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 25 FLIGHT MODEL (Read 4254 times)
Tanya
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FLIGHT MODEL
Dec 28th, 2017 at 5:27pm
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Captains,
There's always room for improvement so feel free to report any issues but:

0. Please make sure you have read the Manual. 770+ handmade pages describing thousands of hard-coded features. Great reading.

1. Please report an issue if you are 100% sure it is a bug. Not sure? Please use General Discussion

2. Please use proper threads. E.g. do not post MCP issues in the FMC thread.

3. One issue ONE post, please.

4. Please provide a reference to the Manual page #.
CS Manual is based on the original Boeing's FCOM. For obvious reasons we cannot do all operators optional equipment variants.
It's not a bug if it's not in the Manual.

In some cases we can consider a reference to an operator's official Manual or CBT.
But any info from a third party software or from personal experience IS NOT a reference material. 

Also the Manual reference page # is absolutely required for all flight related and performance comments as we cannot work with the "slower-faster" kind of data. Official Boeings' numbers are absolutely required.

5. Please provide screenshots and/or screen capture videos for each issue.
Easy to use free services:
- For the screenshots: https://onpaste.com/
- For the videos:  https://screencast-o-matic.com/
Also you can attach an image to your forum post.

6. For all flight related floating issues (FMC, MCP, VNAL/LNAV etc) please SAVE the flight right on the issue, zip all 3 files of the flight (.fxml  .wx  .config) located ....\Users\you\Documents\Prepar3D v4 Files\ , upload the zip to any free hosting service (e.g. Google disc) and include the URL into your report.

COMPLETE AND CORRECT REPORTS WILL BE FORWARDED TO THE DEVELOPMENT TEAM.

CS developers will make marks and comments right in your post as follows:

- The red AIIR# mark in your post means: sounds like a bug but Additional Information Is Required indicating the numbers as per the list above.

- The blue SW means: Should work. So we need more users to confirm the issue.

- Highlight means the items is on the list.

Developers comments are in magenta.

Please DO NOT use any text color/effect other than plain black.

Thank you all for your input!
  
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Wise87
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Re: FLIGHT MODEL
Reply #1 - Jan 1st, 2018 at 6:53pm
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I use a separate joystick for tiller use and the 757 will only let me use my rudder pedals to steer on the ground.

Try this pls http://www.captainsim.org/cgi-bin/yabb2/YaBB.pl?board=y757_suggest
  
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Tim Smith
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Re: FLIGHT MODEL
Reply #2 - Jan 2nd, 2018 at 11:33am
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Target EPR progressively decreases during takeoff roll. Started takeoff with a target of 1.43, by rotation speed that had dropped to 1.3 something, cant recall exact, but as speed built EPR dropped.
  
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Alcides Segovia
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Re: FLIGHT MODEL
Reply #3 - Jan 2nd, 2018 at 11:42am
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FMC target speed in Mach and actual Mach off by 1.3 Mach. Target is .780. Aircfraft cruising at .763. FIXED
  

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Wise87
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Re: FLIGHT MODEL
Reply #4 - Jan 2nd, 2018 at 6:59pm
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Wise87 wrote on Jan 1st, 2018 at 6:53pm:
I use a separate joystick for tiller use and the 757 will only let me use my rudder pedals to steer on the ground.

Try this pls http://www.captainsim.org/cgi-bin/yabb2/YaBB.pl?board=y757_suggest


I'll put in a suggestion but P3Dv4 now has a tiller option built into the sim by default so you can assign any axis and you no longer need FSUIPC to configure a tiller. All other aircraft work just fine with tiller except for the 757.

Yes please. It's a new feature not a bug.
  
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Benjaminbl12
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Re: FLIGHT MODEL
Reply #5 - Jan 2nd, 2018 at 9:31pm
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The reverse thrust buckets on the engines need to be full reverse thrust in order to get the animation. You should be able to do idle reverse thrust and have a section of the animation.

Wrong thread.
Already reported and answered.
Please use proper threads.
  
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Matt Marshall
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Re: FLIGHT MODEL
Reply #6 - Jan 3rd, 2018 at 9:16am
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On the climb out of LGW, in the turn with an increasing tailwind upto 100kts, the speed trend vector was showing a positive trend whilst the speed washed back from 220kts to 174kts. Aircraft didn't respond to speed change and continued to climb at normal rate 2000-2500fpm. Manual intervention required and normal flight path resumed. No further issues with changing wind for duration of flight.

AIIR#6
  
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phantomphlyer
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Re: FLIGHT MODEL
Reply #7 - Jan 3rd, 2018 at 5:36pm
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B757-200 (PW2037) takeoff Rwy 19 KVPS / 15°C / 0 Wind / TOW 109579 KG (acc. TOPCAT - FMC came up with 107439 kg with same Pax / baggage due to different basic weight)) / TO1 Flaps 5.

I computed the takeoff data with TOPCAT and received fhe following data: V1 160-162 VR 162 V2 164 (FMC produced V1 158 VR ? V2 164) / EPR 1.36 / stab trim 4.2.

With autothrottle ON and I selected EPR. The engines accelerated to 1.31 (computed EPR 1.36) and stagnated while the computed EPR decreased with increasing airspeed to 1.27 at lift off.

According to TOPCAT I shoud have had a stop margin of 410 m but I barely reached V1 at the departured end and rotated in the overrun.

I would like to raise the issue again, that the power output or acceleration values are way to low. 

AIIR#4 With all due respect to TOPCAT etc we use numbers from Boeing only.
  
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Tim Smith
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Re: FLIGHT MODEL
Reply #8 - Jan 4th, 2018 at 11:35am
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In flight it took up to 60% N1 before any movement occurred on the EPR gauge.

AIIR#4
  

2018-1-4_22-24-45-327.jpg ( 155 KB | 83 Downloads )
2018-1-4_22-24-45-327.jpg
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phantomphlyer
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Re: FLIGHT MODEL
Reply #9 - Jan 4th, 2018 at 2:37pm
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phantomphlyer wrote on Jan 3rd, 2018 at 5:36pm:
B757-200 (PW2037) takeoff Rwy 19 KVPS / 15°C / 0 Wind / TOW 109579 KG (acc. TOPCAT - FMC came up with 107439 kg with same Pax / baggage due to different basic weight)) / TO1 Flaps 5.

I computed the takeoff data with TOPCAT and received fhe following data: V1 160-162 VR 162 V2 164 (FMC produced V1 158 VR ? V2 164) / EPR 1.36 / stab trim 4.2.

With autothrottle ON and I selected EPR. The engines accelerated to 1.31 (computed EPR 1.36) and stagnated while the computed EPR decreased with increasing airspeed to 1.27 at lift off.

According to TOPCAT I shoud have had a stop margin of 410 m but I barely reached V1 at the departured end and rotated in the overrun.

I would like to raise the issue again, that the power output or acceleration values are way to low. 

AIIR#4 With all due respect to TOPCAT etc we use numbers from Boeing only.


I understand and do agree, but with all due respect then either your V1 calculation or your engine simulation is wrong. The numbers by TOPCAT aren't that far off and I posted them only to illustrate the problem I have with the engine simulation. With the numbers above I do not reach V1 prior the end off runway. By definition at V1 I should still be able to stop the aircraft in the remaining runway.
I do not know if it is the friction or engine model which causes this behaviour, but the acceleration is unrealistic and too slow.
  
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cptryan91
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Re: FLIGHT MODEL
Reply #10 - Jan 4th, 2018 at 3:35pm
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Also +1 on this as acceleration seems too sticky.

AIIR#4
Unfortunately "sticky - non sticky" won't help Smiley
If you want smth to be seriously considered provide Boeing's NUMBERS please

  
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reddishknight
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Re: FLIGHT MODEL
Reply #11 - Jan 4th, 2018 at 4:39pm
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+1 been having this so been doing toga takeoffs which is barely hitting 90% n1 or 92.1%n1 after 3 mins at full power

AIIR#4
  


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Tim Smith
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Re: FLIGHT MODEL
Reply #12 - Jan 5th, 2018 at 12:50pm
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Fuel burn doesn't match flight plans.

3ish hour flight and I burnt about 6000lbs more fuel than the PFPX generated flightplan.

AIIR#4
  
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Scholli04
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Re: FLIGHT MODEL
Reply #13 - Jan 5th, 2018 at 6:38pm
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Tim Smith wrote on Jan 5th, 2018 at 12:50pm:
Fuel burn doesn't match flight plans.

3ish hour flight and I burnt about 6000lbs more fuel than the PFPX generated flightplan.

AIIR#4


I second this one. Your 757 uses approx 13% more fuel than outlined in the Boeing FCOM.

May we see the tables you are referring to pls? The Boeing FCOM page # is fine.

Edit to answer your question: Sure, within the FCOM check page PI.21.4 for instance.
To simplify the test I checked it without winds and under ISA conditions.
If you have a Flight Planning and Performance manual available you could also do a sample flight planning for any given flight with it and compare the values it gives with those seen in your 757.
You will understand that I'm not allowed to post screenshots of the FPPM here in public.  Smiley
If you have it though: 757 FCOM Vol.3, page 04-01-6


Since you don't include fuel burn tables in your manuals I can't provide any reference to the CS manuals, I did however compare it to the tables in the original Boeing FCOM and it's about 13% too much.

These results match with those of PFPX and Simbrief by the way. PFPX and Simbrief are only about 1-2% off compared with the Boeing FCOM values.

  
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Thantheleon
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Re: FLIGHT MODEL
Reply #14 - Jan 5th, 2018 at 11:53pm
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Thanks, fuel burn is on the list.
  
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