Picture a giant plastic egg. I say plastic to give you the image and not as an actual proposed material. This egg should be as thin and light and strong as we can make it. We are going to be pumping some air out of it, not enough to make it collapse, but some, so there will be less pressure on the inside than the outside. The more the better, but we’re not talking about trying to lift the egg by evacuating it of air. We know that we can’t do that. On the other hand, because of the dirigible sized scale of this vessel any quantity that we can evacuate will be helpful. The primary goal though is not to lift the ship through negative pressure. The negative pressure will serve two other primary purposes which we will get into shortly.
We have a vent with a pump at the top of the egg. We can let air into or out of it, or pump it in to create over pressure, or pump it out to create low pressure. Again, the bigger the pressure difference the better, but we are not getting much if any lift by doing this.
Hanging in the middle of the egg are a series of large elastic balloons filled with a quantity of relatively inert light gas. For the sake of argument, let’s say helium, but maybe there is something better for this application.
Inside of each of these elastic balloons is a heating element.
Hanging underneath the egg is a gondola with controls, etc.
The ship sits on the ground and is heavier than air. Everything is pressured at sea level.
To raise the ship we simultaneously do several things. First we start pumping air out of the rigid egg. The negative pressure generated causes the elastic balloons filled with helium to expand just the same way a bag of Doritos will expand on a plane as it gains altitude. We also turn the heating elements in the elastic balloons on, heating the helium, further causing it to expand. The expansion of the balloons increases the pressure in the egg, which we continue to pump out. This process continues until we achieve lift.
We control the amount of lift through several processes. The more we heat the helium balloons the more they expand, the more lift is generated. Evacuating air from the egg also pulles expansion on the balloons generating lift. The more vacuum we pull between the balloons and the eggs means less loss of heat through conduction and helps us keep the balloons heated efficiently.
It is also possible that we have created a large enough pressure differential between the egg and the outside that we are contributing to lift. At any rate, as we rise the pressure decreases, so we can keep pumping air out.
We descend by letting cold air in through the vent, raising pressure, shrinking the elastic balloons and cooling them. We trim the ship by making adjustments within each of the elastic balloons as needed.
The benefits of this design are that we get the lift that we would get in a hot air balloon. Added to that we also get the lift that we would get in a helium filled blimp. We get a lot more lift by using both methods simultaneously.
In something this size, whatever low pressure we are able to make by partially evacuating the egg will also contribute to lift. Percentage wise it might be negligible, but being a large dirigible that small percentage wI’ll still mean some added lifting capacity.
Another benefit is that because all expansion and contraction is occurring within the egg, and that it is being controlled by both pressure and heat, we will have the ability to raise and lower the ship through the atmosphere quickly. It will trim much better than a standard airship or balloon.
Does that make sense?
