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Creare's Parachutist

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Re: Creare's Parachutist

Postby erik » Sun Apr 12, 2020 2:09 pm

Ok, then you could use the paraglider and remove the propulsion section in paraglider.xml
You could also adjust the mass of the crate in the mass_balance section
And you can modify the specifications of the chute in the metrics section.

Erik
Current: Parachutist, Paraglider, Pterosaur, Pilatus PC-9M and variants, ERCO Ercoupe, Fokker Dr.1, Fokker 50, Fokker 100
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Re: Creare's Parachutist

Postby KvnFr824 » Tue Apr 14, 2020 10:07 am

Thank you for the information. I managed to remove the propulsion and change the size and mass of the system. However, this is causing instability. Did you use any particular method to find the aerodynamic coefficients of the model ?

Kévin
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Re: Creare's Parachutist

Postby erik » Tue Apr 14, 2020 12:05 pm

The Aerodynamic coefficients where from a CFD Calculation as mentioned in the header file:
http://www.cobaltcfd.com/pdfs/2016/AIAA-2016-1536.pdf

What I did notice is that a too low drag (both forward-backward and side-to-side) for the object that would simulate the crate/box/mass could cause instabilities. These are the "due_to_pilot" drag, side-fore and pitching moment.
You might want to increase those.

Update:
Oh and you might want to change the pilot area and pilot arm at the start of the aerodynamics section.

Erik
Current: Parachutist, Paraglider, Pterosaur, Pilatus PC-9M and variants, ERCO Ercoupe, Fokker Dr.1, Fokker 50, Fokker 100
Less active: Cessna T-37, T-38, Santa Claus. Previous: General Dynamics F-16. Worked on: Wright Flyer
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Re: Creare's Parachutist

Postby KvnFr824 » Tue Apr 14, 2020 4:45 pm

The dimensions of the canopy are 5m * 1m for approximately 1.5kg, the payload is a box of approximately 50cm * 50cm for a total mass of 10kg. I can't find the stability by only changing these parameters, the pilot area and pilot arm, as well as the "due_to_pilot" drag, side-force and pitching moment.
So do I necessarily have to change the other aerodynamic coefficients ?
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Re: Creare's Parachutist

Postby erik » Tue Apr 14, 2020 9:40 pm

Normally I would say no since the coefficients are normalized so adjusting the parameter values should do the trick.
I'll try the setup tomorrow to see if I can find anything special.

Erik
Current: Parachutist, Paraglider, Pterosaur, Pilatus PC-9M and variants, ERCO Ercoupe, Fokker Dr.1, Fokker 50, Fokker 100
Less active: Cessna T-37, T-38, Santa Claus. Previous: General Dynamics F-16. Worked on: Wright Flyer
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Re: Creare's Parachutist

Postby erik » Wed Apr 15, 2020 8:07 am

Ok, I've created a stripped down version of the paraglider which meets your requirements and is stable for me when run like this:
Code: Select all
fgfs --aircraft=ramair --altitude=1000

http://adalin.com/ehtw.info/dropchute.zip

Erik
Current: Parachutist, Paraglider, Pterosaur, Pilatus PC-9M and variants, ERCO Ercoupe, Fokker Dr.1, Fokker 50, Fokker 100
Less active: Cessna T-37, T-38, Santa Claus. Previous: General Dynamics F-16. Worked on: Wright Flyer
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Re: Creare's Parachutist

Postby KvnFr824 » Wed Apr 15, 2020 9:02 am

Indeed the system is quite stable.
Thank you very much for your help and your reactivity !

Kévin
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Re: Creare's Parachutist

Postby erik » Wed Apr 15, 2020 9:08 am

You're welcome.
Best of luck with the project.

Erik
Current: Parachutist, Paraglider, Pterosaur, Pilatus PC-9M and variants, ERCO Ercoupe, Fokker Dr.1, Fokker 50, Fokker 100
Less active: Cessna T-37, T-38, Santa Claus. Previous: General Dynamics F-16. Worked on: Wright Flyer
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