[HG 2e] Aerofins and streamlining

[h1ro]

Did a quick search but didn't find a discussion centred on my question. I'm not looking for an official answer on this, just a discussion about how people interpret the rules. (But AndrewW and Msprange, please do chime in!)

Aerofins can be added to any ship, there are no requirements for a particular configuration.

It's therefore possible to add aerofins to a partially or unstreamlined ship.

For the partially streamlined ship this would negate the -2dm operating in atmospheres 4+

While the rules don't say you can't, why anyone would put aerofins on an unstreamlined ship is beyond me, so I'll ignore it for now!

The question is, are you all happy with aerofins on a partially streamlined hull?

You can guess from my weighted question that I'm not. I interpret the rules as aerofins require a streamlined hull, your thoughts please.

 

[AnotherDilbert]

Opinion:

Partial streamlining allows a ship to skim gas giants and enter Atmosphere codes of 3 or less, acting in the same way as streamlined ships. In other atmospheres, the ship will be ponderous and unresponsive, reliant on its thrusters to keep it aloft. All Pilot checks will be made with DM-2.

Partially streamlined (and unstreamlined) ships don't fly like airplanes, they balance on their thrusters like rockets at low speed, so can't benefit from wings or fins. My opinion may be influenced by MT.

 

[h1ro]

With anti gravity, nothing need fly like an aeroplane. As mass doesn't figure into the ship designs, we have no idea how or even if, aerodynamic forces apply. If the technology to reduce mass and accelerate at multiple Gs exists, flying like an aeroplane is just so last century.

In part, my question also links into whether ships use their M drive to maintain an orbital position. Technically, a ship in orbit maintains it's altitude by velocity and while that does degrade slowly, in general there's very little thrust needed to maintain orbit. A ship maintaining orbit has a velocity relative to the surface, these days we use heat shields and atmospheric breaking to de-orbit. With anti gravity I'd say de-orbiting would be as simple as riding an elevator down and matching your speed to the speed of rotation of the planet below.

 

[DickTurpin]

Most orbits do not maintain a ship's position over a specific surface location. There is a very specific position, usually quite a ways out, where a ship can match its orbital velocity with the rotation of the planet; geosynchronous orbit or GSO. If an orbiting ship wants to transfer goods or people to/from the surface, they would most likely be in a Low Orbit instead.

As to the function of aerofins, I would say that partially streamlined ships are the main ones that would use them. The rules are very brief so it is impossible to say for certain how the fins function, but I see them more as expanded control surfaces rather than lifting wings that allow a ship to actually fly like an airplane. Even just moving up and down on M-drive thrust causes movement through the air, large control surfaces could stabilize the ship's attitude rather than relying on balancing the mass of the ship over its center of thrust, making the pilot's job much easier.

 

[AnotherDilbert]

With anti gravity, nothing need fly like an aeroplane. As mass doesn't figure into the ship designs, we have no idea how or even if, aerodynamic forces apply. If the technology to reduce mass and accelerate at multiple Gs exists, flying like an aeroplane is just so last century.

Anti-gravity does not reduce mass, it only counters the downward force on the equipped vehicle (and somehow provides thrust).
Traveller ships generally don't use anti-gravity, they rely on their thrusters and possibly aerodynamic surfaces.

In part, my question also links into whether ships use their M drive to maintain an orbital position. Technically, a ship in orbit maintains it's altitude by velocity and while that does degrade slowly, in general there's very little thrust needed to maintain orbit. A ship maintaining orbit has a velocity relative to the surface, these days we use heat shields and atmospheric breaking to de-orbit. With anti gravity I'd say de-orbiting would be as simple as riding an elevator down and matching your speed to the speed of rotation of the planet below.

I haven't bothered to calculate it, but i believe it takes a lot more acceleration than Traveller ships can produce to go "straight down like an elevator", i.e. spiral around down to a moving rotating planet.
It is only at a specific height that the natural orbit lets you stay above a single point on the surface of the planet. (For the Earth it is Geostationary ~36000 km.)

 

[Condottiere]

Aerodynamics is not within my grasp, but I'll commit to an unstreamlined configuration managing to chug along at zeppelin speeds, that is less than a hundred klicks per hour in a standard atmosphere, without requiring constant checks for turbulence.

 

[phavoc]

With anti gravity, nothing need fly like an aeroplane. As mass doesn't figure into the ship designs, we have no idea how or even if, aerodynamic forces apply. If the technology to reduce mass and accelerate at multiple Gs exists, flying like an aeroplane is just so last century.

Anti-gravity does not reduce mass, it only counters the downward force on the equipped vehicle (and somehow provides thrust).
Traveller ships generally don't use anti-gravity, they rely on their thrusters and possibly aerodynamic surfaces.

I agree that anti-gravity doesn't affect mass, which would start another discussion on some of the other issues with Traveller starships/vehicles. However in this case ANY craft equipped with anti-gravity should be able to maneuver in any atmosphere so long as their anti-gravity system is capable of generating enough reverse force to counter the grav field. Cubes, spheres, even a distributed hull design (but it would have to be able to support itself structurally in a grav field) could land. The difference is that aerodynamic ships will be able to maneuver better and move faster than non-aerodynamic ships.

I have always assumed that Traveller ships use their anti-gravity to provide lift, but their thrust is from their main drives. And we know from aerodynamics 101 if you have a non-aerodynamic shape the amount of energy required to move in an atmosphere increases the faster you want to go (as does the heat from friction). It fits the tech model that Traveller has always had. I simply ignore the silly thing about needing thrusters to stay aloft... silly!

 

[Condottiere]

My take on the orbital range manoeuvre drive is that it is based on basic anti-gravity field.

Add a second normal drive to provide some more motivation.

 

[Rikki Tikki Traveller]

Aerospace Engineer here - not being rules specific.

Most ships is Traveller have contra-gravity - so Streamlined (and partially streamlined) ships usually maneuver by altering the gravitic fields and thrust.

Adding Aerofins (wings) allows one of these designs to augment that gravity control with aerodynamic control - like it is used by modern TL7 aircraft.

So, from an engineering point of view, it CAN benefit both Streamlined and Partially Streamlined hull forms. Obviously a streamlined design will still be more maneuverable, as the rules show.

For Partially Streamlined ships, the negative maneuvering DM is offset by the aerofins, giving that hull an EQUIVALENT maneuverability to a streamlined ship. That makes sense to me (I could argue + or - 1 either way as being fine - this is a game after all).

So, I would allow Aerofins on Partially Streamlined hulls.

I realize that this could have a SIGNIFICANT effect on the COST of the ship - don't have the books in front of me, but I suspect that the +10% hull cost of a Streamlined hull is much more expensive than Aerofins - but Hull doesn't cost tonnage and Aerofins do, so it might be a toss up in the long run.

Hope that helps.

 

[Reynard]

I always considered the space shuttle as partial streamlined with aerofins. A brick with wings.

As the core book states under Atmospheric Operations a ship acts similar to aircraft and can be affected by atmospheric condions which wiil call for hazard checks. The ship's configuration determines how well they handle in adverse condition in the form of negative DMs. Extendible aerofins are not part of the craft's normal flight operation. The aerofin system is deployed when the ship needs greater control. Pilot checks aren't just bad weather. If a pilot needs to make anything other than routine maneuvers (hard turns or skimming treetops during a chase) the pilot activates the aerofin system and their ship becomes a sportcar. Also great when there's buffeting winds during a chase.

 

[Condottiere]

It depends on how fast you're going.

An air/raft ascending or descending from orbit isn't going twenty eight thousand kilometres per hour.

 

[AnotherDilbert]

Most ships is Traveller have contra-gravity ...

Only in TNE. In CT, MT, and MgT1 they don't.

 

[AnotherDilbert]

I always considered the space shuttle as partial streamlined with aerofins. A brick with wings.

I would consider it a streamlined airframe. It's a not very impressive, but perfectly functional sail-plane. With a big engine it would fly well enough? It's a space truck, not a fighter.

 

[h1ro]

It depends on how fast you're going.

An air/raft ascending or descending from orbit isn't going twenty eight thousand kilometres per hour.

How so?

A quick statement: While maintaining orbit of a planet or star, a ship uses very little energy, it must insert itself into the orbit at the appropriate speed for it's altitude above the surface but it doesn't need to be constantly using it's M drive to maintain speed. If you're not orbiting something, you need to manoeuvre in order to maintain a position relative to the planet or star, as they are moving, often really quite quickly.

If an air/raft finds itself X hundred/thousand km above the surface it's either orbiting and must bleed speed somehow in order to enter the atmosphere or it must be moving to maintain it's position relative to the planet and if that's the case, how did it get to that speed? OK, if a ship had matched speed and then dropped the air/raft, fair enough but it still needs to manoeuvre to maintain it's position relative to the planet.

Does that make sense?

 

[AnotherDilbert]

Does that make sense?

Yes, very much so.

 

[h1ro]

I haven't bothered to calculate it, but i believe it takes a lot more acceleration than Traveller ships can produce to go "straight down like an elevator", i.e. spiral around down to a moving rotating planet.
It is only at a specific height that the natural orbit lets you stay above a single point on the surface of the planet. (For the Earth it is Geostationary ~36000 km.)

The question therefore is can an M drive simulate the descent of a beanstalk capsule? (I know beanstalks don't figure in Traveller as they're a 2300 thing but it's a good example of how a craft that can ignore gravity can reenter, the assumption as I've read it is that Traveller's grav technology makes beanstalks redundant. But does it?).

Orbital speed for GSO over Earth is just over 11,000km/h, I think the speed the Earth's surface rotates at is about 15-1600km/h.

That's a lot of deceleration over the time it takes to drop 36,000km. I guess the speed of descent will be governed by the craft's ability to change speed in order to stay over the same point on the surface.

The more I think about it, the more it sounds like a colossal traffic jam!

 

[Condottiere]

Atmospheric friction, for one.

For another, as I understand anti gravity fielding, you minus off first the local gravity factor, which gives you buoyancy, and whatever factor remains, is used for propulsion.

 

[Infojunky]

Most ships is Traveller have contra-gravity ...

Only in TNE. In CT, MT, and MgT1 they don't.

Point of Order, Yes only TNE describes Contra Grav as a gravity screen, but the bulk of the rules treat it like earlier editions of gravity drive.

CT, unstated whether or not, specifically. But looking at Striker, we find the statement that a ship's maneuver drive needs to be higher than local gravity for said ship to operate in direct support of ground troops. From that one could make the case that shops do indeed have a sort of gravity drive that acts somewhat like Contragravity.

Thus by extension of above MT does, as the bulk of MT is a retread of the Striker rules in technical details. Furthermore MT states that the direction of of thrust is steerable as well being able boost performance over the nominal maximum, thus allowing ships to operate as contragravity like vehicles.

As for Mongoose, well technical issues are a major blind spot, as such it is up to the individual group to define how they work.

 

[AnotherDilbert]

Most ships is Traveller have contra-gravity ...

Only in TNE. In CT, MT, and MgT1 they don't.

Point of Order, Yes only TNE describes Contra Grav as a gravity screen, but the bulk of the rules treat it like earlier editions of gravity drive.

CT, unstated whether or not, specifically. But looking at Striker, we find the statement that a ship's maneuver drive needs to be higher than local gravity for said ship to operate in direct support of ground troops. From that one could make the case that shops do indeed have a sort of gravity drive that acts somewhat like Contragravity.

Or that spacecraft balances on their thrusters like rockets, as specified in SSOM.
But more telling is LBB2'81 p28 "Gravity" that describes how spacecraft are affected by gravity like they would not be if they had anti-gravity capability.


In MT anti-gravity is specifically a different system from thruster plates (M-drives). You can include both in a ship if you like, but standard designs only have thrusters. The SSOM specifically describes how spacecraft work in atmosphere, they balance on their thrusters.


In MgT1 I agree that the technical details are glossed over, but the optional vector movement system in HG describes how spacecraft are affected by gravity, as anti-gravity capable craft would not be. My conclusion is that spacecraft generally do not have anti-grav capability.

 

[h1ro]

In general, anything MgT - 1e or 2e, can be interpreted any which way you like cos Mongoose have either sat firmly on the fence or just said nothing.

Mostly, I can't say I blame them, they're in a damned if they do, damned if they don't position, so I can fully understand why they take the position they do. Could be I have that wrong, it doesn't matter either way.

It's kinda moot to me. I'm happy with the thread drift. From the original question I got enough to say my stance should be more open and that's good.

I'm interested to hear people's views on my notion of how a ship/craft with [insert magical equipment that allows gravity to be ignored here] to either hold a position in proximity to or orbit a planet and then descend to the planet's surface?