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

[David C. <dp...@gm...>]

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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