Boeing Flap Detent Numbering

[nick2007]

Just out of curiosity...

Th flap detents on most (?) Boeing models appear to be assigned arbitrary numbers (1, 5 ,10 15... 30) which do not appear to correspond to flap/slat deflection angle or wing camber.

I assume that this is a legacy numbering system dating back some years.

Does anyone know the origins/explanation for this?

[dhardesthard]

I only flew the B707 and the flap numbers reflected the flap angles, same for DC 9s, MD 80s and L1011s. However Airbus 320,330 and 340 family used 1,2,3 and Full positions which were not related to flap angles.

[Centaurus]

I assume that this is a legacy numbering system dating back some years.

Does anyone know the origins/explanation for this?
nick2007 is offline Report Post Reply

My understanding from a Boeing (Seattle) instructor pilot in 1978 was that in the case of the Boeing 737 series the flap numbering you described were units of flap - not necessarily corresponding degrees of flap.

[IFixPlanes]

The AMM from the 737 Jurassic (-200) say:
...
The angle of flap extension is measured relative to the wing chord plane.
When the flaps are fully retracted, the trailing edge of the aftflap is aligned with the wing chord plane.
When the flaps are extended to 40 units, the angle between the wing chord plane and the midflap is approximately 43 degrees.
Since the aftflap moves relative to the midflap, the aftflap rotates to an angle of approximately 69 degrees from the wing chord plane.
...

[Jane-DoH]

dhardesthard

I only flew the B707 and the flap numbers reflected the flap angles, same for DC 9s, MD 80s and L1011s.

Makes sense.


Centaurus

My understanding from a Boeing (Seattle) instructor pilot in 1978 was that in the case of the Boeing 737 series the flap numbering you described were units of flap - not necessarily corresponding degrees of flap.

Fascinating, I never knew that.