Well, here’s a stupid (And poorly worded, I might add) question for me to ask the month, maybe someone with a better understanding of math and/or physics could answer…Would it be practicably possible for me to simulate a gun-fired projectile in an off the shelf flight simulator? Jules Verne’s cannon-fired spacecraft from “From the Earth to the Moon,” to be precise. As you can imagine, the flight sim I’m working with doesn’t normally use that manner of propulsion. But since Verne was fairly exact in writing out the technical information for his columbiad, would it be possible for me to calculate how much energy would have been released by the gun’s propellant, translate that into pounds of thrust per second, and try and rig a JATO in the sim to propel the capsule at the equivalent force? Or would this be simply too much for the average person at home (Namely, me) to work out? Not to mention that fact that if Verne got his numbers wrong, it would all be for naught. Although on the plus side, I wouldn’t have to worry about mechanical failure, or the slight problem of NOT turning the crew into stroganoff with the G-force involved.
Well, thanks for your patience,
The flight sim would have to be able to calculate the effects of the atmosphere in hypersonic flight. If it can’t do that, they you can’t come up with a reasonable model.
A flight sim also will almost certainly not have a reasonable gravitational model. It’s probably operating on the assumption that gravity is a constant. Not what you need when trying to shoot a projectile to the Moon. For that matter, flight sims aren’t going to factor in the Moon’s gravity at all. Nor will they have an actual moon. So you’re out of luck.
The basic math behind projectiles is simple. The confounding factor is the atmosphere, and modelling THAT is no easy task. Everything depends on the projectile’s shape and mass. And this projectile is going to be going at an ungodly speed if it is expected to punch through the atmosphere without further propellant. The linear approximations that the flight sims probably use to model the effect of drag just won’t work when you get into those speeds. So that will stop you as well.
What are you trying to accomplish? You just want to have some fun and shoot stuff as high as you can? Or are you trying to do a semi-serious simulation? Write a school paper? What?
If you’re just trying to show what it would take to make Verne’s shell-to-the-moon scenario happen, why not simplify the problem? First, forget about the atmosphere, and forget about the Moon. Just do the calculation for how high a projectile will go if shot straight up from the Earth. Then figure out how big your barrel is, and how much acceleration you’ll need inside the barrel in order to achieve the muzzle velocity you need. That gets you a minimum requirement. Then start adding in other factors to try to refine the answer. You’ll have to make some intelligent simplifications of some of these effects, like atmospheric drag.
To keep the acceleration ‘G’ forces in the barrel low enough for people to survive, I think you’ll find that you need a ‘barrel’ that is miles long. And the buildup of pressure in the ‘barrel’ will be too great, so you’ll need something like an open-ring mass driver. And the atmospheric friction would probably melt anything you could build, so you’ll have to put this thing up on some really high mountain where there is very little atmosphere. Find yourself a mountain range facing in the proper direction to take advantage of the rotation of the Earth, and build your mass driver up along a very long, high ridge line.
The flight sim would have to be able to calculate the effects of the atmosphere in hypersonic flight. If it can’t do that, they you can’t come up with a reasonable model.
A flight sim also will almost certainly not have a reasonable gravitational model. It’s probably operating on the assumption that gravity is a constant. Not what you need when trying to shoot a projectile to the Moon. For that matter, flight sims aren’t going to factor in the Moon’s gravity at all. Nor will they have an actual moon. So you’re out of luck.
The basic math behind projectiles is simple. The confounding factor is the atmosphere, and modelling THAT is no easy task. Everything depends on the projectile’s shape and mass. And this projectile is going to be going at an ungodly speed if it is expected to punch through the atmosphere without further propellant. The linear approximations that the flight sims probably use to model the effect of drag just won’t work when you get into those speeds. So that will stop you as well.
What are you trying to accomplish? You just want to have some fun and shoot stuff as high as you can? Or are you trying to do a semi-serious simulation? Write a school paper? What?
If you’re just trying to show what it would take to make Verne’s shell-to-the-moon scenario happen, why not simplify the problem? First, forget about the atmosphere, and forget about the Moon. Just do the calculation for how high a projectile will go if shot straight up from the Earth. Then figure out how big your barrel is, and how much acceleration you’ll need inside the barrel in order to achieve the muzzle velocity you need. That gets you a minimum requirement. Then start adding in other factors to try to refine the answer. You’ll have to make some intelligent simplifications of some of these effects, like atmospheric drag.
To keep the acceleration ‘G’ forces in the barrel low enough for people to survive, I think you’ll find that you need a ‘barrel’ that is miles long. And the buildup of pressure in the ‘barrel’ will be too great, so you’ll need something like an open-ring mass driver. And the atmospheric friction would probably melt anything you could build, so you’ll have to put this thing up on some really high mountain where there is very little atmosphere. Find yourself a mountain range facing in the proper direction to take advantage of the rotation of the Earth, and build your mass driver up along a very long, high ridge line.
There used to be a sim called “Chuck Yeager’s Advanced Flight Trainer” that modeled the X-15 and the Space Shuttle among others. You could set an initial altitude and speed, and fly from there.
But the Space Shuttle was modeled as a glider with no engine power, and the X-15 only had about 3 minutes of fuel.
Well, thanks for the info, everyone. And thanks especially to Tuckerfan for warning me of the problems with Verne’s numbers. You probably just saved be about 100 man-hours of work, there.
Well, I think I’ll still try to get the project going, though…With the numbers for Verne’s capsule, if not the gun. I’ll just try and shoot for Earth orbit, rather than full escape velocity. I’m optomistic about my chances…the sim I’m using, X-Plane, is considered pretty accurate, even in hypersonic and space launch situations. (NASA thinks so, at least)