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Varmint007

let's try this again.... ;-) Ground track, heading, wind, beta, etc....

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Forgot to check the code snipet box. Sorry! Below is the original.*******Hi all. My first post here, so thanks for taking the time. I'm working on a Navy/Hornet-style HUD for myself, for carrier landings, which possibly I'll release as freeware if it's good enough. I'm almost finished with it, and it works great. EXCEPT... heheh.... the velocity vector needs some tweaking.My main question:1) Is [TrueHeading - ArctanWorldVelocities] equal to the [HeadingDegreesGyro - MagVar - ArctanworldVelocities]? I'm thinking no, or else MS would've used the simpler version in their 747 ground track code. They used DegreesGyro - MagVar. Why?? I can't figure out why the two values wouldn't agree.....And... a few periphery questions.... ;-)2)Is there no variable which directly gives something like [ActualTrack minus WhereAircraftNoseIsActuallyPointing]??? That would be really convenient! I fooled around with using a ratio between VelocityBody lat. and long. , but got strange results, jumping around, etc. The Arctangent of the 2 horizontal world velocities vs. true heading seems to be much more accurate and stable.... Theoretically it seems like the lateral speed component vs. heading could be used, but I've had no success. Anyone get these to work as an indication of track???3) Is INCIDENCE BETA (sideslip) done correctly by Microsoft?? I'm neither an engineer nor computer programmer, but it seems to me that if your nose is pointing at one heading, and your track at another, then you're slipping, whether it has to do with rudder input or wind. How would the pitot tubes know the difference??? It seems like Beta SHOULD be exaclt the difference between heading vs. track. With AOA, in the other axis, if there's a wind that has a vertical component, it registers as change of AoA, no? Why would, for the sake of symmetry, beta no do the same thing? Just curious!

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I can't respond to points 1) and 2) but I think I can help on 3).If your heading and track are different only because of wind effects then there isn't any sideslip as I'll try to explain.If the aircraft is flying with no wind, when there would obviously be no slide slip.The effect of a steady wind is that the air mass in which the aircraft is flying is moving relative to the earth but there is no change in the movement of the aircraft relative to the air mass so there is still no side slip. The same effect would occur in a steady vertical wind and there would be no change in incidence either.Imagine,(and I know it's far fetched) the aircraft flying along the centre-line of a big tank of air. If you move the tank sideways, the aircraft could continue to fly through the tank without sideslipping yet the heading track would be different.Note the emphasis on "steady". If there is short-term gusting then the effects you mention would occur as the aircraft responded.

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Use body velocity to get the true X component:(A:Velocity body X, m/s) (A:Velocity body Z, m/s) atg2 rddgScale it exactly the same as AoA for your velocity vector shifts:(A:Velocity body X, m/s) (A:Velocity body Z, m/s) atg2 rddg((A:Incidence Alpha,degrees)That will show your true velocity vector, but you need to scale it correctly (critical) and make sure the origin is the same as the horizon line. That way the VV will be above the horizon line when you're VS is positive, and below when negative. It will also correctly show your true flight path.Incidence Beta does not appear to be the lateral equivalent of Incidence Alpha.--Jonhttp://forums.avsim.net/user_files/118312.jpg

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"Incidence Beta does not appear to be the lateral equivalent of Incidence Alpha. --Jon" It should be. I finally figured out "Alpha is to Pitch" as "Beta is to Yaw". Beta is normally zero, unless one is in a slip. But, Alpha is normally positive; it supports the weight of the AC. Ron

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Poor choice of words on my part. While beta is probably doing exactly what it's supposed to do, it's inappropriate for a velocity vector, since what you really need is more of a "track" relative to your aircraft.--Jon

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