Crump Posted November 28, 2014 Posted November 28, 2014 The VNE, or never exceed speed, is the V speed which refers to the velocity that should never be exceeded because of the risk of structural failure, due for example to wing or tail deformation, or aeroelastic flutter. On many airspeed indicators the VNE is marked with a red line. This speed is specific to each aircraft model, and represents the edge of its performance envelope in terms of speed. When Vne is flight tested, it is the speed that adverse behavior's occur. There is no safety factor applied. Set off the overspeed warning on a Learjet 60 for example and folks in the back will complain about the very loud rumbling noise coming from the wings even if they do not hear the cockpit aural alarm. In this case, Vne is the edge of the envelope with no safety factor. If Vne is based purely on estimation then it is a function of design cruise speed and wing loading. Generally Vne will be .9 or 10% less than the calculated Vd or maximum structural dive speed.
DD_bongodriver Posted November 28, 2014 Posted November 28, 2014 Overspeed warnings on the Learjet are triggered by Mmo/Vmo not Vne, or at least they are on the 45, no rumbling happens on the 45 either except for the transition through .76 Mach. Vne is not the ultimate limit that would have been discovered in testing, published performance is always factored.
Crump Posted November 28, 2014 Posted November 28, 2014 Overspeed warnings on the Learjet are triggered by Mmo/Vmo not Vne Aircraft with a Vmo/Mmo do not have a defined Vne.... Vmo/Mmo is Vne. They are speeds defined by the appearance of adverse flight behaviors. In this case, high speed flow separation along the wing. That is where the rumbling sound comes from.... Paragraphs (b)(1) through (b)(3) and paragraph © of this section do not apply to aircraft for which a maximum operating speed VMO/MMO is established under Sec. 23.1505©. For those aircraft there must either be a maximum allowable airspeed indication showing the variation of VMO/MMO with altitude or compressibility limitations (as appropriate), or a radial red line marking for VMO/MMO must be made at lowest value of VMO/MMO established for any altitude up to the maximum operating altitude for the airplane. If Vne is flight tested, it is the speed at which adverse behaviors arise. If Vne is calculated (Which most of them are as flight testing it is extremely dangerous.....) then it inlcudes a 10% buffer. http://www.astech-engineering.com/systems/avionics/aircraft/faapart23g.html
DD_bongodriver Posted November 28, 2014 Posted November 28, 2014 Aircraft with a Vmo/Mmo do not have a defined Vne.... They can. b) The maximum structural cruising speed VNO must be established so that it is-- (1) Not less than the minimum value of VC allowed under Sec. 23.335; and (2) Not more than the lesser of-- (i) VC established under Sec. 23.335; or (ii) 0.89 VNE established under paragraph (a) of this section. Note also Mmo/Vmo are to not exceed Vc/Mc and Vd/Md so in fact there are several tested speeds higher. © Paragraphs (a) and (b) of this section do not apply to turbine airplanes or to airplanes for which a design diving speed VD/MD is established under Sec. 23.335(b)(4). For those airplanes, a maximum operating limit speed (VMO/MMO-airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations. VMO/MMO must be established so that it is not greater than the design cruising speed VC/MC and so that it is sufficiently below VD/MD and the maximum speed shown under Sec. 23.251 to make it highly improbable that the latter speeds will be inadvertently exceeded in operations. The speed margin between VMO/MMO and VD/MD or the maximum speed shown under Sec. 23.251 may not be less than the speed margin established between VC/MC and VD/MD under Sec. 23.335(b), or the speed margin found necessary in the flight test conducted under Sec. 23.253. Vmo/Mmo is Vne. It is not, that's why they have different designations.
Crump Posted November 30, 2014 Posted November 30, 2014 (edited) b) The maximum structural cruising speed VNO must be established so that it is-- (1) Not less than the minimum value of VC allowed under Sec. 23.335; and (2) Not more than the lesser of-- (i) VC established under Sec. 23.335; or (ii) 0.89 VNE established under paragraph (a) of this section. Vno is not Vmo/Mmo.... Note also Mmo/Vmo are to not exceed Vc/Mc and Vd/Md so in fact there are several tested speeds higher. You obviously do not understand what this sentence is saying, Bongodriver. It is if your Vmo/Mmo is based of calculated speeds. If the speeds where demonstrated, it would be noted by the addition of "f" for flight. For example, Vd = design dive speed becomes Vdf = demonstrated dive speed. So, If Vne is flight tested, it is the speed at which adverse behaviors arise. If Vne is calculated (Which most of them are as flight testing it is extremely dangerous.....) then it inlcudes a 10% buffer. That is the takeaway, Bongo. If something is based off a calculation, then a 10% safety margin or 1.1 Safety Factor is included. If it the velocity is demonstrated thru flight testing, then the speed is set by the onset of adverse behavior. It is really that simple. Edited November 30, 2014 by Crump
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 Vno is not Vmo/Mmo.... Correct, I didn't say otherwise. You obviously do not understand what this sentence is saying, Bongodriver. I understand my own sentence perfectly thanks.
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 If something is based off a calculation, then a 10% safety margin or 1.1 Safety Factor is included. If it the velocity is demonstrated thru flight testing, then the speed is set by the onset of adverse behavior. It is really that simple. what is even simpler is the flaw in your stated case that the Lear 60 shows adverse flight characteristics at the design speed rather than actual demonstrated limit
SCG_Space_Ghost Posted November 30, 2014 Posted November 30, 2014 And here I was thinking that I cared about the technical stuff... ZZZ...
Crump Posted November 30, 2014 Posted November 30, 2014 As for the Vmo/Mmo becomes Vne in any airplane with an estabilished Vmo/Mmo, it is in black and white stated in plain language. § 23.1505 Airspeed limitations. (a) The never-exceed speed V NE must be established so that it is— (1) Not less than 0.9 times the minimum value of V D allowed under § 23.335; and (2) Not more than the lesser of— (i) 0.9 V D established under § 23.335; or (ii) 0.9 times the maximum speed shown under § 23.251. (b) The maximum structural cruising speed V NO must be established so that it is— (1) Not less than the minimum value of V C allowed under § 23.335; and (2) Not more than the lesser of— (i) V C established under § 23.335; or (ii) 0.89 V NE established under paragraph (a) of this section. © (1) Paragraphs (a) and (b) of this section do not apply to turbine airplanes or to airplanes for which a design diving speed VD/MD is established under § 23.335(b)(4). For those airplanes, a maximum operating limit speed (VMO/MMO airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations. http://www.law.cornell.edu/cfr/text/14/23.1505#c So read the whole thing and do take it out of context. If you establish a Vmo/Mmo then you do not have to redundantly establish a Vne or Vno.
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 And here I was thinking that I cared about the technical stuff... ZZZ... I agree but sometimes these graph monkeys get a bit carried away.
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 As for the Vmo/Mmo becomes Vne in any airplane with an estabilished Vmo/Mmo, it is in black and white stated in plain language. http://www.law.cornell.edu/cfr/text/14/23.1505#c So read the whole thing and do take it out of context. If you establish a Vmo/Mmo then you do not have to redundantly establish a Vne or Vno. Vmo never becomes Vne, Mmo never becomes Mne, they are exclusive, what is simply being said is that Vmo/Mmo are to be the ultimate operating limit subject to the laid out design criteria. either way if you ever do end up in a Learjet 60 you will find no adverse effects at Vmo/Mmo because they are design limitations that fall well within the demonstrated limits that adverse effects are discovered. None of this is particularily relevant to 109's over reving at high altitude. (1) Paragraphs (a) and (b) of this section do not apply to turbine airplanes or to airplanes for which a design diving speed VD/MD is established under § 23.335(b)(4). For those airplanes, a maximum operating limit speed (VMO/MMO airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations. The bold bit might help you.
Crump Posted November 30, 2014 Posted November 30, 2014 what is even simpler is the flaw in your stated case that the Lear 60 shows adverse flight characteristics at the design speed rather than actual demonstrated limit onset of adverse behavior "Onset" means the beginning of adverse behavior...in other words a limit. In terms that might bring some understanding. Speed limit when you Mom takes you to school is 25kph. If your Mom drives 25 Kph then she is at the limit but not exceeding it. It is the onset of adverse behavior. If she drives 26 Kph in your school, then the police can give her a ticket for exceeding the limits and endangering your friends. There must be no vibration or buffeting severe enough to result in structural damage, and each part of the airplane must be free from excessive vibration, under any appropriate speed and power conditions up to VD/MD, or VDF/MDF for turbojets. http://www.law.cornell.edu/cfr/text/14/23.251
Crump Posted November 30, 2014 Posted November 30, 2014 (edited) And here I was thinking that I cared about the technical stuff... It does make a difference for your game. Very few World War II designs had high speed flight investigations. In other-words, most of them are operating on a calculated limit instead of a tested one. It is safe to say that on an airplane with a calculated Vne, we have a 10% Safety margin. On an airplane with a flight tested Vne such as Bf-109, Lagg-3, Spitfire, and P-51 series we do not have a safety margin for published speeds. Edited November 30, 2014 by Crump
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 (edited) Onset" means the beginning of adverse behavior...in other words a limit. In terms that might bring some understanding. Speed limit when you Mom takes you to school is 25kph. If your Mom drives 25 Kph then she is at the limit but not exceeding it. It is the onset of adverse behavior. If she drives 26 Kph in your school, then the police can give her a ticket for exceeding the limits and endangering your friends. OK, so it seems you can understand this from an infants perspective, I thought you might not be big enough to get the bus yet, I will try to keep this simple for you but maybe you have a guardian nearby? "Onset" means the beginning of adverse behavior...in other words a limit. Yes, very good....gold star There must be no vibration or buffeting severe enough to result in structural damage, and each part of the airplane must be free from excessive vibration, under any appropriate speed and power conditions up to VD/MD, or VDF/MDF for turbojets. Great job champ! you quoted a manual....another gold star Set off the overspeed warning on a Learjet 60 for example and folks in the back will complain about the very loud rumbling noise coming from the wings even if they do not hear the cockpit aural alarm. Nice try for imagination but no gold star. You see?.......No?........there must be no vibration in the speed range UP TO Vd/Md Vdf/Mdf but your story says vibration starts at Vmo/Mmo with the overspeed warning, now we know this cannot be true because Vmo/Mmo are speeds that fall well under those limits. Edited November 30, 2014 by DD_bongodriver
Crump Posted November 30, 2014 Posted November 30, 2014 (edited) You see?.......No?........there must be no vibration in the speed range UP TO Vd/Md Vdf/Mdf but your story says vibration starts at Vmo/Mmo with the overspeed warning, now we know this cannot be true because Vmo/Mmo are speeds that fall well under those limits. Why don't you fly a Lear 60 and see for yourself? It does not say there must be no vibration....There must be no vibration or buffeting severe enough to result in structural damage.....in other words no excessive vibration. Since the wings do not come off at the overspeed warning, then it meets the certification standard. Again, set off the overspeed warning on a Learjet 60 for example and folks in the back will complain about the very loud rumbling noise coming from the wings even if they do not hear the cockpit aural alarm.. Why? It is the onset of adverse behavior and the limit has been reached. Edited November 30, 2014 by Crump
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 (edited) Why don't you fly a Lear 60 and see for yourself? It doesn't happen in the Lear45's I flew, sounds like I'll pass on the 60 thanks. It does not say there must be no vibration But it does. There must be no vibration or buffeting severe enough to result in structural damage, and each part of the airplane must be free from excessive vibration, under any appropriate speed and power conditions up to VD/MD, or VDF/MDF for turbojets. You see? the bit in bold? if you are frightening passengers then the vibration is excessive. Why? It is the onset of adverse behavior and the limit has been reached. With zero margin? I don't think so Edited November 30, 2014 by DD_bongodriver
Crump Posted November 30, 2014 Posted November 30, 2014 (edited) With zero margin? I don't think so Again, when the speed is demonstrated thru flight, the speed the onset of adverse behavior occurs is the published limit. This seems crystal clear. What is confusing about it to you? You seem to understand this stuff in terms of driving a car. So if our car developed a wheel shimmy at 55 mph, then the driver would be told that 55 mph is the limit. each part of the airplane must be free from excessive vibration "Excessive" does not "free from vibration". "Excessive" is open to interpretation, in this case the engineers definition and the particular passengers definition who complained did not align. Edited November 30, 2014 by Crump
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 Again, when the speed is demonstrated thru flight, the speed the onset of adverse behavior occurs is the published limit. This seems crystal clear. What is confusing about it to you? So you are saying that in the case of the Lear 60 these are demonstrated speeds and there is absolutely no margin between Mmo and Mdf? and furthermore you are sticking to the claim that demonstrated speeds are not factored in any way to account for variability.....all Lear 60's will fail at exactly the same point? You seem to understand this stuff in terms of driving a car. So if our car developed a wheel shimmy at 55 mph, then the driver would be told that 55 mph is the limit. I don't understand why a car analogy is used but yes, my comprehension here is not really that questionable. "Excessive" is open to interpretation It's actually not.
Crump Posted November 30, 2014 Posted November 30, 2014 (edited) all Lear 60's will fail at exactly the same point? Where do you see a failure point defined? no margin between Mmo and Mdf? Different topic. That is the source of your confusion. We are not discussing the relationship of Vne with Vd or Mmo and Mdf. The topic we have been discussing is the onset of adverse behavior and whether or not you should see any at Vne in your game. If the Vne is calculated then it includes a 10% or 1.1 Safety Margin....you may or may not see the onset of adverse behavior. if the Vne is demonstrated, there is no 1.1 Safety margin and you will see the onset of adverse behavior. An engineers definition of excessive vibration in an airplane is very different from many of the passengers. Edited November 30, 2014 by Crump
DD_bongodriver Posted November 30, 2014 Posted November 30, 2014 Different topic. That is the source of your confusion. We are not discussing the relationship of Vne with Vd or Mmo and Mdf. there is no confusion on my part, I was clearing up the confusion you might cause by equating a Lear 60's Vmo to a Vne which are strictly different things. Where do you see a failure point defined? I assumed you would understand what I meant, I do try to credit you sometimes but alas as always in vain.
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