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FloatGear: Skipjack Kathryn...

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Re: FloatGear: Skipjack Kathryn...

Postby Kugelfang » Sun Jul 31, 2022 9:53 am

TheEagle wrote in Sat Jul 30, 2022 4:06 pm:Have you got data as graphs / spreadsheet whatever that just need to be brought in the right form for JSBsim, or do you need help with actually calculating that data ? ...


I'm looking for a way to calculate the data.
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Re: FloatGear: Skipjack Kathryn...

Postby TheEagle » Sun Jul 31, 2022 10:46 am

Okay, sadly I got about the same problem as you (in general) ! :mrgreen:
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Re: FloatGear: Skipjack Kathryn...

Postby S&J » Sun Jul 31, 2022 8:54 pm

Bouancy force is a product of volume of displaced water.

Knowing the volume of water displaced at light float level allows an FG system to do a quick calculation to determine the value of water weight displaced. This value is equal to the weight of the boat, such that it floats. And can be expressed as an external force in the World Z axis.

So based upon your datum point used a simple height above sea level table could be created to determine volume.

And heh presto your boat would float in FG.
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Re: FloatGear: Skipjack Kathryn...

Postby Kugelfang » Sat Aug 20, 2022 9:35 pm

Is there a property that shows the true course of a vehicle?

Since I'm developing a wind driven boat, the heading is not necessarily the direction of travel. Since I don't have much keel action going on, sometimes I'm going sideways, sometimes backwards. It would be nice to know the true direction of travel.

TIA,

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Re: FloatGear: Skipjack Kathryn...

Postby S&J » Sat Aug 20, 2022 10:23 pm

Use the u-fps and v-fps to calculate the vehicles beta travel.

Use atan2
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Re: FloatGear: Skipjack Kathryn...

Postby TheEagle » Sat Aug 20, 2022 10:28 pm

/orientation/heading-deg + /orientation/beta-deg (or sideslip-deg ?) should give you what you want.
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Re: FloatGear: Skipjack Kathryn...

Postby S&J » Sun Aug 21, 2022 10:12 am

only he'd need to understand his slippage through the water not the air.
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Re: FloatGear: Skipjack Kathryn...

Postby TheEagle » Sun Aug 21, 2022 11:20 am

Hmm … I guess, I forgot that ! :mrgreen: In that case, your hydrodynamics must have some sort of sideforce calculation, which needs exactly what you are searching for, so you should be able to find it there ! :)
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Re: FloatGear: Skipjack Kathryn...

Postby S&J » Sun Aug 21, 2022 7:10 pm

The side force won't give you direction of travel. What you need is the speed to the side and the speed forward. This will give you a beta rad. Add this to the heading and you'll calculate the direction of travel.

So if you have a heading of 175.... A beta angle of 5 then you're travelling at a bearing of 180.
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Re: FloatGear: Skipjack Kathryn...

Postby TheEagle » Sun Aug 21, 2022 10:04 pm

Yeah, but the side force calculation needs some sort of beta-deg (not the aero/beta-deg of course) or beta-rad ! :wink: I thought you could use that …
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Re: FloatGear: Skipjack Kathryn...

Postby Kugelfang » Mon Aug 22, 2022 12:12 am

Thanks guys.

Took a while to find the right properties but I think I got it now. In upper left corner you can see the results. The red line on the outer compass ring indicates the heading of the boat. The green arrow points down to the inner compass showing the true course. So in this screenshot the vessel is facing almost due east yet traveling to the northwest at 307 degrees at 3.4 knots. The wind (dark blue triangle) is coming from due south (180) almost directly over the starboard beam. This appears correct to me though I've not spent a lot of time verifying it.

Image

The Nasal code that got there (and yes, I will eventually refactor to nodes instead of get/set props):

Code: Select all
    #update true course_data indicator/data
    var east_deg_sec = getprop("/fdm/jsbsim/velocities/vrp-v-east-deg_sec");
    var north_deg_sec = getprop("/fdm/jsbsim/velocities/vrp-v-north-deg_sec");
    var true_course_deg = math.atan2(east_deg_sec, north_deg_sec) * R2D;
    #rotate true course pointer on compass
    true_course_indicator.setRotation(true_course_deg * D2R);
    if(true_course_deg < 0)
      {true_course_deg = 360 + true_course_deg;}
    #update true course data display
    true_course_data.setText(sprintf("%.0f Deg", true_course_deg));


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Re: FloatGear: Skipjack Kathryn...

Postby Gijs » Mon Aug 22, 2022 7:27 am

Wouldn't using /orientation/track-deg suffice (or even /orientation/track-magnetic-deg)? It's calculated based on the difference between the current position and that in the previous frame.
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Re: FloatGear: Skipjack Kathryn...

Postby S&J » Mon Aug 22, 2022 8:04 am

Can we assume the sail animation is still WIP, it's rotation seem off.
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Re: FloatGear: Skipjack Kathryn...

Postby TheEagle » Mon Aug 22, 2022 9:32 am

Exactly Gijs ! That was what I was searching for, but from my memory landed at /orientation/beta-deg instead ! :mrgreen:
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Re: FloatGear: Skipjack Kathryn...

Postby wkitty42 » Mon Aug 22, 2022 10:49 am

Kugelfang wrote in Mon Aug 22, 2022 12:12 am:Took a while to find the right properties but I think I got it now. In upper left corner you can see the results. The red line on the outer compass ring indicates the heading of the boat. The green arrow points down to the inner compass showing the true course. So in this screenshot the vessel is facing almost due east yet traveling to the northwest at 307 degrees at 3.4 knots. The wind (dark blue triangle) is coming from due south (180) almost directly over the starboard beam. This appears correct to me though I've not spent a lot of time verifying it.

i notice in your image, your rudder is hard to starboard... what happens if you set it amidship in the same scenario?
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