# Aerodynamics of a Paraglider

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I have a question about the forces and aerodynamics at play during a paraglider's flight.

As I understand it normally flight can be thought of simply in terms of Thrust, Lift, Gravity and Drag.

Imagining a paraglider in flight above a ridge, with no forward movement, remaining at a constant location relative to a spot on the ground.

How does thrust apply in this situation?

Is thrust even present? and if not what balances the forces of drag?

How do the stated forces balance with respect to my stated normal understanding of aerodynamics?

Thanks.

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A paraglider cannot hover, because it cannot generate thrust.

All forms of gliding, technological and animal, have no thrust, but instead harness the energy of falling. The person or animal jumps off a high point, and they begin to fall. This generates airflow past the wings, which in turn generates lift. The lift reduces gravity, and eventually, all the forces balance out at a fixed angle of descent. More lift = shallower descent.

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I have a question about the forces and aerodynamics at play during a paraglider's flight.

As I understand it normally flight can be thought of simply in terms of Thrust, Lift, Gravity and Drag.

Imagining a paraglider in flight above a ridge, with no forward movement, remaining at a constant location relative to a spot on the ground.

How does thrust apply in this situation?

Is thrust even present? and if not what balances the forces of drag?

How do the stated forces balance with respect to my stated normal understanding of aerodynamics?

Thanks.

What Mokele said.

In particular what you are describing sounds like a paraglider heading (and falling relative to the flow) upwind in a rising air current.

Gravity has a slight forward component relative to the flow.

Lift, a force perpendicular to the flow, has a slight forward component relative to the ground.

The drag, a force parallel to the flow, has a slight upward component.

It can all balance out so that the paraglider is stationary.

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Thank you for the great responses.

I think I have it now.

But I would also like to ask another quick one.

A paraglider has a series of open fronted cells begining at the front of the canopy, these hollow cells are sealed at the rear and their shape helps to form the flight profile of the wing when they are filled with air.

Is the air within the cells continually recycled with the air approaching the front of the paraglider? and if so how do they stay a stable shape during flight at varying air speeds and direction?

Or, does the air that initially fill these cells remain? if so how does the 'outside' air interact with the boundary of the cell and the air within?

How does air behave within these cells? Is it 'pressurised' somehow in comparison to the 'outer' air or is something else happening?

Thanks for any help you can provide, there is a real lack of scientific accuracy in normal paragliding resource websites and I am struggling to find some correct science associated with paragliding flight.

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The air that fills the cells mostly remains, creating a pressure gradient at the cell opening that functions to direct air past it almost as if something solid was in the way. It is indeed pressurized as a result.

The flexible membrane also helps, generating a cambered wing, increasing lift. This is actually a big part of how bats fly, and probably played a role in pterosaur flight too.

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Paraglider pilot of ten years' experience here.

First of all: a paraglider definitely can hover, if by "hover" you mean achieve a groundspeed of zero - which is what you described in the original post. This is actually relatively simple in principle:

The glider is constantly moving forwards and downwards through the air. Key parameters are airspeed, which may be typically 30km/h, and sink rate, which may be typically 1.5 m/s. All you need to do is find a ridge where the wind is blowing a constant 25km/h or so perpendicular to the slope. The slope itself will divert the air upwards. If it is steep enough, in a limited region close to the slope, the air will be going up faster than 1.5m/s. If you take off into this wind, your glider will rise to the point where the upward motion of the air balances the downward motion of the glider. If you apply the brakes to reduce your airspeed by 5km/h or so, your airspeed will be 25km/h... and your ground speed will be zero. You're "hovering". But you're doing so only as long as you point directly into the wind and maintain an airspeed equivalent to the windspeed. Note that if the windspeed increases to 30kph, you are now in a dangerous position - even with the brakes fully off, unable to fly into the wind, you are very limited in your options, and must fly downwind. We try to avoid this state of affairs. We do have foot-operated speed systems or hand-operated trimmers that can lower the angle of attack of the wing to increase airspeed, but using it to stay upwind is not advisable.

A paraglider cannot hover like a helicopter, i.e. achieve an airspeed of zero.

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