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

[DS1980]

Show me an article from another manufacturer that states where they derive Vne.

We know from articles on this thread that Mooney has tested their airframes to flutter speed.

[mooniac15u]

Show me an article from another manufacturer that states where they derive Vne.

We know from articles on this thread that Mooney has tested their airframes to flutter speed.

Well, it's not really up to the manufacturer. It is outlined in FAR Part 23.

23.1505 sets Vne as not less than 0.9 VD (established in 23.335) and not more than the lesser of 0.9 VD or the speed demonstrated in 23.251 (which says there can be no buffeting or vibration).

23.335 sets VD at not less than 1.25 VC which is in turn not less than 33 times the sq rt of the wing loading.

23.335 explicitly states that these are Equivalent Airspeeds.

Whether or not Mooney tests to flutter speed doesn't have anything to do with Vne.

Which article states that Mooney tests to flutter speed? I must have missed that.

[DS1980]

Post #64.

 

It doesn't matter what the FAA says about Vne. Currently there is a major push to rewrite part 23. Will the FAA definition of Vne or how it's calculated change? I bet it doesn't, for no other reason than they don't know what it means.

 

While flying, there is a true airspeed at which the frequency magnitude of the air hitting the airframe will cause a resonance that induces flutter. This will happen before the tail or wings separate due to aerodynamic loads. This speed is Vne, whether or not the FAA or the manufacturer knows this speed.

 

Vne is not a red radial line. It is not part 23.

[aviatoreb]

Post #64.

 

It doesn't matter what the FAA says about Vne. Currently there is a major push to rewrite part 23. Will the FAA definition of Vne or how it's calculated change? I bet it doesn't, for no other reason than they don't know what it means.

 

While flying, there is a true airspeed at which the frequency magnitude of the air hitting the airframe will cause a resonance that induces flutter. This will happen before the tail or wings separate due to aerodynamic loads. This speed is Vne, whether or not the FAA or the manufacturer knows this speed.

 

Vne is not a red radial line. It is not part 23.

 

DS1980

 

There are two errors in your statements.

 

First flutter is a nonlinear effect called Hopf bifurcation.  It is not resonance which is a linear phenomenon.  The main resulting difference between the two is that the Hopf gives rise to a limit cycle which increases in magnitude as you increase speed where as resonance is something that happens exactly (or approximately near) a specific magic speed.  And further they are both different in details to how they occur.

 

Second Vne is a made up speed made up by FAA regulations.  So the FAA by definition is correct in whatever they choose to call Vne.  They choose to call it an IAS.  So Vne on my airplane is 196IAS.  Period.  Vne on my airframe does not change with altitude.  Vne is a regulatory legal phrase designed with engineering considerations but nonetheless a regulatory term only.

 

There is indeed a critical TAS where the Hopf bifurcation occurs that is the onset of flutter - this is mathematics and physics.  This is not a marked speed.  Hopefully the FAA during certification did a good job and certified a Vne that is safely below this Hopf TAS in the entire flight envelope of my airplane, meaning from 0 to 24,000 my certified max ceiling, that 196IAS will be below the flutter speed.  So hopefully Vne< Vflutter for every legal altitude which is the intention of choosing Vne for a given certified airplane.  Iregardless of the engine you hang on front if you stay below Vne your wings will not flutter if within that certified altitude range.

 

This becomes confused in experimental airplanes where you can put whatever engine you want, fly at whatever altitude you want and mark your airspeed indicator however you want.

[DS1980]

Maybe I have some physics wrong, but don't focus on terminology. Focus on content.

 

What's the bottom line? There is such thing as Vne, it's a TAS, it's not the radial line, and the FAA doesn't know what it is or what it means although they made up the word.

[jetdriven]

but the radial line keeps you below the flutter TAS at all altitudes the aircraft is capable if, or it has a separate placard or a moveable barber pole.

[DS1980]

I just wanted to explain the difference between all other placarded V speeds and Vne. It went out of control, but Vne is not the never exceed speed. It's just an arbitrary FAA number.

[Super Dave]

Vne is an FAA term used in certifying aircraft. They pretty much get to define it as it relates to certificated aircraft.

Once again I will restate, we all agree that flutter speed is TAS. Vne is defined by the FAA and it is IAS. Vne is there to protect us from flutter speed but it is an oversimplification so it is imperfect. It is not wise to approach Vne without being aware of your TAS.

Reading through this thread leaves me impressed by your knowledge, but I'm in absolute awe over your patience and civility.

[DS1980]

but the radial line keeps you below the flutter TAS at all altitudes the aircraft is capable if, or it has a separate placard or a moveable barber pole.

Can you show me where it says this? I can't find in Part 23 where it states if Vne is based on sea level or service ceiling.

[mooniac15u]

Can you show me where it says this? I can't find in Part 23 where it states if Vne is based on sea level or service ceiling.

 

It's in 23.1545.

 

( c) If VNE or VNO vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range.

[DS1980]

Reading through this thread leaves me impressed by your knowledge, but I'm in absolute awe over your patience and civility.

Well stated. Nothing wrong with playing Devil's advocate? Yes, mooniac is right. But how many people learned something about testing, flutter, arbitrary numbers by the FAA....

Something I learned was what I was calling flutter is actually the "Hopf bifurcation." Thanks for the physics lesson aviator.

But yes, mooniac is a very patient person, and very fun to mess with. Hopefully will be doing it more in the future.

[mooniac15u]

Well stated. Nothing wrong with playing Devil's advocate? Yes, mooniac is right. But how many people learned something about testing, flutter, arbitrary numbers by the FAA....

Something I learned was what I was calling flutter is actually the "Hopf bifurcation." Thanks for the physics lesson aviator.

But yes, mooniac is a very patient person, and very fun to mess with. Hopefully will be doing it more in the future.

Always happy to provide a source of entertainment. It's so much more fun than my real job.

[Guitarmaster]

I have read with great interest this thread. If all my years of flying, I never knew Vne was derived from TAS. Since,

[Guitarmaster]

I have always thought that the CAS or EAS is what the airplane actually feels. I understand now, that the airplane "feels" the higher speed, TAS, but with less molecules so the IAS will indicate lower. Structurally the airplane feels the same load, dynamically, it responds to the higher TAS, hence flutter "I can't pronounce the other word" can be induced at markedly lower IAS. I understand Mach buffet much better now.

Am I pretty close in my understanding?

[Guitarmaster]

I would bet that's the reason for the 20,000ft flap limitation on the 737.

[DS1980]

I have always thought that the CAS or EAS is what the airplane actually feels. I understand now, that the airplane "feels" the higher speed, TAS, but with less molecules so the IAS will indicate lower. Structurally the airplane feels the same load, dynamically, it responds to the higher TAS, hence flutter "I can't pronounce the other word" can be induced at markedly lower IAS. I understand Mach buffet much better now.

Am I pretty close in my understanding?

Nailed it. I liked this discussion.

[Andy95W]

I get the Mach buffet effect at very high altitudes and speeds, the Airbus has the same limitation on flaps above FL200.

Does anyone know how significant this is around 10,000 feet and 150-170 knots? I guess I never thought it might be until now.

Great discussion, by the way.

[Hank]

It's in 23.1545.

 

( c) If VNE or VNO vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range.

 

You DO realize that our Mooneys were certified under CAR 3, not FAR Section 23, right? That was for the original M20, then alphabetical models from A to TN are just variations to the CAR 3 certificate.

 

Wonder what the old regulations say about Vne? Time for some research.

[mooniac15u]

You DO realize that our Mooneys were certified under CAR 3, not FAR Section 23, right? That was for the original M20, then alphabetical models from A to TN are just variations to the CAR 3 certificate.

 

Wonder what the old regulations say about Vne? Time for some research.

 

The CAR 3 requirements were pretty much the same. http://www.navioneer.org/riprelay/Yet%20More%20Navion%20Files/car_part3.pdf

 

3.739 defines Vne with respect to VD

3.184 defines VD and VC based upon wing loading

3.159 specifies that the aircraft must be free of flutter and vibration under all speed and power conditions appropriate for the aircraft.

 

The TCDS specifies where Part 23 changes were incorporated into the certification for each of the Mooney models starting with the M20J.

[Tom]

I genuinely don't mean to bicker, but I think that there is still some incorrect information here.

-The manufacturer determines the Vne, not the FAA.

-The Part 23 sections listed in post #81 define Vne minimum/not less than values, they do not define the Vne. 

 

Adding minimally to the confusion, I recently looked at a 20F POH.  All the values were listed as "CAS" including Vne (not true indicated, as in the TCDS, though Mooniac elucidated that TIAS is CAS).

 

Mooniac's post #89, though, is the nail in the coffin:

"23.1545© If VNE or VNO vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range."

 

In theory, the Vne of every aircraft certainly does change with altitude.  I am sure that every 20F that left Kerrville was in compliance with 23.1545 based on sound engineering.  This said, turbo-normalized F-models can cruise at an altitude above the service celing of the normally aspirated F at a true airspeed above the Vne.  Again, I seriously doubt that the TN STC developers fluttered tested the TN F in complete compliance with Part 23.  If they did, they must have determined that no additional placarding was necessary.  In any event, I must assume that Mooney (back when the Rayjay system was being developed) would have raised holy hell if they thought the TAS of the TN F was going to be a problem.  And of course, history now has shown that it hasn't.  

 

 

[mooniac15u]

I genuinely don't mean to bicker, but I think that there is still some incorrect information here.

-The manufacturer determines the Vne, not the FAA.

-The Part 23 sections listed in post #81 define Vne minimum/not less than values, they do not define the Vne. 

 

Adding minimally to the confusion, I recently looked at a 20F POH.  All the values were listed as "CAS" including Vne (not true indicated, as in the TCDS, though Mooniac elucidated that TIAS is CAS).

 

Mooniac's post #89, though, is the nail in the coffin:

"23.1545© If VNE or VNO vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range."

 

In theory, the Vne of every aircraft certainly does change with altitude.  I am sure that every 20F that left Kerrville was in compliance with 23.1545 based on sound engineering.  This said, turbo-normalized F-models can cruise at an altitude above the service celing of the normally aspirated F at a true airspeed above the Vne.  Again, I seriously doubt that the TN STC developers fluttered tested the TN F in complete compliance with Part 23.  If they did, they must have determined that no additional placarding was necessary.  In any event, I must assume that Mooney (back when the Rayjay system was being developed) would have raised holy hell if they thought the TAS of the TN F was going to be a problem.  And of course, history now has shown that it hasn't.  

 

You are correct.  The manufacturer is responsible for determining the Vne.  However, they have to do so according to Part 23.  The takeaway from Part 23 is just that the Vne isn’t derived from flutter speed.  In fact the manufacturer has to demonstrate that the aircraft is free of flutter and vibration at whatever speed they use for VD whether it is calculated or demonstrated.

 

Just for fun we can run the numbers for an M20F using the formulae in CAR 3 and see what speed Mooney used in their calculation of Vne.  I don’t have an official value of the wing loading for the F but LASAR has a spec sheet that lists it at 16.4 lbs/sq ft so I’ll use that.

 

VC = 38 x sq rt (16.4) = 153.9

 

VD = 1.40 x 153.9 = 215.5

 

Vne is not less than 0.9 x 215.5 which is 193.9.  We’ll call it 194 mph.

 

The TCDS lists the Vne at 200 mph.  Since that is greater than 0.9 VD they must have used a demonstrated VD of 222 mph.

 

So, it is slightly higher than the required minimum but probably not near the flutter speed.

 

 

With respect to the turbo M20F, I suspect it has an altitude limitation to ensure that Vne is safe within the operating envelope.

[DS1980]

Honestly, who knows how the manufacturers set Vne? All Part 23 states are the calculations for a minimum Vne. I'm sure there's a safety factor thats added in. What is it?

 

As far as testing, Mooneys don't shed airframe parts when the going gets rough like the other manufacturers. In any case, operating above the indicated Vne is not legal, and any tests that showed the TN F could do so would not be in compliance.

 

Mooniac really likes math.

[mooniac15u]

 

Adding minimally to the confusion, I recently looked at a 20F POH.  All the values were listed as "CAS" including Vne (not true indicated, as in the TCDS, though Mooniac elucidated that TIAS is CAS).

  

 

Although it probably doesn’t really add anything to the discussion I did come across the old CAR 3 definition of TIAS so I thought I would share it here in case anyone cares:

 

3.46 (b ) "True indicated" or "calibrated" air speed for performance and operating purposes equal to indicator reading corrected for position and instrument errors.

[aviatoreb]

The main confusion I see is the idea that vne might be a synonym for flutter speed - however it is set by manufacturer within FAA rules - it is a legal number - not a critical threshold like flutter speed that is a physics concept with many physical parameters it depends on.