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Anti Gravity Aircars

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Anti Gravity Aircars
Post by Daryl   » Sun Dec 06, 2020 12:45 am

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Could someone with a better imagination than me explain how anti gravity would enable an aircar to fly?
My limited understanding is that if you negated gravity exactly for the vehicle it would proceed to leave the earth at a tangent along the earth's rotation. Initially at the same speed as the original take off point, but at a tangent. However not as often visualised straight up.
Presumably you would then apply thrust by fans or jets to go elsewhere?
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Re: Anti Gravity Aircars
Post by Robert_A_Woodward   » Sun Dec 06, 2020 1:10 am

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Daryl wrote:Could someone with a better imagination than me explain how anti gravity would enable an aircar to fly?
My limited understanding is that if you negated gravity exactly for the vehicle it would proceed to leave the earth at a tangent along the earth's rotation. Initially at the same speed as the original take off point, but at a tangent. However not as often visualised straight up.
Presumably you would then apply thrust by fans or jets to go elsewhere?


I believe that leaving a rotating sphere on a tangent, relative to the point on the sphere that was the start, would appear to be going straight up and then would drift westward as it climbs ever higher.
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Re: Anti Gravity Aircars
Post by Annachie   » Sun Dec 06, 2020 7:05 am

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If you reduce the effect of gravity on the vehicle it would require less lift to fly.

Perhaps that's how it works.
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Re: Anti Gravity Aircars
Post by tlb   » Sun Dec 06, 2020 9:19 am

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If you can vary the amount of anti-gravity, then you could make it negative to lift off and then dial to zero when you reached the desired attitude. At that point you could use control fins to adjust if you wanted or else continue to vary the amount.

If you can angle the effect then you could gain horizontal motion as part of that process.
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Re: Anti Gravity Aircars
Post by Jonathan_S   » Sun Dec 06, 2020 10:08 am

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tlb wrote:If you can vary the amount of anti-gravity, then you could make it negative to lift off and then dial to zero when you reached the desired attitude. At that point you could use control fins to adjust if you wanted or else continue to vary the amount.

If you can angle the effect then you could gain horizontal motion as part of that process.

That should work if you wanted a design that worked entirely off countergrav use fins to translate the primarily vertical motion of gravity and countergrav into a somewhat horizontal motion - but with the size fins you can fit into something that's still roughly car sized your glide ratio is going to suck - so you'd probably be having to lose and regain altitude quite frequently which probably isn't the most pleasant ride - and it's a slow one too.


However honorverse "air cars" are described as having both counter grav and turbines - so they can just use countergrav for vertical takeoff/landing and to maintain altitude while using turbine (jet) engines for forward movement (and likely also for low speed maneuvering; through directional vents).

Though sometimes the singular "turbine", and sometimes the plural "turbines", is used when describing specific aircars - so some designs are presumably single engine while others seem to be at least duel engine.
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Re: Anti Gravity Aircars
Post by tlb   » Sun Dec 06, 2020 3:13 pm

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tlb wrote:If you can vary the amount of anti-gravity, then you could make it negative to lift off and then dial to zero when you reached the desired attitude. At that point you could use control fins to adjust if you wanted or else continue to vary the amount.

If you can angle the effect then you could gain horizontal motion as part of that process.

Jonathan_S wrote:That should work if you wanted a design that worked entirely off countergrav use fins to translate the primarily vertical motion of gravity and countergrav into a somewhat horizontal motion - but with the size fins you can fit into something that's still roughly car sized your glide ratio is going to suck - so you'd probably be having to lose and regain altitude quite frequently which probably isn't the most pleasant ride - and it's a slow one too.

However honorverse "air cars" are described as having both counter grav and turbines - so they can just use countergrav for vertical takeoff/landing and to maintain altitude while using turbine (jet) engines for forward movement (and likely also for low speed maneuvering; through directional vents).

Though sometimes the singular "turbine", and sometimes the plural "turbines", is used when describing specific aircars - so some designs are presumably single engine while others seem to be at least duel engine.

I did not intend to reject thrusters of any type (such as turbines); I was just trying to indicate that anti-gravity can multiple effects, depending on how it works.

However I reject that a purely anti-gravity propulsion system must either be slow or bumpy. Bumpiness is easily cured by a "fly by wire" control system. As for slow, there is every expectation that such a system would have the capacity to exceed several G's in acceleration.

But turbines could just as easily provide more thrust in a more efficient manner.
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Re: Anti Gravity Aircars
Post by Jonathan_S   » Sun Dec 06, 2020 9:30 pm

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tlb wrote:I did not intend to reject thrusters of any type (such as turbines); I was just trying to indicate that anti-gravity can multiple effects, depending on how it works.

However I reject that a purely anti-gravity propulsion system must either be slow or bumpy. Bumpiness is easily cured by a "fly by wire" control system. As for slow, there is every expectation that such a system would have the capacity to exceed several G's in acceleration.

But turbines could just as easily provide more thrust in a more efficient manner.
Not necessarily bumpy; but swooping perhaps? Presumably the antigravity system can simply affect the pull towards the planet by somewhere between full (or possibly more than full) gravity and less than zero gravity (repulsion) That only moves you up or down (ignoring the planet rotating under you and any lateral motion imparted by the wind)

You can, as you noted, use fins to bite into the airflow caused by that rising or falling, and that would convert some of the vertical motion into horizontal motion. But it seems that the fins you could fit into something the size of an air car would be relatively small. I suspect you'd be doing well if you managed to move twice as far laterally as you did horizontally.

If so, then to move the aircar horizontally even a single km you'd need a total change in altitude of 1/2 km.

And as you switch from rising to falling the fins need to make a non-trivial change in direction. So it probably works better to keep rising or falling for a little bit rather than trying to cycle so quickly you kept to within, say, +/- 25 meters of your average "cruising altitude". Even if the inputs are totally smooth simply watching the air car constantly alternate between rising and falling is likely less than the most comfortable thing to observe (though at least if you also stuck in a grav plate it could keep the cabin experiencing a constant apparent acceleration and you wouldn't have to feel the roller coaster set of arcs up and down I think an countergrav + fins powered air car would have to follow. You'd just be left with the visual effect.


But maybe I'm overlooking something. If you've got a different understanding, or a more elegant solution for turning countergrav into horizontal motion, please elaborate. I find the idea quite interesting.
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Re: Anti Gravity Aircars
Post by kzt   » Mon Dec 07, 2020 2:42 am

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You could also use the entire vehicle as a lifting body. There are exceptions where David has given a LOT of thought into how stuff works, but in general he's just paining a picture. Bu9 has people who can actually explain the background stuff well, at least enough to make a non-expert think 'yeah, that could work.'
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Re: Anti Gravity Aircars
Post by tlb   » Mon Dec 07, 2020 10:00 am

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Jonathan_S wrote:But maybe I'm overlooking something. If you've got a different understanding, or a more elegant solution for turning countergrav into horizontal motion, please elaborate. I find the idea quite interesting.

Since I have no ides how anti-gravity could really work, the following is just a description of how I imagine the process.

Suppose anti-gravity works by reflecting gravitons, then as you increase the power of the reflector, it slowly changes from reflecting none to reflecting all that would impinge on your vehicle. This reflection will cause a repulsion; when half of the gravitons are reflected, then that repulsion will balance the half that pass through (making the vehicle effectively weightless). As the field strength is increased past the half way point the vehicle will be accelerated up at a rate that increases with field strength, maxing at the local value of G with full reflection.

What I have been describing so far is the case where the reflecting field is perpendicular to the gravity field. So now consider rotating the reflection field so the new direction of the gravitons is at an angle and the resulting repulsion has a horizontal component. Presto we can have control over both vertical and horizontal motion. This might not result in the horizontal motion having a possible acceleration of more than a fraction of a G, but it does fulfill the requirement of a vehicle moving solely by anti-gravity.

It may help to think of the anti-gravity field as a mirror with a variable reflectivity between zero and one and it is reflecting a beam either back or at an angle.

PS. As I have said before, the most ridiculous image I have seen in science fiction occurs in one of the Star Wars movies where an ox cart is shown hovering without wheels. For a fraction of the energy needed to float that cart with anti-gravity, it could be converted to a vehicle that would leave that ox in the dust.
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Re: Anti Gravity Aircars
Post by Jonathan_S   » Mon Dec 07, 2020 10:19 am

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tlb wrote:
Jonathan_S wrote:But maybe I'm overlooking something. If you've got a different understanding, or a more elegant solution for turning countergrav into horizontal motion, please elaborate. I find the idea quite interesting.

Since I have no ides how anti-gravity could really work, the following is just a description of how I imagine the process.

Suppose anti-gravity works by reflecting gravitons, then as you increase the power of the reflector, it slowly changes from reflecting none to reflecting all that would impinge on your vehicle. This reflection will cause a repulsion; when half of the gravitons are reflected, then that repulsion will balance the half that pass through (making the vehicle effectively weightless). As the field strength is increased past the half way point the vehicle will be accelerated up at a rate that increases with field strength, maxing at the local value of G with full reflection.

What I have been describing so far is the case where the reflecting field is perpendicular to the gravity field. So now consider rotating the reflection field so the new direction of the gravitons is at an angle and the resulting repulsion has a horizontal component. Presto we can have control over both vertical and horizontal motion. This might not result in the horizontal motion having a possible acceleration of more than a fraction of a G, but it does fulfill the requirement of a vehicle moving solely by anti-gravity.

It may help to think of the anti-gravity field as a mirror with a variable reflectivity between zero and one and it is reflecting a beam either back or at an angle.

PS. As I have said before, the most ridiculous image I have seen in science fiction occurs in one of the Star Wars movies where an ox cart is shown hovering without wheels. For a fraction of the energy needed to float that cart with anti-gravity, it could be converted to a vehicle that would leave that ox in the dust.
I certainly agree that if you can angle something to deflect the force then you can build horizontal vector directly rather than by using fins in the airflow.

My working assumption was that countergrav wasn't capable of applying an angled deflection.


But if you could angle the countergrav then why bother with the turbines that we know the air cars have - the angled countergrav would seem to be a more elegant propulsion. (Turbines being more like the ox pulling the hovercart :D). So that reenforces my thought that countergrav can only work directly against gravity - rather than off to an angle.
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