Building an Experimental Airplane, The Vans RV-7A | EP2.3 Rear Wing Spars - Ryan Flys The rear wings spars are built! Spars run the length of the wing giving them their strength. The Van's RV7 has two spars, like many planes: a main spar and a rear spar. The main spar was addressed in the last video, and this time we're constructing the rear spars. Also aluminum, but slightly less bulky, these spars must be constructed by the kit builder.