Aerodynamics (was: fatality Poland 10 June 2023 WS possible hard opening)

1 hour ago, GoneCodFishing said:

That drawing breaks so many laws of physics that just looking at it my ocd is peaking to the point it'll creae northern lights visible in the whole of the northern hemisphere

There are many atavisms and myths in parachutes they are based on the "knowledge" of physics... The slider was invented for vertical openings because there were no others at that time. In horizontal opening, the body towing the parachute with its mass, forcing it to rise during deployment, like any wing. Like for paraglider or kite. A short pushing of the flow alongside the surface of the slider is enough for it to fall.

57 minutes ago, Veis said:

There are many atavisms and myths in parachutes they are based on the "knowledge" of physics... The slider was invented for vertical openings because there were no others at that time. In horizontal opening, the body towing the parachute with its mass, forcing it to rise during deployment, like any wing. Like for paraglider or kite. A short pushing of the flow alongside the surface of the slider is enough for it to fall.

The slider doesn't know what or where is neither horizontal nor vertical. All it knows is relative wind.

If the jumper is moving in the direction of the arrow (so the arrow points the direction of the relative wind) then the canopy would have lined up with the arrow as well.

Here's a horizontal deployment, a vertical deployment, and a deployment with a glide angle as above, as they happen in the real world

5 hours ago, GoneCodFishing said:

The slider doesn't know what or where is neither horizontal nor vertical. All it knows is relative wind.

If the jumper is moving in the direction of the arrow (so the arrow points the direction of the relative wind) then the canopy would have lined up with the arrow as well.

Here's a horizontal deployment, a vertical deployment, and a deployment with a glide angle as above, as they happen in the real world

This is a common misconception. The wing always "knows" where the top is - because the lifting force is always directed upwards (just like the Archimedean force), in the opposite direction to gravity. And the parachute, even at the beginning of the opening, is a wing. At horizontal openings, the towed bucket formed by the skin and the slider rakes the air mass . The slider is a piston, and if the pressure from above, from the volume limited by the skin, turns out to be more than from below, it will inevitably fall.

And this happens from time to time, more often than we would like.

17 hours ago, Veis said:

This is a common misconception. The wing always "knows" where the top is - because the lifting force is always directed upwards (just like the Archimedean force), in the opposite direction to gravity......

No, it is definitely not. Lift is perpendicular (90deg) to the motion of the wing in the fluid (the air in our case).  You can't reinvent physics.

1 hour ago, Remster said:

No, it is definitely not. Lift is perpendicular (90deg) to the motion of the wing in the fluid (the air in our case).  You can't reinvent physics.

This misconception has nothing to do with physics. A parachute unpacked upside down from the bag never tends to dive under the trajectory - it turns over, and always rise only upwards, but with a line twist. The lifting force is indeed related to Archimedean, since it comes from inertia and the interaction of volumes of moving air of different densities. For the same reason, modeling an airplane in a vertical wind tunnel is not equivalent to a horizontal one.

12 hours ago, billvon said:

Nope.  Aerobatic aircraft prove this wrong every day.  You can generate lift upwards (normal cruising flight) or downwards (tight loops.)  You can in fact generate it at any angle you want (arbitrarily steep turns.)  And it doesn't change depending on where gravity is; all the wing cares about is the forces on it caused by the relative wind.

This is far from the truth.

Aerobatic airplanes use minimal lift force, precisely because it limits maneuverability in different directions. They have a very powerful engine in relation to weight and a thin wing profile. Other forces are used more: aerodynamic drag and reactive. And what looks like indifference to the position in space is actually the skill of a pilot who, at high roll angles, uses a vertical tail as a wing.

wow.  what a debate.  everyone sounds so damned certain they are correct.  very hard to pick out what is right and what is wrong when things like this happen.  how are we expected to get to the bottom of this?  nevermind, time to find another distraction.  i think you're all wrong and just making it up at this point.  it's all magic and luck.

2 hours ago, Veis said:

This is far from the truth.

Aerobatic airplanes use minimal lift force, precisely because it limits maneuverability in different directions. They have a very powerful engine in relation to weight and a thin wing profile. Other forces are used more: aerodynamic drag and reactive. And what looks like indifference to the position in space is actually the skill of a pilot who, at high roll angles, uses a vertical tail as a wing.

And aerobatic gliders do what??

Basic aviation forces always apply:

drag - 180 from the direction of motion
thrust - in line with the propeller/jet ( 0 in the case of a glider)
gravity - down regardless of direction of motion
lift - 90deg to the wing's cord (can be broken down into the portion opposing gravity and the remaining vector)

At low speeds, the effect of gravity will have more of an effect on the system.  In the case of a rigid aircraft, that can be considered a single force at the center of mass, but in the case of non-rigid systems (such as a parachute, especially non-pressurized mid deployment) each component will be able to react independently to its net forces.  Hence the bagged canopy dropping due to gravity more than "backward" due to the drag from the PC...  The PC will _mostly_ be creating force opposite the direction of motion, but the PC itself will be dropping vertically from its own mass being affected by gravity.  During a high-speed deployment, this is negligible compared to the amount of drag.  But have that same PC drop out of the reserve container while flying under a big slow main, and you see gravity's larger effect.

So, back to the original question of a horizontal deployment's behavior.
First, given the above, we should expect to see different behavior of the system's components if the movement is very slow horizontal (and little/no vertical movement) vs a highspeed horizontal deployment.  Think of a (true) hop-n-pop from a 200kt DC-9 run vs a Citabria (look it up if needed... nice plane for a single jumper, but recommend a few seconds delay on this one to build speed).

In the first case, we're dealing with a deployment fast enough that the effect of gravity will be minimal during the time of deployment compared to that of drag.  Here the biggest result (assuming no component failure due to the speed) is a fully deployed system where gravity immediately acts to pull the jumper backwards/down under the canopy.

But in the second, even as the PC is still trying to get enough air to inflate, the jumper's angle to the  deploying system will be constantly changing... with a slow enough exit speed, even the PC will be initially dropping due to gravity more than moving backward due to drag.  When the bag comes out (and canopy comes out of the bag) each will have more vertical movement due to gravity at its stage than in the previous case. 

Yes, the pendulum swing begins during deployment in both cases, but is more pronounced during the slow deployment as there is more time for the jumper to swing down as the deployment progresses.

So, I would expect the effect of the relative wind in the first case to be close to that for which the parachute/slider designers intended for the duration of the deployment (i.e. similar to a vertical deployment).  In the case of the slow deployment that began mostly horizontal and finishes mostly vertical, I would expect that the constantly changing angle (relative wing to the line of jumper-to-center-of-slider/wing) could very well introduce more inflation to the wing without the desired pressure on the slider.  The rotation itself might cause the nose to scoop more air during the inflation phase.

Add to all of this, (during a low speed deployment) that lower pressure wind around the (controlled) chaos (constantly changing currents/eddies in and around the fabric trying to inflate) could  easily cause different behaviors. 

All of this is not even to mention that with a slow speed deployment, things like the friction of D-bag/container and canopy/D-bag, and stow bands will take longer to overcome with the lower drag of the PC.  With the longer time, each of these items have more ability to introduce additional undesired chaos.  (such as a spinning D-bag during line play-out).

I do a lot of hop-n-pops, including some short delays and some true h-n-p's.  Horizontal deployments are fun, but aircraft jump-run speed makes a lot of difference as to how organized the deployment progresses*.
 

Just my $.03 (because... inflation)

JW

*had a pilot want to give me a good cut for climb out... 2000' jump run, spectre canopy known to take 800' to deploy, and he wants to be "nice" and slow it to <70ish... with him knowing what I was doing, I reached in and advanced the throttle back to 85+  I, for one, did not complain when USPA upped the minimums to 2500', though after that jump I already had. 

21 hours ago, fcajump said:

Basic aviation forces always apply:

drag - 180 from the direction of motion
thrust - in line with the propeller/jet ( 0 in the case of a glider)
gravity - down regardless of direction of motion
lift - 90deg to the wing's cord (can be broken down into the portion opposing gravity and the remaining vector)

Oh my God, such an "aerodynamic" theory has not been used for a long time)) According to this theory, they tried to build a "Mozhaisky plane" in the 19th century, it could not take off.

It is now believed that the main factor significant for maintaining the aircrafts in flight is a dynamic "bubble" of low pressure air created above the upper surface of the wing. Which tends to move in the opposite direction to gravity, and also affects the surface of the wing. Accordingly, there can be no indifference to the position of the wing, and this works well in practice when creating flying products and components.

What is a wing chord?  )) These are conventions, it can be drawn on the drawing in any way - in several ways. The same is true with the "construction axis" of the aircraft. These are all conventions.

see?  magic, plain and simple.  no other explanation suffices.

I'm picturing the scene in the original 'Planet of the Apes' when Charlton Heston tosses the paper airplane.

3 hours ago, Veis said:

Oh my God, such an "aerodynamic" theory has not been used for a long time)) According to this theory, they tried to build a "Mozhaisky plane" in the 19th century, it could not take off.

It is now believed that the main factor significant for maintaining the aircrafts in flight is a dynamic "bubble" of low pressure air created above the upper surface of the wing. Which tends to move in the opposite direction to gravity, and also affects the surface of the wing. Accordingly, there can be no indifference to the position of the wing, and this works well in practice when creating flying products and components.

What is a wing chord?  )) These are conventions, it can be drawn on the drawing in any way - in several ways. The same is true with the "construction axis" of the aircraft. These are all conventions.

The dynamic bubble does not negate the computation of the basic force vectors, and the lift from the low pressure does not always act in opposition of gravity... (that would depend entirely on the angle of the wing/relative wind/direction of flight...  it does however always act perpendicular to the cord/angle of attack.

Using these conventions and force analysis, many people design, build, and fly a lot of aircraft.

I am not familiar with the "Mozhaisky plane" (other than what is on Wiki), but most early aircraft failed for many reasons, most commonly the lack of power from the engines at the time.  The full understanding of airfoil design (creating a curved lifting surface rather than simply an angled plane) for use in both wings and rotors/propellers being another major limitation to the early aircraft.
 

JW

PS - Thinking about the proposed notion that:
 "dynamic "bubble" of low pressure air created above the upper surface of the wing. Which tends to move in the opposite direction to gravity"
If this were true, most current aircraft would have a big problem... the horizontal stabilizer is designed with a negative lift vector (i.e. pointing "down" with respect to the longitudinal axis) to balance the forward CG.  If the tail wing (horizontal stabilizer) did not product negative lift, the aircraft would not be able to lift off much less fly.

36 minutes ago, fcajump said:

PS - Thinking about the proposed notion that:
 "dynamic "bubble" of low pressure air created above the upper surface of the wing. Which tends to move in the opposite direction to gravity"
If this were true, most current aircraft would have a big problem... the horizontal stabilizer is designed with a negative lift vector (i.e. pointing "down" with respect to the longitudinal axis) to balance the forward CG.  If the tail wing (horizontal stabilizer) did not product negative lift, the aircraft would not be able to lift off much less fly.

This is achieved by the profile, especially the shape of the leading edge, and the installation angle.

Moreover, the wing of an airplane also does not always need to generate a large "bubble" - for example, at high speed. Therefore, the mechanization of the leading-edge slat is used. When a large "bubble" is needed, the slat is pushed out by servo or automatically from own weight.

The first priority is always physical processes, and only then - formulas and arrows in the drawings.

While I am not an aerodynamics engineer, I am a master rigger and pilot.  The above was based on the general aviation training given here for the above, and is still in the current manuals.

However, I am always open to new information and like to expand my knowledge. As you have a (seemingly) very different understanding of the topic, could you please provide published references to where I could read up on your views?

JW

Ps - moderators: this discussion of aerodynamics (or shitshow as someone desired it) has strayed much further from the central topic than I had ever intended to be party. Feel free to move the side discussion to some more appropriate location (gear, bonfire, dumpster fire, etc...) I am willing to continue the discussion elsewhere, but here is not the right venue.

On 6/12/2024 at 4:01 AM, Veis said:

This is far from the truth.

Aerobatic airplanes use minimal lift force, precisely because it limits maneuverability in different directions. They have a very powerful engine in relation to weight and a thin wing profile. Other forces are used more: aerodynamic drag and reactive. And what looks like indifference to the position in space is actually the skill of a pilot who, at high roll angles, uses a vertical tail as a wing.

Your knowledge of physics is what is far from the truth.

1 hour ago, kallend said:

Your knowledge of physics is what is far from the truth.

However, the aerodynamic structures that I develop and produce according to the "wrong" theory are quite workable. And all their disadvantages are from a lack of quality and financing, but not theory))

To simplify understanding, you need to combine this scheme:

and this video

in your thoughts, which remained in another topic after the separation.

3 hours ago, fcajump said:

 

However, I am always open to new information and like to expand my knowledge. As you have a (seemingly) very different understanding of the topic, could you please provide published references to where I could read up on your views?

I first heard about the physical causes of lift in the aircraft model club in the house of creativity of pioneers 35 years ago. Later, I repeatedly encountered such discrepancies, and within one chapter of a textbook or publication, a definition with a perpendicular to the motion vector can be used at the same time - and an illustration next to it, where the lifting force is depicted as the opposite of weight)) This historical incident has no practical impact, since all flying vehicles have long been designed not in abstract "aerodynamics", but in gas-dynamic programs that simulate the interaction of air particles with each other, their groups and volumes, and with surfaces.

11 hours ago, Veis said:

 

 

Ok, please explain to me how the slider can be almost all the way up, yet the canopy is nearly fully inflated.

With the slider that far up, there's no way the canopy can have any form other than a big ball.
It will be directly downwind (relative wind) from the container. 
It doesn't matter if the jumper is falling straight down, moving both down and forward, or moving entirely (or almost entirely) forward.

So the airflow would be going directly against the bottom of the slider and the canopy.

Not from the front.

There are literally thousands of videos that will show this.

7 hours ago, wolfriverjoe said:

19 hours ago, Veis said:

 

Ok, please explain to me how the slider can be almost all the way up, yet the canopy is nearly fully inflated.

The answer is simple: the figure shows the center section, this happens when the wing is inflated about the width of the slider. And in the video, the wing is turned 90 degrees, with the stabilizer on the stream. It doesn't make much matter.

This is how the filling of the center section looks like in experiments with a towing system.

3 hours ago, Veis said:

The answer is simple: the figure shows the center section, this happens when the wing is inflated about the width of the slider. And in the video, the wing is turned 90 degrees, with the stabilizer on the stream. It doesn't make much matter.

This is how the filling of the center section looks like in experiments with a towing system.

 

Ok, it's only a partial representation of the canopy.

Misleading, but ok.

However, the wind vector in your drawing is coming from the front.

It's pretty clear from the pilot chute that the wind is coming from 'below' the canopy in the picture. 
Along with the way the slider is blown upwards.

9 hours ago, billvon said:

who was convinced that aircraft generated lift because the top of their wing was curved. 

Help me understand why this was wrong. He was probably relying on Bernoulli's theorem which we all learned while getting our pilot's license.  

9 hours ago, billvon said:

When I asked how aircraft flew upside down, he claimed that their engines, not lift, kept them aloft. 

I wonder if he was implying the engines were needed to maintain lift. 

1 hour ago, wolfriverjoe said:

Ok, it's only a partial representation of the canopy.

Misleading, but ok.

However, the wind vector in your drawing is coming from the front.

It's pretty clear from the pilot chute that the wind is coming from 'below' the canopy in the picture. 
Along with the way the slider is blown upwards.

In the photo with the towing system attached to the slider, as a full RDS, it can be seen that the lines direction  is rotated at a significant angle to the weather vane (PC). The angle is about 45 degrees - but with a large  suit, and when performing a "braking" this angle will be smaller, but shading and low pressure area larger. For these reasons, but not because of the  lesser desire to rise by deployed wing.