Perfect alignment

How straight are your fins really? This challenge finds out. Fly any rocket, on any motor, above 200 m, and the flight with the least spin during the motor burn wins.

Spin is the fastest roll rate your altimeter's gyro logs while the motor is burning, in degrees per second. Lowest wins.

Why rockets spin

A rocket rolls when its fins push the air unevenly: a fin set a fraction of a degree off the body's axis, a warped fin, or one fillet fatter than the others. The faster the rocket goes, the faster that small error spins it, so the burn, when the rocket is picking up speed hardest, shows it up best.

Tips for a spin-free flight

• Use a fin alignment guide or jig, so every fin goes on at the same spacing and dead straight along the body.
• Check each fin from behind and along the tube before the glue sets. Even a small twist shows up as spin.
• Use flat, stiff fin stock and seal it, so the fins don't warp.
• Keep the fillets the same size on both sides of every fin.
• Fit launch lugs or rail buttons straight along the body. A skewed lug pushes the air sideways too.
• Mount the altimeter firmly so it turns with the rocket and nothing rattles.

Entering your flight

Upload the flight as normal, then fill in what the Required flight details tab lists on its flight page, such as the motor and the launch site, date and time. Then open the Add my flight tab here and pick it. Spin is measured by the altimeter's gyro, so check the Required altimeters tab first.

Fly safely, and follow the safety code of your club or national association.