Flight Question DG De-orbit Profile

[Shifty]

Hello, I'm a total Orbiter newbie; been playing about a week. I worked my way through parts of Go Play In Space! (all except lunar and Mars transfer) and am now working on the checklist scenarios from the Orbiter manual with the stock Delta Glider. I did checklist 1 (launch from KSC, rendezvous and dock with ISS) no problem. Likewise checklist 2 (transfer from ISS to Mir, rendezvous and dock.) But I'm having problems with checklist 3: de-orbit and land at KSC.

I do the de-orbit burn and end up about 4000km from KSC at 100km altitude during the descent, just like the checklist says. But I can't seem to extend my glideslope all the way to KSC. I always seem to lose all my airspeed and have to touch down somewhere in the Central American flatlands. I've tried 4-5 times and keep coming up short. The checklist suggests that I'll have to do banks to bleed off speed, but when I do that I come up even shorter. Is there a descent profile, with suggested AOA, rate of descent, etc that I can follow; the checklist is surprisingly sparse on this point.

I apologize if this question has been addressed before.

Thanks in advance for the assistance!

 

[MaverickSawyer]

The odd thing about the stock DG is the fact that it doesn't allow a high AOA reentry. You have to do multiple skips into and back out of the atmosphere. It's driven me crazy for years, and I've never found a good answer to this issue. :shrug:

 

[PhantomCruiser]

Keep and eye on SurfaceMFD to watch your vertical speed and velocity. There is a balance point that you can find, but it takes practice. Map MFD can give you an idea where you'd plow into the ground with no input changes, so you can use it to keep the "end of the line" near KSC.

For a while it you might think you are mixing paint for all the joystick movements you ae making, but the long and the short of it is that your bank angle mixed with pitch angle determines you glide slope. Bank angle not only determines left and right, but also altitude (watch the verticle speed as you roll over past 90 degrees, it should begin to decrease, sometimes dramatically). Play with the pitch angle to control your speed, when you get down around 40-50 Km altitude you can really bleed off speed (you'll hear the roar and see the flames, but don't panic).

It can be done with the stock MFDs, it just takes practice (and with the stock DG - it may take a lot of practice).

If you have the DGIV; it flys much better, and it has some handy autopilots. There is also the most excellent XR-series of which the XR-1 is a twin (in looks) to the DG and has a number of pretty awesome autopilot programs too (different from the DGIV, but equally awesome).

A few helpful MFDs are Aerobrake and Basesync. Oceanic has a really good tutorial that uses these that helped me tremendously when I first started. http://orbiter-forum.com/showthread.php?t=8425

It uses the DGIV, but the same techniqes will bring in the XR's as well.

I don't use the stock DG much anymore, unless I want to get back to some fundamentals (but with the vectored thrust add-on it's pretty cool!). That being said, a stock DG is performing an over-field break in my current signature...

 

[boogabooga]

The more you bank the delta-glider, the greater the lift will be diverted sideways instead of up. The trick is to bank just the right amount, such that your vertical velocity remains at something like -50 (ish) m/s.

You need to reverse the bank periodically, making so-called "S-turns." You can use the map to see where your ground track intercepts the earth. Try to keep the intersection near your base. And it's O.K. to make a powered approach and landing.


Edit:
:ninja: by PhantomCruiser

But I would add that aerobrake MFD is much more difficult to use for banked stock DG type re-entries than with the XR series which uses a constant AOA re-entry.

 

[Tommy]

With the stock DG, you can actually just fly the thing down with a low AoA. IIRC, that's what Go Play shows. It is possible, and I think I know your mistake.

The lower you go, the faster you will slow down. So if you are coming up short, the way you are, it means you are going too low too soon. You need to stay up higher for a while. You can maintain a good slow descent rate using just the elevator trim keys once you get down to about 65k altitude, so try adjusting the trim to give you about -50 m/s on the VS indicator in SurfaceMFD. Then see if you come up short or long, and next time adjust the VS accordingly. Once you get the hang of it, you will know about how fast you should be going at any given distance from the base, and adjust your altitude and descent rate accordingly. You need to maintain speed longer than you think - you will cover a lot of ground while slowing from 7kms to 6kms, but less than 50 km slowing from 1kms to landing speed.

If it helps, I try to be at 25k - 30k altitude and 2kms velocity when I am 100 km from base.

 

[malisle]

I suggest you to try DG-IV. It will seem a little overcomplicated at first but as soon as you get a hang of it you will love it. The reason I recommend DG-IV is that it has a more realistic aerodynamics than the stock DG, as well as restrictions to descent profile in the form of hull temperature. You may burn up a few (dozens of) times but the first time you get it right you will never burn up again.

I usually use BaseSyncMFD to align my orbital path with the spaceport and then switch to AeroBrakeMFD. It is a piece of software that really makes reentry easy. It calculates where you will end up if you don't change anything (and many other things, but this is important). Foolproof way to make a reentry is to align yourself with the base, circularize at low altitude, set AOA (angle of attack or angle between your velocity vector and the nose of the aircraft) to some angle (between 30°-40°) using autopilot, fire the retro engines anywhere between 1/4 - 1/2 orbit away and burn as long as AeroBrakeMFD doesn't show that you are landing right on top of the spaceport.

If you start to heat up, reduce AOA and when you cool down, return to initial angle, and keep an eye on where you will end up in AeroBrakeMFD. Don't dip to deep into the dense atmosphere or you will lose speed and may not be able to reach spaceport. I never get under 25km until I am atop of the spaceport.

 

[Shifty]

Thanks everyone for the tips! I'll give it a few more tries with the DG (and try flying higher longer), then check out the various MFDs and other vessels. I've peeked into the DGIV before; I'm looking forward to checking it out in more detail.

 

[PhantomCruiser]

The DGIV and XR-1 are both wonderful birds. The added bonus is the XR-1,-2 and -5 all have the same autopilots, so once you figure out one, the others you'll know by default.

 

[Dantassii]

That's 1 of the things I like most about the XR series. All the wonderful, built-in autopilots.

 

[Interceptor]

Here's an unorthadox way of doing this,but it works.

 

[Shifty]

Thanks again to everyone for the assistance! I tried again this evening; let the DG skip off the atmosphere once, watched the ballistic path on the map screen, re-entered and managed to set it down gently on the KSC runway. I did still undershoot a bit; ended up having to use engines to make the final approach, but I'd say the checklists are done. On to bigger and better things.

 

[Cras]

Try Aerobrake, you will be making better and more precise de-orbits in no time.

:thumbup: