I spent some time this morning, trying to figure out the HUD symbology withthe aid of several Shuttle HUD landings, the F-Sim app, and sites such as
www.spaceshuttleguide.com.
I can see that there's 4 HUD modes (No Declutter, Declutter L1, L2, L3), and a height triggered switch from flight director mode to velocity vector.
The symbology is like this:
1. Normal glideslope FD mode, pre Terminal Area Energy Management (HAC, basically)
- Speed tape on the left
- Thick line (rectangle) to left of speed tape, showing actual
- Alt tape to the right (K FT, then ft R radio alt)
- Thick line to the right of the Alt tape with the desired
- Triangle pointer to right of Alt tape showing actual
- Normal attitude ladders in the middle, rotated according to bank
- Boresight pointer / nose position (+ symbol) aligned with attitude ladders, not rotated
- Flight Director (box with lines representing wings and tail) set 5 deg below the boresight
- Flight guidance diamond ... pilot to fly the FD box onto the diamond.
- Speed tape on the left (kts), with a rectangle marking the actual.
2. Normal glideslope, velocity vector (VV) mode
- At around 14kft, the FD symbol disappears.
- Replaced with a VV symbol (a circle with lines for wings and tail)
- The guidance switches from a diamond to a circle, slightly smaller than the VV circle.
- When the runway is in the HUD view, it draws a rectangle for the runway limits (perspective aligned)
- There are two circles, connected with a line, representing the Inner Glideslope (IGS) shallow aim point, and the Outer Glideslope (OGS) steep aim point. The lime between them is the extended centerline
- The OGS glide angle is represented by two opposing triangles, on the 20 degree attitude ladder, rotated to the ladder. This is a visual aid to align the VV with this OGS and aim to the outer glideslope target point.
- The IGS glide angle starts below the OGS, and lifts up at the required pitch rate to transition from OGS to IGS. As the vehicle goes past the OGS, the OCG traingles disappear.
- The actual and commanded speedbrake info is in the bottom right.
3. Declutter mode 1
- Just removes the runway overlay.
3. Declutter mode 2
- Removes the speed and alt tapes, replacing with numbers.
- What's left here is the boresight, the VV, the guidance, the speedbrake commanded & actual.
4. Declutter mode 3
- Just leaves the boresight
The guidance mode is also in the bottom left:
- S-TURN .... high energy, bleed off with roll maneuvers.
- ACQ ... acquisition of the HAC entry point - main glideslope to HAC.
- HDG ... HAC turn heading guidance to the HAC exit
- PRFNL ... extended centerline hunting for the outer glideslope angle
- CAPT ... capture the outer glideslope
- OGS ... on the OGS
- FLARE ... transition OGS to IGS
- FNLFLARE ... final flare for touchdown.
- ... followed by de-rotate of the nose onto the runway.
I can do something similar to this for a future Glideslope 3. In the current implementation, digital guidance is a fairly simple based on having a reference glideslope with Alt, TAS, VSpd, and AoA for a set of range markings. It does not calculate a desired new AoA, etc to correct energy issues. I think it should still work, but the alternative would be a full rewrite of Glideslope to replace the entire guidance core with something that can dynamically generate a solution for landing. (That's a big effort, as that core is largely untouched from the original Glideslope 1, and is a maze of dark and twisty passages.)
I guess the right approach is to do this one bit at a time. Simple HUD first, just the tapes and the FD / VV / Boresight, with the guidance slaved to the digital data. Let's see if that is useful first.
---------- Post added at 02:09 PM ---------- Previous post was at 02:07 PM ----------
I noticed that the Shuttle points its nose exactly where the "Extended runway centerline" ends.
Did this "centerline" also provide visual clues about where to point the nose (or was it a coincidence), or was it "only" meant as an aid in aligning?
Not the nose, but the velocity vector. The extended centerline graphic has a circle at each end, representing the target for your outer glideslope velocity vector, and your inner glideslope velocity vector. The nose is still the + icon in all displays.