XR5 High Payload XR5 Ascent

[Nemoricus]

I've been experimenting recently with launching the XR5 with its nominal maximum payload of 432 metric tons, and I thought I'd offer my experiences with it along with asking for advice.

First off, the XR5 is really unresponsive with that much payload. You have to be gentle with the controls, because otherwise it's easy to overcorrect. I've lost track of the number times I've gone 'Ah! Stop turning! I've let go of the controls already!' because of this. Still, it's something you get used to after a while.

Also, shifting the center of gravity back all the way helps with take off and ensures that you'll not run out of runway. This is particularly important on Ascension Island, as you'd otherwise end up in the drink.

More challenging is being economic with your fuel. In particular, the ascent to the scram phase seems to be particularly important. I've found that a twenty-five degree ascent at about half power to 10km, followed by a full power boost a 100m/s vertical to 24km seems to work well. There, I level off and coast to mach 4.5, then turn on the scrams. I trim to keep my vertical speed at 100 m/s after that, right up until I start hitting 10kpa dynamic pressure, at which point I start pitching to keep it about that number. I usually run out of scram fuel around 6.2 km/s.

Orbital insertion is fairly straightforward, though I usually pitch up to about four degrees to build up a lot of vertical velocity to reduce the dynamic pressure. My latest attempt got me up with about a quarter left in the main fuel.

How have other people done? What do you recommend for flying this heavy bird into orbit?

Also, the attitude hold autopilot on the XR5 seems to be a little jittery and bouncy, and consistently hold a little above the set-point. Anyone else have this problem, or is it just me?

 

[Grover]

i have a rather similar launch routine, but i prefer to blast out of the lower atmosphere as soon as ive turned to launch heading, pitching to 40/50* (as high as possible without decelerating) on full throttle, levelling out smoothly around 25km, once at mach 4.5, the scrams go on, and i keep pitch as low as possible at first to build efficiency, then set the AP to pitch to 1.5* or 2*, then lower the throttle if hull temperatures get a little out of hand

that leaves me at above 50km, near orbital velocity, so its pitch to 20*, shoot outta the atmosphere, open the radiators ASAP, then open all other doors ill need on the journey, cut main engines when ApA is set, then coast to it. if i had aux fuel tanks, ill jetisson these whilst im still suborbital, each one weighs 4 tonnes, so you can save a little fuel by leaving them to burn up

our methods are similar, but we have our differences, i dont know whose is most efficient, but both work. it seems i have the "the atmosphere is the enemy, get out ASAP" approach and you have the "keep the nose and throttle down" approach.

i dont ever believe that there is only one way to perform the procedures we orbinauts do, everyone has their own methods, and nobody can say which is best, because all have their advantages to their user.

nice mini-tutorial though

 

[Wishbone]

A good area for a challenge-type scenario, please remember there is a Lua-script generator at OHM. Cannot subscribe to the "own methods" viewpoint, there should exist one optimal profile for a given combination of launch site/target orbit/payload conditions.

 

[Nemoricus]

The theory behind my low power ascent through the lower atmosphere is that it will minimize gravity losses by taking advantage of the XR5's natural lift. It's also easier to do, as you don't have to fight to raise the XR5's nose to the desired pitch.

And yes, a challenge sounds like a good idea. What do you think would be suitable? ISS ascent? Generic orbit at a specific inclination? Something else entirely?

 

[Tommy]

I'd suggest an ISS ascent, that way everyone is reaching for the same target and it eliminates a variable. You could likely adapt the script from Challenge #1 to account for scram fuel as well as main fuel.

My own testing suggests that a high initial pitch rate gives better efficiency. The lowest 10k of atmo simply provides too much drag. You need to keep velocity down (keep it subsonic), but you also want to get above 10k as quicky as possible. Using reduced throttle to keep the velocity down means a longer period in which you are in the highest drag part of the ascent - and that drag "adds up". Rather, try full throttle and pitch the vessel up as high as needed to keep ACC very low - and begin a smooth pitchdown at 10k, aiming for an ascent rate of less than 100 m/s by the time you hit 20k. Level out if needed to gain velocity at 24k.

I can't promise this works best for a fully loaded XR-5, but it's the best ascent profile for fully loaded XR-2's, DGIV's, and DG's.

 

[Nemoricus]

My own experience suggests that a low power ascent actually does save you fuel in an XR5, but the difference isn't that big. Still, you're not fighting gravity as much as with a high pitch ascent, and your drag losses aren't actually that bad since you aren't trying to power through the dense lower atmosphere.

The time to ascend to 10km isn't that much longer than a high pitch ascent, but you also aren't using as much fuel since the engines are throttled down.

Also, would you mind providing a link to that challenge? I can't seem to find the one you're referring to.

 

[Tommy]

Also, would you mind providing a link to that challenge? I can't seem to find the one you're referring to.

I'm referring to the LUA Challenge #1, which is included with Orbiter 2010 (and later). Can't remember exactly which folder (in scenarios) it's located in. Look for a folder named "Challenges", but I can't say what folder it's in - possible the Orbiter 2010 folder inside the scenarios folder.

I'll try to make a couple test flights to confirm, but I suspect that the higher pitch is more efficient. Remember, a loaded XR-5 needs quite a bit of airspeed just to stay airborne - over 200 m/s - and needs an AoA of just over 5 degrees (which increases drag more than you'ld think). Below 10k alt, even at that relatively low speed drag forces are still going to be around 5 - 7m/s. Increasing the lift means increasing the AoA, which increases drag. My prior tests have all proven that lift isn't cost effective at very low altitudes and airspeeds.

I could be wrong - my tests used similar vessels but not a full XR-5. I have notes from over 400 ascent tests - and a methodology designed to help me determine exactly what the effects of a change in one place have (it's hard to make sure that the ascent from, say, 20k up, is exactly the same on two different flights that use a differnt profile to get to 20k - and have different velocities when they get to 20k).

I will say that from about 20k and up, my profile agrees with yours - even on vessels without scrams. Lift is an essential part of my method - once lift becomes cost effective.

 

[HAL9001]

432 metric tons
First off, the XR5 is really unresponsive with that much payload. You have to be gentle with the controls, because otherwise it's easy to overcorrect. I've lost track of the number times I've gone 'Ah! Stop turning! I've let go of the controls already!' because of this. Still, it's something you get used to after a while.

that's why I have it had with my XR5 wich I set to more power in the cfg and than load with 1000 metric tons of cargo (It can still vertical launch from earth, but it's real hard to stear)

tip:
correct-> from the time the wrong moving stopped you see how much difference is left to your goal-direction/-position/etc... -> correct until half of this difference is gone -> than correct in the opposite direction, til you are at your goal-direction/-position/etc...

 

[orbekler]

...Also, the attitude hold autopilot on the XR5 seems to be a little jittery and bouncy, and consistently hold a little above the set-point. Anyone else have this problem, or is it just me?

Well, usually I correct smoothly but constantly pitch, because the resolution of 0.5° does not assure always the desired vertical speed.

 

[Grover]

ok, ive got a test:

we both use our own techniques, launching from the same place on the same heading, launching to the same orbital altitude, fully loaded of course. assuming that we both burn all our scram fuel, we only take into account the main fuel (no crossfeeding from RCS), the one who burns least is the winner.

i suggest launching from WIN, runway heading, to 300km alt, by any means. sound good? im gonna try it now

 

[Wishbone]

Be sure to set the same values for ISP etc. in the configs or better yet through scenario override. Final RInc at circularisation should be less than 0.10 degree, orbital altitude about 300 kms.

 

[Nemoricus]

I couldn't find a way to set the configuration in the scenario file, but here's a suitable starting point.

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 55985.5070969905
END_ENVIRONMENT

BEGIN_FOCUS
  Ship XR5-01
END_FOCUS

BEGIN_CAMERA
  TARGET XR5-01
  MODE Cockpit
  FOV 40.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_PANEL
END_PANEL

BEGIN_SHIPS
XR5-01:XR5Vanguard
  STATUS Landed Earth
  POS -14.4343728 -7.9701501
  HEADING 118.48
  RCSMODE 0
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000 2:1.000000
  IDS 0:199 100
  NAVFREQ 94 524 84 114
  XPDR 193
  SECONDARY_HUD 3
  LAST_ACTIVE_SECONDARY_HUD 0
  ADCTRL_MODE 7
  TAKEOFF_LANDING_CALLOUTS 0.000000 0.000000 0.000000 0.000000 0.000000
  APU_FUEL_QTY 1
  LOX_QTY 1
  CABIN_O2_LEVEL 0.209000
  CREW_STATE 0
  INTERNAL_SYSTEMS_FAILURE 0
  COGSHIFT_MODES 0 0 0
  MWS_ACTIVE 0
  COOLANT_TEMP 31.200000
  DMG_0 1.000000 Left Wing
  DMG_1 1.000000 Right Wing
  DMG_2 1.000000 Left Aileron
  DMG_3 1.000000 Right Aileron
  DMG_4 1.000000 Landing Gear
  DMG_5 1.000000 Docking Port
  DMG_6 1.000000 Retro Doors
  DMG_7 1.000000 Top Hatch
  DMG_8 1.000000 Radiator
  DMG_9 1.000000 Airbrake
  DMG_10 1.000000 Left Main Engine
  DMG_11 1.000000 Right Main Engine
  DMG_12 1.000000 Left SCRAM Engine
  DMG_13 1.000000 Right SCRAM Engine
  DMG_14 1.000000 Fore Hover Engine
  DMG_15 1.000000 Aft Hover Engine
  DMG_16 1.000000 Left Retro Engine
  DMG_17 1.000000 Right Retro Engine
  DMG_18 1.000000 Forward Lower RCS
  DMG_19 1.000000 Aft Upper RCS
  DMG_20 1.000000 Forward Upper RCS
  DMG_21 1.000000 Aft Lower RCS
  DMG_22 1.000000 Forward Star. RCS
  DMG_23 1.000000 Aft Port RCS
  DMG_24 1.000000 Forward Port RCS
  DMG_25 1.000000 Aft Star. RCS
  DMG_26 1.000000 Outboard Upper Port RCS
  DMG_27 1.000000 Outboard Lower Star. RCS
  DMG_28 1.000000 Outboard Upper Star. RCS
  DMG_29 1.000000 Outboard Lower Port RCS
  DMG_30 1.000000 Aft RCS
  DMG_31 1.000000 Forward RCS
  DMG_32 1.000000 Bay Doors
  DMG_33 1.000000 Elevator
  IS_CRASHED 0
  MET_STARTING_MJD -1.000000
  INTERVAL1_ELAPSED_TIME -1.000000
  INTERVAL2_ELAPSED_TIME -1.000000
  MET_RUNNING 0
  INTERVAL1_RUNNING 0
  INTERVAL2_RUNNING 0
  ACTIVE_MDM 3
  TEMP_SCALE 2
  CUSTOM_AUTOPILOT_MODE 0
  AIRSPEED_HOLD_ENGAGED 0
  SCRAM0DIR 0.000000 0.000000 1.000000
  SCRAM1DIR 0.000000 0.000000 1.000000
  HOVER_BALANCE 0.000000
  MAIN0DIR 0.000000 0.000000 1.000000
  MAIN1DIR 0.000000 0.000000 1.000000
  GIMBAL_BUTTON_STATES 0 0 0 0 0 0
  ATTITUDE_HOLD_DATA 0.000000 0.000000 0 0 0.000000
  DESCENT_HOLD_DATA 0.000000 -3.000000 0
  AIRSPEED_HOLD_DATA 0.000000
  OVERRIDE_INTERLOCKS 0 0
  TERTIARY_HUD_ON 1
  CREW_DISPLAY_INDEX 0
  GEAR 1 1.0000
  RCOVER 0 0.0000
  DOCKINGPORT 0 0.0000
  AIRLOCK 0 0.0000
  IAIRLOCK 0 0.0000
  CHAMBER 0 0.0000
  AIRBRAKE 0 0.0000
  RADIATOR 0 0.0000
  LADDER 0 0.0000
  HATCH 0 0.0000
  SCRAM_DOORS 0 0.0000
  HOVER_DOORS 0 0.0000
  BAY_DOORS 0 0.0000
  ELEVATOR 0 0.0000
  APU_STATUS 1
  EXTCOOLING_STATUS 1
  TRIM 0.000000
  LIGHTS 1 0 1
  XRUMMU_CREW_DATA_VALID 1
  UMMUCREW XI0-Tom_Fisher-37-65-78
  UMMUCREW XI1-Russ_Hicks-29-65-54
  UMMUCREW XI2-Doug_Beachy-36-68-58
  UMMUCREW XI3-Steve_Tyler-24-71-68
  UMMUCREW XI4-Katherine_Quinn-28-67-56
  UMMUCREW XI5-Cameron_Mitchell-36-65-77
  UMMUCREW XI6-Samantha_Carter-33-66-53
  UMMUCREW XI7-Daniel_Jackson-35-68-75
  UMMUCREW XI8-Teal_c-31-64-104
  UMMUCREW XI9-Vala_Mal_Doran-30-67-53
  UMMUCREW XI10-Elizabeth_Weir-36-68-56
  UMMUCREW XI11-John_Sheppard-34-64-77
  UMMUCREW XI12-Rodney_McKay-35-72-90
  UMMUCREW XI13-Teyla_Emmagan-27-68-57
  UMMUCREW XI14-Ronon_Dex-32-63-97
  UMMUCREW XI15-Carson_Beckett-38-74-95
  UMMUCREW XI16-Lee_Adama-26-65-74
  UMMUCREW XI17-Kara_Thrace-26-67-55
  RCS_DOCKING_MODE 0
  ACTIVE_EVA_PORT 0
  PAYLOAD_SCREENS_DATA 0.2 4 1 15
END
XR5-01_Bay:XRPayloadBay
  STATUS Landed Earth
  POS -14.4345606 -7.9700492
  HEADING 118.48
  ATTACHED 0:36,XR5-01
  AFCMODE 7
END
XRParts-01-1:XRParts
  STATUS Landed Earth
  POS -14.4343883 -7.9701978
  HEADING 118.48
  ATTACHED 0:0,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-02-1:XRParts
  STATUS Landed Earth
  POS -14.4343777 -7.9701785
  HEADING 118.48
  ATTACHED 0:1,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-03-1:XRParts
  STATUS Landed Earth
  POS -14.4343645 -7.9701545
  HEADING 118.48
  ATTACHED 0:2,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-04-1:XRParts
  STATUS Landed Earth
  POS -14.4343511 -7.9701300
  HEADING 118.48
  ATTACHED 0:3,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-05-1:XRParts
  STATUS Landed Earth
  POS -14.4343406 -7.9701108
  HEADING 118.48
  ATTACHED 0:4,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-06-1:XRParts
  STATUS Landed Earth
  POS -14.4344369 -7.9701717
  HEADING 118.48
  ATTACHED 0:5,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-07-1:XRParts
  STATUS Landed Earth
  POS -14.4344264 -7.9701524
  HEADING 118.48
  ATTACHED 0:6,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-08-1:XRParts
  STATUS Landed Earth
  POS -14.4344132 -7.9701283
  HEADING 118.48
  ATTACHED 0:7,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-09-1:XRParts
  STATUS Landed Earth
  POS -14.4343998 -7.9701039
  HEADING 118.48
  ATTACHED 0:8,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-10-1:XRParts
  STATUS Landed Earth
  POS -14.4343892 -7.9700846
  HEADING 118.48
  ATTACHED 0:9,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-11-1:XRParts
  STATUS Landed Earth
  POS -14.4344856 -7.9701455
  HEADING 118.48
  ATTACHED 0:10,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-12-1:XRParts
  STATUS Landed Earth
  POS -14.4344750 -7.9701263
  HEADING 118.48
  ATTACHED 0:11,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-13-1:XRParts
  STATUS Landed Earth
  POS -14.4344619 -7.9701022
  HEADING 118.48
  ATTACHED 0:12,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-14-1:XRParts
  STATUS Landed Earth
  POS -14.4344485 -7.9700777
  HEADING 118.48
  ATTACHED 0:13,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-15-1:XRParts
  STATUS Landed Earth
  POS -14.4344379 -7.9700585
  HEADING 118.48
  ATTACHED 0:14,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-16-1:XRParts
  STATUS Landed Earth
  POS -14.4345342 -7.9701194
  HEADING 118.48
  ATTACHED 0:15,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-17-1:XRParts
  STATUS Landed Earth
  POS -14.4345237 -7.9701001
  HEADING 118.48
  ATTACHED 0:16,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-18-1:XRParts
  STATUS Landed Earth
  POS -14.4345105 -7.9700761
  HEADING 118.48
  ATTACHED 0:17,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-19-1:XRParts
  STATUS Landed Earth
  POS -14.4344971 -7.9700516
  HEADING 118.48
  ATTACHED 0:18,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-20-1:XRParts
  STATUS Landed Earth
  POS -14.4344866 -7.9700323
  HEADING 118.48
  ATTACHED 0:19,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-21-1:XRParts
  STATUS Landed Earth
  POS -14.4343777 -7.9701785
  HEADING 118.48
  ATTACHED 0:20,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-22-1:XRParts
  STATUS Landed Earth
  POS -14.4343645 -7.9701545
  HEADING 118.48
  ATTACHED 0:21,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-23-1:XRParts
  STATUS Landed Earth
  POS -14.4343511 -7.9701300
  HEADING 118.48
  ATTACHED 0:22,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-24-1:XRParts
  STATUS Landed Earth
  POS -14.4344264 -7.9701524
  HEADING 118.48
  ATTACHED 0:23,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-25-1:XRParts
  STATUS Landed Earth
  POS -14.4344132 -7.9701283
  HEADING 118.48
  ATTACHED 0:24,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-26-1:XRParts
  STATUS Landed Earth
  POS -14.4343998 -7.9701039
  HEADING 118.48
  ATTACHED 0:25,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-27-1:XRParts
  STATUS Landed Earth
  POS -14.4344750 -7.9701263
  HEADING 118.48
  ATTACHED 0:26,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-28-1:XRParts
  STATUS Landed Earth
  POS -14.4344619 -7.9701022
  HEADING 118.48
  ATTACHED 0:27,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-29-1:XRParts
  STATUS Landed Earth
  POS -14.4344485 -7.9700777
  HEADING 118.48
  ATTACHED 0:28,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-30-1:XRParts
  STATUS Landed Earth
  POS -14.4345237 -7.9701001
  HEADING 118.48
  ATTACHED 0:29,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-31-1:XRParts
  STATUS Landed Earth
  POS -14.4345105 -7.9700761
  HEADING 118.48
  ATTACHED 0:30,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-32-1:XRParts
  STATUS Landed Earth
  POS -14.4344971 -7.9700516
  HEADING 118.48
  ATTACHED 0:31,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-33-1:XRParts
  STATUS Landed Earth
  POS -14.4343645 -7.9701545
  HEADING 118.48
  ATTACHED 0:32,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-34-1:XRParts
  STATUS Landed Earth
  POS -14.4344132 -7.9701283
  HEADING 118.48
  ATTACHED 0:33,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-35-1:XRParts
  STATUS Landed Earth
  POS -14.4344619 -7.9701022
  HEADING 118.48
  ATTACHED 0:34,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
XRParts-36-1:XRParts
  STATUS Landed Earth
  POS -14.4345105 -7.9700761
  HEADING 118.48
  ATTACHED 0:35,XR5-01
  AFCMODE 7
  NAVFREQ 0 0
END
END_SHIPS

Fully loaded XR5, all set to take off from Wideawake's launch runway with 432 metric tons of cargo in the bay.

Settings should be:

MainFuelISP=2
SCRAMFuelISP=0
# These ensure that the XR5 has the same mass due to oxygen loadout.
LOXLoadout=1
LOXConsumptionRate=-1
MainEngineThrust=1
SCRAMfhv=1
SCRAMdmf=1
EnableATMThrustReduction=1

These are the default settings, in any case, and I don't think that any others matter.

Your target is a 300km x 300km orbit from a launch azimuth of 118 degrees. Your goal is to minimize main fuel expenditure on the ascent.

Also, post replays of your best ascents, please!

 

[Grover]

using the above starting scenario, i managed to launch to 300Km orbit with 24.4% fuel remaining in main tanks (56,230.0 Kg)

i forgot to record it, so you'll have to take my word for it, i hope it was enough to prove my attempt as the most efficient!

i saved the scenario once i reached orbit, if anyone wants to check it, (drop it in ..\..\Orbiter2010\Scenarios)

later dawg!

 

[Nemoricus]

My own ascent attempt. 24.8 % main fuel left after the final orbit insertion burn.

Final orbit - 300.00 x 300.08

Main fuel - 57320.6 kg
RCS fuel - 13001.3

Playback is attached.

 

[PennyBlack]

I down took a copy of your scn and your orbit is exellent Grover. Your PeA, ApA and Alt all read 300.1k down to Ecc which is at 0.0000.
Your readouts on the fuel are impressive.

I would like to try this myself, test-pilot stuff.

I got my XR5 on the runway all prep'd.

Vessel... XR5. Standard install of the XR5 Version 1.5 (un-editted)
Cargo... XR-Class Replacement Parts. 420,000Kg (432 metric tons)

Total wieght... 1,004,284Kg (1004 metric tons). Fully fueled with MAIN, RCS, APU, LOX and Scram Juice and the passengers. I'm not likely to throw Sam Carter off am I.

I'll run the trip tomorrow because it's late here, but I'll try to record it as well as supply a scn file for viewing.

:tiphat:

 

[Tommy]

I had a chance to look though my notes, turns out I did make some tests with a loaded XR-5. I found little evidence to suggest that the steeper initial pitch (loaded, an XR-5 can only hold airspeed with a pitch ange of 45 to 50 degrees) was noticably more efficient than a lower initial pitch. I suspect much of this is due to the XR-5's slow acceleration rate - even at a lower pitch you don't gain much speed.

I did notice that I found better results when I pitched down a bit sooner - arround 8k rather than 10k - and had a pitch angle of about 20 degrees by the time I had hit 12k, that's much "shallower" than a DG or XR-2.

The lower pitch above 8k allows the XR-5 to get up to scram speed by 24k so less time is spent holding altitude while you gain velocity. Since the XR-5 accelerates slower, and has a higher scram speed (about 4.5k compared to 3.5k for an XR-2, it's clear that an earlier pitchdown and lower VS will help.

Maybe in a couple days I'll have a chance to make a new flight based on your scenario - but the old tests produced results very much in line with yours. I doubt I'll do better - and if I do it won't be by much!

 

[jthill]

I... I killed them. All. The scram jets, they are too powerful for my tiny mind.

(added by edit

26.0% fuel remaining. Scram efficiency seems to be a matter of running them dry just before they overheat. Recording with 36 cargos makes my poor little box sad, so I settled for a screenshot. It's all DNP management, the scrams just want to run DNP 8-20 like the book says, I lit around 8, it peaked above 17, drifted back down to 4.5 or so by the time I needed the mains again.

Got into this weird Narnia orbit, ApA never came and I eventually had to just rotate 90deg and burn straight up to get there, then recircularize. Didn't take much fuel, it was only 15km or so.

 

[PennyBlack]

I got preloaded body bags on board, such is my predictability. :facepalm:

Getting into orbit is no problem, but with a full load, it's certainly an entertaining challenge. I'm getting better and will try again tonight before watching BSG. I've read the posts since mine and hope they help.

And the Sam Carter cloneing facility is still fully opperational. :thumbup:

 

[Nemoricus]

26.0% fuel remaining. Scram efficiency seems to be a matter of running them dry just before they overheat. Recording with 36 cargos makes my poor little box sad, so I settled for a screenshot. It's all DNP management, the scrams just want to run DNP 8-20 like the book says, I lit around 8, it peaked above 17, drifted back down to 4.5 or so by the time I needed the mains again.

Nice run. Would you mind giving more details of the ascent?

 

[jthill]

Sure. For all the nitty-gritty details I attached a flight data monitor log of one I just did. I ran out of patience getting the last 15km on this one, I ended with 26.1% main, ApA/PeA 300ish/280ish. Same ApA-never-comes orbit.

To reproduce it yourself won't be hard, the basic thing is to pitch so DNP is under control, so you can stop and reverse its change at any time, within seconds, without wrecking L/D. That matters more than anything. With the boundary layers that takes some anticipating, and if DNP drops too much you're either going to fall out of the sky or nose up so much you push AoA off the peak-L/D cliff, so sometimes you have to shove the nose down hard to avoid getting into oscillation (or burn-up-and-die) territory. But mostly I do it with trim alone. Between layers there's a sweet spot for any AoA where VAcc and DNP synch up and you can fly hands off, DNP slowly dropping and VAcc slowly oscillating near zero. Once you can find an ascent path like that, the thing to do is work on finding one with the sustained DNP as low as possible.

There's a playback with that balancing act for the stock DG in the post-your-scores thread under tuts and challenges, the <5400 milestone. I followed the same rules with the XR5 on mains, before and after the scrams, but the XR5 handles AoA's much higher than the DG so it doesn't need any gimbal work.

The scram profile starts out straight out of the book, target DNP 8ish at mach 4.5, do the cutover and manage DNP so the scrams peak below DNP 20. I try to run out of fuel with DNP about 4.5 and Sally getting acerbic about the scram temperature. I haven't experimented much with that last number, higher is definitely worse. One thing you'll see in the logs, I don't mess with pitch much waiting for the scrams to bite. I shut off the mains, open the scram doors, light them up and wait. I don't know how much that matters.