A Little Gear That Could Reshape the Jet Engine
bloomberg.com
bloomberg.com
The reality is probably just that this is a solvable problem that just wasn't worth the work while there were easier efficiency gains to be had.
Yes, everyone knows that, but the spools are not connected by a set of gears as they are in the P&W's new engine.
> Also, as the article mentions, turboprops (essentially jet engines connected to a propeller) already commonly use gearing. I guess you can think of it as a turboprop with a duct.
The new engine is ALSO unlike most installations of turboprop engines in that the fan is driven by the power spool, not a free turbine. The free turbine (in turboprops that have them), which powers the reduction gears for the propeller, runs at a much lower speed than the power turbine.
The whole purpose of decoupling the fans is to give you an even higher bypass ratio - two or three large electric fans driven from one turbine can have a larger swept area than a single large geared turbofan, so can run slower for the same thrust, and hence be quieter.
The noise comes from high speed air alongside slow moving air. A high bypass fan moves more air at slower speed to get the same push. The slower speed means less noise.
One real advantage would be quick throttle response. Gas turbines are slow to ramp up output power which is a real problem when dealing with wind shear on takeoff and landing. A 30 knot wind shear turns your 140 knots air speed turns into 110 knots airspeed. An electric fan's response would be very fast, probably faster than a prop plane.
I don't think you can. The large volume of airflow surrounding the turbine is what makes it a turbofan[1]. Without, it is a turbojet[2]. The airflow from the turbofan surrounds the hot exhaust gas and it is much quieter than the turbojet.
But, other than noise, the rest of your comment makes a lot of sense to me. But I know very little about this stuff.
[1] https://en.wikipedia.org/wiki/Turbofan [2] https://en.wikipedia.org/wiki/Turbojet
Turbojets derive all of their thrust from the turbine exhaust. It's a small, compact engine, which means high power-to-weight ratio, and it's great for small jet fighters. Unfortunately, it also consumes a lot of fuel. Turboprops are at the other end, where the turbine drives the propeller at much faster speeds than a regular 4-stroke engine would. But the exhaust provides next to no thrust.
Turbofans sit in the middle. They provided much better fuel efficiency than a turbojet but greater power than a turbofan. It was very much a "we need a middle solution" type of engine.
As turbines became more efficient and compact, the turbofan became smaller as well. To the point that they could be places on a fighter, but with a smaller bypass ratio. This gives much better fuel efficiency (range), while still retaining high power.
For jetliners, it's all about efficiency, but still retaining a degree of speed. But for a really high-bypass turbofan (50% or more), it's going to be a huge engine. Fighters are between 15-20% now, but you won't see much more than that.
https://en.wikipedia.org/wiki/Bypass_ratio
Tom Clancy wrote a book many years ago in which he discusses this in laymans terms really well: http://www.amazon.com/Fighter-Wing-Clancys-Military-Referenc...
You're mistaken. Prop speeds are comparable between piston and turbine engines. Bigger, slower moving props are preferable. When prop tip speeds approach the transonic region, on either turbine or piston power plants, efficiency goes south.
And BuffloBagel is right, I got that part wrong. I think what I was trying to say is that a turboprop supports faster aircraft speeds than a traditional engine. But yes, the propeller remains subsonic.
Unless you're experimenting with madness: https://en.wikipedia.org/wiki/Republic_XF-84H
Edit: So apparently the Tu-95 does have supersonic turboprops. But I think it's the only production aircraft with them. Also, it's loud as hell. https://en.wikipedia.org/wiki/Tupolev_Tu-95
One Jet engine providing power and thrust and six electric fans along the wings for additional thrust. They have also added batteries, so the single jet engine doesn't need to be big enough to provide full take off power + redundancy. Currently jets require at least 2 engines, each large enough to complete the take off if the other fails. With this system you would need either the jet, or the batteries + fan to complete takeoff in the case of a failure in the other system.
http://www.airbusgroup.com/int/en/news-media/media~item=be67...
http://eandt.theiet.org/magazine/2014/10/rise-of-electric-ai...
And 300 volts is not considered high voltage.
If they upped the voltage to 1,500v (which is the limit before you need much more complicated stuff) it's only 10amp - a simple thin wire would do it.
They'll actually need some very high voltages to make this work. That's going to be an enormous challenge - even simple motor windings, what will you insulate them with?
15MW? That's some serious power, are you sure about that number?
If you watch agentjayz on YouTube he rebuilds turbojets that have been converted to become gas generators for power plants and some of those are easily capable of generating 30000 hp using tech from the 60s.
It really is phenomenal how much power turbine engines can make. There is a thread on the Concorde [2] that goes through a q&a session with the people who operated it. In that thread it says that the engines at idle consumed some 5 metric tons of fuel per hour per engine.
1: http://www.aerospaceweb.org/question/propulsion/q0195.shtml
2: http://www.pprune.org/tech-log/423988-concorde-question.html
> “In other years we hid him [McCune] behind the curtain and slipped him some sandwiches so management wouldn’t know what the investment was,” he jokes.
Maybe a decades-long attention span wouldn't have been required in the first place if the company in question gave their engineers better support.
1. Can/are jet engines ever swapped out after a plane as been put into service? Or will these only ever be sold attached to new aircraft orders.
2. Any idea on what the engine costs? And what percentage of the overall airline cost is engine? I didn't see any references to costs of this engine vs existing models.
Aircraft safety margins are 1.5 (built to handle 1.5x the maximum expected load), while bridges are 5+. The latter aren't constrained by weight, so you might as well go to town with a cheap, heavy design. A lower safety margin is only acceptable though when the expected loading is extremely well defined with very low uncertainty. This takes extensive testing (years for an aircraft), basically reducing the sigma by increasing the sample size.
The engines will be somewhere north of $10m each, but since replacement of parts at required intervals will also cost several million dollars the airlines will look at total cost of ownership to take into account differences in frequency and cost of replacement parts, probably with a health risk premium for the new technology. Comparing that with existing models is more complex, and of course fuel economy savings depend very much on the routes you intend to operate. The engines alone will be worth more than a typical 10-15 year old narrowbodied aircraft (with its engines, midway through maintenance cycle)
http://theflyingengineer.com/flightdeck/pw1100g-gtf/
The gearbox is described as the epicyclic type with the compressor driving the sun gear and the carrier of the five planet gears driving the fan. The article doesn't seem to identify any extra special sauce. It points out that geared turbofans have been used on an airliner in the past, and identifies some design trade-offs. "there may be a performance penalty, marked by slower cruise speeds for the same thrust setting, possibly slower max cruise speeds, slower green dot (best L/D speed), slightly shallower climbs, and possibly degraded single-engine performance. The single engine performance difference is expected to be the most prominent, with a possibly larger yaw, and a definitely reduced climb gradient, consequently lowering obstacle clearances."
My impression based on just reading that article is that, rather than a technological breakthrough enabling the geared approach, Pratt and Whitney have explored a rather neglected area of the design space, to arrive at a more efficient, lower noise engine with slightly worse performance in some other respects. And had to conquer numerous 'ordinary' engineering challenges to make it work.
Move to short and fatal flaw kills people? ZOMG KKKORPORTATION$!!!
Can't win for losing...
Yep, that's how UTC operates. It's amazing they make any money at all.
The fact the product benefits from faster innovation is a function of more efficiently sharing knowledge and data, not spending less time on individual components.
Designing and testing an engine can be done in an agile style. There's nothing intrinsically "software only" about the methodology.
NB: I ran a startup that made software to manage requirements in big projects. I've spent lots of time thinking about different ways to manage things. Including how not to, but that was after we failed.
The only difference for a SaaS startup is that they're their own customer for product development (in the sense that they build and test in-house rather than someone else paying them to build a product). The cost of failure is still there, it's not measured.
It's weird when I realize I can just push something out the door and not have to wait for the reams of paperwork to be complete.
I read a book recently about the history of Supermarine, and what jumped out was the attrition rate of their test pilots. Ditto for the post-war British jet industry.
There is a trade-off point between safety and fast development, but I'm glad we've moved to the side of safety.
Selling thousands of engines too soon and realizing they all suffered from a critical engineering issue could bankrupt your company. There's a lot on the line!
Not only that, they have a bad habit of adopting disproven solutions simply because they 'are mature'.
That is I believe Musk's premise with his rocketry division. It couldn't possibly be this complicated, can it? I hope he turns out to be right. But if he is, gonna be a lot of smug engineers having to take early retirement.
One hull loss per nineteen attempts is not an acceptable failure rate for "the airplane industry", is it? It's difficult for me to put into words the level of respect and admiration I have for the risk-averse, plodding, and methodical aerospace culture that has created modern aviation. (Seriously, have you ever considered the absolute miracle of engineering that is a modern jetliner?) To lump that profession under the same rubric of engineering as the one where a bunch of overcaffeinated "disruptors" write software to get people to click on ads seems... unjust, to put it mildly.
What I meant to convey is that I expect someone to do to commercial aviation what Musk is trying to do to rocketry, and what I expect that to look like is for more effort to be placed into reducing single points of failure by designing complementary systems instead of just putting three of everything on the vehicle and then adding two more layers of stuff to manage it. And also for them to act like progress in software development processes actually applies to them now instead of in thirty years. We got no end of grief for refusing to do pure waterfall, and they were conspicuously silent when we're were able to fix fundamental up front design flaws in 3-8 weeks, and without doing a reenactment of Macbeth starring William Shatner, set in a rehab clinic.
Then again, I expect something to happen to improve the caliber of software developers out there as well, so we'll see how that goes. Often when I expound on the qualities of my profession I am intentionally and consciously imagining that the 30% of my peers that are responsible for 70% of our problems either don't exist, or are off doing something that's not important.
Who the hell is running their analogy department?!?
"Thirty years! That's a big number! We need some kind of comparison that will instantly give the reader perspective. Of course, in this, as in so many other things, the answer lies in pachydermian pregnancy patterns."
~ 0.36 x orbital period of Uranus
~ 1.02 x orbital period of Saturn
~ 5.7 x half-life of colbalt-60
source:
Tough luck... he'll have to adapt just like everyone else. Or go on a strike right with those taxi drivers.