Author Topic: How would you model JATO?  (Read 2806 times)

beachhead1985

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How would you model JATO?
« on: 04 January 2017, 16:36:11 »
I'm interested in modeling JATO as a stores option for some Aerospace units.

Looking at TW, I find there is listed the takeoff rolls for various units, so JATO could shorten that in some cases.

But I cannot find where, if anywhere it says that external stores impinge upon this in any way? Do they prevent fully-laden ASF and CF from taking off vertically (when they can do so; all ASF can, but only special CFs)


***

The basic mechanic I was thinking of is that JATO takes up X-bomb slots depending on the size of the unit from 5-200 tons.

But another use for JATO is getting heavily laden units into the air. So...like the bomb slots or cargo bays are all full...so then where does the JATO go? Bomb Slots if you want to take off faster, no bomb slots if you need it to get off the ground at all?

Simpler to ditch the bomb slots idea?

***

So why not use JATO?

It's an additional +1 piloting roll to maintain control on takeoff, fail and you could stall or over-stress the landing gear and crash on takeoff.

Thanks for your time.
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worktroll

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Re: How would you model JATO?
« Reply #1 on: 04 January 2017, 16:47:49 »
Using JATO taking up bomb slots sort of defeats the purpose of using JATO to lift overloaded planes.

Maybe require 5% of weight for conventionals devoted to additional bracing. ASFs are basically armoured bricks, so you could easily hand-wave bracing requirements.

Then JATO adds two thrust points usable only for takeoff, with the PSR at +1 to avoid fumbling. Fail that, then you have to make a control roll - if you succeed you have to drop all underwing stores, if you fail, you crash horribly while upside down, and the bombs come through the cockpit floor before exploding (the Michael Bay rule ;) )
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HobbesHurlbut

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Re: How would you model JATO?
« Reply #2 on: 04 January 2017, 17:30:38 »
JATO is also a way to get planes take off a runaway that's shorter than they're designed for.
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worktroll

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Re: How would you model JATO?
« Reply #3 on: 04 January 2017, 17:34:12 »
In BT terms, that's irrelevant, as there's no formula for takeoff length in hexes relating to mass, thrust, load etc.

JATO can also be used to land on runways too short - there's that famous footage of a Herk landing on a dime ;)
* No, FASA wasn't big on errata - ColBosch
* The Housebook series is from the 80's and is the foundation of Btech, the 80's heart wrapped in heavy metal that beats to this day - Sigma
* To sum it up: FASAnomics: By Cthulhu, for Cthulhu - Moonsword
* Because Battletech is a conspiracy by Habsburg & Bourbon pretenders - MadCapellan
* The Hellbringer is cool, either way. It's not cool because it's bad, it's cool because it's bad with balls - Nightsky
* It was a glorious time for people who felt that we didn't have enough Marauder variants - HABeas2, re "Empires Aflame"

beachhead1985

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Re: How would you model JATO?
« Reply #4 on: 04 January 2017, 21:14:03 »
Using JATO taking up bomb slots sort of defeats the purpose of using JATO to lift overloaded planes.

Maybe require 5% of weight for conventionals devoted to additional bracing. ASFs are basically armoured bricks, so you could easily hand-wave bracing requirements.

Then JATO adds two thrust points usable only for takeoff, with the PSR at +1 to avoid fumbling. Fail that, then you have to make a control roll - if you succeed you have to drop all underwing stores, if you fail, you crash horribly while upside down, and the bombs come through the cockpit floor before exploding (the Michael Bay rule ;) )

how do thrust points play into take-off rolls?
Epitaph on an Army of Mercenaries

These, in the day when heaven was falling,      Their shoulders held the sky suspended;
The hour when earth's foundations fled,         They stood, and earth's foundations stay;
Followed their mercenary calling,               What God abandoned, these defended,
And took their wages, and are dead.             And saved the sum of things for pay.
     
A.E. Housman

worktroll

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Re: How would you model JATO?
« Reply #5 on: 04 January 2017, 21:22:07 »
It's more that IIRC you need a minimum level of thrust to take off, while bombloads reduce thrust. So if you had a 2/3 bomber, excessive load would reduce that thrusr below the level needed.

(Or am I remembering dropships, not ASF/conventionals?)
* No, FASA wasn't big on errata - ColBosch
* The Housebook series is from the 80's and is the foundation of Btech, the 80's heart wrapped in heavy metal that beats to this day - Sigma
* To sum it up: FASAnomics: By Cthulhu, for Cthulhu - Moonsword
* Because Battletech is a conspiracy by Habsburg & Bourbon pretenders - MadCapellan
* The Hellbringer is cool, either way. It's not cool because it's bad, it's cool because it's bad with balls - Nightsky
* It was a glorious time for people who felt that we didn't have enough Marauder variants - HABeas2, re "Empires Aflame"

beachhead1985

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Re: How would you model JATO?
« Reply #6 on: 04 January 2017, 21:54:25 »
It's more that IIRC you need a minimum level of thrust to take off, while bombloads reduce thrust. So if you had a 2/3 bomber, excessive load would reduce that thrusr below the level needed.

(Or am I remembering dropships, not ASF/conventionals?)

Nono, I think you got it and I think that's key...but to make use of it for excessive bomb loads, do we know the equation to calculate an overload of bombs?

Would that even be useful in this context? A 1/2 aircraft? Sheesh.

Alternatively; is there value in giving a shorter take-off roll in BT? Everything but VSTOLs have the same takeoff, right?
Epitaph on an Army of Mercenaries

These, in the day when heaven was falling,      Their shoulders held the sky suspended;
The hour when earth's foundations fled,         They stood, and earth's foundations stay;
Followed their mercenary calling,               What God abandoned, these defended,
And took their wages, and are dead.             And saved the sum of things for pay.
     
A.E. Housman

worktroll

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Re: How would you model JATO?
« Reply #7 on: 04 January 2017, 22:27:09 »
Takeoff, landing, all these things are effectively abstracted for the sake of 30m hexes & 10-second turns.

Let's be daring and look at the actual rules!  :D

TW v1.2, p88: "Aerodyne DropShips, fighters, and small craft can lift off from a ground map during the Movement Phase (Ground) by accellerating down a runway or open ground until they reach liftoff velocity. The distance required for all units is twenty clear or paved hexes in a continuous line that do not change levels at any point. VSTOL-equipped units can take off in ten hexes. Players need not make a Control Roll for a horizontal liftoff."

<snarky insert - they all appear to have rough-field capacity like a Mig-23 ;) >

So simplest use of JATO/RATO is to allow a DropShip, fighter or small craft to use a 10-hex takeoff run, making a Control Roll using he VTOL Liftoff Modifiers table, and failures as per the Failed Liftoff Maneuver Table (both also on p88). TW makes no mention of thrust.

So let's dig into TO ... nope, nothing there. Can't find any minimum thrust values for TO, TM, or TW, now that I mention it.

Going back to TW, the rule is that a fighter can carry 1 bomb for every 5 tons of mass, but that each increment of 5 bombs reduces safe thrust by one. Unless you're designing 1/2 conventionals in the 5-25 ton range, I can't see - under BT dynamics - any way to model the "overloaded takeoff" aspect.

So let's just wing it, and say that JATO can either a) halve the takeoff distance, or b) allow one additional bomb to be carried. Either use requiring a Control Role using the Vertical Takeoff modifiers & failure rules. So you can take your Mosquito light fighter - 20 tons, normally 6/9, capable of carrying up to 4 bombs at 5/8 - and using JATO tack on a fifth bomb. As it happens, there's no additional thrust loss.

(A 25-ton Hurricane could use JATO to wedge on a sixth bomb, but it's clean 6/9 thrust would drop to 4/6.)

Makes sense as a home rule?
* No, FASA wasn't big on errata - ColBosch
* The Housebook series is from the 80's and is the foundation of Btech, the 80's heart wrapped in heavy metal that beats to this day - Sigma
* To sum it up: FASAnomics: By Cthulhu, for Cthulhu - Moonsword
* Because Battletech is a conspiracy by Habsburg & Bourbon pretenders - MadCapellan
* The Hellbringer is cool, either way. It's not cool because it's bad, it's cool because it's bad with balls - Nightsky
* It was a glorious time for people who felt that we didn't have enough Marauder variants - HABeas2, re "Empires Aflame"

Fireangel

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Re: How would you model JATO?
« Reply #8 on: 08 January 2017, 15:16:18 »
Unless you're designing 1/2 conventionals in the 5-25 ton range, I can't see - under BT dynamics - any way to model the "overloaded takeoff" aspect.

A fighter (aerospace or conventional), fixed wing, or aerodyne aero unit with a thrust rating of 1/2 is barely more than a glider; barely capable of lifting off from the ground, but capable of maintaining altitude.

Quote
Liftoff (p. 88) (after errata)
“A horizontal liftoff takes 2 Thrust Points, and places the aerospace unit on the appropriate hex of the atmospheric map at Velocity 1 heading in the direction the landing strip was oriented on the ground map, and may not spend further thrust points that turn. The unit is not subject to Gravity (p. 80) this turn.”

The thrust does not have to be 'safe thrust', so at 1/2 it is possible to take off and get to a relative Altitude 1 on the low-altitude map, but due to stalling rules and gravity, the fighter cannot climb normally (it can, but it gets complicated fast).

-------------

JATO might be best represented by external equipment intended to allow a non-VTOL/VSTOL aero unit to take off in confined spaces, primarily for rescue and salvage, not for allowing heavy bomb loads.

Seriously, you can load fighters with 1/2 thrust on a carrier and launch them up in the air in order for them to start at altitude; after they drop their bombs, they can climb normally.

In most every other application, as pointed out, it is practically impossible to mount more bombs than thrust, and in the extremely limited cases where it can happen, the base units are so sub-optimal for the task that it is not even funny, and on top of that, can be given more thrust with a simple engine upgrade that in most cases does not even add 1/2 ton to the base engine.

I am Belch II

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Re: How would you model JATO?
« Reply #9 on: 10 January 2017, 11:18:26 »
As a bomb slot. But I don't see how it would help in combat
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beachhead1985

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Re: How would you model JATO?
« Reply #10 on: 10 January 2017, 19:51:53 »
I think you guys are right; I just cant see a worthwhile way to model this in BT without breaking some other rules and adding further complications.
Epitaph on an Army of Mercenaries

These, in the day when heaven was falling,      Their shoulders held the sky suspended;
The hour when earth's foundations fled,         They stood, and earth's foundations stay;
Followed their mercenary calling,               What God abandoned, these defended,
And took their wages, and are dead.             And saved the sum of things for pay.
     
A.E. Housman

Fireangel

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Re: How would you model JATO?
« Reply #11 on: 10 January 2017, 22:02:27 »
The key is that the engines of aero units in BT are simply too powerful to be compared with the engines of modern aircraft.

JATO might be modeled as using cargo and/or omnipod space to add either the VTOL/VSTOL tonnage OR the tonnage difference of a larger engine.

I am still of the mind that it should be used only for special situations and not for getting bomb-laden fighters airborne. Seriously, there are too many better alternatives, up to and including loading the overloaded fighter onto a carrier.



beachhead1985

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Re: How would you model JATO?
« Reply #12 on: 13 January 2017, 23:50:37 »
I think I'll have to give up on this one guys, but thank you for your time.
Epitaph on an Army of Mercenaries

These, in the day when heaven was falling,      Their shoulders held the sky suspended;
The hour when earth's foundations fled,         They stood, and earth's foundations stay;
Followed their mercenary calling,               What God abandoned, these defended,
And took their wages, and are dead.             And saved the sum of things for pay.
     
A.E. Housman

 

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