Flight Question Gliding into KSC unpowered with DGIV

[Interceptor]

Hey Guys any tips on gliding into KSC from reentry unpowered.Can't seem to do this yet, everytime I go to land Atmospheric Auto comes on and I crash the DGIV.Thanks

 

[agentgonzo]

We'll probably need a bit more details rather than just "I crash the DGIV". My first thought would be that you are trying to land on the runway without deploying your landing gear, but that's just because we've got virtually no information to work with.

 

[Urwumpe]

Hey Guys any tips on gliding into KSC from reentry unpowered.Can't seem to do this yet, everytime I go to land Atmospheric Auto comes on and I crash the DGIV.Thanks

Some important details, you need to remember:

1. Entry interface - a law, not negotiable. You need to pass this window in space at the right distance to the base, at the right angle and at the right altitude. For the XR1, I used the following IMFD parameters for a good reentry:

Anticipation (Lead angle from EI to base) : 45°
EI altitude: 120,000 m (120 k)
Flight path angle: -1.2°

If you have this right, the biggest problem is already solved

2. Start with full lift, if you are not sure, how much you need. No bank, AOA at 40°. Keep that until your vertical speed is reaching zero.

3. S-Turns. Bank towards the base, so you can control your descent rate. The more you bank, the more you accelerate downward (as lift is no longer countering gravity). There is a relation between descent rate (your vertical speed) and the deceleration, you experience. Use bank angle to carefully bring your deceleration to 16 m/s².

4. Roll reversal. As you bank, you will fly a curve. if this curve brings you too far away from your base, you need to reverse your bank angle. If you are at 60° left, change it to 60° right.

5. Stop the roll reversals if you are close and slow enough for reaching the base. Mach 3.5 in 100 km distance is for example a good goal.

 

[agentgonzo]

3. S-Turns. Bank towards the base, so you can control your descent rate. The more you bank, the more you accelerate downward (as lift is no longer countering gravity). There is a relation between descent rate (your vertical speed) and the deceleration, you experience. Use bank angle to carefully bring your deceleration to 16 m/s².

4. Roll reversal. As you bank, you will fly a curve. if this curve brings you too far away from your base, you need to reverse your bank angle. If you are at 60° left, change it to 60° right.

Apologies for thread tangent, but you don't *need* to use S-Turns and Roll reversal in orbiter if you don't want to. You can use skip-reentries or just ploughing through the atmosphere at a higher AOA absolutely fine. S-Turns and Roll reversals are used by the shuttle as the 40° AOA was a design decision and the S-Turns prevent a skip-reentry which would lead to a heat-cool-heat-cool-heat... cycle of the TPS which they weren't sure would be a good thing.

 

[Urwumpe]

Apologies for thread tangent, but you don't *need* to use S-Turns and Roll reversal in orbiter if you don't want to. You can use skip-reentries or just ploughing through the atmosphere at a higher AOA absolutely fine.

There are also reasons against Skip entries, and these are accuracy and final reentry angle. What you suggest is fine for people, who like to miss the runway or have no problem with unrealistic heating rates, but it is generally better to stay inside the atmosphere, where you have control over the flight and a more shallow flight path angle.

Orion for example, did not do a Skip reentry in it's early design history, because it is easier. The Skip reentry guidance for Orion is far more complicated as the Shuttle reentry guidance.

Orion was meant to do first a skip reentry using the standard aerobraking guidance of NASA, then does a propulsive maneuver at top of the flight (with special thrusters, which add complexity) and then use an Gemini/Apollo/Shuttle standard guidance algorithm for the final reentry.

And why that all? Because otherwise, the remains of the service module of the CEV would crash on land, in the worst case in the middle of Los Angeles, if the CEV is meant to land in Edwards.

Now, they solved this by again landing on water, with the full costs of the recovery fleets of Apollo.

S-Turns and Roll reversals are used by the shuttle as the 40° AOA was a design decision and the S-Turns prevent a skip-reentry which would lead to a heat-cool-heat-cool-heat... cycle of the TPS which they weren't sure would be a good thing.

Wrong. The Shuttle heat shield could stand such heating patterns far better as an Apollo-type heat shield (as it is capacitive, and not ablative). The problem is the second reentry. You enter at a much steeper angle and will get much higher loads at the second time, if the shuttle would not use bank before skipping for controlling the exit flight path angle. You would be way slower - and still burn up, because you plummet into the atmosphere at a much higher angle.

There are many other examples in engineering. For example, Apollo had a full skip reentry guidance software developed and loaded into the small memory of the AGC. But it was never used. Why? because the normal reentry guidance was much better suited for controlling the reentry, even at higher speeds.

 

[willy88]

Hey Guys any tips on gliding into KSC from reentry unpowered.Can't seem to do this yet, everytime I go to land Atmospheric Auto comes on and I crash the DGIV.Thanks

Switch to the elevon-only mode.

 

[Interceptor]

Great answers guys. Everything seems to be good now I keep coming closer and closer to landing unpowered.Soon very Soon.

 

[Tommy]

The DGIV has a glideslope of about 13 degrees, depending on the load. When you are on final approach, that's the angle you want the velocity ball on the hud to be near, and it should be a bit short of the runway. I try to keep the speed about 150 to 170 m/s. You can come in a bit steeper and use some airbrake to regulate your speed, but don't come in to shallow or you stall short of the runway. The last couple hundred feet of altitude, start pulling back on the stick and bring the velocity ball up to the runway, watch your VS, and let the craft settle as it loses speed. Touchdown is usually about 140 m/s for me.

Here's an annotated flight recording that ends in an unpowered landing of an XR-2. Same technique as a DGIV. Just fast forward though the inverted re-entry, and you'll see how I manage the velocity towards the end.

[ame="http://www.orbithangar.com/searchid.php?ID=3660"]Home Direct[/ame]

Just remember that speed falls quickly at the end, keep a bit more speed than you think you need, then use a bit of airbrakes during final approach if needed.

 

[Interceptor]

Thanks. Tommy always great hearing from you.

 

[Eagle]

Break turns are always good for reducing that pesky altitude and airspeed.

 

[Interceptor]

Thanks Eagle, I'll try that.

 

[Sky Captain]

If you feel you are going to be short of your base you can transit from reentry into hypersonic glide while you still have some 2 - 3 km/s speed and use airbrake if neccesary. That way you have lot more room for error. It`s better to overshoot the base and still have enough altitude to turn back and land than crash land before base

 

[Interceptor]

Great advice Sky Captain. Thanks

 

[RisingFury]

I try to land at velocities between 100 - 120 m/s. The DGIV is capable of landing at some 70 m/s at high AOA before it stalls... so you have a lot of room. I land at around 100 - 120 because that's when DGIV starts losing altitude just fast enough at low AOA... any higher and it still behaves like a glider and you have to force it down and can break the gear.

Try gliding over the runway at same altitude for as long as possible and your DGIV will gently touch the ground. Your landing gear won't hold much more then 3 m/s vertical impact, deppending on the weight, but try to keep it as low as 1 m/s... or if you go slow enough, it won't even display how fast you touched down

 

[Hielor]

I try to land at velocities between 100 - 120 m/s. The DGIV is capable of landing at some 70 m/s at high AOA before it stalls... so you have a lot of room. I land at around 100 - 120 because that's when DGIV starts losing altitude just fast enough at low AOA... any higher and it still behaves like a glider and you have to force it down and can break the gear.

Try gliding over the runway at same altitude for as long as possible and your DGIV will gently touch the ground. Your landing gear won't hold much more then 3 m/s vertical impact, deppending on the weight, but try to keep it as low as 1 m/s... or if you go slow enough, it won't even display how fast you touched down

Be careful though--if you have air surfaces set to AF AUTO, and you end up going too slow, it can turn off the aerodynamic surfaces and result in a crash.

 

[Interceptor]

Good stuff! Guys

 

[MattNW]

It sounds like you are coming in too low and slow. There are two totally worthless things in unpowered landings. Those are altitude above you and runway behind you. Unpowered landing is a trade off of altitude vs airspeed. Run out of either one too soon and you won't be going home tonight. I usually keep a little extra airspeed until I'm certain to make the runway. Once I am certain I can dump the extra airspeed with the airbrake.

 

[Interceptor]

Thanks MattNW