The pulsing smoke is done using the transmitter's sequencer function. The two guys are Horizon pilots and the last I saw they were using DX-18 transmitters. The "lead" plane has a regular setup bound to the transmitter. The second plane has a second receiver, bound to the "lead" plane's transmitter. The second receiver is used only for smoke.

It's a great idea and looks fabulous in the air.

Regards,

Jim