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Please Help: A Question On The Directional Gyro  
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Posted (8 years 6 months 3 weeks 1 day 3 hours ago) and read 2939 times:

I will have my instrument stage check soon, and I will have to be able to explain every instrument as far as to how it functions.

A question I have that nobody has been able to explain to me well is why the directional gyro (heading indicator, if you prefer) needs to have a double gimbal? AFAIK, the gyro only needs to sense yaw, so I don't really get why the need for the other gimbal. I have acces to decomissioned and opened instruments at school to see the internal working if that helps.

BTW, I'm talking for a vacuum driven heading indicator, found in late model C172s.

Thanks for answering  wave 

9 replies: All unread, jump to last
 
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 1, posted (8 years 6 months 3 weeks 1 day 3 hours ago) and read 2935 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Without a double gimbal, rigidity in space would be unattainable.




2H4





Intentionally Left Blank
User currently offlineDc10guy From United States of America, joined Feb 2000, 2685 posts, RR: 6
Reply 2, posted (8 years 6 months 3 weeks 1 day 3 hours ago) and read 2935 times:

You need to see the compass in turns AND when you climb and dive. A gimbal for pitch and a gimbal for roll ...


Next time try the old "dirty Sanchez" She'll love it !!!
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 3, posted (8 years 6 months 3 weeks 1 day 2 hours ago) and read 2924 times:
AIRLINERS.NET CREW
DATABASE EDITOR



Speaking of rigidity in space, I think I just found the coolest example ever:


















2H4





Intentionally Left Blank
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 4, posted (8 years 6 months 3 weeks 13 hours ago) and read 2871 times:

Quoting 2H4 (Reply 1):
rigidity in space would be unattainable



Quoting Dc10guy (Reply 2):
A gimbal for pitch and a gimbal for roll

So what you guys mean is that, say, without a gimbal for pitch, the gyro would precess in the roll axis, which is something we certainly don't want, right?

Quoting 2H4 (Reply 3):
I think I just found the coolest example ever:

The first two pics aren't working  cry 


Thx for the answers so far  Smile


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 5, posted (8 years 6 months 3 weeks 12 hours ago) and read 2862 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting FLY2HMO (Reply 4):
The first two pics aren't working

Here you go:











2H4





Intentionally Left Blank
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 6, posted (8 years 6 months 3 weeks 12 hours ago) and read 2850 times:

Quoting FLY2HMO (Thread starter):
the gyro only needs to sense yaw

Actually the DG does not "sense" yaw. It keeps its rigidity in space and you yaw around it. It might be better to say it is immune to yaw, or ignores yaw.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 7, posted (8 years 6 months 3 weeks 11 hours ago) and read 2839 times:

Quoting 2H4 (Reply 5):
Here you go:

Wow, that is really impressive. Thanks for the pictures.

Quoting SlamClick (Reply 6):
or ignores yaw

So it ignores pitch too, right?


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 8, posted (8 years 6 months 3 weeks 11 hours ago) and read 2830 times:

Quoting FLY2HMO (Reply 7):
So it ignores pitch too, right?

I guess you could say that. And roll too. If it remains rigid in space the compass card (for the drum type) would remain stable, paralell to the earth's surface where you are flying. So the part of the card that you pointed north (by setting the heading from your wet compass) would remain pointed north. When you make a turn, you are flying the window and lubber line around to different parts of the card - giving you a glimpse of the reading there. If you head south you get to see the part of the card that says "south."

That fact might help you more instinctively understand lead/lag and northerly turning error if those are still taught and tested. It helped me understand them.

If that doesn't make sense leave it alone and go back and re-read something that did.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 9, posted (8 years 6 months 3 weeks 11 hours ago) and read 2830 times:

OK thanks to everybody, it was very useful.  yes 

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