What type of an engine malfunction would make a good plot device? [closed]

I am writing a book that follows a colony of people living above Venus, in an Airship. At the beginning of my book, a major engine malfunction is discovered that, if let left uncorrected, will result in the colony being destroyed.There are several critera that this problem must meet I will list them below: 1. This problem will need to be very hard to detect. 2. I would like for the main characters to discover it by hearing a very feint whistling noise coming from an air vent that leads to the engine room. 3. The problem is such that the colony will collapse and fall through the atmosphere.

I know very little about machines so I am hoping that someone will be able to give me a relatively easy answer that I can effectively explain to my readers. I imagine there are innumerable ways that I could achieve this situation, so I will leave you to it!

• en.wikipedia.org/wiki/… The atmosphere of Venus is highly corrosive, might I suggest that the people live in an orbiter instead of an atmospheric airship? Commented Oct 21, 2016 at 23:47
• What kind of engine is it? Commented Oct 21, 2016 at 23:48
• Since a Venusian colony might be an airship, the colony might just drift: toughsf.blogspot.com/2016/10/… Commented Oct 22, 2016 at 0:03
• If the engine needs fuel, then how about running out of fuel and the shuttle that was supposed to deliver more got delayed? Commented Oct 22, 2016 at 2:40
• hard-science is probably not an appropriate tag; you're not looking for equations, cited scientific papers, and proof for every sentence a person says, just a reality-check. Commented Oct 22, 2016 at 3:21

You list three conditions that your problem must meet, but then say that number 2 is an "I would like." So I'm not sure if we must meet number 2.

Systematic weakness in the buoyancy providing 'balloons'.

First, I am working with an assumption of the most practical Venusian cloud city. A large, lightweight colony is constructed and pressurized to normal atmospheric pressure, and then held aloft by balloons. The balloons have a lift gas (doesn't really matter what gas, as long as it is lighter than CO$$_2$$) and are pressurized to atmospheric pressure at that altitude, roughly 0.5 atm at 55 km altitude.

In this case, there is no 'engine' because the whole colony floats instead of having a propulsion system. There would probably be some stabilizing propellers needed to prevent rotation, but no ability to move around in the skies. There would be 'engines' to provide power, the nature of which you haven't really specified. There might be either a fossil fuel or nuclear fission generator for nighttime electric generation when solar isn't available. More likely, you could assume there is a great leap forward in batteries or hydrogen fuel cells, and those can be used in conjunction with solar.

In either case, the electric power system won't be causing the disaster, it will be one (or more) of the buoyancy balloons. They were perforated by some sort of impact event, and the perforations are right along a mechanical high stress area, so they are vulnerable to sudden catastrophic failure.

The great advantage of the lift gas being at the same pressure as the Venusian atmosphere, is there is no sudden decompression event. The CO$$_2$$ atmosphere and the lift gas will slowly mix as the balloon loses buoyancy.

I believe this meets your criteria (minus mentions of the engine, which, as I explained, I don't think this station will have).

1. The perforations are small and hard to detect. They wouldn't be a problem if it weren't for their orientation along one of the highest stress zones of the balloon.

2. This is a gas leak, and although it probably wouldn't be heard, you could have it found in a routine inspection of the buoyancy balloon.

3. This problem will inevitably cause the colony to descend.It won't happen right away, even if the balloon rips, but action must be taken BEFORE the perforations become a major leak.

Final Note:

Regarding point 2, your description of a whistling sound coming from an air vent in the engine room does not describe an actual problem. I have experience with a nuclear fission reactor, a 600# steam plant, gas turbines, and diesel engines. I have actually heard leak in both the steam plant (downstream of a regulation valve, thank god) and diesel plant (jacket water piping, in case you are interested). Both leaks are not 'a very faint whistling noise.' They were an immediate existential crisis for anyone in the same space. Engines run at high temps and high pressures. Leaks tend to be fiascos. I don't think you can get number 2.

• "Leaks tend to be fiascos." Very well put. A chill ran down my spine. Plus one from me. Commented Oct 22, 2016 at 4:17
• Very good thoughts. In light of what you said, the reason I want the feint whistle noise is because I want my main characters to find it by chance, this problem is ideally such that no one would ever detect it otherwise. Secondly, the colony needs an engine to operate all of its life support systems. So I am revising this question to reflect that. It no longer needs to sink. The problem only needs to kill everyone on board. Commented Oct 22, 2016 at 4:58
• Great thought put in, +1 from me. Considering the atmosphere of Venus contains sulfuric acid, you might have some pretty thick balloons, however... would an accidental perforation really happen to a balloon thick enough to resist highly corrosive acid? Would an intentional perforation i.e. sabotage make more sense? Commented Oct 22, 2016 at 7:32