another Kettle of Fish; "Old School" Flight Question(s)

[Wolf72]

Going off of a tangent from this thread https://bg.battletech.com/forums/index.php?topic=84223.0

How does SV/CF/ASF flight work while in atmosphere. From the above thread, SC & DS need to provide a min of 2/3 or just hover in place like some sort of inflated, overweight baron.

I'd always assumed that a made for atmo craft would be able to move to its desired altitude (up to 8 levels high iirc) while inputting the amount of mp it has each turn then it has to continue to burn fuel to keep the momentum going.

A 3/5 CF would use 3 mp to get up to 3 alt upon take off, then spend at least 1 mp per turn to stay aloft in the air at that altitude.  A 1/2 unit could technically put out 2 mp for 16 turns to make it to alt 8 (wait, row 8 on alt map?) then cruise along at 1 once there. So 1 up 1 forward, repeat until at your desired altitude.

Note: I know I could be way off here, or I might be conflating with VtoLs (which I hope I don't have wrong either).  Also I don't actually use them, just read up (lightly) and collect (occasional mech v mech).

Note2: if possible, looking for the simple answers, w/o crazy scenarios (like skidding into a building w/basement and unit on roof, building collapses, and it's the third Friday of the month)

[AlphaMirage]

The cycle is such

Turn 0 - 5/8 Plane on ground at 0 Altitude and Velocity with engines on
Turn 1 - Plane takes off spending 2 Thrust in the process accelerating to Velocity 1 in the atmospheric hex

This is where things get weird because low-altitude vs high-altitude maps, first increasing Velocity or Altitude costs a straight 2 Thrust per Total Warfare regardless of which map you're on.
Presuming you 'must' go up the low altitude map there are 10 layers and you can only achieve a Max Safe Velocity of 2 and you lose half your Velocity each turn.

Turn 2 - Altitude 1 NOE, Spend 2 Thrust to maintain Velocity or fall out of the sky. Spend 2 more Thrust to increase Velocity to 2, 4 Thrust are spent to increase 2 Altitudes
Turn 3 - Altitude 3, Spend 2 Thrust to maintain Velocity at 2. Spend 6 Thrust to increase 3 Altitude
Turn 4 - Altitude 6, Spend 2 Thrust to maintain Velocity at 2, Spend 6 Thrust to increase 3 Altitude
Turn 5 - Altitude 9, Spend 2 Thrust to maintain Velocity at 2, Spend 2 Thrust increase to Low Altitude 10 where High Atmosphere Levels begin, then move to High Atmosphere level 2 then 3 using 4 Thrust.

Turn 6 - High Altitude 3 (54-71km), At High Altitude you only lose 1 Velocity not half so we still spend 2 Thrust to maintain Velocity 2, Spend 4 Thrust to reach Atmospheric Interface Layer (HA Row 5).

Total Cost - 6 Turns, 14 Thrust for Velocity, 26 for Altitude, 72 Fuel Points (due to afterburners)

If you don't need to transit the low altitude map first and can instead go straight to the High Altitude layers then it would be like this
Turn 2 - Ground Level, Spend 4 Thrust to increase Velocity to 2, 4 Thrust to increase Altitude to HA Layer 2 (36-53km)
Turn 3 - HA Layer 2, Spend 2 Thrust to maintain Velocity at 2, 6 Thrust to reach Atmospheric Interface Layer

Total Cost - 3 Turns, 8 Thrust for Velocity, 10 for Altitude, 32 Fuel Points (due to afterburners)

There are also further restrictions, propeller planes, airships, and VTOLs can only operate within low atmosphere (ground level at High Altitude). Conventional Fighters (ICE or Fusion) and non-propeller driven fixed wing support aircraft can reach High Altitude 1 but no further.

Spheroids don't do any of this because they don't typically have a horizonal velocity as they are going vertical (parabolic technically since the nose must point up and to the right or left) so only fight gravity.
Turn 0 - 3/5 Spheroid on landing pad ready to liftoff
Turn 1 - Spheroid spends 2 Thrust to take off, is hovering over the landing pad in atmospheric hex 1.
Turn 1 - Spheroid spends 2 Thrust to fight gravity, 2 more thrust to increase altitude to 2.
if you must transit the low altitude map repeat for 8 more turns
Turn 10 - Spheroid reaches high altitude layer 1.
Turn 15 - Spheroid finally reaches atmospheric interface layer.
Cost - 15 Turns, 32 to fight gravity, 30 to reach atmospheric interface, 122 Fuel Points

If you don't need to transit the low altitude map then
Turn 0 - 3/5 Spheroid on landing pad ready to lift off
Turn 1 - Spheroid spends 2 Thrust to take off, is on ground level map
Turn 2 - Spheroid spends 2 Thrust to fight gravity, 2 more to reach HA layer 1
repeat 4 more times
Costs - 6 Turns, 12 Thrust to fight gravity, 10 to reach space, 42 Fuel Points

Spheroids can Sideslip into adjacent hexes (effective horizonal movement) at the cost 2-3 Thrust (this one is weird) but do not acquire horizonal velocity in the process. Typically this would be either used as a weapon of mass destruction (Spheroid thrusters are devastating) or to adjust a landing zone.

Getting past the Space/Interface Layer and into orbit requires the expenditure of 4 Thrust.

[Wolf72]

well, that is a huge kettle of fish (giving credit to Daryk on that phrase).

ok.  wow, not a day to try brain stuff, but here it goes.

my 1/2 CF or SV (propeller even?) has a really long runway and clear landscape for quite a while

1. start by spending 2 mp to get to velocity 1
2. ooh wait, here is a problem.  I can stay at velocity one or go to alt 1 ... that's basically hovering (talk about aero-boondoggles!)

That 72 points of fuel seems to be a problem too ... what if your fighter (5/8) only carries 3 tons of fuel (CF so ... 640 points) how long will that last you in terms of flying?

2/3 and even 3/5 CF or SV look to be really short range and low level flying machines (unless you go SV propeller with fusion engine -- unlimited range)

[AlphaMirage]

You can use less fuel by just using safe thrust it will just take longer, and is probably not worth it with drag effects. Rising High and Fast is preferable to slow climbing particularly if you have external ordnance as that reduces your safe thrust.

If you can get up to the High Altitude Map you can speed up to 3 Velocity (for conventional fighters) or higher and faster (depending on HA Layer) for Aerospace and Aerodyne Dropships and sustain yourself at the cost of just 2 Thrust so you can go pretty far on that tank of fuel.

4/6 Prop Plane would be a solid low altitude performer. Probably the minimum you'd need for a Super Tucano or Sky Ranger equivalent. A 3/5 or less would make for a solid cargo or surveillance aircraft but not a good combat choice (except for internal bomb loads perhaps). Prop Planes use less fuel than turbine equivalents per point of thrust as explained in TechManual but its different depending on the level at which you build them.

Also ICE Conventional Craft only use half the fuel (as the air is their oxidizer, according to StratOps) as fusion powered craft (with an edge case for fusion ConvAir being the same but that's table rules) but are limited to HA 1.

[Daryk]

Thanks for the credit!  I'm laying low on this discussion because there are others who know WAY more than I do about it... ;)

[Lagrange]

Turn 0 - 5/8 Plane on ground at 0 Altitude and Velocity with engines on
Turn 1 - Plane takes off spending 2 Thrust in the process accelerating to Velocity 1 in the atmospheric hex

I believe you actually accelerate to velocity 2?  Which is then halved to 1.

This is where things get weird because low-altitude vs high-altitude maps, first increasing Velocity or Altitude costs a straight 2 Thrust per Total Warfare regardless of which map you're on.

I believe increasing velocity by 1 only costs 1 thrust on the low altitude map. "Increasing velocity by 1 costs 2 thrust points" appears on page 79 under the High Velocity heading.  No similar verbiage appears under the low velocity heading.

For a 3/5 thrust profile, I believe a rapid takeoff looks like:
Ground turn 1: Take off with 2 thrust points reaching velocity 2 at an altitude of underlying terrain+1.  This may be as low as altitude 1, but if you take off form a hill or mountain it could be higher. We'll assume altitude 1.
Ground turn 2: 2 velocity is halved to 1 (per TW page 84).  Spend 1 thrust point to increase velocity to 2 and 4 thrust points to climb to altitude 3.
Ground turn 3: 2 velocity is halved to 1.  Spend 1 thrust point to increase velocity to 2 and 4 thrust points to climb to altitude 5.
Ground turn 4: 2 velocity is halved to 1.  Spend 1 thrust point to increase velocity to 2 and 4 thrust points to climb to altitude 7.
Ground turn 5: 2 velocity is halved to 1.  Spend 1 thrust point to increase velocity to 2 and 4 thrust points to climb to altitude 9.
Ground turn 6: 2 velocity is halved to 1.  Spend 1 thrust point to increase velocity to 2 and 4 thrust points to climb to altitude 11.  Remove from low altitude map at end of turn and place in atmospheric row 1 on the high altitude map with velocity 1.  The orientation on the high altitude map is unclear, so probably player's choice.  Let's place aimed upwards.
next Space Turn (there are 6 ground turns per space turn): spend 4 thrust to increase velocity to 3 and move to the atmospheric row 4.  At the end of the turn, velocity decreases to 2 at the end of the turn.
Space turn 2: spend 4 thrust points to increase velocity to 4.  Move 4 rows up through the interface hex and into space.

Using the above it's possible to get into space in 3 minutes.

[AlphaMirage]

It does actually say 2 Thrust per Velocity and Altitude for all units operating 'in atmosphere' which includes low altitude, not just limited to high altitude. You also lose 'at least 1 Velocity' each turn according to the same paragraph. I did actually check the errata since you mentioned it before in the other thread.

The 2 for take off is conceivably to add the velocity and a vertical take off might be closer to a harrier's type where you have ducted air then apply velocity to jump parabolically.

Also very interesting that a Spheroid Dropship can 'hop' 8 ground hexes with a single Thrust although you'd still have to make a landing roll if you don't spend the 2 to hover.

[Lagrange]

It does actually say 2 Thrust per Velocity and Altitude for all units operating 'in atmosphere' which includes low altitude, not just limited to high altitude. You also lose 'at least 1 Velocity' each turn according to the same paragraph. I did actually check the errata since you mentioned it before in the other thread.

My assumption is that this, in context, means 'in high altitude atmosphere'. 

If you take the contents of that paragraph and apply them to low altitude as well, you need 6 thrust points to climb out of low altitude.

To see this, suppose you start at velocity 1.  You would (under your interpretation of TW page 79) require 4 thrust points to reach velocity 3 and then 2 more thrust points to climb an altitude (per TW page 84).  At the end of the round, you would reduce velocity by 1 (under your interpretation of TW page 79), so velocity is 2.  And then the low altitude rules on page 84 would halve velocity to 1 at the beginning of the next round.  If you only increased velocity by 1, then the combination of high altitude velocity reduction and low altitude velocity halving would result in velocity 0, creating a stall condition.

I don't think require 6 thrust points (~ 3g) is reasonable, so I interpret page 79 as only applying to high altitude.

[AlphaMirage]

Maybe something for the errata then as the High Altitude Loss and Low Altitude Halving should probably both occur at the end stage (and be an either or kind of situation of 'at least 1') as that is the most logical place for it to occur. Otherwise yes I agree with you 6 thrust is certainly a lot to ask for even mediocre performance.

[Lagrange]

Maybe something for the errata then as the High Altitude Loss and Low Altitude Halving should probably both occur at the end stage (and be an either or kind of situation of 'at least 1') as that is the most logical place for it to occur.

Or these are rules are meant to not be applied simultaneously.

[Vehrec]

I know for a fact that some WW2 aircraft would take upwards of 20-30 minutes to climb to altitude after take off to only 7.6 kilometers altitude.  I've even found a report on a B-17G taking over 40 minutes to reach that altitude.  Clearly, fusion rockets with TWRs of like 3 are what the system was designed for, not heavy bombers with 4000 supercharged horsepower turning 4 props.  That's a power/mass ratio of uh, 0.089 hp/lb (150 W/kg)  Like, no duh the system breaks down at this level.  We're dealing with a plane that has a thrust rating of, in battletech terms, .1/.15.  Other real-world subsonic aircraft aren't much better, because they're also blessed with TWRs far below unity.  Concorde was a .3/.5, 747s are .2/.3s, and the Space Shuttle, at max acceleration, topped out around 4/6.