Vne vs. Vmo

[Hatbox]

1. What is the difference between Vmo and Vne?

2. Is there a reason that piston a/c have a Vne, and turbine a/c have a Vmo? or is this a correlation that I have incorrectly developed?

[GGCC]

A quick check of Google will give you all of the V numbers, there is a difference between the two you inquired about....simply

VNE Never exceed speed.
VNO Maximum structural cruising speed or maximum speed for normal operations.

I used to get that stuff from "The Ground Up" do they still use it in training

[Needtofly]

From my understanding witch could be wrong is that Vne is a fixed speed and Vmo changes with altitude because it is a % of Mach speed. In the KA the Vmo is measured by a Barbara Pull.
Correct me if I am wrong.

[GGCC]

I stole this from the ATP Forum, hope no one minds....


(quote)
colin
Bristol Instructor

Join Date: Jul 2004
Posts: 1,920
Re: V Speeds (VMO, VNE, VD)
Hello Lance
If you look in Principles of Flight in Chapter 1 you will find all the definitions for the V speeds. Similarly if you look in Chapter 15 of POF you'll find the section on the gust envelope which describes Va,Vb,Vc,Vd. This describes the maximum design load factor that can be tolerated at a particular speed.
Vmo is your normal maximum operating IAS followed by Vne your never exceed speed IAS
Mmo is your normal maximum operating mach no followed by Mne your never exceed mach no..
Vmo and Vc are very similar speeds because Vc is the design cruising speed.
Vne and Vd are also similar speeds with Vd being the maximum design dive speed.
Vdf is the maximum IAS demonstrated at certification and Mdf is the maximum mach no. demonstrated at certification.
Below is the extract from CS25 for the Maximum Operating Limit Speed.
Hope this helps
Colin
CS 25.1505 Maximum operating limit
speed
The maximum operating limit speed (VMO/MMO, airspeed or Mach number, whichever is critical at a particular altitude) is a speed that may not be
deliberately exceeded in any regime of flight (climb, cruise, or descent), unless a higher speed is authorised for flight test or pilot training
operations. VMO/MMO must be established so that it is not greater than the design cruising speed VC and so that it is sufficiently below VD/MD or VDF/MDF,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 VDF/MDF may not be less than that determined under
CS 25.335(b) or found necessary during the flight tests conducted under CS 25.253. (end quote)

[ahramin]

A Barbara Pull? Really?

As for the original question, different certification standards.

[Machdiamond]

The Bristol instructor quote is confused. Vmo and Vne have the same meaning. You do not have a Vne after a Vmo because you must never exceed Vmo. I have never seen Mne, I don't think it exists in regulations.

Vne is indeed associated with piston planes and Vmo with turbines (including turboprops).

Vmo is expressed in knots and is generally a constant. At some altitude (the knee altitude), the limit is expressed in Mach so you have Mmo.
Vmo=Mmo at the knee altitude. Typical knee altitude is around 20,000 ft.

[Needtofly]

A Barbara Pull? Really?

I am sorry that is what I have been told I would love for you to clear it up for me.

[Needtofly]

.....Barber Pole.....because the needle looks like a Barber Pole....

did you really think it was called a Barbara Pull or are you just yanking our chains?

I know it is not called a Barber pole. But I always though it was clever hahaha.
But reading Machdiamond post clears thing up for me.
Thanks

[ahramin]

It always amazes me that this new generation is able to actually do anything useful. I can't figure out how they do it laboring under the handicaps they have. The other day I had to explain to someone that <6 was not some weird smiley face that she hadn't seen yet. Think about it, an entire generation of kids who think math symbols and punctuation marks are included in keyboards for the purposes of sending smiley faces.

[xsbank]

Pilot Dar, I sure hope thats a simulator...

[Machdiamond]

Pilot DAR is a test pilot, he is allowed to deal with close shaved barber poles (although poles expats are mostly known as plumbers, there are barber poles as well). This reminds me of Henry Fonda barber scene in my name is nobody, same deal.

[JohnnyHotRocks]

Bwahaahahahahahahahaha.....that is fricken hilarious!!!!!!!!!!!

[co-joe]

Vmo is based on TAS and so the indicated value of it decreases with altitude. The true value of it never changes. I think it requires some sort of air data computer to display.
Vne is a red line painted on your airspeed indicator.

I was a little confused by the barbara pull thing too. Thanks for clearing that up clarence.

[Machdiamond]

Vmo is based on TAS and so the indicated value of it decreases with altitude.

This is incorrect. Vmo is an indicated airspeed and generally constant with altitude until Mmo becomes the limit.

There were times where Vmo was expressed in EAS so you had a small change with altitude, but nowadays everybody uses IAS for Vmo. Sometimes you have a constant Vmo from sea level to 10000ft or so and then a higher constant Vmo above that, then a switch to Mmo.

These offsets are generally driven by birdstrike requirements for example, or different upset manoeuver margins at high altitudes.

Here is the rule:
====

523.1505 Airspeed Limitations

(a) The never-exceed speed VNE must be established so that it is:

(1) Not less than 0.9 times the minimum value of VD allowed under 523.335; and

(2) Not more than the lesser of:

(i) 0.9 VD established under 523.335; or

(ii) 0.9 times the maximum speed shown under 523.251.

(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 523.335; and

(2) Not more than the lesser of:

(i) VC established under 523.335; or

(ii) 0.89 VNE established under paragraph (a) of this section.

(c) Paragraphs (a) and (b) of this section do not apply to turbine aeroplanes or to aeroplanes for which a design diving speed VD/MD is established under 523.335 (b)(4). For those aeroplanes, 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 authorised 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 523.251 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 523.251 may not be less than the speed margin established between VC/MC and VD/MD under 523.335 (b), or the speed margin found necessary in the flight test conducted under 523.253.

[ahramin]

I just hate it when someone comes along who knows what they are talking about .

[schnitzel2k3]

One is a limitation, the other is a goal.