Winds Aloft - mine are off, too - FlightDEK D180

[SammyQ2]

I thought my winds aloft were off, so on a recent cross country I flew the four cardinal headings.  I was about 4,500'.  This is what I got:

Heading   Wind Direction   Wind speed

360                 242                    20
270                 334                    18
180                 251                    31
090                 271                    08

Averaged:       274                    19

I recently had an IFR static check performed and everything was right on the money.  I also did the compass calibration using our airport's compass rose.

The only check I have not yet made was flying down the runway at different speeds, as mentioned in the thread posted on November 12.

Is there any literature out there about static ports & best locations?  I was looking at a turbine aircraft and it had flush ports with multiple holes drilled.  Maybe that would make a difference.

Any other suggestions?

Sam

 

[PhantomPholly]

Re: Winds Aloft - mine are off, too - FlightDEK D1

Include your IAS and GPS ground speed in your writeup, and confirm your "Heading" was magnetic.

First thought - have you run the compass calibration on the ground?

Also, it is actually possible for the wind to vary a bit in speed and direction - perhaps not as much as your numbers suggest, but somewhat.

Plotting those four vectors indicates a wind varying between NW and SW averaging about 18knots. The two runs 360 and 180 are probably the most accurate because they both indicate mostly cross-wind.

So, my first hunch is your variance is mostly caused by a small magnetic error plus some small wind variation aloft.

 

[DBRV10]

Re: Winds Aloft - mine are off, too - FlightDEK D1

You will most likely have a static problem, not a leak but a pressure error.

You have not mentioned the aircraft, but if its an RV and you have used a nice static port eiether side like I did..... you will most likely have a static error.

Refer to my earlier posts.

Cheers

DB

 

[SammyQ2]

Re: Winds Aloft - mine are off, too - FlightDEK D1

The aircraft is a Quickie Q-200. It has a static port on each side of the tailcone. Here is a photo on my blog: www.samhoskins.blogspot.com

Yes, I performed the compass calibration on the ground, with the engine and systems running, per the Dynon installation manual. The heading was magnetic, as displayed on my D180.

 

[khorton]

Re: Winds Aloft - mine are off, too - FlightDEK D1

You will most likely have a static problem, not a leak but a pressure error.

The cause of this problem could also be a static system leak, and many amateur-built aircraft have such leaks, so it is worthwhile to check for one.

 

[SammyQ2]

Re: Winds Aloft - mine are off, too - FlightDEK D1

As I said in the first post: I recently had an IFR static check performed and everything was right on the money.

 

[dynonsupport]

Re: Winds Aloft - mine are off, too - FlightDEK D1

A static check doesn't verify accuracy in the air- it verifies that your equipment shows the right data when given specific pressure. If your static port is not performing correctly, it will read wrong pressure in flight. There's no way to check for this on the ground unless you have a wind tunnel.

What the IFR check does tell you is that there is nothing wrong with the EFIS, since it reads correct when given correct pressures.

 

[PhantomPholly]

Re: Winds Aloft - mine are off, too - FlightDEK D1

What those numbers say to me is that your IAS is reading about 10-11 knots low at that airspeed / altitude.  Since you cannot change pitot pressure, the only way to correct that would be to either move or trick the static ports into having a lower pressure (increase the pitot/static differential).

Some folks have used tiny pieces of tape as dams in front of or behind the tiny port holes, or angled the ports slightly to adjust the reading.  This is a rather arcane science, because anything you change might "fix" it at one airspeed / altitude and make it "worse" in another phase of flight.

My personal flight profile would lead me to try some experimenting along those lines, as (like you) I would like to see accurate winds aloft.

Good luck!