Ep 3 Flaps & Pitot Static Test - Task-Based Flight Test Series

We start testing our new experimental amateur built aircraft in earnest! Starting with Test Card 2 and the flap check, then we get hot and heavy into analyzing telemetry (flight data recorder) data to determine the error in our indicated airspeed. We'll compute true airspeed using wind-corrected patterns and GPS ground speed to then convert to calibrated airspeed. The difference between the calibrated airspeed and indicated airspeed is the pitot-static error. This is important to 1) determine if your airspeed indication is in the ballpark of accurate, and 2) see how far off your True Airspeed indication is on your modern EFIS. I argue why the manufacturers like Garmin and Dynon should allow us experimental customers to add our calibration curve to affect an accurate true airspeed. I'll explain how to import the .csv file from your EFIS to determine the pitot-static error!
Consider following Cleared Direct on IG at / cleared_direct_resources
0:00 Intro
0:56 Pinned Comment from Ep 2
2:04 Flap Check
4:43 Pitot-Static Test Brief
12:12 Unfortunate Execution
12:50 Debrief
18:16 Manipulating EFIS fdr data (telemetry)
21:28 Outro

[@brianberezowski5352]

You're knocking it out of the park with this series Steve. All cards on the table ... some of this is above my pay grade. Having said that, any information that improves my basic knowledge and understanding of how instruments, systems, components relate and understanding better what we "SEE" displayed and how accurate that is and how that relates to handling and flight characteristics with respect to being a safer pilot is nothing but a Positive in my book. Keep up the GREAT work. Looking forward to the next video. Best regards CYQT 👍🇨🇦👍

[@edwinscox]

Wow! another data nerd! Your level of detail is both impressive and intimidating. How many people can do it in this much statistical detail? You show an impressive ability to collect and analyze the data that you can collect.

[@tenthtonman]

I know external drives are easy but it's a pain to loose drives. You might consider a home NAS configuration for drive redundancy. Been awesome to follow this whole project; your videos are great.

[@craigsanders6925]

My first thought as well, even a second drive to back up would be good. Everything fails sooner or later... Really enjoying the testing info!!

[@ibgarrett]

i agree on not putting cameras outside the plane on first (or several first) flights. I have camera positions built into my plane for future use, but I have no intention of using those positions for a while.

[@corbinschad1]

A small leak in the pito system could cause the drift, or an oversized pito drain hole. It could also be a placement issue with the static port. If you hold an altitude with the gps and try different speeds at the same gps altitude; you could at least get a rough idea on the function of the static port. Maybe even try taping the pito drain hole and see what happens. Thanks for bringing us with.

[@flynjay7178]

Great episode as always. You may need to go out to the Pacific coast and get a few tracts when there is a constant smooth on-shore flow. Get outside of any mountain influence.

[@CLEAREDDIRECT]

Oh yeah?! I’m unaware of this phenomenon. But I believe it… these mountains are kicking my ass

[@HollywoodRebel]

Great episode! I have been fighting with my pitot system recently in my RANS S7. I have a GRT EFIS that then connects to a basic round ASI but the EFIS seems to always be 5mph higher. Any chance you would share these spread sheets for our own informational gathering? Also, is a performance table on the list for this series? Keep them coming, great content!

[@Joe_Not_A_Fed]

As you mentioned...no aircraft speed indicating system is perfect, and for the most part, a person can live with that...as long as it makes sense. The fact that the error between indicated and calibrated increases with higher airspeeds...opposite to what Garmin said...is confusing, and well worth looking into. Yeah, it might be because of rough air, but an almost 10% deviation at 104 kts, would have to have been one heck of a wild ride. Bend is rarely calm but I would want some serious proof that you chose to perform flight tests, on that nutso of a day. The error is so linear. It feels like an instrumentation calibration issue. It could be a pitot/static leak or blockage...but my conspiracy theory is that it has something to do with how your Garmin is converting air pressure signals into airspeed. But, it couldn't hurt to do a quick check for mud daubers.

[@richardturner6278]

Another great episode Steve. In the process of planning my build I've been wondering about the correct placement of the pitot tube and static locations. I've seen where builders have trouble with inaccurate readings because they were not installed in the proper location for the specific aircraft. I understand the static port needs to be back out of the slipstream but how critical is the placement of the pitot tube for accurate readings on speed and AoA? I understand some designs are more sensitive to placement of these components. Many people seem to have speeds that read 5mph off . Is placement the culprit? Love to hear your thoughts on this. Thx.

[@davidgill5448]

Really interesting video-thanks! I have two thoughts. One is that all your leg times seem to be about 1 minute. I wonder if a longer leg length would give a more representative average speed and be more tolerant of fluctuations. The paper you reference doesn't seem to have any leg time recommendations in it other than a settling time after turning the corner so, unfortunately, no help there. Secondly, how much is your GPS speed varying within the 1 minute? I noticed the other day that when I was flying what seemed to be a consistent IAS on what I thought was a non-gusty day, the ground speed varied a lot. I don't know if the problem was GPS accuracy or wind - so I intend to try again with multiple GPS receivers. It might be worth checking a standard deviation on your ground speed and IAS and maybe not using the data unless the standard variation is really low within the leg. Otherwise, the average value seems really suspect.

[@CLEAREDDIRECT]

Great points! I kept the leg to about 1 minute to minimize wind variance. I’m open to all suggestions and will report back on longer legs.

[@nicwaugh1]

Steve, would it not be true that the errors are so repeatable that the data has to be good? The R2 on the error was 0.94. if the data was bad, should the R2 be less than say 0.1? If you did the test once, sure, but you did it 6 times and the errors were consistent.

[@Brad-kk4yf]

If it's not that adahrs, my gut is telling me that a pitot leak is a plausible culprit....error is directly proportional to pressure. But my random thought for brainstorming purposes, the 1st place I'd look is around MY general lack of confidence in those online calculators like the one you used to back into the CAS from TAS. I've had those sorts of calculators spit out incorrect numbers so I don't blindly trust them.... maybe rounding errors or maybe bad constants or other assumptions they might use hidden in the back end. You've probably already verified it but thought I'd throw that out there anyway

[@CLEAREDDIRECT]

Thanks! Good points. I’ll doubly check for leaks and probably have an avionics shop hook up the pneumatics for a ground test. I’ve verified the online calculators are correct 👍