Re: [Flightgear-devel] Abnormal surface friction factor

[Wayne B. <kil...@co...>]

I took another look and evaluated what I did aircraft side compared to the current source build and it appears to all be functioning as it was. It still shows visually what cover your sitting on, and the 30-50 rolling cover shows tires sunk down almost to the rims. So I guess nothing has changed, only my memory as to what all I could land on at the time. At 30 rolling, given long enough at full throttle the tundra tires actually eventually start to roll and you can take off. That is a bit odd to me. Time shouldn’t really be a factor as to why it should start to roll?

So we should still only need to change material settings for a given landcover if we were so inclined. This would be fine with me. If I can find a happy medium where default tires are too sticky and the large tundra tires work, that’s all I’m looking for.
I do think some large tracts of land being excluded from landing based solely on the cover growing on them isn’t the right way to go. In some cases yes, marshes, etc. I would rather err on the side of accessibility though than exclude millions of acres that absolutely should have spots you can land in. Tree and shrub collision would be the next logical step, I think.

@Erik,
After looking at your current work to eventually have the weather scenarios accounted for in the friction factors. It’s actually really easy to follow along what you have done already. If you have no objections and I get the gumption, I might submit some code leveraged from the gear work I did aircraft side. I had setup the cub and 172 to sink in the softer materials and snow, so you had a visual clue as to why you couldn’t move on a particular landcover. I don’t see why we couldn’t port this to the source instead and get it on all aircraft. I have a good start on the values needed to distinguish between a normal tire and a large tire. I’d have to take a close look to see if any of the other undercarriage work would apply, like skies and floats. Beings they were contacts and not bogies, I think, they probably don’t apply here.

I did a bit of work on the snow and ice aircraft side, I didn’t think to do the same for wet and dry as your doing for the seasonal changes, but that is a really good addition as well. As far as snow goes, I might need to add “dry snow” as it is really sticky until melted from friction. On aircraft without driven wheels, it’s not likely to ever heat up and get wet and slippery. So I would have to see how your settings compare to what I did aircraft side before I could make much of a comment.
We had talked about the ice awhile back and I know you got it back in there, at least for solid ice. It was the “partial ice” shader effect that was problematic. I’d still like to come up with a plan for that as I can’t imagine any scenario that wouldn’t make landing on a slab of ice an absolute gas. Can you stop in time or not?

Also I see you included a slot for an eventual hydrodynamics. That would be ideal to get that in the source. It might have a better chance of getting expanded on if it were a built in part of the source. There is so much that can be done in these disciplines to enhance the simulator.

Some might submit that this is a “flight” simulator, not a ground reaction simulator. I would argue that aircraft need both if you really want to do it justice.

@Dany, thanks again for the input and explanations.

Wayne

From: Dany
Sent: Sunday, June 18, 2023 12:23 PM
To: fli...@li...
Subject: Re: [Flightgear-devel] Abnormal surface friction factor

@wlbragg, to summarize a bit more:

Erik Hofman wrote
> Ah, that one I remember: it's to normalize rolling friction values to 
> that of rubber tires on asphalt. So yes, it's intentional.

> This would allow a different friction factor for different terrains 
> while preserving the possibility to set the friction coefficients in 
> the JSBSim configuration file. 

1- The 50 factor from (geodinfo) rolling_friction ---> (FG) 
rolling_friction-factor is not deleterious, it is a tool for 
normalization. Applied to every terrain material.

2- This normalization factor allows the rolling coefficients of 
different materials to be taken into account (proportionality), while 
leaving control over the final rolling friction coefficient, which is 
also proportional to the value given in the FDM (rolling_friction).



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