Wind vector on D100

[dries]

Hi guys

I just downloaded v 5.1.1 and am now running it. most seems OK except for the wind vector - it seems real useful but it doesn't seem to be displayed. Do I have to actively select it enabled or will it automatically be displayed when a GPS input is active?

I am driving the GPS input through the D120 input from my Garmin 430 as per the installation instructions and need info on getting this vector displayed.

Any thoughts
Dries

 

[PhantomPholly]

I'm pretty sure it has to be enabled in setup.

On a related note, I consistently get readings of wind vectors much higher than actual. I suspect it is because my airspeed consistently reads high - probably the result of a less-than-perfect placement of the static ports.

 

[dries]

Hey there

Thanks for that but I did look in the setup menu and didn't seem to find anything. If you do come across where it is please let me know.

On a similar but slightly different note - I'm having trouble getting the clock to update the zulu time and/ or adjust the local time and time zone correction from zulu time - any idea where I can look?

Thanks
Dries

 

[Brantel]

You must have a GPS fix, be moving and have OAT available for this to work.

It must also be turned on in the EFIS > SETUP > CLUTTR menu "WIND" is the parameter you want to set active.

 

[Roger_Lee]

If your indication of wind vector is thought to be too high, are you comparing it to indicated air speed and the ground speed or the true air speed which reads just under the OAT?

 

[PhantomPholly]

If your indication of wind vector is thought to be too high, are you comparing it to indicated air speed and the ground speed or the true air speed which reads just under the OAT?

Both.  

8,500'; 24inches/2400rpm; Lancair 320 expected TAS in the vicinity of 200mph - 220mph.
Altimeter ~ 30.00
Surface Temp ~ 85F
IAS ~ 200mph (intuitively too high, although I'd love to see it)
TAS ~ 240mph (not bloody likely at 8 gph)
GS ~ 215mph
Wind Vector - about 35mph on the nose
Turn around 180 degrees, wait to settle.  GS ~ 195mph; Wind ~ 50mph on the nose...

In other words, everything is in error about as I would expect given that the IAS is off by 30-40mph.

 

[dynonsupport]

I think you have the problem understood. If IAS is high, other calculations that depend on it, like TAS and winds, will be incorrect.

 

[PhantomPholly]

Not unexpected.

Too bad your AOA pitot does not also encompass static ports. It is devilishly tricky to find the right place to install static ports on glass airplanes, and who wants to keep drilling holes in their beautiful paint?

 

[dynonsupport]

Under the wing (where most pitots are) is not a good location for static either. We've seen aircraft with static here, and when you pitch up, the pressure under the wing increases, and your altitude goes down. This causes a few problems for autopilots....

 

[khorton]

Not unexpected.

Too bad your AOA pitot does not also encompass static ports.  It is devilishly tricky to find the right place to install static ports on glass airplanes, and who wants to keep drilling holes in their beautiful paint?

Your IAS is reading high, which means the static pressure is too low.

Have you done a static system leak check?  The pressure in the cockpit of many aircraft is lower than ambient pressure, so static system leaks in the cockpit often produce too high IASs.

If the static system has no leaks, you might try messing around with dams behind your static port(s).  A protrusion with a vertical face behind the static port will increase the pressure sensed at the port.  Start with a fairly low dam, perhaps 1/16" high, perhaps 1/2" behind the static port, and then increase the dam height on subsequent flights until you find one that works.  The higher the dam is, and the closer it is to the static port, the more effect it will have.  You can bias the effect towards high or low IASs by changing the rotational angle of the dam with respect to the static port.

Keep in mind that as soon as you add this dam you have changed the errors in the airspeed system, so you'll need to figure out a new approach IAS each time you change the geometry of the dam.

 

[PhantomPholly]

Not unexpected.

Too bad your AOA pitot does not also encompass static ports.  It is devilishly tricky to find the right place to install static ports on glass airplanes, and who wants to keep drilling holes in their beautiful paint?

Your IAS is reading high, which means the static pressure is too low.

Have you done a static system leak check?  The pressure in the cockpit of many aircraft is lower than ambient pressure, so static system leaks in the cockpit often produce too high IASs.

Leak check professionally accomplished a few weeks ago. Several bad connectors replaced. Altitude reported on Cockpit air is closer to GPS altitude, and airspeed a bit more realistic, than that reported using external static.

If the static system has no leaks, you might try messing around with dams behind your static port(s).  A protrusion with a vertical face behind the static port will increase the pressure sensed at the port.  Start with a fairly low dam, perhaps 1/16" high, perhaps 1/2" behind the static port, and then increase the dam height on subsequent flights until you find one that works.  The higher the dam is, and the closer it is to the static port, the more effect it will have.  You can bias the effect towards high or low IASs by changing the rotational angle of the dam with respect to the static port.

Keep in mind that as soon as you add this dam you have changed the errors in the airspeed system, so you'll need to figure out a new approach IAS each time you change the geometry of the dam.

Great idea - I'll try this next flight with a little duct tape!

 

[khorton]

Great idea - I'll try this next flight with a little duct tape!

I should add a big caveat - while static dams have been used successfully on many aircraft types to address static source position error, I personally have never been involved in a project where they were used.  Thus I don't have a good basis to recommend dam height or distance from the static port.  I am quite certain that a dam 1/16" high will have a too small effect to fix your large error, but I felt it better to start too small, and work up from there.  Don't be discouraged if you see little to no effect with the initial small dam.  Simply try a higher one, and keep iterating until you get an acceptable solution.  

Your technique of averaging calculated TASs from into and with the wind is probably a good quick and dirty technique to get you in the correct ballpark.  Once you get close, you may want to switch to a more accurate test technique to refine the dam details.  I can walk you through a more complicated, but more accurate test technique if you are interested.

If you do successfully use a static source dam to fix your problem, I'd be very interested in learning the details of dam height and distance from static ports that you end up with, and seeing a few pictures.

 

[PhantomPholly]

These are my static ports (interconnected via a line which goes up across the "ceiling" inside the cabin).

Using this photo as a guide, they are located directly beneath the leading edge of the aft windows about level with the stripe.

I'm actually thinking of using tiny pieces of duct tape directly behind the hole on the port body.  My guess is that a small dam closer to the hole will have the same effect as a larger one further back, but it is merely a guess...

 

[khorton]

These are my static ports (interconnected via a line which goes up across the "ceiling" inside the cabin).

Using this photo as a guide, they are located directly beneath the leading edge of the aft windows about level with the stripe.

I'm actually thinking of using tiny pieces of duct tape directly behind the hole on the port body. My guess is that a small dam closer to the hole will have the same effect as a larger one further back, but it is merely a guess...

Is that the location that Lancair recommended for the static ports? That location looks a bit too close to the upper surface of the wing. Wings, by design, create a low pressure area above them. This low pressure area may extend high enough to affect the pressure sensed by your static ports. I would suspect that the pressure error may vary quite significantly as the angle of attack varies. I suspect you may find that even with a static port dam that you can only get small errors in a small range of IAS.

I recommend that you consider moving the static ports further aft, to get them clear of the low pressure area created by the wing. Perhaps somewhere in the area of the "3" in that photo. You will likely still have errors, but I expect that the errors will be smaller, and less affected by changes in angle of attack. These smaller, more constant errors, may be easier to correct with static port dams.

This is going to be an interesting science project. Keep us informed of your progress. Expect to invest quite a few flights trying different static port dam geometries.

 

[PhantomPholly]

Hehe - drilling more holes in my plane is not an option!

The error is not large, even at very high altitude. Worst case - I'll just live with it.

Will make my first experiment tomorrow.

 

[khorton]

Hehe - drilling more holes in my plane is not an option!

The error is not large, even at very high altitude.  Worst case - I'll just live with it.

Keep in mind that if the source of your airspeed error is static source position error that this affects your altimeter too.  You said in an earlier post that you think your IAS is reading 30 - 40 mph too high.  If it is reading 30 mph too high at 8500 ft, your altimeter will be reading about 500 ft too high.  This is too big an error to ignore, even if you only fly VFR.

 

[PhantomPholly]

Hehe - drilling more holes in my plane is not an option!

The error is not large, even at very high altitude.  Worst case - I'll just live with it.

Keep in mind that if the source of your airspeed error is static source position error that this affects your altimeter too.  You said in an earlier post that you think your IAS is reading 30 - 40 mph too high.  If it is reading 30 mph too high at 8500 ft, your altimeter will be reading about 500 ft too high.  This is too big an error to ignore, even if you only fly VFR.

Good point, but then that doesn't track with the fact that my altitude tracked within 300' of GPS altitude all the way up to 17,500'.

At this point I think we're drifting back into a discussion we've had before. I'll try the dams and see if I can get it perfect; flying VFR these days until I build more confidence in the install, so I have a while to tweak it.

 

[khorton]

Hehe - drilling more holes in my plane is not an option!

The error is not large, even at very high altitude.  Worst case - I'll just live with it.

Keep in mind that if the source of your airspeed error is static source position error that this affects your altimeter too.  You said in an earlier post that you think your IAS is reading 30 - 40 mph too high.  If it is reading 30 mph too high at 8500 ft, your altimeter will be reading about 500 ft too high.  This is too big an error to ignore, even if you only fly VFR.

Good point, but then that doesn't track with the fact that my altitude tracked within 300' of GPS altitude all the way up to 17,500'.

At this point I think we're drifting back into a discussion we've had before.  I'll try the dams and see if I can get it perfect; flying VFR these days until I build more confidence in the install, so I have a while to tweak it.

GPS altitude is a very different thing than barometric altitude, so there is little to be learned by comparing the two.  For example, if you sit on top of a 17,500 ft mountain, staring at a GPS, the GPS altitude should be relatively constant.  But, if you also have a barometric altimeter, with the altimeter setting from a low altitude airport, the barometric altitude displayed on the altimeter will vary as the temperature of the air between you and the airport varies.  This variation can easily be several hundred feet at the altitude of your mountain.

For a bit more info, see Lies Your Barometric Altimeter Tells You.

Assuming you have no static system leaks and insignificant ASI instrument error, the source of your high ASI readings must be in the static system position error.  Just to be sure you are hunting the right thing, it is worthwhile doing one last quick static system leak check, and an ASI instrument error check at a single airspeed in the cruise airspeed range.  

The static system leak check should take less than five minutes.  Block off one static port with a piece of tape, and push a piece of rubber tubing against the fuselage over the other static port.  Gently suck on the end of the tubing until the altimeter has climbed 1000 ft.  Put your tongue over the end of the tube to hold the suction constant, and watch the altimeter.  It should descend less than 100 ft in one minute.  When you are done, release the suction slowly to avoid damaging the ASI or altimeter.

Do an ASI instrument error check at a single cruise speed as described in this old Kitplanes article by Jim Weir.  Note that his recent Kitplanes article has huge errors in the table of ASI readings vs water manometer height.  More info here.

Happy hunting.

 

[PhantomPholly]

Yup, we had this discussion before!

In order for me to keep my tongue on the static port and watch the altimeter, my tongue would need to be 3' long. That's 2' longer than it is even at my lewdest....

 

[khorton]

Yup, we had this discussion before!

In order for me to keep my tongue on the static port and watch the altimeter, my tongue would need to be 3' long.

That is why I suggested the use of a piece of rubber tube.   One end goes over the static port, the other end goes in the mouth.  The tube can be as long as needed so you van have the head high enough to see the altimeter.