muller@gn.ecn.purdue.edu (Mark B. Muller) (02/23/90)
From: muller@gn.ecn.purdue.edu (Mark B. Muller) >From: tek@CS.UCLA.EDU > >Here is a question for you aero experts: > >What are the important differences between turbojet and turbofan >airplane engines? > >My limited understanding is that a turbofan is a turbojet with a >bypass added. So some of the air goes around the ignition area and >then rejoins the exhaust flow. Is there any other basic difference? > Basically, this is correct. The Trubofan gets a some thrust from the air accelerated only by the fan. In the case of a high-bypass ratio turbofan, this thrust is most of the thrust of the engine, while in a low bypass ratio engine, it is smaller. Since there is the addition of the fan, the exhaust of the "core" is reduced in velocity and thrust in order to gain the thrhust from the fan >Why is bypassing a "good thing"? What does it accomplish? > The way things work out, it is more efficient for an engine to accelerate a large amount of air a by a small amount, than to accelerate a small amount of air by a lot, making high bypass ration turbofans with their huge fans significantly more efficient than straight turbojets. >How does changing the "bypass ratio" affect the engine performance? > In general, the larger the bypass ratio, the more efficient the engine. Of course, the price one pays for this increase is a larger engine, and poorer performance in the sonic and supersonic ranges, which is why fighter aircraft typically have low bypass ratio engines. >Does turbofan performance tend to be limited by different factors than >turbojet performance? As stated above, the turbojets tend to be able to have their peak efficiency at higher speeds. >-ted >Ted Kim *-------------------------------------------------------------------------* * Mark Muller Undergraduate at Purdue University * * muller@gn.ecn.purdue.edu Aeronautics & Astronautics Engineering * *-------------------------------------------------------------------------*