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Maximum possible lift??

Postby gierschi@flightgear » Tue Apr 05, 2016 8:52 am

Hey guys,

what is the maximum possible negative or positive lift (sum of ridge lift, thermal lift and wave lift) you can get in FlightGear? Can the vertical wind velocity influence an passenger plane (like A320) a lot or is it exclusive for gliders?

best regards,
Sebastian
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Re: Maximum possible lift??

Postby Thorsten » Tue Apr 05, 2016 10:43 am

I don't think it's limited in any way, FG will simulate whatever you ask it to. I'm not entirely sure about what will occur in practice, updrafts in thunderstorms can be of the order of 12-14 m/s I suppose.

And it'll lift anything that doesn't run on a magic FDM, I've felt noticeable thermals with an F-16 in-sim.
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Re: Maximum possible lift??

Postby gierschi@flightgear » Fri Apr 08, 2016 10:41 am

Okay, and is it correct, that the FG property ''/environment/wind-from-down-fps'' is positive when the wind is coming from down (a thermal/lift) and negative when you have a wind blowing in the direction of the ground. And simultaneously the properties ''/fdm/jsbsim/atmosphere/total-wind-down-fps'' and ''/fdm/jsbsim/atmosphere/turb-down-fps'' are negativ when the wind or turbulent portion is coming from down and positive when the wind blows in the direction of the ground? So the definition is exactly the other way around in JSBSim as it is also realized for the horizontal winds??
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Re: Maximum possible lift??

Postby gierschi@flightgear » Tue Apr 19, 2016 7:49 am

No idea?
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Re: Maximum possible lift??

Postby Alant » Tue Apr 19, 2016 8:53 am

Lift is determined by the airflow over the aircraft. Flightgear imposes no limits on how this is calculated.

The important thing is that airspeed and ground speed are not the same thing. If the aircraft is flying north with an indicated airspeed of 100 kts, and the wind is coming from the north at 30 kts, then the ground speed would be 70 kts. The same applies to vertical gusts.

I think that you are confused unnecessarily
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Re: Maximum possible lift??

Postby gierschi@flightgear » Tue Apr 19, 2016 12:52 pm

Thanks for the reply

You mean the True Airspeed instead of the indicated airspeed??

My second question asks for the sign of the mentioned properties:
The FG property ''/environment/wind-from-down-fps'' is positive when the wind is coming from down (a thermal/lift) and negative when you have a wind blowing in the direction of the ground. And simultaneously the properties ''/fdm/jsbsim/atmosphere/total-wind-down-fps'' and ''/fdm/jsbsim/atmosphere/turb-down-fps'' are negativ when the wind or turbulent portion is coming from down and positive when the wind blows in the direction of the ground?
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Re: Maximum possible lift??  

Postby Alant » Tue Apr 19, 2016 1:09 pm

It seems that the JSBSim ones are equal to, but opposite in sense, to the ones in environment. The clue is the inclusion of the word "from" in ''/environment/wind-from-down-fps''.

No doubt this has a historical origin as a North wind is one that comes from the North, but actually the air is travelling in a southerly direction.
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Re: Maximum possible lift??

Postby Richard » Tue Apr 19, 2016 1:36 pm

gierschi@flightgear wrote in Tue Apr 19, 2016 12:52 pm:You mean the True Airspeed instead of the indicated airspeed


True Airspeed (TAS) and indicated airspeed (CAS) are different things again.

TAS is the speed of the aircraft relative to the outside air. https://en.wikipedia.org/wiki/True_airspeed

CAS is based on what instruments would read. https://en.wikipedia.org/wiki/Calibrated_airspeed

Ground Speed is the speed over the ground. If there is wind this will be reduced by the wind.
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