Forum: Technology

In high bypass engines, it's about 80%. What about low bypass? My guess is around 20-50%. Any details would be great ie an F119 vs an F101.

F-16.net Sponsor

The A-10 TF-34s were 85% bypass/thrust

They're 'mixed flow' so it's hard to say; one would have to compute the mass of air times the velocity for the separate flows, (Fan/Core) but even then this wouldn't be 'true' IMO.

The 'true' thrust of a 'mixed-flow engine' is the total exiting the nozzle.

You take the bypass air, and the core engine exhaust, mix it in the augmentor duct, then the mass exits the nozzle as a whole.

Now percent of airflow is a different matter. If the BPR is 1/1 the same amount of air goes through the core as around it, so 50%/50% (But this isn't thrust)

So...

F101-GE-102 - BPR 1.91/1
F100-PW-220 - BPR 0.71/1
F100-PW-229 - BPR 0.36/1
F110-GE-100/129 - BPR 0.87/1
F404-GE-402 - BPR 0.27/1
F414-GE-400 - BPR 0.40/1
TF-34 - BPR 6.2/1
F117 - BPR 5.8/1
F119 - BPR 0.20/1-0.30/1? (Unofficial sources vary - no official source)
F135 - BPR 0.57/1 http://www.pw.utc.com/media_center/assets/me_f135_product_card.pdf

On something like the High-BPR TF34, you have separate fan and core flows (something to measure at the individual exhausts, mass x velocity) But when you're mixing the lower speed fan air into the higher speed core air while still inside the engine, then exhausting it through the same nozzle, the flow of the faster/slower air will impact the other to some degree prior to exhaust.

Shrug

TEG

I'm wondering how much more dry thrust one can gain from increasing BPR if everything else is the same.

shingen wrote:

I'm wondering how much more dry thrust one can gain from increasing BPR if everything else is the same.

Everything else the same, are you making the core smaller? Or making the fan bigger?

To increase the diameter of the fan, you'd increase the diameter of the engine; in a Fighter application you'd need to completely redesign the fuselage and engine-bay; on the Bone it would be a serious engine nacelle redesign.

To decrease the diameter of core, you're talking less power available to turn your fan, or talking a lot less power (% wise) thus reducing your overall exhaust velocity.

In a mixed flow engine you may gain thrust or better SFC, but you'll worsen thrust lapse, and reduce specific thrust at speed/altitude (IE your NON-AB upper/right flight envelope will be affected.)

What is an aerospace propulsion (jets) engineer to do? Shrug

How about decrease the BPR, increase the fan's pressure ratio and give it some more RPM to increase airflow?

This is what PW did to the F100 to produce the PW-229. More air, higher fan pressure ratio, higher core pressure ratio (yielding 32/1 OPR versus 24/1) The RPM of both the fan and core have increased (allowing the higher pressures and flow), More fuel nozzles for better spray, more even, and higher tepms in the combustion chamber, and a higher flow augmentor with a rider range of function.

So as you can see, the PW-229 has a SMALLER BPR than the previous F100 series and still makes MORE power. GE followed similar redesign for the GE-132; lower BPR, higher pressures/temps.

Today the PW-229 not only makes more power, but lasts almost 50% longer by adopting some of the technology developed for the F119 and F135 series engines.

Awesome info.

How does the sfc of the 229 compare to the previous model? I assume the afterburning sfc is lower.

Thanks so much.

It is lower a bit, the SFC at MAX improved more than the SFC at MIL, but then the pilots don't have to use 'burner as much.

So with the INCREASED thrust, and the slightly improved SFC, the fuel flow (PPH) of the PW-229 is still going to be higher at MIL/MAX respectively. On the up side with the increased thrust, the operator can reduce power settings when not needed and SAVE fuel. (Or not use MAX take offs, given proper conditions)

Cheers

TEG

Forum: Technology

What % of thrust in a turbofan comes from the fan?