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Driver170

High cruise alt PFPX on short trips

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Hi i'm using PFPX with TOPCAT and the 737 ngx 800 Winglet.


 


I done a short flight from EGPF to EGGP it gave me FL300 and my FMS was 200 OPT. Now this is not right surely? soon as i hit TC i would be descending right away. so i changed my cruise alt to FL230 i got that alt from real world flight plans.


 


is anyone else suffer from these crazy alt calculations from PFPX? 


 


I have to say its fine when on long flights from glasgow to spain lets say its always on the money. BUT its these short flights thats the problem.


 


below is my FP i did change the alt to FL230 


 


https://www.dropbox....14) #1.pdf?dl=0


 


Vernon Howells

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Like they say, the most efficient flight path is a parabola.

 

It's usually beneficial to climb as high as you can, sometimes even to a point where the T/C and T/D overlap or are very close to each other as then you would essentially be gliding down to your destination with minimal fuel usage. If you take a lower flight level, you'd be using up fuel in cruise as well. Yes, you would use slightly more fuel in climbing those extra 1000s of feet but it would still be beneficial as compared to a cruise on a lower flight level for a long time.

 

Apart from that, you have other factors such as wind, weather, weight, airspace restrictions, etc. A real world flight would take a lot of those items into consideration when planning a short route and I've seen some EK flights that would level off in the early 30Ks for a flight that's only about 300NM or so.

 

I would say make two plans in PFPX. One that has a high altitude climb with a very short cruise phase and another with a lower altitude and longer time in cruise. See which one gives you better fuel planning. Do keep in mind that changing altitude alone will not result in a substantial number if other factors such as weight, wind, etc are largely variable at the two altitudes.

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is anyone else suffer from these crazy alt calculations from PFPX? 

 

Eh...I wouldn't say "suffer."  You have to remember what's going on here.  Higher altitude is more efficient, and in some cases, a planner will calculate that having essentially no cruise portion might be a more optimal solution.  This might be because of fuel burn (remember that descents are usually IDLE - which is lowest fuel burn), wind, ATC-requirements, and a whole bunch of other factors.

 

One of the things that really rubs me the wrong way about simmers (no offense) is that they assume they know what's right, or wrong, and if it doesn't make obvious sense, then it's a problem.

 

This isn't a problem - you just don't fully understand it.  That's why the forums are here.

 

 

 

I see nothing wrong with what you're seeing.  Seems pretty normal to me.  In line with what Karan mentioned, you could always plan the flight by forcing PFPX to use a lower altitude to compare your fuel burn.  Remember that PFPX isn't programmed to give you what "makes sense;" it's programmed to give you an optimal solution.

 

UPS came to a more optimal solution not by planning the shortest routes for their trucks, but by using routes that made no left turns in certain areas.  Not obvious - still more optimal.


Kyle Rodgers

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Vernon's right, the planner should decide the route is too short for the altitude to be attained and descended from, and reduce it or recommend a change.


Steve Waite: Engineer at codelegend.com

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Vernon's right, the planner should decide the route is too short for the altitude to be attained and descended from, and reduce it or recommend a change.

 

Yes and no.  If it can't get to the altitude, that's one thing.  A climb leading right up to a descent is another...from my understanding, it could've done it, but it just didn't look right to him.


Kyle Rodgers

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High 200s seems about right for that distance (162 NM). Not taking any (if any) ATC / airspace restrictions into consideration.

 

FL300 is used routinely real world from Oslo to Stavanger (182 NM).

 

So, PFPX isn't doing anything crazy here.

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If you descending in VNAV you are following the vertical path and you're not descending at IDLE thrust but rather with thrust to maintain on the VPA and speed !!

 

 

I don't fully understand it kyle? I think thats quite rude.

 

Infact i do and i take in consideration with this http://www.nats-uk.ead-it.com

 

Thats where i get my cruising alt for routes within the UNITED KINGDOM so you telling me i just type in point A to point B ? Nope! i do alot of hard work and prep and have a good setup here i'm not just that normal simmer what presses Z and goes watch the footie.

 

Yes PFPX is right but surely somehow take short flights into consideration. but i know where its going about being optimal. But every route is alot lower than 30k

 

 

I didn't say i was right and blaming PFPX just looking for another way about this? But its obvious i just type in a new cruise alt which i can obtain from real world FP.

 

 

Thanks for that explanation krazyk i do understand where you are coming from!

Daniel whats oslo like? Will have to do a trip up there...

 

Fsx time though ;)

 

Been watching just planes 737 800 norwegian air from oslo :D


Vernon Howells

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FL300 is used routinely real world from Oslo to Stavanger (182 NM).

 

An increase in climb rate would help with Vernon's route, since the planner is pulling the altitude from common data rather than calculate it.


Steve Waite: Engineer at codelegend.com

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Well nats only permit FL 145 to 245 for my flight and most in the UK so what i'm trying to do is select an alt within that range to match my FMC but i'm always off by a few k


Vernon Howells

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If you descending in VNAV you are following the vertical path and you're not descending at IDLE thrust but rather with thrust to maintain on the VPA and speed !!

 

Seems like you don't understand this, either.

 

Right at the top of descent, where do your throttle levers go?  It does this from T/D until the first altitude restriction.  Thereafter, depending on the aircraft's software, it will continue to do the same, or it will enter geometric path (similar to the 777 - which is what you're describing), but the first segment is always what?

 

 

IDLE.

 

 

 

 


I don't fully understand it kyle? I think thats quite rude.

 

Facts aren't rude.  It was an honest observation.  If I said something here that you knew was false, I'd encourage you to call me out as well.  It's not rude to point out inaccuracies.  I do know that it doesn't feel too good to be on the receiving end of being called out, but it's life.

 

You called something a problem that's not a problem.  This points to a lack of understanding.  Fact.  End.  No need to get offended by it.  Learn.  Move on.

 

Like I said - it might not feel good, but if someone says you're incorrect, your efforts might be better spent going back and re-educating yourself instead of getting upset at the person who called you out.  You have - twice now - used partially incorrect information in an effort to prove something is incorrect, when you, yourself, are the one who is incorrect.

 

 

 


Thats where i get my cruising alt for routes within the UNITED KINGDOM so you telling me i just type in point A to point B ? Nope! i do alot of hard work and prep and have a good setup here i'm not just that normal simmer what presses Z and goes watch the footie.

 

Good for you.  A lot of people add a lot of work into their flights and still end up wrong.  Sure, I lumped you in with simmers and their expectation that their limited understanding is the way of the world, but that doesn't mean I'm saying you're the worst of the lot.  Nowhere in my posts have I asserted that.  I've only mentioned the one reference: your limited viewpoint of what goes on in the real world is just that - limited.  Do not believe, and do not assert that you know what is correct and incorrect unless you know it for a fact.  You called something a problem that wasn't a problem.

 

Had I not called you out on it, others might believe you're right, and falsely believe that PFPX is doing something wrong.  It's not.


Kyle Rodgers

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Daniel whats oslo like? Will have to do a trip up there...

Fsx time though ;)

Been watching just planes 737 800 norwegian air from oslo :D

 

Oslo is a great place to be flying into using FSX. Make sure you join Vatsim, if you haven't already. Oslo is very active with good controllers. 

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I wasn't pointing fingers at PFPX kyle and saying it was wrong! I'm asking if others on this have the same HIGH alt fix on short flights and with the experience of this what sha'll i do?

 

Go with PFPX alt or get another manual alt put in?

 

I never once said i had a problem on my post at the start i'm asking if others have these on short flights?

 

Of course, i'm a big boy, i'll learn and move on ;)

 

To be honest if you just gave an ANSWER like Krazyk did above that would of been plenty thankyou! And that was the kinda answer i was looking for!

Daniel the reason i left vatsim was the lack of controllers its a pitty.

 

Will do a flight into oslo this week but off for a BBQ tonight :) in the mean time happy contrails guys !!!!


Vernon Howells

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Have a good one Vernon!


Steve Waite: Engineer at codelegend.com

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Vernon's right, the planner should decide the route is too short for the altitude to be attained and descended from, and reduce it or recommend a change.

 

Most flight planning software has a minimum cruise time that is rather short, on the order of two minutes or so.  It's not uncommon to see real-world flight plans that have the TOC and TOD only minutes apart.

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