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"Watch the VSI- SIR!" A salutary lesson in instrument flying.

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"Watch the VSI- SIR!" A salutary lesson in instrument flying.

Old 21st Jun 2012, 07:29
  #21 (permalink)  
Join Date: Jul 2007
Location: Australia
Age: 69
Posts: 1,320
even a normal VSI (an IVSI is much better) will show you a divergence in altitude that is ABOUT to happen
Can you explain what you mean by that Chimbu, not quite sure I understand what you are trying to impart.
Arnold E is offline  
Old 21st Jun 2012, 07:39
  #22 (permalink)  
Join Date: Feb 2006
Location: The Zoo
Posts: 335
A VSI will respond to an altitude change before an altimeter.
kalavo is offline  
Old 21st Jun 2012, 08:38
  #23 (permalink)  

Grandpa Aerotart
Join Date: Jun 2000
Location: SWP
Posts: 4,620
Especially an IVSI.

An IVSI/VSI will be displaying a rate of change for some seconds before a meaningful change in altitude occurs - keep it on 0 rate and altitude cannot change.

but the VSI tells you what has happened, it does not tell you what is about to happen, as does the AI.
Ahhh...then how come, in the wind shear avoidance manouver do they tell you (after aggressively firewalling the thrust levers, rolling wings level and pitching up to the PLIs, ensuring speed break retracted etc etc) to monitor the IVSI?

What instrument will indicate you're flying out of the microburst/not going to hit the ground first - the AI, ASI or the IVSI?

IVSI/VSI were described as trend instruments when I were a lad.

Last edited by Chimbu chuckles; 21st Jun 2012 at 08:59.
Chimbu chuckles is offline  
Old 21st Jun 2012, 10:26
  #24 (permalink)  
Join Date: Jul 2007
Location: France
Posts: 610
IFR suggestions


Both served me well during my career, I always used the VSI as a trend instrument and the actual IVSI as a real time reflection of what the aircraft was doing.

Tmbstory is offline  
Old 21st Jun 2012, 10:37
  #25 (permalink)  
Join Date: Aug 1998
Location: Ex-pat Aussie in the UK
Posts: 4,523
The VSI is brilliant because it is the only instrument which requires no mental processing to interpret it. Needle pointing up - you're going up. Needle pointing down - you're going down.

That's very important when you are experiencing confusion in the cockpit, however that is brought about (the leans, high workload, somatogravic or black hole illusions etc)

The AH needs you to interpret pitch attitude to the background picture and relate that to speed/adjustment, the ASI needs you to read the speed and relate that to the performance, the altimeter needle goes down on the right and up on the left of the instrument etc etc.
Checkboard is offline  
Old 21st Jun 2012, 10:42
  #26 (permalink)  
Join Date: Aug 2007
Location: You know where the Opera House is? Well....no where near there.
Posts: 53
I agree Wally,

I think the ASI is very important when it comes to night departures.

By the way people, somotogravic illusion doesn't only affect high performance aircraft, I distinctly remember a night I experienced it in a C152! I remember looking at the ASI thinking, the ASI is broken, it's over-reading, the AH is reading 7 degrees nose up correctly, then once I checked the VSI, I worked out I was descending. The AH was a little lazy though...(by the way, not the first 'distinctly rememberable' event of mine from a lazy AH!)

I have a fair whack of hours in the C310. They will climb at about 500 fpm at Vy and MTOW. But if they're taking off light, they'll initially get over 2000 fpm. This means big attitude differences depending on weight.

So a C310's climb attitude departing with a heap of fuel and a few footy players on board will be very different after you've burnt some fuel and unloaded your pax.

So how do you know what attitude you need for your night departure? Initially reference it to the ASI. You need to absolutely nail your nominated climb speed. Check the ASI, work out if you need to pitch up or down, then stare at your AH and pitch up or down as required. Then quickly look at the ASI, to see if the attitude is working to provide you with your nominated climb speed. Of course as part of this scan you need to check the DG and VSI.

I'm not trying to tell people how to suck eggs here, but I would hate to see somebody read all of these posts, then take-off at night, staring at the VSI and thinking this will stop them spearing in.
CaptainInsaneO is offline  
Old 21st Jun 2012, 17:26
  #27 (permalink)  
Join Date: Sep 2006
Location: Los Angeles, USA
Age: 48
Posts: 1,633
The EVS technology is simple and can be a life saver. As prices come down, it should be considered for all all-weather aircraft, from singles up to jets. I certainly will try to get one installed when I get my "real" (as in final) travel plane..
AdamFrisch is offline  

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