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WIP video about Jet Engines, urgently requesting feedback! (Patreon)

Published:
2025-11-12 12:54:27
Edited:
2025-11-12 15:27:23
Imported:
2026-09

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  • 563594551.mp4

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Content

DEADLINE FOR FEEDBACK - 13/11, 5PM UK TIMEWe've got an exciting video coming out very soon!

We'd love to hear your feedback and suggestions as we wrap up this video all about jet engines!

It's a little rough around the edges as we still need to finish some animations (as stated in the video) and some are mistimed so please look at the content rather than the timing, but as always we appreciate you watching and reviewing this cut!

Is there anything wrong? Any other questions? Anything more you'd like to see? Explanations you don't think do a good enough job or lack depth? Let us know!Thank you so much for all your help and support recently, we know it's been crazy with WIPs and we hope you've been enjoying it, we really appreciate you all!

-Team Ve

Comments

cliv

The material science was pretty interesting, but you sort of blew right past the huge increase in bypass ratio. Today most of the airflow (80% of the thrust) is around the turbine. In the first jet engines most of the thrust was from the turbine. When they started to send more air around, efficiency kept increasing. It got to the point where people would say it is more of a ducted propeller (80%) than a jet.

Kat Seibert

I understand that this was mostly about the turbine blades but I do agree with Cliv that the bypass ratio is a big part of why modern jets are so efficient. Having said that this was a great video and far more interesting to me than your pure math videos.

Kate Proctor

2 Comments: -- It might be interesting to touch on why fighter jets do not use high by pass, or even any by pass -- In the early 90s, I visited one of the RR engine plants for work. I was searched for cameras on the way in and on the way out. I was not allowed to see the ends of the turbine blades. It is VERY interesting that today they allow filming even. Clearly their value-add has changed...

Bernardo

It's been a long time since I took thermo, but I always thought that the efficiency gained in a jet engine from high pressures and temperatures came from the pressure ratio (and its impact on the Brayton cycle) rather than the temperature ratio (and its impact on the Carnot cycle). I'm gonna have to think about that one. (I just looked up their P-V diagrams for the first time in over 20 years, just to check that I'm even remembering the names correctly.) Like the other commenters said, I had always thought that the biggest contributor to jet engine efficiency in transport airplanes was the high-bypass turbofan: "Moving more air by less" means that you get the same thrust (change in the air's momentum per second, and momentum is mv) for less power (change in the air's kinetic energy per second, which is ½ mv²) because the m-per-second goes up and the delta v goes down. But now I want to compare the change in those m and v numbers from early jets to today (easy to estimate by using the inlet diameter, the cruise speed, the density of air at 30-40k feet, and the drag of the airplane assuming a reasonable L/D) against the increase in temperatures and pressures inside the engine (I don't know the temperatures but I do have a chart of how jet engines' overall pressure ratio has gone up over the decades) to estimate which factor improves the efficiency more (more bypass or more heat and pressure) and by how much. Might be a fun project for the weekend, but I don't have time in the next 24h...

Lionel Pöffel

Absolutely fascinating. I didn't find factual problems, just one weird wording: At 33:01 Derek says: "10^... atoms, that is more stars than in the observable universe" I suppose a better wording would be something like "those are more atoms than there are stars in the observable universe"

John Cox

Overall: Good to see you out in the field again, Derek! The last few videos have had your commentary, and it's really cool that you're building up other educators, but it's fun to see you being out there again exploring a physics and engineering topic. Feedback: 0:47: "Turbofan engine" Suggest mentioning that this is a "high bypass" engine. Contrast with "low bypass" turbofan engine, which you'll commonly find on fighter jets. Less thrust, but by reducing the diameter of the fan, the RPM can be increased while keeping the blade tips subsonic, and this gets turned into higher max velocity of the exhaust, which means higher top speed. 4:48: -55C to 1500C. Don't forget thermal stress microfractures. Might as well add to the list of design stresses :). 7:48: Is this heating and stretching realtime? 10:07: "The metal, effectively, gets softer" Is this before the body-centered-cubic -> face-centered-cubic deformation? During? Maybe it's just an artifact of the footage, but it looks like the metal piece glows briefly and dims again a couple times during the deformation, which makes me think that this is more than a simple temperature change. 17:42: "actually getting stronger" Suggest adding a note that this explanation will take a while. The professor was a bit difficult to follow. I really appreciate letting him have his time and explanation and not cutting it into multiple chunks, but it was difficult for me to follow. 23:33 "so both of them become stuck" I'm sorry, but I don't understand how two blocks being vertically out of phase contributes to the continuously growing strength of the material as the temperature increases. 27:57 "this is one of our furnaces" Unclear that this was a transition from the academic back to the molds. 28:23 "start by pouring molten superalloy" Animation does not fill the cavities on the top left and top right. Is this intentional? 29:51 "columbnar crystals" (spelling?) First mention of these crystals by name that I can recall. Were these supposed to be introduced previously? 31:17 "a blade of a single crystal" That is a beautiful thing. 36:42 "this is the final barrier" Could we get a brief recap? There's been a lot of layers and processes by this point and it's hard to remember what they are. Other thoughts: (1) How is the air compressed in the turbine? This may not be the right video for it, but the video did start by asking how a jet engine worked and then didn't explain this part. Is that too much for this video? (2) Not for the video, but check out the startup Whisper Aero. They are trying to manufacture a turbine stage in which the outer edge of the blades are part of a spinning ring. If they can get it balanced (and it's looking like they are), that could increase efficiency and reduce turbulence noise by significantly reducing blade tip vortices. Probably won't be in a full size jet turbine anytime soon given the hostile thermal and mechanical environment, but still useful for electric motor turbines.

David Guest

I didn't think that there was enough to distinguish between creep (time dependent deformation) and yielding due to loss of strength at high temperature, which appears to be the main thing shown in the tensile tests in the video. They are very different phenomenon, and I feel like viewers will come away from the video thinking that creep is the latter. Another thing I find fascinating related to jet engines that I might have liked to see is foreign object damage (aka bird strike or other objects larger than dust) and the special requirements to protect the safety of passengers when those impacts inevitably occur.

Zeus

0:58 "10% of air gets compressed" - technically, the fan also compresses the air, which eventually expands in the nozzle; just not as much. What this (and many other) jet engine animations omits for supposed clarity are all the *stator* blades. There are actually (about) twice as many blades as this animation shows, and they are just as important for both the compressor and the turbine (esp. multi-stage ones). The fan normally also has stator blades behind it, and they make it a compressor stage, too. Of course, they are somewhat less technically challenging to make, so are less interesting in the context of this video. But I feel sad for them. They are not that trivial either: on most engines, many stages have adjustable stator blades.

Zeus

(Sorry, I'll make several comments on the go as it must be close to the deadline. An airspace engineer and a pilot here, by the way). The logic about squeezing more air for combustion (~4:00) applies to piston engines, too. By mid-40s, turbocharged (or engine-driven-compressed) piston engines were common, and this allowed them to fly almost as high as jets. Perhaps it would be more correct to say that it is the compressor that is the point here and not the "jet" per se.

Zeus

4:22 Oh no! "Air is dense enough for lift, but thin enough that drag drops down dramatically". HUGE misconception, and very common, too! Drag and lift have absolutely the same nature. They have the same dependency on density and airspeed. And if you want to have that much of lift (and you want exactly the weight amount of it, right?) you'll have an appropriate amount of drag to pay for it, no matter what. The ratio between them is the famous lift-to-drag ratio, and it doesn't change dramatically in normal cruise flight. (Let's omit the wave drag at higher Mach numbers for simplicity). It will vary slightly depending on how the wing is optimised, but that's not the point. The point is that in thinner air, the same lift AND drag will happen at a higher speed. As simple as that. Of all things, Derek, please fix this - you can't have such mistakes on your channel! Damn the stator vanes.

Zeus

11:49 "...down to the steel turbine blades". Yet you are showing a compressor stage at that moment. I understand it may be difficult to find correct archive footage, yet I find it's misleading. Maybe it's better to show something generic here, given that you've already shown this clip shortly before.

Zeus

Otherwise, great! Yes, as others said, it would probably be fair to mention that the efficiency was gained "to a large extent" (or some such) due to these blades rather than just "because". But the high bypass ratio is (to a large extent :) just an extensive expansion, whereas the focus of this video - turbine blades - are actually a marvel.

idanfri

Hopefully I'm not too late. At 26:43 you say that the grain boundaries are the weak points. This is true in the context of creep at high temperatures, but actually the grain boundaries serve a strengthening mechanism at low temperatures where diffusion isn't an issue, but the crystalline mismatch sereves as a barrier for dislocations.