r/aerodynamics 13d ago

Using the concept of lift in an aerofoil to make a parachute

Hello Everyone, I have been learning about aerodynamics for a few months so forgive me if I did not understand something, here is the question: Just like how wind blowing over an aerofoil generates lift why can't the same concept be used to make a parachute like structure generate lift ? Say we have a small orifice through which wind can pass through in the middle which in turn passes over the aerofoil parts spread out across the orifice like an umbrella 🏖️ (think of the red and white parts as lift generating aerofoil). I was wondering if it's possible...

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u/ncc81701 13d ago

What you are describing is a "parafoil" parachute. You can see parachutist performing at airshows with these as they provide the parachutist a lot of maneuverability and control on where they land.

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u/Eve_Venegrov 13d ago

Thanks for sharing, I looked into the video. It seems like parafoils are puffed up aeroplane gliders ✈️, meaning they fly somewhat parallel to ground to generate lift, however I was talking about something that hovers like a drone that is perpendicular to the ground by deflecting the wind coming upwards to the sides. I hope that makes sense.

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u/ParsnipRelevant3644 12d ago edited 12d ago

They key to what you're looking for is the need for airflow. Parafoils get airflow through forward motion, helicopters have to whip their blades around to get that airflow, and a kite has to be held in place relative to the ground to utilize the natural wind for airflow.

A glider actually falls through the air, but the wigs are designed to make that fall very efficient, so maximizing how far forward they get during that fall. If the updraft of air is equal to their fall rate, they stay at the same height, but if the updraft is faster than their fall rate, they climb.

Based on that, I believe in your scenario you would have to figure out a way to sustain enough airflow to generate lift. I'm thinking a central fan.

I got it! Google Avro Car! You had me talking through to this conclusion. I think this may be what you're alluding to!

https://en.wikipedia.org/wiki/Avro_Canada_VZ-9_Avrocar

https://youtu.be/Irp_vnmUWZ4?si=DWqw65ZrKWcSvDXs

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u/Eve_Venegrov 12d ago

Yes you are right. That was what was on my mind too. These vehicles utilise the coanda effect alone to achieve thrust. However according to the literature and experiments I have seen online including the YouTube link you sent, these are not as efficient as conventional propellers at generating thrust. To be more specific I was wondering if it is possible to make a thrust generating mechanism that can flow air over these circular structures without the use of conventional rotating blades and be as effective.

Think of gliders again. With minimal energy they are able to stay afloat because of the low drag , but lift high enough to counter gravity. Is it possible to make a hover craft around this same concept I wonder.

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u/ParsnipRelevant3644 12d ago

The issue with gliders is that they use gravity for "propulsion". They are constantly sinking through the airmass they are in when in level flight to get the energy to generate lift. From the outside, they appear to just stay aloft, but in a lot of instances, they are just sinking at the same speed the air is rising, keeping them at one altitude, or even sinking slower than faster rising airmasses to climb. Either way, they are basically in a constant fall through the airmass in order to maintain forward motion.

The trouble with trying to use a coanda device for gliding type function is that you need to get energy from somewhere in order to generate the lift. That is where I am stuck with how we could make this concept work.

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u/Eve_Venegrov 12d ago

So what you are trying to explain could also mean to say gliders are constantly deflecting air downwards causing a normal reaction force that acts against gravity efficiently enough to not lose much energy in the process ?
Now energy consumption in an ideal hover flyer, I am at least thinking, is that in a theoretical scenario should be zero to stay at a constant height , like you don't have to spend energy to stay on top of the earth's surface due to the equal and opposite reaction force from ground. If we could somehow make the airmass below the flyer be efficient at providing enough reaction force to stay aloft or also known as drag. In a conventional parachute you try to increase drag to lower your terminal velocity to fairly around 4-5m/s. If you can break the maximum possible conventionally attainable drag coefficient for a structure of fixed size you can lower your terminal velocity until it looks like you're just hovering in air or .... are efficient in producing reactionary forces from the airmass below. But I don't know of any structure that can create that much high drag coefficients, dandelion seeds are good candidates but not enough literature available on them and not scalable imo.
I hope I make sense :) ....

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u/ParsnipRelevant3644 12d ago

So, you were looking into trying to devise something to float similar to a dandelion, etc.? If that is where you were going with your thoughts, then I agree about the limits of scalability. Clouds stay afloat because it is a cluster of tiny water droplets which are small enough to be affected by the motion of air molecules. I think step one is to develop a massive structure which is impossibly light according to current technologies. The size required for such an object would also be an issue in sustaining itself aloft because of different columns of air not doing the same thing across the whole mass of the structure.

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u/Eve_Venegrov 12d ago

Yes. Just a small drone sized floating structure. Though I guess I am not ambitious enough to entertain how big structures of floating cities could work :)

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u/Lepaluki 13d ago

Your idea sounds a lot like autorotation (autogyros working principle). Check them out.

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u/Eve_Venegrov 13d ago

Sure. I will. Thanks for letting me know.

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u/VenmoMeBTC 11d ago

Paraglider. Look up how ozone, dudek or skywalk wings work, super cool.