Flight Question Take off issue with the XR2

[C3PO]

because the XR-2 has such a powerful engine compared to a regular jet, I get up to V-1 and then throttle down to about 20%, take off, and retract at about 50 meters. Then I turn to my correct heading at a low (low for xr-2), speed to avoid wing stress, pitch up a little and kick the throttle. I climb at about 40-50 degrees to about 15km and begin leveling out and collecting speed for SCRAMs.

I use a slightly different method, mainly because the XR-2's wings don't generate very efficient lift at low speed.

At V1 I rotate to ~15°, raise the gear ASAP, and continue to rotate to ~50° while banking towards the launch heading. I sometimes get a gear warning just as the gear finishes retracting. If I have the joystick connected, I throttle down to 80% at V1.
Getting to higher altitude quickly is important because the main engines aren't as efficient in thicker air. You can save a fair amount of fuel if you can go ballistic on the correct heading as soon as possible.

I don't like to fly at large negative AoA, so I lower the thrust a bit to help level off at SCRAM altitude. You can even use bank to level out. Large negative Gs would be very uncomfortable for the crew/passengers.

 

[johan]

Large negative Gs would be very uncomfortable for the crew/passengers.

I've been using large negative G every single time I launch in the XR2, and my passengers never complain! :lol:

Anyway, I suspect using large negative G is an inefficient way to fly, next time I'll try what you do (with the throttle) and see if it makes an appreciable difference.

 

[n122vu]

I use the profile & procedures outlined in the XR flight manual. Works well and I've never had a problem.

 

[Gr_Chris_pilot]

120m/s autothrottle after v1 and climb 20deg until gear is up... then 60-70deg full power until 25-30k and scram ready speed...

Even 120m/s (233knots) is too much for a single tyre gear system... The only commercial aircraft i know that can safely rotate close to that speed is the Concorde 111m/s (217Knots) with an amazing 4 tyre gear system of course

 

[johan]

Right, so I did some burns to test it out. Every run was done up till Mach 4, closing the throttle smartly - since this is the point where you would switch to scram, and the rest of the ascent is a separate matter.

I used the same scenario for all runs, where we're sitting in an XR2 at Cape Canaveral, ready to ascend to the ISS - only to make this repeatable, I included no heading change - just accelerate straight on the runway heading, with different pitch profiles.

The last few runs I did with the attitude hold autopilot, so they should be quite accurately reproduce-able. The rest I flew by joystick, so your mileage my vary slightly.

[Edit: Also, no fiddling with the throttle at takeoff - pitch up all the way at rotate speed, and retract the gear as soon as we have wheels up. Yes I know you'd never do this in a real aircraft unless you had suicidal tendencies.]

I highlighted some of the more impressive runs.

Profile Main fuel left at M4
80° -> 15km, full throttle, level at 21km 9721
80° -> 18km, close throttle, level at 20km 9665
90° -> 15km, pitch up to inverted level at 20km 9805
70° -> 15km, full throttle, level at 21km 9802
70° -> 18km, close throttle, level at 20km 9718
60° -> 15km, full throttle, level at 20km 9820
60° -> 18km, close throttle, level at 20km 9769
50° -> 16km, full throttle, level at 21km 9801
80° -> 10km, 40° -> 18km, full throttle, level at 20km 9758
80° -> 8km, 40° -> 18km, full throttle, level at 21km 9790
70° -> 8km, 30° -> 18km, full throttle, level at 21km 9847 80° -> 3km, lose 5° per km altitude, full throttle, level at 20km 9915 80° -> 4km, lose 5° per km altitude, full throttle, level at 20km 9927 80° -> 9km, lose 7.5° per km altitude, full throttle, level at 20km 9872