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HomeHomeDiscussionsDiscussionsiFly General Di...iFly General Di...What are the criteria for calculating headingWhat are the criteria for calculating heading
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10/21/2014 10:02 AM
 

Question 1: I don't have an android or any other cell phone with much more than voice and texting capability. Nor do I own an ipad. Most of my money went into building an aircraft. :-)

Question 2: No, I don't plan to fly IFR. I hold an IFR rating. but I just don't like to fly IFR.

 
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10/21/2014 10:07 AM
 

Mike, I understand your logic, but we simply do not know know accurate the hiking compass may be. Without something else as a reference, I don't know of a way to test it. It may be great, but we don't know that. I need something I can hang my technical hat on, and don't have a potential problem with signing the logs.

Even though I'm working on an experimental aircraft, I still have to sign the logs. An A&P who claimed to align an aircraft compass with a hiking compass would be open to question from the FAA. They can ask very nasty questions, fine the foo out of you, and even pull your certificates.

 
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10/21/2014 10:12 AM
 
greg piehl wrote:
Out of curiosity and to find an answer to your initial question, I had the opportunity to test your theory of using aircraft speed and heading on a commercial flight yesterday. Using the iFly app on the iPad during a long taxi of at least 10,000 ft (at Dulles), I monitored the Track reading. Assuming the aircraft was following the centerline of the taxiway, the reading didnot vary by more than 1 degree. This was verified at speeds of of between 6 knots to 20 knots. Of course not knowing the actual taxiway heading does not conclude an accurate reading of direction. However, on takeoff up to rotation (approx. 135 knots), the Track reading was rock solid at 300 degrees, which is exactly what the published heading for that runway is. Granted this was only one direction, I think it is safe to assume that you can at least verify your compass card using these numbers. There is no wind involved here as the aicfraft is still on the ground. (It's following its gear, not its rudder). I don't know that I would substitute this for a proper compass swing, but it sure seems accurate enough to get you in the ballpark. My GPS status was at least 3 bars, a strong enough signal to get an accurate reading.
By the way, I often use (4 to 6 commercial flight a month) the iFly app to beta test without having to fly the plane, and to know when I'm actually going to arrive at my destination. Way more accurate than they tell you!

Now that is useful information. It suggests I might be able to do the alignment in the air, which would be good enough to get me to the compass rose, and I would not have a problem with logging that approach.

Within 25 miles or so of my home airport, I don't have a problem using the level of accuracy I have at the moment. There are plenty of landmarks. But going off to the rose is another problem: too many similar-looking mountains, and a fair amount of desert.

 
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10/21/2014 6:33 PM
 
I would be very cautious in the air, as any wind at all will cause a crab of the aircraft, thus changing your compass reading by several degrees or even substantially more. Why not just fly by the ifly to your destination? Then you can use the airport compass to check. And actually, and I have reservations of saying this, is the compass going to be obsolete with certified gps? Certainly not by the FAA, as they will last year's issues in a 5 or 10.
 
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10/22/2014 10:10 AM
 
greg piehl wrote:
I would be very cautious in the air, as any wind at all will cause a crab of the aircraft, thus changing your compass reading by several degrees or even substantially more. Why not just fly by the ifly to your destination? Then you can use the airport compass to check. And actually, and I have reservations of saying this, is the compass going to be obsolete with certified gps? Certainly not by the FAA, as they will last year's issues in a 5 or 10.

You are correct about the crab angle. Perhaps I should say I will use this as a means of alignment only if it is obvious the compass has a serious error. Usually, though, I can eyeball my ground track and compare it to the aircraft heading, and get some idea if a serious error exists.

A far as flying to the destination without being reasonably sure about compass heading, I think if you saw the area from the air, you'd know why. Those who are interested (including, obviosly, yourself) should look at the flight path from Alpine, Texas, to Pecos, Texas. I've flown it (although in reverse) with a compass and gps in another airplane. I learned to fly in a similar environment, and I still didn't feel totally comfortable.

I agree that the FAA holds on to things forever, but I feel the problem is worse than that: they hold onto things they no longer need, and get rid of other things we still need. I wouldn't trust any navigatonal aid of which I'm aware without some sort of backup.

The gps can be jammed; I've flown through a couple of areas in the country where the gps quit every time I went through that area. I had to use the compass to maintain my previous heading, until the gps worked again. It looked to me as though there was some sort of interferring signal in that area.

Me, I'd like to see them keep VORs as a backup for the same reason.

 
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