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

[Sean M. <se...@se...>]

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...<mailto: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...<mailto:jsb...@li...>>
Sent: Friday, April 20, 2018 7:28 PM
To: jsbsim-devel@lists sourceforge. net <jsb...@li...<mailto:jsb...@li...>>
Cc: Simon & Julie <sim...@go...<mailto: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...<mailto: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...<mailto: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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