Strut Compression

[whamil77 183]

While looking at a replay of a landing, I noticed the main landing gear struts do not extend inflight.  The compression of the strut is exactly the same in flight as it is on the ground.  Thinking it was just a replay anomaly, I performed a takeoff from a spot view perspective.  Same result.  I then looked at the model with MCX.  Carenado modeled the main landing gear struts with the full range of motion.  I tried various values of static and dynamic compression as well as static cg height, to no avail. 

 

I have noticed other aircraft seem to have the same problem.  Is this a P3D problem or an aircraft problem?

 

[whamil77 183]

Never mind.....     Carenado had inserted a 4.0 maximum compression ratio (hard to do when the static compression is already 0.4).  I changed it to 2.5 (2.5 X 0.4 = 1.0) and it works properly.  It wasn't that the strut wasn't extending.  It was already extended fully on the ground.  It wouldn't compress on landing. 

[FDEdev 955]

Confirm you made your tests at MTOW as this is the only weight which results in a valid assessment concerning the shockstrut simulation in FSX/P3D.

BTW, there might be a reason why they have chosen this compression ratio. The nosegear shockstrut has already very little travel and if your 'corrected' 525 sits even lower, chances are that the nosewheel digs deep into the runway during braking. Especially at high weight. 

[whamil77 183]

In reality, strut compression doesn't vary drastically with Gross Weight because Gross Weight doesn't vary drastically as a percentage of MTOW.   The minimum weights in the CJ2 charts are 9000# which is 73% of MTOW.  That last 27% of weight doesn't change strut compression very much.  In the case of the CJ2, a strut compression of 0.4 at MTOW would equal about 0.3, at 9000#, not even noticeable without a ruler.  In the Carenado CJ2 case there was almost no compression at ~ 11,000#, totally unreal.  I changed the settings to get the airplane to sit correctly but I do get some minor digging (not enough to see unless the camera angle is only a few feet away). 

I have actually done more work with AI aircraft struts.  Once I get the .air file and aircraft.cfg file to the point the airplane flies well (few do well right out of the box and almost none land appropriately), I then change the strut numbers to get the proper compression. 

[FDEdev 955]

'In reality' doesn't help much if FSX doesn't calculate compression in a realistic way.  Furthermore IRL a lot depends on maintenance if the shock struts are filled correctly.

Especially in case of a trailing link landing gear.  Contrary to this I've never seen a nosewheel that digs into the runway IRL.  In FSX you simply can't have both in some cases.

Of course, if you know that you e.g. never fly the Citation with more than e.g. 50% fuel and no pax you can adjust the whole contact points section to a more realistic setting which is only valid for a certain weight range. 

BTW, a strange statement that 'almost no plane lands appropriately out of the box'.

  

 

[whamil77 183]

The landing statement was respect to AI aircraft.  Few land in a manner that wouldn't frighten passengers.  Most either flare very high, stall, and crash to the runway, or just crash to the runway without the flare and stall.  With most, much work is needed with the .air file and .cfg file on AI aircraft. 

[FDEdev 955]

Now that makes sense, thanx for the explanation :)