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i need another opinion on energy of flight...

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Patrick

Tue Nov 23 2010, 04:16AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

so i need to know how much energy it takes to levitate 1Kg an infinatly short distance above a table, for per second....

basically i need the same acceleration as one earth G upward, to cancel the natural, or god's G downward.

so i was thinking K=(1/2)mV^2 right ? so [0.5 * (1Kg * 9.8m/s* 9.8m/s )] = 48 joules needed per second of the desired levitation. (essentially i am constantly accelerating upward at +1G against -1G downward, thus a net zero acceleration, or levitation, like a helicopter or DeSeversky lifter at hover.)

so, i need a sanity and goof check from others who are good at physics. does 48 joules per second, for each Kg sound plausible? i will ignore minor losses of turblence, conversion type ineffciencies, i will consider those losses seperatley.

Pinky's Brain

Tue Nov 23 2010, 04:34AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Down to zero.

It partly depends on the amount of feedback downward movement of the weight causes in the upward force. Induction based levitation can have positive feedback, air cushion will have positive feedback ... a magnet above a superconductor will obviously have positive feedback.

Can't really afford to ignore turbulence, the limited space for air to escape from under the object is too significant ... otherwise hovercrafts could fly ;)

Ruben

Tue Nov 23 2010, 04:43AM

Registered Member #3263 Joined: Sat Oct 02 2010, 04:43AM
Location: Sydney, Australia
Posts: 34

K= (1/2)mV^2 is the kinetic energy of an object with some velocity V. you have plugged in the values of acceleration though. (g=9.8ms^-2) check the dimensions of your equation and you wont get joules.

from a theoretical perspective, you don't require any energy to levitate an object (a magnet levitating above a superconductor does not violate conservation of energy), only to change its position in a gravitational field (K=mgh).

I would conservatively approach your problem by saying you require 9.8N/kg of thrust to levitate the object, and then calculate the energy required to produce said thrust...however you may be producing it -- however, hovercraft cant fly, so the actual figure may be significantly less.

Patrick

Tue Nov 23 2010, 04:45AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

but i dont mean hovercraft, i mean like an electric ducted fan pointed striaght down.

Ruben

Tue Nov 23 2010, 04:49AM

Registered Member #3263 Joined: Sat Oct 02 2010, 04:43AM
Location: Sydney, Australia
Posts: 34

In that case you do requre 9.8 N/kg of thrust. Similarly 19.6 N would accelerate your object upwards at 9.8 ms^-2. In this case you would very quickly reach a finite height above the table. I don't know by how much the ground effect would reduce the thrust you require when close to the table.

Patrick

Tue Nov 23 2010, 04:52AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ruben wrote ...

K= (1/2)mV^2 is the kinetic energy of an object with some velocity V. you have plugged in the values of acceleration though. (g=9.8ms^-2) check the dimensions of your equation and you wont get joules.

yes, i relize i botched the units/formula/math/everything else....

Ruben wrote ...

from a theoretical perspective, you don't require any energy to levitate an object (a magnet levitating above a superconductor does not violate conservation of energy), only to change its position in a gravitational field (K=mgh).

i have to think about this one for awhile....

Ruben wrote ...

I would conservatively approach your problem by saying you require 9.8N/kg of thrust to levitate the object, and then calculate the energy required to produce said thrust...however you may be producing it -- however, hovercraft cant fly, so the actual figure may be significantly less.

9.8N/Kg is better, your right, sh*t. but the hovercraft is a pressure relation not a mass ejection relation. so the hovercraft example as you rightly point out is useless for my purpose.

also, i am tipsy from the beer.

EDIT: as i begin to sober up , a thought becomes apparent, i can choose the quantity of mass ejected, i can choose the exhasut velocity, and if these two multiply out to 9.8N/Kg then i have my theoretcial ideal energy consumption.

Pinky's Brain

Tue Nov 23 2010, 05:05AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Patrick wrote ...

but i dont mean hovercraft, i mean like an electric ducted fan pointed striaght down.

With what is effectively a skirt hanging an infinitesimal distance above the ground, sounds like a hovercraft to me.

As long as the table is solid mass ejection will automatically translate to pressure.

Patrick

Tue Nov 23 2010, 05:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Pinky's Brain wrote ...

With what is effectively a skirt hanging an infinitesimal distance above the ground, sounds like a hovercraft to me.

As long as the table is solid mass ejection will automatically translate to pressure.

yes you are right that was a poor example on my part. i would like to anyalyze a imaginary DeSeversky device 6*6*4 inch volume hovering 100 feet AGL. ( small device, large distance )

thrust:

2 years ago when i figured a lot of this out, this wiki page must not have existed in its present form.

upon further review, i think it is neccasary to specify conditions which cause thrust, only then will the output power be useful. this is complicated so i need to consider it some more, i could be wrong.

Pinky's Brain

Tue Nov 23 2010, 06:47AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

If only part of the object has to hover and other parts can change configuration other possibilities open up to reduce energy as well.

Think for instance how a squid moves upward in water, reduced drag while applying thrust ... increased drag while falling and getting ready to thrust.

Non fixed wing insects can use the same type of effect to reduce the energy necessary to hover.

Patrick

Tue Nov 23 2010, 06:54AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

from wiki -> power (watts) = thrust (newtons) x speed (metres/second)

if stationary hover is equal to a speed of 9.8m/s, and i have a 1Kg sphere of lead, or styrofoam,
then 9.8N = 1Kg so 9.8N * 9.8m/s = 96 watts for each second of desired hover.

or am i not thinking clearly...

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