Air-breathing mode laser propulsion experiment with a long-pulse transversely excited (TE) CO₂ laser is carried out, and its ignition problem is solved with the ignition needle of lightcraft. Owing to the ignition needle, an order of magnitude reduction in the ignition threshold is demonstrated. The result is compared with previous study. The momentum coupling coefficient is also measured in the experiment and its dependence upon laser pulse energy (6-14 J) and pulse width (20, 32, and 40 \mu s) is discussed.