Jet aircraft speed on departure

[Jean-Frederik Dion 819740]

I find quite unrealistic the way aircrafts behave on departure below 10k, especially jets. They roll, rotate, accelerate to 250K GS then at a certain altitude their speed increases up to 450K GS before they reduce back to 250kts until they reach 10k. It's pretty hard to get a realistic departure sequence because of that.

 

Is this a known issue? Personnally, I'ld like an option to discard the 250kts restriction on departure, as in many countries there's no speed limit on departure.

[Ross Carlson]

What program are you talking about?

[James Hudson 951027]

IN real life, thats the rule, its not just VATSIM. Most aircraft, non heavies, they can depart at a Indicated Airspeed IAS of around the 150s. GS depending on winds would be close.

[Chris Brew 814351]

I believe JF is referring to TWRTrainer

[Jean-Frederik Dion 819740]

yup TWR trainer, sorry about the delay..

[Ross Carlson]

I'm not seeing this problem. Jets accelerate to 250 and stay there until 10k, and then they accelerate to 450. I'm not seeing the increase to 450 then decrease to 250 as you described.

[Istvan Varadi]

It's not 250K GS until 10k, it's 250K IAS (indicated airspeed), which means that as they go higher, their ground speed (actually, their TAS, true airspeed) increases continuously, while the IAS stays the same. Above 10k, they accelerate somewhat, but e.g. a B737 only to about 260-300 knots IAS, depending on altitude and thrust settings. It's their true airspeed that reaches 450 knots, and you get the ground speed by adding the relative wind speed to TAS.

 

Istvan

[Jean-Frederik Dion 819740]

I'm still looking into that problem as it seems to only happen at some airports, in some circomstances. Ross, I'll email you some files when I get to isolate the problem.

 

One more thing though. Props do behave unrealisticly by reaching 250 knots (seems TWRt doesn't care GS/IAS Istvan), which is pretty fast for a climbing turboprop. It almost makes it impossible to get a jet p[Mod - Happy Thoughts] by a prop, below 10k.

[Ross Carlson]

One more thing though. Props do behave unrealisticly by reaching 250 knots (seems TWRt doesn't care GS/IAS Istvan), which is pretty fast for a climbing turboprop. It almost makes it impossible to get a jet p[Mod - Happy Thoughts] by a prop, below 10k.

 

Yeah, TWRTrainer doesn't simulate different climb and cruise speeds. It just has one speed that it uses for each engine type. (Prop, Tprop, Jet, Helo) As soon as an aircraft lifts off, it accelerates to that speed and will retain that speed no matter what it's doing (climbing, descending, or level flight) until you give it a different speed command.

 

Note that twrtrainer is not meant to simulate accurate behavior for departures once they leave the ground. Unless the aircraft is staying in the pattern, it'll be sent to the departure controller anyway, which is outside the realm of what twrtrainer was designed to simulate.

 

If you wish to control the speeds of departures during their climb to cruise alt, then use the dot commands.

[Jean-Frederik Dion 819740]

Despite the fact that it's not made for terminal control, TWRtrainer does the job pretty well, and is more user friendly than ACsim in my opinion.

 

Tonight while doing some terminal training I figured out what the problem is on the departing aircraft speed. I'm not asking for a fix here, just to let you know... Initially, a jet aircraft accelerates to 450 knots and as soon as you command him to climb higher than 10000 it will drasticly reduce to 250 kts and when p[Mod - Happy Thoughts]ing 10k will gradually increase the speed.

[Ross Carlson]

There must be more to it. When I test this, and by looking at the code, jets depart and accelerate to 250 and stay there until crossing 10k. I've never seen a jet accelerate beyond 250 then slow back down, unless told to do so with speed commands.

[Jean-Frederik Dion 819740]

Indeed, there must be more to it... I've no clue how it's writen but I know what I see.

 

Here's AFR347 given the following: CTO (5000 as defined in the apt file.

And here he is, a few sweeps after I gave him: CM 10001.

 

Maybe I have the wrong version? v1.0.101

[Ross Carlson]

Send me your apt and air files, and I'll see if I can reproduce the problem on my end. My email is vatsim at metacraft dot com.