Too much bounce in my step

[OBIO]

I am having issues with the freeware Alphasim Jag...namely I can not land the plane without it developing fatal bouncing. Even after gentle, shallow approach landings of 145knots, with very very gentle wheel touch downs.....the plane starts bouncing and keeps bouncing until the gear fails and I get a crash.

I did some contact point location changes....they were 2 feet ahead of the actual tire locations. I made NO changes to the dampening and compression ratios whatsoever. I did add the scrape points. I also added contact points for the inner tires on the main gear...but I have them commented out....with or without the inner tires, the plane bounces just the same. Others have commented that they have no issues landing this bird. Warhorse47 (I think) stated that he also had the bouncies. Could one of you gurus take a look at the contact points and tell me how to put a bra on this girl to reduce the unlovely bouncing?

[contact_points]
static_pitch = 1.6
static_cg_height = 8.2
tailwheel_lock = 0
gear_system_type = 1
max_number_of_points = 9

point.0 = 1, 11.5026, 0, -8.55, 2500, 0, 1, 25, 0.11, 3, 0.8, 6, 4, 0, 260, 300 //front gear
point.1 = 1, -7.42, -4.5998, -8.1166, 2500, 1, 1.2, 0, 0.5, 2.5, 0.85, 5, 7, 2, 260, 300 //left out tire
point.2 = 1, -7.42, -3.3, -8.1166, 2500, 1, 1.2, 0, 0.5, 2.5, 0.85, 5, 7, 2, 260, 300 //left inner tire
point.3 = 1, -7.42, 4.5998, -8.1166, 2500, 2, 1.2, 0, 0.5, 2.5, 0.85, 7, 5, 3, 260, 300 //right out tire
point.4 = 1, -7.42, 3.3, -8.1166, 2500, 2, 1.2, 0, 0.5, 2.5, 0.85, 7, 5, 3, 260, 300 //right inner tire
point.5 = 2, -12.128, -14.158, -0.728, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0 //left wing scrape
point.6 = 2, -12.128, 14.306, -0.728, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0 //right wing scrape
point.7 = 2, -18.275, 0, -3.298, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0 //tail scrape
point.8 = 2, 23.092, 0, -3.465, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0 //nose scrape

I got it! Tweaked the static compression and the dampening ratio (I think those are the ones I tweaked) and the bird lands great now. 3 nice landings in a row....then I did a hard landing and had a few bounces, which were to be expected, but the bird settled down nicely.

[contact_points]
static_pitch = 1.6
static_cg_height = 8.2
tailwheel_lock = 0
gear_system_type = 1
max_number_of_points = 7

point.0 = 1, 11.5026, 0, -8.55, 2500, 0, 1, 25, 0.35, 3, 0.8, 6, 4, 0, 260, 300
point.1 = 1, -7.42, -4.5998, -8.1166, 2500, 1, 1.2, 0, 0.75, 2.5, 0.85, 5, 7, 2, 260, 300
point.2 = 1, -7.42, 4.5998, -8.1166, 2500, 2, 1.2, 0, 0.75, 2.5, 0.85, 7, 5, 3, 260, 300
point.3 = 2, -12.128, -14.158, -0.728, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0
point.4 = 2, -12.128, 14.306, -0.728, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0
point.5 = 2, -18.275, 0, -3.298, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0
point.6 = 2, 23.092, 0, -3.465, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0

OBIO

 

[Milton Shupe]

Also replied in the FS9 thread.

Yes, the static compression of a little over 1" is way unrealistic. The max-static ratio is also too high at 3.0.

The other thing you can check is the CoG. The front wheel should carry about 20% of the weight. If it is less than 10%, you will get some bounce especially with a stiff nose gear.

There is no way I know of to measure this. I usually play with the CoG at 25% MAC plus or minus until it feels correct. Ensure that the CoG is placed at 1/4 wing cord and that the gear points are under the tires.

 

[Ivan]

For CFS1, I wrote up a little spreadsheet to calculate the weights on each wheel given the gear contact points. It figured out the angles by itself. It doesn't take into account additional loads such as fuel or ammunition though and it doesn't take into account the amount of compression caused by the weight. After that, I just set the spring rates to be proportional to the weight and so far the bounce has gone away every time I have tried.

I had intended it for tail draggers, but it seems to work for nose gear as well. Just need to find the thing. Haven't had to use it in a while.

- Ivan.

 

[Ivan]

Oh yeah, at least for CFS1, damping should be from about 1/5 to 1/2 of the spring rate. Yeah, I know you folks probably are not working with CFS1.

- Ivan.