Pitch is everything

[Andy_R]

OK, stupid question time, but would love to know the answer...........

Do different wings have different A of A's?

Or is it a constant regardless of wing shape/chord/ span etc.?

[High Wing Drifter]

Do different wings have different A of A's?

Yes, most certainly. Low drag swept wing designs can tolerate incredibly high AoA as can delta wings, just look at past footage (sadly) of Concorde on Final approach. They are generally low lift wings with about +3deg positive pitch in the cruise at umpteen-loads knots, as the speed decays they rely on high AoA (as well as high lift stuff like slats'n'flaps) to stay in the air.

As for chord/span. Flaps increase the AoA of the wing, creating more lift, hence the reason why you can pitch at cruise attitudes when well below cruise speed.

[18greens]

Theres a lot of discussion here about pitch and AOA which are undoubtedly important. In fact AOA is very important but...

Was the original question not about flying the picture or flying the attitude when he referred to pitch being very important.

If you lost all of the instruments in a light aircraft you could still fly and land it in VMC without difficulty if you had a grasp of attitude rather than flying the numbers.

In any light ac if you covered up all of the insts I bet you could make a decent fist of a landing based on the noise the engine is making and the attitude of the ac outside the window.

Attitude adjustments are far easier to do by looking out the window rather than chasing the ASI. (Ask any IMC student, a peek is worth a thousand scans)

[Shaggy Sheep Driver]

Do different wings have different A of A's?

Or is it a constant regardless of wing shape/chord/ span etc.?

Cloud69 - not a stupid question at all. I'll try not to give a stupid answer.

To add to HWD's answer, the A of A is actually the angle between the mean wing chord and the airflow - that is, the angle at which the wing is presented to the airflow. So a wing doesnt 'have' an A of A, but 'experiences' whatever A of A it is presented with.

The problem comes when the A of A reaches the angle at which the airflow can no longer follow the top surface of the wing, and breaks away. This is the stall. That angle depends on the design of the wing - including aspect ratio (chord to span ratio), and cross-sectional profile. These factors also affect how the wing behaves at high A of A - for instance, whether the airflow suddenly detaches, or does so more progessivly - or not at all.

The example of Concorde HWD gives is interesting - narrow delta wings like that will work at extremely high A of As without stalling - but the drag goes up at a phenominal rate, so as a delta is pitched up it genertaes more lift and more drag (as do all wings). But whereas a conventional wing will reach a stallling angle (around 15 degrees on most light aircraft) the delta just goes generating more lift and more drag - much more drag. Soon it reaches a point where, despite full engine power, the only way is down, and the aeroplanes sinks earthwards.

SSD

[High Wing Drifter]

In any light ac if you covered up all of the insts I bet you could make a decent fist of a landing based on the noise the engine is making and the attitude of the ac outside the window.

I doubt you could sense the wind noise different of say 10kts and on approach you may well have the engine on idle or low power so I doubt those cues will work well. However, the level of mushyness in the handling should be an excellent indicator. You know how utterly unresponsive the a/c just prior to the stall and how realtively unresponsive it is on approach. The difference in 15kts is quite marked (on the little un's I've flown anyway).

[Andy_R]

Thanks for that guys!!!

[stiknruda]

FFF

FFF

In short, generaly civvy aerobatic capable machines don't have an AoA indicator.

So how does the aerobatic pilot assess AoA? Quite simply through practice, initially one stalls or departs from the attitude being flown, then one begins to register the buffet, then one learns to ease off and only mildly "nibble the buffet", for greatest effect.

Then an amazing thing happens - you suddenly realise that the buffet and ensuing stall happen at a certain stick position, regardless of speed, bank, etc! That it works just the same for negative as for positive G makes flying even more magic, ie whilst inverted, the same stick position will cause the aircraft to stall regardless of configuration.

The military have AoA indicators primarily to assist the operator turning the flying machine into a weapons platform and doing so in as simple a manner as possible.

So very simplistically, even those unfortunates who have to to fly William T's aeroplane's have an accurately calibrated AoA indicator - it's called the column/yoke or stick!

Stik

[englishal]

However, the level of mushyness in the handling should be an excellent indicator.

I did this exercise once, covering up all instruments except for oil temp, and oil pressure and flew back in, joined and landed.

Very interesting it was too, combining the visual attitude with the "feel" of the aircraft and I made a perfect landing. I often wonder why people spiral to their death when an ASI fails or they take off with the pitot cover still on.....?

[FlyingForFun]

Stik - thanks for that, very interesting. The only time I've inadvertantly stalled an aircraft was at the top of a loop, and I knew I'd stalled because I registered the buffet.....

But I think your reply has confirmed my earlier reply, and that of others: during non-aerobatic flight, the principal way of telling the AoA is by a combination of power and, more importantly, attitude - but that's not true for aerobatic flight.

FFF
----------------

[slim_slag]

Hmm, I think the discussion of aerobatic flight came from an earlier significant misunderstanding of what the thread is about (which probably comes from a misunderstanding of aerodynamics). Then it got onto how you can detect the stall without using an AoA indicator. None of this from you FFF, but surely it's the same wing on the way to the aerobatic box as it is in the aerobatic box

[Sans Anoraque]

Englishal - I suspect that kind of excercise would be more than interesting for someone with my level of experience!

After all, some pilots still manage to stall on final turn, even with fully working ASIs.

[slim_slag]

I think you would do just fine Anoraque, you should try it. People stall-spin-die on the base-final turn because they use rudder in an attempt to tighten the turn, not because they have poor airspeed/pitch control.

[englishal]

You should do it with an instructor then

Another interesting exercise is to fly to the local area, then fly back in, join and land using nothing but the rudder, trim and power......ok, not land, but take it to the runway using trim only, you can use the stick / yoke to flare if you like