bernoulli's principle

[joemama]

are projectiles subject to bernoulli's principle if tehy are rounded? if they are isent there a way to make a bullet that has more resistance to projectile moton using lift?

[thespeedycicada]

Use the spell check next time please! but yes i do belive they are subject to it but i have no clue as to what your second question was try saying it differently and try to make an effort on spelling.

[SpudUke5]

Yes spherical objects are. For Example: If you ever shot a spherical object such as a marble as fast speeds, you notice that the marle moves upward because the low pressure is is trying to equal with the high pressure so the high pressure pushes the marble upward. But, if the marble is perfectly spherical, is shouldnt move upward because the pressure should be equal on all sides since a circle is perfectly rounded.

Im not sure about your other question. As far as im concerned, a bullet flys pretty straight. But if you want to tamper with that stuff, then go ahead.

[Los Frijoles]

It is well known that rifling or putting a roll axis spin on the projectile increases accuracy and sometimes range, but it has been observed that unless the projectile has fins or wings or something, the time from when it is fired to when it hits the ground is equal to the time if it was dropped from the same height it was fired.

So, if you want some lift, put wings on it (wings have a slight tendency to get ripped off during launch if they are not secured very well).

[VH_man]

yes, everything drops at 9.85 meters per second per second, not taking into account drag.

[joemama]

yes, everything drops at 9.85 meters per second per second, not taking into account drag.

9.85m2 8)

[joemama]

It is well known that rifling or putting a roll axis spin on the projectile increases accuracy and sometimes range, but it has been observed that unless the projectile has fins or wings or something, the time from when it is fired to when it hits the ground is equal to the time if it was dropped from the same height it was fired.

So, if you want some lift, put wings on it (wings have a slight tendency to get ripped off during launch if they are not secured very well).

thanx you this is what i was asking, sorry for bad spelling.

[VH_man]

you can also give the projectile topspin if its spherical. this spin will actually work like an airplane wing and give it lift... aka why my airsoft gun can shoot an airsoft pellet 150 feet at 300 FPS...........

[chaos]

you can also give the projectile topspin if its spherical. this spin will actually work like an airplane wing and give it lift... aka why my airsoft gun can shoot an airsoft pellet 150 feet at 300 FPS...........

actually that would be backspin, top spin would tend to make the projectile curve towards the ground faster.

[dongfang]

Hi,

So how does one make the projectile spin around any other axis than that of the barrel? Cut a groove along the top inside(?) of the barrel to blow the ball into a spin, or how?

Could be interesting for my golf ball accelerator.

Regards
Soren

[jackssmirkingrevenge]

have a look here

Hop-up & Bernoulli's principle

The term Hop-up describes the back-spin put on airsoft pellets and BB's to increase their range and (vertical) accuracy via Bernoulli's principle. Hop-up acts somewhat like the rifling on the barrel of a firearm, but without the increase in horizontal accuracy. Also, being light-weight, airsoft pellets are still affected by wind when fired.

Airsoft hop-up devices apply a backspin to the pellet so that the pressure force acts on the pellet opposite to the direction that gravity is pulling it. This causes the pellet to fall less over a given distance than it would without the spin applied to it.

In airsoft guns this is often implemented as a rubber piece at the rear of the barrel that is thicker at the top of the barrel than the bottom. As the pellet moves past this piece it tends to roll, inducing a backspin. This is occasionally adjustable so that the effect can be tuned to suit the weight or speed of the pellet, and each player's preference.

Bernoulli's principle as applied to an airsoft pellet is as follows. As a spinless spherical pellet flies along its trajectory through the air, the pressures on all sides of the pellet are equal because the air is traveling the same velocity relative to the surface of the pellet. If a spin is applied to the pellet about an axis perpendicular to the velocity vector (for example a backspin) the air will be rushing slower (relative to the pellet surface) on the side that is spinning away from the velocity vector and faster on the side that is spinning towards the velocity vector. Bernoulli's principle says this difference in fluid velocity implies a difference in pressures, which is a force that will cause the pellet to move in a direction perpendicular to the velocity vector.

Another cause of the apparent lift on an airsoft pellet is the Magnus effect. There is a layer of non-moving air on the surface of the pellet (boundary layer). This is why a golf ball has dimples; this layer acts like ball bearings. In the case of a spinning ball, this layer gets thrown off at an angle. Newton's laws say that in order for air to be thrown in one direction, the ball has to move in the other direction. According to the Magnus explanation, the rotating ball would throw air downward and to the rear, thus giving lift. The air on the bottom of the ball is slowed down, so when the separated air comes back together, it is lower than the middle of the ball, appearing like a comet's tail pointing down. This can be verified in wind tunnels and is very well documented in fluid dynamics textbooks.

[dongfang]

Hi,

Thanks a lot. I might be able to get that to work by gluing some pieces of rubber or small diameter PVC hose to the inside of the barrel. It's slightly oversize for the GBs is shoots anyway.

Backspin must be really effective with GB .. they were made for it.

Regards
Soren

[jackssmirkingrevenge]

Personally I don't believe in hopup or backspin - what rotational energy is going into spinning the ball is lost from the kinetic energy of the ball's forward motion, which adds up to lack of efficiency which I despise.

[Hotwired]

...and increases inaccuracy.

Airsoft and paintball is the only place it belongs and I have doubts on paintball as the reduced energy means the paint has a lower chance of breaking.

[jimmy101]

Personally I don't believe in hopup or backspin - what rotational energy is going into spinning the ball is lost from the kinetic energy of the ball's forward motion, which adds up to lack of efficiency which I despise.

But the entire point of a hopup is to trade power (kinetic energy, velocity) for accuracy (reproducibility). Same with a rifled barrel, some of the energy in the propellant is used to spin the round, around the axis of flight for a rifled barrel. For a hopup the round is spun perpendicular (usually about the x-axis). In both cases there is less KE in the round, but the round is much more accurate.

Besides, it is likely that a paintball barrel (or any smooth barrel) will always impart spin to the round. The problem is each round will get a different spin, one will rise, the next will hook left etc. The hopup makes the spin more consistant.

Getting the maximum KE is great if you are trying to hit a barn. If you are trying to hit a target smaller than a barn, then trading KE for accuracy makes sense.

Of course, for most spudguns, people are basically trying to hit a barn.