Bryan Becker
Topic Author
Posts: 327
Joined: Fri Mar 02, 2001 12:38 pm

Bypass Ratio

I would like to know what thismeans I know what bypass is but how do you read this?

4.9-to-1 and 6-to-1,

Does that mean for every 4.9lb's of air sucked in only 1 pound goes through the engine and the rest go through the bypass? please help me on this!!!!!!!!!!!!

-BryanBecker

flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Bypass Ratio

You're correct.

Aero42
Posts: 18
Joined: Wed Oct 25, 2000 1:28 am

RE: Bypass Ratio

Bypass ratio is the area ratio's the bypass area to the jet intake area. A 4.9 to 1 bypass ratio would mean that the area of the bypass on an engine is 4.9 times that of the area of the jet intake.

avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Bypass Ratio

Just to be picky, 4.9 lb would go through the bypass, and 1 lb through the core, totalling 5.9 lb.

aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm

Avt007

if you really want to be picky, it is 4.9 & 1 slugs of air, not pounds. It's a ratio of mass, not weight.

aaron
-I put new AA birdstrike pictures at hawke.50megs.com tonight if anyone cares to see blood, guts, and aircraft damage

aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm

Aero42

>>>Bypass ratio is the area ratio's the bypass area to the jet intake area. A 4.9 to 1 bypass ratio would mean that the area of the bypass on an engine is 4.9 times that of the area of the jet intake. <<<

Is that what they are teaching at CalPoly?

is that going to be the average frontal surface area? ...or just at the beginning of the duct?

aaron

310_engineer
Posts: 163
Joined: Tue Dec 05, 2000 7:16 am

RE: Bypass Ratio

Bypass ratio = secondary airflow / primary airflow

aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm

RE: Bypass Ratio

310 engineer, my last post was an attempt at sarcasm. Apparently the aerospace engineering program at CalPoly is a bit lacking.

wtf are they teaching these kids?

aaron

Top Gun
Posts: 103
Joined: Wed May 19, 1999 8:13 am

RE: Bypass Ratio

To give you an idea of what sort of ratio is out there, the 777's GE90's are aprox. 8:1 (units). An older turbo jet is 1:1 (JT8D's as on the 737-200's) not to create confusion that is not a bypass engine.

A turbo fan is a Bypass
A turbo jet is not.

aria
Posts: 31
Joined: Wed Oct 17, 2007 5:08 am

RE: Bypass Ratio

Aaron atp:

Hello....thank God someone out there knows all the answers to everything....now I can sleep at night knowing that the next generation will be taken care of...
Aria

aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm

Aria

I thank god for that too... After all, if enough of those impressionable daytona beach kids were to read that second reply to the original post, we could convince the world engineering community to amend the definition of bypass-ratio based on popular belief of the ignorant-masses.

Maybe we could even get them to present a working play-doh scale model of a GE-90 to the Royal Aeronautical Society as a basis for this bold new theorem.

have a nice evening and I'm sure you will sleep well.

aaron

northstardc4m
Posts: 2870
Joined: Fri Apr 28, 2000 11:23 am

RE: Bypass Ratio

just to correct Aria....

Turbojets have a 0 to 1 ratio.. no bypass at all...

Early low ratio turbofans like the JT3D, Conway etc had ratios of 1 to 1 or less ( Convays were .4 to 1)

Wasnt till the C-5 and 747 program the High Ratio Bypass (4 to 1 or greater) really took off, mostly because there simply wasnt the demand for engines that size... and if you didnt need the power.. heck gas was cheap   and noise didnt matter much   so buy a spey or jt8d or whatever....
Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety.

310_engineer
Posts: 163
Joined: Tue Dec 05, 2000 7:16 am

RE: Bypass Ratio

Top gun

FYI JT8D Is not a turbojet but a low bypass turbofan

Top Gun
Posts: 103
Joined: Wed May 19, 1999 8:13 am

RE: Bypass Ratio

I'm sorry I was shooting my mouth of again and infact the JT8D's are Bypass. Silly me.

310_engineer
Posts: 163
Joined: Tue Dec 05, 2000 7:16 am

RE: Bypass Ratio

You are forgiven

timz
Posts: 6310
Joined: Fri Sep 17, 1999 7:43 am

Terminology

The term "turbojet" is used in the NOAA DP and STAR charts (if nowhere else) referring to jets in general. We fans like to suppose there are no turbojet airliners out there (except the Concorde) but we might get outvoted.

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