More efficient: prop or jet?

caliginousface

caliginousface

Frank N. Beans
Hey all,
Had a friend ask me, a plane a prop and jet of similar size, which is more efficient. Would like to hear more than just opinion if that's not too much to ask. Thanks!
 
caliginousface said:
Hey all,
Had a friend as me, a plane a prop and jet of similar size, which is more efficient. Would like to hear more than just opinion if that's not too much to ask. Thanks!
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depends. long haul its more efficient for a jet, short haul its t-prop time.

watch the new dash 8 -400's blow the doors off 50-70 seaters on short hauls
 
Depends entirely on the mission. Type of flying I do - coast to coast & international - there is only one choice, and it has to cruise above .80M.
 
Thanks for the answers btw, but he wants more that I can't give him (I'm a bad lover?).

So...Why is a prop more efficient for short hauls. Why can they fly faster arrivals and/or approaches?
 
Why can they fly faster arrivals and/or approaches?
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The ole' shiny jets are much slicker through the air and therefore make it much harder for them to slow down so they generally have to start slowing down miles before a t-prop would.

T-props have the huge props sticking out there that create massive amounts of drag and weight and it makes the airplane much easier to slow down if desired, as well as having the ability to move the prop angles to also help you in slowing down.

In lamens terms ;)
 
Depends on your definition of "efficient". The PC12 can carry more gas than most people have space in their bladder, that can be called efficient. A DC8 can carry about 95,000#s about 4500 miles on 150,000 pounds of fuel, that can be called efficient.

Time and fuel used aren't always the best benchmarks, but they are probably the most common.
 
caliginousface said:
Hey all,
Had a friend ask me, a plane a prop and jet of similar size, which is more efficient. Would like to hear more than just opinion if that's not too much to ask. Thanks!
Click to expand...

Depends on how far you'd like to fly!

Jets whizz a lot of gas below the tropopause and you don't enjoy the economics of a jet until you're able to get up high and cruise for a long time.

Turboprops are very efficient in the teens and low 20's.
 
Hmmmmm.....well, I can go from Sacramento to San Diego in my Beech for about $175 AND stop on a dime. Can you?? :rolleyes:

Oh yeah, it'll also take me about 4 1/2 hours.
 
Different powerplants will be optimum for different speed (Mach) regimes.

In order of increasing Mach,

Turboprop -> Turbofan -> Turbojet -> Ramjet -> Scramjet -> Rocket

Over short routes you are unlikely to average a high speed for very long, so there is no sense in carrying a high-speed powerplant. Even if each powerplant is operated in its optimum speed range, the turboprop will be the most fuel efficient. From an efficiency standpoint it is always better to accelerate a large mass of air a little bit than a small mass of air a whole lot. It would use less fuel to fly a turboprop transcon than it would an equivalent sized jet, but it would just take too damn long.
 
Just to add on...the propulsive efficiency of turborpops and jets have much to do with the speed at which they fly.

A turboprop will reach about 80% efficiency at around 280kts, then drops off sharply.

A jet's propulsive efficiency actually increases with speed. A jet would reach 100% propulsive efficiency if its inlet air equalled its exhaust velocity. Although efficient, you still have to throw a lot of fuel around to get the thrust levels to reach those speeds. Probably not a good idea on a 300 mile leg.

So, the answer to your friend's question...how far do you want to fly?
 
B767Driver said:
A jet would reach 100% propulsive efficiency if its inlet air equalled its exhaust velocity.
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On a transport type I'm guessing this would happen at some point after the wings separated from the fuselage? (Don't know much about arrowdynamics.)
 
Cessnaflyer said:
Enter the Unducted Prop Fan.

[FONT=ARIAL, Helvetica, Geneva][FONT=ARIAL, Helvetica, Geneva][FONT=ARIAL, Helvetica, Geneva]http://www.airliners.net/open.file/0001821/L/[/FONT][/FONT][/FONT]

I really wish this would come to fruition.
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Sidious said:
That just looks wicked! Ive never even heard of this.
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I remember seeing these things in Popular Science in the early to mid 80's. I guess they haven't worked out so well, or the manufacturers are afraid of the public opinion regarding props.
 
B767Driver said:
Just to add on...the propulsive efficiency of turborpops and jets have much to do with the speed at which they fly.

A turboprop will reach about 80% efficiency at around 280kts, then drops off sharply.

A jet's propulsive efficiency actually increases with speed. A jet would reach 100% propulsive efficiency if its inlet air equalled its exhaust velocity. Although efficient, you still have to throw a lot of fuel around to get the thrust levels to reach those speeds. Probably not a good idea on a 300 mile leg.

So, the answer to your friend's question...how far do you want to fly?
Click to expand...

Doug Taylor said:
Depends on how far you'd like to fly!

Jets whizz a lot of gas below the tropopause and you don't enjoy the economics of a jet until you're able to get up high and cruise for a long time.

Turboprops are very efficient in the teens and low 20's.
Click to expand...

Dugie8 said:
Depends on your definition of "efficient". The PC12 can carry more gas than most people have space in their bladder, that can be called efficient. A DC8 can carry about 95,000#s about 4500 miles on 150,000 pounds of fuel, that can be called efficient.

Time and fuel used aren't always the best benchmarks, but they are probably the most common.
Click to expand...

Realms09 said:
Different powerplants will be optimum for different speed (Mach) regimes.

In order of increasing Mach,

Turboprop -> Turbofan -> Turbojet -> Ramjet -> Scramjet -> Rocket

Over short routes you are unlikely to average a high speed for very long, so there is no sense in carrying a high-speed powerplant. Even if each powerplant is operated in its optimum speed range, the turboprop will be the most fuel efficient. From an efficiency standpoint it is always better to accelerate a large mass of air a little bit than a small mass of air a whole lot. It would use less fuel to fly a turboprop transcon than it would an equivalent sized jet, but it would just take too damn long.
Click to expand...

Thanks for the responses!
 
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