A lot of worlds over 1g gravity. How do 1G thrust ships take off?

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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Sun Feb 03, 2019 1:02 pm

Moppy wrote: I don't think mixing Traveller editions is a good idea.
I can agree that MgT and T5 need not rely on each other, but older editions (especially CT) informs later editions since they set the expectations of what Traveller is.

In a specific case, such as "How does anti-gravity work?" we only find hints here and there, and only by using several hints, probably from several editions, can we find a good picture of how it might work.

But of course there are too many editions to keep track of them all and we don't have all of them, so can't use them. What we use in our own games is not the same as the virtual concept of Traveller canon and the OTU.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby Moppy » Sun Feb 03, 2019 1:55 pm

Old School wrote:
Sat Feb 02, 2019 7:36 pm
I have attached a picture of an Imperial Treasure Ship ... Can each of you involved in this debate explain the process by which this ship lands and takes off?
If un-aided, It doesn't under Mongoose 2 rules. I would house rule it to have gravity-defying machinery ("anti-gravity").

Does anyone have a list of scenarios (any edition) that have similar situations?

I would be interested to see what fraction of published stuff is broken assuming the rules as written.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby phavoc » Sun Feb 03, 2019 3:24 pm

AnotherDilbert wrote:
Sun Feb 03, 2019 4:05 am
Old School wrote:
Sat Feb 02, 2019 7:36 pm
I have attached a picture of an Imperial Treasure Ship, which is a 1600 ton, 1G capable ship opersted by the Imperial Navy. In the Pirates of Drinax adventure “Treasure Ship”, this ship lands and later departs from the downport on Acrid under its own power. Acrid is a size A, 1.4 G world, with a violent atmosphere that requires atmospheric weather control to allow ships to land safely.

Can each of you involved in this debate explain the process by which this ship lands and takes off?
I would say that it normally couldn't, but phavoc mentioned that repulsor beams could assist too heavy craft on some starports?
Occam's razor is applicable here. In CT repulsors were specifically mentioned as a way for overloaded ships to take off. However they are non de-canonized, and therefore cannot be used in the MGT universe.

Your response illustrates my point. Counter-grav/anti-grav systems are present and in use. The entire discussion centered around the idea that there could not be additional systems included in an amorphous design system. Some previous systems called it out, others make no mention of it. It is far easier, and more logical, to accept that it's present because it makes the model work. It's like solving an equation.

Not even the choice of "1G ships can't land on planets with more than 1G" is broken by the material presented.

I'd also like to point out the logistical and retail fallacy of having to constantly refer back 1-5 or editions of a game to understand it. That's neither practical for most people nor common sense. As you have stated in this thread MGT is much like CT in that it does not detail out everything. MattS has said as much in multiple posts. Using Occam's razor and the canon material presented within this edition, CG works even if it's not mentioned. And it requires no handwavium to get around a rule. It requires no logistical nightmare of trying to quote bits and pieces from 30 years and multiple previous editions. Nor does it require a harrowing, twisted viewpoint of the aforementioned bits and pieces. It simply works without upsetting anything.

And with that I believe my point has been sustained. Thanks to everyone for playing. I'm done.

PS - If there still cannot be agreement, then I propose a new rule - all starships are equipped with flubber invented by an absent minded professor. It worked at Disney, it's gotta work here!
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby Condottiere » Sun Feb 03, 2019 3:53 pm

You need to have any form of lifters listed on the bill of materials, it's not exactly cheap.

The vectoring in MegaTraveller seems a retcon; there are scifi ships that can physically move their thrusters to the required angle.

Also, if the thrusters are at the ass end of the ship, I'm going to guess you'll need more than a ninety degree vector angle to keep the ship straight.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby dragoner » Sun Feb 03, 2019 5:11 pm

Condottiere wrote:
Sun Feb 03, 2019 3:53 pm
The vectoring in MegaTraveller seems a retcon; there are scifi ships that can physically move their thrusters to the required angle.
Gimbaled thrust is old tech:

Gimbaled thrust is the system of thrust vectoring used in most rockets, including the Space Shuttle, the Saturn V lunar rockets, and the Falcon 9.

https://en.wikipedia.org/wiki/Gimbaled_thrust
Also, if the thrusters are at the ass end of the ship, I'm going to guess you'll need more than a ninety degree vector angle to keep the ship straight.
Anything more than a few degrees will cause the vehicle to tumble, even in atmosphere you can do the 'flip and burn', that's how the Falcon rockets have been landing.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby Sigtrygg » Sun Feb 03, 2019 6:23 pm

phavoc wrote:
Sun Feb 03, 2019 3:24 pm
In CT repulsors were specifically mentioned as a way for overloaded ships to take off. However they are non de-canonized, and therefore cannot be used in the MGT universe.
You keep making that claim.
Where is CT canon does it mention using ground based repulsors to aid lift off? I have a vague memory of Dragon magazine article but that is not canonical for the OTU.

Non decanonised is a double negative which means they would be allowed.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Sun Feb 03, 2019 7:43 pm

phavoc wrote: And with that I believe my point has been sustained. Thanks to everyone for playing. I'm done.
We will have to agree to disagree.

We have failed to convince each other about more or less anything, and disagree about even the nature of gravity and artificial gravity. Agreement will not be reached.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby phavoc » Sun Feb 03, 2019 7:56 pm

Sigtrygg wrote:
Sun Feb 03, 2019 6:23 pm
phavoc wrote:
Sun Feb 03, 2019 3:24 pm
In CT repulsors were specifically mentioned as a way for overloaded ships to take off. However they are non de-canonized, and therefore cannot be used in the MGT universe.
You keep making that claim.
Where is CT canon does it mention using ground based repulsors to aid lift off? I have a vague memory of Dragon magazine article but that is not canonical for the OTU.

Non decanonised is a double negative which means they would be allowed.
Yes, in CT, where the article below originated, repulsors were part of the available tech. As they were in other versions. MGT does not have them (at least as part of the Imperial universe). I had a typo above, the 'non decanonized' should have been 'now decanoized'.

Dragon issue#59 - https://annarchive.com/files/Drmg059.pdf Here is the text of the boost grid:

"B: Main Boost-Grid. The boost-grid is the heart of any spaceport with the technological base to support one. At older ports, ships must land under their own power, relying upon pilot expertise to avoid mid-air collisions or dangerously clumsy set downs. Here, the boost grid can reach out with gravitic force and either ease a ship to its landing pad or boost a ship from the ground into orbit.Using power from the main city power reactor (not in area of map), the boost-grid can focus gravitic energy with micrometer precision. The grid is composed of tungsten-steel rails 10 cm wide, set into the flat surface of the landing field in a precisely defined pattern. The energy conducted along these rails is perfectly controlled by the main computers in the Port Authority building. Any ship of up to 7,500 tons that is capable of landing on the field can be lifted up into high orbit, or can be brought down out of orbit and landed gently on the field. The point of focus can be moved by computer control in such away as to take hold of objects as far as sixty degrees from the vertical line through the center of the grid; the range,or effective “reach,” is 50,000 kilometers.

The main advantage of the boost grid is that the ship being boosted into orbit has no need to use its own drives, or indeed even to have a working drive. The grid can, for instance, boost prefabricated sections of a larger ship up into orbit to be assembled in weightlessness. In general, the grid is used to lower shuttles and small spacecraft that nevertheless do have a backup drive for use in case of grid failure. The boosting and lowering of cargo and passenger containers with-out drives is not considered safe enough to justify the economy of such a measure.The fuel saved by a ship using the grid instead of its own thrusters is on the order of one ton of fuel times the ship’s drive number times the ship’s mass in kilotons (but always a minimum savings due to use of the grid of one ton of fuel). Thus, a 5,000-ton ship using 2G drive to escape the world’s gravity would use ten tons of fuel, which could be saved by use of the boost-grid.

The grid has 100 channels, meaning that up to 100 ships can be simultaneously handled by the grid, so long as the total tonnage being boosted does not exceed 7,500 tons. This multi-channel capacity helps cut down the average waiting time for use of the grid.The procedure for a small ship — a Scout, for example—taking off from the grid would be as follows: After final approval for takeoff is received from the Port Authority computers, the ship, under its own power, flies up from its current docking bay (location M, see text below)until it is within the cone of the grid’s effectiveness. At an altitude of about thirty meters, the gravitic focus of the boost-grid is aligned upon the ship, and a gentle force begins to push it away from the planet, while the ship’s own maneuver drives are throttled back to an “idle” setting. The grid has the precision to release the ship either into an escape orbit, any of a number of closed orbits, or exactly into the orbit of the High Port.For more on the High Port and its own boost-grids, see below."


This article was published in 1982, before Megatraveller in 1987. Conceptually the idea is good, though the fuel calculation of 10 tons of fuel being consumed just to get to orbit seems rather high to me.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby Sigtrygg » Sun Feb 03, 2019 7:57 pm

That's the one, I think I have that issue in the loft somewhere.

It's not CT canon though.

It is fanon at best.

The canonical starport description by LKW is in JTAS 7, and it doesn't mention repulsor grids.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby Annatar Giftbringer » Sun Feb 03, 2019 8:21 pm

Alright, here goes...

First off, I believe that these rules are intentionally vague, to leave some wiggle-room for each group and how they want things to function.

I only use Mongoose Traveller, so reading this discussion with its references to other editions has been illuminating. I was unable to find any reference to using Flyer(winged) to pilot spaceships in second edition, so it's either been removed or I suck at finding stuff. One thing I have found is this:
Element Cruisers Ebook, p.51 wrote:Secondary lifter/manoeuvring units are positioned across the main hull, enabling precise low-thrust movements as well as rapid yaw, pitch and roll. Lifting capacity is sufficient that a Amara-class cruiser could hover above, or even land on, the surface of a body of up to 0.177g, however it has no landing legs and would likely suffer damage due to sagging on anything but completely flat ground
With that said, I do believe that some ships more or less have to be able to hover and perform vertical takeoffs and landings, even if local gravity exceeds 1G. They could do this by vectoring M-drive output, by "grav-floating" or other means. If thrust vectoring is the way to go, I'd guess that 25% of normal thrust isn't a thing in MgT, something like that should have been mentioned in the rules. There's also no way to overload the drives to 400% normal power. It is however possible to gain 1 additinal point of thrust for a single round (6 minutes), according to the Core Rulebook (Overload Drive, p.160). This is normally a difficult (10+) check, which makes it a bit more difficult to succeed with than something I'd want every ship to fiddle with around the star port. By taking more time the check becomes 8+, and in a non-combat environment, I'm not even sure I'd demand a dice roll. It would only be needed when a 1G ship attempts takeoff from a 1G+ planet, and if failed, they could just try again (after an embarrasing call to star port control and some service).

So, by overloading the drives, even a ship with 1G drives should be able to take off, assuming 100% thrust can be vectored.



Repulsors could be used to give ships a little help, both for landing and takeoff. Sure, they're in the High Technology chapter (called tractor beams, p.69), but so are particle beam turrets, and both are in use by official ship designs.



The hovering part could be due to the same technology that lets grav vehicles fly. Perhaps M-drives are even grav vehicle drives deluxe? As far as I understand, grav vehicles can hover, and use some form of gravity manipulation to do it. So, what's to say (some) starships can't do the same thing? It's possible to float in water, by having the right boyancy. This won't let an object ignore the water and currents around it, it just won't sink. So what's to say a starship, that already manipulates gravity for propulsion and crew comfort, can't "grav-float", and use its thrusters to move around? Do we know the limits of grav vehicles? Can they fly regardless of how strong the local gravity is? is it even stated anywhere within Mongoose books that grav vehicles can't fly outside of a gravity well?



After some pondering, I've decided that for me personally, it works like this:
Streamlined ships can hover, or grav-float, withing gravity wells, just like grav vehicles. Sure, there's probably a limit to how strong the local gravity can be, and for how long they can float, but it's enough that normal takeoffs and landings aren't an issue. Combine grav-floating with M-drive thrust, and even 1G ships can handle normal planets. The additional costs for this (if any, depends on how one imagines that M-drives work) is covered by the additional costs for streamlined hulls. Kinda like how Star Wars does it, with repulsors and main thrusters.

Standard non-capital sized hulls can land on planets, but they need to do it by thrusters only. Thrust can be directed downwards (for short periods) and if the ships' drives aren't powerful enough to overcome local gravity, the ship's engineer needs to overload the drive, temporarily boosing it by +1. By taking extra time the task is Average, and most of the time a check won't even be needed.



There, that's how I'm gonna do it. Hope it makes some sense (wrote it while tired). Note that this is my personal homebrew solution and nothing even remotely official in any way, but it works for me :)
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby phavoc » Sun Feb 03, 2019 8:23 pm

I dunno if it was blessed by GDW or just submitted. Dragon had a far larger distribution than JTAS did at the time, so getting anything about the game in print is a good thing.

Conceptually boost grids fall within what a repulsor beam does. Whether you want to consider it canon, semi-canon, grapeshot or otherwise is entirely voluntary. I'd have to dig up my old Judges Guild 50 starbases to see that they had in their stuff. That was officially sanctioned material. And, before we go too far down this particular rabbit hole, CT04 Leviathan WAS a canonical publication carrying the GDW logo, and it had jump torpedoes in it. Granted they were later declared heretical, but for at time they were accepted.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Sun Feb 03, 2019 8:54 pm

Annatar Giftbringer wrote: I was unable to find any reference to using Flyer(winged) to pilot spaceships in second edition, so it's either been removed or I suck at finding stuff.
It's removed, that is why I quoted MgT1. It was in the (near identical) Atmospheric Operations section in Spacecraft Operations.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Sun Feb 03, 2019 9:12 pm

Sigtrygg wrote: The canonical starport description by LKW is in JTAS 7, and it doesn't mention repulsor grids.
"Champa lnterstellar Starport" details one example starport, It makes no claims about starports in general IIRC.


Not that I would consider Repulsors common.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby Condottiere » Sun Feb 03, 2019 11:04 pm

1. How do airliners take off? Their engines can generate enough thrust, aided by aerodynamics.

2. Obviously, if 1.0 thrust isn't enough to escape Terran standard, wouldn't the answer be that you buy a 1.3 rated accelerator, and fix it to cruise at eighty percent optimum.

3. And if you don't fancy retconning the manoeuvre drives, amputate some part of the spaceship you don't need or fancy, to bring the volume in line with required performance.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby HalC » Mon Feb 04, 2019 2:09 am

Page 5 of Mongoose Starports:

"A runway for non-VTOL craft will be present if there is an atmosphere." There is more in the preceding paragraph about 50 pads, etc etc.. etc (King an I go a long way back!)

In any event - Things to keep in the back of your mind are:

Mongoose Traveller is a legacy system in the sense that things developed since 1979 were preserved going forward. It meant that things couldn't change TOO much when MegaTraveller hit the market, couldn't change too much when Traveller: The New Era hit the market (although in that instance, BOY did things get changed!!!), T4 build on previous thing, as did GURPS Traveller, T20, Hero Traveller, T5 and....

Mongoose Traveller (Granted, MgT came out before T5, but I purchased the developmental T5 before I even knew MgT existed).

So - what are the legacy issues? Simply put, the state of the art world building rules were not present in Traveller until MegatTraveller's World Builder's Handbook came out in 1987. Four years prior, SCOUTS came out. Very little attempt had been made to determine what the gravity values were for worlds in general, and due to the fact that many worlds created at Random were so small that they not only had a low surface gravity value, but were unable to retain water vapor, which in turn means that they can't have any surface water after a sufficient amount of time has passed.

Next legacy issue? SPINWARD MARCHES CAMPAIGN went the route of inflicting stellar data on the various star systems, never minding the fact that the results they published violated in great numbers - the rules presented in either of SCOUTS or the world building rules in MEGATRAVELLER itself. Despite this, much of the data remains unchanged. Good or Bad, that is definitely a legacy issue.


In all? The powers that be didn't want to have to deal with runways or wheeled landing gear. After the Millennium Falcon Took off from its bay, rotated in place, and clawed its way into outerspace, the days of wheeled take off and landing was numbered.

Now to the nitty gritty - Manuever Drive acceleration values are predicated on VOLUME instead of MASS. My question now becomes "So what?" Marc and Company were not rocket scientists. They were war game enthusiasts, history lovers, writers, etc - so pre-Internet days, is it hard to understand that they didn't have all the latest information at their fingertips" Despite all these issues, Traveller somehow, is still going strong. Go back to 1978, get a list of all the role playing games in existence, all the game worlds that were developed and sold commercially - and ask yourself "how many are still around in some shape or form absent RPGNOW.COM"? If I weren't unemployed, I'd purchase a copy of the military based campaigns simply because that kind of thing floats my boat even if I don't play Mongoose Traveller. If I had the money?

I'd splurge and buy for use with Fantasy Grounds - the Mongoose Traveller 1st edition Traveller package and RUN campaigns over the internet like I do with GURPS TRAVELLER. But, money being tight, I have to pay the mortgage and stuff first.

In any event, I digress. Early Traveller didn't have much in the way of World building materials. Traveller 2300 did, and I sort of wish that the powers that be had done more work with it. But hey, they made their decisions and it is water under the bridge. Flying into space works in a Traveller universe simply because there is no "limit" to reaction mass being pushed away. In theory? A ship with a .01 G thruster can lift off of Earth. Why? Because unlike Rockets whose reaction mass runs out, the Traveller Maneuver Drive never runs out. Getting off of a world, any world, means you have to build up escape VELOCITY. Granted, you're moving at an acceleration of .098 meters per second per second, but over time, that value builds up.

So, how does one measure thrust? GURPS TRAVELLER has the following to say:

"To find space acceleration, add up the thrust in tons: This is 40 per TL10 M-drive or 100 per TL12 M-drive. Divide by the ship’s weight in tons (not displacement tons). The
result is the ship’s space acceleration (sAccel) in G."

CT, MT, T4, T20, MgT, HT, and T5 never defined the weight of the ship nor the thrust of the engines in actual thrust values. Instead, they used a handwavium approach saying a ship gains Maneuver 1 if it has X percent of its hull volume taken up by Maneuver drives. As noted elsewhere, adding on Armor 15 to the ship didn't change its acceleration value (and it should have), largely because the handwavium approach kept the game simple.

In the end? Either revamp the entire system so it meets a gritty realistic mode that some people can live with, or accept that yes, there are issues, but sweep it under the rug - there is a gaming crew coming over and they want FUN - not a physics lecture.

Now me? I keep wishing that they had done a better job documenting the exodus from Earth outwards, or the exodus from various main worlds to the unpopulated worlds. I wish they had written that such an such a world was settled in 572 from humans with eyes of blue. All 3,000 of them founded SafeHaven and promptly lost half their population to the alien rodents who, despite being unable to live on human based food, ate it none the less and deprived the settlers of their much needed food. But hey, that's the historian in me wanting to know why of things in addition to the what of things and how of things etc.

;)

I'm still playing in Traveller despite my first exposure to it came at the hands of Richard Ess at U.B. in 1980.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Mon Feb 04, 2019 12:52 pm

Moppy wrote: Not a lot of people understand physics, nor do they want to. I gave up when I asked how many ships had wheels and got no answer.
There is no absolute answer.

Landing gear, like most details, are not detailed. MgT2 has all of this to say:
MgT2, p143 wrote:Ships have landing gear, allowing them to touch down ‘in the wild’, which requires an ... Pilot check, depending on local terrain. They can also land on bodies of water.
OK, ships have landing gear...

Gurps had this to say:
ISW, p170 wrote:An airframe-hull ship can actually fly to or from orbit, its hull generating lift so that the ship’s drive doesn’t have to do all the work of overcoming gravity. This will work even if the ship’s space acceleration rating is lower than local gravity.

T5 details this, and landing wheels are included on configuration Airframe (ships with wings). But no spacecraft are detailed in T5, so no wheels are specified on any specific craft.


The Subbie and some other spacecraft have wings. I have always assumed they are not just a decoration, but functional and hence that those spacecraft also have wheels to be able to use the wings. This is not specified anywhere, but I believe it is a reasonable assumption. Why else would the craft have wings?


As already quoted in this thread, runways for spacecraft are mentioned in canon from CT to Gurps and T5.


I do not see any basic scientific problem with aircraft taking off and landing on runways, we can even do it today. I'm baffled why anyone should see this as a problem, scientific or otherwise?
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby phavoc » Mon Feb 04, 2019 1:50 pm

AnotherDilbert wrote:
Mon Feb 04, 2019 12:52 pm
I do not see any basic scientific problem with aircraft taking off and landing on runways, we can even do it today. I'm baffled why anyone should see this as a problem, scientific or otherwise?
Traveller ships are (a) too heavy to generate lift for takeoff and (b) many designs have too much drag, such as the Type-R, that counter any lift, and (c) wing design is, in fact, a science and the illustrations for these ships show the wings to be of the wrong design. I'm baffled why this is such a hard idea to understand. No handwavium or multiple book versions is required (well, maybe a few books on aeronautical science to prove the point). This concept has been proven time and again since the age of flight began.

The idea of a take-off / landing strip regardless of whether or not the ship has wheels, landing skids, thrusters, anti-grav or anything else, remains the same in any century - safety. It's far better for the ship to suffer an emergency on/in the area dedicated for takeoffs and landings than it is over occupied buildings, passenger terminals, etc. Also helps for airtraffic control, by having landing craft come in one direction and craft taking off going in another.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Mon Feb 04, 2019 4:30 pm

phavoc wrote: Traveller ships are (a) too heavy to generate lift for takeoff ...
All Traveller spacecraft have insufficient lift, regardless of mass, velocity, or wing size or shape? Bold claim, please prove it.

As I believe you have already quoted, lift can be described by
Image, i.e. wing area × air density × airflow speed squared × a term Image that includes all fiddly aerodynamic detail, including wing shape, current angle of attack, air viscosity, and flow speed.

Absolutely nothing in this says that 5000 tonne aircraft are impossible or can't take off, it just says they need big wings and/or high take off speed. Even high air density, as is probable on a hi-grav world, would help.

phavoc wrote: ... and (b) many designs have too much drag, such as the Type-R, that counter any lift, ...
Drag is per definition perpendicular to lift and cannot under any circumstances counter it.

Neither you, nor anyone else, can accurately estimate drag from a hand drawing of an aircraft. Until we have a windtunnel test, or at least a detailed engineering specifications, of the aircraft in question drag is unknown.

If I am wrong, and you can accurately calculate lift and drag for the Subbie during take off, please do so with, say, two significant digits.

phavoc wrote: ... and (c) wing design is, in fact, a science and the illustrations for these ships show the wings to be of the wrong design.
Please calculate Image for the Subbie during take off at 500 km/h with, say, two significant digits. If you can't your claim is baseless, and in no sense scientific.

Show me a photograph or an engineering specification of a TL12 spacecraft and I might believe you. A hand drawing by someone who has never seen one does not count.

Can you estimate current lift, drag, and max take off weight of this aircraft based on this picture alone?
Image

phavoc wrote: I'm baffled why this is such a hard idea to understand.
You come with unsubstantiated claims that appear unlikely. Until you prove them, or at least support them, I will disregard your claims that heavy aircraft can't possibly fly.

Aircraft can fly, we know this, I hope we can agree.
Aircraft can take off and land, we know this, I hope we can agree.
You claim, without example or evidence, that Traveller ships in general can't take off. If you have the science that shows this, show us. If you have an example of a major aircraft designer attempting to design a wing for a 5000 tonne aircraft and failing, show us.
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby phavoc » Mon Feb 04, 2019 7:44 pm

Sure. It's pointless but I'll do it (again).

AN-225 - heaviest aircraft made to date (https://en.wikipedia.org/wiki/Antonov_An-225_Mriya). Stats for the wing are in there, as is a view of the aircraft itself. The An-225's pressurized cargo hold is 1,300 m3 (46,000 cu ft) in volume; 6.4 m (21 ft 0 in) wide, 4.4 m (14 ft) high, and 43.35 m (142 ft 3 in) long. Wing tip to wing tip is 88 m. The Type-R is 10.5 m wide, 6 m high and 51 m long. At it's widest the craft is 27 m (wing tip to wing tip) - from the MGTv2 deckplan. Scale from illustrations of the Type-R are varied. A simple sample will show this, but all we have are various illustrations and not actual ones from reality (unlike the ones provided for An-225 or the Concorde).

Type-R subsidized Merchant (image from Traveller wiki here - https://wiki.travellerrpg.com/Type_R_c ... d_Merchant). Better image here - Image

Better image here - (https://traveller.chromeblack.com/a-dum ... d-news-09/)

AN-225, max takeoff is about 640 tons. Type-R is 4,000 tons. We don't know the thrust capacity of the Type-R. If you can provide me the type of airfoil and angle of attack I can plug the rest in. Even you ( I would hope) would have to agree the Type-R wing is not at all efficient compared to any known aircraft. Using the scale person you can also see that the wing area, when compared to even the Concorde, is quite small. Let's assume the image above has windows that aren't recessed (further increasing drag). What about the launch on top? That, too, will increase drag.

Here's another image - https://forum.rpg.net/index.php?threads ... 246/page-3. Again we have a very non-aerodynamic craft, with a relatively small wing area, a massive non-aerodynamic wing root, and creating additional drag with the launch. And, using the AN-225, the Type-R is at least 6x heavier than the AN-225 with vastly less wing space to provide aerodynamic lift.

The illustrations you have provided show craft with aerodynamic structure as well as wings designed specifically to create lift via airflow. I have continually acknowledged the fact that craft of this type (and weight) WILL generate lift as the descend. But that is possible only so long as they are moving forward at velocity (and no, I can't tell you their stall speed - though at 4,000 tons I would suspect it would be quite high).

When you add all of this together what does it tell us? That these craft could descend from orbit, much like the shuttle could or the X-series lifting bodies did when dropped from an aircraft. But their design precludes them taking off like conventional aircraft using aerodynamic lift. The alternatives proposed have been thrusters (overloaded), or some anti-grav/contragrav.

If you are asking for proof I would ask you the same. Unfortunately neither of us can provide proof for mythical craft. Therefore all we can do is provide current real-world examples of aircraft, physical and aerodynamic laws. And those laws, especially for flight, are very unforgiving when it comes to drag. And as anyone who's studied aerodynamics will tell you, drag is a bitch when you are trying to fly. Power can overcome a LOT of drag - but there is not only a limit, but also the more drag you have, the power you have to apply, and the more inefficient your flight profile becomes due to the fact that air compresses the faster you go, which increases both drag and the need for more power. And lift depends on air flowing faster underneath the wing than above it, hence the need for an angle of attack of the Type-R airfoil (or any Traveller craft thinking it can generate lift). If you look at the drawings for either the Concorde or An-225 you will see the wings are designed to do this.

Without all of this the ships cannot fly using real-world physics. To be specific, they cannot generate enough lift to stay aloft to land or takeoff using lift generated by aerodynamic effects. However, if you alter the equations by adding lift through some other means (such as thrusters or anti-gravity), then the formula would change. To determine that you have to provide all of the above requested information as well as the amount of lift being provided in another manner. For example, if the wings were able to provide 1% of the necessary lift to take off at say 100kts (you must have some airflow in order to generate lift), then the other 99% of the lifting force would need to come from some other mechanism (even from a repulsor grid if you had one).

I don't suppose you'll agree with much of the above, but that's the basic science behind lift, and it's why I keep saying Traveller vessels can't utilize their structures to take off or land - and by that I mean in a controlled manner, with the craft going where you want, as fast as you want, and as slow as you need to in order to safely land exactly where you want it. I think it's already been established that some landing pad and other landing areas required precise control and little to no forward movement - hence the craft must generate lift from something other than airflow over it's surface. Even a brick can descend from great altitudes, but it doesn't meet the commonly accepted definition of flight.

I await your rebuttal.
AnotherDilbert
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Re: A lot of worlds over 1g gravity. How do 1G thrust ships take off?

Postby AnotherDilbert » Tue Feb 05, 2019 12:34 am

phavoc wrote: AN-225 - heaviest aircraft made to date (https://en.wikipedia.org/wiki/Antonov_An-225_Mriya).
Yes, agreed, this shows that 600 tonne aircraft can fly. It does not at all show that 6000 tonne aircraft can't fly.

phavoc wrote: The Type-R is 10.5 m wide, 6 m high and 51 m long. At it's widest the craft is 27 m (wing tip to wing tip) - from the MGTv2 deckplan.
Well, the lower deck is double height, so the internal height is about 9 m, or perhaps 10 m externally.

phavoc wrote: Scale from illustrations of the Type-R are varied. A simple sample will show this, but all we have are various illustrations and not actual ones from reality ...
I agree completely. We have many illustrations of the same craft that don't agree with each other. So which is the correct one with the correct dimensions?

phavoc wrote: Type-R is 4,000 tons. We don't know the thrust capacity of the Type-R.
We know it can achieve a nominal acceleration of 1 g ≈ 10 m/s², so it must have a thrust of about 40 MN. Quite a bit more than the roughly 1.4 MN of an An-225.

phavoc wrote: If you can provide me the type of airfoil and angle of attack I can plug the rest in.
You have claimed that it can't possibly fly, since you can immediately see what the aerodynamic properties of the wing are, so you tell me? Or simply show that it can't possibly fly with any possible wing profile.

I have no idea what the properties would be, and can absolutely not estimate them from a hand drawing.

And I guess that William H. Keith, Jr, who, I believe, draw the original Subbie illustration and deckplan didn't calculate, or even bother considering, the lift coefficient either.

phavoc wrote: Even you ( I would hope) would have to agree the Type-R wing is not at all efficient compared to any known aircraft. Using the scale person you can also see that the wing area, when compared to even the Concorde, is quite small.
Yes, I agree that the wing seems to be too small and probably with an inefficient shape. I can't prove it, of course, especially as I don't know how large it actually is.

phavoc wrote: Let's assume the image above has windows that aren't recessed (further increasing drag). What about the launch on top? That, too, will increase drag.
Yes, we don't know the drag either, do we?

Yet earlier you claimed, spcifically about the Subbie:
phavoc wrote: ... and (b) many designs have too much drag, such as the Type-R, that counter any lift, ...
I still don't understand what that means, given that drag and lift are perpendicular components of the same thing. How could it counter itself?

phavoc wrote: The illustrations you have provided show craft with aerodynamic structure as well as wings designed specifically to create lift via airflow. I have continually acknowledged the fact that craft of this type (and weight) WILL generate lift as the descend. But that is possible only so long as they are moving forward at velocity (and no, I can't tell you their stall speed - though at 4,000 tons I would suspect it would be quite high).
The only illustration I used was of the Concorde. It can evidently take off, fly, and land on its own. Yet none of us can see that from the picture, can we? We can't even see the wing clearly. Which was my point.

phavoc wrote: When you add all of this together what does it tell us? That these craft could descend from orbit, much like the shuttle could or the X-series lifting bodies did when dropped from an aircraft. But their design precludes them taking off like conventional aircraft using aerodynamic lift.
Yes, you have repeatedly stated that you believe that. Yet you can't back that up with a single measurement or even calculated lift example. That makes your statement just a guess as far as I can see.

And I will note again that even the lowly experimental TL6 X-24 (without any wings) could climb if it turned on some thrust. It is only without any thrust that it, and the shuttle, could only descend, just like any other aircraft. So I fail to see that it says just about anything about the Subbie with quite a lot of thrust.

phavoc wrote: If you are asking for proof I would ask you the same. Unfortunately neither of us can provide proof for mythical craft.
Quite, I agree completely. Thank you for stating my point so eloquently.

So how can you state so categorically that no possible Traveller ship can fly?
phavoc wrote: Traveller ships are (a) too heavy to generate lift for takeoff ...

phavoc wrote: Therefore all we can do is provide current real-world examples of aircraft, physical and aerodynamic laws.
I agree completely that current aircraft can fly and that physics will continue to work in the future. But, as we seem to agree, we have very little reliable data about 'mythical craft'.

phavoc wrote: And those laws, especially for flight, are very unforgiving when it comes to drag. And as anyone who's studied aerodynamics will tell you, drag is a bitch when you are trying to fly. Power can overcome a LOT of drag - but there is not only a limit, but also the more drag you have, the power you have to apply, and the more inefficient your flight profile becomes due to the fact that air compresses the faster you go, which increases both drag and the need for more power. And lift depends on air flowing faster underneath the wing than above it, hence the need for an angle of attack of the Type-R airfoil (or any Traveller craft thinking it can generate lift). If you look at the drawings for either the Concorde or An-225 you will see the wings are designed to do this.
Yes, that is a nice bit of waffle, and undoubtably correct, yet says nothing specific about any specific craft, much less all possible craft.

Laws of Physics are formulas, if you can't put numbers on the specific dependencies, you can't use them.

For a 4000 tonne Subbie in a 1 g gravity field we know that it weighs 4000 tonnes, aka it is pulled towards the planet by a force of 40 MN. Too see if it can take off we have to calculate if the lift (at the moment of take off with e.g. current air flow speed including wind, angle of attack, air density and viscosity) is bigger than, or smaller than, 40 MN. There is no way we can calculate actual lift for 'mythical craft', hence no way to determine if they can actually fly.

phavoc wrote: Without all of this the ships cannot fly using real-world physics. To be specific, they cannot generate enough lift to stay aloft to land or takeoff using lift generated by aerodynamic effects. However, if you alter the equations by adding lift through some other means (such as thrusters or anti-gravity), then the formula would change. To determine that you have to provide all of the above requested information as well as the amount of lift being provided in another manner. For example, if the wings were able to provide 1% of the necessary lift to take off at say 100kts (you must have some airflow in order to generate lift), then the other 99% of the lifting force would need to come from some other mechanism (even from a repulsor grid if you had one).
Yes, I agree completely. But we still can't calculate lift for any specific 'mythical craft', much less all possible 'mythical craft', so we still don't know if they can fly.

phavoc wrote: I don't suppose you'll agree with much of the above, but that's the basic science behind lift, and it's why I keep saying Traveller vessels can't utilize their structures to take off or land ...
Yes, I agree about the science but not about your extra assumptions. You just assume that lift is not sufficient, without demonstrating it. With specific numbers.

Without quantifying lift, which we can't do from an illustration, we don't know if any 'mythical craft' will fly. Without that we cannot, as you stated, 'provide proof for mythical craft'.

So I still don't understand how you so categorically can state that no possible Traveller ship can fly?
phavoc wrote: Traveller ships are (a) too heavy to generate lift for takeoff ...

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