What do speed mods do to the yellow/ red arc / Vne?

[mooniac15u]

Just to muddy the water - My 1965 Mark 21 Owners Manual calls Vne a "certified calibrated airspeed" ...

I am in agreement that typical speed mod STCs for vintage Mooneys do not change the certified spec

CAS is just IAS corrected for installation and instrument errors.

[DS1980]

Don't know what else to say. Folks, Vne is a true airspeed.

Prove that Vne is arbitrary. What manufacturer said that?

You're all over the place. First you say that Vne is not based on anything. Then you say it builds in a safety margin based on aerodynamic forces. Wouldn't there have to be a known phenomenon to build in a safety margin, either from flight testing or structural analysis?

[DS1980]

Yes, because the owners manual is always right.

In reference to the SB, why does it call for the new ASIs to be TRUE airspeed indicators?

[mooniac15u]

I didn't say it wasn't based on anything. I said it is not necessarily related to flutter. Even Krueger said it can be based on different things. What I said was that as a published limitation it is an IAS. As such it builds in a margin of error to compensate for the limits of the envelope. There is no requirement for the Vne of a given airframe to be anywhere near its actual aerodynamic limitations. If it isn't based on an aerodynamic limitation and both the FAA and the POH label it IAS then it is IAS.

I agree that true aerodynamic limitations are TAS. It's just that there is no requirement that the Vne be near the limit.

[mooniac15u]

Yes, because the owners manual is always right.

In reference to the SB, why does it call for the new ASIs to be TRUE airspeed indicators?

That's just an ASI that has the ability to convert to TAS for a small section of the cruise speed. The Vne is in the IAS section above that. You may also note that there are four ASI options. Two with TAS and two without.

[mooniac15u]

Then you say it builds in a safety margin based on aerodynamic forces. Wouldn't there have to be a known phenomenon to build in a safety margin, either from flight testing or structural analysis?

Not really. They have to demonstrate that the indicated airspeed limitations are safe across the flight envelope. They don't have to flight test for actual structural limitations. That would result in a lot of destroyed prototype airframes. I imagine they know the flutter speed from wind tunnel testing but that may not be anywhere near Vne. Flutter speed is what Kruger was pointing out as being a TAS.

[DS1980]

stale mate

[Tom]

To summarize much:
-The OP asked about the 20F. The TCDS for the 20F lists the VNE as "(174 knots) True Ind."
-To my knowledge, no mod STC allows an increase to the F VNE listed in the TCDS
-Operating at a true airspeed above 174 knots isn't legal
-Flutter is indeed related to everything in and around the airplane
-Emperically there hasn't been a Mooney lost to flutter (including all the turbo-normalized F-models) but this could change
-Most 20F owners dream every night to be so lucky as to have their 20F somehow start to exceed 174 in level flight
-As stated, the mods won't change the TCDS speed ranges and in real-life won't allow the 20F to go over VNE in level flight (turbocharger notwithstanding)

On a related note, read how attorney turned armchair aeronautical engineer Mike Danko pulls the flutter trump card on the Flint Aero President (whose company has provided safe products for decades):
http://www.aviationlawmonitor.com/2010/03/articles/general-aviation/the-trouble-with-tip-tanks/

[mooniac15u]

TIAS is not TAS.

[carusoam]

So...

VNE is a limitation set by the manufacturer. They tested up to that point. They did not test to destruction that happens somewhere after that...

Similar to demonstrated cross-wind component capabilities.

Running into trouble with excessive cross wind is often recovered by a go around.

Running into trouble after exceeding VNE may not be recoverable.

When you exceed the recommendation / limitation you are now known as a test pilot.

-a-

[Tom]

TIAS is not TAS.

What is TIAS and how is it different than TAS? I've never heard of TIAS.

[PTK]

The pitot tube measures airspeed through sensing air pressure. As altitude increases air density decreases. To sustain lift speed has to increase. The equation that relates these is q=1/2ρv^2. q is dynamic pressure the pitot tube sees, ρ ιs air density and v is speed.

The pitot tube measures this pressure as an IAS and constant pressure means a constant IAS. A given AOA will predictably produce a certain amount of lift.

Flutter is different. Vne is based TAS. In order to not exceed a given TAS Vne, the Vne IAS has to decrease as altitude increases.

One of these days I'm going to plot on excel of altitude as a function of IAS and come up with a constant TAS plot that shows this.

One of these days!

[Marauder]

The pitot tube measures airspeed through sensing air pressure. As altitude increases air density decreases. To sustain lift speed has to increase. The equation that relates these is q=1/2ρv^2. q is dynamic pressure the pitot tube sees, ρ ιs air density and v is speed.

The pitot tube measures this pressure as an IAS and constant pressure means a constant IAS. A given AOA will predictably produce a certain amount of lift.

Flutter is different. Vne is based TAS. In order to not exceed a given TAS Vne, the Vne IAS has to decrease as altitude increases.

One of these days I'm going to plot on excel of altitude as a function of IAS and come up with a constant TAS plot that shows this.

One of these days!

Looks like Peter stayed at a Holiday Inn Express last night. Nice explanation!

[PTK]

How did you know Chris?!

 

Breakfast is a joke! They need to improve on that dept!

[mooniac15u]

The pitot tube measures airspeed through sensing air pressure. As altitude increases air density decreases. To sustain lift speed has to increase. The equation that relates these is q=1/2ρv^2. q is dynamic pressure the pitot tube sees, ρ ιs air density and v is speed.

The pitot tube measures this pressure as an IAS and constant pressure means a constant IAS. A given AOA will predictably produce a certain amount of lift.

Flutter is different. Vne is based TAS. In order to not exceed a given TAS Vne, the Vne IAS has to decrease as altitude increases.

One of these days I'm going to plot on excel of altitude as a function of IAS and come up with a constant TAS plot that shows this.

One of these days!

 

Flutter speed is TAS.  Agreed.

 

Vne would also be TAS if it were derived from flutter speed.  It is not.

 

Please provide a link to the portion of the certification process where flutter speed is used to establish Vne.  Please provide the mathematical relationship between flutter speed and Vne.

[Marauder]

Here we go! I give the guy credit for sleeping at a Holiday Inn Express, then the hotel manager says he slept in his car in the parking lot. Peter -- what say you...

[Tom]

I don't know what AOA has to do with the discussion unless our friendly M20F is approaching the Q-corner, but it appears as though someone is starting to appreciate the utility of knowing the AOA.

TAS is the TRUE airspeed. We know it's true because they called it true. The VNE for the F is 174 TAS. It doesn't need to get more complicated than that.
Whether or not we can correctly determine TAS with the plumbing and instrumentation we have on and in the airframe is another matter, but more pertinent TAS calculation formulas can be found on the wiki page on the subject of true airspeed:

http://en.wikipedia.org/wiki/True_airspeed

I assume that dive/flutter testing data is only available in the Mooney company archives. I further assume that the Mooney company practices the industry standard of being conservative it setting speed limits during the certification process. We all can only assume that VNE was set what it is because of flutter concerns (and not mach tuck, inadequate cowling strength, etc).

Again, empirically flutter or other forms of catastrophic airframe failures fortunately have to date not been an issue for the Mooney line, including routine operation by some pilots over 174 TAS in their F models.
 

[mooniac15u]

I don't know what AOA has to do with the discussion unless our friendly M20F is approaching the Q-corner, but it appears as though someone is starting to appreciate the utility of knowing the AOA.

TAS is the TRUE airspeed. We know it's true because they called it true. The VNE for the F is 174 TAS. It doesn't need to get more complicated than that.

Whether or not we can correctly determine TAS with the plumbing and instrumentation we have on and in the airframe is another matter, but more pertinent TAS calculation formulas can be found on the wiki page on the subject of true airspeed:

http://en.wikipedia.org/wiki/True_airspeed

I assume that dive/flutter testing data is only available in the Mooney company archives. I further assume that the Mooney company practices the industry standard of being conservative it setting speed limits during the certification process. We all can only assume that VNE was set what it is because of flutter concerns (and not mach tuck, inadequate cowling strength, etc).

Again, empirically flutter or other forms of catastrophic airframe failures fortunately have to date not been an issue for the Mooney line, including routine operation by some pilots over 174 TAS in their F models.

 

 

Please show documentation that the Vne has been published as a TAS.

[mooniac15u]

What is TIAS and how is it different than TAS? I've never heard of TIAS.

 

TIAS is effectively CAS.  CAS is specific to a particular airplane because it includes installation and instrument errors so it is not used to describe airspeeds in the TCDS.  It is the airspeed that would be indicated if there were no measurement error.

[Tom]

TIAS is effectively CAS.  CAS is specific to a particular airplane because it includes installation and instrument errors so it is not used to describe airspeeds in the TCDS.  It is the airspeed that would be indicated if there were no measurement error.

The only circumstance where CAS is true is at standard conditions (which no one operates at).  CAS is thus only on very rare occasion true airspeed. 

 

A regular airspeed indicator in a Mooney is simply a pressure measurement calibrated to, amongst other things, a given pressure and temperature. We know that pressure and temperature and not constant (enter ideal gas law).

  

When you place a "T" or "true" statement along side an airspeed you are stating that the airspeed is the speed at which the airplane is slicing through the air.  It is true because you've calibrated your pressure measurement for density, which of course is related to temperature and pressure.  There simply are not different "trues."

You seem to be making up a concept of "true indicated air speed" as being different than true airspeed.  True airspeed is true airspeed, pure and simple.  Adding "indicated" is at best used in a context where the speaker is referencing the function of the true airspeed indicator itself.  If not referencing the function of the instrument, in the aviation world that I grew up in, adding "indicated" suggests that the speaker doesn't understand the concept of true airspeed, which seems to be the case here.  You've stated that TAS and TIAS are not the same thing, and now are starting TIAS is effectively CAS when it is not. 

 

Documentation that VNE is knots true:

http://www.67m20e.com/Mooney%20TCDS%202A3%20Rev%2052%20dtd%209DEC10.pdf

 

Please cite a reference that states that there is a difference between true airspeed and true indicated airspeed.

[mooniac15u]

The only circumstance where CAS is true is at standard conditions (which no one operates at).  CAS is thus only on very rare occasion true airspeed. 

 

A regular airspeed indicator in a Mooney is simply a pressure measurement calibrated to, amongst other things, a given pressure and temperature. We know that pressure and temperature and not constant (enter ideal gas law).

  

When you place a "T" or "true" statement along side an airspeed you are stating that the airspeed is the speed at which the airplane is slicing through the air.  It is true because you've calibrated your pressure measurement for density, which of course is related to temperature and pressure.  There simply are not different "trues."

You seem to be making up a concept of "true indicated air speed" as being different than true airspeed.  True airspeed is true airspeed, pure and simple.  Adding "indicated" is at best used in a context where the speaker is referencing the function of the true airspeed indicator itself.  If not referencing the function of the instrument, in the aviation world that I grew up in, adding "indicated" suggests that the speaker doesn't understand the concept of true airspeed, which seems to be the case here.  You've stated that TAS and TIAS are not the same thing, and now are starting TIAS is effectively CAS when it is not. 

 

Documentation that VNE is knots true:

http://www.67m20e.com/Mooney%20TCDS%202A3%20Rev%2052%20dtd%209DEC10.pdf

 

Please cite a reference that states that there is a difference between true airspeed and true indicated airspeed.

 

Just look at that table.  All of those airspeeds are published as indicated in your POH and labeled as indicated on your ASI.

 

TIAS is an outdated term that unfortunately sounds like TAS but you really can't just ignore the presence of the term "indicated".  True just means actual.  In TAS it is your actual airspeed and in TIAS it is your actual indicated airspeed.  TIAS is effectively CAS.

 

Since this term isn't really commonly used it is difficult to find a good definition.  If you search around a bit online you see some good discussions about it such as this one:

 

http://www.cessna120-140.org/forum/viewtopic.php?t=11247

[mooniac15u]

You can see how TIAS was used in the old CAR: http://www.navioneer.org/riprelay/Yet%20More%20Navion%20Files/car_part3.pdf

 

Take a look at 3.757 to see how TIAS was used to describe Indicated Airspeed for markings on the ASI.  Particularly the items that we all know to be IAS.

[mooniac15u]

The only circumstance where CAS is true is at standard conditions (which no one operates at).  CAS is thus only on very rare occasion true airspeed. 

 

A regular airspeed indicator in a Mooney is simply a pressure measurement calibrated to, amongst other things, a given pressure and temperature. We know that pressure and temperature and not constant (enter ideal gas law).

  

When you place a "T" or "true" statement along side an airspeed you are stating that the airspeed is the speed at which the airplane is slicing through the air.  It is true because you've calibrated your pressure measurement for density, which of course is related to temperature and pressure.  There simply are not different "trues."

You seem to be making up a concept of "true indicated air speed" as being different than true airspeed.  True airspeed is true airspeed, pure and simple.  Adding "indicated" is at best used in a context where the speaker is referencing the function of the true airspeed indicator itself.  If not referencing the function of the instrument, in the aviation world that I grew up in, adding "indicated" suggests that the speaker doesn't understand the concept of true airspeed, which seems to be the case here.  You've stated that TAS and TIAS are not the same thing, and now are starting TIAS is effectively CAS when it is not. 

 

Documentation that VNE is knots true:

http://www.67m20e.com/Mooney%20TCDS%202A3%20Rev%2052%20dtd%209DEC10.pdf

 

Please cite a reference that states that there is a difference between true airspeed and true indicated airspeed.

 

Let's assume for the sake of discussion that you are right and TIAS is TAS...  If that's the case then all the other airspeeds in that chart are also TAS.

 

So I take my hypothetical M20F out for a spin and decide to land at KFNL in Colorado with a field elevation of 5016' and its a hot day (80 deg F).  I'm at pattern altitude (~6000') and I've slowed to my gear speed of 120 mph.  But wait, I'm at 120 mph indicated and my limitation is 120 mph true.  I do a quick calculation and find that I'm really doing 137 mph TAS.  Uh oh!  So another quick calclulation and I see that I need to slow to 105 mph IAS to put my gear down.

 

Now I'm in the pattern at 105 mph and I'd like to put my flaps down.  Can't do it yet because I'm still at 120 mph TAS.  I have to slow to 88 mph in order to be below my 105mph TAS limitation.

 

 

 

So, can we all agree that the gear and flap speeds are always IAS?  Since they are labeled as TIAS in this table it is clear that TIAS is a form of IAS.

[Awful_Charlie]

Bravo POH has Vne 195Knots and cruise speed performance up to 214knots - that's going to be a bit difficult if they are the same units! (or the cruise sheet should stop/have a big warning at 195knots) Fortunately the first is noted as being KIAS/KCAS and the latter as KTAS

 

Does no-one remember their "ICE-T" from PPL theory?

 

I think you are looking at 14 CFR 4a.708 for Vne, which is derived from 4a.72-99

[PTK]

The point is this:

 

To the extent the reason for Vne is to avoid flutter we have to be talking TAS and not IAS.

 

As altitude increases flutter damping decreases, we go faster and the more the ASI lies. 

 

Trusting Vne as read on the ASI can make for a very bad day. It doesn't always mean that we're safe as long as we stay below red line. 

 

Bad things can happen way before red line on the ASI!

 

For flutter protection we need to know our TAS.

 

The beauty of certificated airplanes is that if we keep it inside its envelope we're fine as long as we're below redline.