I understand that the speed tape should be Indicated Air Speed.
But, isn't Vne and Stall Speed a function of True Air Speed and not Indicated Air Speed.
Therefore, shouldn't these speeds marked on the airspeed tape automatically adjust up and down with altitude change?
TAS
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Walter Casey
- Posts: 10
- Joined: Sun Jun 23, 2013 6:33 pm
Re: TAS
Walter (Mike) Casey - You can download a rewritten EFIS Pilots Guide at http://www.caseyspm.com/RV7A.html
Re: TAS
Stall speed is an indicated airspeed. The tape automatically adjusts the stall speed for changes in load (normal acceleration).
Vne can be given as indicated or true. The SET MENU, Primary Flight Display section has a "Convert Vne from TAS to IAS" setting that will use Vne as a true airspeed and adjust the upper tape limit automatically.
Vne can be given as indicated or true. The SET MENU, Primary Flight Display section has a "Convert Vne from TAS to IAS" setting that will use Vne as a true airspeed and adjust the upper tape limit automatically.
Re: TAS
As Jeff said, at gross weight and 1g loading, the aircraft will stall at a certain indicated (actually calibrated, to be precise) airspeed, regardless of altitude or temperature.
Vne is much more complicated. For many aircraft it is set to provide a 10% speed margin from flutter. There are many possible flutter modes. Some scale exactly like rho-V squared (air density times true airspeed squared) which, by definition, is indicated airspeed squared. But other modes scale differently, and you need both air density and true airspeed to determine if it is safe. For certified aircraft, Vne expressed in indicated airspeed must provide an adequate margin over flutter up to the aircraft's published service ceiling, or, the aircraft must be placarded for differing Vne's based on altitude. For experimental aircraft, you are on your own.
(side note: the aircraft that tend to have flutter issues up high often depend on viscous damping by the air to keep their wings from flapping like a bird. This description fits gliders with long, flexible wings, but usually not powered aircraft with relatively stiff wings.)
More than you ever wanted to know!
Vne is much more complicated. For many aircraft it is set to provide a 10% speed margin from flutter. There are many possible flutter modes. Some scale exactly like rho-V squared (air density times true airspeed squared) which, by definition, is indicated airspeed squared. But other modes scale differently, and you need both air density and true airspeed to determine if it is safe. For certified aircraft, Vne expressed in indicated airspeed must provide an adequate margin over flutter up to the aircraft's published service ceiling, or, the aircraft must be placarded for differing Vne's based on altitude. For experimental aircraft, you are on your own.
(side note: the aircraft that tend to have flutter issues up high often depend on viscous damping by the air to keep their wings from flapping like a bird. This description fits gliders with long, flexible wings, but usually not powered aircraft with relatively stiff wings.)
More than you ever wanted to know!