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Azorean Groundnets with FGAirports

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Re: Azorean Groundnets with FGAirports

Postby AzulProfundo » Fri Jun 04, 2021 7:10 pm

Johan G wrote in Fri Jun 04, 2021 9:12 am:Looking up the Bombardier Q200 performance (the closest I could find performance data on without searching too much), takeoff distance is 3280 ft and landing field length 2560 ft (both at sea level and ISA conditions).[2] So unfortunately it looks like the AI traffic likely works like it should. Are you sure it is the right aircraft type for those flights?


They (SATA) use it on a daily basis to operate on that runway. Perhaps is a special version of the aircraft, or they do other things (like limited weight from passengers and fuel) in order to takeoff from a shorter than usual runway. The landing distance is within limits though, but the aircraft is not able to land properly.

The simulator is the ideal place to test what happens. The DH8-200 model is not the best, but the 300 behaves more closely to the specifications, so I can do a takeoff test there.
Off course, the definite answer should come from the pilots operating that route. I can search in Portuguese fora to see if know more about it, or even get a contact.

On the portreekid comments about the code: I don't remember to see any acceleration value in the performance database. So, where is it reading this value?
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Re: Azorean Groundnets with FGAirports

Postby wkitty42 » Fri Jun 04, 2021 7:39 pm

portreekid wrote in Fri Jun 04, 2021 3:14 pm:AFAIR there is one constant distance in C++ that is always added. This could be a problem for short runways.

looks like that ACCEL_POINT needs to be changed to something calculated (or taken directly) from the craft's performance record instead of being hard coded like it is...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
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Re: Azorean Groundnets with FGAirports

Postby Johan G » Fri Jun 04, 2021 8:38 pm

wkitty42 wrote in Fri Jun 04, 2021 7:39 pm:looks like that ACCEL_POINT needs to be changed to something calculated (or taken directly) from the craft's performance record instead of being hard coded like it is...

Ah. I note now that some aircraft classes in AI/Aircraft/performancedb.xml have the lines (this is the generic turboprop_transport category)
Code: Select all
      <acceleration-kts-hour>6.0</acceleration-kts-hour>
      <deceleration-kts-hour>2.0</deceleration-kts-hour>

While other probably inherit that from the aircraft category, judging from that all aircraft seem to have a line like (this is what the Dash8-200 / Q200 use)
Code: Select all
      <base>turboprop_transport</base>
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Re: Azorean Groundnets with FGAirports

Postby wkitty42 » Sat Jun 05, 2021 12:02 am

yep! so the ACCEL_POINT can be calculated from the aircraft's performance instead of being assumed and hard coded so that all craft act like the long haul jets the AI traffic manager seems to have been written to handle by default... this should bring the AITM more into alignment for less powerful craft... the question is if this value is also used in the route calculations when the AITM created the ballistic route the craft will fly from departure to arrival...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
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Re: Azorean Groundnets with FGAirports

Postby AzulProfundo » Mon Jun 07, 2021 5:46 pm

From the discussion above, I think it will be possible to solve the question, subject to modifications and tests. One thing I can do is to modify the file for the DH4 and DH3 (the DH2 is an alias, and also the aircraft model), introducing the acceleration and deceleration figures, and seeing the results. BTW, units for those should be kts-hour-hour or kts-hour2.

[Edit] My wrong. Knots are nautical miles per hour, so knots per hour is OK. SI units is m/s2. Accepting the value above (6) and the length of 1000m for the MTOW, it should take 18 seconds to be airborne...

Other suggestion is to create a new base class, like "turboprop_shortfieldoperations", from where aircraft in that category could inherit the values allowing such operations.
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Re: Azorean Groundnets with FGAirports

Postby AzulProfundo » Tue Jun 08, 2021 11:38 pm

A takeoff run with the Dash8-200 of the default hangar, in ISA conditions and the MTOW, gave me 21 seconds to get airborne after 850 meters of runway. I have used the LPPD - Ponta Delgada runway, just to be safe and avoid ditching into the sea... :D
To succeed in taking off from LPCR - Corvo, I will reduce the weight in about 3000 lbs and put 15º flaps (instead of the usual 5º).

Doing some simple maths on this test, acceleration was 2.74 m/s2 or 5.3 kt/s, which is a little bit lower than the figure found in the performance file (6.0). On the other hand, the deceleration seams very slow in the performance file, in fact the aircraft need less runway in landing than in the takeoff.

For those interested in replaying the test, I have put in tape (file available through google drive).

To re-run, just use the above mentioned plane from Rwy 12 of LPPD, and load it to 36300 lb. I used a manual METAR:
LPPD 080800Z 12005KT 9999 CAVOK 15/07 Q1013

The fgtape:
https://drive.google.com/file/d/1Q0Jw0_IUSRU8x_sWUnWLnY-df63mlbz0/view?usp=sharing
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