djolds1 wrote:Its just those first few hundred meters per second dv before the ram-air effect is possible. Twelve seconds at 3gees to boost upto 350m/s. Early designs such as the Saenger Silverbird and Soviet Keldysh used sleds, but the efficiency of QED/ARC makes a sled superfluous. Twelve seconds of low altitude QED/ARC burn per flight doesn't seem very significant. And using one type of engine (QED/ARC-RBCC) eliminates additional complexity.
Well you don't get 3g out of those engines though.. in my current tests i calculated with 2 x 6GW Reactors. At 1500s ISP they produce a thrust of ~1631 kN, so a bit over 0.5g for a 300ton ship. They burn, or rather heat 110kg of propellant per second. Thats almost 8 tons of propellant for just accelerating to 350 m/s and you need some additional energy for a climb to 8-10km altitude to avoid too high dynamic pressures. Also you loose some energy to drag. So i guess we're more looking at 10-15 tons propellant used to get to 350 m/s.
To compare that to ducted fans, i get about the same thrust with just 300-400MW shaft power with a total fan area of 16 m^2. Also they would probably not weigh so much more than the propellant saved by using them.
Also those fans would be more like axial compressors with a pressure ratio of about 1:4. They would sit in the airflow path to the QED engine and would benefit the pressure ratio of the engine up to about M2.8.
Heres a little pic i made for roughly illustrating the concept:
Its very basic but shows the general idea.
Oh, IMO forget "Rasterscan the underbody." Instead, scan the REB inside a "standard" (sc)ramjet engine tube. The forebody/diffuser locks forward for "pure" ARC mode, but retracts to allow airflow. Place the REB generator in the engine tube like the rocket engine in a "standard" RBCC.
Yep i thought something like that too.. just use the standard QED engine and feed it with air from a seperate inlet channel.. (see pic above)