FPV (Birdy)
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Joined: Feb 2017
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From: Isla Grande
Yep, the deeper you dig....
I've also stumbled to explain the lift theory I was taught many moons ago (Bernoulli)
It seems dead wrong now. Still looking for a better easy to understand explanation....
I've also stumbled to explain the lift theory I was taught many moons ago (Bernoulli)
It seems dead wrong now. Still looking for a better easy to understand explanation....
Joined: Jun 2014
Posts: 346
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From: Mordor
Joined: Dec 2002
Aviation Qualifications: ATP+Mil
Posts: 3,985
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From: Where the Quaboag River flows, USA
I think the standard is the fuselage reference line—body angle. It was for the Global HUD.
Also, remember the US and the British reverse the meaning of Angie of Attack and Angke of Incidence. Lastly, AoA gauges don’t display angle but dimensionless units between zero and stall AoA.
Also, remember the US and the British reverse the meaning of Angie of Attack and Angke of Incidence. Lastly, AoA gauges don’t display angle but dimensionless units between zero and stall AoA.
Joined: Sep 1998
Posts: 1,615
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From: wherever
I think the standard is the fuselage reference line—body angle. It was for the Global HUD.
Also, remember the US and the British reverse the meaning of Angie of Attack and Angke of Incidence. Lastly, AoA gauges don’t display angle but dimensionless units between zero and stall AoA.
Also, remember the US and the British reverse the meaning of Angie of Attack and Angke of Incidence. Lastly, AoA gauges don’t display angle but dimensionless units between zero and stall AoA.
*very loose term as you may well meet an intervention before stalling or AoA max.
CSeries in normal mode does a lovely job of maintaining a variable AoA limit if you just hold it at the Soft or Hard sidestick limit.
Many aircraft will push before you get too close.
Joined: Feb 2013
Posts: 92
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From: UK
I have in the past worked out a L/D for the B757 at around 20:1, so that tallies with your figures (I am pleased to say)! Never took the time to work it out for the A321, but would imagine with some decent winglets it must be a bit higher.
Regarding deck angle, I've often wondered when pushing a trolley from back to front whether there is an incline to the wing root then it goes down hill towards the cockpit?! There has to be a bending moment in the fuselage, certainly on the longer fuselages.
Regarding deck angle, I've often wondered when pushing a trolley from back to front whether there is an incline to the wing root then it goes down hill towards the cockpit?! There has to be a bending moment in the fuselage, certainly on the longer fuselages.
Joined: Feb 2009
Posts: 379
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From: Seattle
Don't confuse "vane angle" with AOA
In Post #20 S&R makes reference to zero vane angle being a long way from zero AOA. This is common for a couple of reasons.
1. AOA vanes measure the angle of the flow where they are located (normally on the side of the forebody). Flow anywhere near the airplane is distorted by the airplane. A change of AOA of one degree will most likely result in a change of vane angle that is significantly more than one degree.
2. The AOA range of interest most often extends on both sides of zero. Often it is found to be easier to deal with a sensor whose "position" takes on only positive values. As such, the vane instrumentation may be set up to have a zero reading correspond to an airplane AOA that is quite negative so as not to have to deal with negative values.
Most often a conversion is provide within the airplane's instrumentation to convert raw "vane angle" to "AOA" that is then used for displays and potentially as part of the control system augmentation. AOA is most typically an indication of the longitudinal angle of the free stream airflow with respect to the fuselage.
A related point of interest is the AOA at which zero lift occurs. For a high speed, clean wing configuration zero lift usually occurs at close to zero AOA. At low speed where trailing edge flaps are often deployed and trailing edge control surfaces such as ailerons may be drooped, zero lift occurs at an AOA that is considerably below zero.
I concur with the previous comments regarding complexity of wing shape and twist such that defining the true zero incidence angle for the wing itself is complex and varies with wing configuration, fuel loading, airplane weight, speed, Mach number, and load factor. It is much simpler to reference AOA to a more stable, less variable geometry reference such as fuselage angle.
1. AOA vanes measure the angle of the flow where they are located (normally on the side of the forebody). Flow anywhere near the airplane is distorted by the airplane. A change of AOA of one degree will most likely result in a change of vane angle that is significantly more than one degree.
2. The AOA range of interest most often extends on both sides of zero. Often it is found to be easier to deal with a sensor whose "position" takes on only positive values. As such, the vane instrumentation may be set up to have a zero reading correspond to an airplane AOA that is quite negative so as not to have to deal with negative values.
Most often a conversion is provide within the airplane's instrumentation to convert raw "vane angle" to "AOA" that is then used for displays and potentially as part of the control system augmentation. AOA is most typically an indication of the longitudinal angle of the free stream airflow with respect to the fuselage.
A related point of interest is the AOA at which zero lift occurs. For a high speed, clean wing configuration zero lift usually occurs at close to zero AOA. At low speed where trailing edge flaps are often deployed and trailing edge control surfaces such as ailerons may be drooped, zero lift occurs at an AOA that is considerably below zero.
I concur with the previous comments regarding complexity of wing shape and twist such that defining the true zero incidence angle for the wing itself is complex and varies with wing configuration, fuel loading, airplane weight, speed, Mach number, and load factor. It is much simpler to reference AOA to a more stable, less variable geometry reference such as fuselage angle.
Last edited by FCeng84; 5th February 2018 at 21:51. Reason: Fix typo and add airplane weight as a factor
