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Re: [Jsbsim-devel] F-35 VTOL Engine Modeling
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From: Simon & J. <sim...@go...> - 2018-04-20 22:11:49
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Well I asked a simple question....
No one answered..... Was it too hard ?
I looked at the engine xml file you linked too and from it could answer the question myself.
From this I can see that your proposed method, or existing method is not the only way and that my proposal using a single external force per nozel could be done.
How now to progress...
On 20 April 2018, at 22:26, Sean McLeod <se...@se...> wrote:
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Simon your replies aren’t very clear.
“No it's not, just looked at the engine xml files....”
I took that to refer to my comment about the particular model modelling 3 separate engine types (main engine, lift fan, roll engines).
‘Intercepted’ – I presume you mean interpolated? Again took that to mean that the model wasn’t modelling a turbine engine in the normal way.
“Is it possible to rename the thrust such that it's not applied in the normal way?”
I don’t have any real idea what you’re suggesting/asking me.
I assume now that your “No it’ not” was actually referring to my statement – “Probably the easiest way…”?
If I don’t understand your question about whether it’s “possible to rename the thrust…” and you’re asking a question implying you’re not sure then using the implementation that I pointed to by the existing F-35B model is definitely going to be easier for me versus making source code changes to JSBSim to add support for multiple thrusters on engines or trying to decipher your question.
So I’m not saying it can’t be done since I don’t really know what you’re proposing.
Cheers
From: Simon & Julie <sim...@go...>
Sent: Friday, April 20, 2018 10:38 PM
To: Sean McLeod <se...@se...>; jsbsim-devel@lists sourceforge. net <jsb...@li...>
Subject: Re: [Jsbsim-devel] F-35 VTOL Engine Modeling
Ok.....
I'm confused......
I thought I answered the original question.... But if ya wanna accept it can't be done,
Well who am I to argue.
Oh yeah ..... I'm a fight modeller
On 20 April 2018, at 20:55, Sean McLeod <se...@se...> wrote:
Hi Simon
I’m confused, how is the lift fan engine any different to the CFM56 included with JSBSim used in the 737 etc.?
https://github.com/FGMEMBERS/F-35B/blob/master/Engines/liftfan.xml
Cheers
From: Simon & Julie <sim...@go...>
Sent: Friday, April 20, 2018 9:22 PM
To: Sean McLeod <se...@se...>; jsbsim-devel@lists sourceforge. net <jsb...@li...>
Subject: Re: [Jsbsim-devel] F-35 VTOL Engine Modeling
No it's not, just looked at the engine xml files.... There's a table so the thrust can be intercepted.
Simon.
On 20 April 2018, at 20:12, Sean McLeod <se...@se...> wrote:
Hi
I see in this F-35B model they model 3 separate engines. Probably the easiest for now as opposed to adding multi-thruster support to engines.
https://github.com/FGMEMBERS/F-35B
Cheers
From: Simon & Julie via Jsbsim-devel <jsb...@li...>
Sent: Friday, April 20, 2018 7:28 PM
To: jsbsim-devel@lists sourceforge. net <jsb...@li...>
Cc: Simon & Julie <sim...@go...>
Subject: Re: [Jsbsim-devel] F-35 VTOL Engine Modeling
Is it possible to rename the thrust such that it's not applied in the normal way ?
I'm not a great fan of jet engines, which is exactly what i said when I stood up one day in the middle of the design department whilst working at Rolls Royce Derby on the Trent 100.
If it is you only need the same amount of external forces as you have nozzles.
Simon.
On 20 April 2018, at 17:27, David Culp <dp...@gm...> wrote:
Hi Sean,
As for the F-22, yes thrust vectoring should work as you described. I don't know why the model doesn't do it that way.
As for the F-35/Harrier, this came up before, and IIRC the best solution was to use the proper number of engines, apply a "reverser" to the one nozzle to cut the thrust by some amount, then have the remainder sent to an external force which acts as the other nozzle.
Dave
On Fri, Apr 20, 2018, 8:50 AM Sean McLeod <se...@se...> wrote:
Hi
In terms of modeling the engine layout of an F-35 or a Harrier for that matter in JSBSim can an engine have multiple thrusters defined? With some mechanism to control what percentage of the current thrust is diverted out each thruster and a property to change the thruster’s orientation during flight?
Here is a typical definition for a single (per engine) thruster with a fixed orientation. Pitching and yawing moments will be calculated based on the thruster’s relative location to the cg during flight.
<propulsion>
<engine file="CFM56">
<location unit="IN">
<x> 540 </x>
<y> -193 </y>
<z> -40 </z>
</location>
<feed>0</feed>
<feed>2</feed>
<thruster file="direct">
<location unit="IN">
<x> 540 </x>
<y> -193 </y>
<z> -40 </z>
</location>
<orient unit="DEG">
<roll> 0 </roll>
<pitch> 0 </pitch>
<yaw> 0 </yaw>
</orient>
</thruster>
</engine>
Looking at the F-22 example included with JSBSim I was expecting to see a thruster with a property for the thruster’s pitch angle orientation that could be modified during flight but instead the thruster has a fixed orientation of (0, 0, 0) and instead a pitching moment is added to the aerodynamics section to model the thrust vectoring.
<function name="aero/coefficient/CmDtv">
<description>Pitch_moment_due_to_thrust_vectoring</description>
Having a quick look at the code in FGEngine it looks like it only supports a single thruster?
And having a quick look at FGThtuster it looks like it automatically creates the following properties.
propulsion/engine[0]/pitch-angle-rad
propulsion/engine[0]/yaw-angle-rad
So in theory the F-22 model could make use of these instead of creating a pitching moment in the aerodynamics section to model to the thrust vectoring?
So at the moment it looks like for the F-35 VTOL case one option is to add 4 engines each with a thruster, one of which swivels in pitch, the other 3 are fixed, and then have a mechanism in the FCS to map the throttle command to 4 individual throttle commands?
Or is there a better/easier mechanism to model this in JSBSim currently?
Cheers
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