Here's a bit I just found about X-15 plane.
"The pilot would start a gentle pushover at about 70,000 feet for a heating flight so that he could level out at around 100,000 feet or less, and all control would be done with aerodynamic control surfaces. [58, p.189] For altitude flights, the pilots continued upward at a fairly steep angle and either continued to engine burnout or shut the engine down at a predetermined speed or altitude. They would spend two-to-five minutes out of the atmosphere in a weightless condition. [26, p.92] When above 200,000 feet, the aerodynamic controls had no effect, and pilots had to use the reaction control system for attitude control. [7, p.198] Speed flights would be done at the lowest altitudes, around 50,000 feet, and would have the longest ranges, around 400 miles. Control would be with aerodynamic control surfaces only. For speed flights, it was NACA practice to increase speed by one half Mach number for each successive flight. [15, p.322]"
100 k feet is 30.5 km. 200 k feet is 61 km. We also know that X-43 did have a controlled flight at 33 km. So, wz8 cruise altitude is likely between those two figures. Probably closer to 33 than to 61 km. Speed wise, who knows. X-43 did mach 9.6 at just 33 km. X-43 was perhaps more of a big scramjet missile than a real plane, though. So perhaps X-15 comparison is more apt. mach 6.7 at 31 km. Interestingly, due to controllability, X-15 had highest speed at said, fairly low altitude, even though it could reach much higher (100 km) in a ballistic trajectory. X-15 is also a good comparison due to its liquid rocket fuel engine. It used up 6.8 tons of rocket fuel in 80-90 seconds.
"The pilot would start a gentle pushover at about 70,000 feet for a heating flight so that he could level out at around 100,000 feet or less, and all control would be done with aerodynamic control surfaces. [58, p.189] For altitude flights, the pilots continued upward at a fairly steep angle and either continued to engine burnout or shut the engine down at a predetermined speed or altitude. They would spend two-to-five minutes out of the atmosphere in a weightless condition. [26, p.92] When above 200,000 feet, the aerodynamic controls had no effect, and pilots had to use the reaction control system for attitude control. [7, p.198] Speed flights would be done at the lowest altitudes, around 50,000 feet, and would have the longest ranges, around 400 miles. Control would be with aerodynamic control surfaces only. For speed flights, it was NACA practice to increase speed by one half Mach number for each successive flight. [15, p.322]"
100 k feet is 30.5 km. 200 k feet is 61 km. We also know that X-43 did have a controlled flight at 33 km. So, wz8 cruise altitude is likely between those two figures. Probably closer to 33 than to 61 km. Speed wise, who knows. X-43 did mach 9.6 at just 33 km. X-43 was perhaps more of a big scramjet missile than a real plane, though. So perhaps X-15 comparison is more apt. mach 6.7 at 31 km. Interestingly, due to controllability, X-15 had highest speed at said, fairly low altitude, even though it could reach much higher (100 km) in a ballistic trajectory. X-15 is also a good comparison due to its liquid rocket fuel engine. It used up 6.8 tons of rocket fuel in 80-90 seconds.
