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Old 07-17-2008, 08:41 AM   #1
James.Denholm
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Question A pilot gets his wings! And then asks for help.

Well, today is a special day for me. Today, I made my first complete trip, from the Cape to ISS, then from the ISS to Acension Island. Happy days! To make it all the better, it was using a standard (gasp) XR1!

Now, I'll be truthfull. The acent left something to be desired, didn't exactly stick to the flight plan in the manual. That's fixable with practice. Now, the docking, that was a bit un-orthidox. Lot's of frantic oh-crap-not-lined-up-properly stuff, especialy in the last couple of meters. But, hey, I got there.

No, the real problem was re-entry. I was using ar81's re-entry tutorial (thanks, btw, ar81). Only at 20km up did I realise that the XR1 had an auto-pilot would hold my Angle Of Attack... Actualy, it was fun to do, even if it ended, "landed" on the sea, 200 km away from the island. In the last... oh, maybe 20 seconds, the coolant temprature went critical, and the landing was done without instruments, at night. Scary, but I made it (no idea what the contact speed was, exept there was no injury of any kind). Didn't have enough fuel to even gargle with, but, hey, whatever. I (as well as the other 4 people on board) lived, and that's what matters. :beach:

Enough of my blabbering! Now, that plea for help. I have two questions:

1. You flight experts, do you mind sharing some of the tips of the trade when it comes to re-entry? Like, at what altitude is it safe to get out of the 40 degrees AoA?

2. What's the optimum altitude/airspeed combos for the XR1 when it comes to altitude flight? What's the approximate range of the XR1 at these altitude/airspeed combos? Any above 500 kms?

Thanks.
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Old 07-17-2008, 09:04 AM   #2
Urwumpe
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Quote:
Originally Posted by James.Denholm View Post
 1. You flight experts, do you mind sharing some of the tips of the trade when it comes to re-entry? Like, at what altitude is it safe to get out of the 40 degrees AoA?

2. What's the optimum altitude/airspeed combos for the XR1 when it comes to altitude flight? What's the approximate range of the XR1 at these altitude/airspeed combos? Any above 500 kms?
Well, I use the following reentry setup in IMFD: Ant 45, ReA 1.5, Alt 120 km.

I aim for 16 m/s deceleration, which gets me perfectly to my target. At about Mach 4, I drop the nose and enter a shallow glide.

Now the trick is to get rid of enough energy to make a good landing. You should overfly the landing site (touchdown point of the runway) at about Mach 1.5 and 10km altitude. Wait a few seconds and fly a hard circle, while also dropping to 3 km altitude. If you do everything right, you are now in front of the runway, almost lined up and in a steep glide.
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Old 07-17-2008, 12:52 PM   #3
ar81
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Quote:
Originally Posted by James.Denholm View Post
 1. You flight experts, do you mind sharing some of the tips of the trade when it comes to re-entry? Like, at what altitude is it safe to get out of the 40 degrees AoA?

2. What's the optimum altitude/airspeed combos for the XR1 when it comes to altitude flight? What's the approximate range of the XR1 at these altitude/airspeed combos? Any above 500 kms?

Thanks.
This what I do, but it may not be the only solution...

1.At 15km altitude
2.I set a fix AoA and I use lineal RCS in the upper atmosphere to adjust impact point. I always end up over surface base marker when I am at 15 km, and from there I glide to the runway.
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Old 07-17-2008, 03:44 PM   #4
Scarecrow
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Quote:
Originally Posted by James.Denholm View Post
 Enough of my blabbering! Now, that plea for help. I have two questions:

1. You flight experts, do you mind sharing some of the tips of the trade when it comes to re-entry? Like, at what altitude is it safe to get out of the 40 degrees AoA?

2. What's the optimum altitude/airspeed combos for the XR1 when it comes to altitude flight? What's the approximate range of the XR1 at these altitude/airspeed combos? Any above 500 kms?

Thanks.
This is how I make a reentry with the XR1 and DGIV (and once you've got a feel for it, it works with the XR5, and I would expect the upcoming XR2 as well, though the little ships are good for playing around with and learning):

[My suggestions for what MFDs should be open will be in brackets, like this]

Entry from low, roughly circular Earth orbit:

[Map and Orbit MFDs open to start]
1. Wait until you will pass over your target base on your next orbit (Map MFD with TRK mode off is fine for this).

2. When you are as close as reasonably possible (it doesn't need to be exact, and you can play with the timing) to on the opposite side of the earth from your target base, burn retrograde until your PeA is 50km.

[Switch the Orbit MFD to a Surface MFD, set to display speed over ground]
[Zoom in on the Map MFD, and position the view so that you can see your target Base and your ship. I don't like to have the view following my ship]
3. Wait until you pass 115km, and then close up all your external doors (hover doors, radiators, etc.) and set the autopilot to hold a 40 degree AoA.

4. If your Map MFD shows you going to the left of the base, bank right, if you're too far to the right, bank left. Don't be afraid to use the maximum bank angle the AP will allow, but be aware that as you bank, you turn because you redirect your lift sideways. This means that you may have to pitch down to generate more lift and not fall to fast. That means that you'll have proportionally more lift sideways, which might be just what you want.

5. Try to keep your vertical velocity between -100 m/s and 0 m/s. This is not set in stone, and sometimes you must descend more or less quickly, or even rise to reduce drag (more on that later), but it's a good place to start.

Your altitude is controlled by your vertical velocity. Vertical velocity is controlled by your vertical acceleration (which, very conveniently, is also displayed on the Surface MFD). Vertical acceleration is controlled by lift. Lift is controlled by your AoA, which is also displayed on the Surface MFD. There are two factors that control what your altitude should be: Your hull temperature, and whether you're on track to over or undershoot your target base. If you're about to turn into a flying cinder, then reduce your AoA. If not, then pay attention to your landing site. Nothing, (aside from reentry MFD, which I will not address here) beats intuition for this, but some good numbers to keep in mind are that when you're 1000km from the base, you should be going at about Mach 7 or 8, you should be at Mach 3 when you're about 50km away. If you're going too fast, you need more drag, which means sinking into the atmosphere more. If you're going too slow, rise. To sink, increase your AoA, and to rise, reduce your AoA (peak lift is generated at about 12 degrees AoA).

6. When you get to Mach 3, lose the autopilot, and forget all the rules about AoA stated previously. You probably don't need to worry about your hull temp anymore, just about getting on the ground in the right place. From here, fly like a regular airplane, gliding. You should be about 50 km away from the base. Remember, if you're too far away, go up (this time by pulling back, because you're flying like a regular plane), and if you're too fast, go down, and use the airbrake. If you're really far short of the base, use your engines to get to the speed you should be at (if you have any fuel left, if not, either have fun with the water landing and hope your ship floats, or aim for a particularly soft looking field). You should go subsonic as you're lining up for approach.

7. Land. Preferably on the runway. Alive. With the gear intact (that last one always gives me trouble).
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Old 07-17-2008, 04:03 PM   #5
orwellkid
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Maybe I'm a bit strange, guaging by how everyone else is doing it, but this is how I roll:

Typically my XR flights operate between Earth -> ISS -> Moon -> ISS -> Earth
So for re-entry, I'm usually leaving the space station.

What I do, is stay docked to the ISS until my orbit is gonna take me over KSC during the KSC day (night landings are t3h suck). When I'm in the optimum orbit, I undock, turn retrograde and chill until I'm floating over Australia.

I then do a direct deorbit from the ISS altitude setting PeA ~30-40km. I then use AeroBrake MFD to judge the required AoA. Typically this flight gives me a MaxG of ~3G, which ain't too bad, and well within the operational limits of the XR1.

But yeah, usually start ~35 AoA and just play with it to "put the thing on the thing" (target crosshair on the base). Typically, I pop out around 30km at around Mach 3 as I pass over the KSC tile. Just fly over the runway, make a nice 270-degree right-hand turn and Bob's your Uncle.

HTH.

_O.K._
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Old 07-17-2008, 07:12 PM   #6
Belisarius
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Don't forget you can go in a bit faster than these suggestions, maybe up to Mach 5 or 6, then use the airbrake from 18km on down. Put the brakes back off when you reach Mach 2, at around 3000m high.

I always use the autopilot to hold the alt steady at 14km while I'm doing that, then circle down and enjoy the view.
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Old 07-17-2008, 07:50 PM   #7
ar81
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Originally Posted by Belisarius View Post
 I always use the autopilot to hold the alt steady at 14km while I'm doing that, then circle down and enjoy the view.
I prefer to end on top of base marker at 15 km and then glide to the runway. Vertical speed is energy you might need for the glide.
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Old 07-18-2008, 10:11 AM   #8
James.Denholm
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Thanks guys! This information is a real help (at least, it looks like it, I'll have a closer read when I have the time).

BTW, I just realised that I forgot to use the XR1's airbrakes during my re-entry, and I was just wondering, is there a temprature limit for the airbrakes? As in, can using the airbrakes result in a hull breach?

Thanks again.
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Old 07-18-2008, 04:17 PM   #9
dbeachy1
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Quote:
Originally Posted by James.Denholm View Post
 BTW, I just realised that I forgot to use the XR1's airbrakes during my re-entry, and I was just wondering, is there a temprature limit for the airbrakes? As in, can using the airbrakes result in a hull breach?

Thanks again.
Deploying the airbrakes does not reduce the temperature limit for any hull surfaces, so you may deploy them whenever you want. There is currently no special dynamic pressure limit for deploying them, either -- i.e., just the standard hull max dynamic pressure limit still applies.

So in a nutshell you may deploy the airbrakes whenever you want without compromising hull or flight control surface integrity.
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Old 07-18-2008, 11:18 PM   #10
James.Denholm
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Awesome, thanks Doug!
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Old 02-22-2009, 12:24 AM   #11
EliNaut
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Hm. Aerobrake MFD anyone?
Works perfectly for me just about every time.
Even more convenient with the XR's attitude ap.
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Old 02-22-2009, 12:37 AM   #12
Eagle
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I'm a little surprised you overcooked your coolant. I keep my radiator open whenever I'm above the atmo (or above dust on the moon). I don't close it until my deorbit burn in LEO or a few min before reentry otherwise. (realistically do it at a point in your mission where you can abort the reentry if the doors don't close)

If you're short of your target and still have some scram fuel you can open those doors for a little extra speed. Really useful if you're doing a big plane change during reentry.

Quote:
Originally Posted by EliNaut View Post
 Hm. Aerobrake MFD anyone?
Works perfectly for me just about every time.
Even more convenient with the XR's attitude ap.
Agreed. Aerobrake MFD is the tool for planning reentries.


Oh, and congratulations on your successful mission.
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