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Good sims require good FDMs (the "thing" that makes an aircraft behave like an aircraft).

Brakes / reversers efficiency

Postby V12 » Tue Jan 09, 2018 12:41 pm

How can I change brake and reversers efficiency ? Some aircrafts have too powerfull brakes and (or) reversers. There are other aircrafts with too weak reversers. Are there some parameters to modify that behaviour ?
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Re: Brakes / reversers efficiency

Postby Thorsten » Tue Jan 09, 2018 1:58 pm

For JSBSim at least, the drag / friction coefficients in the FDM definitions should do the trick. Reversers might depend on the implementation, whether they're hacky or not.
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Re: Brakes / reversers efficiency

Postby V12 » Tue Jan 09, 2018 3:50 pm

Thank You, I will check it.
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Re: Brakes / reversers efficiency  

Postby daveculp » Tue Jan 09, 2018 8:59 pm

For reversers on a JSBSim airplane check to see if there is a system file called "reverser.xml". You can modify the reversing value there (I use a value of 2.0 radians, but others may use different values). If there is no such file, then the author may have implemented it in nasal.

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Re: Brakes / reversers efficiency

Postby V12 » Tue Jan 09, 2018 9:08 pm

I tested Concorde with brakes friction lowered from 0.8 to 0.5 and braking distance to full stop was significant longer. That thing works ! I need check reversers.
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Re: Brakes / reversers efficiency

Postby daveculp » Tue Jan 09, 2018 9:41 pm

Here's a graphic illustrating the meaning of "reverser angle" in JSBSim:

Image
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Re: Brakes / reversers efficiency

Postby V12 » Wed Jan 10, 2018 4:37 am

Thank You for explanation.

EDIT :
Solved.
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Re: Brakes / reversers efficiency

Postby radi » Thu Jan 11, 2018 1:36 am

V12 wrote in Tue Jan 09, 2018 9:08 pm:I tested Concorde with brakes friction lowered from 0.8 to 0.5 and braking distance to full stop was significant longer. That thing works ! I need check reversers.

I came to the same conclusion, values for static friction around 0.5 seem to give reasonably realistic brake deceleration around 3 m/s^2.

http://wiki.flightgear.org/Airliner_brake_performance
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Re: Brakes / reversers efficiency

Postby V12 » Thu Jan 11, 2018 6:30 pm

At Edwards AFB I made tests of brake efficiency from 180 kts to full stop :
Concorde 16 secs / 5.8ms-2, 750 meters of braking - unrealistic
A340, B777, A380 omega similar to Concorde - considered as strongly unrealistic
B707 23 secs / 4ms-2, 1100 meters of braking considered as possible
IDG A318 27 secs / 3.4ms-2, 1300 meters of braking - should be OK
IDG A330 31 secs / 3ms-2, 1500 meters of braking - again OK
B747 36 secs / 2.6ms-2, 1700 meters of braking - considered as realistic

Repair of the unrealistic aircraft is simple, as Thorsten wrote in his post :
Thorsten wrote in Tue Jan 09, 2018 1:58 pm:For JSBSim at least, the drag / friction coefficients in the FDM definitions should do the trick. Reversers might depend on the implementation, whether they're hacky or not.


EDIT :
My Concorde (https://github.com/BAWV12/Concorde) has been fixed - now is 30 secs / 3ms-2 and around 1450 meters from 180 kts to full stop with gross weight 130 tons. With that parameters and maximum landing weight 111 tons is still possible land at Paro, but it is very difficult. Landing at Merida (SVMD, Venezuela) is almost attempt for suicide.
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Re: Brakes / reversers efficiency

Postby Isaak » Fri Jan 12, 2018 9:36 am

I 'll take a look at the 777's brake system. I 've never experienced it braking unrealistic because I almost never brake manually after landing, but making it more realistic is certainly important for those scenarios where you do have to intervene.
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Re: Brakes / reversers efficiency

Postby V12 » Fri Jan 12, 2018 2:26 pm

If basic information about mean braking deceleration about 3.5 m/s2 is correct, You should try set static friction 0.5 and dynamic friction to 0.4.
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Re: Brakes / reversers efficiency

Postby V12 » Sat Jan 13, 2018 4:57 pm

I made some tests with 777-300ER and friction 0.5/0.4. Landing distance was more realistic, than with standard setup 1.0/0.9. Even better is 0.4/0.3 setup.
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Re: Brakes / reversers efficiency

Postby V12 » Sat Jan 20, 2018 5:24 pm

New test with B737YV :
Braking from 180 kts, 15 seconds, deceleration 6.1ms-2, braking distance 700 meters - unrealistic.
With friction lowered from 0.8 to 0.4 (static) and 0.5 to 0.3 (dynamic) :
Braking 27 seconds, deceleration 3.4ms-2, 1300 meters of braking is more realistic.
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Re: Brakes / reversers efficiency

Postby Octal450 » Sat Jan 20, 2018 5:30 pm

I lowered mine on the Airbus to around the right values. I can change the 738 also when I've got time.
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