FlyingMonkey Posted July 8, 2014 Report Posted July 8, 2014 Hey all... During my condition inspection last month at Lockwood Aviation, I had the OAT relocated from the belly of my airplane (where readings were clearly being contaminated by hot exhaust air) to the factory wing inspection panel position. I now get what look like really good, valid true airspeed calculations. I was also hoping improved OAT accuracy would improve accuracy of the D-100 wind arrow. In my airplane the arrow generally gives believable wind direction, but unbelievable wind speeds. On my last flight where surface winds were calm to 3 knots, at 2500 feet the Dynon read a steady 13 knots, which seemed hard to believe. I know winds vary a lot with altitude, and if surface winds (surface is 940 ft) were 3kt I would easily believe 6-8 knots at 2500 feet...but 13 just seems incorrect. The wind speed indication is obviously not critical flight information and falls under the "nice to have" or "isn't that interesting" categories. But if there is a way to increase the accuracy of that information, I'd like to hear it. Or maybe I'm just naive and the wind really is that different from 0 to 1500 AGL?
S4Flier Posted July 8, 2014 Report Posted July 8, 2014 The winds can be quite a bit different at 1500 AGL from the surface. I'd suggest checking the forecast at 3k MSL then interpolating for general correctness test.
Ed Cesnalis Posted July 8, 2014 Report Posted July 8, 2014 10-13 knot gradient would be small for a calm day around here.
FlyingMonkey Posted July 8, 2014 Author Report Posted July 8, 2014 Hmm...maybe I really am just naive! CT, I'd expect that in your area, but on a calm day here in relatively flat Georgia, I just figured that was an unrealistic change. Apparently I was wrong!
coppercity Posted July 8, 2014 Report Posted July 8, 2014 You can try a compass calibration on the D100, the magnetic heading feeds into the wind calculation as well.
FlyingMonkey Posted July 8, 2014 Author Report Posted July 8, 2014 You can try a compass calibration on the D100, the magnetic heading feeds into the wind calculation as well. That would just affect wind direction though, not wind speed...right?
Ed Cesnalis Posted July 8, 2014 Report Posted July 8, 2014 to simply confirm wind speed: put your nose into the wind, note gs put your tail into the wind, note gs subtract higher gs from lower gs and dived by 2 ps: your slip/skid ball can add error, the wind calcs assume you fly coordinated.
Duane Jefts Posted July 8, 2014 Report Posted July 8, 2014 On an approach from, say 3000 ft, watch the wind direction and speed all the way to the surface. You should note about a 45 degree change in direction of the wind as you decend. When on short final, the direction and speed should approximate the surface wind. Best done with a good verifiable surface wind. eg. look at the windsock.
Ed Cesnalis Posted July 8, 2014 Report Posted July 8, 2014 Pancake TX? really? Isn't that disgusting?
GravityKnight Posted July 8, 2014 Report Posted July 8, 2014 Andy, None of the 3 CT's I fly have ever seemed accurate either. The other day it was reading 36 knots, but based on some rough quick calculations (flying into it) it was more like 20-25 knots.
CT4ME Posted July 8, 2014 Report Posted July 8, 2014 Mine varies, but it's usually in the ballpark. When it shows a headwind, my gps groundspeed usually reflects the difference closely.
FlyingMonkey Posted July 8, 2014 Author Report Posted July 8, 2014 I will pay attention to GPS groundspeed in relation to the wind arrow next time I'm flying in winds. Like GravityKnight, I've seen 25-35kt winds indicated by the arrow that could not possibly be correct. But now that the OAT is relocated I will have to pay close attention for a while to see if it's near accurate. I was just assuming a 13kt differential in 1500ft on a calm day was wrong, but from responses here it looks like I will actually have to check and "do the math" to find out.
Ed Cesnalis Posted July 8, 2014 Report Posted July 8, 2014 If my wind calculation results in 35kt SE indicated wind while I'm southbound and winds are actually 25kt SE then the error is from perceived drift. If my magnetometer is true then I just need a little right rudder trim and the wind speed will correct. If you correct your wind speed with your rudder does it correct your sight tubes? CTSWs are happy to fly a bit sideways plus our panels's slip skid balls are prone to encourage flying a bit sideways and doing so seems to effect wind speed calcs and fuel management more than it effects performance.
FlyingMonkey Posted July 8, 2014 Author Report Posted July 8, 2014 I am often glancing at the wingtips relative to the horizon to see if I'm flying a little out, next time I'll check on the wind arrow too and note the effects of making those little changes.
Ed Cesnalis Posted July 19, 2014 Report Posted July 19, 2014 I just tested my wind arrow / data. I moved my nose right and left and the wind-speed changed 10kts. When I first tried I was seeing a 25kt east wind and as I moved the nose it went to a 15kt wind and a slight change in direction too. 15 was the right number.
FlyingMonkey Posted July 19, 2014 Author Report Posted July 19, 2014 I just tested my wind arrow / data. I moved my nose right and left and the wind-speed changed 10kts. When I first tried I was seeing a 25kt east wind and as I moved the nose it went to a 15kt wind and a slight change in direction too. 15 was the right number. Thanks CT, that's really good info! Last week was my week on pager duty at work (busy), and now we're socked in here, probably for the next week, so all the things I've been wanting to test have been put on hold until weather improves.
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