Re: [Jsbsim-devel] F-35 VTOL Engine Modeling

[Simon & J. <sim...@go...>]

"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? "

An engine can't have multiple thrusters, but that's not to say that an engines thrust can't be split up and applied at different places and orientations


"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?"

 Yes this can be done very simply, such that there's a single engine, and it's thrust is altered by any losses due to redirection and applied and varied at any direction required

There's no requirement for multiple engines.


Simon.



On 20 April 2018, at 16:50, Sean McLeod <se...@se...> wrote:

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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