Once a paper airplane leaves your hand, nothing pushes it forward any more. It's a glider, sliding gently downhill through the air the whole way. Everything interesting about its flight is about how well it manages that slide: how shallow the slope is, how steady it stays, and how it responds when something disturbs it.
Three forces on a glider
Weight pulls straight down. Drag is the air resisting the plane's motion; it points backward along the flight path. Lift is made by the wings moving through the air, and it points at right angles to the path. In a steady glide, lift and drag together exactly balance weight. That's why the glide path has to slope downward: tilting the path lets part of the weight keep pulling the plane forward against drag.
NASA Glenn's three forces on a glider page shows the same balance with the maths. The useful takeaway is simple: a plane with less drag, or more lift for its weight, can glide along a flatter slope and travel farther from the same height.
The angle the wing meets the air
A wing makes lift by meeting the oncoming air at a small angle, called the angle of attack. That's the angle between the wing and the direction the plane is actually moving, not the direction you aimed it. More angle gives more lift, up to a point. Past that point the air stops following the top of the wing smoothly, lift drops away, and the plane stalls.
That's the swoop-and-drop you see from a plane thrown upward, or one with its back edges bent up too far: the nose rises, the angle grows, the plane slows, and down it goes. It's also why a harder throw doesn't fix a stall. More speed just makes a bigger swoop.
Balance: where the weight sits
A paper airplane balances around its centre of gravity, the point where you could rest it on a fingertip. Most designs put that point well forward by piling folded layers in the nose: rolled edges, locks, square and tucked noses all do this. A forward balance makes the plane tend to point into its direction of travel, the way the feathers on an arrow keep it pointing forward.
Too far forward and the plane noses down into a dive; too far back and it pitches up and stalls. You can shift the balance with a paper clip on the nose, but it also adds weight, so treat it as an experiment rather than an upgrade. Try it on a plane that stalls, not one that already dives.
What the back edges do
Bending the back edge of both wings up a little pushes the tail down and the nose up. Pilots call a control surface like that an elevator, and it's the main trim you have on a paper plane. Small changes make a big difference: a millimetre can turn a dive into a glide, and two millimetres can turn that glide into a stall. Bend one side more than the other and you've made ailerons, which roll and turn the plane. That's exactly how the stunt setups like the Boomerang and Corkscrew work.
Why the wings make a V
Seen from behind, most of our planes open into a shallow V, with the wingtips higher than the body. That angle is called dihedral. If a gust tips the plane onto one side, the lower wing ends up meeting the air at a slightly better angle than the upper one, which helps roll the plane back level. Too much V makes a plane wobble side to side; wings drooping below level make it roll over.
Wind: ground speed isn't airspeed
A wing only cares about the air moving past it. Throw into a light headwind and the plane has plenty of airflow while barely moving over the ground; throw downwind and it covers ground quickly but may not have enough airflow to fly well. That's why outdoor distances are hard to compare, and why a "record" set downwind says more about the wind than the plane.
See it for yourself
Fold a Dart. Throw it three times with the back edges flat, then bend both up about 1 mm and throw three more. Then bend them up 3 mm. You'll probably see the path go from a dive to a glide to a stall-and-drop, the whole of this article in nine throws. Then try the same trims in the app, where the model shows the angles and forces you can't see on paper.
Keep going
- Flight workshopWhy your paper airplane dives, stalls, or turnsName the flight pattern first, then make the one small change that matches it. A field guide to dives, stalls, turns and rolls.
- Before you foldChoosing paper for a paper airplanePrinter paper is the right place to start. When to switch, what gsm means, why Letter and A4 give different planes, and how to compare two papers fairly.
- Choose a designDart or glider: which paper airplane should you make?Pick a plane by what you want it to do and where you will throw it. How darts and gliders differ, with suggestions from all 44 designs.
- Try an experimentHow to run a fair paper airplane flight testA tape measure, a starting line and ten throws: how to find out whether a change really helped, with a printable log and a worked scoring example.
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