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A310 TRP - Takeoff and Climb N1/EPR and Pack Correction

 
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K.Haroon
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Joined: 11 Dec 2005
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PostPosted: Mon Apr 26, 2010 3:20 pm    Post subject: A310 TRP - Takeoff and Climb N1/EPR and Pack Correction Reply with quote

A310 - Determining Takeoff and Initial Climb N1/EPR using TRP and applying Pack correction.

1) Takeoff N1/EPR

If the engines are OFF the TRP considers the Packs to be OFF regardless of the Pack push button position. So with engines OFF, TRP calculates the N1/EPR considering the packs are OFF. After engine start it reduces the N1/EPR to cater for Pack correction if the Pack push buttons are ON. Selecting the Pack push buttons to OFF increases the N1/EPR displayed on the TRP. With Packs ON the reduction (i.e. Pack correction) is 0.7 N1 in GE engines and 0.017 EPR in PW engines. So while making the takeoff data card (for takeoff with Packs ON) without using the performance charts, T/O and Flex N1/EPR calculated by the TRP can be used after subtracting 0.7 in GE engines and 0.017 in PW engines (i.e. Pack correction).

Example (as observed on a flight):

PW Engines OFF
TRP Flex Temp 55
Flex EPR 1.385

PW Engines ON
TRP Flex Temp 55
Flex EPR 1.370 with Packs ON
Flex EPR 1.385 with Packs OFF

That means with engines OFF while making the takeoff data card we need to subtract 0.017 from 1.385 Flex EPR which becomes 1.368 same as what TRP calculates after engine start. Just a difference of 0.002 which is negligible.

Note: The engines I am talking about are GE 80C2A8 and PW4152


2) Initial Climb N1/EPR

Now coming to the issue of determining Initial Climb N1/EPR. As discussed earlier, with engines OFF the TRP will consider the Packs to be OFF and thus the Climb N1/EPR calculated by it will be reduced after engine start if the Packs push buttons are ON (i.e. Pack correction). However this Climb N1/EPR will be valid for field elevation altitude where A/C is parked. As the altitude increases after takeoff the Climb N1/EPR will keep on increasing (till flat rating cut off). Since we keep the takeoff N1/EPR up till 1500 feet we dont need Climb N1/EPR for an altitude less than 1500 feet. That means we need to consult the performance charts for determining the Climb N1/EPR and cannot use the TRP on ground to determine the correct Initial Climb N1/EPR for an altitude above 1500 feet. The performance chart values for Climb N1/EPR are based on Packs ON (unlike Takeoff N1/EPR) thus we dont need to make Pack corrections. However if the Packs will be OFF for climb then we need to add 1.2 N1 for GE engines and 0.030 EPR for PW engines.

Example (as observed on a flight):

TRP TAT 33

GE Engine OFF
CL (On Ground, elev 48 ft) 95.1

GE Engine ON
CL (On Ground, elev 48 ft) 94.7

GE Engine After Takeoff
CL (At 1500 Feet AGL) 96.1

Above data shows the difference between TRP CL on ground and 1500 feet AGL. That means to determine the initial Climb N1/EPR on ground for takeoff data card, we need to consult the performance charts. It is interesting to note in the above example that after engine start (to cater for Pack correction) the reduction in Climb N1 is only 0.4 (i.e. from 95.1 to 94.7). Whereas the reduction should have been 1.2 (i.e. from 95.1 to 93.9) according to what the performance chart says (i.e. with Packs OFF add 1.2 that means with Packs ON, as it is the case after engine start, it should be -1.2).

Why TRP does not reduce the CL value by 1.2? Sorry No Idea. I guess I need to collect more data on this to understand. However one thing seems to be certain that application of Pack correction manually for takeoff data card (1.2 for GE and 0.030 for PW) to TRP CL value on ground with engines OFF will further increase the difference for CL N1/EPR at ground and 1500 feet AGL. Thus increasing the error.

Note: The engines I am talking about are GE 80C2A8 and PW4000

Please feel free to disagree and correct me.


Last edited by K.Haroon on Thu Mar 22, 2012 9:07 am; edited 2 times in total
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K.Haroon
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Joined: 11 Dec 2005
Posts: 1292

PostPosted: Thu Apr 29, 2010 8:32 pm    Post subject: Reply with quote

Got some more data today. This time for a PW engine:

TRP TAT 35

PW Engine OFF
CL (On Ground, Elev 37 ft) 1.330 EPR

PW Engine ON
CL (On Ground, Elev 37 ft) 1.313 EPR

GE Engine After Takeoff
CL (At 1500 Feet AGL) initially 1.335 then 1.332 EPR

Again after engine start (to cater for Pack correction) the reduction in Climb EPR was only 0.017 (i.e. from 1.330 to 1.313). Whereas the reduction should have been .030 (i.e. from 1.330 to 1.300) according to what the performance chart says (i.e. with Packs OFF add 0.030 that means with Packs ON, as it is the case after engine start, it should be -0.030). Why TRP does not reduce the CL value by 0.030? Again No Idea.
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