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  • Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.

    Post 16 Update

    Post 17 Warning

One thing FSX does not model well

K

Ken Stallings

Guest
My Skyhawk finished its annual last week, and I've been waiting a full week for time off from work plus reasonable winds to stretch her legs. Today was the best we've had here in Portales for a while -- variable winds 310 to 010, 10 knots with gusts to 17 knots! Like I said, it was the best we've had for a while!! :icon_lol:

Anyway, knocked out three in the pattern and let me tell you, the winds at surface was only half the story. Right about the 500 foot AGL mark there was a ten knot sheer factor with the winds going from north at 10 knots to north at 20 knots!

You could really feel it in the aircraft too! It wasn't until I got on short final that the airspeed gauge settled down to anything reliable. Prior to that point, the sucker was variable from 85 KIAS to 70 KIAS as I held a bit more power than normal on final. Finally, below 500 feet it settled down to a known power setting (1700 RPM) yeilding a known approach airspeed (70 KIAS).

This is something FSX simply does not model well. It seems the variations don't come fast enough nor have quite the affect on a smaller aircraft like the Skyhawk which it should. The interesting thing is even on the military simulator of the MQ-1B Predator that Link built it has the same issue.

There's also a very noticeable difference in how various aircraft react. Heavier aircraft are much more stable in these types of variable wind conditions. A C-310R weighing around 4,000 to 5,000 pounds on landing is significantly more stable than a Skyhawk weighing between 1500 and 2000 pounds on landing.

Cheers,

Ken
 
FSX models wind effects quite good (EDIT: let's make that "reasonable").
The problem really is how the stockers and most third party addons that copy stock airfiles are configured to fly in maple sirup rather than air.
There are not really an awfull lot of aircraft out there that actually model coupled moi.
 
its one of the reasons i've never stepped foot in a 157. my first flight out we followed a 157 in for landing. i was in a cherokee which is a much larger plane ( i'm afraid of heights and prefer bigger planes ). The ocean breeze coming into watsonville muni was bouncing that little 157 around like it was a leaf. We of course stayed nice and steady, with the pilot almost ( probably was really ) bored out of his skull.. 'I cant help but wonder if ASE isnt set up for wind shear? i havent had a great deal of time to use it yet, but i know FSX by itself simply doesnt do it well.. On the other hand, most universities use a Cray computer to model parts of the weather system.. it simply may not be possible to do it in fsx..
 
Mathias said:
FSX models wind effects quite good.
The problem really is how the stockers and most third party addons that copy stock airfiles are configured to fly in maple sirup rather than air.
There are not really an awfull lot of aircraft out there that actually model coupled moi.
Click to expand...

Thats very true as well. its not just MOI's but the entire fde has to be set up correctly. The limitation there is that most devs want an FDE out in three months or so. Thats not a lot of time for accuracy. if we had a year and a half to go through each and every single calculation there is for the FDE then maybe perhaps we'd have an accurate model. Also, theres not a lot of us that have degrees in fluid dynamics. i figure we would if we wanted to make a career out of aerodynamics, but most of us still do this for fun.

The difficulty with Coupled Yaw MOI is finding the formula for determining it. i've searched high and lo, found a lot of negative FS gobbledygook about how its unimportant and gone so far as to create my own formula which seems to work ( although i suspect its not exactly accurate ). theres a lot of talk about it, but very little that goes into figuring it out. I cant blame anyone for not using it..
 
Even a 747-400 at a light weight, say 350,000 lbs seems to be quite a kite in the gusty air! Max wt landings at 664,000 lbs are generally much easier, even if taking up a lot of real estate at an over the fence of 160 knots. In a fair breeze the Supercub can require an active stick and throttle and it's not done flying till it's tied down. Even our $50,000,000 full motion sims do not do a sophisticated job of modeling dynamic weather except for the windshear scenarios, which are canned.

Where FS weather really falls down is at weather boundaries at high altitude, 180 degree 70 knot windshifts in less than a second have been common in the jets stream as modeled, with predictable results!

The Super Computer is probably the current best bet and might not be capable of large scale real time computations.

It is what it is, and does an OK job within it's limits!

Cheers: T
 
You can get a pretty decent shearr effect in FSX.. but not from default weather themes.. and not even from real-time weather.

You have to set one up yourself.. which kinda spoils it, because you know exaclty where it happens, and how strong it will be.

In the user-defined weather, just set up two wind layers having different winds (even different directions). I played around once and did something extreme.. 30knot headwind that switched to a 30knot tailwind at 100agl.

I fell right out of the sky.. :isadizzy:
 
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