Post by: Just thinking on 28/07/2021 11:19:19
Post by: Bored chemist on 28/07/2021 11:21:56
https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/
Planes actually fly by pushing air down.
Post by: Just thinking on 28/07/2021 11:40:42
Planes actually fly by pushing air down.I will have to think long and hard about that. Thanks for the link I found that very interesting.
Post by: Bored chemist on 28/07/2021 12:20:27
Post by: Just thinking on 28/07/2021 12:36:53
https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svgThat is very true for initial tack off and for rapid clime but how can this work when inverted. And it can.
Post by: vhfpmr on 28/07/2021 15:04:42
Hold your hand flat, like a wing, and stick it out of the window of a moving car (without letting people think you're signalling a turn). You can feel the air pushing your hand up or down as you adjust the angle of attack.https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svgThat is very true for initial tack off and for rapid clime but how can this work when inverted. And it can.
Look at the strange attitude of the fuselage here because the pilot has had to keep the wing angle of attack the same in space, but reversed relative to the plane, the green line shows the horizontal, but the black line is where the horizontal normally lies when the plane is flying the right way up. If the pilot had kept the fuselage nearer horizontal, as it is when not inverted, the wings would have been pushing the plane toward the ground.
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Post by: Just thinking on 28/07/2021 15:35:18
Quote from: Bored chemist on Yesterday at 21:20:27Well done you have hit the nail on the head with only one little detail missing. With the plane inverted we will need to increase the power as there will be moor drag as the attack angle is increased and as a result of increased attack angle, the inverted wing is generating the low pressure to generate lift. So just as you described the hand out of the car window even a flat surface can produce lift. A flat surface is moor dependant on the positive pressure from the underside.
https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svg
That is very true for initial tack off and for rapid clime but how can this work when inverted. And it can.
Hold your hand flat, like a wing, and stick it out of the window of a moving car (without letting people think you're signalling a turn). You can feel the air pushing your hand up or down as you adjust the angle of attack.
Look at the strange attitude of the fuselage here because the pilot has had to keep the wing angle of attack the same in space, but reversed relative to the plane, the green line shows the horizontal, but the black line is where the horizontal normally lies when the plane is flying the right way up. If the pilot had kept the fuselage nearer horizontal, as it is when not inverted, the wings would have been pushing the plane toward the ground.
* Inverted.png (104.38 kB . 369x218 - viewed 7 times)
Post by: Petrochemicals on 28/07/2021 19:43:10
The wings on a stunt plane are designed to fly in Australia and the set to the fuselage are equal, the profile of the wing chord is the same, the angle on the fuselage is 90 degrees. This allows the economic and easy stunt antics. They are not the economy that Easy jet look for though.Inverted.png (104.38 kB . 369x218 - viewed 10524 times)
The thrust moves the plane forward, gravity makes the plane sink, as the thrust draws the plane from the nose the equal wing profile (chord) sinks downward, thusthe wing is not parrallell to the airflow, the wing is side on if you understand the exaggeration. The airflow then creates the lift. This is turbulence on the wing though and is inefficient and can lead to a stall and the falling from the sky (which I am assured planes do not do).
Basically on a normal wing it is a managed fall by the use of thrust. Very very inefficient.
Post by: alancalverd on 29/07/2021 15:19:44
Most Cessnas will not sustain inverted flight because the engines don't work upside down for very long. Even the 152 Aerobat is not certified for sustained inversion though you can push though a fair bit of negative g.
The standard Cessna wing has a very steep and asymmetric laminar-flow aerofoil and Fowler flaps, which give you optimum lift and drag control for getting in and out of small fields but aren't at all efficient when inverted.
Aircraft designed and rated for aerobatics, such as the Extra 300, have almost symmetric aerofoils and simple flaps (if any) so they work just as well at any orientation to the ground, plus a lot more power to weight ratio, and fuel and oil systems that work upside down. Likewise most fighters.
One of the problems of Spitfires and Hurricanes was the failure of the float carburettor in a steep dive or sustained inversion. Their opposition. ME109s and the like, had direct fuel injection. I never understood why the Merlin engine, and indeed most petrol-engined cars, did not adopt this vastly superior system, which only appeared in most small planes in the 1990s
Post by: Bored chemist on 29/07/2021 15:27:03
I never understood why the Merlin engine, and indeed most petrol-engined cars, did not adopt this vastly superior system, which only appeared in most small planes in the 1990sIt is unusual for cars to be driven upside down.
I'm trying to work out how you connect the fuel pipe to the tank in a way that still works if it's upside down.
I know one of the early approaches was a flexible pipe in the tank, with a weight on the end of it, but I'd like to think there's something more sophisticated.
Post by: alancalverd on 29/07/2021 15:40:54
That said, an aerobatic glider (e.g. Blanik L13) flies pretty well upside down without an engine.
Post by: Just thinking on 29/07/2021 16:18:09
How can a plane fly upside down? There are many wing designs and levels of aircraft performance but my post is aimed at the very basic level. Let's start with a basic Cessna aircraft it has the typical standard airfoil square wing the rounded tapering top surface of the wing is designed to reduce the air pressure and suck the wing up while the bottom surface of the wing compressors the air and pushes the wing up. So the big question is if the wing is designed to lift the aircraft how is it possible for the plane to invert its attitude and maintain level flight. So can you answer this tricky question or do I need to explain it to you?The Cessna 172 for example weighs in at close to one tone fully loaded one and a half ton so if the wing can lift this weight when inverted one would think that now we have one and a half ton of plane and over one and a half ton of inverted wing lift giving a total of over three ton of force pulling down so the question is how can these basic aircraft maintain inverted flight even for a very short time. The wing will have to generate over one and a half ton of lift when inverted this completely contradicts the basic principle and wing design for flight. But yet it can.
Post by: Just thinking on 29/07/2021 16:40:16
I'm trying to work out how you connect the fuel pipe to the tank in a way that still works if it's upside down.Maybe a type of slide valve with feed pipes top and bottom of the tank.
I know one of the early approaches was a flexible pipe in the tank, with a weight on the end of it, but I'd like to think there's something more sophisticated.
Post by: Bored chemist on 29/07/2021 16:59:24
so the question is how can these basic aircraft maintain inverted flight even for a very short time.By altering the angle of attack.
See above.
Post by: Just thinking on 29/07/2021 17:27:04
By altering the angle of attack.That is the main part angle of attack for the Cessna 172 we would need maximum forward velocity and full throttle then invert and hold with as much angle of attack as posable the increased angle will allow for greater positive pressure on the lower surface of the wing and generate a pore but just adequate negative pressure over the upper surface.
See above.
Post by: alancalverd on 29/07/2021 17:35:53
The C172 is not certified for sustained inverted flight for several reasons. Holding full throttle won't help because even with the latest IO-360 fuel injection motor the gravity-fed fuel and oil systems won't allow the engine to develop any power at all after a few seconds. You might even set fire to the engine compartment if you push all the buttons at once and roll an old O-320 carburettor model.
Of course things may have changed since I last flew a 172, five days ago, but the NACA2412 aerofoil has been pretty constant since 1955.
An aerobatically-certified aircraft will generate almost equal lift with the wing inverted because the aerofoil is almost symmetrical.
Post by: Bored chemist on 29/07/2021 17:45:46
" flies upside down badly until the engine realises it has no fuel supply" and
"power-dives"
Post by: Just thinking on 29/07/2021 17:49:05
An aerobatically-certified aircraft will generate pretty much equal lift with the wing inverted because the aerofoil is almost symmetrical.That is true the purpose design of the aerobatic plane it also has a lot moor engine power wing strength and typically relies on greater positive pressure and less negative pressure across the wing. But the fact remains that the 172 can fly inverted for those silly enuff to try.
Post by: alancalverd on 29/07/2021 17:58:18
See reply #10.
But I haven't inverted a glider for about 50 years, so maybe the laws of aerodynamics have changed.
Post by: Just thinking on 29/07/2021 18:09:07
But I haven't inverted a glider for about 50 years, so maybe the laws of aerodynamics have changed.The glider is reliant on thermal lift for the most part so this still remains true when inverted.
Post by: alancalverd on 30/07/2021 00:01:41
There are plenty of elementary texts on aerofoils, well worth studying before trying to explain it to others. I think it was part of the National Curriculum for 10-year-olds a few years ago.
Bored Chemist knows a lot more about aerodynamics than NASA, who keep designing asymmetric aerofoils in the mistaken belief that the upper surface has some influence on lift. You would think that they would have learned their lesson after 105 years and billions of dollars getting it wrong.
If you visit a science museum, beware! They will try to kid you that aeroplanes can fly and the world is not flat.
Post by: Just thinking on 30/07/2021 00:34:29
There are plenty of elementary texts on aerofoils, well worth studying before trying to explain it to others. I think it was part of the National Curriculum for 10-year-olds a few years ago.I'm not quite sure where you are going but I never questioned any of the many airfoils and wing designs that exist only that of the very simple Cessna 172 as an example of my question how can a plane fly inverted. And I think the question has been quite reasonably explained we all know that it starts with an increased angle of attack. ps Did you know that the boing 707 and your sweet concord have bean flown fully inverted at least in the process of a barrel roll.
Bored Chemist knows a lot more about aerodynamics than NASA, who keep designing asymmetric aerofoils in the mistaken belief that the upper surface has some influence on lift. You would think that they would have learned their lesson after 105 years and billions of dollars getting it wrong.
If you visit a science museum, beware! They will try to kid you that aeroplanes can fly and the world is not flat.
Post by: alancalverd on 30/07/2021 01:00:07
Post by: Petrochemicals on 30/07/2021 01:06:54
Drivel.Yes but that is up for debate whether a plane utilises the low pressure high pressure principle of boomerangs or the magnus effect, or whether a aeroplane simply planes the air, creating the pressure beneath the wing. Me personally believe the 2nd.
There are plenty of elementary texts on aerofoils, well worth studying before trying to explain it to others. I think it was part of the National Curriculum for 10-year-olds a few years ago.
Bored Chemist knows a lot more about aerodynamics than NASA, who keep designing asymmetric aerofoils in the mistaken belief that the upper surface has some influence on lift. You would think that they would have learned their lesson after 105 years and billions of dollars getting it wrong.
If you visit a science museum, beware! They will try to kid you that aeroplanes can fly and the world is not flat.
As to how a plane can fly upside down, think why a plane cannot fly upside down.
Post by: Just thinking on 30/07/2021 01:14:55
No, the angle of attack of a symmetric airfoil is the same whichever way up the plane is flying. The 707 and Concorde airfoils are almost symmetric. The C172 wing is highly cambered and asymmetric for max lift and low cruise speed. Combined with differential ailerons, Fowler flaps, and a faired strut, it really doesn't work well upside down. It's actually a much more complicated shape than the Boeing in cruise mode. Interestingly the 707 is quite a good glider: the airfoil has a very flat lift/drag curve over a wide range of speeds and a max of about 15:1 at 200kt, whereas the 172 maxes at around 8:1 at 65 kt and mimics a piano if you get it a few knots wrong.They are very interesting facts If you look closely at the footage of the 707 rolling you will notice that it plummets very quickly when inverted maybe just a case of little or no down elevator it was more of a corkscrew than a level barrel roll. Possibly the pilot did not want to over stress the airframe by torquing it.
Post by: Just thinking on 30/07/2021 01:38:02
Yes but that is up for debate whether a plane utilises the low pressure high pressure principle of boomerangs or the magnus effect, or whether a aeroplane simply planes the air, creating the pressure beneath the wing. Me personally believe the 2nd.I feel that there is more going on with the underside of the wing than credit is given. Think of it as a flat stone skipping on the water the faster a plane flys the more the air is like water ore another example waterskiing the wing of the plane is air skiing..
As to how a plane can fly upside down, think why a plane cannot fly upside down.
Post by: alancalverd on 30/07/2021 10:27:57
Yes but that is up for debate whether a plane utilises the low pressure high pressure principle of boomerangs or the magnus effect, or whether a aeroplane simply planes the air, creating the pressure beneath the wing. Me personally believe the 2nd.As you increase the angle of attack, the pressure below the wing obviously increases until α = 90°. But as shown in the video clip, when α > 15° or thereabouts, the flow over the upper surface becomes turbulent and, er, the lift decreases sharply, producing a stall condition.
Only an idiot, an aerodynamicist or a qualified flying instructor would conclude that this implies that the airflow over the upper surface contributes significantly to lift. A born genius like yourself knows that airplanes are held up by faith, magic, and the underside of the wing.
Thousands of fools all over the world are busy right now removing dew, frost or insects from the upper surfaces, and designing ever more "efficient" curves that clearly contribute nothing to controlled flight. O we of little faith!
Post by: alancalverd on 30/07/2021 10:31:48
As to how a plane can fly upside down, think why a plane cannot fly upside down.Eppur si muove (Galileo)
"Now raise the nose and roll 180" (Charlie Kovac DFC, who taught me how to do it)
Post by: alancalverd on 30/07/2021 10:44:07
Possibly the pilot did not want to over stress the airframe by torquing it.It's a serious consideration for transport aircraft. Most are rated for + 2.5 -1g, so don't like sustained inverted flight where the wing root stress is effectively -1g because there is no margin for error or gusts. I've seen a military KC135 tanker fly an aerobatic sequence (with empty tanks!) because the design and demonstrated limits are a bit wider (and the USAF is populated by lunatics) but it's not something you'd do with an airliner even if the seats were empty.
Most gliders are rated at +5 -3g and fighters go a lot further, so fly inverted quite happily. I think the Pitts Special biplane is stressed to ± 10g, by which time most pilots have lost interest in the proceedings.
Post by: Petrochemicals on 30/07/2021 11:21:13
An airplane is held up by the wing having an angle onto the oncoming air, thus planing it. If wings needed to be aerofoil, flat shape wings would now work but yet they do.Yes but that is up for debate whether a plane utilises the low pressure high pressure principle of boomerangs or the magnus effect, or whether a aeroplane simply planes the air, creating the pressure beneath the wing. Me personally believe the 2nd.As you increase the angle of attack, the pressure below the wing obviously increases until α = 90°. But as shown in the video clip, when α > 15° or thereabouts, the flow over the upper surface becomes turbulent and, er, the lift decreases sharply, producing a stall condition.
Only an idiot, an aerodynamicist or a qualified flying instructor would conclude that this implies that the airflow over the upper surface contributes significantly to lift. A born genius like yourself knows that airplanes are held up by faith, magic, and the underside of the wing.
Thousands of fools all over the world are busy right now removing dew, frost or insects from the upper surfaces, and designing ever more "efficient" curves that clearly contribute nothing to controlled flight. O we of little faith!
The stall demonstrated is the leaking of air from beneath the wing to the top of the wing which creates destructive turbulence, due to the angle and trim that is required upside down and the lack of thrust capability that is required to summount this turbulence that most planes exhibit, this is why the planes have a bit of trouble flying upside down.
They also remove rivets from wings, as well as barn doors and gremlins as the efficiency tends to drop.
Post by: alancalverd on 30/07/2021 13:57:23
The stall demonstrated is the leaking of air from beneath the wing to the top of the wing which creates destructive turbulence, due to the angle and trim that is required upside down and the lack of thrust capability that is required to summount this turbulence that most planes exhibit, this is why the planes have a bit of trouble flying upside down.Air leaking through solid aluminum. Never thought of that before.
Perhaps it's the high pressure air creeping round to fill the low pressure area above the wing, but you have stated that there is no pressure reduction above the wing. And the air above the wing is still moving backwards at 50 - 70 kt in the video.
Those fools who run wind tunnels and design airplanes, cars and golf balls talk about boundary layer separation, but what do they know about fluid dynamics?
We do control leakage with spoilers, but these are fitted at the maximum camber and open both above and below the wing. Mostly on gliders and other very high performance aerofoils. They reduce lift and increase drag, but don't induce a stall.
Post by: Bored chemist on 30/07/2021 18:14:38
They also remove rivets from wings, as well as barn doors and gremlins as the efficiency tends to dropThanks for sharing.
Post by: Just thinking on 30/07/2021 18:44:52
Quote from: Petrochemicals on Yesterday at 20:21:13If you live close to an airport it drops the price of real estate but that's better than some places where planes only drop bombs.
They also remove rivets from wings, as well as barn doors and gremlins as the efficiency tends to drop
Thanks for sharing.
Post by: Petrochemicals on 30/07/2021 20:22:11
speed holes alanThe stall demonstrated is the leaking of air from beneath the wing to the top of the wing which creates destructive turbulence, due to the angle and trim that is required upside down and the lack of thrust capability that is required to summount this turbulence that most planes exhibit, this is why the planes have a bit of trouble flying upside down.Air leaking through solid aluminum. Never thought of that before.
Perhaps it's the high pressure air creeping round to fill the low pressure area above the wing,sounds like capitulation
but you have stated that there is no pressure reduction above the wing. And the air above the wing is still moving backwards at 50 - 70 kt in the video.No I didn't, if a falling object creates a bow wave of pressure, it has to create negative pressure to the stern, or rear., the area it has just passed through., something to do with vacuum creation.
Post by: alancalverd on 31/07/2021 00:08:05
If you live close to an airport it drops the price of real estate but that's better than some places where planes only drop bombs.We had to defend the noise of a gliding club when a new neighbor complained to the local magistrates. He had just bought a house 100 yards from the end of the main runway. Magistrate read the deposition then said "The reason you can buy any house you like is because, among other things, this has been an active airfield since 1939. Case dismissed."
Post by: Bored chemist on 31/07/2021 00:13:27
Post by: alancalverd on 31/07/2021 00:13:53
something to do with vacuum creation.But that would create lift from the upper surface, which you and BC do not believe in.
Fortunately, modern cars don't use carburettors, which rely on the same (Bernouilli) principle as the upper surface of a wing. Just as well because you tell me that the laws of physics have changed and Bernouilli no longer applies. I must get rid of the carb on the old Cessna - it's hard enough to fly with only half the wing generating lift, and if the carb doesn't suck petrol, we are doomed.
Post by: Bored chemist on 31/07/2021 13:50:35
and BC do not believe in.That's not what I said...
Post by: Just thinking on 31/07/2021 14:02:03
Quote from: Petrochemicals on Today at 05:22:11In a normally aspirated engine is the air sucked in or pushed into the carburetor.
something to do with vacuum creation.
But that would create lift from the upper surface, which you and BC do not believe in.
Fortunately, modern cars don't use carburettors, which rely on the same (Bernouilli) principle as the upper surface of a wing. Just as well because you tell me that the laws of physics have changed and Bernouilli no longer applies. I must get rid of the carb on the old Cessna - it's hard enough to fly with only half the wing generating lift, and if the carb doesn't suck petrol, we are doomed.
Post by: Bored chemist on 31/07/2021 14:57:14
In a normally aspirated engine is the air sucked in or pushed into the carburetor.Anywhere except a physics classroom, the fuel an air are sucked through the carburettor.
In a physics classroom, the external air pressure pushes fuel and air into the carburettor.
Post by: Just thinking on 31/07/2021 15:05:09
Quote from: Just thinking on Yesterday at 23:02:03I always considered it both as we cant have high pressure without low pressure so one works with the other to move air.
In a normally aspirated engine is the air sucked in or pushed into the carburetor.
Anywhere except a physics classroom, the fuel an air are sucked through the carburettor.
In a physics classroom, the external air pressure pushes fuel and air into the carburettor.
Post by: alancalverd on 31/07/2021 15:41:07
We use the word "sucked" to distinguish it from a single-point injection carb, where a pump forces fuel into an unrestricted throat.
We also tend to use "suck" to distinguish ambient carbs from supercharged units where an auxiliary compressor (sometimes called a blower) raises the input air pressure above ambient.
Post by: Just thinking on 31/07/2021 15:57:35
The essential component of a draught carburettor is its venturi - a narrowing of the throat. Air flowing through the throat speeds up in the restriction, so the local static pressure is lower than ambient and fuel is sucked into the flow.The purpose of the venturi is to increase the velocity of the air and fuel mix to the combustion chamber for better response.
Post by: Bored chemist on 31/07/2021 16:02:00
The essential component of a draught carburettor is its venturi - a narrowing of the throat. Air flowing through the throat speeds up in the restriction, so the local static pressure is lower than ambient and fuel is sucked into the flow.And in all three uses, if you used the word in a physics class, you would be berated for it.
We use the word "sucked" to distinguish it from a single-point injection carb, where a pump forces fuel into an unrestricted throat.
We also tend to use "suck" to distinguish ambient carbs from supercharged units where an auxiliary compressor (sometimes called a blower) raises the input air pressure above ambient.
The purpose of the venturi is to increase the velocity of the air and fuel mix to the combustion chamber for better response.
No, it's so the Bernoulli effect drops the pressure. so that the external pressure can push fuel into the mixture.
Post by: Just thinking on 31/07/2021 16:17:26
No, it's so the Bernoulli effect drops the pressure. so that the external pressure can push fuel into the mixture.Not really as the carburetors throttle butterfly is at the upper side of the venturi and the fuel jet and the butterfly is more restrictive than the venturi so the venturi only comes into effect during full throttle to assist with the high demand of high RPM.
Post by: Petrochemicals on 31/07/2021 18:54:56
I think you are confusing me with someone else. How much upward lift do you think a wing creates, given that all around it is air? Secondly why does air need to travel faster over a wing anyway, it is because they are quantum entangled? If you take the low road and I take the high road, you may be in Scotland before me, only if you left at the same time or later, there are people who took the high road and are already by lock lomond before you even left. The high road has more people on it because it is longer, but traffic pressure is the same on both roads. However as the high road has a steep decent the traffic pressure on it is less as the gradient causes the traffic to rush. In fact the gradient is very steep and if you fall you may tumble and bump other traffic, then the low road traffic may have to come up to the high road descent to ensure that all is OK, but this creates terrible congestion on the low road descent.something to do with vacuum creation.But that would create lift from the upper surface, which you and BC do not believe in.
Fortunately, modern cars don't use carburettors, which rely on the same (Bernouilli) principle as the upper surface of a wing. Just as well because you tell me that the laws of physics have changed and Bernouilli no longer applies. I must get rid of the carb on the old Cessna - it's hard enough to fly with only half the wing generating lift, and if the carb doesn't suck petrol, we are doomed.
Post by: alancalverd on 01/08/2021 00:27:20
And in all three uses, if you used the word in a physics class, you would be berated for it.Have you ever drunk anything through a straw? Or maybe sat in the cockpit of an aeroplane and wondered what that instrument labelled "suction" actually measures? How does your diaphragm work?
Nobody gets berated for telling the obvious truth in my classes.
Post by: alancalverd on 01/08/2021 00:38:26
the carburetors throttle butterfly is at the upper side of the venturi
Before the next lecture, I recommend you study the diagram of a carburetor and pay attention to the direction of the airflow arrows. Remember most flat-four aircraft engines use an updraft carb. that To avoid meeting the Grim Reaper (or worse, failing Airframes and Engines Part 1), be careful not to confuse the choke valve with the throttle butterfly.
Post by: alancalverd on 01/08/2021 00:51:26
How much upward lift do you think a wing creates, given that all around it is air?Cessna 172, just over a tonne in level flight. Blanik, about half that (either way up). AN225, 640 tonnes. There being nothing else around but moving air, and since neither aircraft stays aloft if it's not moving, one must assume that it's something to do with the motion of air.
Admittedly Aristotle thought otherwise, but as his log book does not record any actual flights I do not consider him an authority on aerodynamics.
Post by: Just thinking on 01/08/2021 01:10:08
Before the next lecture, I recommend you study the diagram of a carburetor and pay attention to the direction of the airflow arrows. Remember most flat-four aircraft engines use an updraft carb. that To avoid meeting the Grim Reaper, be careful not to confuse the choke valve with the throttle butterfly.Simple steps for carburetor operation Step 1. at idle the manifold pressure is very low as the throttle butterfly is closed to idle at this point the idle fuel jet is in operation below the throttle butterfly step 2. Don't forget the choke if it is cold it will open the throttle a little to raise the idle speed and chock the carburetor chamber raising the pressure pulling in moor fuel. Step 3. Don't forget to turn the choke off after a short time or you will be low on power waste fuel and foul the plugs. Step 4. give it full throttle the manifold pressure will drop but the venture in the carburetor will maintain the pressure to drag/suck the fuel in via the main jet. See it wasn't so hard. OK we will have our morning tea brack now after the brack we will discuss shut down procedures. Don't forget Tuesday parachute instructions you may need them I will remind you again at the end of today's lessons.
Post by: Bored chemist on 01/08/2021 11:42:42
It is always interesting to listen to experts who know more about something than the people who design, teach and do it. Maybe they would like to explain why a bumble bee can't fly.And the point made by physics teachers remains valid.And in all three uses, if you used the word in a physics class, you would be berated for it.Have you ever drunk anything through a straw? Or maybe sat in the cockpit of an aeroplane and wondered what that instrument labelled "suction" actually measures? How does your diaphragm work?
Nobody gets berated for telling the obvious truth in my classes.
A vacuum isn't anything, so it can't do anything.
In particular, it can't suck.
The atmospheric pressure pushed the drink up the straw.
In addition to the other problems you would face, you couldn't suck a drink through a straw if you were in a vacuum.
Post by: alancalverd on 01/08/2021 18:10:31
In addition to the other problems you would face, you couldn't suck a drink through a straw if you were in a vacuum.There's a subtle clue in the word "airplane".
Post by: Bored chemist on 01/08/2021 18:12:51
Do you plan to explicitly list all the things I just abbreviated toIn addition to the other problems you would face, you couldn't suck a drink through a straw if you were in a vacuum.There's a subtle clue in the word "airplane".
In addition to the other problems you would face,or should we just take them as read?
Post by: alancalverd on 01/08/2021 18:22:25
Post by: Just thinking on 01/08/2021 22:12:15
Post by: Bored chemist on 01/08/2021 22:38:56
What is the piston doing to the air-fuel mixture?Getting out of the way.
Post by: Just thinking on 01/08/2021 22:46:35
Post by: Bored chemist on 01/08/2021 23:19:57
One could compare a gun firing the bullet is pushed out by high pressure not so much sucked out by low pressure.Do you know what "the induction stroke" means?
Post by: Just thinking on 01/08/2021 23:51:05
Do you know what "the induction stroke" means?Yes, it is the intake stroke just before the compression stroke then the firing stroke, and last the exhaust stroke. providing that we are referring to a four stroke engine.
Post by: Petrochemicals on 02/08/2021 01:20:49
Post by: Just thinking on 02/08/2021 01:29:45
Does an aeroplane engine push or pull, if it pushes it would need to compress the air, yet if it pulls the outflow is inconcequential. A propellor, relies on pushing. The gaseous nature of air means it is far more likely to fill the void in a non directional manner than being ejected in a non directional manner, especially if the power unit is travelling forward.If you stand in front of a propeller you will be sucked in and stand at the back of a propeller you will be blown away. So we have suck and push. We could say it's the two sides of one coin.
Post by: Bored chemist on 02/08/2021 10:03:57
And, in what way do you think t resembles a gun firing?Do you know what "the induction stroke" means?Yes, it is the intake stroke just before the compression stroke then the firing stroke, and last the exhaust stroke. providing that we are referring to a four stroke engine.
Post by: alancalverd on 02/08/2021 10:07:33
If you measure the pressures around an aerofoil at a positive angle of attack, you find the pressure above to be negative and below to be positive.
With a complex aerofoil like Cessna's NACA2412 the upper surface force is about 3 times the lower surface force in the region of normal flight, say 3° < α < 10°. This makes it very difficult to fly inverted (even if the plane was stressed to do so) as the wing does its best to pull you downwards until it is very close to the stall angle (α > -15°).
A simple symmetric aerofoil generates the same lift either way up (definition of "symmetric"). The only essential difference in a practical airplane is the angle of incidence (the angle between the wing chord and the longitudinal axis of the fuselage) which is close to zero for an aerobatic monoplane like the Extra, and the offset between the AOI of the wing and the stabiliser (can be zero for an "all-flying tail" or a canard). Problem with setting both AOIs to zero and using two symmetric aerofoils is the reduced pitch stability, which is why you might want to show off in an Extra, but take your family on holiday in a Cessna.
Post by: Bored chemist on 02/08/2021 10:22:25
I think I have found BC's problem.Yes, my "problem" is that I remember what I was taught at school.
There is no such thing as a negative pressure; Molecules hitting a surface push on it; they can not pull.
You can measure differences in pressure from any datum you choose.
But pressures are, in fact, positive.
So...
If you measure the pressures around an aerofoil at a positive angle of attack, you find the pressure above to be negative and below to be positive.No.
These pressures will all be positive; some more so than others.
Post by: Just thinking on 02/08/2021 10:59:36
And, in what way do you think t resembles a gun firing?[/quote TheAnd, in what way do you think t resembles a gun firing?The intake stroke of the engine is the minus presser the outside presser is the positive presser flip the coin and in the gun, the firing is the positive presser and the outside presser is the minus presser same thing in reverse. Internal vs external.
Post by: alancalverd on 02/08/2021 11:46:43
There is no such thing as a negative pressure;There is no such thing as negative money, but lots of people and businesses have overdrafts, or commitments greater than their current asset values. The concept of negative numbers is very useful.
The attraction of "zero ambient pressure" fluid dynamics is that you can use the same analysis over a range of ambient pressures. Not hugely important (but still convenient) with liquids but for practical aviation purposes lift = ½ρAClv2 where v is true air speed. Since indicated air speed u is inversely dependent on air density ρ, the lift generated by a subsonic wing in normal (non-stalled) flight is thus simply related to the indicated air speed at any altitude, making life a lot easier when calculating required and limiting bank angles.
Apart from French, Latin, rugby and cricket, most of what I learned in school turned out to have little practical use. A bit more German might have been handy.
Post by: Just thinking on 02/08/2021 11:53:11
Post by: Bored chemist on 02/08/2021 11:56:41
The concept of negative numbers is very useful.I know a mathematician who really didn't like negative numbers.
He would stop at nothing to avoid them.
However, all pressures are still positive and a vacuum can't suck.
Post by: Just thinking on 02/08/2021 12:08:51
However, all pressures are still positive and a vacuum can't suck.That makes sense high presser has authority over the presser that is lower.
Post by: alancalverd on 02/08/2021 12:10:03
The curved surface of the aerofoil is corrupted in inverted flight and acts as a flat surface
Corruption is a (frequently fatal) problem with Rogallo wings in negative g, but the shape of a rigid airfoil shouldn't change when it's inverted. And again you are only considering asymmetric airfoils - a symmetric wing (e.g. NACA 0010) works exactly the same either way up. I think "rigid sail" boats use a symmetric foil so they can tack into wind.
And if you want to get really complicated, try https://www.scienceabc.com/eyeopeners/can-helicopter-fly-upside.html
Post by: Just thinking on 02/08/2021 12:16:34
Corruption is a (frequently fatal) problem with Rogallo wings in negative g, but the shape of a rigid airfoil shouldn't change when it's inverted. And again you are only considering asymmetric airfoils - a symmetric wing (e.g. NACA 0010) works exactly the same either way up. I think "rigid sail" boats use a symmetric foil so they can tack into wind.In normal flite the airfoil works as intended but if we over rotate the upper surface will lose lift so when inverted the upper surface now at the bottom is over rotated and loses lift so becomes a surface that gains a positive presser.
And if you want to get really complicated, try https://www.scienceabc.com/eyeopeners/can-helicopter-fly-upside.html
Post by: alancalverd on 02/08/2021 12:32:23
Post by: Just thinking on 02/08/2021 12:44:01
Still depends on what was "intended". A Cessna 172 is designed to get in and out of short fields and cruise sdately qatThat may well be true but if we look at a simple example let's say a plank of wood 8x1 if we place that in a wind tunnel and including the surface to the airflow it will generate lift and that is with no aerofoil at all. The braking airflow over the top will generate lift and the bottom surface will pick up the airflow and react to the positive pressure that it is being exposed to.
Post by: alancalverd on 02/08/2021 12:55:16
Post by: Bored chemist on 02/08/2021 13:12:23
Anything that deflects the wind is an airfoil, but some are better than others. If you sharpen the leading edge of your plank, you won't be far from an F104 wing!I forget the details, but there is a quote which says something like "A tea-tray will fly if you put a jet engine on it."
It looks like they checked.
Post by: Just thinking on 02/08/2021 13:15:32
Anything that deflects the wind is an airfoil, but some are better than others. If you sharpen the leading edge of your plank, you won't be far from an F104 wing!Bingo, see that's the basic fundamentals of any wing only the increased aerofoil is for lower speed but still can work when pushed in the inverted with the increased angle of attack.
Post by: Bored chemist on 02/08/2021 13:27:41
Planes actually fly by pushing air down.
Anything that deflects the wind is an airfoil,Snap!
Post by: Just thinking on 02/08/2021 14:15:53
Post by: alancalverd on 02/08/2021 16:11:43
The upper surface does not push anything down, but contributes 60 - 70% of the lift.Planes actually fly by pushing air down.Anything that deflects the wind is an airfoil,Snap!
Post by: Bored chemist on 02/08/2021 16:19:20
The upper surface does not push anything down, but contributes 60 - 70% of the lift.Not really.
It may well provide 70% of the pressure difference.
There isn't a mechanism for the air molecules to pull on it and lift it.
Post by: alancalverd on 02/08/2021 16:20:48
Bingo, see that's the basic fundamentals of any wing only the increased aerofoil is for lower speed but still can work when pushed in the inverted with the increased angle of attack.Except that single-surface and steep-camber foils (Rogallo wing, yacht sail, Wright airfoil, most bird wings, wind turbine) may stall before they produce positive lift if inverted.
Post by: alancalverd on 02/08/2021 16:22:03
Not really.So if we have a flat upper surface, the wing will generate as much lift as a curved one? Why don't airplane designers (or birds) know this?
Apropos tea trays, "flies like a piano" is a common insult, originally ascribed to Hanna Reitsch. Interestingly the German slang for a grand piano is "flugel" because it looks just like a pigeon wing. So at least one Nazi had a sense of humor.
Post by: Just thinking on 03/08/2021 10:54:14
So if we have a flat upper surface, the wing will generate as much lift as a curved one? Why don't airplane designers (or birds) know this?Bats have strange wings but they flap them very fast. When birds fly their wings move like the motion of pedaling a boat.
Apropos tea trays, "flies like a piano" is a common insult, originally ascribed to Hanna Reitsch. Interestingly the German slang for a grand piano is "flugel" because it looks just like a pigeon wing. So at least one Nazi had a sense of humor.
Post by: alancalverd on 03/08/2021 12:10:32
When birds fly their wings move like the motion of pedaling a boat.Exactly the error that led to the deaths of many aviation pioneers. All birds flap their wings to take off, but those that fly furthest and longest hardly move their wings at all once they are airborne. Whilst brave but unobservant souls played with ornithopters, Cayley, Chanute and Lilienthal experimented with rigid gliders, as did the Wrights until they had developed a sufficiently light engine.
How do birds do it? Asymmetric airfoils! Why don't birds fly upside down? Asymmetric airfoils!
Bats actually alternate between powered and gliding flight, but most insects rely on continuous rowing action of a fairly flat wing.
Post by: Bored chemist on 03/08/2021 12:52:18
Why don't airplane designers (or birds) know this?They might.
A better question is why don't you understand Newton's 3rd law.
You can't exert an upward force on the plane without exerting a downward force on something else.
Why don't birds fly upside down?
Why don't ...birds) know this?The birds, as usual, know better than the pilot.
Post by: Petrochemicals on 03/08/2021 13:32:25
It is to negate the stall . They may generate as much lift but due to the characteristics of airflow, much of the lift would be lost due to turbulence on the wing following edgeNot really.So if we have a flat upper surface, the wing will generate as much lift as a curved one? Why don't airplane designers (or birds) know this?
https://en.m.wikipedia.org/wiki/Stall_(fluid_dynamics)
If wings generate lift by low pressure why do aeroplanes not travel with wings parallel to the motion of flight. As you know this would reduce drag by a great amount.
As for the designers who know so much, they took 60 years to develop wingtip to negate that pesky drag from high pressure wing tip vortices thus increacing efficiency 20 percent. If any side during Ww2 had invented these they would have won the war for sure.
https://en.m.wikipedia.org/wiki/Wing_tip#:~:text=A%20wing%20tip%20(or%20wingtip,Squared-off
Post by: alancalverd on 03/08/2021 13:57:45
Petrochemicals: look at the pressure distribution of a practical airfoil at various angles of attack. Apologies for the long reference but it's a very good diagram: https://www.bing.com/images/search?view=detailV2&ccid=BQBH2y3M&id=4D0E3B5E4D74833FC98EFF8F5E5831012152F50F&thid=OIP.BQBH2y3MxFErOvjegxoFCAHaFj&mediaurl=https%3a%2f%2fwww.learnpick.in%2fuserfiles%2fresources_conversion_files%2fpresentation_aero_lab_ppt_2_1463470542_205162-14.jpg&cdnurl=https%3a%2f%2fth.bing.com%2fth%2fid%2fR.050047db2dccc4512b3af8de831a0508%3frik%3dD%252fVSIQExWF6P%252fw%26pid%3dImgRaw%26r%3d0&exph=2250&expw=3000&q=Airfoil+Pressure+Distribution&simid=607997099557851178&FORM=IRPRST&ck=49A29C9DD2065B6908EEE8F8E712DEA3&selectedIndex=8&ajaxhist=0&ajaxserp=0
As for winglets
Quote
The initial concept dates back to 1897, when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices.Practical implementation, as with all things aviational, depends on compromise and getting a nice smooth curve with an acceptable strength/weight ratio does require some clever materials engineering. I can't find your "20%" figure but Cessna certainly fitted droop tips in the 1950s to improve low speed handling.
Post by: alancalverd on 03/08/2021 14:11:29
The birds, as usual, know better than the pilot.An interesting clip, but one wing beat doesn't equate to sustained inverted flight. Some pigeons tumble in flight (it's a genetic defect), and swifts in particular are unstable in roll (negative glide dihedral) which makes them very agile, but they don't spend more than a beat inverted.
Post by: Bored chemist on 03/08/2021 14:24:06
Ask the hummingbirds.The birds, as usual, know better than the pilot.An interesting clip, but one wing beat doesn't equate to sustained inverted flight. Some pigeons tumble in flight (it's a genetic defect), and swifts in particular are unstable in roll (negative glide dihedral) which makes them very agile, but they don't spend more than a beat inverted.
Post by: alancalverd on 03/08/2021 17:12:28
Post by: Petrochemicals on 03/08/2021 19:18:20
Petrochemicals: look at the pressure distribution of a practical airfoil at various angles of attack. Apologies for the long reference but it's a very good diagram: https://www.bing.com/images/search?view=detailV2&ccid=BQBH2y3M&id=4D0E3B5E4D74833FC98EFF8F5E5831012152F50F&thid=OIP.BQBH2y3MxFErOvjegxoFCAHaFj&mediaurl=https%3a%2f%2fwww.learnpick.in%2fuserfiles%2fresources_conversion_files%2fpresentation_aero_lab_ppt_2_1463470542_205162-14.jpg&cdnurl=https%3a%2f%2fth.bing.com%2fth%2fid%2fR.050047db2dccc4512b3af8de831a0508%3frik%3dD%252fVSIQExWF6P%252fw%26pid%3dImgRaw%26r%3d0&exph=2250&expw=3000&q=Airfoil+Pressure+Distribution&simid=607997099557851178&FORM=IRPRST&ck=49A29C9DD2065B6908EEE8F8E712DEA3&selectedIndex=8&ajaxhist=0&ajaxserp=0I am not saying there is not negative pressure, if you bludgeon air out of the way you tend to get it, but it relies on the angle of the lower surface, set it to parallel and you get positive pressure ontop of the wing.
IYes, 1897 to
As for wingletsQuoteThe initial concept dates back to 1897, when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices.Practical implementation, as with all things aviational, depends on compromise and getting a nice smooth curve with an acceptable strength/weight ratio does require some clever materials engineering.
Quote
which was rolled out in 1990that's an engineering circle that certainly is beyond reproach
Post by: Just thinking on 04/08/2021 01:25:53
Quote from: Just thinking on Yesterday at 19:54:14Yes, birds flap their wings for powered flight and if all goes well they can then glide I have noticed that at a high elevation and in cold arias that the birds need to work harder to maintain flight no dought due to thinner air and lack of thermals. many fools have plummeted to their death trying to do what only a bird can do.
When birds fly their wings move like the motion of pedaling a boat.
Exactly the error that led to the deaths of many aviation pioneers. All birds flap their wings to take off, but those that fly furthest and longest hardly move their wings at all once they are airborne. Whilst brave but unobservant souls played with ornithopters, Cayley, Chanute and Lilienthal experimented with rigid gliders, as did the Wrights until they had developed a sufficiently light engine.
How do birds do it? Asymmetric airfoils! Why don't birds fly upside down? Asymmetric airfoils!
Bats actually alternate between powered and gliding flight, but most insects rely on continuous rowing action of a fairly flat wing.
Post by: alancalverd on 04/08/2021 09:30:50
Post by: Just thinking on 04/08/2021 09:45:03
Depends on local circumstances. Desert vultures ride dry thermals up to around 12,000 ft and Andean condors soar in ridge and wave lift to over 18,000 ft. Flapping at high altitude is actually difficult because it demands a lot of oxygen and although birds have amazingly efficient lungs, they don't have superchargers, so large carrion-eaters tend to be good gliders. Little point in a raptor flying high because the prey will have run away by the time he has descended!A little bit of the topic but in Australia, they think that the wedge tail eagle which is very much like the American bald eagle can see a rabbit from 6000 feet and come down for lunch.
Post by: Bored chemist on 04/08/2021 10:56:27
Little point in a raptor flying high because the prey will have run away by the time he has descended!This is why we use the phrase "eagle eyed" for people who are shortsighted... or not.
Post by: Just thinking on 04/08/2021 11:15:29
Quote from: alancalverd on Today at 18:30:50I think I will start a new topic/ post on just what the smallest object the human eye can see and this will depend on the object the light and the background contrast and whether or not the object is moving.
Little point in a raptor flying high because the prey will have run away by the time he has descended!
This is why we use the phrase "eagle eyed" for people who are shortsighted... or not.
Post by: Bored chemist on 04/08/2021 11:18:54
That could be a very short thread.Quote from: alancalverd on Today at 18:30:50I think I will start a new topic/ post on just what the smallest object the human eye can see and this will depend on the object the light and the background contrast and whether or not the object is moving.
Little point in a raptor flying high because the prey will have run away by the time he has descended!
This is why we use the phrase "eagle eyed" for people who are shortsighted... or not.
With brighter lighting.you could see what the camera "saw" here.
https://www.nationalgeographic.com/science/article/trapped-atom-photograph-long-exposure-competition-spd
Post by: alancalverd on 04/08/2021 11:31:11
Maximum human acuity is about 0.008°.
Post by: Bored chemist on 04/08/2021 12:56:19
Australia where the rabbit may be a long way from any cover so the bird can catch it in a lowlevel chase, but British rabbits tend to feed close to homeThe rabbits in Australia are British rabbits.
Both live in warrens.
Both hide from predators in the same way.
Post by: Just thinking on 04/08/2021 13:09:56
That could be a very short thread.That is very true we can see a star that is equivalent to a grain of sand at a distance of many tens of miles away due to the intense light that is emitted. Here on earth with the light that is available, we can see an object that is 6 inches in diameter at a distance of about 2 kilometers provided that the object is of a light color before a dark background and if the object is moving it will be easier to detect this is an extreme case taking into account perfect eye site.
With brighter lighting.you could see what the camera "saw" here.
https://www.nationalgeographic.com/science/article/trapped-atom-photograph-long-exposure-competition-spd
Post by: Bored chemist on 04/08/2021 13:11:11
Post by: Just thinking on 04/08/2021 13:28:59
If it is adequately lit, you can see a single atom at a million miles.I believe that is true. It is very interesting to me as to how light can reveal its self on such a fin level but it certainly can. I think some of the brighter stars are at that level of scale and we can see them with the naked eye.
Post by: Just thinking on 15/09/2021 14:27:49
Here's my little bit, too, JT:Thanks for that CC. yes we can get lift in many ways these days the fighter jet planes are more like rockets the way that they can fly. You make some interesting points regarding wing shape and the main reason for a plane with conventional wing design being able to fly inverted as you pointed out it is done by increst angle of attack and adequate engine power just don't forget that your elevator control is also reversed when inverted.
Post by: Bored chemist on 15/09/2021 14:31:09
I think some of the brighter stars are at that level of scaleThey are bigger than an atom.
Oddly, they may not look like it.
The well lit single atom, and the distant star are both diffraction limited dots.
The image you would see would be the limits of your eye rather than anything to do with the object.
Post by: Just thinking on 15/09/2021 14:55:22
The well lit single atom, and the distant star are both diffraction limited dots.I think I understand what your saying a star five light years away is like a golf ball at the distance of the moon we can never see the golf ball at that distance but if it was as hot as a star we will see its light. That is its diffracted and distorted light.
The image you would see would be the limits of your eye rather than anything to do with the object.
Post by: alancalverd on 15/09/2021 16:20:19
Quote
But/t, I have seen aerobatic biplanes fly just above the ground
perfectly horizontally, with no angle of attack!?
The angle of attack is the angle between the wing chord and the vector of motion. Not to be confused with the angle of incidence, which is the angle between the wing chord and longitudinal axis of the aircraft.
Most modern aerobatic planes are "taildraggers" with a small (maybe zero) angle of incidence but a high angle of attack when they start moving. This configuration is lighter than a tricycle undercarriage but is more difficult to handle on the ground.
A symmetrical aerofoil will generate the same lift either way up if the angle of attack is the same. Most explanatory diagrams show large AOAs to emphasise the contributions of the upper and lower surfaces and the effects of turbulence, but level flight may only involve a couple of degrees, so the aerobatic demonstrator may be flying with the wing chord very close to horizontal when inverted.
Post by: Just thinking on 16/09/2021 13:52:46
Planes normally do fly upside down Down Under.And we drive on the wrong side of the road upside down. The U.S. fly right side up and they drive on the right side of the road.LOL.
Post by: chris on 17/09/2021 13:03:08
Post by: Just thinking on 17/09/2021 13:45:33
This may help: https://www.thenakedscientists.com/articles/science-features/how-does-wing-workThanks, Chris this article goes a long way to explain the nature of lift and flight. I find it very interesting how the paper aeroplane can fly without the aid of aerofoil but this can be explained by the nature of weight to air density ratio with forward velocity even a ball can be projected the paper plane is aided by the curvature of the wing even if it is by slite change of forward and rear edge deformation. There are so many variations in aircraft wing design as there are so many variations in propulsion and power.
Post by: alancalverd on 17/09/2021 22:17:59
the paper aeroplane can fly without the aid of aerofoilNot true! A flat plate is an aerofoil, just not a very good one. At any nonzero angle of attack the leading edge develops turbulence over the upper surface, so it makes sense to smooth it into....well, a curve like a wing seems to work pretty well.....
Post by: Just thinking on 18/09/2021 07:03:16
Not true! A flat plate is an aerofoil, just not a very good one. At any nonzero angle of attack the leading edge develops turbulence over the upper surface, so it makes sense to smooth it into....well, a curve like a wing seems to work pretty well.....I guess there are many paper plain designs but the standard type works quite well with a tiny bit of slat and a little upward flap..