PPL exam compass errors

[gemma10]

Thread starter probably wondering why he asked the question now. He got a satisfactory answer after two replies, then the thread drifts all over the place even to carb ice. It would be great if we all understood every technicality of every aircraft subpart but we dont as we are all still learning. Brilliant piece by Keith Williams, I wonder how many ATPL`s could recite that.

[Big Pistons Forever]

Originally Posted by gemma10

. Brilliant piece by Keith Williams, I wonder how many ATPL`s could recite that.

Not very many because it is useless information they memorized to pass their ATPL exams and then flushed from their brain to make room for information that actually can be used in flight.

[dubbleyew eight]

I suggest that mach jump goes and gets himself an Airpath brand Aircraft compass and pulls it apart.
some people only ever learn by having the evidence in front of them.

[Mach Jump]

I suggest that mach jump goes and gets himself an Airpath brand Aircraft compass and pulls it apart.
some people only ever learn by having the evidence in front of them.

I guess I'm going to have to do that now. I'll let you know what I find.


MJ

[Mach Jump]

I couldn't find an Airpath compass to dismantle, so I Wrote to Airpath and asked the question. Here is their reply.

I don't know if this will settle your argument, but basically you are both correct. The card assembly is balanced for the vertical component of the earth's flux lines based upon the surveyed strength by NOAA for a given latitude and hemisphere. A small weight is applied to level the display level, non-accelerated flight. The pendular design of the card assembly helps minimize (but not eliminate) the dip errors when turning and accel/decal environments. Hope this helps.

Gil Stone
President
Airpath Instrument Company

Sorry, dubbleyew eight, you are right.


MJ

[Baikonour]

Thanks to MJ for that and well done to Airpath for responding

Interestingly, it implies that compasses sold at different latitudes therefore should have different counterweights. Which makes sense but is not something I think would have been practically possible or commercially desirable. A compass made for Florida will be a nuisance in Scandinavia and vice versa!

B.

[Mach Jump]

Interestingly, it implies that compasses sold at different latitudes therefore should have different counterweights. Which makes sense but is not something I think would have been practically possible or commercially desirable. A compass made for Florida will be a nuisance in Scandinavia and vice versa!

Yes. I believed that the whole point of the pendular suspension of the compass card was to eliminate the need for balance weights, so that the compass could be used anywhere in the world.

It looks like anyone thinking of flying from London to Capetown will have to consider the need to change the compass half way.


MJ

[Mach Jump]

Yes. I believed that the whole point of the pendular suspension of the compass card was to eliminate the need for balance weights, so that the compass could be used anywhere in the world.

It looks like anyone thinking of flying from London to Capetown will have to consider the need to change the compass half way.

A little more info from Airpath, after further enquiry, including the above London - Capetown example.

Only if airplane was moving base from north to south would there be any noticeable difference and any compass will function in any location. Static balance would be slightly off (1-3 degrees) but design incorporates 18 degrees of tilt/turn.

GS

Since the magnetic dip is 60 odd degress+ in the uk, and 60 odd degrees- in South Africa, I'm more confused than ever now!



MJ

[fireflybob]

Since the magnetic dip is 60 odd degress+ in the uk, and 60 odd degrees- in South Africa, I'm more confused than ever now!

Me too!

Not so sure this is correct.

The pendular design of the card assembly helps minimize (but not eliminate) the dip errors when turning and accel/decal environments.

But surely similar magnitude errors in both hemispheres?

Confused?

[FullWings]

I fitted one of these to my last glider, no errors at all!



You can even use it as an attitude reference should all the rest of your instruments fail.

[fireflybob]

I fitted one of these to my last glider, no errors at all!

Apart from the obvious answer, FW, what is it?