Flight Question XR5 ascent fuel problems

[dallatorretdu]

Hello, It's been a while but i'm back here with two questions.
I'll post one later since this one is more important.
Well as the title says it regards the XR5 Vanguard from Altea Aerospace aircraft.
Quite intriguing piece of ship, I have it here from a year now and never seriously tested it.
It's too big and i cannot launch it with a vector (I use the HLLV from kulch), still he can't even make a direct-style ascent (I red it somewhere).
So here I go:
Departurefrom KSC on the runway. The takeoff is entirely made by main trusters. After getting the gears up i set the Scrams to 100% and the main at 10%, keeping an AOA of +10° - +15° so the direction vector was over 5°
after few minutes I was in space and scrams were getting useless.
I waited to get to my ApA (apoapis right?) for make a prograde burn.
Well.. I reached 18% fuel without establishing a safe orbit and I was even Unaligned so...
My altitude at ApA was +-250km
the ship cargo bay was empty
I consumed just like 30% of the scram fuel
The ship has been updated

I found space tugs unreliable for intercepting duties and I wanted to build up a space station without just clicking add, ok, dock here, add, that sounds stupid...
The Xr5 may be the answer, and maybe the knowledge on how to aquire the right equatorial inclination from takeoff but that's another topic​

Anybody can give me some tips?
Tank you anyone :tiphat:

 

[Cras]

sounds to me you need to level out your ascent a bit. Stay in the atmosphere longer so you can use up all your Scram fuel.

 

[dgatsoulis]

{snip}...After getting the gears up i set the Scrams to 100% and the main at 10%, keeping an AOA of +10° - +15° so the direction vector was over 5°...{snip}

Where exactly does it say in the XR flight operations manual, that that's the way to take off in an XR5? You ignited the SCRAM engines way too early.
Please read pages 31-35 "Walkthrough: Launch from KSC to Low-Earth-Orbit" for the correct ascent to orbit procedure.

{snip}...and maybe the knowledge on how to aquire the right equatorial inclination...{snip}

You may want to use Enjo's [ame="http://www.orbithangar.com/searchid.php?ID=2802"]Launch MFD[/ame] or george7378's [ame="http://orbithangar.com/searchid.php?ID=5757"]Space Calculators V2[/ame] or you can make a search for launch azimuth in the forums and in Google to learn a bit more.

Hope this helps

 

[Grover]

heres my own ascent procedure, its never failed me:

if you have no cargo, lose about 25% scram fuel, it is simply unusable

take off and roll to heading, keeping well below mach 1

engage the AP to hold 45* pitch and no roll, max the thrust and keep it there

at 17km, set the AP to hold 2* pitch, you will be almost level at ~25km

accelerate at this state to mach 4, then open the scram doors, let off the mains, and light the scrams

leave it to do its thing, if the balance between scram fuel and scram temperature shows that you'll heat up before you run out of fuel, dump a bit of fuel (or keep it for after re-entry)

after scram cutoff (wither at max diffuser temp, or no fuel) pitch to 20* and hit the mains till your ApA is at your target, then MECO

you should be high enough to be able to deploy radiators and get in your orbital state

continue mission as planned

its never failed me!

 

[Ripley]

dallatorretdu, you really don't need it, since your English is quite good, but may I humbly advertise to you my ITA translation of the XR Flight Operations Manual 2.6?

 

[Aeadar]

My procedure for launching an (unloaded) XR5:

1. As Grover says, lose at least 25% Scram fuel. I reduce mine to about 65%.

2. Preset Airspeed AP to 215kps. Preset Attitude AP to about 15 degrees.

3. When you're ready to take-off (APU on and AF Ctrl on), engage the Airspeed AP.

4. As you begin to roll, switch to the Attitude AP and wait for the "V1" callout.

5. At V1 Callout, engage the Attitude AP. The nose will begin to come up as you hear "Rotate".

6. At the "Wheels up" callout, hit 'G' to raise gear.

7. At this point, if needed, Use the bank controls (numpad 4 and 6) to turn to your desired heading.

8. Once at the proper heading, I disengage the Airspeed AP, go to full throttle, and increase pitch to 50-60 degrees. You won't have to keep it there for long; you'll be passing through 7 or 8k altitude by the time you get to 50 degrees.

9. After passing through Mach1, begin bringing the pitch down keeping an eye on altitude and temps. I try to be about 40k altitude as I pass through Mach5.

10. After Mach5 and before Mach6, I cutoff main engines, open the Scram doors and start bringing up the Scram throttle.

40k may be a bit high, and you may start coming down a bit, but that's ok; you'll reach max scram efficiency very quickly that way. Just keep an eye on your temps; raise pitch a bit if your temps are coming up, reduce pitch (to around 0-2.5 degrees) if the temps are dropping.
Scram shutdown when Scram inlet temps go red. At this point I coast until I've dumped the remaining Scram fuel (usually about 4-5%), then re-engage the mains for the final push. Once my APA is at my desired altitude (for me about 500k), cutoff the mains and wait for Apoapsis to circularize your orbit.

Hope this helps.

Good Luck!

 

[dallatorretdu]

Okay, tank you everyone. Following every tips you gave to me I decided to engage the scram engines at mark 4 at 25k KM and slowly got to 50-60% scram fuel (then the intake temperature was nearly 8000)
The Main fuel is 45% I just need to get to my ApA and adjust my PeA.

If I can ask... I downloaded a complex azimuth calculator where I filled every launch information and the information of the earth (precompiled)
He told me to launch at 15° ascending and ... 150 Descending I guess.
So... i pointed my compass at 15° but in orbit i got to 32° instead of 64°

Probably I'm not off topic since this is still an ascending issue :thumbup:

 

[garyw]

Okay, tank you everyone. Following every tips you gave to me I decided to engage the scram engines at mark 4 at 25k KM and slowly got to 50-60% scram fuel (then the intake temperature was nearly 8000)
The Main fuel is 45% I just need to get to my ApA and adjust my PeA.

Do you slowly shut down the main engines when you ignite the scrams?

 

[orbekler]

...If I can ask... I downloaded a complex azimuth calculator where I filled every launch information and the information of the earth (precompiled)
He told me to launch at 15° ascending and ... 150 Descending I guess.
So... i pointed my compass at 15° but in orbit i got to 32° instead of 64°...

Which is your destination?

 

[dallatorretdu]

Yes, i shut the mains slowly when igniting the scrams, mains were completely off when scrams were already at 100.000+

Departure from SRC space poligon: LON 101.138; LAT 1.308;
Target: a module of mir-2 in orbit INC 67.0041; LAN 236; ECC 0.0648; ALT +-250km;

The ascending azimuth vas 19.7.
I think i made everithing quite good

 

[Cras]

I aim for a constant dynamic pressure when I fly SCRAM ascent with any XR vessel. 10Kpa.

Keep it at that and I find I do quite well with the fuel.

However, I have not flown a SCRAM ascent in a while. I prefer to just attach velcro rockets and take it up that way.

 

[dallatorretdu]

I aim for a constant dynamic pressure when I fly SCRAM ascent with any XR vessel. 10Kpa.

I'm not able to do that, at the start of the scram ascent i got 40kpa, then for most of the travel 8kpa lowering.
In his last launch I made (theorically the same, just redo many times) i trued to get 10kpa stables but my ascent wasn't stable. Uh I got the point of the launch mfd and the azimuth calculator too. This time my orbit was off by just 1°, even if my launch is worked on what I see on the MFD, not the datas it tells to me like "intercept time" and other big words (I'm based on the azimuth ascending and descending and the plot graph in the background)

Tank you everyone! :tiphat:

Now cross the fingers for the intercept

 

[Cras]

What exactly do you mean by that it was not stable?

For the main engine ascent from the runway just get up as fast as you can, to like...I dunno 30 km? Level out, hit mach four. Kill the mains, Turn on the SCRAMS, fall back into the atmosphere, watch them kick into high gear, then adjust your pitch to maintain the constant dynamic pressure. Eventually you will be so high that the dynamic pressure will just drop. I recommend never going below like 2.5 degrees in pitch and if the dynamic pressure still drops, then let it drop.

 

[jthill]

I aim for a constant dynamic pressure when I fly SCRAM ascent with any XR vessel. 10Kpa.

Was that a typo? The scrams are _much_ more efficient in the high 20's/low 30's. I keep VAcc as low as hull temperature will allow while the scrams are lit. Trying it just now I didn't dump fuel, hit MECO at 200km ApA and ~65% main, 35% scram remaining.

 

[Cras]

Not a typo. I find any higher in dynamic pressure and there is too much heat on the hull....wasted energy.


BUt again, there may be better ways, as I never use the SCRAMS on the XR-2 anymore. Yes I know this is an XR-5 thread, but I have used the same procedure when messing about with the XR-5 before to very acceptable results.