nigelspeedy
New Member
It would be nice to be able to do the AoA calibration at different flap settings. I notice that the pre stall warning is very different between flaps 0/20/40 degrees.
Cheers
Nigel
Cheers
Nigel
AoA linked to flap setting
- Thread starter nigelspeedy
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vlittle
Active Member
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- May 7, 2006
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- 542
I'm not sure that this is necessary. Stalling indicated AoA does not depend on flap position, although stalling pitch and airspeed do.
Airspeed indicators show the difference between clean and flaps extended stalling speed, which leads to the conclusion that stalling iAoA must also change, but it does not.
Second order effects may change iAoA and leading edge devices will definitely do so, but not conventional trailing edge flaps.
After all, if stalling iAoA changed with flap position, different parts of the wings would stall differently depending on flap position, leading to some pretty exciting changes in stall behaviour.
Note: I'm using iAoA here to represent indicated AoA from a probe and NOT the Engineer's definition of AoA which depends on the trailing edge position of the wing (camber). There is a difference and it leads to confusion between real-world results using a probe and results using the formal definition.
Airspeed indicators show the difference between clean and flaps extended stalling speed, which leads to the conclusion that stalling iAoA must also change, but it does not.
Second order effects may change iAoA and leading edge devices will definitely do so, but not conventional trailing edge flaps.
After all, if stalling iAoA changed with flap position, different parts of the wings would stall differently depending on flap position, leading to some pretty exciting changes in stall behaviour.
Note: I'm using iAoA here to represent indicated AoA from a probe and NOT the Engineer's definition of AoA which depends on the trailing edge position of the wing (camber). There is a difference and it leads to confusion between real-world results using a probe and results using the formal definition.
Hi Vern!
I'm not entirely sure that's correct--the NASA report on my airfoil used a fixed reference (not varying with the trailing edge of the flap), and critical AoA changes fairly dramatically with flap position:
Additionally, Alpha Systems documentation mentions the indicated angle where stall actually occurs will depend on flap position.
As for stall happening differently across different parts of the wing, this already happens even without flaps--washout, changes in airfoil shape with span, and even propwash can do this. (Interestingly, my airplane's critical angle of attack changes by almost 2.6 degrees if the propeller is windmilling--apparently, the wake behind it is pretty awful).
I'm not entirely sure that's correct--the NASA report on my airfoil used a fixed reference (not varying with the trailing edge of the flap), and critical AoA changes fairly dramatically with flap position:
| Flap Position | Critical AoA |
| -10° | 15.2° |
| 0° | 13.2° |
| 10° | 12.2° |
Additionally, Alpha Systems documentation mentions the indicated angle where stall actually occurs will depend on flap position.
As for stall happening differently across different parts of the wing, this already happens even without flaps--washout, changes in airfoil shape with span, and even propwash can do this. (Interestingly, my airplane's critical angle of attack changes by almost 2.6 degrees if the propeller is windmilling--apparently, the wake behind it is pretty awful).