Dual STI build log

[109JB]

If OAT is off , TAS will be off too. It would have to be off quite a bit but it is just a thought.

[Shadowrider]

IAS/TAS update: My OAT is accurate, within 1degree of atis/awos. I also went to the compass rose and did a calibration on my magnatrometer. Replaced press to connect fittings and with barbed coupler, and did a pitot/static leak check. I have been on Vans forum a bunch as there is lots of great info in regards to garmin. I used some info I found there and tested my pitot system, from the wings into the G3x, using a syringe. "Not recommend, you must be very careful" Brought my indicated airpseed up to 186 and it held there for many mins. I figured higher the pressure the higher the leak maybe? Then I brought my altitude up to 6000' and it held altitude without any altitude loss. So I am guessing I don't have a leak especially because Cory's and my plane indicates the exact same. 5400rpm we true at 105mph and 5200 rpm we true at 102. I "think" we are indicating about 8mph slow. I remember riding in another kitfox that had oratex and he said he thinks he is indicating about 10mph slow. Got me thinking what do we all have the same? I have our static source at the same location as he did so maybe its a static source issue while flying.(We are all G3X users) On vans forum, I guess many have low indicated airspeed because the static source is getting pressurized. One user recommended taping a washer around the static source to help protect it. What I am thinking is on oratex is a much thinner finish so the static port sticks out of the fabric slightly causing it to pressurize the static port. So I just taped a washer on today to try, and low and behold I was seeing about 8mph higher TAS. It was too bumpy today to record data but based on what my grounspeed was and what I calculate TAS be, I think I am pretty close now. I flew a triangle pattern and watched my wind speed readout and it showed 340 degree at 13 mph no matter what direction I flew. Usually it shows at least 10mph, or greater if I have a actual tailwind. I honestly cant believe I have flown this long and not figured it out. I am going to 3d print some type of washer that I can use the 3m two side tape that is used for vg's and attach a static port protector. I may need to increase or decrease thickness once I record some numbers. My goal is to get my TAS as close as possible so my wind readout is more accurate for off airport landings. I know this probably should of been done in flight test, but I never did the flight test where you fly in a triangle to calibriate TAS because I figured there wasn't anything I could change??

[alexM]

You should sell airspeed correction kits. You'd make millions!

Great idea trying that.

[Geek]

Another great Dustin Garmin G3X piece of gouge (In Navy-speak "gouge" = important information)!! Think when I do mine I will put a spacer behind the Oratex which I can do cause I now know about this ahead of time. Thanks Dustin!!

Gary

[jiott]

Great idea Dustin; I think I will go out and try to accurately calibrate my airspeed now that I know something can actually be done about it.

[PapuaPilot]

Great idea Dustin; I think I will go out and try to accurately calibrate my airspeed now that I know something can actually be done about it.

Ditto. I should do this too.

Do you guys have one static port or two? I ended up installing a second one on the opposite side of the fuselage.

[jiott]

I just have one static port, left side low under the lifting handle. Two would probably be somewhat better.

Actually I have never worried too much about airspeed accuracy because after flying the same aircraft for a while you get used to the speeds shown on the indicator and know precisely when it is going to stall, etc. Those numbers get in your head no matter if they are somewhat off. If I recalibrate I may have to relearn some of those numbers-not too thrilling after 8 years of flying, but I suppose better accuracy is nice to have.

[jiott]

I guess I will need to recalibrate my AOA indicator also; not very difficult on the Dynon system.

[109JB]

Glad you got yours fixed. My analog gauge in the KF 4 I rebuilt is a bit further off. About 90 mph actual reads 120 mph on the gauge. Low speed is pretty close and shows no-flap stall buffet at 35 mph which I suppose is about right. Static is vented to the cockpit. Will be running a new static line to a tube type static port but not until warmer weather arrives.

[Shadowrider]

I am going to check AOA if it needs to be re-calibrated, but I suspect the error is only showing up on the faster end. Made a few 3d printed printed "static guards" of different sizes. Going to start with the one that is the same thickness of the washer I used and go from there.