Glareshield mounted compass?

On Thursday, March 13, 2014 1:04:03 AM UTC-5, Echo wrote:
It's part of my manufacturer issued type certificate as well as a part 91 reg. As a professional pilot, I just assume not hang my livelihood out there with some hokie backup compass. That being said, I agree that it's useless with the exception of a very few scenarios.

Understood - which is why I still have an aviation compass in my cockpit - but I refuse to be less safe (reduced visibility) to satisfy some bogus FAR requirement. So I found the smallest certified aircraft compass (the little PZL KI-13A) that I could mount in an inconspicuous location on my panel.

Sometimes, it's the little things in life...

Kirk
66

On Thursday, March 13, 2014 12:04:03 AM UTC-6, Echo wrote:
It's part of my manufacturer issued type certificate as well as a part 91 reg. As a professional pilot, I just assume not hang my livelihood out there with some hokie backup compass. That being said, I agree that it's useless with the exception of a very few scenarios. I do love the DC9 series compass. So much swing error that it has to be mounted on the aft cockpit bulkhead. Seen it many times. Awesome. Incredible that thing was designed looking at slide rules through thick glasses before we even engineered the Lunar Lander. What a TANK.



Jordan

E

I agree with that you must comply with the manufacturers type certificate, but I can't seem to the find any part 91 regs that require one for glider?

Brian

Glider=aircraft unless the SSA pulled a waiver from the FAA for that too...

I think some of you are underestimating the potential value of a magnetic compass when properly used. If you can't see out the window any more, holding a southerly heading (in the northern hemisphere) may keep your wings attached long enough for you to get to where you can see out again... assuming you don't reach the ground first.
On a southerly heading the compass can help you avoid a spiral dive by indicating turns - even without a gyro. Instead of "Needle, ball, airspeed..." the scan becomes "Compass, yaw string, airspeed..."
The southerly heading is critical as it avoids the northerly turning error and acceleration errors associated with the use of a magnetic compass on other headings.
In the southern hemisphere you head north instead.
Of course, if you have a GPS with a moving map display... and the light is still on... you can do the same thing by keeping the track straight - in any direction (it doesn't have any compass errors).
I consider a compass cheap, reliable insurance. I wouldn't fly without one.
Mike Koerner

Most people here also didn't get any partial panel instrument training either. I'm not sure I agree about southern only heading. Lead/lag errors are the only issues that apply to the compass when associated with non-east/west headings. If turning towarda northern heading you'd overshoot the compass heading and undershoot the rollout to a southern heading. Either way it won't be accurate in the short term. Are you thinking just due to the physics of a compass that it's more likely to be stable and leas prone to swinging if the magnetic pull is behind the gauge? I don't think that would make a difference. It's been a while since my most active CFII days, so I could be missing something...

E

In the northern hemisphere, when turning from a northerly heading, a magnetic compass will lag behind the turn (or even initially start to turn in the opposite direction). It would be difficult to effectively use that that information to maintain wings-level flight.
In turning from a southerly heading, on the other hand, the compass will lead the turn - exaggerating the amount you've turned. Since you are trying to avoid turns altogether, lead is not at all bad. You just need to respond with appropriate restraint to avoid excessive roll oscillations.
On an easterly or westerly heading, the acceleration error swings the compass toward the north as you speed up and toward the south when you slow down.. To the degree you only look at the compass when you are flying straight and level, it works fine. But as things start to go haywire, speed corrections are going to play havoc with your ability to keep the wings level.
In between headings present an amalgamation of these errors.
So if all you have is a magnetic compass, airspeed indicator and ball (or yaw string)... head south. That's what I was taught. I admit, I haven't practiced this teaching, or (fortunately) had the need to implement it, but it seems to make sense anyway.
This assumes that you are not trying to navigate to some specific heading. Whether you roll out on the right heading or not is not the issue. In this case you're just trying to maintain a heading to keep the wings level (and attached) until you get back into VMC. Other options are a benign spiral or induced spin.
Mike Koerner

Ah yes, thanks. Been close to 7 years since I was an active CFI-I. BUT...when I used to teach a lot of partial panel, we'd do a demo of the turn coordinator failing during a partial panel scenario...never went well. Point being, most guys would mess themselves up and pull their wings off before a mag compass will get them out of the clouds successfully. Only a very few with RECENT practice in IFR partial panel training would have a chance. There's a reason why I and most other CFIG teach the benign spiral. Simple and effective.

E

I recall a warning somewhere in the Dash-1 that went something like,
"WARNING - Instrument flight with the magnetic compass is an emergency
procedure." My partial panel practice always included a working needle and
ball.


"Echo" wrote in message
...
Ah yes, thanks. Been close to 7 years since I was an active CFI-I.
BUT...when I used to teach a lot of partial panel, we'd do a demo of the
turn coordinator failing during a partial panel scenario...never went well.
Point being, most guys would mess themselves up and pull their wings off
before a mag compass will get them out of the clouds successfully. Only a
very few with RECENT practice in IFR partial panel training would have a
chance. There's a reason why I and most other CFIG teach the benign spiral.
Simple and effective.

E

On Friday, March 21, 2014 10:04:16 PM UTC-6, Mike Koerner wrote:
In the northern hemisphere, when turning from a northerly heading, a magnetic compass will lag behind the turn (or even initially start to turn in the opposite direction). It would be difficult to effectively use that that information to maintain wings-level flight.

In turning from a southerly heading, on the other hand, the compass will lead the turn - exaggerating the amount you've turned. Since you are trying to avoid turns altogether, lead is not at all bad. You just need to respond with appropriate restraint to avoid excessive roll oscillations.

On an easterly or westerly heading, the acceleration error swings the compass toward the north as you speed up and toward the south when you slow down. To the degree you only look at the compass when you are flying straight and level, it works fine. But as things start to go haywire, speed corrections are going to play havoc with your ability to keep the wings level.

In between headings present an amalgamation of these errors.

So if all you have is a magnetic compass, airspeed indicator and ball (or yaw string)... head south. That's what I was taught. I admit, I haven't practiced this teaching, or (fortunately) had the need to implement it, but it seems to make sense anyway.

This assumes that you are not trying to navigate to some specific heading.. Whether you roll out on the right heading or not is not the issue. In this case you're just trying to maintain a heading to keep the wings level (and attached) until you get back into VMC. Other options are a benign spiral or induced spin.

Mike Koerner

I actually tried this from the back seat of a G103 while wearing "Foggles" to restrict my view to the panel. With a safety pilot in the front seat watching for traffic I found it surprisingly easy to maintain a wings-level southerly course. However, I do have an instrument rating with a lot of partial panel practice. Although I will do everything I can to avoid the necessity of using the trick for real in cloud, I think it might work.

How about inside a bumpy Cumulus cloud?