As a result of making the BirdDog plane for use on Laythe, I got interested in seeing if I could fly the plane into Kerbin orbit as an SSTO Spaceplane (one of the more difficult things to do in KSP, or so I hear tell). I stripped down the BirdDog, removing the rover parts and putting the TurboJet on in place of the regular jet engine, replacing one of the jet fuel tanks with a fuel/oxidizer tank, and adding four of the 24-77 radial rocket engines. I tried a few times to fly the modified BirdDog to orbit... but I always came up a little short, usually ending with the plane splashing down in an ocean landing (which breaks up the plane, but Corfrey Kerman and his cockpit managed to survive each time for Naval pickup). The best I did was an apoapsis of 110 km and a periapsis of 47 km... and another gliding splashdown in the ocean. So, as much as I have come to distrust the immediate urge to add MOAR FUEL, I modified the plane by adding another half tank of fuel/oxidizer (which helped with the CG after using the fuel up as well). And...I got into orbit:
With 31 units of oxidizer left (and a bit more fuel), the ship had 204 m/s of delta-V left upon reaching orbit (according to MechJeb's data readouts). So after a day in space, I fired the rocket engines again and brought the ship back, using up most of the oxidizer in the process.
Reentry heading toward KSC, which the plane passed over at about 14,000 meters.
I had a little jet fuel left to run the engines a bit to help me line up on the runway, then landed without a problem.
Almost out of fuel, Corfrey Kerman had returned safely to KSC. So ended my first successful SSTO spaceplane flight.