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Author Topic: The Workhorse Universal Heavy ASF  (Read 1609 times)

Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #30 on: 15 November 2021, 10:11:07 »
Something spherical with four engines out on booms
The Mammoth is the only standard design I'm aware of with this flavor.  The ability to asymmetrically power opposite drives should enable a fast spin.   If you could additionally reverse the engine units (Firefly style) it would enable you to decelerate. 

DevianID

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Re: The Workhorse Universal Heavy ASF
« Reply #31 on: 16 November 2021, 00:41:26 »
In thinking, quirks could probably handle this.  There are already quirks for being bad in atmosphere, so an expensive space vector quirk would work well (it needs to be double cost of the negative probably)

Cannonshop

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Re: The Workhorse Universal Heavy ASF
« Reply #32 on: 16 November 2021, 09:22:23 »
The Mammoth is the only standard design I'm aware of with this flavor.  The ability to asymmetrically power opposite drives should enable a fast spin.   If you could additionally reverse the engine units (Firefly style) it would enable you to decelerate.

the mammoth's engines are STILL close to the center of mass/center of gravity, which is like a centerline mount in that it's going to give you a smoother ride during boost phase, but it's not exactly 'maneuverable'-the placement is more about being able to put down in a socket without expensive, massive, leg-jacks and still have the engines clear to thrust on takeoff.

For what I'm talking about, it's more like "Let's build something with a hell of a lot of thrust, that can flip and spin and side-walk, but it doesn't need landing gear or atmospheric flaps and it doesn't need to be streamlined."

Which is why  i'm saying you can't do it with 'quirks' and get what you're looking for-the layout just doesn't work, you'd probably need an entirely different record sheet and crit table to get that 'B5 starfury effect' in your movement profile-where you can thrust backwards or sideways at the same rates you're going forward.

The Battletech(tm) universe isn't the kind of setting where such a beast could evolve naturally-everything, and I mean everything, in Battletech is focused on the ground game, with ASF and Naval assets being dual-focused at best.  It's a "Warriors who sometimes fight in space" type universe, not a "Spacers who sometimes go to war" type universe.  When someone kindly tries to tack on elements of the latter, it ends up being klunky and kludged because of that.
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Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #33 on: 16 November 2021, 19:38:53 »
the mammoth's engines are STILL close to the center of mass/center of gravity, which is like a centerline mount in that it's going to give you a smoother ride during boost phase, but it's not exactly 'maneuverable'-the placement is more about being able to put down in a socket without expensive, massive, leg-jacks and still have the engines clear to thrust on takeoff.
The Mammoth engines are apparently about 130 meters from the center of mass.  The angular momentum of a uniform sphere is 2/5 M*r^2 = 352e6 tons*m^2.  For an acceleration potential of .5g in an engine, the force is F=ma=52K tons * 4.9 m/s^2=254800 tons*m/s^2 and the torque is Fr =33e6 tons*m^2/s^2.  These imply the rotational acceleration is .09375 radians/s^2.  To do a 180, you want to accelerate with one engine on halfway and then one engine on the other way.  This implies each thrust needs to traverse pi/2 radians.  Using sqrt(2 * pi/2) = ~6 seconds + the same to decelerate suggests the Mammoth could reverse orientation in 12 seconds with zero angular momentum.



idea weenie

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Re: The Workhorse Universal Heavy ASF
« Reply #34 on: 16 November 2021, 21:18:07 »
The Mammoth engines are apparently about 130 meters from the center of mass.  The angular momentum of a uniform sphere is 2/5 M*r^2 = 352e6 tons*m^2.  For an acceleration potential of .5g in an engine, the force is F=ma=52K tons * 4.9 m/s^2=254800 tons*m/s^2 and the torque is Fr =33e6 tons*m^2/s^2.  These imply the rotational acceleration is .09375 radians/s^2.  To do a 180, you want to accelerate with one engine on halfway and then one engine on the other way.  This implies each thrust needs to traverse pi/2 radians.  Using sqrt(2 * pi/2) = ~6 seconds + the same to decelerate suggests the Mammoth could reverse orientation in 12 seconds with zero angular momentum.

Doesn't this require that the engine is pointing at right angles to the hull?  Instead most Dropships have the engines mainly point 'down', so you would get rotational thrust by turning off the engines on one side but not as fast as you calculated.  Now I'm looking at the angle created between the center of that engine bell and the center of the ship's mass, and a line going directly down from the center of mass, and wondering if you would use the sin or cosine of that angle to make the calculations (likely cosine).

Basically a ship with its engines at its equator would be able to have excellent maneuverability since all the engines are at right angles to the hull, but a ship with all its engines in a cluster at the base would not have as much maneuverability since most of their thrust would still be going towards the Dropship's center of the mass

Cannonshop

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Re: The Workhorse Universal Heavy ASF
« Reply #35 on: 16 November 2021, 23:22:50 »
Doesn't this require that the engine is pointing at right angles to the hull?  Instead most Dropships have the engines mainly point 'down', so you would get rotational thrust by turning off the engines on one side but not as fast as you calculated.  Now I'm looking at the angle created between the center of that engine bell and the center of the ship's mass, and a line going directly down from the center of mass, and wondering if you would use the sin or cosine of that angle to make the calculations (likely cosine).

Basically a ship with its engines at its equator would be able to have excellent maneuverability since all the engines are at right angles to the hull, but a ship with all its engines in a cluster at the base would not have as much maneuverability since most of their thrust would still be going towards the Dropship's center of the mass

I'm kinda thinking he's presuming the engines can be rotated or spun, or have outlets on each end to get that kind of spin, seeing as there's no drag in space to help with the turnover.

"If ye love wealth better than liberty,
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better than the animating contest of freedom,
go home from us in peace.
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May your chains set lightly upon you,
and may posterity forget that you were our countrymen."-Samuel Adams

DevianID

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Re: The Workhorse Universal Heavy ASF
« Reply #36 on: 17 November 2021, 00:41:55 »
If the engines are all pointing down, you fire the other engine to slow down the first.  Hence why turns take 12 seconds if his math is correct.  They would take 6 seconds if the second engine could spin and provide 2x the thrust.  Now, with 4 engines and a 3/5 speed, 1 thrust from 1/4th your engines is hitting overthrust, so overthrusting an engine to spin a mammoth 180 in 12 seconds is NOT recommended.

Spinning a 180 in 12 seconds, the peak centrifugal force for people at the edge of the hull would be almost 4gs (the SI of 20 can handle 10g so the ship will be fine).  So people on the bottom of the ship would be smooshed and people at the top of the nose would fly into the ceiling.  If the crew are all on the deck 36 meters or less from the center of the hull, its a 'comfortable' 1 g.  Better alert your crew to get midship before a 12 second 180!

Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #37 on: 17 November 2021, 02:09:30 »
Doesn't this require that the engine is pointing at right angles to the hull? 
The mammoth has 4 equidistant engine units spaced around the equator and pointing aft.  To generate the spin, you have one fire and the opposite one not for 6 seconds, then shut off the original one for 6 seconds while you let the opposite one fire. 

For @Cannonshop: this should work with the fixed engine units depicted in the art as long as you have fine control over their on/off state.
If the engines are all pointing down, you fire the other engine to slow down the first.  Hence why turns take 12 seconds if his math is correct.  They would take 6 seconds if the second engine could spin and provide 2x the thrust.  Now, with 4 engines and a 3/5 speed, 1 thrust from 1/4th your engines is hitting overthrust, so overthrusting an engine to spin a mammoth 180 in 12 seconds is NOT recommended.
If .75 thrust is used instead, the time becomes ~14 seconds.
Spinning a 180 in 12 seconds, the peak centrifugal force for people at the edge of the hull would be almost 4gs (the SI of 20 can handle 10g so the ship will be fine).  So people on the bottom of the ship would be smooshed and people at the top of the nose would fly into the ceiling.  If the crew are all on the deck 36 meters or less from the center of the hull, its a 'comfortable' 1 g.  Better alert your crew to get midship before a 12 second 180!
Let's go with .75 thrust, since it's a fair point that we should be cautious about max thrust.  It takes 7 seconds to reach to reach peak rotational velocity.  If we go with 130m radius, that means the rotational longitude experiences a peak velocity of v = 2 * pi/2 * 130m / 7s = 58 m/s (=2x average velocity).   This creates a centrepital force of 58 m/s *58 m/s /130 m = 25.9 m/s^2 which is 2.6g.  That's definitely in the broken-bones-if-you-aren't-prepared regime. 

The equations are much friendlier at smallcraft scales (a factor of 6 less centrepital accel), but I'm not aware of any Mammoth-style smallcraft.

DevianID

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Re: The Workhorse Universal Heavy ASF
« Reply #38 on: 17 November 2021, 02:37:25 »
Quote
That's definitely in the broken-bones-if-you-aren't-prepared regime

Yep, BUT that is spinning a 180 in 14 seconds, across a 1 minute turn, meaning if you didnt slow down immediately you could spin the ship 1080 degrees with just 3 thrust from 1/4th your engines.  If the crew are centrally located (red alert) you could spin like a top in 1 minute for no ill effects, corkscrewing all the while over.  Ships in btech are fast! after all.

Also means round dropships dont need grav decks after all--they are grav decks.  So you can drift all you want, spinning end over, so the bottom half of your ship has 'normal' gravity (though you need to walk on the ceiling on the top half of your ship)

Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #39 on: 17 November 2021, 21:19:50 »
Also means round dropships dont need grav decks after all--they are grav decks.  So you can drift all you want, spinning end over, so the bottom half of your ship has 'normal' gravity (though you need to walk on the ceiling on the top half of your ship)
This is something I hadn't appreciated.  It makes coasting a much more viable activity.  In practice, I expect you would want to spin the ship on its central axis, which should be doable (more slowly) using attitude thrusters.  Ever room would have two floors: the thrust-floor (when the main engine is on) and the out-floor (when the ship is spinning without thrust).

DevianID

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Re: The Workhorse Universal Heavy ASF
« Reply #40 on: 17 November 2021, 23:51:41 »
Quote
Ever room would have two floors: the thrust-floor (when the main engine is on) and the out-floor (when the ship is spinning without thrust).
And probably a net in the bigger rooms for 'oops' crates/items left unsecured.
Im reminded of the expanse when the tool box was left open before heavy combat maneuvering.  Yeah, definitely arresting nets in the tech bay.

Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #41 on: 19 January 2022, 07:11:34 »
I was trying to figure out external stores for fuel related to some configurations and seem to be missing some critical rule.   Maybe someone knows where the right rules are?

TM page 196 says "external stores hardpoints, which may be used to carry... additional fuel tanks...".  However, TM page 346 does not list fuel as an option.  Additionally, the "Extended Fuel Tanks" entry on page 244 does not cover aerospace fighters, even in the errata.

The TM errata page 25 says: "The internal fuel capacity of an OmniFighter's base configuration must be fixed...Additional fuel may be pod-mounted, however."  In this context, pod-mounted seems to refer to an omnipod, which implies you can mount an extra ton of fuel internally on a ton-for-ton basis.  That's interesting---it suggests that good omnifighter designs should have relatively little fixed fuel?

Daryk

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Re: The Workhorse Universal Heavy ASF
« Reply #42 on: 19 January 2022, 18:33:58 »
I wouldn't sweat page 346 much... the heading there is "External Stores Hardpoint Weapons", and fuel isn't a weapon.

Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #43 on: 19 January 2022, 19:51:22 »
I wouldn't sweat page 346 much... the heading there is "External Stores Hardpoint Weapons", and fuel isn't a weapon.
I found the rule: it's SO page 35 under 'external fuel tanks'. 

The TM errata remains pretty interesting from a design perspective, as there are some missions which require much less fuel than others.  An example of a very low fuel mission is a ballistic high speed pass (either defensive or offensive).  Being able to customize fuel via omnipods is something I'd like to explore.

Daryk

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Re: The Workhorse Universal Heavy ASF
« Reply #44 on: 19 January 2022, 20:39:03 »
Glad you found it!   :thumbsup:

Lagrange

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Re: The Workhorse Universal Heavy ASF
« Reply #45 on: 23 January 2022, 20:45:02 »
I added some tweaks around fuel usage.  It looks like 3 tons as a baseline and then omnipod mounting to reach either 5 or 6.5 tons is a good approach.  Aside from that,

  • Added a C (Cargo) configuration which is pure cargo.  It's not revolutionary, but a single pilot 40 ton carrier is actually not-to-terrible for short hauls in fuel rich environments
  • Changed the I(Infantry) configuration to downgrade to 8 tons of battle armor and added an ERPPC+Capacitor.  This gives the infantry transport a long range punch if that's necessary/helpful, although it must choose between use the ERPPC and the Arrow IV.

 

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