Center of Mass

Ignatz Takes Me to School

Fri, Feb 19, 2021 at 12:02 PM


I had been considering the visual changes to the GM Box Hauler when it suddenly struck me...

The concept doesn't work as you have imagined it.

The reason for this should be obvious in the little tech drawing below...

What we have is an issue of the line of delivered thrust relative to the center of mass.

The illustration at 'B' is what you pictured in the file you sent me. It looks good, but there is no way that a ship attached to the cargo container at that point could fly a straight course. It would inevitably start to rotate as indicated because the thrust is offset relative to the center of mass of the cargo container being moved.

At 'A' I have pictured how it might work with a smaller container, here by moving the attachment point to the rear of the cargo container and angling the thruster cones. Of course, this arrangement does not fly 'straight' relative to the ship, but rather straight relative to the line of thrust through the center of mass of the cargo. Kind of catty-wompus. In fact, if the cargo mass becomes large enough, the whole idea of locking on with a nose pin becomes a liability and it would be far easier to just make a simple pusher ship.

However, the concept works quite well - at 'C' - if we pair up the GM Haulers on either side of large cargo containers. Larger cargo containers would thus have matched 'locking points' on two, four or even six sides (for a hex-shaped container) to enable the haulers to deliver balanced thrust to the load. The thrust is now in line to the relative center of mass being moved and everybody is happy (the captains of the haulers perhaps less so because it means splitting the profits). [Note: The fact of the haulers being upside-down with respect to one another means nothing in outer space, especially since each ship has its own artificial gravity.]

When you think about it, this paired working is exactly how groups of tug boats work to manoeuvre large ocean liners. A single, small tug on one side of the vessel is going to have an extremely difficult time doing much more than pushing the larger vessel to one side. Assisting in straight line travel would be extremely difficult.

Your modular Coleoptera class hauler design doesn't suffer from this problem. Having the cargo affixed to mounting racks along the side allows the crew to balance the mass and load relative to the line of thrust delivered by the engines at the rear. And since the engines are effectively behind any mass being moved we still have the option of either angling the direction of the thruster cones or else balancing the thrust from the four engines to compensate for any cargo loading imbalance.

Again, this is all theoretical stuff and makes no difference whatsoever to the model building, but I thought you might want to think on this one if it plays any part in your novels.


- Ignatz