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trying to spin

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trying to spin

Postby copeaviation » Thu Dec 26, 2013 11:30 am

hi all
i was recently flying and thought id do some spinning but found out it was impossible to spin it. i was wondering if it was the sim not modelling it or if it was my bad flying to get it to spin.
any feedback on the ability to spin would be appreciated. many thanks.
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Re: trying to spin

Postby islandmonkey » Thu Dec 26, 2013 12:27 pm

Hello there and welcome to the forum!

Just one question - what aircraft were you flying? For obvious reasons heavy aircraft fail to spin properly - I have observed on the 777-200ER and on other airliners that when the aircraft banks too much it pitches down heavily to the point where an unrecoverable nosedive occurs.
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Re: trying to spin

Postby hvengel » Thu Dec 26, 2013 6:27 pm

For JSBSim aircraft spins need to be explicitly modeled and most aircraft do not do this. The JSBSim P-51D will spin in a realistic fashion. There may be other as well but I don't know which off hand.
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Re: trying to spin

Postby Kabuki » Thu Dec 26, 2013 7:00 pm

I've wondered about this myself, because I've been unable to induce a spin when I tried a while ago. I can't remember which plane I was flying, but it just would not do it. OTOH, @hvengel says the Mustang will spin... My experience with this plane is limited, but it's sure not as "forgiving" as a Zero.

IMHO, the Zero is about due for a FDM makeover. It's a great plane for learning how to fly (taxi and takeoff) a taildragger, but heck... you can make maneuvers in that plane that would probably dismember the pilot, let alone break the wings.
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Re: trying to spin

Postby Thorsten » Fri Dec 27, 2013 9:32 am

To my knowledge only the P-51D and the DR-400 will spin properly.
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Re: trying to spin

Postby sim » Sat Dec 28, 2013 3:13 pm

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Re: trying to spin

Postby dany93 » Sun Dec 29, 2013 3:42 pm

copeaviation wrote in Thu Dec 26, 2013 11:30 am:any feedback on the ability to spin would be appreciated.

Hi, copeaviation, and welcome.

I presume you are speaking about stall and spin. Meaning that you have to make the aircraft asymmetrically stall for spinning.
As written above, experiments have been made, but only on a few JSBSim models. Most JSBSim aircraft do not spin, some others (YASim) make illusion but often not realistically.

Robin DR-400 JSBSim (PAF, Patrouille de France version). Different from the official (main site) YASim version.
Unfortunately not perfect...
If you are interested, I've recently (slightly) improved its behavior (spinning and slip skid ball). I can upload it and give you a special link.

For the C172P, you have to add some extra lines in the FDM (Aircraft\c172p\c172p.xml). See this post. But be careful, I'm afraid they may be not exactly fitted to the present version.
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Re: trying to spin

Postby stuart » Sun Dec 29, 2013 9:37 pm

Hi dany93,

Thanks for reminding me of your work on the JSBSim spin model.

As the maintainer of the C172P in the base package, I'd be interested in integrating your work, if you'd be happy for me to do do.

I took a quick look at the changes in the post from 2010, but it looks like the FDM has moved on somewhat, as each of the sections are quite different. Can I simply add the Assymetric stall sections to the end of the <product> groups? Or would you be interested in revisiting this with the latest FDM at all?

Thanks,

-Stuart
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Re: trying to spin

Postby dany93 » Sun Dec 29, 2013 11:47 pm

Hi Stuart,

With great pleasure.

I think adding the Asymmetric stall sections at the right places should be enough. However, it would be better and more simple for you that I try integrating them into the latest FDM. Just let me some time to look at this and test.
As I'm still with FG 2.10, I may do it with this FG version if the very last C172P is not compatible (canevas ?). I hope it will be enough for the FDM. Or possibly by taking only the last FDM. I'll see.

And many thanks for maintaining this aircraft.

Cheers,

Dany
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Re: trying to spin

Postby dany93 » Mon Dec 30, 2013 5:35 pm

Hi Stuart,

I've added the code lines for "spin and stall" in the C172P's last FDM (downloaded from the official site, 20130826 version).
In fact, the values needed to be fitted for the present FDM.

The spinning effect is obtained, but (as could be expected) with some imperfections.

Results:

1) With throttle at 0 (engine at idle):
- in a straight trajectory (wings levelled), the aircraft tends to "parachute" (baloon?) at constant AoA instead of diving. It can be true, I do not know this aircrfaft IRL.
Buffeting appears, the slip skid ball (unfortunately not very visible) is to be kept well centered before stall, do not let the aircraft yaw (control with rudder) to avoid spinning. That seems normal. Spin can be severe if we insist on holding the yoke back.
- in a turn, the spin did not easily occur for the same "parachuting" reason, even with the stick full backward. The stall AoA was hardly attained. Now, it can be obtained after increasing elevator efficiency, which seems sensible, not excessive after my tests.

2) With enough throttle, steep turns (stick pulled) can give severe spins when large AoA's are attained. Obviously worst with too much rudder (slip skid ball outwards). Correct (at least qualitatively.

3) In forward slip (throttle at 0), the upper (downwind) wing falls down when stall occurs, which is correct. However, from my point of view, the bank angle is too weak in forward slipping. Rudder efficiency seems slightly low (for decrabbing with crosswind at landing). After more testing, I've slightly increased rudder efficiency, not only for crosswind decrabbing but also because it's an important control for spin recovery. Even after this, I think it's still a bit weak.

I did not want to change noticeably (at risk of degradation) the general handling of the FDM in normal operation. I've only modified two or three minor parameters in order to obtain stall spinning. Let me know if you feel I've degraded something (I don't think so).
Future tests will probably bring some ideas for refinements, but I think the best is to have a first version. Would it be only to decide if it can be considered as an improvement, with no drawbacks.

The FDM is ready to be sent, what do you prefer ? Personal mail? A link? The file is a bit long to be inserted into the forum, unless someone else is interested. I don't want to pollute.

Dany
Last edited by dany93 on Wed Jan 22, 2014 11:44 am, edited 1 time in total.
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Re: trying to spin

Postby dany93 » Fri Jan 03, 2014 2:54 pm

Hi Stuart,

No response ?
For you and those interested (if any ?), a link to the FDM C172P_stall-and-spin_FDM_20140103

If anyone would like testing it, replacement procedure:
- under FlightGear\data\Aircraft\c172p\, displace c172p.xml to another place to keep it as a backup, (or simply rename it, e.g. c172p_ini.xml)
- replace it for this (new) c172p.xml.
It should work at least with FG 2.12 and 2.10.
"Auto-coordination" NOT activated, of course !

Dany
Last edited by dany93 on Sun Jan 05, 2014 3:30 pm, edited 1 time in total.
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Re: trying to spin

Postby stuart » Fri Jan 03, 2014 3:25 pm

Hi Dany,

Sorry for the delay in responding. For some reason I missed your previous post.

Thanks very much for the updated FDM. I'll take it for a spin :)

-Stuart
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Re: trying to spin

Postby daveculp » Sat Jan 04, 2014 10:46 pm

The F-100 model from my hanger will "depart", or begin to enter a spin if the ailerons are moved too much at high AOA. This is not an actual spin, but close.
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Re: trying to spin

Postby Necolatis » Mon Jan 06, 2014 7:17 am

Should a single engine jet fighter be able to spin?

If so how do I put it into spin?
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Re: trying to spin

Postby hamzaalloush » Mon Jan 06, 2014 8:30 am

@dany93,

i tried your fdm config file,

there is a slight improvement in the controls that i can't put my finger on, is that what you ment by increase effectivness?

i found that indeed the rudder is better suited now for crosswind approach, it seems to move the plane around with more force thus coming in smoother in centerline, i don't know if there is an effect or it's placebo lol, but this what i would describe it

also, i agree with your other points, the aircraft does indeed baloon foreward when maintain level wings with decreasing throttle.

i found the spin effect however a little increased, tried going in a spin on the left wing and the aircraft rolled about 60* left, nose down. trying to recover by pitching up while lossing altitude caused it to "snap spin" and tip over into the ground. a little snappy, but is this supposed to be the way it spins?

again, thanks for making these improvement on the c172p
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