In my various Motor cars fitted with normally aspirated petrol engines fitted with Carburettors, I often fitted a Vacuum Gauge directly connected/piped to the inlet manifold, to register manifold vacuum.

The Gauge dial was coloured Green, Yellow, and Red and the needle registered the Vacuum in these areas.

For economical cruising the needle should be kept in the green area, with the foot lifted off the throttle (greatest vacuum). Entering the red area indicated the throttle was being pushed down unnecessarily hard (breaking the vacuum), therefore; "wasting fuel!".... ...!

I wonder if there is a default Sim Vacuum Gauge which does the same job, for normally aspirated, carburettor, Piston engined aircraft?

Paul...G-BPLF...FS 2004...and a 1931 Brooklands Riley 9... ...!

Brett_Henderson wrote on Sep 2^nd, 2010 at 4:12pm:


...of course!... ...!

Its the word "Pressure" which is/was fooling me...I was looking for a "Vacuum" Gauge. A "depression" in the Manifold!

Thanks for the reminder, Brett, I will find it useful to fit into simple aircraft which are not fitted with the gauge as standard...
It is a useful fitment to gain an idea of economical performance during flight.

Paul...G-BPLF...FS 2004....FS Nav....and a gentle tweak of the throttle... ...!

P.S. Some aircraft, (Default Beech Baron 58), are fitted with a small "Suction Gauge", registering + - 5 on the dial. What does that indicate?

beaky wrote on Sep 2^nd, 2010 at 7:14pm:


That's a biggie when flying by instruments. Many moons ago, I took off in a C172.. all was well until about 30 seconds into the climb. Earlier that day, a guy changed the battery, and failed to properly re-attach the vacuum hose .. it jiggled loose. It was a beautiful VFR, so no worries.. but when you lose the vacuum, you loose BOTH your heading indicator AND your attitude indicator.

Instrument traning prepares you for this.. and I can tell ya that flying in the clouds without those gauges is mind-bending. And it's why the third gyro-instrument (turn-coordinator), is electric. That, paired with the compass can keep you pointed in the right direction (and assure you that the wings are level).. but you gotta deduce your pitch by by your airspeed and power-setting, and back that up with a vertical speed/altitude.

While we're on the topic of of perilous failures... ponder what would happen if your pitot tube froze over completely, but the static port did not.

Excellent ! 

It's kind of a "what if" scenario and question; designed mostly to get new pilots to think about the pitot/static system, rather than just memorize enough about it to pass a test.

IF the pitot-tube iced over completely.. like you answered.. it would lock the current pressure in that side of the system.. and since the airspeed indicator works off of the DIFFERENCE between pitot and static pressures.. the airspeed indicator becomes a sort of altimeter.

What's particularly perilious, is that in a busy IFR cockpit, you rely on an airpseed indicator to backup altitude/attitude references. Let's say you want to execute a climbing turn.. and during this turn, you notice that your airspeed is increasing. Normally, that would mean that you're descending; so your instinct is to pull up a bit. In this scenario, that would cause the airspeed to increase even more, and if you pull up even more, you'll see an airspeed nearing Vne, while the stall horn starts blaring 

And of course the opposite is true.. if, during that turn you see your airspeed decreasing, you're instinct is to pitch down, which of course just causes the airspeed indication to continue drecreasing... and you end up looking at an airspeed needle nearing zero, in an airplane nearing Vne 

patchz wrote on Sep 9^th, 2010 at 7:01am:
Tempted but I'll let this one go  .

Brett_Henderson wrote on Sep 3^rd, 2010 at 8:12am:

Aha... partial- partial panel flying...   

I recently read some very good advice that relates to this sort of unfortunate circumstance, although it refers specifically to "what to do if you get stuck on top in a J3 Cub (which usually only has ball, compass, altimeter and ASI) and need to descend through the clouds".

The recommended technique is to set throttle at idle, dial in full up trim as it slows down, then sit on your hands and hook your legs under the seat (so you won't touch any controls).
Then you just wait until you break out... if you are lucky enough to do so before you hit something harder than a cloud.   

Brett_Henderson wrote on Sep 9^th, 2010 at 10:13pm:


Thats why I was always taught to carry post-it notes in your flightbag.  If you have an instrument giving funny readings and can't trust it, cover it up.  A lot easier to do partial panel without a malfunctioning instrument in the scan.  I even flew VFR once with a bad vacuum pump and the instruments still were throwing me off with a tumbling AI and spinning heading.