How do you know 'when' an aircraft has stalled?

[Powerin]

How can a tailplane stall if it is flat on both upper and lower surfaces and does not have an aerofoil section. Just asking.Alan.

You can even use a flat board as a wing. As long as it has a positive angle of attack in the required direction of lift it will fly. Mind you it will have very nasty stall characteristics and will probably stall at a fairly low AoA. Be it an aerofoil or a flat plate, when the airflow separates from the surface in the direction of lift, you lose the majority of that lift...ie it stalls.

 

 

[turboplanner]

You can even use a flat board as a wing. As long as it has a positive angle of attack in the required direction of lift it will fly. Mind you it will have very nasty stall characteristics and will probably stall at a fairly low AoA. Be it an aerofoil or a flat plate, when the airflow separates from the surface in the direction of lift, you lose the majority of that lift...ie it stalls.

Yes, you just need to add a heap of power until it works. Bernoulli is the one that lets you do the same thing with 80 hp

 

 

[J170 Owner]

This question was asked by Mr DJP and I have really enjoyed thinking about it. Just wish I had more time to research and study more on the subject.But what a good question - so I thought it would be something worth while discussing, hope you don't mind me pinching your question DJ!

When the angle of attack exceeds the angle for maximum lift?

 

 

[David Isaac]

Tubs, the fallacious part of the Bernouli theory is the part that claims the air over the top of the wing arrives at the trailing edge the same time as the air underneath the wing. In actual fact it arrives over the top before the air at the bottom arrives and a combination of Newtons laws and circulating currents as well as a bit of the half Venturi theory all contribute to the lift.

 

As to the answer to the original question I will stick to my original answer in post #10, because the only way you know you have exceeded the max A of A for the wing in one G flight is when the elevator reaches its stops or in more than 1 G flight when past the 'stall stick' position. Those of us that have done aerobatics know you can stall an aircraft in any attitude if you exceed the stall stick position, including in a vertical dive. When spinning with a steep nose down attitude the aircraft remains stalled for the whole descent. In some aircraft like the Piper Cub and the AAK Hornet in a 1G stall, you have to hawl the stick back with both hands just to get some sink. In other aircraft when in a fully developed stall at the critical A of A, such as a Cherokee 235, or a C182/180/185 all you need do is go to full power without changing your 'attitude' and they will climb out of the stall. Explain that one for another teaser.

 

 

[Guest ozzie]

[it seems the Flybetter books have just opened a 'can of worms' in Poland, with raging arguments on Newton Vs Bernoulli on their pilot chat sites. Almost 1.8 GB of hits on the website in the last couple of days.]

 

From this mornings Flybetter facebook post.

 

100 plus years of aviation and the boffins still can't work out the questions and answers.

 

 

[J170 Owner]

Seems to be a lot of physics experts on this forum!

 

 

[David Isaac]

So David Isaac, I was wondering why you like this?

Sorry Uncle Dave, I missed your question. I liked it because in a clean 1G stall that is exactly what happens. Both states must occur to be true in a 1G stall. Of course you could convert height into speed by lowering the nose without thrust and it has the same effect as thrust and that immediately alters the A of A so a stalled state no longer exists because the descent 'power' is more than drag even though lift will be less than weight on the descent.

I hope that makes sense.

 

 

[Guest davidh10]

... In other aircraft when in a fully developed stall at the critical A of A, such as a Cherokee 235, or a C182/180/185 all you need do is go to full power without changing your 'attitude' and they will climb out of the stall. Explain that one for another teaser.

The only thing that occurs to me is that the thrust line is such that it changes the attitude of the stalled aircraft as you add power and thus decreases the AoA below stall.

 

Those of us that have done aerobatics know you can stall an aircraft in any attitude if you exceed the stall stick position, including in a vertical dive.

A very important point, David. Some replies have been focussed solely on the S/L flight in calm conditions situation, but even in RAA aircraft, where aerobatics are not applicable, you can get chucked around in moderate to heavy turbulence to a degree that makes it difficult to rely on the simple "nose drop" or "wing drop" concepts. If the turbulence is such that the aircraft is not flying in a straight line, in any plane, then your only indication will be the response or lack thereof to control inputs.

 

Seems to be a lot of physics experts on this forum!

I don't profess to be an expert, but physics and chemistry were my favourite subjects, so my highest marks were in physics and chemistry. To contrast that, I failed English at one stage!

 

 

[shags_j]

I can't remember if it was the RA mag or one of the others but it had a long article on the myths of flight. Went through all the different theories and identified that, basically, while Bernoulli's principle may assist in flight, the true reason a wing flies is AoA. Higher Alpha, higher lift. Kind of follows from the Lift equation. Lift is a factor of a whole series of factors (AoA, Camber (read bernoulli's), Rho, Surface Area, Velocity).

 

Was a good article.

 

 

[fly_tornado]

Can someone who understands Bernoulli explain ground effect?

 

 

[turboplanner]

F-T Bernoulli has nothing to do with ground effect, it's just a half venturi. Air speeding up lowers in pressure.

 

Once you get close enough to the ground the downwash from the top of the wing traps the air your are flying over, compressing it, so pressure increases and increased pressure = more lift.

 

Not so effective in high wing aircraft because the wing never gets low enough to trap enough air.

 

 

[fly_tornado]

Maybe a diagram might help explain it a bit better?

 

 

[facthunter]

Adding power as David describes gives increase of forward speed. This will lower the angle at which the relative airflow meets the wing, so you may be unstalled immediately. I say may, because the propwash also makes the elevators/ rudder more effective, so it depends on what you are doing with them, AND the aircraft attitude. But let's not complicate matters. The quickest and most effective stall recovery ( minimum loss of height and controllable), will involve power and having the nose in exactly the right position. Nev

 

 

[turboplanner]

A very important point, David. Some replies have been focussed solely on the S/L flight in calm conditions situation, but even in RAA aircraft, where aerobatics are not applicable, you can get chucked around in moderate to heavy turbulence to a degree that makes it difficult to rely on the simple "nose drop" or "wing drop" concepts. If the turbulence is such that the aircraft is not flying in a straight line, in any plane, then your only indication will be the response or lack thereof to control inputs.

That's why I'm so disappointed it was a nothing question.

 

Many instructors only teach stalls straight and level without power and if you're lucky the more exciting with power, but indentifying what is going on in a steep turn or other abnormal action is where knowledge could save lives.

 

 

[turboplanner]

so far no one has explained what is actually happening to the aircraft when it is stalled, not approaching the stall, but when it is stalled!

I don't think they knew MM, some sort of screwed up question I think

 

 

[fly_tornado]

so far no one has explained what is actually happening to the aircraft when it is stalled, not approaching the stall, but when it is stalled!

the wing stops generating lift. what happens depends on your overall attitude when you stall.

 

 

[Guernsey]

the wing stops generating lift. what happens depends on your overall attitude when you stall.

I never stall because I always fly with a 'Positive Attitude'

 

Alan.

 

 

[fly_tornado]

[skeptic36]

Stall questions seem to invoke alot of different opinions , I get on a Supercub forum and the question was asked" what is a moose stall", it's been a few pages and the discussion rages .

That's easy, it's like at Flemington where they keep the horses before the races except they are wider to accommodate the antlers.

 

 

[fly_tornado]

So having resolved the stalling issue somewhat, can anyone explain why the half venturi effect that Turbo invented mentioned works? Why do the wingtip vortexs flow the direction they do. If my understanding of Bernoulli is correct they should flow the other way, ie onto the wing?

 

 

[turboplanner]

Forget it then F_T, you go and do your research and stop parasiting off us.

 

 

[Guernsey]

Well guys this has been a very interesting post indeed however in spite of all that has been posted I am going to keep my explanations that I have always used and use the KISS principle.

 

To explain how or why anything works when we come to aerodynamics is sometimes very difficult so I show HOW it works. I am sure that you have all used a piece of paper where you hang it from the top edge, bend it down towards you in a curve, similar to the leading edge of a wing and blown over the top of it. Bingo, the paper rises because of lift generated over the paper. Seeing is believing.

 

Ground effect...air is compressed between the wing and the ground creating a cushion of air. Simple explanations which, whilst not being entirely correct, will satisfy most students. The fact that it happens is more important than why unless of course you want to go into the aerodynamic physics of the whole thing then all of the above posts make very interesting studies.

 

I know that I am now going to get a barrage of differences of opinions as I get torn appart by some of you guys. Oh well, it is a forum after all.

 

For your information my best subjects at college were maths and physics and a group of us in my final year studied aerodynamics so I am amazed that nobody on this forum has even touched on the subject of the 'Lunar Effect '. No doubt you all know that it is the gravitational pull of the moon which causes our seas to rise and fall approx every six hours and that this varies in different parts of the world. Where I came from we had some of the largest tides in the world at certain times of the year ( 32 feet in the Bay of St. Malo ) where the Channel Islands are located. We therefore experimented with this gravitational pull on an aircraft and had remarkable results. We used a Jodel aircraft from the Guernsey Aero Club which is constructed of wood and fabric with no effects whatsoever, but when we used an all metal aircraft its rate of climb increased as the tide was coming up (more magnetic pull) and decreased when the tide was going down.

 

At the high tide the pull was the greatest and the reverse applied at low tide. Now to get back to stalling the same applied; if you stalled the aircraft when the tide was rising you could hold off the stall longer and the ultimate sink was less severe. We all talk about the ability to hold an aircraft 'on the prop' with power but nobody talks about holding the aircraft in the 'Lunar Effect', so next time you are trying to take off from a marginal airstrip, make sure you take off when the tide is coming up. Common sense after all.

 

I am absolutely amazed at some of you who suggest that you're experts when you have never heard of this.

 

The strength of the ' Magnetic Effect ' is inversely proportional to the square root of the strength of this article. .

 

Alan...the guy with natural magnetism.

 

 

[David Isaac]

Lunar effect alright Alan, and you are suffering from it ....... Expert luney

 

 

[Guernsey]

Well if I tick all of the boxes, does that make me a Lunartick.

 

Alan.

 

 

[turboplanner]

Well if I tick all of the boxes, does that make me a Lunartick.Alan.

You don't have to go to the trouble Alan.

 

Interesting what you said about the tides. In the book Area 51 they made a small mention of using the earth's magnetic lines for extra lift. I think the idea was the the U2's may get greater range. There was no mention of what the results were, but that's not surprising because they wouldn't let out a benefit like that during the Cold War.