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Old 30th July 2004 | 08:52
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SR71

Mach 3
 
Joined: Aug 1998
Posts: 624
Likes: 1
From: Stratosphere
Am I the only one who isn't sure they've got the big picture with respect to "green dot" speed?

I realize there may be some confusion in my mind about the speed in question.

In our Tech manual this speed is known as the:

"Flaps Up Manoeuvering Speed"

I've heard this described in the past to be equivalent to Min Clean speed with flaps up.

However, further on in the Tech Manual the definition is given as:

"...an output of the SWC computed for the actual gross weight in question by the FMC. It represents best airspeed (climb or driftdown) for an aircraft in the clean configuration."

To me, this sounds like V_md i.e., where the (L/D) is maximum, and the speed I want to aim for, say, in the event of a double engine failure in order to maximize my glide range.

However, I am not clear whether or not it is actually more like "Best Range Speed", typically 20kts more than V_md, and where the ratio of (V/D) is a maximum and would therefore be the speed you get when you enter a CI = 0.

If this is true, in the case of a double engine failure I want to aim at a somewhat lower speed than green dot speed to achieve V_md.

The Smiths FMC Guide indicates (as one might expect) that the FMC TGT SPD on the ENG OUT CLB page is the speed for max (L/D) and is typically 20 kts above Minimum Manoeuvering Speed.

So whats up? Whats the definitive answer to the following questions:

1) Is green dot speed V_md or Best Range Speed, ~=1.3*V_md?
2) In the event of a double engine failure, I want V_md. May I compute this as ~=(FMC TGT SPD on the ENG OUT CLB page ) - 20kts? This would mean V_md for the 737 is ~=190-200kts....
3) Is there any correlation between "green dot" speed as Minimum Clean speed and Best Range Speed, ~=1.3*V_md?

I believe the reference to "green dot" speed as Minimum Clean speed is, technically at least, erroneous.

Last edited by SR71; 30th July 2004 at 10:03.
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