tube pitot, and I get a wind arrow and speed on my old D-100.

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Andy & CT, according to the Dynon info that is exactly what the second hole provides. It is referred to a the AOA/Boom Pitot by Dynon.

My LS has two pitots, is that only redundancy, or could that provided cross wind info? Does crosswind show on the SWs EFIS?

 

Doug,

 

Your CT flies in the relative wind, no sensor can sense the wind because along with the plane the sensor is drifting with the wind.  Winds have to be calculated.  To see winds in a CTSW would depend on the EFIS.  I would think if the EFIS has GPS it would show winds.

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Doug,

 

Your CT flies in the relative wind, no sensor can sense the wind because along with the plane the sensor is drifting with the wind. Winds have to be calculated. To see winds in a CTSW would depend on the EFIS. I would think if the EFIS has GPS it would show winds.

Yes, that is certainly true. So, how is the crosswind calculated and headwind calculated on the EFIS?

P.S. Thanks to all for not reposting Burgers. It is much easier to ignore him.

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Yes, that is certainly true. So, how is the crosswind calculated and headwind calculated on the EFIS?

P.S. Thanks to all for not reposting Burgers. It is much easier to ignore him.

 

 

1st TAS is calculated using IAS and OAT

 

Then GPS GS is compared to IAS or CAS to get headwind/tailwind component.

THen GPS track is compared to magnetic heading to get x-wind drift.

 

IAS or CAS plus minus headwind/tailwind adjusted for crosswind drift is enough info to calc wind direction and velocity.

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Andy & CT, according to the Dynon info that is exactly what the second hole provides. It is referred to a the AOA/Boom Pitot by Dynon.

My LS has two pitots, is that only redundancy, or could that provided cross wind info? Does crosswind show on the SWs EFIS?

Just redundancy, one for each AHARS.

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1st TAS is calculated using IAS and OAT

 

Then GPS GS is compared to IAS or CAS to get headwind/tailwind component.

THen GPS track is compared to magnetic heading to get x-wind drift.

 

IAS or CAS plus minus headwind/tailwind adjusted for crosswind drift is enough info to calc wind direction and velocity.

Just to make a point, it won't be perfect since the EFIS uses IAS and not CAS. But, it will be close enough!

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Just to make a point, it won't be perfect since the EFIS uses IAS and not CAS. But, it will be close enough!

 

My EFIS has tables in the set up to adjust.  Try yawing left and right and watch the effect on your wind calculations, I think the CT often flies sideways off heading a bit causes the winds to report incorrectly but the other side of the coin is a little yawing and you can easily see from the reported winds when your nose is really i the relative wind.

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Just got back from a 2hr site seeing trip and compared Dynon altitude readings with 3 independent GPS sources.

My private strip is at 300 ft AMSL set the Dynon on 300 ft and the Dynon GPS was reading 312 ,Garmin 795 reading 304 and Ipad 298 ft.

Cruising with auto pilot set at 5500 and stable the Dynon gps was indicating 5605 ,Garmin 5596 and Ipad 5580 ft AMSL.

The difference between Dynon and GPS in flight was between 60 and 105 ft ,the only time they corresponded was before take of and after landing.

This leads me to conclude that with inaccurate airspeed and altitude readings the static vent on my CTLS is located in a negative pressure area.

I know that Flight Design has not changed the position of the static vent ,but has any one verified the indicated air speeds and altitudes in flight on the CTSL or CTSW ?(BY THE WAY just clocked up 100 hrs in 12 weeks)

Karl

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