Is Vne a true airspeed or a indicated airspeed?

[Axel]

Piston powered airplanes have Vne. Turbine powered airplanes are limited by Vmo/Mmo. There is some crossover point where the Mmo will occur at a lower indicated airspeed than Vmo, at which point the aircraft is mach limited vice speed limited.

Regardless of how, where why, what or who the airplane is powered or limited or what deeply complex calculations, variables, factors, constants, instants, Great Aunts and Fire Ants go into these wildly complex calculations all these limits are...

...get ready...

Indexed on and read directly from the airspeed indicator either as a red line or a barber pole. Therefore, the answer to the initial question is:

Vne is an indicated airspeed.

 

[MAJIC9]

Rally, you're getting two different answers, because they're in two different contexts.

What Axel says IS true.. for as long as you stay within manufacturers limits (or fly a plane with a barber pole.. or EFIS where computer performs same function).

It would NOT be true if you took a C-172 and slapped a PT-6 on it (or something bigger). That 158kts (indicated) red line would simply not apply if you were to take that highly modified 172 up to 40k feet..(if you could even get it that high). In other words, that red line would not mean that you're below critical flutter speed. Stay below specified service ceiling, and you'll be OK following the markings on the airspeed indicator. Note the discussion here is about using an airspeed indicator that has a fixed red line. Barber pole is there for a reason

I hope that illustrates why there are two answers.

 

[Rally]

My original question was on a experimental. So you slap a turbo normalized 0-320 on C-172 get it up to FL 270 and you might have issues. So Vne as I was discussing is indicated on certified aircraft but Vne could possible higher say C-172 160 knts indicated redline but at altitude cld be much higher.

Thanks

 

[DGdaPilot]

2 correct answers to 1 question? God I love aviation. <sarcasm>

 

[Rally]

So the answer is Vne is fixed indicated on aircraft without a barberpole such as a C-172 but really. Vne is ultimately on any aircraft a true airspeed such as a RV-6 or a mustang midget or a velocity etc.

Now the real question now that after 20 post we have sorted it out.

Imagine a C172 has a Vne of 160 knots INDICATED. We get a what cert experimental provisional etc and put a turbonormalized 0-470 on the front. What everyone is saying that at 160 knots indicated at FL250 we will have a flutter or other aerodynamic problem?

 

[ackattacker]

So the answer is Vne is fixed indicated on aircraft without a barberpole such as a C-172 but really. Vne is ultimately on any aircraft a true airspeed such as a RV-6 or a mustang midget or a velocity etc.

Now the real question now that after 20 post we have sorted it out.

Imagine a C172 has a Vne of 160 knots INDICATED. We get a what cert experimental provisional etc and put a turbonormalized 0-470 on the front. What everyone is saying that at 160 knots indicated at FL250 we will have a flutter or other aerodynamic problem?

It is unfortunately much more complicated than that. Vne could be established for many reasons, beyond flutter. Many of those reasons directly correlate with indicated airspeed, some correlate with true airspeed, whatever. What it really means is that if you take your turbonormalized experimental C172 up to FL250 then you are a test pilot, and you really don't know what kind of problems you are going to run into. You are operating outside the certification envelope, and going where the factory hasn't predicted or tested. That's not to say it definately shouldn't be done. But it should be done with some understanding of the risks and what kind of potential problems *may* exist.

 

[Flysher]

I always wondered this, the caravan's maximum airspeed is limited by a VMO number, but how come there is no VNO or yellow arc on the airspeed indicator?

 

[mzaharis]

Question from a guy that has never flown anything faster or higher performing than a PA28-180 - Does a barber pole merely adjust to the appropriate IAS for Mmo, based on temperature and density (the latter not impacting mach, but IAS)?

 

[avbug]

Both Vne and Mmo are indicated speeds, indicated on your airspeed indicator. The barber pole is adjusted by an air data computer to account for ambient conditions...but it's still an indicated airspeed.

Frequently we refer to IAS in the cockpit as meaning only our indicated speed in MPH or KIAS...and refer to Mach as something else. Incorrect. Both are indicated airspeeds, with mach merely being a percentage of a relative scale, whereas indicated airspeed in terms of KIAS or MPIAS is merely really a study of air density.

Vne occurs at higher and higher airspeeds with an increase in density altitude, and in certain aircraft ceases to become a limiting factor when the Mmo limit occurs at a lesser point on the airspeed indicator than Vne. Hence the limitation of Vne or Mmo, which ever occurs first.

 

[Rally]

I always wondered this, the caravan's maximum airspeed is limited by a VMO number, but how come there is no VNO or yellow arc on the airspeed indicator?

Turbine aircraft don't have a yellow arc. I think this is mostly FAR 23/25 or what ever it is that lists what must take place.