Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
A Fuel Question, Jet V Prop  
User currently offlineReadytotaxi From United Kingdom, joined Dec 2006, 3169 posts, RR: 2
Posted (6 years 3 months 2 days 23 hours ago) and read 8912 times:

I have no idea so decided to ask the experts.
A 4 engine jet v a 4 engine prop traveling at same speed over 1,000 miles, which would eat the most fuel?

I kinda think its the jet but not sure, reason for the question?
A friend said "with the price of fuel rising why don't airlines use props and take longer to get there and save money."
Is there any logic to her question?


you don't get a second chance to make a first impression!
10 replies: All unread, jump to last
 
User currently onlineFlighty From United States of America, joined Apr 2007, 8395 posts, RR: 3
Reply 1, posted (6 years 3 months 2 days 23 hours ago) and read 8903 times:

I can answer this.

The substance of your question is: comparing a Q400 propliner at 350 knots with a slowed-down E-170 at 350 knots, which burns more fuel? The propliner would burn a lot less fuel.

One problem with your friend's point is, there is no "4 engine prop" for a 1,000 mile journey that compares with a "4 engine jet" other than perhaps an Avro RJ85, which is a fuel guzzler. Other than a Dash-7, which is outdated.

Generally speaking, the Q400 saves around 30-40% compared to its nearest competitor, ironically Bombardier's own CRJ-705 by the same manufacturer. So your friend is right, in theory journeys up to 1,000 miles should be flown by prop to save fuel. The problem is, props are a bit slow. At 1,000 miles, you will spend 1 extra hour in-flight compared to a jet. A jet is most fuel efficient at cruise speeds (550mph or 475 knots). So, slowing them down won't help anything.

Anything over 1,000 miles should be considered impractical for a prop in airline service.

Given today's available new aircraft, we could say that 300-400 new Q400 aircraft, flying missions up to 750 miles, would improve our national fuel efficiency compared to the smaller jets we use. As for bigger jets, there is no moden large prop to provide comparison.


User currently offlineFuturecaptain From , joined Dec 1969, posts, RR:
Reply 2, posted (6 years 3 months 2 days 23 hours ago) and read 8903 times:



Quoting Readytotaxi (Thread starter):
A 4 engine jet v a 4 engine prop traveling at same speed over 1,000 miles, which would eat the most fuel?

Are we assuming both planes are the same size too? Props just don't like to be scaled up too big so a jet will generally carry several times what a prop will on a given route. I know you only asked about fuel burn, but payload in return for the fuel burned is a consideration too.
In general though a jet will burn more fuel on a given route. In return, in general, a jet is faster and the engine is more reliable than a prop.

Quoting Readytotaxi (Thread starter):
"with the price of fuel rising why don't airlines use props and take longer to get there and save money."

American (ATR)
Continental (Q400)
Frontier/Lynx (Q400)
Horizon(Q400)
Island Air (Q400)
ASA (ATR)
Fed Ex (ATR)

And that is just the tip of the iceberg. Props are in service all over the world.


User currently offlineReadytotaxi From United Kingdom, joined Dec 2006, 3169 posts, RR: 2
Reply 3, posted (6 years 3 months 2 days 22 hours ago) and read 8888 times:



Quoting Flighty (Reply 1):

Thank you, excellent reply.



you don't get a second chance to make a first impression!
User currently offlineReadytotaxi From United Kingdom, joined Dec 2006, 3169 posts, RR: 2
Reply 4, posted (6 years 3 months 2 days 22 hours ago) and read 8885 times:



Quoting Futurecaptain (Reply 2):

Thank you, I don't think she had considered payload, just bums on seats



you don't get a second chance to make a first impression!
User currently offline9VSIO From United Kingdom, joined Dec 2006, 708 posts, RR: 2
Reply 5, posted (6 years 3 months 2 days 11 hours ago) and read 8791 times:
Support Airliners.net - become a First Class Member!

What happens if we talk piston prop instead of turbo-prop?


Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
User currently offlineKELPkid From United States of America, joined Nov 2005, 6343 posts, RR: 3
Reply 6, posted (6 years 3 months 2 days 10 hours ago) and read 8774 times:



Quoting 9VSIO (Reply 5):
What happens if we talk piston prop instead of turbo-prop?

For a GA-sized plane, piston powerplants are definitely more fuel effecient. I think as you go up in size, that advantage disappears...also, piston powerplants usually have much reduced power output at typical turbine cruise altitudes.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineThegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 7, posted (6 years 3 months 2 days 8 hours ago) and read 8754 times:



Quoting Readytotaxi (Thread starter):
I have no idea so decided to ask the experts.
A 4 engine jet v a 4 engine prop traveling at same speed over 1,000 miles, which would eat the most fuel?

The jet will eat the most fuel, but the prop will not fly as fast. With more expensive fuel, I expect turboprops to sell better after just about becoming extinct in the late 1990s. Both ATR and Bombardier are looking at stretching their ATR-72 and Q400 respectively. 1000mi is a long way for a prop to fly though. You are looking at paying more than a 30min flight time penalty over that sort of sector length though. Props would likely be confined to sectors less than about 400mi (644km)

Of course, they will be twins, not quads.


User currently offlineRwessel From United States of America, joined Jan 2007, 2309 posts, RR: 2
Reply 8, posted (6 years 3 months 1 day 17 hours ago) and read 8644 times:
Support Airliners.net - become a First Class Member!



Quoting KELPkid (Reply 6):
piston powerplants usually have much reduced power output at typical turbine cruise altitudes.

As, of course, do turbines. And you can't even turbo charge a turbine to compensate.

Large piston internal combustion engines are not necessarily much less efficient that turbines of the same output, but become massively impractical from a complexity, reliability, and/or mass standpoint. For example, there are 90,000shp marine diesels that are 52% efficient in common use, and the best Otto cycle engine have made it to about 60% in the lab. Large gas turbines generally run in the mid-to-high 60s, and some of the largest, when coupled with devices to extract and reuse the excess heat energy in their exhaust streams (for example, you can heat a boiler and run a steam turbine with the exhaust), can make it up into the eighties, but of course that's at least theoretically possible for piston ICEs as well. But don't make too much of the apparent difference - the large piston ICEs are built with more of an emphasis on cost and reliability. Of course large output turbines are miniscule compared to their piston equivalents, and tend to run much smoother.

Small turbines, OTOH, have significant issues trying to maintain a high compression ratio, but it can be done. Very small turbines often run in the low-to-mid 20s, while the best small(er) piston ICEs are in the upper 20s to mid 30s. Basically it’s easier to seal a small combustion chamber with a piston ring than it is to control the leakage past the turbine.


User currently offlineKELPkid From United States of America, joined Nov 2005, 6343 posts, RR: 3
Reply 9, posted (6 years 3 months 1 day 17 hours ago) and read 8635 times:



Quoting Rwessel (Reply 8):
As, of course, do turbines. And you can't even turbo charge a turbine to compensate.

Large piston internal combustion engines are not necessarily much less efficient that turbines of the same output, but become massively impractical from a complexity, reliability, and/or mass standpoint.

It would be nice if Pratt and Whitney still engineered behemoth radials, and if Curtiss-Wright were still around to try and make the case for "corncob" radials in this day and age  Wink I'd love to see what could become of a modern large aviation piston engineering effort, like about propliner-sized engines...Wonder what kind of weight savings we'd see with modern technology advances? Wouldn't it be cool, too, if someone tried a modern aviation turbodiesel (large, of course, not like the Thielert or the SMA engines), you could even run it off of Jet-A fuel  Smile



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineThegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 10, posted (6 years 3 months 1 day 6 hours ago) and read 8600 times:



Quoting Rwessel (Reply 8):

I think your efficiency numbers are largely optimistic, except the the 52% for a turbo-compound diesel. Going from memory a theoretical Otto cycle needs to get over 10:1 compression to reach 60% efficiency, and that assumes instantaneous combustion and no pumping losses. A gas turbine backed by a steam plant can crack 60% efficiency in practice. It could only get into 80% if the waste heat is productively used.


Top Of Page
Forum Index

Reply To This Topic A Fuel Question, Jet V Prop
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
How Does A Turbo Jet/prop Work? posted Sun Jan 21 2007 05:21:03 by FL370
Transporting Aviation Fuel Question posted Mon May 15 2006 19:20:43 by TK787
Birdstrike Jet/prop/research/opinions? posted Wed Nov 6 2002 23:46:13 by Ukair
B-747 Fuel Question posted Mon Oct 21 2002 08:10:34 by Mikeclod
Fuel Question posted Mon Aug 12 2002 09:20:30 by Dash8King
Fuel Question posted Sun Apr 28 2002 07:17:29 by Alee
Question About Cockpit (Jet Vs Prop)... posted Wed Aug 14 2002 03:50:18 by GotAirbus
What Price To Airlines Pay For Jet Fuel? posted Mon Apr 7 2008 06:11:01 by MOBflyer
Owning Your Own Jet(noise Related Question) posted Mon Mar 17 2008 00:20:34 by Sovietjet
Fuel, Wt, And Emergency Landing Question posted Sat Dec 15 2007 02:36:26 by Davescj
A320 Vs A321 Fuel Question posted Fri Aug 29 2008 07:19:37 by Panais
A319 Vs A320 Fuel Question posted Sat Jul 26 2008 06:19:20 by Panais
737 Fuel Question posted Mon Nov 19 2007 12:51:41 by Captainsimon
How Does A Turbo Jet/prop Work? posted Sun Jan 21 2007 05:21:03 by FL370
Transporting Aviation Fuel Question posted Mon May 15 2006 19:20:43 by TK787
Birdstrike Jet/prop/research/opinions? posted Wed Nov 6 2002 23:46:13 by Ukair
B-747 Fuel Question posted Mon Oct 21 2002 08:10:34 by Mikeclod
Fuel Question posted Mon Aug 12 2002 09:20:30 by Dash8King
Fuel Question posted Sun Apr 28 2002 07:17:29 by Alee
Question About Cockpit (Jet Vs Prop)... posted Wed Aug 14 2002 03:50:18 by GotAirbus

Sponsor Message:
Printer friendly format