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sharpdoug
12-27-2010, 07:51 AM
Yesterday we were flying on a long cross country. My friends plane is RV-8 mine is an RV-6 both Hartzell CS with Lyc. 360's. Manifold pressure 22.1 RPM's 2450. We were .3 miles apart same altitude. (8500' on a heading of 192) My winds aloft were showing 355 at 37, his were 020 at 41. Both units are 4500's and we had exactly the same GPS ground speed of 212.

Trevor or Rob is this a calibration issue or static error in my plane? We flew exactly the same course on auto pilot, we were never more than .4 miles apart for a 2 hour trip. The ground speeds never varied from one another, but the indicated winds direction and speed were never the same.
I checked the winds aloft on XM weather but the arrows are not degree specific.
I know my IAS is about 10 knots high, so my TAS is also 10 out. Is there a settings adjustment for this in the EFIS?
Thank you for your help.

Trevor Conroy
12-27-2010, 09:12 AM
Winds aloft uses GPS data as well as IAS/TAS. If your IAS is off, it will significantly affect the winds aloft calculation. There is an adjustment for airspeed, but we caution using that feature as it is for calibration during a VFR/IFR certification. Have you gotten a VFR/IFR cert yet (pitot/static check)?

sharpdoug
12-27-2010, 09:22 AM
Yes I got an IFR pitot static check after my annual. The sticker says altimeter, transponder, and static system tests as required FAR 91.411 an 91.413 and comply FAR 43 Appendix E and F ...etc. I do not think they adjusted anything.
Doug

Trevor Conroy
12-27-2010, 09:29 AM
What indication do you have that it is 10kts off? If it passed a p/s check, you should be golden.

sharpdoug
12-27-2010, 02:39 PM
The other item that differ from the RV-8 to mine was his outside air temperature was reading 2-3 degrees warmer than mine. It is rare when a RV-6 is reading the same ground speed as an RV-8. When it does, I would think all the numbers should read the same.

garymail
12-27-2010, 03:41 PM
Unless the Outside Air Temp.; Indicated Airspeed and compass are nuts on, there will be an error, the more any of these are out of parameter, the greater the error. I would suggest first, calibrate the compass again; second, use a good manometer to calibrate your airspeed, you can build one quite simply suing a clear plexi hose and water to measure inches of water calibrated to indicated airspeed; third, check your OAT against a known value. Then give it a try, it is, after all, a computer, garbage in, garbage out! ( I also has to do with AL-GOREythm's)

Trevor Conroy
12-27-2010, 05:02 PM
There are a number of factors like OAT, IAS, and heading that will greatly affect the trigonometry required to calculate winds aloft. If your heading is a degree or two different, OAT a few degrees different, or IAS a few knots off, it will change the winds greatly. Ensure the OAT is accurate, ensure IAS is accurate, and ensure your magnetometer is properly aligned.

DONVS
12-27-2010, 08:32 PM
Trevor and Sharpdoug,
Your indicated airspeed as checked during an ifr cert does not take into account static system errors other than leaks. If you have flush ports or any other mounting issues both your altitude and airspeed will be off by anywhere from a few to possibly as much as 20 k and 1500 ft. The best way to check this is to fly a gps four leg course and maintain altitude and airspeed within 50 ft 2 k. compare with your ground speed from the gps. Do this flight very early in as close to zero wind as possible. You may need to do a static port ramp adjustment.

sharpdoug
12-29-2010, 06:19 AM
i am planning to redo magnetometers calibration, as far as OAT I plan on moving the sensors at my annual in March. Currently in the probes are inside the wing root fairing and will move them out into the inspection panels. I will go back to Avionics Unlimited and see about IAS calibration, I did pay $300 for the test. As far as the static ports I used the ones on the Cessna's from ACS. Flat aluminum plate with the hole in the center. I have heard a lot of talk about those not working on a RV, changing them now would be a lot of work. So if I could change the IAS in the AFS instead that would be easier.

DONVS
12-29-2010, 03:33 PM
I installed flush ports and the fix was not that difficult. I removed the screw on connection, drilled out the port to allow the Van's pop rivet to be installed. Drove out the mandrel and cleaned all chips out and re-installed the static line. That was it. Only took about an hour.

larco
12-29-2010, 03:48 PM
A quick fix for the static ports is -------cut the head off of a vans standard static port pop rivet and while using a toothpick or a used pop rivet mandrel for alignment, epoxy or JB weld the head onto the flat static port. It works as we have done several this way and it has brought the airspeed in flight right in with the rest of us. They should stay on forever. Larry

DONVS
12-29-2010, 04:42 PM
Larry I guess I do things the hard way. Your way is much faster. Don

sharpdoug
12-30-2010, 10:19 AM
Did it change the readings in IAS? Thanks

larco
12-30-2010, 12:47 PM
Two examples are, A friend with the flat ports flew often with several of us who have the vans style and was always reading about 8-10 miles off in cruise, after this fix we were all about the same. Another friend had a pitot static combo inlet mounted on the wing and was off as well. after changing to the vans style it read the same as us. This fix came from another local pilot who had an a/s indication error and have heard it has worked for several more. Larry

DONVS
12-30-2010, 09:05 PM
<y ,ethod also changed both the IAS and the altitude .

DONVS
12-30-2010, 09:06 PM
Make that My method

rshannon
01-02-2011, 09:09 PM
Larry, I'm not familiar with the Van's parts and setup you describe. I see they have a static port kit on the web store [STATIC-KIT] but there's no picture. Can you post a picture or two? I'm currently using a static port from ACS that sits up about 3/32" off the fuselage and, like others here, I have ~8 MPH error at cruise. Thanks.

larco
01-04-2011, 04:35 PM
This is an RV kit that includes a large pop rivet for each side of the fuselage. Not sure how it would work on a Murphy. I believe that the static ports are very relative to specific aircraft. An example would be the Glastar, it has a very unique port and placement. Larry

rshannon
01-04-2011, 08:39 PM
Yes, of course, it may or may not be appropriate for other planes. I'm just trying to learn what it looks like. Does the kit just rely on the holes (rivets sans mandrels) to equalize inside & outside ambient pressures, or is static plumbing somehow connected to the inside of these large rivet heads, or...?

larco
01-05-2011, 05:44 PM
OK. Vans stuff is quite simplistic, sometimes it will make you laugh but it always works. You, at the proper location on the fuselage, drill a 1/8" hole, install a 1/8" large faced domed pop rivet, drive the mandrel out of the pop rivet with the broken off piece of the mandrel, then attach the static system hose with the help of some RTV to the pop rivet inside of the fuselage and route it to where you want it to go. Larry

garymail
01-05-2011, 06:31 PM
An IFR cert does not look at indicated airspeed, youcan do that with a manometer (many easy to build ones on web sites) using a column of wter in a clear plastic tube. The IFR cert only looks at altimeter and encoder output, and transponder code and mode C.

rshannon
01-05-2011, 07:17 PM
Wow. Thanks for clarifying, Larry. Your suspicion or prediction was on target. I'm thinking this is not a worthwhile mod for my Rebel after all. ;)

The ~8 MPH high IAS error is more than I'd like, and plumbing tests indicate everything is tight, so I'll experiment with a small angle positioned on the face of the static port "disk", just aft the port, as I've seen others have done, including Cessna on some of their recent vintage 172's.