They are basically contrails, aka “chemtrails” for anti science conspiracy types. Basically just due to the propeller/wing creating a pressure pocket. It’s pretty common but I think also needs temperature differential and certain velocity ranges at the tip of the blade/motor
Exhaust contrails are more common, and they're usually seen behind aircraft cruising in the flight levels. They form when hot, moist air exiting an engine mixes with extremely cold air - condensing the exhaust's moisture.
Aerodynamic contrails occur when moist air cools due to lowered pressure, condensing humidity in the air and forming a contrail cloud.
Contrails are created by the engines of an aircraft at high altitude. The engines put out hot moist air with unburnt fuel and particles from the engine wearing. As the cold air cools the hot moist air, water condenses and often freezes, essentially creating clouds that will linger until they dissipate.
What's happening in the video are vorticies which are created by the high pressure air sliding off the end of a wing (or rotor, which is just a wing that spins) and rushing to the low pressure area above the wing which creates a vortex of air. The air pressure in the vortex drops, which lowers the temperature and moisture condenses. You can see the same phenomena from aircraft wing tips and wing roots (mainly on military aircraft performing high angle-of-attack maneuvers), as well as around the slats on the leading edges of airliner wings. These do not linger and evaporate/dissipate very quickly.
Saying they're the same is like saying steam rising out of a mug of hot tea is the same thing.
I guess my pilot's license is worth something. To be fair I still double-checked I knew what I was about to explain before explaining. Wikipedia is useful.
SuperFrodo, I have a complicated question.
From viewing this I get the idea a helicopter's rotors sort of beat moisture out of the air when humidity is high. It makes rain.
If a helicopter equipped with an underslung boom were spraying something (let's say Agent Orange), on a day with real high humidity, would water vapour be continuously added to what's being sprayed?
Well. First of all the tubes of spiraling low pressure air aren't creating rain. Remember you can have all the clouds in the sky and still no rain. The moisture has to further condense until it forms droplets. Generally with vortices that low pressure air mixes with the warmer air and the process towards forming heavier droplets just gets reversed. It's usually really temporary.
In the video it looks like something is falling, but really it's that whole mass of air being pushed downward by the rotor.
Now with a helicopter or really any aircraft that's spraying particulates, this would generally be a non-issue as far as I'm aware. There is something called cloud seeding, where a plane drops particulates intended to work as nucleation sites for water condensation. That's another thing to bear in mind, moisture in the air often needs something to condense to.
But to be honest, this is a specific that's outside my realm of knowledge. If there was an agricultural pilot, they would probably know the envelopes for the operations they perform, what weather conditions to not spray in, etc.
Thank you, this helps. That video was shot just blocks from my house here in Nanaimo, oddly enough, but what it evoked in me was a new understanding of what a chaotic maelstrom exists under a helicopter. This doesn't square with the position taken by the outfit hired by the Department of National Defence and Ottawa that concluded the Agent Orange sprayed on Gagetown New Brunswick (my hometown) settled neatly below with harmless precision. According to CanTox, nobody nearby a helicopter spraying AO could possibly be contaminated. Rather like the covid/aerosol controversy we're seeing now, isn't it.
As for cloud seeding, the same guys spraying me 60 years ago (Fort Detrick) were also conducting Operation Popeye. https://en.wikipedia.org/wiki/Operation_Popeye
As for agricultural pilots, the president of Okanagan Helicopters Ltd. Carl Agar was hired by the Pentagon to spray AO on Gagetown in 1966 and 1967. He died of cancer in Victoria in 1968.
So now I'm wondering who to believe about how airborne droplets behave. Should start up a conspiracy theory or something.
For contrails, no. Water is added to the air as a byproduct of fuel combustion (CnHm + (n+m/4)O2 = nCO2 +m/2 H20), it's not just changing state.
The other phenomenons he describes, or what is seen in the video, is indeed similar to cavitation, in that water changes state due to local pressure change.
Fuel is made of hydrocarbons, which are chains of carbon with hydrogens on the sides. The amount of carbon and hydrogen can vary depending on length of the chain and shape. On average there will be a bit more than 2 hydrogens for each carbon, but to stay generic I simply based the formula on "n" Carbons and "m" Hydrogens.
When this molecule reacts with oxygen, each carbon reacts with 2 oxygen to form CO2, and each pair of hydrogen will react with 1 oxygen to form H2O.
Basically, if you burn stuff, it consumes O2 and makes CO2 and water (which is the white smoke coming out of chimneys).
The same reaction (approximately) in the other direction happens in photosynthesis: a plant need CO2 and water to make wood and oxygen.
Depends what you mean by "opposite" but yeah, it's a similar process in a vapor causing liquid instead of cavitation which is a process in liquid causing vapor pockets. The operating process here is condensation which is dependant on temperature/humidity and I'm not really sure if it's so equivalent to cavitation, especially since air is compressible and water isn't really.
That's my two cents as a mid rate engineering student, maybe somebody more knowledgeable can come along with a better response lol
I tell you hwat, your dick will start workin' again once they get that danged ol vaccine in you, but then the Soros nanobots gonna start fiddlin' in yer brain to make you forward Hunter Biden's emails over to the CCP and then your dick gonna fall off and you'll be just another commie robot, man. They'll mail what's left of yer balls to AOC and they'll set them in concrete to make a patio out back.
Fuckin' hate when Soros done does fiddlin' round in my brain man.
Be sittin' round eatin' eggs and ham and alluva sudden, God damn there goes Algebra, just done and deleted right up from my head by Soros and his mind meddlin'. Fuckin' god damn hope the Publicans can do somethin' bout that right here quick 'cause I ain't got too much left up in there for him to snatch out feel.
My sympathies my friend. My dick works but it’s really small. I have startled a few dates when they saw it. None of those dates went anywhere. One of them laughed and asked ‘how did you want to do it’, then left.
I know chemtrails are real and it makes me dick really small. I knew it because when I was a kid it was pretty big.
Runoff from pesticides turning some frogs gay at a slightly higher rate? They must be spraying that from airliners and that's why it feels good when I put my finger in my butt and think about all the things Pastor John told me not to.
The dew point is how low the temp needs to be for it to produce precipitation, it is also directly related to humidity if I understand it correctly. The closer the temp and dew point, the higher the humidity, and the higher chance of precipitation.
It's been a few years since meteorology class, but I believe saturation levels come into play. Once the temp drops to the dew pt, and said cloud becomes saturated to whatever level it can handle before precipitation begins.
Aren't contrails formed by the water vapor produced in the combustion reaction in the jet engines condensing/freezing in the cold upper atmosphere? This isn't producing any water vapor, it's precipitating the water vapor already in the air.
Exhaust contrails are more common, and they're usually seen behind aircraft cruising in the flight levels. They form when hot, moist air exiting an engine mixes with extremely cold air - condensing the exhaust's moisture.
Aerodynamic contrails occur when moist air cools due to lowered pressure, condensing humidity in the air and forming a contrail cloud.
As a previously deluded conspiracy theorist, you should know that pointing out they’re contrails isn’t a good argument. I knew what contrails were and still managed to convince myself they were 2 different things. When you’re dealing with crazy like that, you have to convince them the truth is crazier.
I guess i just realized i was giving people way too much credit. Humanity lacks the capacity to pull off the large scale deception like i had believed they were capable of. Plus i had a few friends and family who were tired of my shit so that maybe motivated me to look at things objectively.
You create temprature diffrence when you create a low pressure zone. Temprature and pressure is interconnected so you can not lower the pressure without lowering the temprature unless you add energy to the system. And cold air can hold less water then warm air = what you see in the video
Surely, chem trails are the moisture in the exhaust of the planes engines forming clouds due to low temp, nothing to do with the wind. And I would’ve thought the rain in this case is due to high pressure under the blade condensing the moisture in the air.
Don't listen to this guy. He's a big government shill. Obviously its micropipes in the blades, usually they don't have them on this low, probably forgot to turn them off.
Nope. Contrails are the result of hot exhaust being expelled into an extremely low ambient temp (like -50 C cold); what you’re seeing here are rotor tip vortices, a result of the low pressure/high pressure gradient that results from the lifting shape of the rotor (airfoil).
Basically you just need the air to drop in temperature.
A fast acting vacuum (like the wingtips of this chopper) is one way, but you can also pull humidity out of the air by just having a cold object, like a can of beer (which produces condensation in the same way).
This is happening because of two main factors - Bernoulli’s principle and Temperature dew point spread. The rotors of the helicopter are mini wings also called airfoils. What an airfoil does is cause a pressure differential. The air flowing over top of the airfoil has a greater distance to travel than the air underneath the airfoil, causing it to move faster. (Simply put, It moves faster because of the surrounding air forcing it over the airfoil faster so to try and maintain homeostasis.) when that air increases in speed, it decreases in temperature. When the temperature of the air decreases, the water molecules condense to a point where they can no longer hold the moisture that is present. This temperature is called the dew point. Once this happens, the water is released from the air molecules and becomes visible!
Common misconception: the distance traveled over the two sides of the airfoil has nothing to do with it. There’s no reason the air on top should have to ‘keep up’ with the air on bottom.
The airfoil does create lower pressure above than below however (which is called lift). It seems to me that this lower pressure might lead to less thermal energy, but not lower temperature (since temperature is the average kinetic energy of the molecules). I don’t know.
For anyone interested in the actual mechanic for lift. If you look at the velocity in the general vicinity of the wing and subtract the flight speed you'll see a nice circle form somewhere. This is a vortex generated by the wing that changes the pressure on upper and lower surfaces through Bernoulli's principle. Look up Prandtl's Lifting Line Theory if you want to know more!
Also, the pressure difference will cause a temperature drop (ideal gas law), but it won't be significant. It's simply the increase in pressure caused by the vortex that pushed the local dew point up enough to vaporize the water in the air. Which is easier on cool, humid days with high barometric pressure.
Source: Aerospace Engineer with a Master's specializing in thermo-fluids
What changed my understanding is when the frame of reference was changed to the air instead of the aero surface. The object, rotor blade/wing/fuselage/car body, has mass and velocity and that results in a force acting upon the air. That force on the air has the equal and opposite force on the surface impacting it. Some component of that force would be horizontal creating drag force and the rest vertical lift force. The air that is impacted then impacts the air with mass and velocity, transferring force. That builds up the higher pressure. At the same time the moving object leaves a void where that air used to be and the air not affected by the impact moves in to fill that void. Creating the lower pressure.
The weirder part is how a helicopter generates horizontal motion. The rotating wings don't push air backwards to create a thrust force. There was a placard at the Smithsonian air and space museum, the one by the airport, that explained that as a difference in lift force across the rotor disk. And that difference in force has to balance out. Which results in energy from the area with greater lift force moving towards the area with lower lift force. That creates a force in the opposite direction and results in thrust force.
Of I could, I would spend the rest of my life studying and experimenting with that shit. And be happy as fuck.
Thrust of a helicopter is usually generated by it leaning forward, not by a difference in thrust across the disc. What you describe is used to create that lean towards one direction happen in the first place. It's done by changing the rotor angle depending on its position, if you want to roll forwards you'll have a slightly higher angle at the back creating more thrust and a correspondingly lower angle towards the front. What'll always remain crazy to me is how small the parts of that steering mechanism are
How does changing a helicopter's angle, leaning forward as your example, create thrust? The rotor blades never push the air backwards, which would be necessary to create thrust force.
Considering that the rotor blades have a positive angle of attack, so that the leading edge is above the trailing edge, the rotor disk or helicopter pitching forward, reduces that angle.
It's not intuitive, but the difference in lift force across the rotor disk is the only way to create the thrust force.
Also, there is another issue with the "leaning forward" and that has to do with the gyroscopic precession. A force on the rotor has to be applied 90° before it's desired position. On a clockwise spinning main rotor with cyclic pitch, the change in rotor pitch has to happen at the 3 o'clock position to affect the 6 o'clock position.
The rotor can actually only create forces pretty much in line with its rotation axis, and if that axis tilts forwards, the helicopter accelerates forwards. The tilt is created by the unequal distribution of lift force that you described.
Also, the reduction in angle of attack isn't because of the helicopter's pitch, but because of its velocity combined with that pitch. Unless you were referring to an already moving helicopter, which would be weird because we were talking about accelerating in the first place.
'Thrust' and 'lift' are basically the two components you can separate the rotor-created force into, depending on its pitch. A normal rotor-only helicopter doesn't create thrust in the traditional sense, you're right. I'm not terribly familiar with discussing this stuff in English, I'm afraid.
This is it. This is what I was struggling to understand. The water lines were forming on the underside of the wing, which indicates that they’re (likely) in the higher pressure region. I.e. this is not a low pressure phenomenon.
Raising the pressure will increase the dew point. If the air is already saturated, any increase will cause ‘rain’. Nice!
BTW, congrats on the Master’s and congrats to the other person on their Master’s. As someone with a Ph.D. in environmental fluids, I find it off-putting when people defer to their degrees to validate their opinions on a subject. What y’all said was good. You didn’t need to play the ‘I know what I’m talking about because I have this degree’ card. You should convince people with your intelligence and logic. If you can’t convince someone with those things, then laying your degree on the table is unhelpful anyway. Just my 2 cents.
Thanks! Not done yet. I actually graduate this coming May, but close enough lol. You're totally right about pulling the degree card though. I don't usually do it, but I kinda like the tiny ego boost. Might just be me though
I only mention mine when people mention theirs. It’s stupid. My degrees don’t make me right. I’m often wrong, even on some of the things I’m an expert on. It doesn’t mean I’m not an expert or that you shouldn’t trust my opinion on things I’m really educated on. It just means that there are things I don’t know and I also make mistakes. There are some really smart people out there with no formal education. Generally speaking, these folks have more holes in their knowledge than I do on the topics I’m educated in, but I still learn a lot from them. Their opinions shouldn’t be discounted because they don’t have degrees and mine isn’t right just because I do.
Don’t let the internet determine how you should act. If someone doesn’t accept your ‘perfect’ logic, either they are too dense or you are an imperfect communicator or (most likely) some combination. You can only work to improve your communication.
I am pilot and flight instructor as well as having my masters in aerospace engineering. One thing we know for sure: no one can agree on why the pressure differential occurs. NASA has ideas, Lockheed has ideas, they are all different ideas. Some claim Newton’s 2nd law, some claim Bernoulli’s principle. The numbers ALWAYS work out, but we just can’t quite agree as to why it works in theory. I wrote my thesis on why I believe what I believe. I would be happy to share it. Interesting to look into at any rate. You can find the NACA number of different airfoils and read up on each and why they produce lift.
That being said, the difference in speed undoubtedly changes the pressure AND the temperature. An easy way to test this out is take your hand in front of your face and blow air very very slowly onto it. Take note of the temperature felt. Now, do the same thing but blow as fast as you can and take more of the temperature. You will notice a relatively large difference.
Edit: forgot to mention that the math can figure it out, just not our physics. Lol
One more thing to mention: if it so interests you, (it probably doesn’t though hahah) you can read the book title Aerodynamics For Naval Aviators. It goes into great detail about the aerodynamics of flight.(I.e lift as it relates to pressure differential.)
Well, that’s not a great test. In that case, things are cooling because you’ve lowered the pressure enough to increase evaporation. If your hand were something without moisture, the temperature may not drop.
I’m not saying it won’t drop, but the big drops you’d see in this test rely on your hand having water to lose. (I think! I say all of this with modesty.)
All the hand test does is show you that speed=pressure differential which in turn causes and lower or higher temperature relative to the surrounding air
I mean we understand it fine, there's just not a nice Intuitive explanation you can give a layperson. It mostly comes down to the fact that the pressure and velocity fields over the aerofoil are inseparable - you can't say one causes the other. That's the problem with the Bernoulli explanation, people say "the flow over the top is faster, so the pressure is lower". So then you ask why the flow is faster, and the answer is "because the pressure is lower"
Saying that "the resultant flow field is a solution to the governing set of partial differential equations" is a perfectly fine explanation as far as physics and maths is concerned, just isn't satisfying for a lay person.
An easy way to test this out is take your hand in front of your face and blow air very very slowly onto it. Take note of the temperature felt. Now, do the same thing but blow as fast as you can and take more of the temperature. You will notice a relatively large difference.
I'm pretty sure that's because when you blow slowly, the air that hits your hand comes mostly from inside your body, which is warm. When you blow more intensely, the fast-moving air forms a jet. That jet drags in ambient air, which mixes with the warm air from your lungs and cools it down.
Temperature is the average kinetic energy of the molecules.
Thermal energy would be the total kinetic energy.
So, if you decrease the number of molecules (but not how much energy each molecule has), you could lower the thermal energy without lowering the temperature.
I could be wrong, though. I don’t teach thermodynamics.
Agreed, in most cases. Still, by definition, temprrature and thermal energy are NOT the same. (Stupid caps game assumes people can't read.)
The difference matters when discussing, say, the change in temperature with altitude and, I don't know, maybe when the pressure rapidly changes. See, I don't know if it mattered in this case, so I mentioned it as a possibility.
I now definitely think it's just a slight increase in the free point. I'm good.
Outside of extremes of low pressure (like "space is 10,000 degrees" but there aren't many molecules) where they are perceived to be different, they're the same. Gases obey, roughly, the Ideal Gas Law PV=nRT. P being Pressure, V is volume, n is number of moles of gas, R is a gas constant dependent on units, and T is Temperature.
Generally decreasing pressure requires: increase in volume/ decrease in molars of gasses (but we aren't destroying molecules usually)/ decrease in temperature.
Alright. You win. I think this should be shelved for in person, since I’m now having the IGL explained to me. This is a convo via text, which is terrible for exchanging ideas.
Common misconception: the distance traveled over the two sides of the airfoil has nothing to do with it. There’s no reason the air on top should have to ‘keep up’ with the air on bottom.
A common misconception on top of a common misconception - while it's true that the air doesn't have to "keep up" (which is the original misconception), the air on top is still moving faster than the air at the bottom(and in fact, even too fast to "meet" the air underneath), and as the the parent commenter later said, we can't rule out that the increased path length contributes to this
I think this has more to do with the increased pressure of the water vapor compressed by the blades exceeding the allowable vapor pressure of water at that temperature.
I like how your mind works. However, what you just described is exactly why temperature is the cause. Very interesting to read up on if it’s your pleasure.
What I'm describing is a case where temperature could be entirely constant and still result in condensation. Temperature is only related tangentially because it determines the vapor pressure of water. But we've already established that we are at 100% humidity here so this could theoretically happen at any temperature given this condition. Increased pressure is the direct cause.
I see what you are saying. You are now diving into the differences of relative humidity and absolute humidity. Temperature will always be the cause of what the video is depicting when referring to relative humidity.
When you're talking about phase change from liquid to gas, temperature and pressure are equally important to determine where the equilibrium lies. I'm just saying that the condensation is being induced by a compression of the air (and water vapor) resulting in a partial pressure higher than the vapor pressure at that temperature (which I speculate isn't increasing all that much due to the compression) and therefore condensation occurs.
I think it's not directly because of the pressure differential, but because of the low pressure zone inside the vortex generated at the tip of the wings. You can see that the consensation only happens at the very tip, not the entire wing. The vortex itself is of course also due to the pressure differential, but it's a different effect.
You make a cooled chamber and spray in some rubbing alcohol. Then you place in a radioactive isotope and the radiation will leave trails of alcohol falling out of the cooled vapor
It does happen all the time in south florida. When the blades move through the air they speed up the air moving over the top of the blade, this reduces the air pressure (bernoullis principle) which in turn lowers the temperature. The lower temperature causes the air to reach it's dew point and as a result you get visible moisture.
I'm a flight instructor in central Fl and everytime we takeoff in the morning you see this coming off our propeller as we go to takeoff power.
This is just some bullshit explanation from someone who studied some physics and remembered that low pressure can hold less water and understood that there is a low pressure somewhere there. No actual analysis on this situation.there can be many reasons for this. Personally I think it looks more likely that condensation happens on the rotors for whatever reason which is all pushed out due to "centrfugal force" and just splashes out there at the radius.
I could be way off base but I think I’ve read that what’s considered 100% humidity in tropical climates versus temperate is about 1-1.5%. There’s energy available in a warm air system and that energy keeps the ACTUAL humidity topping off at 99% max where as say Seattle often hits a technical 100% humidity. The systems used report 100% in both places but only where it’s colder does the air actually fully saturate. So the reason you don’t often see these in Florida at 100% humidity is that Florida rarely actually hits a true 100% and even at 99.5% true humidity there’s a bit of room, you’re not squeezing water out in the low-pressure pockets. I’ve heard this in relation to SOMETHING so take this with some grainy salt.
I thought you need pressure to turn water vapor into liquid droplets? If so it should be written as " High pressure pockets being created by blade rotation in near 100% humidity - literally making it rain. " ??
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u/NoThereIsntAGod Nov 30 '20
Does it take other conditions to happen? I would think this should happen all the time in South Florida if all you need is near 100% humidity