How a turbofan works

[Gnarly Gnu]

Neat animations.... check the site.

 

 

 

[spacesailor]

Looks good, But they dont seem to work if small, as in "light aircraft", and the fuel consumption is out of this world!.

 

The first of them starting with mr Whittle, were very under powered, ending with the Vulcan V bomber.

 

Lets have a reply from a turbine helicopter user, as to Ltrs per hour.

 

spacesailor

 

 

[pylon500]

The Solar T-62 core , typically uses between 60 and 80 litres an hour.

 

 

[facthunter]

The animation is a high bypass axial flow turbofan engine and would be multi spool. Some axial flow engines are prone to stalling, so many smaller ones are centrifugal compressors and are much less sensitive to manage, but probably less efficient. They use lots of fuel unless you get altitude and the smaller ones have to operate at very high RPM. Metallurgy improvements have permitted much higher turbine temps to be used and the efficiency improves with temp and pressure increase. They are expensive compared to the alternative Piston engines where used in the same environment,(turboprop) but many times more reliable these days. PT-6 is a good example. Nev

 

 

[nomadpete]

So, now we see the inner workings of Turbs...

 

 

[ayavner]

the one on tarantulas is pretty cool too

 

 

[spacesailor]

Hi Arther, 70 Lts p hour sure beats a "half-VW hummelbird"s 6 Lts p hour, thats more than the fuel tank capacity of my car!.

 

The Bird's 3,6 Lts p 100 Klms, is much better than my cars 13 Lts p 100Klms,

 

If only I had a brain I could FLY like an eagle.

 

spacesailor

 

 

[mnewbery]

It's all about the Reynolds number. A turbine the size of your thumb feels air molecules like they are ball bearings.

 

The Rolls RB-211 has a compression ratio of 27:1 at sea level but the colder less dense air at cruise allows a compression ratio around 39:1. Depending on the altitude the engine can produce 25 to 30 MW

 

Newer turbines will go as high as 50:1 but the flight level atmosphere is 1:100 as dense as at sea level.

 

The pumping losses on a small turbine are huge because of the effect of the Reynolds number on high speed air travelling through relatively smaller cross sections.

 

Refer this link, page 18 for a deeper understanding

 

The History of North American Small Gas Turbine Aircraft Engines

 

http://books.google.ca/books?id=V0SnFt8JGokC&pg=PR3&source=gbs_selected_pages&cad=2#v=onepage&q&f=false

 

For reference 1 sea level atmosphere is 14.69 pounds per square inch (PSI) or 1 Bar. Petrol engines top out reliably around 55 PSI boost for short bursts, diesels can go a little more. The maximum overall compression ratio would be (let's say 60 PSI boost) 4 Bar x 18:1 or 72:1 less the pumping losses. I'm not going into how or why this is bad for smog production but it really is. A piston warbird will see 60 inches MAP or +1 bar of boost on top of approximately an 8:1 compression ratio but at the expense of TBO.

 

The Solar T-62 is a centrifugal turbine found in the early Chinook helicopter that produces around 80-95 HP for 65Kg but it has a woeful 5:1 compression ratio and only runs at one speed.

 

Often a turbine isn't the best choice for an application, rather it's the only choice. Everything else will still use pistons.

 

 

[mnewbery]

One example of a 4 to 6 tonne helicopter uses 400 Kg or 490 litres of jet fuel per hour. A Boeing 747 on full fuel averages out at one litre per second per engine door to door.

 

In comparison a Bell jet ranger will use 80-90 Kg per hour or a quarter of the fuel to produce one fifth the power.

 

 

[Downunder]

All true, but I still WANT one.......

 

http://www.sonexaircraft.com/subsonex/index.html