AoA : default or addon ?

[FDEdev 955]

50 minutes ago, vortex681 said:

Sorry but I’m struggling to see how an angle-of-attack gauge will show you vertical acceleration. You can be in level flight with a low AoA or a high AoA.

Because strong sudden up/downdrafts alter the AoA. Since the VSI is usually heavily dampened you only get an immediate feedback from the AoA gauge in the sim.  

[martin-w 3,289]

5 hours ago, FDEdev said:

Because strong sudden up/downdrafts alter the AoA. Since the VSI is usually heavily dampened you only get an immediate feedback from the AoA gauge in the sim.  

 

Dont think so. Alpha only changes if air speed changes.

[LHookins 3,118]

45 minutes ago, martin-w said:

Dont think so. Alpha only changes if air speed changes.

I keep an AoA display up a lot of the time on the Shift-Z text.  A lot of times it is not constant, and an updraft or downdraft will change slightly the angle the wind is hitting the wing, which changes the AoA.  In turbulence it's all over the place.

The changes might be minor, but they're useful input.

Hook

[FDEdev 955]

1 hour ago, martin-w said:

Dont think so. Alpha only changes if air speed changes.

I don't care if you think so, that's plain and simple wrong. That's basic aerodynamics.  

Edited March 3, 2020 by FDEdev

[martin-w 3,289]

1 hour ago, FDEdev said:

I don't care if you think so, that's plain and simple wrong. That's basic aerodynamics.  

Not really, angle of attack is nothing to do with getting an up draft or down draft. Angle of attack is the pitch relative to the velocity vector. Faster equals lower Alpha and slower equals higher Alpha.

 

Think you might be confused as to what angle of attack or Alpha actally is.

Edited March 3, 2020 by martin-w

[martin-w 3,289]

1 hour ago, LHookins said:

I keep an AoA display up a lot of the time on the Shift-Z text.  A lot of times it is not constant, and an updraft or downdraft will change slightly the angle the wind is hitting the wing, which changes the AoA.  In turbulence it's all over the place.

The changes might be minor, but they're useful input.

Hook

 

Well yes, if airspeed changes as a result of turbulence, up drafts, down drafts, alpha will change. But that's not always the case. Updrafts and downdrats can occur without being a causal factor for velocity change. So it's hardly giving you accurate "feedback" as to vertical speed which was the original premise.

Your change in angle of attack could just as easily been as a result of velocity change not vertical speed variability.

[ual763 361]

8 minutes ago, martin-w said:

Not really, angle of attack is nothing to with getting an up draft or down draft. Angle of attack is the pitch relative to the velocity vector. Faster equals lower Alpha and slower equals higher Alpha.

 

Think you might be confused as to what angle of attack or Alpha actally is.

You're assuming the updrafts/downdrafts are always at a 90° angle to the wing chord with no horizontal component.  If there is any horizontal movement to said updraft/downdraft, (which 99.9% of the time there is), there will be fluctuations in airspeed and also coincidentally AoA.

[LHookins 3,118]

20 minutes ago, martin-w said:

Think you might be confused as to what angle of attack or Alpha actally is.

Martin, you're a smart guy, but I think your concept of angle of attack is a little simplistic.  I've been flying with an AoA indicator since 2007 so I have a good idea what affects it.

The AoA gauge in the Icon is the best I've seen.

Hook

[FDEdev 955]

25 minutes ago, martin-w said:

Faster equals lower Alpha and slower equals higher Alpha.

Suggest to do a bit of basic research before posting. It's e.g. essential knowledge that stall speed increases with bank angle (stall AoA remains the same)

 

Edited March 3, 2020 by FDEdev

[Bob Scott 7,779]

4 hours ago, martin-w said:

Not really, angle of attack is nothing to do with getting an up draft or down draft. Angle of attack is the pitch relative to the velocity vector. Faster equals lower Alpha and slower equals higher Alpha.

 

Think you might be confused as to what angle of attack or Alpha actally is.

No, I have to agree with FDEDev here.

"Faster equals lower Alpha and slower equals higher Alpha" is true in straight and level flight with all else remaining equal (weight, air density, lift device config etc).  Otherwise, I can fly fast at a very high alpha (e.g. a high-G turn), and slow with a low alpha (a pushover from slow flight). 

In an up/downdraft scenario, you have a sudden perturbation of the vertical component of the air mass velocity vector, and the aircraft leaves the equilibrium condition of straight and level flight as it climbs/descends in the draft. 

If only the airspeed changes, say for example in a decreasing headwind wind shear scenario. the AoA does not change as a result of the suddenly reduced headwind.   Until a correction is made, the AoA remains the same at the reduced airspeed, resulting in a loss of lift and a descent.  The AoA only changes when the pilot/autopilot pulls the nose up to stop the resulting descent.  In a draft, the vertical component of the relative wind is changed while the pitch is not, resulting in a change in AoA.

 

[Dominique_K 10,156]

On 3/2/2020 at 8:56 AM, LHookins said:

I've always had an AoA display of some kind in all my sim aircraft.  It was the first gauge I designed.  I've currently got it on the Shift-Z text.  I've found it very useful

Is it a panel gauge or a small HUD on the glare shield ? The HUD allows peripheral vision without having to lower your eyes, don’t you think ? 

[martin-w 3,289]

15 hours ago, LHookins said:

Martin, you're a smart guy, but I think your concept of angle of attack is a little simplistic.  I've been flying with an AoA indicator since 2007 so I have a good idea what affects it.

The AoA gauge in the Icon is the best I've seen.

Hook

 

Nope it's not simplistic. The definition of angle attack is fact. If you have an angle of attack indicator, and you are using that to determine vertical speed it's not being used for it's intended purpose. All it will tell you is angle of attack and that is determined by changes in velocity not sink rate or climb rate. Thus, a change in velocity will change the angle of attack. So it's a very inaccurate indicator of vertical speed.

You wont know with any certainty if vertical speed is changing simply because the angle of attack indicator quivers. AoA could remain the same with a draft from directly above or below.

 

 

Edited March 4, 2020 by martin-w

[Dominique_K 10,156]

As the OP allow me to refocus it to my original intent which was to discuss how much an AoA mini-HUD is a help to fly stall-borderline final approach in a difficult airfield (very short runway, high trees, windshears at the edge of a cliff etc.) . I observe that some several pilots have one and that indeed, the HSI is of little help and that VSI is a little late to react.

Edited March 4, 2020 by domkle

[martin-w 3,289]

14 hours ago, w6kd said:

The AoA only changes when the pilot/autopilot pulls the nose up to stop the resulting descent.  In a draft, the vertical component of the relative wind is changed while the pitch is not, resulting in a change in AoA.

 

 

VELOCITY alters angle of attack. Pitching the nose up will only change the angle of attack as a result of reduction in velocity.

 

Thus... in a scenario where there is an updraft from directly beneath the aircraft and no change in velocity... the angle of attack stays the same. Same in reverse, if there is a downdraft from directly above, and thus no change in velocity, angle of attack remains the same.

Thus... if using an angle of attack indicator for the purpose of detecting changes in vertical speed, its inaccurate. A deflection of the indicator only tells you for certain that angle of attack has changed due to a velocity change. And that can happen with no up or down draft. And an up or down draft can occur with no angle of attack change.

[martin-w 3,289]

14 hours ago, w6kd said:

No, I have to agree with FDEDev here.

"Faster equals lower Alpha and slower equals higher Alpha" is true in straight and level flight.

 

No Bob. It's true when in level flight or climbing or descending. You can be climbing with nose pitched up 10 degrees with a 5 degree angle of attack. Similarly you can be descending with nose 0 degrees but a 10 degree angle of attack. Or nose 10 degrees down and a 6 degree angle of attack.

 

Pitch and angle of attack are not the same. Angle of attack is how many degrees the nose is up or down in relation to the flight path angle (velocity vector) 

 

14 hours ago, w6kd said: