Effect of Bank Angle and Pitch changes on Stall Speed

[rankamateur]

Andy you have the floor(or the speaking stone, or what ever you use down there)

 

 

[ayavner]

While we wait on Andy - this cleared it up for me (thanks djpacro)

 

http://www.eaavideo.org/video.aspx?v=4105230997001

 

 

[motzartmerv]

Thanks Rank. I was commenting on Kaz's comments in another thread which related to her assuming an increased stall speed with extra bank angle in a slipping turn.

 

The general idea that the stall speed increases in a turn is of course correct, and the amount it increases by depends on the bank angle etc.

 

But in a descending turn where there is no extra increase in angle of attack, there should no t be an increase in the stall speed. Or a better way to put it, there wont be an increase in the speed the that the stalling angle is reached.

 

We all know the stall speed increases by the square root of the G loading, so if there is no extra G, then it follows that there is no increase in the stall speed.

 

It is the extra Angle of attack (read back pressure) that increases the G loading, and there for the stalling speed in a "level" turn.

 

Reduce the thought experiment to the absurd- Imagine rolling a 90 deg angle of bank turn, but not pulling the stick back. The aeroplane wont stall at a higher speed, it will just descend. Its not until you try and pull the level turn that the stall speed will increase.

 

 

[Happyflyer]

Thanks Rank. I was commenting on Kaz's comments in another thread which related to her assuming an increased stall speed with extra bank angle in a slipping turn.The general idea that the stall speed increases in a turn is of course correct, and the amount it increases by depends on the bank angle etc.

But in a descending turn where there is no extra increase in angle of attack, there should no t be an increase in the stall speed. Or a better way to put it, there wont be an increase in the speed the that the stalling angle is reached.

 

We all know the stall speed increases by the square root of the G loading, so if there is no extra G, then it follows that there is no increase in the stall speed.

 

It is the extra Angle of attack (read back pressure) that increases the G loading, and there for the stalling speed in a "level" turn.

 

Reduce the thought experiment to the absurd- Imagine rolling a 90 deg angle of bank turn, but not pulling the stick back. The aeroplane wont stall at a higher speed, it will just descend. Its not until you try and pull the level turn that the stall speed will increase.

Your theory is of course quite correct, it is possible to do a descending turn without pulling more than one g, but I would suggest it is also possible to pull lots of "g" in a desceding turn, think the spiral dive. Imagine the decsending turn onto final that has been left a bit late, bank angle is incrased and stick pulled back to make the turn to get back on track, add out of balance and it's your classic stall spin scenario.

 

 

[facthunter]

One "G" is level unaccelerated flight. If the plane changes track it requires a force. Some of it can come from the keel surface if you don't bank, but if you resolve the vertical and the side ways force it will always be more than one G in level flight.. The wings can provide the greater force (lift) to turn rapidly for obvious reasons and it is done by increasing the angle of attack to the relative airflow and the elevator(s) do that. Till you pull the stick back it doesn't happen. No extra lift force.. The banked plane won't turn but the nose will drop because the plane will weathercock and you will end up near vertical, depending on the rudder position. Don't try it unless in a suitable plane. as the speed increases quickly. Nev

 

 

[motzartmerv]

Your theory is of course quite correct, it is possible to do a descending turn without pulling more than one g, but I would suggest it is also possible to pull lots of "g" in a descending turn, think the spiral dive. Imagine the decsending turn onto final that has been left a bit late, bank angle is incrased and stick pulled back to make the turn to get back on track, add out of balance and it's your classic stall spin scenario.

Your 100% correct. Your point is the same as my point, in that Angle of attack is 'independent ' of bank angle. So you can have high bank angle with NO increase in AofA, or conversely as you pointed out, you can have s light bank angle with HIGH AofA.

I spose the point we should be making is that Attitude (Including Bank angle) has nothing to do with AofA. So assuming just because you are banked increases the VS is not correct.

 

 

[Himat]

Yes, it is possible to do a 1G descending turn, but probably not a sustained 1G descending turn. At least not for very long if the turn is to be coordinated.

 

The reason is that whatever turn rate measured in fractions of G is then also the acceleration down against the ground. The 1G descending turn is not only descending, it accelerating downwards. The plane will all the time be accelerating downwards, descending at an all the time increasing speed. Quite quickly the plane will either run out of height or reach Vne.

 

There is some special cases where the plane can keep its height in a 1G turn, one is an aerobatic airplane with the power, rudder and side area to fly sustained knife edge. But then the turn is anything but coordinated.

 

 

[motzartmerv]

True, but secondary to the point. Bank angle alone does not increase the g loading, or the stall speed. :)

 

 

[dan3111]

Stall speed can often be a loose term thrown around , there is a lot of different opinions on what it is . There sure is a lot of LSA manufacture that interrupt stall speed in different ways to get there planes on raa rego . The way I was tought is the point of minimum speed the aircraft crease to maintance level flight . That means not sinking at 500 feet per minute still with controls working . LSA manufactures are meant to test there stall speeds at gross weight but ofter wonder how they pass any stall speed test with a 600 foot sink rate at that point . So i would think is very hard to work out any true stall speed in a high bank turn in a nose down decent . It's more a case of measuring the minimum speed the controls work at as you are not maintaining high . Speed ,angle of attack and wing area gives you minimin level fight speed (stall speed ) Dan

 

 

[kaz3g]

True, but secondary to the point. Bank angle alone does not increase the g loading, or the stall speed. :)

Being banked because you are turning the aircraft fairly rapidly from a short, tight base onto final, irrespective of whether the aircraft is also descending and in a slipped condition, does increase the g loading and consequently the stall speed. Hit some wind shear about the same time and something exciting is almost bound to happen.

 

I should add that in a descending turn it is the bottom wing which stalls first but in a climbing turn under power it will be the top wing which gives a really interesting outcome for those caught unawares.

 

Kaz

 

 

[facthunter]

You always have a one "G" load plus something that changes the direction of travel unless you are accelerating downwards. At 32 fps/per second, you are weightless. Nev

 

 

[kaz3g]

Sorry Nev...did you edit or am I just too old?

 

Kaz

 

 

[facthunter]

That's the acceleration required.. (What you get freefall in a vacuum) Nev

 

 

[kaz3g]

That's the acceleration required.. (What you get freefall in a vacuum) Nev

I missed your second per second:im stupid:

 

 

[facthunter]

You are forgiven. Nev

 

 

[motzartmerv]

Being banked because you are turning the aircraft fairly rapidly from a short, tight base onto final, irrespective of whether the aircraft is also descending and in a slipped condition, does increase the g loading and consequently the stall speed.Kaz

Why?

 

 

[kaz3g]

Why was I turning rather rapidly from base onto final? Because I did a very tight circuit to fit into a slot while a number of others were also in line to do their spot landings.

 

That left me high and close and that meant I had to descend quickly (flaps and slip) and turn quickly (more bank). Wasn't very pretty and I picked up too much speed when I shoved the nose down which then had me float over the mark.

 

Kaz

 

 

[Happyflyer]

I should add that in a descending turn it is the bottom wing which stalls first but in a climbing turn under power it will be the top wing which gives a really interesting outcome for those caught unawares.Kaz

When I stall an aircraft in a climbing turn and I am in balance neither wing drops, just the nose. When I stall it in a climbing turn out of balance with too much bottom rudder the lower wing drops and if I have too much top rudder the higher wing drops. I would think a more powerful engine and bigger propeller may affect this and the wing drop will be more pronounced depending on the direction of rotation of the prop.

 

 

[planesmaker]

When para dropping in c182, descent with power on at 65kt full flap and 80' bank angle, balanced turn. Aircraft will maintain that condition hands off with a high decent rate. Stall "speed " is a misnomer, it stalls at a particular AofA, we use the ASI as a measure of AoA in flight at 1g if more than 1g stall " speed" increases but unfortunately we don't have g meters and quick brains to work out the new stall speed accurately, add unbalanced turn and things do get complicated. An AofA meter would be the way to go. Tom

 

 

[facthunter]

Happy flyer,the right amount of rudder will counteract the prop effect. The higher nose attitude will normally make the wing drop more rapid. IF you have a really powerful motor, and large prop, you may run out of aileron and rudder. Nev

 

 

[motzartmerv]

Why was I turning rather rapidly from base onto final? Because I did a very tight circuit to fit into a slot while a number of others were also in line to do their spot landings.That left me high and close and that meant I had to descend quickly (flaps and slip) and turn quickly (more bank). Wasn't very pretty and I picked up too much speed when I shoved the nose down which then had me float over the mark.

 

Kaz

No, I meant why does the stall speed increase in the turn you described?

 

 

[kaz3g]

Because of the increasing angle of attack of the wings until past the critical angle brought about by the increased rate of turn which was achieved by increasing angle of bank which inevitably meant that the angle of attack of the lower wing was greater than that of the top wing causing the bottom wing to stall first (and it did).

 

Kaz

 

 

[motzartmerv]

i thought you said 30 deg bank angle?

 

 

[rankamateur]

I find that hard to believe Kaz, I would be happy to have learned a tenth of what you have forgotten about flying.

 

 

[kaz3g]

Hi Merv

 

I was understating the rate of turn when I said:

 

"I was flying a right hand circuit as required and was much too high on a very tight base so I opened the barn doors and flew a curving base in a side slip. Nose pretty much level, tad below. Bit more than 30 deg bank..."

 

I made this a little clearer when I said in a following post that:

 

"...I was banking fairly hard to make the turn onto final as I side slipped as well."

 

A gently curved base and a little bit of a slip on final (Spitfire circuits ) actually give me a much better view of things than a square bash because there isn't any view over the nose while floating along at 45 Kn with the flaps hanging straight down. I'll try and take a photo once I throw off the nasty lurgie that has stuck with me for weeks.

 

Kaz