Change Forum... Civil Aviation Travel, Polls & Prefs Tech/Ops Aviation Hobby Aviation Photography Photography Feedback Trip Reports Military Av & Space Non-Aviation Site Related LIVE Chat My Starred Topics | Profile | New Topic | Forum Index | Help | Search
 VSI Dail Display
 Novice From United Kingdom, joined Aug 2012, 90 posts, RR: 0Posted Fri Nov 30 2012 13:37:27 UTC (2 years 12 months 1 day 23 hours ago) and read 3064 times:

 "The VSI uses a logarithmic scale display that has a greater sensitivity at small rate of climb or descent (ROC/ROD) values. Zero is usually at the 9 o'clock position with the ROC scale above a ROD scale below" How come the VSI uses a logarithmic scale display as the VSI goes up in 100 increments and not multiples like a logarithmic scale? and anyone explain why the VSI has a greater sensitivity at a small rate of climb or descent values? Thanks
 tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 80 Reply 1, posted Fri Nov 30 2012 15:26:17 UTC (2 years 12 months 1 day 21 hours ago) and read 3036 times:

 Quoting Novice (Thread starter):How come the VSI uses a logarithmic scale display as the VSI goes up in 100 increments and not multiples like a logarithmic scale?

Here's a standard Boeing PFD:

Take a look at the VSI on the right side...the physical distance between 0 and 1 is considerably bigger than the difference between 1 and 2, which is again bigger than the difference between 2 and 6. That's what they're talking about. The same angular movement of the needle corresponds to far more FPM at high deflection than low.

 Quoting Novice (Thread starter):and anyone explain why the VSI has a greater sensitivity at a small rate of climb or descent values?

It's not that the instrument is more sensitive, it's that the display *scale* is logarithmic so that a change in rate causes a much bigger deflection at low rates than at high rates. Otherwise, if the scale was linear and full throw, small rates (what you care about when trying to accurately hold altitude) would be impossible to see.

 flyingturtle From Switzerland, joined Oct 2011, 3773 posts, RR: 16 Reply 2, posted Fri Nov 30 2012 15:54:50 UTC (2 years 12 months 1 day 21 hours ago) and read 3029 times:

In a rapid descent, it does not matter if you are falling down with 11'000 or 12'000 fpm.

But during the approach, the very same difference (namely, 1000 fpm) between a 2000 fpm and a 3000 fpm descent matters much more.

The scale gives you accuracy - but only where it is important.

David

 Keeping calm is terrorism against those who want to live in fear.
 Novice From United Kingdom, joined Aug 2012, 90 posts, RR: 0 Reply 3, posted Thu Dec 6 2012 16:10:27 UTC (2 years 11 months 3 weeks 4 days 20 hours ago) and read 2713 times:

 Thanks for explaining that guys and that diagram really helped cheers Tom
 Top Of Page Change Forum... Civil Aviation Travel, Polls & Prefs Tech/Ops Aviation Hobby Aviation Photography Photography Feedback Trip Reports Military Av & Space Non-Aviation Site Related LIVE Chat Forum Index

Reply To This Topic VSI Dail Display
• Tech/Ops related posts only!
• Not Tech/Ops related? Use the other forums
• No adverts of any kind. This includes web pages.
• No hostile language or criticizing of others.
• Do not post copyright protected material.
• Use relevant and describing topics.
• DETAILED RULES

 Similar topics: More similar topics...
Display Windows FCU Vs MCP posted Fri Dec 16 2011 02:47:43 by Nomik
737NG Flight Deck Display Configurations posted Thu Sep 15 2011 16:05:15 by WestJetForLife
737 NG ND Display posted Fri Aug 27 2010 04:58:54 by smartt1982
Spiroid Winglet On Display On A Falcon 50 At Osh posted Tue Jul 27 2010 08:08:33 by MD-90
Heads Up Display Unit posted Sat Jun 6 2009 12:20:43 by Propilot83
777 LCD Display Frames posted Mon Jun 18 2007 05:18:28 by Speedracer1407
Zulu Time In The FMS Display? posted Sun May 14 2006 19:30:14 by Wardialer
747-400 With LCD Display`s`? posted Sat Oct 15 2005 12:14:19 by Qantas744ER
737NG Flight Deck Display Formats posted Wed Sep 14 2005 12:52:16 by ZSOFN
747 Section On Display posted Wed Aug 31 2005 08:48:26 by EconoBoy