Old 744 Forum

Archived posts

EPR target PW 4056

Page: 1

Author Post
Member
Registered: Jan 2014
Posts: 299
Location: France (LFQQ)
Hello Hardy,

Please have a look at this SITU :

http://www.hoppie.nl/forum/var/--Event_record_2015-JUL-06_16-07-32.situ

Isn't the CRZ EPR target a little bit too low ? If the aircraft encounters some turbulences, I think it could be difficult to maintain a safe airspeed with such a low target.

I made my step climb 40 NM before TODAK, and the CLB EPR target was also very low, giving me a climb rate of 600 FPM between FL380 and FL400.

I run PSX v.10.0.5

Regards
_______________
Jean-philippe
Moderator
Registered: May 2009
Posts: 5140
Hi Jean-philippe,

I've increased it already some months ago. I'll recheck it later this year.

When in turbulence you need to reduce your airspeed.

Also, you are near MAX ALT; you can't expect steep climb rates.

I think 1.48 agrees with the official performance database. If it requires an adjustment then it will be the actual net thrust itself at 1.48, not the FMC limit.


Regards,

|-|ardy
Member
Registered: Jan 2014
Posts: 299
Location: France (LFQQ)
I was surprised to see the EPR at 1.47 with a 1.48 target, just to maintain M0.84 at FL400. At this weight at the end of cruise, the MAX ALT is about 42000 ft. I didn't see such limitation with GE or RR engines, as far as I can remember. But maybe the PW's are less powerful ?

I let you see and do something (or not). Thanks Hardy.
_______________
Jean-philippe
Moderator
Registered: May 2009
Posts: 5140
The PW EPR values are much lower than the RR values because they use two different kinds of EPR indication systems (core EPR versus integrated EPR). See pages 511 and 512, the grey text boxes.

Actually, the PW has slightly more power. But when you are near the "coffin corners" the fine-tuning of the engine models gets extremely difficult because the parameters are so sensitive under these conditions. A change of 0.0001% and you'll get a few knots more or less.


|-|ardy

Page: 1

Old 744 Forum is powered by UseBB 1 Forum Software