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Driver170

flap maneuvering speed and minimum maneuvering speed

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During Flap Retraction for landing, you get the minimum flap speed in green and below it somewhere you get the amber hockey bar - (minimum maneuvering speed)

 

Now it says in the FCTM - (flap maneuvering speed) These speeds guarantee full maneuver capability or at least 40° of bank (25° of bank and 15° overshoot) to stick shaker.

 

My confusion is can the 737 safely go below the minimum flap speed the green 1, 5, 10-15, without dropping to the next flap setting and drop to the orange hockey bar? Minimum maneuvering speed?


Vernon Howells

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Minimum safe operating speed by definition is 1.3 x stall speed, and the stall speed varies with flap configuration.  I may be simplifying this but the familiar V speeds are Vs stall clean and Vs1 stall landing configuration.

 

It took me a short time to understand flap maneuvering speeds because I'd gone decades with maneuvering speed Va as the highest speed you could safely do an extreme maneuver and stall instead of breaking the airplane.  The flap speeds are the lowest speed you can safely maeuver and not stall.  Not wise to go slower.


Dan Downs KCRP

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The flap speeds are the lowest speed you can safely maeuver and not stall.  Not wise to go slower.

 

This provides 40* of bank 30* degrees of bank and 15* overshoot!

 

Now, below this you should see the orange hockey stick. Why is this even still shown as in no way can you go below the minimum flap speed the green markings? And why doesn't flaps 30 or 40 have the green markings but only shows the green Vref?

I'll correct the first line - 25* of bank and 15* overshoot


Vernon Howells

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You can go below the flap maneuvering speed but you're in a speed region where you can no longer perform rapid maneuvering. Normally, you don't reduce safety of flight by eliminating options.


Dan Downs KCRP

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This provides 40* of bank 30* degrees of bank and 15* overshoot!

 

Now, below this you should see the orange hockey stick. Why is this even still shown as in no way can you go below the minimum flap speed the green markings? And why doesn't flaps 30 or 40 have the green markings but only shows the green Vref?

I'll correct the first line - 25* of bank and 15* overshoot

Page 1.15 of the FCTM explains it graphically. The flap manoeuver speeds have an extra margin over the minimum manoeuvre speed. More than 1.6g. That's 51 deg bank plus. So you could go down to the minimum manoeuvre speed (top of the amber band) and still pull up to 1.3 g (40 deg bank). But in doing so you are reducing the extra margin you had by observing the flap speeds.

 

Page 1.15 also gives you the relationship between Vref40 and each flap speed. These bug speeds are a defined amount apart for simplicity, dating from the days of manually bugged ASIs.

 

 

Now it says in the FCTM - (flap maneuvering speed) These speeds guarantee full maneuver capability or at least 40° of bank (25° of bank and 15° overshoot) to stick shaker.

It also says this:

 

The minimum maneuver speed should not be confused with the flap maneuvering speeds. The flap maneuvering speeds are computed based on airplane weight, while the minimum maneuver speed is computed using airplane angle of attack and current airspeed. These two speeds provide independent means to ensure that the current airspeed provides at least full maneuver capability for terminal-area maneuvering.

 


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Yes. The airplane can fly happily as long as you are above the Red Army. Think of a windshear escape maneuver and GPwS maneuve, you will be flying just or touching the Pitch Limit indicator with the airspeed within the Vmms.

 

Like other people have already pointed out, what you will lose is the stall margin against G loading.

 

What the book tries to say (you can try in flight sim, and please give it a go to help you understand), at the flap maneuvering speed if you do a 40deg level turn the red army ( stick shaker speed) will move up to where the flap maneuvering speed speed it. Because the stall speed change with G loading and G loading varies with AOB ( the equation is G = 1/cos AOB )

 

Therefore the lower the speed you go below flap maneuvering the more limiting the AOB or G loading you have before you get stick shaker. Until you hit the 1G stick shaker speed which is at the top of the red army in straight and level flight.

 

Hope it helps to clear things up if not making it more complicated to understand.


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Driverrab that makes it alot clearer for me now! I see it now haha i just got that light buld :)

 

Thanks to the rest of you guys too.

 

Driverrab i have a question about being under the flap manoevering speed during takeoff when retracting the flaps.

 

Lets say Flaps 5 takeoff, you retract from F5 to F1 at V2 + 15 the white bug and accelarating. Now you'll be under F1 manoevering speed (1) green bug. Will the AC now be limited to 30* of bank? 15+15 for overshoot?


Vernon Howells

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Lets say Flaps 5 takeoff, you retract from F5 to F1 at V2 + 15 the white bug and accelarating. Now you'll be under F1 manoevering speed (1) green bug. Will the AC now be limited to 30* of bank? 15+15 for overshoot?

 

Yes, but not for long (as you'll be accelerating). This is why you select the next stage of flap when accelerating through the manoeuvring speed for the current setting (i.e. select Up at the Flap 1 bug) -- I would guess the rationale is that by the time the flaps have actually retracted, you'll probably have accelerated above or very close to the appropriate speed anyway.

 

When slowing down, of course, you select each stage of flap by the appropriate manoeuvre speed (so, for example, whilst decelerating you might select Flap 5 at around Flap 5+5kts so that you have Flap 5 green by the time you get to the Flap 5 bug).

 

It's also a reason why you might look at the SID and decide that you might actually want to hold the flap and speed intervene in order to get a full 30 deg bank (for example, if a sharp turn is required shortly after takeoff). The FD should only command 15 degrees of bank below the appropriate manoeuvring speed for the configuration, so if you accelerate & retract 'early' in this case you won't get as tight a turn as you might want.


Simon Kelsey

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What the book tries to say (you can try in flight sim, and please give it a go to help you understand), at the flap maneuvering speed if you do a 40deg level turn the red army ( stick shaker speed) will move up to where the flap maneuvering speed speed it. Because the stall speed change with G loading and G loading varies with AOB ( the equation is G = 1/cos AOB )

 

 

However, also there is a bug, because the red army will snap back to its original 1g value when you bank beyond that angle where it coincides with the yellow bar. Still awaiting a fix in SP1d.

 

Lets say Flaps 5 takeoff, you retract from F5 to F1 at V2 + 15 the white bug and accelarating. Now you'll be under F1 manoevering speed (1) green bug. Will the AC now be limited to 30* of bank? 15+15 for overshoot?

 

No, you are still above the yellow bar which gives 1.3g maneuver margin, which equals 40° bank. To find a more precise value we can look at the graph: you will have about 1.45g of maneuver margin when retracting flaps from 5 to 1 at V2+15.

 

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However, also there is a bug, because the red army will snap back to its original 1g value when you bank beyond that angle where it coincides with the yellow bar. Still awaiting a fix in SP1d.

 

I was going to mention that! Why does it snap back!? So its a bug then.

 

I hope things do get sorted out on the next update.

 

No, you are still above the yellow bar which gives 1.3g maneuver margin,

 

And also because the AC is accelarating?

Yes, but not for long (as you'll be accelerating). This is why you select the next stage of flap when accelerating through the manoeuvring speed for the current setting (i.e. select Up at the Flap 1 bug) -- I would guess the rationale is that by the time the flaps have actually retracted, you'll probably have accelerated above or very close to the appropriate speed anyway.

 

When slowing down, of course, you select each stage of flap by the appropriate manoeuvre speed (so, for example, whilst decelerating you might select Flap 5 at around Flap 5+5kts so that you have Flap 5 green by the time you get to the Flap 5 bug).

 

It's also a reason why you might look at the SID and decide that you might actually want to hold the flap and speed intervene in order to get a full 30 deg bank (for example, if a sharp turn is required shortly after takeoff). The FD should only command 15 degrees of bank below the appropriate manoeuvring speed for the configuration, so if you accelerate & retract 'early' in this case you won't get as tight a turn as you might want.

 

Thanks alot i'm starting to make sense of this now! You mentioned 30* of bank is that 15* bank + 15* overshoot?

To find a more precise value we can look at the graph: you will have about 1.45g of maneuver margin when retracting flaps from 5 to 1 at V2+15.

 

Looked at the graph but not sure how to read it. Its kinda complicated!!


Vernon Howells

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And also because the AC is accelarating?

 

No, the amber bar is the 1.3g limit for the speed you are currently at. The accelerating part covers you for the temporary loss of margin as you retract flap. It means you can select Flap 1 before reaching the appropriate bug speed because you will very soon be at that speed. But if you observe the flap manoeuvre speeds you will always be well in excess of 1.3g (40 deg bank) limits. Please study the graph on page 1.15 of the FCTM. It has all the answers.

Lets say Flaps 5 takeoff, you retract from F5 to F1 at V2 + 15 the white bug and accelarating. Now you'll be under F1 manoevering speed (1) green bug. Will the AC now be limited to 30* of bank? 15+15 for overshoot?

 

Why are you even considering doing this? V2+15 is barely more than the V2+10 the FD will guide you to initially, so retracting flap at that bug is only about 5 knots increase in speed.

 

Where did you get the idea of a 30 deg limit in this case? Anyway it will be easier to understand the concepts if you forget the +15 for overshoot and only think of the limit itself.


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Bottom line - don't go below the flap speeds (except as following the take-off profile).


Matt Cee

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Why are you even considering doing this? V2+15 is barely more than the V2+10 the FD will guide you to initially, so retracting flap at that bug is only about 5 knots increase in speed.

 

Thats when you retract from Flaps 5 to Flaps 1


Vernon Howells

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Lets say Flaps 5 takeoff, you retract from F5 to F1 at V2 + 15 the white bug and accelarating. Now you'll be under F1 manoevering speed (1) green bug. Will the AC now be limited to 30* of bank? 15+15 for overshoot?

 

 


Why are you even considering doing this? V2+15 is barely more than the V2+10 the FD will guide you to initially, so retracting flap at that bug is only about 5 knots increase in speed.

 

Minimum of V2+15 and accelerating gets a Flaps 1 call from me. SOP.


Matt Cee

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Minimum of V2+15 and accelerating gets a Flaps 1 call from me. SOP.

 

Well thats the procedure i know and doing :)


Vernon Howells

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