The question asks whether a design is feasible without actually disclosing the design. P.S. Steam engines can use the exact same fuel as jet engines. The problem is not that the fuel is too heavy, the problem is that water is heavy.

Imagine a gyrocopter with a steam engine instead of an internal combustion engine. That's it. Also, fuel is still heavy. I'm looking for an answer that deals with any issues this aircraft may have. If you have information to share, please feel free to post an answer.

"A gyrocopter with a steam engine instead of an internal combustion engine" is nowhere near sufficient to judge whether the deign is feasible or not. What kind of steam engine? How does the boiler work? How much water does it carry? Does it have a condenser? Etc. VTC because the question needs vastly more details than provided.

@AlexP this isn't an RMIQ question. I don't have to flesh out every detail of the design. If I had all the numbers and knew exactly what specifications every part of the system had, I wouldn't need to ask this question. I don't think details such as "how does the boiler work" are important. It's a boiler, it boils. Furthermore, this design doesn't need to be empirically proven somehow: the idea just needs to be rationalised.

airplane crashes have way too high of a death risk so they started using gyrocopters. what? I'm pretty sure airplanes are significantly safer than gyrocopters. Also, "risk of death" is not really something that held back early aviators.

@Dragongeek no, in fact. Gyrocopters fly at lower speeds and the rotors generate lift just by moving, unlike helicopters which have to spin them. Thus, they can't stall and if they lose power they just glide. Also, it's still plausible that airplanes are not adopted because of safety. After all, not everyone is willing to risk their life for a test run :p

Helicopters also autorotate when they lose power; in fact, the standard flight rules for helicopters are designed to always maintain enough altitude to autorotate for a landing in case of an engine failure.

@Cadence Gyrocopter rotors are designed to autorotate in flight though, and gyrocopter pilots sometimes land using autorotation, so I would expect that they would be a fair bit better at autorotation. Since the blade is already in motion, there isn't a need to start autorotation and therefore an engine failure from even low altitudes should be easily survivable.

(a) "Reality Check" is a phrase that has a history on this stack. It's now a synonym of "science-based." Due to it's previous meanings and use, it's a bad choice to use it at all. (b) I removed the internal-consistency tag because it has a specific purpose that you're not using and specific rules that you're not obeying. Please remember to read tag wikis.

VTC:Too Story-Based. Steam powered aircraft were built and worked. There's a difference between "is it technilogically possible?" (which your assertion obviously is) and "would it turn out that way?" which is completely story-based. It will if you write your story that way. It won't if you write your story that way.

This question is similar to: Extremely compact nuclear reactor?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. Otherwise, you might have asked "How might a nuclear head be used to power steam generator sufficiently small for a gyrocopter with XX range in mind, and Y payload?"

@Escaped dental patient that question deals with the nuclear reactor as the primary subject. This question takes the gyrocopter as its primary subject and merely assumes the presence of an advanced nuclear reactor, without asking for the nuclear reactor itself to be rationalized. I have already laid out how the nuclear reactor is to be used in the question: as a substitute for burning fuel to heat water.

@JBH steam-powered fixed-wing aircraft were built and worked, but the only example of a steam-powered rotor aircraft is the Giffard helicopter and Enrico Forlanini's steam helicopter, neither of which achieved a height above 13 meters and did not fly for any distance.

@IMP9024 You're missing the point. The purpose of this site is NOT to produce scientifically verifiable answers. If that's what you want, head over to one of the science and/or engineering stacks. We're here to help you rationalize an idea for your imaginary world. Nothing more. It's utterly irrelevant that, in Real Life, steam-powered helicopters/gyrocopters were limited. The development of technology demonstrates all they needed was time to become viable. The information provided more than adequately provides support for the inclusion of them in your world. Thus, a story-based question.

@JBH If you believe that the information provided is enough support to rationalize their development, please post an answer to that effect. Just because the answer seems obvious to you does not make the question story-based.

@IMP9024 Once again, you're missing the point. A question is story-based when too many circumstantial issues can influence the answer. The short version of this is, "it's viable if you write your story that way, it's not viable if you write your story that way." In greater detail: there's historical evidence that steam-powered aircraft existed and history has proven that as technology evolves it often becomes smaller, lighter, cheaper and more powerful. Since our focus is to help you rationalize your imaginary world and NOT to validate ... (Continued)

... science, you have more than enough to proceed. Whether or not it's viable depends on how you write your story. Do you have an actual problem to solve? Because everything is viable in your imaginary world and whether or not it's viable in the Real World isn't a question this stack answers. Thus, VTC:Too Story-Based.

This is in the reopen queue. I can't vote to reopen as the original problems I saw remain. But, to make a point, making the engine smaller significantly contributes to the viability of the gyrocopter. However, that's a pretty obtuse argument for the majority close reason. In the end, I must agree... question isn't about nuclear reactors. Can you reword the question to remove the word "feasible" (and any similar alternative) and focus on a problem to solve? I'd vote to reopen, then.

@JBH I've edited it to focus on one aspect of gyrocopters that also doesn't invalidate the existing answer.

I've voted to reopen your question and it appears I was the final reopen vote. However... A significant part of the confusion here is that your backstory is all about nuclear power and then, suddenly and without explanation, you shift to talking about steam engines. That's really confusing. You need to delete the first paragraph and rewrite the third paragraph to remove the reference to the nuclear reactor manufacturer. Or, alternatively, you need to add a paragraph that explains why the nuclear reactor is irrelevant and you want to focus on steam engines.