IRS's are not needed for an IVSI. This link gives a good explanation of an IVSIhttp://www.allstar.fiu.edu/aero/PSI.htmThe IVSI has accelerometers inside the case to reduce the lag. They have been around for a long time and are not as fancy as you would think.C McCarthy

>"Baro rate from the ADC is pretty much instantaneous VS, so>does the IRS still add some pitch rate lead as with the old>style IVSIs? Or is it just a convenient way to collect the>data to the DUs?">>The ADC's are still sensing altitude change by measuring air>pressure changes, so it won't be as fast as the IRS's. The>plumbing to the ADC's from the probes is quite long, so I'd>imagine that there would be some kind of delay. The IRS's areI was just reading an article in Business & Commercial Aviation about Embraer's new corporate jet model (the "Lineage") currently under development. It will have the pitot and static pressure transducers integrated directly into the pitot mast, with an ARINC 429 data bus feeding the ADC's - thus eliminating all traditional pitot/static plumbing in the aircraft. It should greatly simplify maintenance on the air data systems, and I'm sure will be the wave of the future...Jim Barrett

"It will have the pitot and static pressure transducers integrated directly into the pitot mast, with an ARINC 429 data bus feeding the ADC's - thus eliminating all traditional pitot/static plumbing in the aircraft."This is the case with all newer generation aircraft (B777's, 737NG's, Airbuses, etc), although you may find traditional plumbing being used for the standby instrumentation.Cheers.Q>

Ye but it would still be no use in a cessna (or similar aircraft).Such small and light planes are very sensitive for even the smallest air turbulences, therefore you mostly get a bumpy ride on it. Thus, the acclerometer would drive the VSI crazy.Just my 2 cents, plz correct me if I´m wrong.

Ever been in a 737 Classic in even quite moderate turbulence? They shake around a lot too. Doesn't stop them using an IVSI. The electronics within the instrument filters out higher frequencies from turbulence and keeps the sustained accelerations.Accelerometers sound high-tech, but in this case they aren't. It's basically a mass on a stiff spring. Nothing fancy. Also, there is no such thing as an Inertial Lead System. "Inertial Lead" is simply the predictive term from the accelerometer in the instrument added to the heavily lagged baro VSI to produce IVSI.The main reason you might not bother with an IVSI in a Cessna is because it's not really worth it. The Mark I Vertical Accelerometer (better known as "the seat of your pants") does a much better job of telling you that you are deviating from your altitude than an IVSI ever could. :)Kevin

I don´t think you could really compare the turbulence behavior of a 737 and a Cessna.And those electronics within the instrument smoothing the IVSI you are talking about would already be too much for a C172.Btw, this seems to be drifting too far away from PMDG related topics, still interesting to know:-roll

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