Problem Delta Glider launch into orbit

[Sivodave]

Hello guys

I'm new to Orbiter and I've started to learn with the DG. I've been watching tutorials on youtube and read documentation but I'm still having issues in launching the DG.

My problem is the following: once I've taken off and set my heading (to the ISS for instance) I can't keep the pitch-up attitude necessary for gaining rapidly altitude. For instance I bring the velocity vector to 30 degrees and it immediately starts to fall down. It is very hard to keep it up and actually I often get to a point where I can't pitch-up at all. Obviously to reach orbit we need horizontal velocity but I also need to be able to go up to gain altitude.

I'm really frustrated for this, since I think I'm doing everything as the tutorials show...it should be rather simple but still I can't reach orbit properly....do you have any suggestion?

Thanks very much in advance.

Cheers

Davide

 

[Scav]

Two things off the top of my head:

RCS to ROT (Rotation)
AF CTRL (control surfaces) to ON.

 

[PhantomCruiser]

i certainly understand the initial frustration. It really is a matter of finding the balance point of when to pitch up, then later over.

For the moment, lets forget about reaching the ISS and work on getting to LEO.

Begin your takeoff roll, and get head east (more or less) once you've got your wheels up. Pitch up to 60-70 degrees until you get clear of the "thick" air, then gradually bring the nose down, you can use the trim to assist, but I rarely ever do.
Keep and eye on the surface MFD and watch vertical acceleration, and you can watch how the numbers change depending on your inputs on the control stick. There are elements that are counter intuitive, I had the hardest time explaining to a coworker that going straight up might get you to space, but you need to go forward to stay there (she still didn't get it, even after a demo).


Another idea would be to upgrade to the DGIV, it's at Dan's site (you can find it in the links). It's got some really great autopilots that can do things hands free. Then you can watch and mimic what it does manually in a later flight.
There is also the XR fleet from Doug, but while it's got some great autopilot programs, you still will have to do a bit of flying to get to orbit.

And as in all things, if you want to get good at it, practice.

Take a look at the tutorials page also, Tex has a really good one that will get you to the ISS with the DGIV. (Just remember, there's no "oops" in space)

 

[Scav]

Also expanding on my own reply (which was really little more than a quick thought spilled out into a post) --

Reason I pointed out the two control subsets is this: I was visualizing from your description trying to maintain control of the vehicle in the upper atmosphere. It's at that point where the control surfaces (AF control) become more or less useless, therefore RCS is more optimal.

On the other side of the coin, at low velocities and in the denser lower altitudes RCS is less effective than the control surfaces.

 

[PhantomCruiser]

I just took the stock DG to LEO to make sure my directions were sound. And as I passed 45 Km altitude I was holding about 15 degrees nose up and engaged the scrams (DG w/ scrams in the stock scenario folder). Holding this pitch angle really all you need to do is keep the velocity vector above the horizon, in between 50 and 60 Km altitude you can really gain horizontal speed, don't worry so much about how altitude, it'll happen all on it's own.

Once you get to about 65 Km altitude, kill the scrams and keep holding the nose above the horizon (I aimed for about 5 degrees up, but it varies).

On the Orbit MFD, watch PeA, when it gets to around 250-300 Km, kill your engines and coast. The next number to look at is ApT (Time to Apoapsis, and it should be counting down) when it gets to about 100 seconds or so, roll to Prograde. It'll be a selection button on the bottom of the generic HUD, or use the left bracket hotkey "[". When the ApT get to around 25 seconds, burn full throttle to circularize your orbit.

Still watching Orbit MFD, watch the Ecc number, and it basically shows you how "out of round" your orbit is, if Ecc=0 your orbit is perfect, but really any small number is fine.

Take a look at ApA and PeA. Apa is the high point of your orbit while PeA is the low point. As long as PeA is above 200 your A-OK.

Learning how to read the displays will greatly enhance your abilities, but it takes time. Failing in an epic manner is something that most of us have done, so don't feel bad. At least the stock DG is indestructible.

 

[Sivodave]

Hello guys.

Thanks very much for your tips. I've spent few more hours (!) this afternoon but not joy at all. I can confirm that AF is On and I have tried to have RCS on ROL both from the beginning and after having reached the upper atmosphere (approx 30 km). When I reach 30 Km of altitude, I disengage the AF so I maneuver only with the RCS.

Actually my problem is not really the atmospheric flight but flying in the upper atmosphere. Despite I continuously pitch up (using lots of RCS fuel) the velocity vector inevitable goes down and I can't recover it at all. Isn't it strange? In the upper atmosphere I shouldn't have any lift effect on the DG, thus if I pitch up the velocity vector should pitch up accordingly.

Also I need to keep applying pitch up to keep the DG attitude pitched up. Which means using a lot of RCS. As soon as I release the pitch up command the ship immediately pitches down.

Anyway I've loaded the DGIV and it's really cool. I think I will learn to go in orbit with the autopilot (on the other hand the Shuttle did the ascent on the autopilot as well!) since I want to get up and running with orbital maneuvers asap and start building space stations!

I will keep practicing with the DG anyway.

Cheers

Davide

 

[PhantomCruiser]

I'll break out the stock DG on occasion to practice fundamentals.

I usually don't turn AF off until I'm way up there, usually because I forgot. When I tried it yesterday (?) I had tons of RCS fuel once I got to LEO. Maybe you are switching over to RCS too soon... It's got the power to pitch vertical right after the takeoff roll and reach escape velocity (just a few later it runs out of fuel). So it's just a matter of figuring out an efficient ascent profile. Don't sweat it, since you are playing around with the -IV you'll be able to pick up on what it does and apply that to your own manual attempts later.

I would guess that the DG-IV is the workhorse of many an orbinaut. Something else you may want to look for is the "Shuttle Fleet". If you do a web search for "shuttle fleet simviation" you should find it with no troubles. The stock shuttle is plenty "fly-able" but it's a handful (no CG shifting, among other things). Plus the 'fleet has AutoFCS autopilit for recovery and landing. For a hands free (except for lowering the gear) reentry.

It'll upen the door for some really great mission packs for station building. Thorton's ISS for on, with Donamy's ISS A-Z to complete the construction. There's lots to do in LEO.

Ciao for now.

 

[Sivodave]

Ok guys I've made it! :thumbup::thumbup:

I'm still doing a lot of RCS thrusting but I think I'm understanding the technique to flight the DG in LEO...not easy but a lot of fun! I have noticed that it's better to keep the AF ON up to 45 Km...previously I was always relying on the RCS past 30 Km but I think at that altitude the atmosphere is still too dense for the RCS to work properly...understanding that helped me quite a lot!

Thanks for your help guys...some more ascents before dinner now

Davide

 

[ADSWNJ]

Hi Davide-

Can you make a table of speed, altitude, pitch and ApA on one of your ascents. E.g. each 5km of altitude, hit Ctrl-P to pause it, make a note of those values, then Ctrl-P to unpause it. From the profile, it's going to be easier to see what you are doing.

I am wondering if you are climbing too high before you have enough speed, and therefore getting into a difficult environment (e.g. 50KM alt, 1500 m/s). The real trick to getting to orbit is simply to get to around 7500 m/s speed, with a gentle ascent profile, and let the increasing centrifugal force help support your ascent up to 200km ApA and beyond.

Re AF or RCS - I would typically leave it on to much higher altitudes, until there's essentially no dynamic pressure left to exploit. It doesn't do you any harm to leave it on to high altitudes, so don't worry so much about this.

 

[DaveS]

One thing if do not use a joystick is to use the pitch trim which can be controlled by the Insert and Delete keys. This allows you to trim the pitch the natural stable pitch angle as you ascend avoiding as much as possible bouncing up and down.

 

[Sivodave]

Hi Davide-

Can you make a table of speed, altitude, pitch and ApA on one of your ascents. E.g. each 5km of altitude, hit Ctrl-P to pause it, make a note of those values, then Ctrl-P to unpause it. From the profile, it's going to be easier to see what you are doing.

Thanks very much ADSWNJ...you're very kind. I've attached a TXT file with the profile of one of my ascent. I haven't reached orbit since by now it is clear that I'm really doing something wrong.

My discomfort lays in the fact that I can't keep a stable attitude. The velocity vector has as a strong tendency of drifting downwards and the ship doesn't hold its attitude if I pitch up to maintain the VV at certain angle. As soon as I release the elevator, the ship starts a rather "violent" rocking motion, pitching up and down constantly.

It's probably to do with the dynamic characteristics of the DG and I'm probably exciting one of its longitudinal modes. It all tutorial I've watched on Youtube, I don't see the DG swinging up and down as it happens with me.

I've also tried to re-install Orbiter but the result doesn't change....so the problem it's in the pilot (me :hmm

What do you think?

Thanks again very much for your help.

Cheers

Davide

 

[PhantomCruiser]

If I can figure out how, I'll record a playback. You should be able to watch it and at least "see" how I'm doing it. Maybe that'd be of some use?

 

[ADSWNJ]

Thanks very much ADSWNJ...you're very kind. I've attached a TXT file with the profile of one of my ascent. I haven't reached orbit since by now it is clear that I'm really doing something wrong.

My discomfort lays in the fact that I can't keep a stable attitude. The velocity vector has as a strong tendency of drifting downwards and the ship doesn't hold its attitude if I pitch up to maintain the VV at certain angle. As soon as I release the elevator, the ship starts a rather "violent" rocking motion, pitching up and down constantly.

It's probably to do with the dynamic characteristics of the DG and I'm probably exciting one of its longitudinal modes. It all tutorial I've watched on Youtube, I don't see the DG swinging up and down as it happens with me.

I've also tried to re-install Orbiter but the result doesn't change....so the problem it's in the pilot (me :hmm

What do you think?

Thanks again very much for your help.

Cheers

Davide

Thanks for the data. I haven't had a chance to run a couple of reference launches yet (due to Real Life), but I will for you.

Here's what I see...

You are pitching up almost like a Space Shuttle. In doing this, you trade altitude for true airspeed. The problem is, you are flying a Delta Glider, that likes to use its wings in the lower atmosphere, so you are most likely fully stalled on those wings and so getting no value from the airfoil's lift.

Do this ...

Try keeping your max pitch to 20 degrees, and focus on building your air speed. You need to get to over 7000 m/s horizontal component, so you need to keep the pointy end closer to the horizon to keep continually building that TAS.

At your desired ApA, cut all engines (even if at say 85km) and watch the ship coast up to the apoapsis ('apo' = apart = highest point of the orbit). It may drift down a little bit (say 5km of ApA) due to residual air resistance, but you will definitely be in orbit. Final thing to remember, as you get to the apoapsis (i.e. ApT gets close to zero), hit the Prorate autopilot, and then do 10-20 secs of main engine whilst watching your PeA (periapsis altitude) come from a negative number up to 200km. This is a 'circularization burn' and puts you into a stable orbit (as opposed to a ballistic orbit which will crash back to Earth a half-orbit or less later!).

----

Here's a profile for the "DG-S ready for takeoff" base scenario. Put the Orbit MFD on one side, and Surface on the other. Hit DST to get ApA rather than ApR heights, and look to the Surface MFD or the HUD for all other numbers in my file.

You take off on bearing 330, so you need to roll right to 090 off the runway, then follow this profile. I came up very gently (sub 15 degrees pitch), but had a smooth acceleration throughout the ascent. Notice after about 35km, I was almost horizontal, building speed to lift my altitude from a combination of centrifugal force and airfoil lift. Also - as I got to 7000 m/s+, the ApA moved very quickly .. i.e. within 15 secs it went from 93km to 208km.

This is by no means a super-clean ascent. I was left with 2029kg of SCRAM fuel, and 4792kg of main fuel. I always think that the SCRAM fuel should be all gone if I do it properly, so I tried 3 or 4 more times, and although I could burn the fuel down to sub-1000kg, it seemed like the flight took forever (as you need to keep the Mach number below 8.00 for the scrams to work). I'm sure you can beat this, but it was a quick & dirty ascent...

Hope this helps.

 

[PhantomCruiser]

It sounds like we do DG style acsents in a very similar manner. Only I'm usually holding about 5-10 degrees nose up at 50Km altitude, during most of my scram burn and watching to keep my altitude below 60. When I get there I just pitch down a bit to stay in the zone.

In between 85-100Km altitude I'll wind up shutting down the mains and coast uphill. So like I said, I think we're pretty much on the same page as far as our methodology.

Well, I gave it an attempt here playing off an external harddrive. Not my best work, I could hardly read the hud at lower altitudes, and this keybaord is strange...
But the overall gist is the same. I can do better (really, I can) but this is about the best I can do for now, but you should get the idea. Just hold the nose at around 8 to 10 degrees up. Physics does the rest for you.

Drop this file into your orbiter/scenarios/playbacks folder and take a look.

 

[ADSWNJ]

That playback did not record, Phantom? It looks just like a starting scenario.

Anyway Davide - I hope this is enough to get you into orbit. It's a good experience getting back in a starter ship like the DG for an ascent to orbit, but I highly recommend you download and play with the XR-series vessels (e.g. XR-2, XR-5) next, as they are a whole new experience and in my view, much more realistic to fly.

 

[Aeadar]

That playback did not record, Phantom? It looks just like a starting scenario.

I believe an associated file in the 'flights' folder is required for playback, in addition to the 'playback' file.

 

[dgatsoulis]

Actually, it's a subfolder inside the "Flights" folder, named exactly the same as the recorded scenario. It should contain 3 files (.ATC .ATT .POS) for each vessel present in the scenario.

 

[SanderBuruma]

I've made a little video (7m 38s) of me putting the default DG into orbit:
https://www.youtube.com/watch?v=NfLh9aKfVoM&list=UUlyaOcai3QxX45lFEoOvBWA

I think key is to monitor your DNP from the surface MFD (Shift+F1 & Shift+S) and putting your trim all the way up while using ROT KILL (numpad 5)
I tried to accelerate time a bit while simultaneously trying to make it to an orbit aligned to the ISS orbit because I got bored.

After take off retract your landing gear, load the surface MFD and note your DNP, then keep pitching up until it starts dropping. Activate killrot and start pitching down again until the DNP-drop slows down while raising your trim until your pitch remains constant, then just adjust your pitch constantly to keep your vAcc at <2m/s while keeping vertical speed at roughly 200m/s (which should decrease as you go faster and faster). At a speed of about 4km/s you can afford to pitch to ~5-10° and let your vertical speed exceed 200m/s while you monitor your apoapsis until it exceeds 180km. When it does, cut off your engine (hotkey *) and wait until you reach the apoapsis, this is when your vertical velocity becomes zero. Press [ to face prograde just before reaching apoapsis and use your main engine (hotky +) to raise your periaps to >150km.
This should get you into orbit without being excessively wasteful of your fuel.

All MFDs can be simply opened and controlled by pressing shift+F1 & shift+# where # is a letter. Surface MFD is S, orbit O, orbit sync Y, orbit alignment A, docking UI is D and so on. There is also a MNU button below each MFD which will tell you how to navigate the MFDs with hotkeys. Imo this is time well spent because the buttons are much quicker than your mouse.

 

[Sivodave]

Hello all.

Apologies for replying only now...I was on holiday and I didn't have a chance to play with Orbiter while away

But I'm back and I've tried your suggestions and it works rather well. I've notices that it's easy for me to use a joystick to get to orbit and using the notepad keys for orbital maneuvers. I'll keep practicing ascents.

I was having a look at the XR spacecraft and wow they look really good...and complex to pilot too! But it's all good fun.

thanks again for your help guys.

have a nice weekend



Davide

 

[PhantomCruiser]

Glad you are having fun, and figured out the ascent. The XR fleet has a really good flight profile, and once you get to your desired heading, the keyboard is a natural input method.

I find myself only using a flight stick for takeoff and landings, most everything else is a numpad.