CaptKurt posted this sometime ago, I hope it helps you Herzie:
A float plane – or land plane for that matter – will jump into the air at start up when the contact points define the aircraft as sitting below the surface instead of on top of it. There is a a few inches leeway but if it is too far below the surface, it jumps into the air.
The aircraft.cfg file has a section called [CONTACT_POINTS] that defines how, and how high above the surface an aircraft sits on the ground, or floats on water. It also defines the scrape points where the aircraft body and wings will come into contact with the surface if landing wheels up, but that should be beyond the issue of a float plane leaping into the air at start up. Adjusting the contact points so the aircraft sits on the surface and not below should cure the problem.
When the aircraft.cfg file is opened you will see the [CONTACT_POINTS] section which looks like this:
[CONTACT_POINTS]
point.0=1.000, -11.567, 0.000, -1.257, 1574.803, 0.000, 0.542, 41.640, 0.321, 2.500, 0.700, 5.000, 5.000, 0.000, 0.000, 0.000
point.1=1.000, 7.673, -4.500, -5.163, 1574.803, 1.000, 0.542, 0.000, 0.428, 2.500, 0.701, 5.000, 5.000, 2.000, 0.000, 0.000
point.2=1.000, 7.673, 4.500, -5.163, 1574.803, 2.000, 0.542, 0.000, 0.428, 2.500, 0.701, 5.000, 5.000, 3.000, 0.000, 0.000
point.3=2.000, 4.6, -21.3, 0.1, 1574.803, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 5.000, 0.000, 0.000
point.4=2.000, 4.6, 21.3, 0.1, 1574.803, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 6.000, 0.000, 0.000
point.5=2.000, -14.167, 0.000, 0.6, 1574.803, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 9.000, 0.000, 0.000
point.6=2.000, 9.667, 0.000, -1.833, 1574.803, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 4.000, 0.000, 0.000
static_pitch=11.646
static_cg_height=4.001
In order to fix the leaping into the air problem you only need the first four numbers of each row plus the static_pitch and static_cg_height numbers, as these define how the aircraft will sit on a surface. See the example below:
[CONTACT_POINTS]
point.0=1.000, -16.167, 0.000, -0.417,
point.1=1.000, 2.833, -4.500, -4.333,
point.2=1.000, 2.833, 4.500, -4.333,
point.3=2.000, -1.000, -20.917, 1.167,
point.4=2.000, -1.000, 20.917, 1.167,
point.5=2.000, -16.167, 0.000, -0.083,
point.6=2.000, 7.667, 0.000, -0.333,
Point 0 is usually the tail or nose (or main float) Using point.0 as the example this is what these numbers mean:
Point.0=1.000 (can also be 2.000. 3.000 or 4.000 in the first position)
This defines what the point is. (note: the trailing zeros are not needed)
1.000 means it is a landing gear/wheel.
2.000 means it's a "scrape" point and hitting it will be a crash.
3.000 means it's a skid and should, well, skid!
4.000 means it's a float and should work well in water only
A float plane must have contact points that are defined as 4.000
-16.167
This defines forward/aft measurement from the middle of the model (not necessarily the center of gravity!)
0.000
This defines left/right measurement from the center of the model
-0.417
This defines up/down measurement from the centerline of the model
Note that point.1 and point.2 are usually the left and right landing gear (or floats):
In these 2 lines the only difference from how point.0 is defined will be that the third number will be negative for the left side (point.1=1.000, 2.833, -4.500, -4.333) and positive for the right side (point.2 =1.000, 2.833, 4.500, -4.333)
static_pitch=11.646
static_cg_height=4.001
These two effect at what angle the airplane sits and how far above or below the surface when you load a flight.
The static_cg_height defines where the plane is in relation to the surface when the flight is loaded. If your airplane drops when you start a flight, try decreasing the static_cg_height. If it jumps into the air try the opposite, increasing the static cg height.
The static_pitch defines the angle the plane sits at. If the aircraft lands on its tail or nose first when starting a flight, you need to adjust it.
The most obvious place to start looking for the jumping cause is the static_cg_height. But it could possibly be the contact points or static_pitch or a combination. The scrape points should not be the cause because if they are in contact or below the surface you will explode, not jump.
Hope this helps.
