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Calling V1 early

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Calling V1 early

Old 23rd Feb 2006, 09:03
  #121 (permalink)  
 
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Hi guys, if I'm not mistaken Vmcg certification is based on 7 knots cross wind component and dry RWY. Is that right? I just remember to have read it somewhere.
Cheers.
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Old 23rd Feb 2006, 10:44
  #122 (permalink)  
 
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You would have read it in an old British regulation. JARs and FARs no longer take account of crosswind when testing for VMCG - hence the comments about potential control difficulty if you do have an engine failure at high speed with an adverse crosswind and go.
Alex Whittingham is offline  
Old 23rd Feb 2006, 11:23
  #123 (permalink)  
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.. to add to Alex's post .. for Vmcg

(a) FAR25 is nil wind and I presume JAR/EASA25 is the same .. don't usually keep up to date with the latter

(b) UK BCAR D (replaced by JAR25 around 1979 ?) called up 7kt crosswind

(c) the basic philosophy is that Vmcg puts a line in the sand and there is no expectation that well behaved aeroplanes from polite society would be silly enough to spend much of their little lives in that area. As a consequence the probability of combining a Vmcg-limited takeoff with a V1 failure under strong crosswind conditions .. at aft CG, etc., is sufficiently low that the certification doesn't worry too much about it. Keep in mind that the Design Standards don't seek guarantees .. only that the calculated probability of catastrophe is very low .. not zero.

However, for some cases, especially short distance near empty positioning flights, it might be a consideration. I can recall one operator for whom I did some contract work which had a regular such positioning flight. In such circumstances it is useful for the pilots to realise that if they combine a min weight/speed takeoff schedule with a strong crosswind they perhaps exposure the operation to a risk which is unnecessary with (generally) a heap of spare runway. If, on the other hand, the runway is very short, then you either wear the risk or defer the departure until the wind abates a bit. Keep in mind that the increase in Vmcg is in the range 0.5 to 1.0 (plus) kt/kt with crosswind so, given that some aircraft have pretty high crosswind limits, it is worth keeping the problem in the back of the mind.

Vmcg is determined effectively for nil nosewheel cornering capability so, with the max aft CG, it very much emulates a wet runway failure case. However, I wouldn't plan on saving my neck by relying on cornering capabilities in the heat of the moment.
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Old 23rd Feb 2006, 15:22
  #124 (permalink)  
 
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Popay,

I believe that the UK CAA cerftified some aircraft in the 70's/80's using a 7 knot crosswind for the VMCG.

However, today, neither the FAA nor JAA require any crosswind accountability for VMCG.

This is one of J_T's pet subjects, so standby for his response...

Mutt
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Old 23rd Feb 2006, 16:22
  #125 (permalink)  
 
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Originally Posted by Old Smokey

Streamline,

You’d better have a good lawyer, a very very good one.
Old Smokey
Old Smokey, I agree. Do not get me wrong. I go wet if I have to.
Basically wet RTOW are artificially blown up because of reversers and reduced screen. That´s why I try to outlaw this habbit (wet when not really wet)

Thanks for your arguments it gives me some more ammunition.

Never came across a VMCG V1 where I had to use full thrust at the same time.

In good cooperation.

Stream

Last edited by Streamline; 23rd Feb 2006 at 16:40.
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Old 23rd Feb 2006, 16:46
  #126 (permalink)  
 
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If you're sufficiently concerned with V1=Vr at low weights (that is, weights well below the RTOW) and in a strong cross-wind, by all means run your finger up or down the RTOW page to find a V1 comfortably above Vr, all the way to the RTOW if you want.

It's an approved procedure when Wind Shear may be a risk, perfectly legal, and, performance at the actual lower weight will be much better than at the RTOW for which figures you are using.

Have I managed to make a 180 turn on this 'Lower V1' thread to advocating a higher V1? The plot thickens.

Mutt, "This is one of J_T's pet subjects, so standby for his response...", and that's only his written word, the real life display is a piece of real showmanship!

Streamline, it seems that we were simultaneously posting. Yup, I read your original post as referring to other's habits, not your own. They'd better have a good lawyer. We Irish Awstralians never did quite master the Queen's English.....

Regards,

Old Smokey
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