Welcome to Flightinfo.com

  • Register now and join the discussion
  • Friendliest aviation Ccmmunity on the web
  • Modern site for PC's, Phones, Tablets - no 3rd party apps required
  • Ask questions, help others, promote aviation
  • Share the passion for aviation
  • Invite everyone to Flightinfo.com and let's have fun

Variable bypass?

Welcome to Flightinfo.com

  • Register now and join the discussion
  • Modern secure site, no 3rd party apps required
  • Invite your friends
  • Share the passion of aviation
  • Friendliest aviation community on the web

GravityHater

Well-known member
Joined
Aug 12, 2004
Posts
1,168
Is there a turbofan out there that can mechanically alter the bypass ratio in flight? Especially is there one in regular civilian use?
 
GravityHater said:
of my question?
To learn things.

No...... what would be the point of a variable bypass setup? In the case of the SR-71 I guess it has to do with efficiency across the performance envelope and transonic shock wave issues.
 
9GClub said:
what would be the point of a variable bypass setup?

"the turbojet is more efficient at low altitude;
the turbofan is more efficient at high altitude"

my thought was divert fan air into the core at low altitude. (and go as much 'fan' as possible at high altitude)
I'm sure there is some reasoning why not, it could be even that the quoted statement above is somehow invalid or incomplete.

Thanks
 
I'd think that the -fan would be more efficient at low altitude (just speculating, I have to check my books) because of the greater air density. Seems like at higher altitudes you'd want everything going through the core. Low-bypass turbofans/ turbojets are certainly better in high-speed applications.
 
whoa fellas, the SR-71 does not have a "variable bypass ratio" engine at all. Just like the MIG-21, they both have pure turbojet engines (read NO bypass) with variable GEOMETRY inlets.


The reason behind the design is to allow the formation of an oblique shockwave at the tip of the cone that would feed the inlet with air at subsonic speed (necessary for the engine operation), while the aircraft flies at supersonic speeds. The cone retracts and extends depending on the speed of the aircraft as to obtain the optimal angle of that shockwave to feed subsonic air to the inlet with the least stagnation pressure loss as possible.
 
GravityHater said:
"the turbojet is more efficient at low altitude;
the turbofan is more efficient at high altitude"
I agree, I'm pretty sure 9G is right. I think you've got it backwards.
 
But can the mig do a negative 4G inverted dive?
 

Latest resources

Back
Top