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V min definition

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V min definition

Old 4th Feb 2002, 23:32
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VEJ
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Question V min definition

Anybody got an idea what the official definition is for Vmin?. .Also called when applied to 0 flaps Minimum clean.
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Old 5th Feb 2002, 00:22
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I'm not sure about the official definition but Boeing says that this speed "provides margin to stick shaker for at least an inadvertent 15 overshoot beyond the normal 25 angle of bank".
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Old 5th Feb 2002, 01:56
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VEJ,

I am presuming that your question relates to minimum V2 speed schedules ?

Current requirements for V2min are

(a) for the initial takeoff

(i) 1.20Vs for two- and three-holers. .(ii) 1.15Vs for four-holers. .(iii) 1.10Vmca

assuming that the Vr schedule permits the aircraft to achieve this speed.

It is common for the AFM to schedule performance both for the minimum schedule and slightly higher speeds - the latter to take advantage of the improvement in climb gradient.

(b) for final climb OEI minimum speed is 1.25Vs.

If you were interested in checking the requirements for a particular make and model, you would need to run a search on superseded regs as well after checking the certification basis in the TCDS for the model to trap any minor differences applicable to older aircraft.
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Old 5th Feb 2002, 03:03
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Lightbulb

What I mean is what Fresca is talking about.. .But the problem is: does Vmin only apply in the descent or also in the climb.. .I'am flying the Dash-8 right now and we have Vmin speeds for Flaps 0,5,10,15 and 35. So for all flap ranges. But the problem is that nobody seems to know if Vmin is only applicable for the descent or also for the takeoff.. .Thats the reason I'am looking for the definition. <img src="confused.gif" border="0">
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Old 5th Feb 2002, 03:46
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Lightbulb

VEJ, let me try:. .For an MD11, VMIN is the slowest speed the FMS will permit in manual operation (A/T off). There is a continuous FMS information on the airspeed indicator during all phases of flight, configuration, altitude, etc., and the pilot can recognize it when an amber band becomes visible on the speed tape. The amber foot means:

VMIN for TO mode: . .Slats Ext – 1.2 Vs. .Slats Ret – 1.25 Vs

VMIN for climb, cruise and descent – Clean configuration. VMIN above all engine acceleration altitude is:. .Low Speed (for Mach &lt; 0.5) – 1.3 Vs or 1.2g to stickshaker, whichever is higher.. .High Speed (for Mach &gt; or = 0.5) - 1.2g to buffet (FAA), or 1.3g to buffet (JAA/CAA).

VMIN for approach and landing - All Configurations:. .Gear dn - 1.3 Vs. .Gear up - 1.3 Vs or 1.2g to stickshaker, whichever is higher.

VMIN for G/A:. .The current airspeed at G/A initiation, or. .1.2 Vs for flaps &gt; or = 31 deg., or. .1.3 Vs for falaps &lt; 31 deg. for current configuration, whichever is higher.

Note: Minimum speed for A/T operation is amber foot plus 5 ktnots.

Regards...
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Old 5th Feb 2002, 06:51
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Talking

Have you heard the one about the Dutchman, the Icelander and the Aussie?

I did and I couldn't understand a bloody word.

K.I.S.S.

[ 05 February 2002: Message edited by: crackerjack ]</p>
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Old 5th Feb 2002, 07:16
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VEJ,

Try viewing the minimum speed schedules as just that .. a minimum below which the risks of mishap increase unacceptably due to the aircraft's getting a bit too close to the boundary flight conditions, mainly Vs. The minimum speeds try to protect us, somewhat, against our propensity for manipulative heavy-handedness and distraction.

Therefore it is prudent to apply the published minimum values whenever you are in the relevant configuration.

For a smaller aircraft such at the Dash, and I don't have a specimen AFM on hand to check, the limitations may be scheduled conservatively without clarification as to phase of flight. If that is the case then, in the absence of other AFM advice, it would be prudent to use the more (most) conservative data for phases of flight which don't appear to have specific limitations published. The principal aim is to keep a reasonable margin above current stall speed.

It might be useful if you go to the FAA website and review the current regulatory words in the FARs for background. At the very least this will show you where the data in downfourgreen's post originate via the AFM (but be aware that the current published FAR requirements might be a little different to those which were current at the time that the design standards were frozen for any given make and model of aircraft).

. .The bank angle consideration relates to the variation of load factor ("g" if you prefer) with bank which, in effect, causes the wing to think that the aircraft gross weight is varying. This, in turn, affects the present stall speed value.

The bank angles published in the manufacturer's AFM or FCOM (or by the operator's ops engineers in the company operations manual) relate to the increase in actual stall speed (it might be easier to think of this in terms of the "equivalent" weight increase) needed to trip the stick shaker for the current configuration.

. .Does this help ? .. or merely muddy the waters further ? .. it is never easy to explain things in text when a picture makes it much easier.
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