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Old 08-26-2021, 11:35 AM   #1
hal
 
Join Date: Aug 2004
Location: Buffalo, New York
Default Vectored thrust vs Straight Thrust

Hello Folks,
Thought I'd ask a simple question...

Let's say for the sake of argument, you dig in and research what it takes to build a TL 10 thruster module. You obey all of the rules listed in GURPS TRAVELLER (or GURPS CLASSIC TRAVELLER if using PDF). But instead of building the module with vectored thrust, you build it as a straight thrust engine.

OK, so what you ask? What if you could build straight thrust engine modules that could provide 2G's thrust and also include sufficient standard thrusters to provide 2G's of thrust. As long as you thrust straight ahead, you can do 4 Gs. If you need to use Vectored Thrust, you need to utilize only 2 G's thrust.

So the new question becomes this:

If you use a 2 G vectored thrust to rotate your ship such that you're now 180 degress from your last built up vector of thrust - how long would it take at 2 G's to turn a 200 dTon hull around 180 degrees before you can use 4 G of thrust in opposition to your original vector?

What if I could get to 2G thrust vectored, and 4 G thrust unvectored - for a total thrust of 6 Gs. Would it really function any more differently than if it were built with nothing but vectored thrust modules?

Just curious to hear other's thoughts.

Hal
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Old 08-26-2021, 11:38 AM   #2
hal
 
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Default Re: Vectored thrust vs Straight Thrust

By the by...

I looked at the volume that was filled by a TL 12 vectored thrust module, and then reverse engineered the stats on a TL 10 vectored thrust module, and found there to be a significant amount of wasted space in the TL 10 version. I had to believe it was done so as to preserve easy numbers. Current rules for a TL 10 thrust module grants 40 sTons of thrust, whereas one engineered to the same degree of space utilization as a TL 12 Thrust module - would result in a TL 10 49 sTon thrust for the module.

But here is where things get really fun...

A TL 10 module without vectored thrust, would produce 69 sTons of thrust per module.

One could have SERIOUS Fun with a straight thrust module that adds thrust in only one direction.

Just a thought.
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Old 08-27-2021, 10:42 AM   #3
Mark Caliber
 
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Default Re: Vectored thrust vs Straight Thrust

Alright, I'm not going to be able to do any math, but I'm familiar with how vectored thrusters are used currently and we should be able to adapt that knowledge to this situation.

Harrier Jump Jets and V-22 Osprey* use vectored thrust for vertical take off and landings. So temporarily they can use the thrust to 'hover' and once airborne, they switch the thrust so that they can propel themselves forward.

The other more common application of vectored thrust is to enable jet fighters to turn faster. But once they have completed their maneuver, the thrusters are reset for straight thrust.


As in real life, starship designers would not use vectored thrusters, unless the craft being designed has a specific function that would require the use of a vectored thruster.

So yeah. Straight thrusters do work "more effectively" than vectored thrusters.

That's also why spaceships employ very low powered maneuver thrusters that reorient the ship and then employ a very powerful main drive to alter the course of the ship.



* Yes, I know that the V-22 uses propellers, but those propellers are vectoring airflow (like a jet turbine vectors airflow) in a similar principle.
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Old 08-27-2021, 12:33 PM   #4
Fred Brackin
 
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Default Re: Vectored thrust vs Straight Thrust

Quote:
Originally Posted by Mark Caliber View Post
A


As in real life, starship designers would not use vectored thrusters, unless the craft being designed has a specific function that would require the use of a vectored thruster.
That function is belly-landing rather than tail-sitting. If a ship can land like an airplane it'll be much easier to load and unload than if it's a streamlined shape sitting on it's rear end.

I was reading a sort of add-on to the classic Solar Queen stories by Andre Norton.

Back in the 50's when Ms. Norton knew no more about spaceships than she ould have learned from looking at a picture of a V-2 the archetypal Free
Trader ship Solar Queen looked like a V-2 with pointy nose, tail fins and everything in between.

It even landed on those tail fins. A V-2 does sit on its' fins before launching but it isn't designed to land except by going nose first and exploding.

In this story from the 90s the Queen had not only sprouted landing legs it shot out 4 anchors from its' nose to set guy wires to keep it from getting blown over.

So if Traveller ships are going to look like the Millenium Falcon and land on their bellies (which does have its' practical benefits) they're going to need vectored thrust.

Very large ships that never land probably don't have vectored thrust.
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Old 11-09-2021, 10:11 PM   #5
Mr Frost
 
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Default Re: Vectored thrust vs Straight Thrust

Quote:
Originally Posted by Mark Caliber View Post
Alright, I'm not going to be able to do any math, but I'm familiar with how vectored thrusters are used currently and we should be able to adapt that knowledge to this situation.

Harrier Jump Jets and V-22 Osprey* use vectored thrust for vertical take off and landings. So temporarily they can use the thrust to 'hover' and once airborne, they switch the thrust so that they can propel themselves forward.

The other more common application of vectored thrust is to enable jet fighters to turn faster. But once they have completed their maneuver, the thrusters are reset for straight thrust.


As in real life, starship designers would not use vectored thrusters, unless the craft being designed has a specific function that would require the use of a vectored thruster.

So yeah. Straight thrusters do work "more effectively" than vectored thrusters.

That's also why spaceships employ very low powered maneuver thrusters that reorient the ship and then employ a very powerful main drive to alter the course of the ship.



* Yes, I know that the V-22 uses propellers, but those propellers are vectoring airflow (like a jet turbine vectors airflow) in a similar principle.
I have it that gravitic drives are inherently 3D thrust vectoring and that making them not doesn't really save you anything .
Maneuver drives I have work on slightly different principles and the bulk of the drive (about 80%) is a mostly normal gravitic drive , the important bit (the thruster plate that creates the point in space these drives interact with) doesn't compromise the 3D thrust vectoring properties in any way .
This then makes most Traveller design standards believable .


The advantage of 3D thrust vectoring for spaceships (other than vertical landing etc) is that they can control their movement very precisely making docking etc something the typical pilot can manage regularly . Without 3D thrust vectoring docking at starports (especially given the enormous variety of design of both ship and port in Traveller) would be so dificult and time consuming that trade world probably girind to a halt except for advanced A.I. controlled bulk freighters of specific design with a starport also carfully kept to standard design and that isn't Traveller .
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Last edited by Mr Frost; 11-09-2021 at 10:15 PM. Reason: Wookies live on Endor !
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Old 11-13-2021, 07:17 AM   #6
Daigoro
 
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Default Re: Vectored thrust vs Straight Thrust

Quote:
Originally Posted by Fred Brackin View Post
So if Traveller ships are going to look like the Millenium Falcon and land on their bellies (which does have its' practical benefits) they're going to need vectored thrust.
The Mandalorian's Razor Crest is nicely shown using its vector thrust engines in landing scenes, if one wants a visual example.
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Old 11-13-2021, 05:55 PM   #7
malloyd
 
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Default Re: Vectored thrust vs Straight Thrust

Quote:
Originally Posted by Fred Brackin View Post
That function is belly-landing rather than tail-sitting. If a ship can land like an airplane it'll be much easier to load and unload than if it's a streamlined shape sitting on it's rear end.
Though in a setting like Traveller, with contragravity and thrusters that can generate or kill orbital velocities in a couple minutes, the "streamlined" bit can be pretty optional. Maybe ships thrusters are routinely dorsally mounted in the center of their bellies, and ships lift in a pancake orientation. If you are willing to take 15 minutes to clear the dense part of the atmosphere you don't need to go so fast that generates particularly bad aerodynamic stresses, certainly not compared to those generated by multi-G drives.
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