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The airships that I have imagined use anti-gravitational engines to allow them to hover above Earth's surface. I was thinking of having four of the engines around the vessel's hull. Could these engines be rotated at an angle to allow the ship to be propelled through the air, or would auxiliary engines be required? The speed would not have to exceed 40 knots.

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closed as primarily opinion-based by Gryphon, Ender Look, Measure of despare., JBH, Shadowzee Feb 12 at 3:40

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Welcome to Worldbuilding, Lucas A.! If you have a moment, please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods, and how we do things here. Have fun! $\endgroup$ – Gryphon Feb 12 at 0:22
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    $\begingroup$ We can't really answer this, as your "anti-gravitationl engines" have no basis in reality, and thus their operation, whether angled or not, is up to you. As a result, I'm voting to close as POB. $\endgroup$ – Gryphon Feb 12 at 0:23
  • $\begingroup$ Hi, Lucas. You might want to provide more detail about how your engines work, and perhaps clarify if you are looking for the physics behind whether changing the thrust vector will work for forward propulsion. If you're looking for equations to support the reality of the idea, I suggest perhaps using the Reality-Check and Science-Based tags. $\endgroup$ – Arkenstein XII Feb 12 at 0:35
  • $\begingroup$ An airship is an aerostat. A flying boat is an aeroplane, which is a kind of aerodyne. Since the vessel described in the question is sustained by engine thrust alone, without support from the air, it's neither an airship nor a flying boatd; it is not an aircraft at all. $\endgroup$ – AlexP Feb 12 at 1:02
  • $\begingroup$ Hello Lucas. Your question is unclear to me. What's the point of an airship (blimp, zeppelin, dirigible, etc.) if you have anti-grav engines? You could anti-grav a classic Lincoln Continental and ride in better style with better control (moving a big balloon around is no small thing). $\endgroup$ – JBH Feb 12 at 3:20
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Here's my take on this;

The fact that you've used the term 'anti-gravity' as opposed to a thruster of some sort means that you intend the engines to nullify the effect of gravity directly, rather than counteract it via upward thrust.

A hovercraft for example could be defined as anti-gravity because it applies a constant upward thrust by virtue of an engine pushing air down underneath it. That constant flow of air being forced under the vehicle allows the vehicle to hover, or defy gravity, in a manner that allows it to be directed over the ground by a different set of fans or thrusters. But, that's not true anti-gravity; it's more counter-gravity.

If we think of anti-gravity as that downward pointing fan that acts on gravity only, it would allow your airship to float, but you're still going to need a conventional thruster of some kind to push it through the air in the lateral direction. The reason for that is that gravity only works in this instance in a singular direction - down. This is a simplification, but functionally accurate for the purposes of a planet bound airship.

If you're using a counter-gravity system that applies conventional upward thrust, then yes you can tilt the engines a little to provide lateral thrust as well. This is how helicopters and VTOL aircraft actually work.

But, if you're actually nullifying gravity, then it's safe to say that your craft is in effect massless in relation to the Earth, but that doesn't solve the problem of lateral movement, particularly through an atmosphere. For that, you need thrusters that are more conventional, throwing something out the back in a manner that pushes you in the opposite direction. This could be a propeller, turbofan engine or anything that applies enough forward thrust to the airship to counteract wind resistance and push forward.

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As Tim B II mentions, gravity-nullifying devices can't really be used for thrust. Your best bet would be a set of external thrusters.

However.

You can get a very small amount of propulsion from these devices. By reducing the power of a specific anti-gravity device, or a combination of them, you'll change the balance of the craft. So long as the others are sufficient to keep the craft aloft, you'll actually be able to tilt the craft and gain some lateral movement. This could be supplemented with things such as moving ballast around to turn the ship. It would be slow. It would be akward. But if you have no thrust capabilities, it might work.

Your best bet is to put some proper thrust-producing devices on it, and some control surfaces. But in an emergency, there's other options.

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