Why it's so hard to build a jet engine
construction-physics.com
construction-physics.com
> The engine has one CMC component, a turbine shroud lining its hottest zone, so it can operate at up to 2400 F. The CMC needs less cooling air than nickel-based super-alloys and is part of a suite of technologies that contribute to 15 percent fuel savings for LEAP over its predecessor, the CFM 56 engine.
> GE’s CMC is made of silicon carbide (SiC) ceramic fibers (containing silicon and carbon in equal amounts) coated with a proprietary material containing boron nitride. The coated fibers are shaped into a “preform” that is embedded in SiC containing 10–15 percent silicon.
In a rotating part, subject to high centrifugal forces and vibrations and shocks, I think that the risk of unpredictable fractures may be too high for a ceramic, even a composite one.
Silicon carbide ceramic has low toughness. A composite should be better, but still far from metallic alloys.
I have seen mentions of research about the feasibility of using silicon carbide composite ceramics for rotating parts, with the goal of reducing their mass and increasing their working temperature, in comparison with metallic parts, but it is unlikely that this has reached the stage of being used in production engines.
Ceramics, e.g. derivatives of zirconia, are frequently used for turbine blades, but only as ceramic thermal barrier coatings on metallic blades, not for the body of the blades.
Another interesting thing is some engines cannot withstand certain RPM ranges as the compressor and power turbine can get into a catastrophic resonance. A good example is the T700 (used in the Blackhawk).
What do you mean by "metals don't actually withstand temperature"? As in the raw metal would melt were it not for the cooling vanes?
'If powered down, the engine would destroy itself' - from what? Overheating?
The lower power setting on shutdown does what? Spin it at a low RPM so it doesn't decrease in temp too quickly?
Metals don't need to melt to fail. Increasing the temperature leads to gradual reduction of yields limits. For example, the yield stress of steel drops to 50% if it reaches around 500 degrees.
Another example: “jet fuel can’t melt steel.”
Image search for a turbine blade and you’ll understand as soon as you see it.
The reason you can’t shut the engine down or power off suddenly is because the blades and housing cool at different speeds, the clearance between the blade tips and housing is as close as possible.
To help with this, hot air from the turbine is sprayed onto the outside of the casing via a hot bleed air bypass when the ecm determines its necessary.
If you shut down suddenly the tips of the blades can contact the housing and best case rub, worst case break.
There’s another problem along these lines which really exemplifies how tight these tolerances are, on the a320, you need to do a bowed rotor procedure if you’ve been sitting with the engines off for 45 minutes before you restart. This involves turning the engine over with the apu to equalize the cooling throughout the engine because the core of the engine cools slower but there’s two shafts running through the middle. These shafts “bend” because the outside is cold but the middle is hot, they can then rub against each other ruining bearings etc.
Turbo timers are a legacy from the days when turbos were primarily oil cooled and synthetic oil wasn't common and shutting down a glowing hot turbo would tend to create sludge if done habitually.
This is similar to the rocket engines where the thrust nozzle and its extension are cooled by the fuel otherwise they would melt or fail structurally.
They creep. Have you seen, for instance, Blu-tac or glue fail? It doesn't go at once, but slowly, over a period of time. At high temperatures most metals (others on this thread have mentioned single-crystal blades) behave a bit like that.
Although steel is also weaker at temperatures far below its melting point, yes. A simple observation of a blacksmith at work should tell you that. And a think some new jets may be running hotter than Tm for steel now?
> The lower power setting on shutdown does what? Spin it at a low RPM so it doesn't decrease in temp too quickly?
Yup, or more relevantly evenly, although those tend to be related. Given almost all materials expand as they get hotter and contract as they cool, different cooling rates between parts -> different contraction rates -> different relative shape -> Very Bad in precision machinery.
You have to shut things down step by step, so that rigidity is supplied to the metals as the inertial forces are reduced.
A small addition to the sibling comments: Combustion temperatures in modern turbines are around 1400C, if I recall correctly, but the best nickel superalloys go up to 1050C or thereabouts (for long-term operation). To close this gap, the use of high-temperature alloys is supplemented with active cooling and ceramic coatings, as stated by GP.
To get max performance modern engines run hot, aka ox rich, and the regen cooling is generally not enough. So in addition to that, critical surfaces such as nozzle also get protected by injecting a thin layer of fuel. This biases combustion to be fuel heavy in localized areas which is less hot. Of course all of this happens in an extremely dynamic environment where gasses are moving at 2km/s+.
[1] https://en.wikipedia.org/wiki/RS-25#/media/File:Ssme_schemat...
Oxygen-rich means you have extra oxygen which doesn’t combust. That necessarily reduces performance. Most rocket engines run fuel rich because hot oxygen is a chemical terrorist.
Why do turbines have a static duct and micron tolerances for the blades (and creep requirements) instead of a rotating (attached to the blades) duct that can be tensioned separately, and (presumably) no creep/micron tolerances?
If you had a spinning duct, you'd presumably need a stationary shaft in the middle for mounting the vanes, and would have similar tolerance issues between the tips of the stationary vanes and the rotating duct. There's reasons that it might be easier to solve (the duct can be lower temperature) and reasons it's harder (bearings for a giant spinning duct). Not sure if anyone has tried such a design.
Some researchers from the academic lab where I work have been working on a turbine configuration in which ceramic turbine blades undergo compressive, instead of tensile, stresses in rotation: https://www.exonetik.com/turbo Interesting stuff, but it's a huge challenge to bring entirely new jet engines, as TFA mentions, to certification and market.
> The MT power-to-weight ratio is better than a heavy gas turbine because the reduction of turbine diameters causes an increase in shaft rotational speed. [0]
> A similar microturbine built by the Belgian Katholieke Universiteit Leuven has a rotor diameter of 20 mm and is expected to produce about 1,000 W (1.3 hp). [0]
Efficiency is not fantastic at these scales. But, imagine trying to get that amount of power from a different kind of thermodynamic engine with the same mass-volume budget. For certain scenarios, this tradeoff would be amazing. EV charging is something that comes to mind. If the generator is only 50lbs and fits within a lunch box, you could keep it in your car just like a spare tire. I think the efficiency can be compensated for when considering the benefits of distributed generation, cost & form factor.
One of the other advantages of the smaller engines is that you can use techniques that are wildly infeasible in larger engines. For example, Capstone uses a zero-friction air bearing in their solutions:
> Key to the Capstone design is its use of air bearings, which provides maintenance and fluid-free operation for the lifetime of the turbine and reduces the system to a single moving part. This also eliminates the need for any cooling or other secondary systems. [1]
Does anyone know how the efficiency per liter of engine volume compares to these small turbine engines?
Vegetable oils are nonvolatile, but also generally nontoxic and hence mostly environmentally benign. (You can choke a river or foul ground-dwelling creatures given sufficient quantities, but a few 100 ml won't cause major problems.)
Anti-knock capability of a fuel has very little to do with how "lightweight" they are. Methane, the lightest hydrocarbon and gaseous at any kind of condition you'll find in an engine, has an octane rating of 120. And diesel fuel, substantially heavier than gasoline, as a much lower octane rating than gasoline.
What I was aware of was that early automobiles typically ran on what we'd now call "distillate", which were lighter fractions of petroleum, some just barely liquid (I don't know specific components), with a result that air-fuel mixes ignited readily at low compression ratios (say, 6:1, as opposed to current petrol engines which are in the range generally of 8:1 to 12:1, with some high-performance engines going as hihg as 16:1).
Anti-knock additives (initially ethanol or methanol, later tetraethyl lead, now ... other stuff, including again alcohol) brought up compression ratios and engine efficiency / power. This information I'm remembering from Yergin's The Prize, FWIW.
Diesel operates at generally higher compression ratios, 14:1 to 23:1 per Wikipedia, which I thought translated to higher octane equivalent, but whatever's impeding ignition point isn't that. I know some (most?) diesel engines are fuel-injected, which permits timing of fuel introduction at maximum compression, but not all as I understand.
I'm doing some online sleuthing about this as I'm curious. Volatility itself may play a role, where petrol vapourises whilst diesel aerosolises. The latter is still a fuel-air suspension but with much lower equivalent surface area (and hence, ignition rate) than a vapour would be.
Early gasoline was more or less output straight from the refinery distillation tower, yes. Octane rating varied a lot depending on the quality of the crude oil, but usually something in the range of 50-70. Thus necessitating the low compression ratios on those early gasoline engines. But the volatility of that gasoline was approximately similar to modern day gasoline.
What was then developed were various further processing steps to improve the octane rating of gasoline (and as the demand for gasoline increased, to increase the fraction of gasoline that you could get from a given amount of crude oil), like dehydrogenation, catalytic cracking, alkylation etc. First these were used for producing high octane aviation gasoline, but after WWII these processes were also put into use to produce automotive gasoline, enabling higher compression ratios in cars. Anti-knock additives helped a bit as well.
> This information I'm remembering from Yergin's The Prize, FWIW.
A pretty good book, I hear. I should read it.
> Diesel operates at generally higher compression ratios, 14:1 to 23:1 per Wikipedia, which I thought translated to higher octane equivalent, but whatever's impeding ignition point isn't that. I know some (most?) diesel engines are fuel-injected, which permits timing of fuel introduction at maximum compression, but not all as I understand.
Diesels inject ALL of the fuel during the combustion stroke. During the compression stroke, they only compress air. Which is why they can have so high compression ratios, there's no fuel vapor mixed with the air that may ignite and cause knock or detonation. Due to the high temperature and pressure in the air caused by the compression, the fuel ignites by itself more or less immediately as it's injected. No spark plug needed.
If you think about it, diesels want something which is sort-of the opposite of an anti-knock (octane) rating. You want the fuel to ignite by itself as soon as it's injected, not resist ignition. For diesel fuel this scale is called the 'cetane' rating, FWIW.
> I'm doing some online sleuthing about this as I'm curious. Volatility itself may play a role, where petrol vapourises whilst diesel aerosolises. The latter is still a fuel-air suspension but with much lower equivalent surface area (and hence, ignition rate) than a vapour would be.
I believe you're sort-of right here. Diesel fuel is injected under high pressure, modern common-rail injection systems reach injection pressures of up to 2000 bar FWIW, which causes the fuel to be atomized into small droplets. The actual burn process AFAIU is sort-of a liquid burn process where fuel vaporizes from the droplets and immediately ignites.
On The Prize, it's really phenomenal, and that's from someone who disagrees pretty strongly with Yergin on his general cozyness to the petroleum industry and enthusiasm for its future prospects. As a history the book is a brilliant work, there's an accompanying PBS/BBC miniseries, and the wealth of information contained (and number of head-turning new-to-me revelations) can't be briefly described. If you're into that sort of thing, I'd also recommend as much of Vaclav Smil as you can stand, though would suggest starting with Energy and Civilization, a look at human history through the lens of energy.
The octane ratings you give are about what I recall from Yergin's description (if that's where I first heard it, again, somewhat vague decade-plus recollection).
My understanding of diesel ignition is somewhat informed by WWII-era triple-expansion steamships, which burned bunker fuel, that requiring a lot of heating (utilising spent steam) just to get it flowing toward the boiler, then again getting toasted immediately before going into the burners. External combustion, obviously, but the challenge of getting a very nonvolatile fuel to burn left an impression. That engine room visit left an impression as well....
Otherwise, appreciate the additional knowledge, it fits pretty well with my own weaker understanding. Interesting especially about cetane. Looking that up, the name comes from Hexadecade, a/k/a C16H34, or a sixteen-chain hydrocarbon (double the carbon-atom count of octane, a/k/a C8H18).
<https://en.wikipedia.org/wiki/Hexadecane>
<https://en.wikipedia.org/wiki/Cetane_number>
And for octane: <https://en.wikipedia.org/wiki/Octane_rating>
Yes, bunker fuel is very much non-volatile stuff. As an aside, they did eventually figure out that you could run slow-running big diesel engines on that stuff too. Perhaps you've seen pictures of such massive engines big as houses, if not e.g. https://www.youtube.com/watch?v=K30_jf-aA_U
These big diesels have some things in common with the old triple-expansion steam engines, e.g. they are directly connected to the propshaft (and thus they turn slowly, about 100 rpm max or thereabouts), and the engines themselves are reversible, so there's no need for any reduction gearing or gearboxes.
Similarly to steam ships, they need steam lines in the fuel tanks to heat the fuel so it can be pumped, and then further heated to 130C or thereabouts in order to be injected. So they need a small auxiliary steam boiler just for producing the steam to heat the fuel; modern ships often have an 'exhaust heat recovery boiler', which as the name implies utilizes the hot exhaust from the main engine to produce the steam, so that the auxiliary boiler isn't needed when the main engine is running.
Yeah, soaking your sleeping bag with canola oil would be a pretty bad problem. But a methanol or ethanol spill can also do significant damage.
Xylene or citrus terpenes might be nicer, even if the lethal dose is lower than for ethanol.
I’m saying this as someone in the aviation industry. Turbines are amazing pieces of machinery and incredibly reliable, BUT incredibly expensive to operate.
They require all kinds of specialized maintenance and what I would call “exotic” oils that won’t break down in the harsh environment.
It’d make a really great generator for a vehicle, but I don’t think the economics will work out for a family car anytime soon.
They'd certainly be quieter than a microturbine and not need fuel brought in.
This is an idea that needs to go away. We should not burn food for fuel, and there are a lot of externalities in growing corn and then turning it into ethanol that people are not considering.
Corn-based ethanol is just a very inefficient form of solar energy. Use solar panels instead and skip the middleman.
It's not that stupid, we still have many millions of people in utter food insecurity, and not just in the "third world" but also across our Western nation.
IMHO, people should come before cars when it comes to distribution of food, and we should electrify automotive to get rid of the entire issue anyway. What few renewable fuels we have, we will sooner or later need to power air flight and ocean-crossing ships, as we do not have any alternative to some sort of combustible fuel for either purpose.
As an aside, corn ethanol is not made with the type of corn that could be used for human consumption. We could use those same fields to produce human food, but refer back to the first paragraph of this post for why we don't do that.
A diesel ICE engine can be surprisingly efficient and is not particularly expensive compared to a turbine.
You can also run a diesel engine on green fuels.
Reliability, efficiency/cost of operation, and noise is probably the priorities that come way ahead of weight.
Compared to reciprocating engine-powered CHP, they tend to produce a slightly higher proportion of their energy output in the form of heat than electricity, and the plant is about about 60% of the volume and half the weight - so they make most sense in constrained spaces or for rooftop installations.
Turbos float on a layer of motor oil, and have a crude design compared to combustion-sustaining turbines.
A Falcon 9's Merlin 1D engine is reported to cost $400K. Its jet kinetic power in vacuum is 1.5 GW, in an engine with a mass of ~500 kg.
$0.27/kW is insanely cheap for a heat engine.
There are likely some compromises engineers can make when the engine is only running for that amount of time with refurbishment in between each 6 minute runtime.
High rpms, noise and the difficulty in adjusting the power output quickly, killed the project.
Well, I'm dumb, it says max motor RPM 8500, so I don't think you'd get close to what's needed as a generator :D
20:1 reduction gear, off you go.
Their idea was cogeneration, but I’m not sure if the math works out if you have a low efficiency turbine. We just usually don’t need that many BTUs to run a water heater and furnace versus electricity to run everything else. And with heat pumps becoming more of a thing that’s just becoming more apparent.
[1] Turbine Overview: https://www.powermems.be/gasturbine.html
[2] Turboshaft Setup: https://www.powermems.be/Turboshaft.html
[3] 1,200,000 RPM on Aerodynamic Bearings Test Runs: https://www.powermems.be/Pen_setup.html
There's a little bit further from the author (Tobias Waumans) afterward, yet not much publication [4]
[4] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C13&q=T.+...
Mostly a summary pub on the work on the aerodynamic bearing setup in Journal of Micromechanics and Microengineering [5]
[5] Aerodynamic Bearing (pdf): https://lirias.kuleuven.be/retrieve/160403
Electric propellor planes have similar problems at high altitude that you're pushing thin air.
What are the efficiency gains you're thinking about?
In any case, electric engines don't need oxygen.
Coffin corner is a real thing.
Theory != Practice. If that were the only variable, then yes. Electric would be great. But it's not. It's far from the only thing in play. Lift also suffers from thinner air. Pure electric (as-in battery/solid state energy storage) could have 100% efficiency (specifically in converting prop/turbine torque to thrust of moving air), and it'd still have a terrible efficiency problem with current day tech.
Electric's primary efficiency and efficacy issue is regarding the total operating weight of the aircraft compounded by how that weight does not meaningfully decrease as the battery banks are depleted as compared to consumable fuels. Weight is your biggest enemy in flight, not power nor mechanical efficiency.
Hybrid electric (be it consumable fuel through a generator or fuel cells) is much more promising, but rarely what people mean when discussing "electric propulsion" (without the hybrid qualifier), and still has issues of it's own.
They are air, oxygen really, constrained.
You are right that the electric motors themselves won't suffer from the same oxygen starvation, but as the other commenter noted, the props or impeller blades will. They need something to push, there isn't much up there.
I'm not sure how it has to do with electric propulsion, though - I'd think systems like NERVA is a more exciting solution in this kind of domain(jk).
Short haul passenger flights are not about speed but about getting directly to the stopover, without the unpredictability of ground transport. A "powered glider" with separating assist for the climbout could be a great match for that task.
And the tug would obviously not really be a tug, but a winged battery directly attached to the aircraft it supports, with barely enough wing for a controlled return. An electric drop tank. Not exactly unheard of in military aviation (except for the "electric", obviously)
Fighter aircraft are generally built for speed and have (even relative to commercial aviation) often fairly low range. The equivalent to "tugging" would be external jettisonable fuel tanks, and we have seen those in military use since at least WWII. Given the general lack of electric propulsion in military use, that seems reasonable. The other model has been JATO packs applied to both fighter and cargo aircraft (Fat Albert, a C-130 Hercules, is often fitted with these for air-show demos). Not electrical power, but an external boost assist.
For drone craft, there are deployment scenarios in which a large cargo plane drops (electrically-powered) drone swarms. I don't know the extent to which this has been deployed, but again it's similar.
If a military were to adopt tugs, I'd expect them to be applied to drone or cargo missions, either with a drone tug (similar to the cargo-plane model above, but possibly with remotely-piloted / autonomous tugs), or with some capability for lofting a battery pack that could be detached and flown back to the take-off site after contributing to initial take-off and climb. That is complicated, but might fit certain mission profiles, and for a relatively slow long-haul cargo mission might make the cut.
Worth also noting that most EV aviation concepts are for relatively modest cargoes and distances. The more viable range from 2--12 passengers for perhaps 100--200 km at low speeds. I've seen some more ambitious proposals, but they strike me as not especially viable.
Turnaround time for planes is short enough that you’d need to do a battery-swap rather than a battery-charge anyway.
A winged battery which could drop away at ~FL20--30 or so and return to either the origin field or some secondary collection point might be all you need, rather than tossing batteries out the cargo bay throughout the flight.
I also suspect that most EV aviation will be shorter haul such that a large set of drops wouldn't be necessary.
Without doing hard calculations, it intuitively feels pretty marginal potential flight weight savings for the operational complexity it would add
[1] https://aviation.stackexchange.com/questions/47262/how-much-...
Worth noting that EV aircraft flight segments are likely far shorter (100--500 km, maybe at a stretch 1,000 km, not the ~5,000 km of JFK->LAX), and cruise much slower (~100--300 knots, say), so climb-out would be a proportionately larger share of the energy budget.
And ditching 20% of your energy storage mass immediately on attaining altitude would still be a considerable savings for the remainder of the flight as that mass doesn't need to be kept aloft.
EV aviation (and aviation itself) is a battle of thin percentages. EV aviation itself has relied strongly on materials advances (advanced fibre composites), and reducing crew (ultimately: autonomous piloting). The need for cabin crew for safety reasons remains, and would be a significant hurdle. The extent to which non-revenue occupants and payload can be minimised likely plays a huge role in any eventual success. A 19% reduction is nothing to be sneezed at, if it can be achieved without significant other compromise.
Not sure about electrifying engines for slower planes, that currently use turboprops. Would that be an electric prop too?
General aviation is still running on pistons. Not because small jet engines can't be built, but because they don't get cheaper as they get smaller. 6-passenger bizjet sized engines seem to be the lower economic limit.
Williams tried and tried. They built good small jet engines, all the way down to jetpack size, but those never got cheap.[1] There are "very light jets", but the smallest in production, the Cirrus Vision Jet, is around US$2 million.
https://turb.aero/ (latest news is from March 2023, not sure the company is still afloat?)
https://www.turbotech-aero.com/
Interestingly, the turbotech engines at least are recuperated engines, which is kind of unusual. But they claim it's necessary to get decent efficiency of such a small engine.
Exactly. It's bad enough with conservatively engineered piston engines. Adding apex seals is gonna make it a whole lot worse.
* High RPMs are bad in a aero engine. There are very few (no?) propellers on GA airplanes which operate above 3k RPM, so you need a reduction gearbox. That cuts into your weight savings and also reduces reliability.
* Vibration isn’t a significant concern for GA airplanes.
* Throttle response is not a significant concern in GA-sized reciprocating engines.
* Poor efficiency is a major problem because 1 lb of extra fuel is 1 lb less payload. All airplanes are limited by takeoff weight. (The 3000 HP-class radials built by Wright and P&W at the end of WWII are some of the most efficient reciprocating engines ever built)
* Maintenance is a huge concern for GA owners because labor costs $200/hr. Airplanes with 1200 TBO engines sell for a noticeable discount to airplanes with 2000 TBO engines.
> fatigue failures around its rectangular windows caused two crashes, resulting in it being withdrawn from service
While the accident investigation reports refer to "windows", which really doesn't help matters, the failure point was the ADF antenna mounting cutout. The passenger windows had rounded corners and did not fail in service.
The Comet was not withdrawn from service, they re-engineered and launched the Comet 4 (with oval windows, but that choice was to reduce manufacturing costs) in 1958, but the Boeing 707 was introduced that year and the DC-8 in 1959, ending the Comet's status as the only in-service jet airliner it held between 1952 and the grounding of the Comet 1 in 1954. The Comet 4 continued to fly in revenue service until at least the mid 1970s with lower-tier airlines.
The decision to bury the engines in the wings was one of the deciding factors for airlines - engines in nacelles are easier and cheaper to service and swap if required. Re-engining the Comet 4 to new more efficient turbofan engines the DC-8 and Boeing 707 introduced in 1960 and 1961 respectively required a new wing, but a podded engine was much easier to swap on to an existing airframe and this was done for many of the Boeing and Douglas aircraft.
The last Comet-derived aircraft - the Hawker Siddeley Nimrod - flew until 2011 in the RAF. They did look at upgrading them with new wings and avionics, but the plan was scrapped when they discovered that in the grand tradition of British engineering every fuselage was built slightly differently and they couldn't make replacement parts to a standard plan.
Anyway that's my rant in to the void today :)
They did have a "best of" collection at one point, not sure now. Also a lot of flight test stories, ATC stories.
They're extremely easy to build, having no moving parts, and only requiring some steel tubing, a welder and a large propane tank. I've already done it and can attest to this being true.
The "best" part is that they're incredibly, obnoxiously loud. Like wear earplugs and ear muffs at the same time loud. Efficiency isn't great, you can expect maybe 20-100 lbs thrust from larger models but I suppose that's more than enough for "let's grab an old bicycle and do something really stupid" (oh and look pulsejets up on youtube for sure, it'll open up a whole world for you in under 20 minutes)
A great DIY from a great YouTuber
Cheap rockets can be vastly simpler than turbojet engines. Reusability (I'm talking about reusability of an orbital rocket, suborbital reusable rockets can be rather simple, as e.g. Armadillo Aerospace and Masten Space achievements show) adds a lot to the order, but increasing the size the square-cube law improves things to an extent.
The more complex rocket engine includes a pump. But today it's feasible not to make a turbopump, but instead use electric pump - batteries get better, and Electron rocket from Rocket Lab uses this approach for years already.
With jet engines you necessarily have to accept incoming air, compress it and burn with fuel - otherwise it's not a jet engine. Batteries are unfortunately still a bit heavy, so electrical aviation is just getting off the ground slowly.
An electric pump still sounds much more complex than a jet engine, which has, I believe, one moving part to both compress that incoming air and harness the exhaust. Admittedly, it's a moving part subject to high stresses, high temperatures, stringent balancing requirements, and demanding aerodynamics, so the larger number of parts in the electric pump might still be easier to make.
Ultimately I think long-distance aviation will probably get electrified by way of abundant renewable energy powering electrical synthesis of synfuel on the ground which its engines burn.
You most certainly can, and it was done. Why do you think otherwise?
> The liquid will just stay in the tank unless there's something pressurizing it to a higher pressure than you achieve inside the rocket's combustion chamber, won't it?
True, but you can have the pressure in the tank bigger than in the combustion chamber, right?
> An electric pump still sounds much more complex than a jet engine, which has, I believe, one moving part to both compress that incoming air and harness the exhaust. Admittedly, it's a moving part subject to high stresses, high temperatures, stringent balancing requirements, and demanding aerodynamics, so the larger number of parts in the electric pump might still be easier to make.
Yes, the additional materials requirements and others can make single rotating part harder to get right than electrical parts, which can be developed independently from the rest of the system.
I guess you can if people have done it. I've never built a rocket myself, so I don't know, but I thought the combustion-chamber pressure had to be crazily high to get the high exhaust velocity you need for propulsion.
Thank you very much for enlightening me!
French Diamant rocket, the one used to launch their first satellite, had a pressure-fed first stage. Lunar Expedition Module from Apollo program had a pressure-fed ascent stage.
This occurs in a broader cultural context. A society that dreams, enjoys science fiction, rewards hard study of advanced topics and so forth, can produce the work force to staff companies capable of going to the stars.
Let us encourage that.
Russia in contrast didn't develop its crewed spaceflight capability, it uses the technology left from the USSR. Russia maintains that technology, but progress with the improvements is rather slow. So Russia wasn't lagging in a sense of having - and using - a technology, but definitely was and is lagging in a sense of developing a new technology.
As we see, the lagging of US - in a sense of having and using a technology - was for 9 years, and lagging of Russia - in a sense of having and using technology - for now is about 5 years.
In a sense of developing new crewed space technology Russia is lagging roughly since the dissolution of the USSR, so 30+ years. There were quite a few attempts - again, in crewed space technology - but little results.
I think we can date the US's crewed-spaceflight inferiority to Russia to roughly 01972, when Apollo ended; Russia had launched the first space station the year before, and though the US would briefly operate Skylab in 01973–4, but would not catch up to the Russians again in crewed spaceflight until 02020. The Space Shuttle boondoggle made it possible for sufficiently motivated people to deny this until 02011.
But the Shuttle was capable of solo flights for couple of weeks without adverse effects of Soyuz - that is, Shuttle was bigger, and that's useful.
Shuttle brought the bigger crew - more than twice bigger, so there could be better specialization and division of labor, and even the amount of tasks done per unit of time.
Shuttle brought significant payload capability - so the crew could make final preparations before the payload would be launched. Similarly Shuttle can "dock" to Hubble to service it. Or crew could work on orbit in SpaceLab which Shuttle carried to orbit and back. Those are advantages.
Shuttle was more gentle in landing - of course, when things went well. Landing on the strip without passing significant acceleration moments before that - that's another advantage.
I don't think SU and Russia had technical superiority over US - except admittedly safety of the Shuttle, and except those periods when US hadn't have the capability at all. Safety is a big item, so Russia can claim superiority for this reason, and also for simplicity and cheapness, but better US solutions - e.g. with Crew Dragon - suggest it's normal that flying to space better - for many reasons, some of which are shown above - may be either more expensive or will require significant changes, like e.g. modern America companies are pushing.
Now Russia doesn't have much of superiority left, and little capabilities to attain it, or at least it seems so. It's arguably better to have the ability to develop to the needed level, than just to carefully preserve achievements of the past.
Those Russian engines were so good that the US has bought a lot of them and used them many years after they were made.
Certain American manufacturers have ..... been making smaller engines that they can mass produce and have gone taken the efficiency approach a step further.
American Saturn-1 had 8 H-1 engines on the first stage - Wernher von Braun wasn't against putting a bunch of existing engines when he hadn't have a bigger one.
> They were also pretty efficient.
It's pretty impressive SpaceX made full-flow combustion engine to work. Does it improve things enough to justify the complex development? I'm not sure - the Isp isn't that great comparing with even some kerosene engines, and oxygen-rich turbopumps would deliver similar results with less complex development program. On the other hand Raptors are perhaps a good deal in a long term.
For comparison there were apparently 30 NK-15 engines on the first stage of the N1. (from Wikipedia of course)
What I did read somewhere was that they had a production line and they filmed it all so they could see what happened to any engine during production and go back to the recordings if something went wrong with it.
I'm not a Russophile at all, but I suspect that there were clever people who solved problems and others quietly took note of it.
While a portion of air progresses through the turbine, it passes through the phases of the cycle.
During the first phase, the air passes through the compressor section of the turbine, where it is compressed adiabatically. During the second phase, fuel is added to the air and it burns, heating the air, which expands at an approximately constant pressure. During the third phase, the exhaust gases pass through the expander section of the turbine, being expanded adiabatically.
The last phase of the cycle, which closes the thermodynamic cycle, by reaching the ambient temperature and pressure, happens in the external atmosphere, for the exhaust gases. The meaning of this phase for an open-cycle engine is that its computation provides the value of the energy lost in the exhaust gases, which reduces the achievable efficiency.
This thermodynamic cycle, which approximates what happens in a gas turbine, is named by Americans the Brayton cycle, even if the historically-correct name is the Joule cycle.
(George B. Brayton has patented an engine using this cycle in 1872, without explaining it, but James Prescott Joule had published an article analyzing in great detail this cycle, “On the Air-Engine”, already in 1851, 21 years earlier. Moreover, already in 1859, a textbook by Rankine, “A Manual of the Steam Engine and other Prime Movers”, where all the thermodynamic cycles known at that time were discussed, attributed this cycle to Joule, 13 years before the Brayton patent. Not only the work of Joule happened much earlier than that of Brayton, but the publications of Joule and Rankine have been very important in the development of the industry of thermal engines, unlike the engines produced by Brayton, which had a very limited commercial success and which had a negligible contribution to the education of the engineers working in this domain. Therefore, the use of the term "Brayton cycle" does not appear to be based on any reason, except that Brayton was American and Joule British.)
Oh but there is. I would love to see more European alternatives to US designs even at 5% less efficiency and power. Surely it can’t be that expensive to create an engine in 2025 similar to the state of the art 2005, when you have all the hindsight plus unlimited access to the original design?
Events of this week show that this will be very important.
Europe does have enough aerospace talent to make a jet engine especially at the cutting edge, but there's a significant amount of tech transfer between the US and Europe happening at the same time.
The manufacturers market share should be led by CFM with 44% followed by Pratt & Whitney with 29% and then Rolls-Royce and General Electric with 10% each.
1: https://en.m.wikipedia.org/wiki/List_of_turbofan_manufacture...
See Thru Jet Engine [video] - https://news.ycombinator.com/item?id=32145297 - July 2022 (70 comments)
A commercial engine can operate for a cumulative 1 year between overhauls, according to that figure, as of 2010. The military ones last 1/10th as long. I can only imagine how much more challenging it is to iterate on designs when you are dealing with problems that take 10 times longer to manifest.
[1]: https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_pr...
Where is Russian Sukhoi?
It will be interesting to see if UAC emerges as a serious competitor to Boeing and Airbus (and COMAC) in the near future.
[0] https://rostec.ru/media/news/rostekh-peredal-partiyu-seriyny...
If the Russians manage to do this, it would be another example of the stupidity of the sanctions.
I bet COMAC is cheering them on too.
Furthermore, the sanctions demonstrated that there is sovereign risk associated with purchasing Western airliners.
Finally, IIRC the airline's regrets were largely related to the poor early reliability of the French-built parts, specifically combustors, for the Superjet engines. It remains to be seen how the new Russian engines will perform.
And airlines in most countries have far more to worry about buying aircraft whose maintenance depends on a faraway pariah state and that are not certified in Europe than they do about US sanctions targeting them. And even if they do, still not necessarily more difficult to circumvent the sanctions (as Mahan Air did with wet leased 747s) and access a worldwide parts supply and MRO market than rely on being able to maintain and sell on your Russian aircraft at reasonable price and timeliness...
It would also be surprising if the new Russian engines were competitive on performance with new Western engines, and likewise with other components they've had to switch to domestic manufacture for.
By that you mean a state sanctioned by the US and the EU, which together comprise about 10% of the world's population.
Even Iran is flying old Western aircraft
Trust me, we're not rushing out to buy shitty Russian aircraft as a hedge.
The Wikipedia page on Bombardier is ... not especially clear about present ownership, though apparently debt incurred developing the CSeries (Airbus 220) aircraft lead to spin-outs of much of the core business, including large shares (50% and then another acquisition) of CSeries ops by Airbus.
<https://en.wikipedia.org/wiki/Bombardier_Inc.>
The top of the article seems to portray Bombardier as an independent company, other bits not so much.
Shortly thereafter, Airbus came in and acquired a controlling stake of Bombardier Aviation, took over the CS planes, and agreed to manufacture them in the US (Airbus manufacturing is in the EU).
The way it played out seemed to me as if Boeing and Airbus conspired to kill off a viable competitor after they saw how well received the CS100 and CS300 were.
This is all on top of the overall financial troubles the company was facing.
I could be entirely off the mark, so I will let those more knowledgeable chime in from here.
De Havilland was owned by Bombardier, but Viking Air bought De Havilland's designs and Dash 8, and renamed the holding company De Havilland.
There are many variants of [the French Microturbo TRI 60] engine and it is used in many missiles and UAVs, as listed below. Aside from the known uses listed below, it is widely speculated that Iran illegally purchased many TRI 60 engines from Microturbo to assemble C-802 cruise missiles purchased from China. It is unclear which variant was purchased. Iran also reverse-engineered this engine as the Toloue-4 turbojet engine. Toloue-4 is used in several Iranian military equipment including Iran's copy of C-802, the Noor missile.
It's fascinating how many engineering artifacts turn out to have been invented just once. This is the same engine used in Storm Shadow / SCALP EG, so both sides in the Ukraine war are firing variants of a 1970s miniature French jet engine at each other.
What's hard is to build a competitive jet engine. And there, it happens naturally, by itself: the best marketable jet engine is the one where marginal increase of complexity and cost matches marginal fuel savings: buy simpler/cheaper ones and you waste more money on fuel than you save buying the engine, buy a more complex/expensive one and you don't justify the costs with your fuel savings.
Because an engine runs for tens of thousands of hours - some over 100K hours - so 1% of performance improvement is worth ~1000 tons of fuel - there is a lot of complexity that can be pushed into the solution while still being profitable - and competition ensures this is the case.
That's why it is incredibly hard to make a competitive jet engine.