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F-S scale on the attitude indicator

Posted: Wed Apr 14, 2021 11:08 pm
by flyingturtle
I just wondered about this thingy here...

https://commons.wikimedia.org/wiki/File ... orizon.jpg

What does the

F
_

-

-
_

S


scale on the left mean?

My guess is "Fast - Slow", but that can't be...

Re: F-S scale on the attitude indicator

Posted: Thu Apr 15, 2021 12:19 am
by Starlionblue
Image

My guess is that it is an angle of attack index, and the letters do indeed mean Fast and Slow. Many fast jets use angle of attack as a reference on approach.


You can see the index on the left of this F/A-18 HUD.

Image

F-16.

Image

You can see the same on the Airbus BackUp Speed Scale (BUSS) which appears if you've lost significant parts of your air data. The speed scale becomes purely an AoA reference.

Image

Re: F-S scale on the attitude indicator

Posted: Thu Apr 15, 2021 2:37 am
by SoCalPilot
Its an angle of attack indicator and the F means Fast and the S means slow. Used primarily for maintaining landing speeds but can also be used for initial climbout speeds.

Re: F-S scale on the attitude indicator

Posted: Thu Apr 15, 2021 8:12 am
by flyingturtle
Thank you all! :cheerful:

Re: F-S scale on the attitude indicator

Posted: Thu Apr 15, 2021 12:17 pm
by thepinkmachine
Depends on type. On ATR and older 737 / 767 (before speed tape was introduced) it was speed deviation from reference selected speed on the Airspeed indicator. It was quite useful

Re: F-S scale on the attitude indicator

Posted: Thu Apr 15, 2021 3:52 pm
by 744lover
thepinkmachine wrote:
Depends on type. On ATR and older 737 / 767 (before speed tape was introduced) it was speed deviation from reference selected speed on the Airspeed indicator. It was quite useful


Same for the Classic 747 series....

Image

Re: F-S scale on the attitude indicator

Posted: Thu Apr 15, 2021 5:01 pm
by flyingturtle
Wow, thanks again!

This makes my FlightGear insanity a bit... more comfortable.

Re: F-S scale on the attitude indicator

Posted: Fri Apr 16, 2021 7:04 am
by VSMUT
thepinkmachine wrote:
Depends on type. On ATR and...


Indeed, displayed on the EADI:

Image

IMO, easier to work with than the speed tape of the -600, but lacks all the other useful stuff the speed tape comes with.

Re: F-S scale on the attitude indicator

Posted: Fri Apr 23, 2021 11:46 pm
by LimaFoxTango
On the Dash 8 100/300 there was a Fast/Slow indicator which was referenced against 1.3Vs (1.3 times stall speed) for current configuration (ie flap setting) which was the center mark.....IIRC

Re: F-S scale on the attitude indicator

Posted: Sun Apr 25, 2021 9:20 am
by Horstroad
flyingturtle wrote:

My guess is "Fast - Slow", but that can't be...


Your guess is correct. It's an indication for the current air speed in relation to the speed set for the auto throttle / speed command system.