puzzling flaps 10 on 737

[Tapshi]

While going through the FPPM, I was comparing various performance limited weights with different flap settings. Everything was as expected for each flap setting, except for flaps 10. There is a considerable decrease in airplane performance when using flaps 10. I'll present some data to verify this.
This is for takeoff field limit wt on dry runway with OAT 32 degrees, PA 4000', field length available 2880 meters, 20 kts HW and 1% slope. Aircraft is a 737-800W 24k.
The resulting weights along with various flap settings are as follows
Flaps 1 - 64.4 T
Flaps 5 - 66.3 T
Flaps 10 - 65.8 T
Flaps 15 - 67.2 T
Flaps 25 - 67.8 T
the story is the same for all weights with performance falling with flaps 10. Any ideas why this is so? Any aerodynamic reason?

[KriVa]

Could it be this is a 737 with the Short Field Package added?

[Eric Janson]

@Tapshi

Suggest you look at the limiting codes for each flap setting. You will find your take-off is limited by different criteria for different flap settings.

For Flaps 1 and 5 it is most likely field/obstacle limits
For flaps 15/25 you are most likely climb limited - although there may be an improved climb using higher V2.
Flaps 10 is probably close to where this changeover occurs

[BOAC]

Cannot offer any answer there, Tapshi. Eric - he specifies 'takeoff field limit wt' so I don't think WAT is relevant, and the 15 and 25 would drop as well?

Tapshi - any chance of a scan (de-identified, of course:)) of these tables? F10 is not a common product in my experience for RTOW tables.

[RAT 5]

Could this have anything to do with this aspect of the configuration:

F10 has the same TE as F5 but has full extension on LED, same as F15. This might give some more increase in drag than lift. The flap manoeuvring speed for F10 is same as F5, but you need more power for performance.
I suspect the change in TE has more effect that change in LED.

[Denti]

Actually the LED status depends on installed short field performance kit or not. LED sequencing is changed with that kit.

[Mach E Avelli]

My guess is Rat is on the money. Flap 10 was optimum under some conditions for the old Jurassic (200) series. Later Classics still had the gate position, but I never saw any take-off data for flap 10 on a Classic.

[Denti]

Oh, there is take off data for flaps 10, and in some rare cases it is still the optimum setting even on the NG.

[billyt]

Is Flaps25 an option for take off on the 73? Would you not get the gear horn once you selected gear up?

[B-HKD]

Is Flaps25 an option for take off on the 73? Would you not get the gear horn once you selected gear up?

You are thinking of 747/57/67/77/87

These aircraft have Flaps 25/30 as approved normal landing configurations. So if for whatever reason you were to do a Flaps 25 takeoff, while ignoring the takeoff configuration warning, you would of course get a gear config warning once selecting it up after takeoff.

However, the 737 also has a Flaps 40 setting (just like the 727 did), and thus Flaps 25 is a approved takeoff configuration. Hence no reason for a config warning on gear up selection.

[Sciolistes]

F10 has the same TE as F5 but has full extension on LEDWe have short field NGs so LED go full extend after F25. Selecting F10 shows the same tape speed as for F5. However, the position indicator shows movement and the increase in drag is noticeable so there is an increased TE extension for F10 vs F5.

[sevenstrokeroll]

wasn't there a change in Leading Edge Device deployment setting after the Air Florida crash into the Potomac river?

I seem to recall that the British did some research finding that the fully extended LED's were better in icing conditions.

[A37575]

When I first flew the 737-200 back in 1976 Boeing supplied the runway analysis charts at our company request. We operated from coral strips in the Central and SW Pacific region. The take off settings available were flaps 1,2,5,10, 15 and 25. Boeing recommended at the time we use Flap 10 for all take off's using Improved Climb (V2 Overspeed) for heavier weights runway length permitting. Their point was it would be all too easy to inadvertently select the wrong flap setting when the choice was six of them. Anyway, a choice of six runway analyses for one runway was going overboard.

[stator vane]

cut and pasted from current 737-800 manual

Takeoff configuration warning is armed when the airplane is on the ground and either or both forward thrust levers are advanced for takeoff. Takeoff
configuration warning activates if:
• trailing edge flaps are not in the flaps 1 through 25 takeoff range, or
• trailing edge flaps are in a skew or asymmetry condition, or have
uncommanded motion, or
• leading edge devices are not configured for takeoff or have uncommanded
motion, or
• speed brake lever is not in the DOWN position,

as regarding the configuration warning with ldg gear NOT down:

Flaps 15 through 25 –
• either forward thrust lever set below approximately 20 degrees or an
engine not running, and the other thrust lever less than 34 degrees; thelanding gear warning horn cannot be silenced with the landing gear
warning HORN CUTOUT switch.

[ImbracableCrunk]

We have short field NGs so LED go full extend after F25. Selecting F10 shows the same tape speed as for F5. However, the position indicator shows movement and the increase in drag is noticeable so there is an increased TE extension for F10 vs F5.

I agree. Sometimes I can hold an assigned speed (say 190knts) at F5 on the G/S, and sometimes I can't. F10 fixes that.

[FlightPathOBN]

so there is an increased TE extension for F10 vs F5.

Doesnt flaps 10 have a LE extension vs 5?

[Yeelep]

On all but SFP equipt NG's the LE moves to full extend at F10, SFP planes at F30.