OHM Glideslope 2.7 for Orbiter 2010

[ADSWNJ]

If anyone is interested, I made a DGIV glideslope.

One needs to add the following line to <orbiter root>Config\MFD\GS2\GS2.cfg
GLIDESLOPE DGIV "DGIV"


It includes a scenario. To deorbit in the scenario, enter the BaseSyncMFD and set
ANG to 1.4
ANT to 26
ALT to 70

Burn when indicated.

W00t! Genesis of a new exchange in interesting reference slopes. Unless anyone has a problem, I'll roll these into subsequent releases (with attribution).

---------- Post added at 12:53 AM ---------- Previous post was at 12:44 AM ----------

Thanks!

But I think I should elaborate. I avoid using the throttle as much as I possibly can. So I use various MFDs to give me a solution that I can plug into IMFDs dV program and burn. To me this is how space ships are supposed to work. Mainly because that is how the Shuttle worked...and I suffer from massive STS nostalgia and I pretty much put Shuttle like procedures onto every Space Plane I fly in Orbiter, including the XR-2.

So right now I am experimenting on the proper offset required to get my old de-orbit procedure to line up with the XR2 glideslope that you have supplied. So far, I am close, but still a little short. I think I should get it soon.

And I have also bounced between the .7 angle and a .8 angle. My old procedure was a 1.2 angle so, there is a little bit that needs adapting. I like the .7 and .8 more and using this MFD as I can better utilize the crossrange.

Anyway, enough of that...... I look forward to your work on this. And when ever you want something tested or whatever, I am game :thumbup:

Thanks Cras - really appreciated. I agree with the desire to minimize dV, especially when you have plane changes. Whilst it's easy to use BaseSync to blast Normal to zero out the crossrange, and then glide straight down a +-2 degree DelAz slope, there's definite satisfaction in starting say 600km off track and pull it in.

On the 0.7º angle - I have been playing with gentler angles (e.g. 0.4-0.5º), so that you can keep a constant AoA at 40º and adjust VSPD (or VACC) by rolling up to 130º. My dream would be to have the autopilot be able to roll these aggressive angles under full control, varying DelAz up to 15º at the top of descent, down to 0º error at the HAC entry. Crazy eh?

 

[C3PO]

You don't have to burn that much out of plane if you're early enough. If you lower your orbit (reduce SMa) the ground track will move a bit eastward, and will add up on future orbits.

The XR-fleet has a large acceptable AoA range during reentry, and you get much preciser vertical control with AoA then with bank input. I've reentered from a 400 km circular orbit without any problems on a 1.6° angle.

---------- Post added at 04:12 PM ---------- Previous post was at 02:11 AM ----------

And on the crossrange..... 600 km? I just took an XR-2 weighing 65.5 Ton (50% main fuel) down to Canaveral from 400 km with a closest approach of 1800 km. And it wasn't even that close to the limit. And I didn't use any fuel except for RCS

 

[asbjos]

Actually, the Space Shuttles had a cross range of over 2000 km. And they had much smaller wings and worse aerodynamics than the very optimistic XR2 Ravenstar.

From Wikipedia:

Crossrange 1,085 nmi (2,009 km; 1,249 mi)

 

[Cras]

yeah, so far a 0.8 angle has been more than enough to overcome a 600km offset. The crossrange with the right re-entry profile is more than enough to get to the base of target.

I just need to better nail the EI location. I am thinking I need to aim more like 100km downrange. My last attempt was 50km. And was still a bit short.

 

[C3PO]

yeah, so far a 0.8 angle has been more than enough to overcome a 600km offset. The crossrange with the right re-entry profile is more than enough to get to the base of target.

I just need to better nail the EI location. I am thinking I need to aim more like 100km downrange. My last attempt was 50km. And was still a bit short.

Are you doing hands-off reentries?

 

[Cras]

Are you doing hands-off reentries?

No. I am just trying to avoid messing about the AoA until later in the re-entry. I can easily recover a misplaced EI my just lowering the AoA, but it is just something I want to avoid.

 

[C3PO]

No. I am just trying to avoid messing about the AoA until later in the re-entry. I can easily recover a misplaced EI my just lowering the AoA, but it is just something I want to avoid.

Oh I see. But the whole point with space-planes is to have more control on reentry. :lol: It's fun working out that kind of stuff, but the AoA should start to decrease quite early in the descent. Maybe you can use the built in AP in GS2. I haven't tried it yet.

 

[Cras]

Oh I see. But the whole point with space-planes is to have more control on reentry. :lol: It's fun working out that kind of stuff, but the AoA should start to decrease quite early in the descent. Maybe you can use the built in AP in GS2. I haven't tried it yet.

I say I start lowering it around....

3500 m/s or so?

Slowly as well, transition from just re-entry to actually flying the thing in the air.

I should say that my real goal is to prevent skipping on the atmosphere during re-entry. With the XR-2 it is pretty much a piece of cake to salvage even the worst of re-entry burns with AoA adjustments and accept the numerous up and downs of the vertical speed.....

That is fine I suppose, but not very elegant, and I see it as an extra challenge to keep the whole process as streamlined, if that is the right word, as possible. Always trying to perform the best of anything. The best re-entry, the best rendezvous, the best lunar landing, what have you. I would be well and bored with Orbiter if I didn't still have that drive I suppose.

I have used the GS2s AP with the G42-200 to successful landings. Works nicely.

 

[ADSWNJ]

Oh I see. But the whole point with space-planes is to have more control on reentry. :lol: It's fun working out that kind of stuff, but the AoA should start to decrease quite early in the descent. Maybe you can use the built in AP in GS2. I haven't tried it yet.

The AoA is one of the variables tracked on the reference glideslopes. That means that the GS2 DATA and GS2 TAPE screens can show current AoA versus reference. For the XR-2 reentry slopes, you'll see it's 40 or so at the top of the entry slope, and slowly drops to low-30's coming towards the HAC. Pre-HAC (say 20-40km away), drop to zero, and get everything straight and level to assist the HAC entry turn.

At least that's how I fly it. If you have different profiles for the XR, or for different ships, then post your reference slopes and we can all try them out! (E.g. chatting with blixel on his 'cannonball runs' from KSC to WIN in 21 minutes, he's doing super-aggressive braking with up to 70 degrees AoA, and final approaches at 40+ degree steep and sharp circles to land!)

 

[C3PO]

The RX-fleet has a point where the L/D curve "breaks", and you can "balance" on this point with 0.5° AoA changes. Initially it's around 41° AoA but it slowly creeps down as you slow down. Combined with bank you can be very precise in vertical control while getting the crossrange you need.

As per usual I use the reference a bit different then anyone else. :lol:
I fly the first part is pretty normal, but I've made a custom slope for the final glide to the HAC.
I've been testing to find the minimum energy you need to make it to the HAC on a straight glide. I plan to use the energy readout to make the TAEM S-turns. Once I get down to ~MACH 6 I pitch down to zero VACC and do S-turns @~30°bank until the energy is just over the minimum.

As long as we don't have variable speed brake, I'm going to have to make profiles for different weights.

 

[ADSWNJ]

Pretty interesting, C3PO. I would definitely add those reference slopes per weight into the main distribution for others to experiment with.

With those 30º S-turns, are you still maintaining a zero VACC, as of course you lose a partial component of lift as you bank the lift vector over, so are you adjusting AoA to create more lift to compensate?

 

[C3PO]

I do S-turns roughly like the STS did. I keep a vertical speed to stay at the correct altitude, and use the turns to loose excess energy. You have to increase lift to maintain the slope, and that will also increase the drag. Once you reach the correct energy you can glide straight to the HAC entry.

The trick is to find points with the correct energy from MACH 8 down to HAC entry. I was wondering about the Range parameter in the glideslope file. Does it include the HAC turn, or is it the distance to the runway?

 

[ADSWNJ]

I do S-turns roughly like the STS did. I keep a vertical speed to stay at the correct altitude, and use the turns to loose excess energy. You have to increase lift to maintain the slope, and that will also increase the drag. Once you reach the correct energy you can glide straight to the HAC entry.

Yes - that's the obvious bit. But you were talking about finding the ideal L/D point, then getting to zero VACC, then using bank to reduce excess energy. All good, but if you were on optimal lift-to-drag for minimum energy entry, then you would struggle to maintain a zero VACC (i.e. you would need more lift to compensate for the angle on the lift vector, but you were already at the best you can get). Hmm!

(In practice, I'm sure it all works out by gut feel anyway!)

The trick is to find points with the correct energy from MACH 8 down to HAC entry. I was wondering about the Range parameter in the glideslope file. Does it include the HAC turn, or is it the distance to the runway?

Both actually. The Range is true range to runway, summing the descent to HAC, the HAC turn (respecting the geometry), and the final descent. There's also a "To HAC" range on most of the screens too, which is just the first step to the HAC.

 

[Donamy]

Below Mach 10, the STS starts lowering it's AOA to maintain lift, while in the S-turn.

 

[C3PO]

Yes - that's the obvious bit. But you were talking about finding the ideal L/D point, then getting to zero VACC, then using bank to reduce excess energy. All good, but if you were on optimal lift-to-drag for minimum energy entry, then you would struggle to maintain a zero VACC (i.e. you would need more lift to compensate for the angle on the lift vector, but you were already at the best you can get). Hmm!

(In practice, I'm sure it all works out by gut feel anyway!)



Both actually. The Range is true range to runway, summing the descent to HAC, the HAC turn (respecting the geometry), and the final descent. There's also a "To HAC" range on most of the screens too, which is just the first step to the HAC.

I'm trying to find the range/energy points where I can glide straight to HAC entry on correct energy. The VACC isn't zero all the way, just to the next point. The points aren't actually the minimum energy, just the energy I can glide straight in with good elevon/rudder control. In a XR craft you can recover from a low'ish energy state, and there's always the option to switch to a "shorter" and/or smaller diameter HAC. You can even shorten the final glide.

Below Mach 10, the STS starts lowering it's AOA to maintain lift, while in the S-turn.

:thumbup: That's what I'm trying to replicate. IIRC the HorSit had a readout of the energy so you'd know when to stop doing the S-turns.

 

[ADSWNJ]

That's what I'm trying to replicate. IIRC the HorSit had a readout of the energy so you'd know when to stop doing the S-turns.

The GS2 HSIT, GS2 VSIT and the GS2 DATA screens all have this information.

Maybe a bit of info on the Total Energy calc would be useful...

Total Energy = Potential Energy + Kinetic Energy

Potential Energy = PE on ground - PE at current alt

Potential Energy on ground = G M(planet) M(ship) / (rwy alt + radius of earth), where G is the universal gravitational constant, and assuming a spherical planet.

PE at alt = G M(p) M(s) / (alt + radius earth)

Kinetic Energy = 1/2 * M(ship) * TAS^2


The calculation of reference energy interpolates reference ALT and TAS for your current range, then calculates Total Energy from the equations above. Current Total Energy is then compared to Reference Total Energy to give you the delta TE and the color coding.

Thus the calculation of when you are on energy is simply with reference to a reference glideslope, which is usually generated from a previous flight SAV save track function.


So what does all this mean? Well - you need to save your reference tracks at a number of points down the slope, then try to see if you can get from there to the HAC without a turn. If so, you were "on energy" at that point. If high or low, note the save point, adjust the reference and then adjust your altitude in the scenario save. And iterate!

-o-o-o-

Another thing to think about... I have been wondering if a climb at the HAC entry point would be useful. E.g. say you are 40km to the HAC, doing 2000 m/s, and you are worried about getting slow enough to "grip" the turn entry without sliding out on the outside of the turn (i.e. going straight on because of too much forward speed). Pull up into a 30º or 40º bank, which will rapidly trade speed into altitude, then turn at the top and enjoy a steeper HAC turn onto final. I haven't done one of these yet, but I think it has merit.

 

[C3PO]

I was talking about the HorSit screen on the real Shuttles.

I'm not calculating the energy. I just work backwards from HAC entry, because I know the Alt/Speed state that I want to be at.

Then I look at a segment prior to this point. If HAC entry is at 20 km/450 m/s, I try to fly at 800 m/s and note deceleration and Vvel. Then I calculate the altitude and range where I need to be at 800 m/s. I re-fly the segment to check if the numbers have changed too much due to change in altitude. It may take a few tests until the segment has the correct "feel". Then I repeat the procedure for the next segment.

You can trade speed for altitude, but that's not the best option. The deceleration is much lower up there, and you have even less air for "grip" in the turn. A better option is to widen your HAC and/or choose the HAC that needs the most energy. It might even be better to go a bit lower while doing high-G turns at the limit of the wing stress, and then climb up again for the HAC entry.

But the point of the straight-in energy slope that I'm trying to make is to be on energy long before you get that close.

 

[ADSWNJ]

Thanks 3PO. Interesting discussion. I'd be really interested in reviewing some of your save files (SAV function) as you come to conclusions about your reference entry. If you need different selection points on the slope (e.g. by altitude or range), or if you would also like to see DelAz and bank in the comments of the save file, let me know and I'll do a config item enabled setting for you.

If you can get me a perfect HAC turn from altitude to finals (XR-2 or XR-5), with good TAS and feeling in good positive control, I'd be interested in really studying this. I tend to be somewhere between too hot, so the entry loses 'grip', and too cold, where I am struggling to make the turn without dropping below 200 m/s TAS.

 

[C3PO]

It is difficult to compute a Terminal Area Energy Management (TAEM) that works with all types of craft. There are so many variables to account for, mainly lift and drag for different speeds and altitudes. That's why I prefer the empirical methods.


Even a perfect HAC entry is hard to describe without knowing the angle you enter it on. (That might be a useful readout to have on the GS2 HSIT screen) I like to enter just short of 270° from final. This means that I'm heading for the furthest RWY end, and the HAC that's on the opposite side of the RWY. If I get too low/slow I have the option to switch to straight in on the closer end. Planning and situational awareness is paramount on deadstick landings.

The HAC I use starts at 22 km for a full 360° with a radius of 10 km. and I enter at 450 m/s. (I use my own version of Aproaid that I really should release at some point). The slope is around -15° during the turn.

The way to manage energy in the HAC turn is counter intuitive. If you're low/slow you should tighten the turn to reduce the distance, and then loosen it again to align the turn with the final approach. If you're high/fast you have two options. Either use a larger radius to increase distance, or "move" the HAC further away from the RWY to make the glide shallower. You can also use a combination of both methods. You don't have to follow the lines on the MFD. Many people get so focused on chasing the lines and forget to keep track of where they're supposed to end up.


I never use the closed HAC because I tend to loose too much speed during the turn. The HAC turns were designed to get rid of excess speed in a controlled manner so you could arrive with high energy and not risk falling short. The STS could not add energy, only remove it.

 

[Cras]

To throw out how I tend to use the HACs with XR-2s. I use something around 5km to 10km HAC close for the cross of the runway. So I fly no more than a complete rotation. Though I did fly an open HAC the other day, it is a really interesting path, not one I was familiar with. It really isnt even a HAC, its like flying a base leg to final approach. I find it tremendously useful actually to use with the Shuttle into Wideawake where I find a straight in approach more appealing than a HAC due to the inclination of my spacestation, runway 12 lines up so nicely for the track I am on.

I want to enter around 60 to 70 thousand feet, and exit around 15 to 18 thousand feet. And want to come out at a fairly low speed. I tend to be flying the entire HAC with the speed brake extended. My target landing speed is 120 meters per second.