Science Question (II) - gliders in a lava lamp.

[Sunstorm]

Imagine there are mini-gliders in a jar full of liquid. These gliders are neutrally bouyant.

Each mini-glider is trimmed to fly upwards and in a circle.

Upon heating the liquid - a mini-thermal would form, which would make the gliders fly upward in gentle circles. When the gliders hit the cooler liquid above, they would sink, until they hit the hot liquid below.

Would this concept work?

[Brandon Chng]

yes provided:

jar is big enough for the liquid to cool off at a faster rate at the top than the liquid being heated below.
thermal is good enough to actually get gliders to glide, rather than float.
that you don't take into account what the convection current does at the top of the enclosed jar.

[flybywire]

Not sufficient data to process into useful information, how big is the jar, how fast is the heating, what buoyancy of the aircraft etc.

[DL8698]

If the glider is neutrally bouyant it means it is displacing an amount of liquid that has the exact equal weight of the glider, and is actually floating in the liquid, like a helium balloon in the atmosphere. The glider is no longer a glider, like we usually take it to mean, ie an aircraft without engine which trades off height for forward speed in order for an airflow to develop over the wings. When the air that the glider is descending in rises at exactly the same rate as the glider is descending then the glider remains at a constant altitude.

Air is much less dense than the liquid in a java lamp therefore the glider can fly in air as there is very little drag, but it will only float in the liquid as drag will be so tremendous that it is impossible to imagine the glider making forward progress in the liquid.

Although this is a hypothetical situation, it is still an impossible scenario as liquid is not compressible therefore, Bernoulli's Theory which is the usual explanation for lift developing on an airfoil shape when moved forward, cannot work with a liquid. Some lift can be generated by virtue of the angle that the wing is pointing upwards compared to the direction of forward motion (similar to the hydroplanes of a submarine) but this is highly inefficient lift and causes tremendous drag.

Therefore, the gliders will merely move around at the mercy of the moving liquid, like so many pieces of floating drift wood. They will never glide in the sense that we usually apply to gliders flying in air.

[mave]

Glider or no glider, In a jar of liquid, I can only think of convection.
..

[cdckjn]

Not exactly a Scientific reply but

I think the description of being like drift wood us correct as the liquid is more viscious than air. So what I think will happen will be the gliders as they are neutral bouyant, will be lifted up by the heated liquid and as they reach the top, then the glider will start to sink straight down and then repeat again. The "areodynamic" shape of the glider will not play a part in the movement of the glider.

[Jack_Chen]

Believe it or not, I think the glider will behave like the 'lava' in a lava lamp, it only goes up, it may not necessary go down. The lava are liquid bubbles, hard any resistance going up nor down, the glider goes up through convection but the shape may cause resistance for it to drop, eventually maybe.

[Sunstorm]

I think the description of being like drift wood us correct as the liquid is more viscious than air. So what I think will happen will be the gliders as they are neutral bouyant, will be lifted up by the heated liquid and as they reach the top, then the glider will start to sink straight down and then repeat again. The "areodynamic" shape of the glider will not play a part in the movement of the glider.

Hi, didn't expect so many replies to my daydream.

Well maybe the key thing is 'neutrally bouyant' - so they are like driftwood, or drifting in space.

What if we change the gliders to being heavier than the liquid? Assuming their CGs are correct, I guess perhaps the jar can be given a good shake! A glider from the top would then start to sink to the bottom in lazy circles.

Oh well, this is a hypothetical situation anyway. Good to think about.

[muddy]

if the gliders are not already "flying" in the first place.. aerodynamics will not play much of a role.. they'll just be air plane shaped objects floating in the liquid.

and its really difficult to think of them as neutrally bouyant.. neutrally bouyant would mean that they have the same weight as the water being displaced.. but cold and warm water have different weight (different density).. so if neutrally bouyant in warm water, they wun be neutrally bouyant in cold water..

and besides, if you heat a jar of water from the bottom, convection will take place so quickly... the cold layer above will disappear before you know it..

if this is asked in exam, i sure will raise hand to ask the teacher to explain.. haha..

but its good to see science questions in the forum.. quite fun..

[Lockheed]

science question

It has already been invented. It is called the Lava Lamp. Same principles.

[Ghostfit]

Dunno izzit because of the Windy conditions or the Rains !


...you guys really need to go out and fly more often !