# Pressure inside the zeppelin for it to float

• Fluid mechanics
In summary, the Zeppelin was a successful airship that had many flights before the Hindenburg disaster.
Fluid mechanics

## Homework Statement

A zeppelin of an ellipsoid shape (a=32m, b=c=a/3) iz filled with hydrogen. Pressure of the surrounding air is 100 000 Pa. Temperature of air and hydrogen is 20°C. The mass of an empty (not filled with hydrogen) zeppelin is 10 000 kg. What does the pressure of hydrogen inside the zeppelin have to be, so that the zeppelin floats in air?

V=(4*π*a*b*c)/3
pV=nRT

## The Attempt at a Solution

I got the volume of the zeppelin
V=(4*π*a*b*c)/3 = 2859,55 m3

Then I calculated the weight of this volume of air:

pV = mRT

m = (p*V)/(RT) = 3398,8 kg

What do you think m is and what are the units? Have you done the dimensional analysis of the ideal gas law including the units of all the involved quantities. Please post your full working with all of this.

Fluid mechanics said:

## Homework Statement

A zeppelin of an ellipsoid shape (a=32m, b=c=a/3) iz filled with hydrogen. Pressure of the surrounding air is 100 000 Pa. Temperature of air and hydrogen is 20°C. The mass of an empty (not filled with hydrogen) zeppelin is 10 000 kg. What does the pressure of hydrogen inside the zeppelin have to be, so that the zeppelin still floats in air?

V=(4*π*a*b*c)/3
pV=nRT

## The Attempt at a Solution

I got the volume of the zeppelin
V=(4*π*a*b*c)/3 = 2859,55 m3

Then I calculated the weight of this volume of air:

pV = mRT

m = (p*V)/(RT) = 3398,8 kg

Hi Fluid Mechanics. Welcome to PF!

I am not sure what the question is asking because if the Zeppelin was empty (no air, no hydrogen) it would still float. The addition of the hydrogen is to displace the air. To do that you just need to put in enough hydrogen to fill the volume at 100,000 Pa.

So maybe you have to just determine whether the Zeppelin floats with that much H. What is the condition required in order for the Zeppelin to experience positive buoyancy? What is the overall density of the Zeppelin with nothing inside? What is the mass of air that it displaces (assuming no air inside)? What is the mass of H at 100,000 Pa that fills that volume? Add that to the Zeppelin mass. Does the Zeppelin still float?

Check your calculation again for the volume of the ellipsoid. The formula is correct but your calculation is wrong. Just approximating: 4 x 32 x 10 x 10 = 12,800 m3

AM

As I interpret the question, it is asking what partial pressure of Hydrogen is required so that the net buoyancy of the air-hydrogen mixture (at ambient pressure of one atmosphere, of course) is sufficient to support the craft.

Of course in an actual Zeppelin using hydrogen for lift, one would not mix hydrogen with air in a rigid enclosure. Instead, one typically uses flexible hydrogen-filled gas bags within a rigid but vented enclosure. The hydrogen pressure within the bags is ambient, always. https://en.wikipedia.org/wiki/Airship

Last edited:
diogenesNY, Andrew Mason and CWatters
jbriggs444 said:
As I interpret the question, it is asking what partial pressure of Hydrogen is required so that the net buoyancy of the air-hydrogen mixture (at ambient pressure of one atmosphere, of course) is sufficient to support the craft.
That makes sense. But the question says it is "filled with hydrogen". It should say, "filled with a mixture of air and hydrogen" and ask what "partial pressure of hydrogen" would be required to make the ship float.

AM

jbriggs444
Its either a badly designed question or a trick question. Especially for anyone that knows how a Zeppelin worked (rather than some fictional rigid airship).

CWatters said:
Its either a badly designed question or a trick question. Especially for anyone that knows how a Zeppelin worked (rather than some fictional rigid airship).
Yes. This Zeppellin with a mixture of air and hydrogen throughout would be a floating bomb. The Hindenburg at least tried to keep the hydrogen and air separate (but something obviously failed).

AM

This certainly sounds like one of those questions is complicated and full of distractors, while the real answer is just "the same hydrogen pressure as the outside air pressure". But that's treating the zeppelin as a balloon, not a rigid structure full of balloons as they really are.

Andrew Mason said:
Yes. This Zeppellin with a mixture of air and hydrogen throughout would be a floating bomb. The Hindenburg at least tried to keep the hydrogen and air separate (but something obviously failed).

AM
As you may know, the Hindenburg had 63 flights before the accident. Flew as far as Rio de Janeiro. Graf Zeppelin made 590 flights totaling almost 1.7 million kilometers and first airship circumnavigate the world and first to flight non-stop across Pacific. 21 Zeppelins in total were made before WW1

## 1. What is the ideal pressure inside a zeppelin for it to float?

The ideal pressure inside a zeppelin for it to float is slightly higher than the atmospheric pressure outside. This is because the higher pressure inside the zeppelin creates a buoyant force that helps it stay afloat.

## 2. How does the pressure inside a zeppelin affect its ability to float?

The pressure inside a zeppelin is directly related to its ability to float. If the pressure inside is too low, the zeppelin will not be able to generate enough lift to stay afloat. If the pressure is too high, it can cause the zeppelin to become too heavy and sink.

## 3. Can the pressure inside a zeppelin be adjusted while it is in flight?

Yes, the pressure inside a zeppelin can be adjusted while it is in flight. This is typically done by pumping in or releasing gas from the internal gas bags. By adjusting the pressure, the pilot can control the altitude and stability of the zeppelin.

## 4. What happens to the pressure inside a zeppelin when it changes altitude?

As a zeppelin changes altitude, the pressure inside also changes. This is because the air pressure outside decreases as the zeppelin ascends, causing the internal pressure to become relatively higher. To maintain the ideal pressure for floating, the pilot must adjust the gas bags accordingly.

## 5. How does the shape and size of a zeppelin affect the pressure inside?

The shape and size of a zeppelin play a crucial role in determining the pressure inside. A larger zeppelin will require a higher pressure to stay afloat compared to a smaller one. Additionally, the shape of the zeppelin affects the distribution of pressure and can impact its stability and maneuverability.

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