# How does buoyant force react with an acceleration $g$ load?

If a blimp with a certain amount of helium buoyancy accelerated enough to perform, let say, a +2G maneuver, would the buoyant helium force scale along with the weight force?

All the mass particles would experience a force of $$mass*g*load$$ factor --> mass*9.81*2.0

The equation for buoyant force is $$V*rho*g$$ This leads me to believe that the g in the buoyant force equation would scale as well?

If that is the case what would happen during a -1.0G maneuver. Would the buoyant force vector direction flip flop along with the weight force?

• – BowlOfRed Oct 29 '18 at 21:24
• Haha I posted that question as well. They didn't really answer what I needed to know. I want to know from a purely physics perspective (using equations and variables) what happens to the buoyant force as the load factor changes due to acceleration of the aircraft. – Jason Oct 29 '18 at 22:06
• The buoyant force is a result of the pressure from the surrounding fluid (in this case air). If the vehicle accelerates enough to induce "2G's worth of force" it leads me to believe the air also experiences the same acceleration. This would lead me to believe the buoyant force would scale by the same accord, but I need to know mathematically. – Jason Oct 29 '18 at 22:12

In an airplane "load factor" is the ratio of lift generated by the wing compared to the weight. In unaccelerated flight, it will be equal to 1 (or often given as 1g). The load changes as lift generated by the wing changes.

The important point is that the load factor isn't a cause of anything, it's a result. The increase of lift from the wing causes the plane to accelerate and change the perceived value of $$g$$. It's not the case that load factor on a plane is changing the lift of anything.

In a plane where the only lift device is a wing, then the two are correlated. Doubling the wing lift doubles the load factor.

If you had some sort of buoyancy device, then there's no control you can apply to it. It will (within a specified altitude range) give you a nearly constant force, and that force will always be away from the ground. So it won't change the load factor on the craft. Likewise, increasing the lift from the wing won't change the buoyant force either (either in magnitude or direction). They just continue to sum together as any other set of forces do.

Of course such a hypothetical device would probably be large, and it's difficult to imagine how you'd separate out the immense drag forces (that I've ignored).

If the blimp aircraft is accelerating through the surrounding fluid (in this case air) enough to perceive 2g's then doesn't the air being moved have to experience the same acceleration?

This is a different concept. The mere fact of the aircraft's motion will cause the surrounding air to be accelerated and contribute to drag. I've been assuming that drag is constant for this craft. But it still doesn't affect the buoyancy. A craft moving forward at a constant speed and the same craft turning in a tight horizontal circle (and therefore experiencing large accelerations) will still have the same buoyant force and approximately the same drag.

• Okay, so let's say the blimp has wings. Let's say the increase in lift force on the wings causes the blimp like aircraft to accelerate enough that it experiences a 2g perceived load. What happens the buoyant lift force? If the blimp aircraft is accelerating through the surrounding fluid (in this case air) enough to perceive 2g's then doesn't the air being moved have to experience the same acceleration? Does this change the buoyant lift force? – Jason Oct 29 '18 at 22:31
• Doesn't matter to me if the wings or peter pan dust causes the acceleration, but in my scenario can we pretend the aircraft with buoyant lift is accelerating enough to perceive 2g's? Then what happens to the buoyant lift force? – Jason Oct 29 '18 at 22:33
• Exactly what I said above, nothing. The buoyant force is constant in the accelerating and non-accelerating cases. You have no means of changing the buoyant force. – BowlOfRed Oct 29 '18 at 22:35
• physics.stackexchange.com/questions/226036/… ....is this a different scenario entirely? Somewhat similar question where the response implies acceleration does affect buoyant force. Is it because the fluid medium is part of the system and accelerating along with everything else? – Jason Oct 29 '18 at 22:38
• In that problem the beaker (containing the fluid) is accelerating, causing pressure changes in the fluid. In your problem the bulk atmosphere is not accelerating, so maintains constant pressure (at a given altitude). – BowlOfRed Oct 29 '18 at 22:42