Speeds!!
Speeds!!
"NO" or normal operating limits are below "NE" or never exceed limits, which are the same as "MO" or maximum operating - the difference here is terminology.
What determines the maximum operating speed?
Firstly structural considerations are used to determine a theoretical Vd/Md - the design limit. This is the limit to which flight testing is allowed to take the a/c.
If (as often happens) a handling or flutter deficiency is found below that, then a lower limit of "Vdf", or flight design limit is laid down.
Finally , Vne/Mne/Vmo/Mmo is determined as a margin below Vdf. The actual margin is a function of the certification standard - for light aircraft codes it's simply 10%, for "higher" codes like part 25 it's rather more complex.
The use of Vno/Mno is about 2-tier limits. Basically you are given a limit which you should not NORMALLY go beyond, but if you do you know that up to Vne/Mne there is no risk and you need not report it. If you go beyond that there is a risk of structural damage and/or unacceptable handling characteristics being met. Some organisations prefer 2-tier limits, some do not.
G
What determines the maximum operating speed?
Firstly structural considerations are used to determine a theoretical Vd/Md - the design limit. This is the limit to which flight testing is allowed to take the a/c.
If (as often happens) a handling or flutter deficiency is found below that, then a lower limit of "Vdf", or flight design limit is laid down.
Finally , Vne/Mne/Vmo/Mmo is determined as a margin below Vdf. The actual margin is a function of the certification standard - for light aircraft codes it's simply 10%, for "higher" codes like part 25 it's rather more complex.
The use of Vno/Mno is about 2-tier limits. Basically you are given a limit which you should not NORMALLY go beyond, but if you do you know that up to Vne/Mne there is no risk and you need not report it. If you go beyond that there is a risk of structural damage and/or unacceptable handling characteristics being met. Some organisations prefer 2-tier limits, some do not.
G
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Join Date: Aug 2001
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As I understand, it is safe to travel through the VMO region (in still air) therefore why have a VMO pointer, wouln't it be better to have a VNO pointer? Also what variable drives this VMO pointer? Is it mainly driven by OAT?
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Join Date: May 2001
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Hm. I thought it went like this: JAR 23 aircraft have Vno / Vne, while JAR 25 aircraft have Vmo / Mmo..?
Larger aircraft have a greater margin to Vd (design dive speed, where no excess flutter will occur etc; JAR 25-335) ... Because these are often jet engine powered; an upset in attitude (pitch down) is more difficult to arrest, and speed build-up more rapid, whereas a JAR 23 a/c will most probably have a propeller (more drag) and speed build-up is slower (pull to flight idle, and problem solved), allowing the pilot to correct the upset in a timely manner even though the margin to Vd is 10% (?).
Either way, I think the difference between Vno and Vmo is only in the safety margin. Large a/c = greater margin, and it is not safe to exceed Vmo anymore than it is to excee Vne.
Am I completely off the mark? Anyone?
Larger aircraft have a greater margin to Vd (design dive speed, where no excess flutter will occur etc; JAR 25-335) ... Because these are often jet engine powered; an upset in attitude (pitch down) is more difficult to arrest, and speed build-up more rapid, whereas a JAR 23 a/c will most probably have a propeller (more drag) and speed build-up is slower (pull to flight idle, and problem solved), allowing the pilot to correct the upset in a timely manner even though the margin to Vd is 10% (?).
Either way, I think the difference between Vno and Vmo is only in the safety margin. Large a/c = greater margin, and it is not safe to exceed Vmo anymore than it is to excee Vne.
Am I completely off the mark? Anyone?
