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PSR/PNR Calculations

 
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rusty1983



Joined: 10 Jul 2017
Posts: 5

PostPosted: Tue Jul 11, 2017 6:10 am    Post subject: PSR\PNR calculation Reply with quote

Hello,

I got during my IR rating exam an interesting PSR\PNR question where I am going right now crazy to get to a solution. I asked now already everyone at flight schools, looked in different forums, but could not find an answer. I even asked already the authority, but they were not authorized to help me... Rolling Eyes

Hopefully you guys can help me here with a solution.

The question simple:
- distance A to B 2000NM
- TAS, wind, endurance constant
- 5000kg fuel (+500kg extra)
- PET from A 1200NM

what is the PNR\PSR?

answeres: I cant remember the values any more but for the approach process it should be not an issue. There were 5 answeres and I chose c.) which was 1200NM (same as PET and which is wrong).

My approach was the following, due to the fact that there are to less variables for calculations, no given fuel flow,..., it's more a theoretical question. TAS, wind, endurance are constant, so I thought it might be one of the rare cases where PET=PSR, which leads me to another question:
- Can PSR be equal PET and\or is PSR always more\less then PET?

I assume that when there is no wind and PET is exactly half of the distance, is there also PSR half of the distance or more\less?

In the example above I know I have headwind doe to the fact that PET is closer to B, so if PSR is maybe always more then PET then there might was only one answer which was more then 1200nm...

Or maybe I am completely wrong...,
anyways, appreciate your help in this case!

BR, Rusty

BTW.: I'd like to add the formula for

PSR (distance)= (H x O x E) \ (H+O)

With that you can calculate directly the distance and must not use the time formula and then the v=s\t
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Koosvr



Joined: 19 Jun 2016
Posts: 3

PostPosted: Fri Jul 28, 2017 5:53 am    Post subject: PNR/PSR Reply with quote

What were the options provided?
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Koosvr



Joined: 19 Jun 2016
Posts: 3

PostPosted: Fri Jul 28, 2017 6:08 am    Post subject: Reply with quote

From what I can see, one has to work with factors:

H gs = 1200/2000 = .6
O gs = 800/2000 = .4

Thus PNR = H*O*E/H+O
= .6*.4*1/1
=.24

2000*.24 = 480

PNR = 2000-480 = 1520
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rusty1983



Joined: 10 Jul 2017
Posts: 5

PostPosted: Mon Sep 11, 2017 9:34 am    Post subject: Reply with quote

Hello Koosvr, thank you for the feedback.
If it is like this, then I am really in a problem, because I never did in all examples, mock exams or figured out at any theory book, such a way to come to a solution!
But at least I understand what you did and next time Ill try it like this.

Unfortunately I got another one at the next exam...where again I thought, c'mon CAA really!? Who is the Sadist behind such questions!?

Dist. A - B = 1200Nm
PSR is 84% of AB
PET is 60% of AB
Endurance = 8h24mins

What is the Groundspeed from PSR to A?

I am going already crazy with these questions...everyone I ask, no one has a clue
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