Shimmy

[kickerpicker]

I have recently downloaded and installed some CRJ's which I believe are some of the sleekest and beautiful aircraft made.. My problem is that when I climb out form an airport they begin to shimmy. I have tried reducing the speed, the climb speed, lowered flaps, etc.., but the shimmy is there and the aircraft sometimes climbs uncontrollably during the shimmy. I have a CRJ-900 that will shimmy constantly after takeoff.. I have never gotten this airplane to it's assigned altitude! It's disgusting, because it's such a beautiful airplane, and I don' know how to correct this problem.. I have Windows 7, and other than trying to download scenery, it has worked very well on FS2004.

Roy

[jgf]

Unless the aircraft is poorly designed initially, shimmy is almost always caused by an overspeed situation; this can also cause excessive climb rates. Many airplanes do not need full throttle for takeoff, and for many that do throttling back once airborne is standard.

This overspeed is not Vmax but rather exceeding the envelope; a plane capable of supersonic flight at 40k ft may be nearly uncontrollable above 250kts at 5000ft.

[kickerpicker]

I appreciate your input on this, but the aircraft in question is not supersonic.. The shimmying begins soon after take off with the airspeed set at 250 on A/P.. That's my usual routine with IFR cross country traffic.. Until now, I have not had a problem with this, but I'm believing that your former statement about "poorly designed" may be the case... The paint is pretty, but the insides are rotten, me thinks!! But, they are FREE and that is certainly something to be glad of here. Not all designers, well intentioned and benevolent as they may be, can get it right, first time, every time, huh? I really appreciate all the designers efforts... They make this sim interesting!! Roy

[Avechelice]

Hello,

Maybe this ..................
http://www.flightsim.com/vbfs/showth...ight=posky+crj

Regards.

[jgf]

... the aircraft in question is not supersonic.. ...

Didn't say it was, just using that as an example. Many times people have posted about poor handling, particularly of combat jets ...when they were trying to do Mach 1 at 8000ft. But the principle is true for any aircraft, though many lack the power to exceed their envelope in normal flight.

[kickerpicker]

OK, I went into the aircraft config file and changed (empty_weight_pitch_MOI) FROM 1374924 TO 374924 in the acft config. This is a recommendation from POSKY on this aircraft.. When I selected the airplane to test it, and the cockpit view came up, the airplane was sitting there at the gate trembling!! Then I remembered that it did the same thing BEFORE I made the change, so the problem is still there.. Someone here suggested that a typo in the contact points could DEFINITELY cause a shimmy on the ground, but I don't have a clue where to look for a typo in the contact points. Is there maybe a fix where I could copy and paste some contact points from a stable aircraft?? The other CRJ's that I have are not CRJ-900.. Are they interchangeable with different types of CRJ's?? I looked at the cfg file for a 200 that I have that is a very stable airplane and there really is too much difference with my limited experience to try and exchange the data.. Roy

[jgf]

Look for a period instead of a comma in the contact points lines (there should be no periods). Don't change any numeric values without specific instructions, you could make matters much worse, even having an airplane that wouldn't take off.

Increasing MOIs rather than decreasing them can sometimes cure the shakes, but altering them either way will also affect flight dynamics.

You can swap MOIs and flight tuning between similar aircraft (if the aircraft are too dissimilar you may get unexpected results), but not contact points; the latter specify the physical presence of the aircraft and are quite individual.

[kickerpicker]

They are all commas.. This airplane is going into the trash heap and I'll try to download it again or find a replacement, but thanks for the help any way.. Too bad.. It was a beautiful bird... Roy

[jgf]

It happens. I've scrapped many otherwise fine aircraft because of handling issues. While almost all can be cured, it becomes a matter of would you rather spend a week (much of it trial and error) tweaking one aircraft, or dump it and start flying another.