A typical, but not only, rocket design is for the airframe to be split near the middle. A drogue parachute is a small parachute used to stabilize and slow the descent of the rocket. The rocket should descent horizontally to the ground to maximize drag. A drogue is usually much smaller than the main parachute. For example, a five pound rocket may use a 12” drogue parachute.
A drogue is not always needed. For example, a two pound, 2.6” diameter rocket that falls horizontally without a drogue probably does not need one. For example, a 50” long, 2.6” diameter airframe of a 2 pound rocket will fall at about 35 feet/second if the airframe falls horizontally. Provided the rocket will fall horizontally without a drogue, a drogue is not needed.
A drogue and main parachute can sometimes be deployed from the same location. This technique usually requires sufficient airframe diameter to contain a canister to hold the main and drogue, and separate ejection charges for each. One problem with this technique is the potential for the main parachute to become tangled with the drogue. This risk can be reduced by making the drogue’s bridle longer than the main’s bridle so that the parachute’s cannot meet. The drogue should deflate when main inflates.
Submitted by: Dean A. Roth