Author Topic: Question about instruments  (Read 5077 times)

Offline Frank N. O.

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Question about instruments
« on: November 09, 2006, 05:13:43 AM »
Not really sure it belongs here but here goes. After looking at several different GA instruments then I got a few questions. How come all airspeed indicators have the scale turned upside down compared to that of a car? And how come some dash mounted compasses seem to rotate mirrored of the horizon? Isn't that a bit confusing?

The turn indicator has marking for the 2 minute turn, but the lines for it seems to match some on the artificial horizon but they can't be the same can they? Theones on the turn indicator must be measured in a different way than the artificial horizon otherwise there wouldn't be two right?

Lastly, is there a good article on the internet about VOR navigation? I assume there's a reason there are two VOR instruments.
Btw, speaking of VOR, are they still the main nav aids or are they reduced to secondary back-up instruments now?

Frank
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Offline Baradium

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Re: Question about instruments
« Reply #1 on: November 09, 2006, 06:39:17 AM »
Don't remember about the airspeed off hand.

Compasses:   Think of a card mounted flat on the dash.  The card always points north.     Well, you're reading the back end of the card.  If you turn left, the card turns clockwise.  The text appears to move from the right to the left since you're reading the back of the card.

The reason the compasses on the dash (btw, they all turn that way) turn "backwards" is because you are reading the actual compass, but from the back.

The directional gyro, which is vertical mounted is a completely different item.


The turn coordinator has no relation to an attitude indicator.  The bank required for a given rate or turn changes with airspeed (higher airspeed means higher bank).  The line on a turn coordinator always means 180 degrees in a minute (2 minutes for a circle) and thus doesn't have a bearing on what your actual angle of bank is.  You can do without one or the other (turn coordinator or artificial horizon) but you really need at least one.  You can uise a turn coordator to maintain control if you don't have an artificial horizon.


VORs are fairly important.  Having dual VORs allows you to identify fixes defined by two intersecting radials from different VORs.  DME also helps.  Distance Measuring Equipment tells you your slant range (true) distance from a VOR and some fixes are defined that way.  We use GPS in our aircraft *usually* to define VORs and fixes, but VORs are still very useful.
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Offline Frank N. O.

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Re: Question about instruments
« Reply #2 on: November 09, 2006, 07:40:55 PM »
Ah, good informative answers, thank you  |:)\

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline Voidhawk9

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Re: Question about instruments
« Reply #3 on: November 12, 2006, 10:08:13 AM »
Angle of bank required for a rate-1 turn:
Take your airspeed, and drop the final digit. Then add 7. This gives the required bank angle in degrees.

For example. You are flying at 150kts. Drop the final digit, so you now have 15. Add 7. 22deg is your required bank angle. :)

Weird, but it works.  ;D

Offline tundra_flier

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Re: Question about instruments
« Reply #4 on: November 17, 2006, 05:48:41 AM »
Angle of bank required for a rate-1 turn:
Take your airspeed, and drop the final digit. Then add 7. This gives the required bank angle in degrees.

For example. You are flying at 150kts. Drop the final digit, so you now have 15. Add 7. 22deg is your required bank angle. :)

Weird, but it works. ;D

Cool!  I love rules of thumb like that!

Phil

Offline Thunder Eagle

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Re: Question about instruments
« Reply #5 on: November 29, 2006, 08:53:44 PM »
For those who are curious, here's a Wikipedia entry which discusses the derivation of this rule of thumb:

http://en.wikipedia.org/wiki/ROT

They use 10 instead of 7.  I've seen 5 elsewhere.  I'm guessing this number would vary depending on what speed range you need.  For instance, 5 works better if you're in the neighborhood of 100 kts.

Offline snader

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Re: Question about instruments
« Reply #6 on: February 04, 2007, 07:59:43 AM »
Like baradium said, VOR can be used to calculate point to point distance by using slant range to the station and intercepting radials.

Also don't forget VOR approaches and most modern aircraft use VOR as an input into the FMS to give a possibility for VOR/VOR/ADIRU(or IRU) fix for their PPOS (present position or FMS position). This is not a very likely scenario though nowadays because the normal FMS nav is pretty much GPS/IRS nowaday's.
VOR is much more accurate than ADF (wich is on the way out).


If u are more interested in how a VOR works I'd be happy to explain it in detail if u want.

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Offline chuckar101

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Re: Question about instruments
« Reply #7 on: March 26, 2007, 07:03:52 PM »
Also Frank the Attitude Indicator tells you the airplanes relative position compared to the horizon whereas the turn coordinator is a rate instrument and gives you either rate of roll or turn.  The dual vor thing is also a safety thing.  You'll notice that in aircraft everything is backed up, so if something fails you still have the ability to fly accurately and navigate.
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Offline Baradium

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Re: Question about instruments
« Reply #8 on: March 26, 2007, 07:23:01 PM »
Also Frank the Attitude Indicator tells you the airplanes relative position compared to the horizon whereas the turn coordinator is a rate instrument and gives you either rate of roll or turn. The dual vor thing is also a safety thing. You'll notice that in aircraft everything is backed up, so if something fails you still have the ability to fly accurately and navigate.

You sure about a turn coordinator giving rate of roll?
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"

Offline chuckar101

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Re: Question about instruments
« Reply #9 on: March 26, 2007, 11:54:44 PM »
Positive, when its a turn coordinator when you initiate the turn it will give you rate of roll and once established in the turn it gives you the rate of turn.  Now a slip-skid indicator just gives you rate of turn.
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Offline Baradium

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Re: Question about instruments
« Reply #10 on: March 27, 2007, 07:07:40 AM »
Positive, when its a turn coordinator when you initiate the turn it will give you rate of roll and once established in the turn it gives you the rate of turn. Now a slip-skid indicator just gives you rate of turn.

The slip skid indicator is "the ball" and doesn't care what your rate of turn is, just tells you whether flight is coordinated.


I looked into the turn coordinator.  You are correct...  and apparently we have "turn indicators" in our 1900s (the ones that don't have an aircraft display), which I called turn coordinators as well.  These are the ones with just a needle and do not provide any rate of roll information.

So I was thinking back to those and thinking "these things sure don't seem to move until we actually start turning!"

You win this round!   :P     ::bow::
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"

Offline Gulfstream Driver

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Re: Question about instruments
« Reply #11 on: March 28, 2007, 04:13:34 PM »
The old style was called a Turn and Slip indicator, since it had the turn indicator and the inclinometer on the same instrument. 
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Offline chuckar101

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Re: Question about instruments
« Reply #12 on: April 07, 2007, 12:02:18 AM »
Just wanted to get the correct info out there.  No need to bow
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Offline snader

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Re: Question about instruments
« Reply #13 on: May 09, 2007, 09:22:45 PM »
wow, I didn't know that either  ::bow::

Arguing over the internet is like competing in the special olympics, u may win but u are still retarded.