This is concerning the Ranger's thrusters : VTOL mode, while working fine with just the ranger fuselage, is not achievable when equipping the Cooper engines. It moves the center of mass to the rear and makes the craft do a backflip when trying a VTOL takeoff or landing with full throttle. Even with maximum pitch to balance and RCS, it just can't be done. It clearly isn't supposed to act like that. I understand it is difficult to balance these crafts, but here you just can't takeoff, with minimum thrust, the instant you're off the ground, even full SAS and RCS can't save you. The problem is fixed by either in an editor, angling better the VTOL thrust, setting the engines mass to near 0 or moving the center of mass and lift further front.
Another bug I found, is that the landing gears of the Ranger have a weird behavior. While in the air or even on the ground, if you deploy the landing gears, the craft will start to spin like there is no tomorrow. Actually, the landing gears clearly are applying an external force : if you're on the ground with the craft upside down, deploy the gears and you'll start moving forward at around 10 m/s, creating the cleanest ground travel method. You're kept on the ground because the force isn't parallel to the craft but angled with the craft's axis.
I also found out that the Ranger's engines keep flaming out as others have already told you but not because of an intake air issue, but because they consume too much electric charge. It's a behavior I have never seen, but the Cooper engines consume more electricity the more thrust they produce, to the point when electricty generated by the craft (around 170Ec/s) is overcome by the consumption. When electric charge is then depleted, the right engine shutdowns (for some reason, it's always the right one) and the craft starts spinning as the other one still functions. Sometimes, both engines will keep working but you'll lose all SAS control and a lot of stability as all Ec is used by the engines working slower.
Hope it helps, I looove the Ranger. ^^