#3745 Aerospace movement on Ground Maps missing ability to facing change by spending thrust points

stable 0.38

Looking closely at the Aerospace movement. It appears that the ability for Aerospace units to turn additional facings by spending thrust points isn't available to Aerospace units on the ground maps.

There is a specific question and official answer relating to MegaMek and Aerospace movement on forums.


This refers to TW on pg84, "additional facing changes."


  • Nicholas Walczak

    • Resolution: none --> accepted
    • Milestone: undetermined --> stable 0.36
  • Nicholas Walczak

    Well, this one is fun.

    So, this functionality is there. However, on ground maps aeros must move 8 ground map hexes before being able to make a facing change.

    Here's what TW says on pg 84:

    Aerospace fighters and aerodyne DropShips and small craft can also spend Thrust Points to gain additional facing changes. At any point in their movement, such units may spend Thrust Points equal to half their current velocity (round up) to change facing one hexside. However, they may not do so if they have already changed facing in that hex or if this is the first hex of their movement.

    The important part is the last sentence. It says that aeros can't make two facing changes in one hex. Alternatively, you could think of it as saying that an aero has to move 1 hex before making another facing change. 1 low-altitude hex, or 8 ground hexes.

    That is how MM implements it. On ground maps, aeros have to move 8 hexes before being able to make a facing change, regardless of whether it's free or not. Comments in the code link to a post on the btech forums, but it appears that the post is gone now.

    This contradicts what Xotl says in the linked post. I made a post on the forums to get some clarification: http://bg.battletech.com/forums/index.php/topic,29842.0.html

  • Eddy Cullen

    Eddy Cullen - 2013-06-02

    My vote is that you can turn after moving 1 hex.

    If you're below the minimum number of hexes for a free turn (which is carried-over from previous turns), then you must pay 50% (rounded up) of your velocity in thrust points.

    Example for an ASF with thrust point (TP) 5/8:

    Round 1, initial Velocity v0:
    * Spend 2 TP to accelerate to v2 (32 movement).
    * Move forward 1
    * Spend 1 TP to turn right.
    * Move forward 12.
    * Make free turn to the left.
    * Move forward 16.
    * Make free turn to the left.
    * Move forward 3; movement points exhausted (32).

    Round 2, initial velocity 1 (2 divided by 2, round down), moved forward 3 at end of last turn:
    * Spend 3 TP to to accelerate to v4 (64 movement).
    * Move forward 17.
    * Free turn right. (17 + 3 == 20, enough for free turn)
    * Move forward 5.
    * Spend 2 TP to turn right (5TP total for turn).
    * Move forward 6.
    * Spend 2 TP to turn right (7TP total for turn) - make piloting role for TP exceeding safe (more than 5).
    * Move forward 20 - not enough TP to make more non-free turns.
    * Free turn right.
    * Move forward 16; movement points exhausted (64).

    Round 3, initial velocity 2 (4 divided by 2, round down), moved forward 16 at end of last turn:
    * Free turn right - Moved 16 on last turn.
    * Move forward 32; movement points exhausted (48).
    * Free turn left.

    Round 4, initial velocity 1:
    * must move 8 for next free turn or 1 to spend TP to turn.

    Last edit: Eddy Cullen 2013-06-02
  • Nicholas Walczak

    The issue with this is that it creates an inconsistency in scales.

    At the atmosphere scale, to make a U-turn you'd have to make a horseshoe pattern that is 3 hexes wide. That is, if I'm facing "north" in one hex I have to move, turn, move, turn, move, turn. This would yield the tightest possible 180-degree turn. This requires 3 atmosphere hexes, which would equate to 3 16x17 ground mapsheets.

    Now, the exact same pattern could be applied on a ground map if we don't require 8 hexes between facing changes, allowing an aero to make a 180 degree turn in 3 ground hexes which means a u-turn in 1 atmosphere hex instead of 3.

    This would imply that aeros are more maneuverable on ground maps, since they can make significantly tighter turns.

    I wasn't sure how coherent my explanation was, so I'll attach a screenshot that illustrates it.

    I hadn't really considered this scenario before, but thinking about it now I'm more certain that the way Megamek does it now is the correct way.

  • Dylan Myers

    Dylan Myers - 2013-06-03

    The way MM implements it is the correct way as far as I'm concerned.

  • Nicholas Walczak

    Yea, I agree. However, the in the linked post Xotl claims it's wrong. I want to get a reply back before closing this. I don't think there's anything left to do until I get a reply to my post on the battletech forums.

  • Dylan Myers

    Dylan Myers - 2013-06-03

    Just do me a favor, if you do get a reply back from him and he says that we're wrong... when you change it, make an unofficial option to keep using the exisiting method. I hate rules stupidity ;)

  • Sebastian Brocks

    I sent a PM to Xotl regarding this ruling, and explained your reasoning. Let's hope he rescinds that ruling.

    • Nicholas Walczak

      I already PMed Xotl, but he's on vacation. Moonsword is taking over for him while he's gone, and I PMed him as well. Both have replied to me and asked to make a post on the errata forum, which I have done. I'm awaiting a reponse to that post. It's linked in the second post in this bug that I made.

  • Anonymous - 2013-06-03

    The ground map movement speed is inconsistent with the atmospheric movement; the ratio is 1:16, so to be consistent, you'd have to move a minimum of 16, not the 8 in the ground movement table.

    I think the right approach to this is the one Dylan suggests: put in the correct (according to the rules) implementation and add an option to switch on something more... consistent.

    As for what that consistent thing should be... well, I actually think it should be a maneuver like those in the canonical rules (Split-S, barrel-roll, etc.). These maneuvers should be called 'Xg Turn' and they should have pre-set movement patterns, based on the velocity.

    I haven't done the maths yet, so don't know what they'd look like exactly, but fundamentally, they'd be "forward X, turn, forward X" patterns, based on the g of the turn and the current velocity.

    FTR, the human spine can withstand about 12g before collapsing and with a pressurised flight suit, extremely fit pilots can manage a 10g turn, but anything above 4 risks g-loc (g-force induced loss of consciousness).

    Modern airframes, such as the Eurofighter and F22 can easily cope with 15g+; they literally have to be dialed-back to keep the squishy in the cockpit alive ;)

    I'd suggest adding 4g, 6g and 8g turns; 4g without a pilot roll (unless beyond safe thrust), 6g with a small penalty and 8g with a significant penalty. If you're feeling sadistic, you could put in a 10g turn with like a -8 penalty ;)

    Don't worry about the maths, I know an aerospace engineer or two ;)

    Clearly, the maneuver stuff is more of an RFE, than a bug fix...

  • Eddy Cullen

    Eddy Cullen - 2013-06-03

    Damn it... forgot to sign-in on that last post...

    Anyway, I just did the maths and actually, doing a u-turn is possible at velocity 1 (48m/s); you'd need to pull a sustained 9.6g, but you could do it... And it would take a turn with a radius of 150m (Well, 152.7887...) or 5 hexes... so a 180 degree turn @ velocity 1 would require a start and end point that were 10 hexes apart (or is that 9 or 11?, damned out-by-one shizzle...) and you'd need to pull 9.6g for 10 seconds, which would be a super-human feat...

    So, no, I don't think you should be able to turn-about in a single turn - EVER!!! (The numbers get WORSE for higher velocities!!!!

    So, the correct answer, is that you cannot make a U-turn in a single round of momement and that your ability to turn should be strictly based on the minimum for the velocity, which goes up in (atleast) 8s for every point of velocity, with NO exceptions!!!.

    The only exception I can see would be a 'jink' maneuver, which would be a set turn-move-turn pattern, that allowed you to shift your flight path slightly to the left or right...

    Damn, I love numbers!

  • Nicholas Walczak

    • assigned_to: Nicholas Walczak
  • Nicholas Walczak

    • Milestone: stable 0.36 --> post-stable 0.36
  • Nicholas Walczak

    It may take a while to get a response on this, and since I don't think it's an actual issue, I'm going to move it to post-stable.

  • Taharqa

    Taharqa - 2013-07-23

    I am the one who implemented the 8 hex minimum for thrust-based facing changes and that was based on a response from Welshman to a rules query on the old boards. I just PM'ed xotl on the boards and alerted him to the history of that decision.

  • Hammer

    Hammer - 2013-08-15

    While at Gen Con I got clarification on this. It's coded correctly. Closing this one.

  • Hammer

    Hammer - 2013-08-15
    • status: open --> closed
    • Resolution: accepted --> invalid
  • Taharqa

    Taharqa - 2013-09-06

    It is not coded correctly at the moment because turn by thrust is not working. On the ground map, you should be able to turn by thrust (spending MP) between 8 hexes and the minimum free turn. Thats straight from Welshman's mouth and it is consistent with the rules. Without this rule in place, it is virtually impossible to maneuver aeros on the ground map.

    I have opened another bug about at [#3841].



    Bugs: #3841

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