8
$\begingroup$

I don't completely understand why the strings on paraglider/paramotors (connecting the vehicle/person to the parafoil) are so long. Couldn't they be made shorter to reduce the amount of space used? It just seems like an unnecessary feature. Sorry if I'm missing something elementary.

$\endgroup$
4
  • 7
    $\begingroup$ When you are asking "why isn't it done differently", it helps to explain what problem you are trying to solve. Paragliders have long cords. So what? $\endgroup$
    – Simon
    Commented Oct 26, 2016 at 6:24
  • $\begingroup$ @Simon Thanks for the response! I think the main problem is the amount of space having such a large structure takes up. You could make it more compact and still have the same result if you could shorten the cords. This would help if, say, you had lots of people/vehicles mounted to parafoils. I've been thinking about a related concept for a while and shortening the strings would be useful; the parafoils would simply be used for cruising and gliding once in the air, so they wouldn't have to store fuel and so forth. $\endgroup$ Commented Oct 27, 2016 at 2:14
  • $\begingroup$ @bobthepie, you could reinforce the structure. It's called a hang glider. However, that loses the main advantage of a paraglide—you can no longer pack it into a back-pack small enough for to carry around on your back. And even with the motor it still packs much better than the hang glider. $\endgroup$
    – Jan Hudec
    Commented Oct 27, 2016 at 5:00
  • $\begingroup$ I don't understand what you mean by "amount of space". I don't see how it could be smaller than packed away in a back-pack $\endgroup$
    – Simon
    Commented Oct 28, 2016 at 15:01

1 Answer 1

8
$\begingroup$

The answer to this is mechanical leverage.

For this, you must understand that the center of mass for a paramotor is usually just above the pilot's head, and that the center of lift is more upwards.

enter image description here

The shorter the strings on a paramotor, the harder that it is to climb, because the length of the effort arm is reduced, requiring a greater power to tilt the paramotor into a climb.

As the motor power increases, you don't actually go much faster. You tip backward, and maintain speed. This is what helps you climb, essentially comboing the wing with the elevator.

The long strings allow for slower, more efficient flight by increasing leverage. This is the same mechanics that are used in most trainer crafts (outside the military) to allow the learner a long, slow flight.

2023 edit

I was reviewing this answer, and realized that I explained the pitch leverage, but did not explain roll leverage, and the benefit that long strings have in this scenario.

In the spirit of the old answer, consider this front view of a paraglider which is flying.

enter image description here

Ft in this case is the tension force that the pilot feels from the outermost lines. It is made of two components. The horizontal component, Fh, is how much the lines pull outward on the pilot. The lift force, Fl, is the amount of lift force that a pilot feels in flight.

As you can see, Fh is not an especially useful force. While it keeps the glider's shape rigid, which is good, but you're sacrificing lift to do this. by increasing the line length, you can get rid of unneeded rigidity, and in its place directly increase the lift. There's a balance to be struck here, as with all things aviation.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .