Aircraft cfg adjustments

[Navtech]

Carenado Skymaster 337
That strange .. I use those contact points (I think it"s the originals) and I have no problems ...

[contact_points]

point.0 = 1, -4.4, 0.0, -3.90, 1500, 0, 0.68, 35, 0.2297, 1.6573, 0.80, 6.0, 6.0, 0, 152, 180
point.1 = 1, -12.2, -3.8, -3.38, 1500, 1, 0.67, 0, 0.0984, 2.9668, 0.85, 6.0, 6.0, 2, 152, 200
point.2 = 1, -12.2, 3.8, -3.38, 1500, 2, 0.67, 0, 0.0984, 2.9668, 0.85, 6.0, 6.0, 2, 152, 200
point.3 = 2, -14.0, -19.1, 2.8, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0
point.4 = 2, -14.0, 19.1, 2.8, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0
point.5 = 2, -27.0, -5.0, 1.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0
point.6 = 2, -27.0, 5.0, 1.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0
point.7 = 2, -13.0, -1.4, -2.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0
point.8 = 2, -13.0, 1.4, -2.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0
point.9 = 2, -8.0, 0, -1.9, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0


static_pitch = 3 //Degrees
static_cg_height = 3.4 //Feet
gear_system_type=0 //Electric

[pfflyers]

I guess it's like Fleet Canuck had problems with the C185 and I didn't, I got probs with the C337 and you don't. Go figure.

I guess if I'm the only one having troubles it would explain why there's no commonly available "fix."

[Milton Shupe]

Carenado Skymaster 337
That strange .. I use those contact points (I think it"s the originals) and I have no problems ...

[contact_points]

point.0 = 1, -4.4, 0.0, -3.90, 1500, 0, 0.68, 35, 0.2297, 1.6573, 0.80, 6.0, 6.0, 0, 152, 180
point.1 = 1, -12.2, -3.8, -3.38, 1500, 1, 0.67, 0, 0.0984, 2.9668, 0.85, 6.0, 6.0, 2, 152, 200
point.2 = 1, -12.2, 3.8, -3.38, 1500, 2, 0.67, 0, 0.0984, 2.9668, 0.85, 6.0, 6.0, 2, 152, 200
point.3 = 2, -14.0, -19.1, 2.8, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0
point.4 = 2, -14.0, 19.1, 2.8, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0
point.5 = 2, -27.0, -5.0, 1.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0
point.6 = 2, -27.0, 5.0, 1.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0
point.7 = 2, -13.0, -1.4, -2.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0
point.8 = 2, -13.0, 1.4, -2.0, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0
point.9 = 2, -8.0, 0, -1.9, 1500, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0


static_pitch = 3 //Degrees
static_cg_height = 3.4 //Feet
gear_system_type=0 //Electric

Sorry I do not have this aircraft (yet) but on first blush I would say that the suspension is too stiff and the MOI's are too low.

One of the big mistakes most designers make for gear suspension is to assume that the oleos only have an inch or less of compression. Kind of like only what you see on the ground happening are the limits, and not taking into account "hanging gear".

Ever see a car raised with a frame lift or jack, how far the suspension hangs down?

If you look at the mains above (point 1 and 2) you will see that the static compression is .0984' or 1.2". That means the total weight of the aircraft only compresses the suspension from hanging gear to static compression of 1.2". Then notice the 2.9968 max to static ratio. That says the total available suspension is 2.9968 times 1.2", or 3.6".

So, we have a very stiff suspension with very little allowable movement. In reality, the numbers would be very different.

One can easily change these numbers while remaining true to the original animation design (assuming that it matches the animation of the model).

1) Multiply the static compression (converted to feet: .0984' X 12 = 1.2") by the max-static ratio of 2.9968 = 3.538" total suspension available.

2) Use at least 50% of that for static compression (up to 80% if you like): 3.538" time 50% = 1.769". Convert this to feet for the new contact point entry. 1.769" divided by 12 = .147'

3) Divide the total suspension available by the new static compression: 3.538" / 1.769" = 2.0 max-static ratio.

4) Once you do this you will have to adjust the vertical distance to ground for the mains since the gear will now be compressed more sitting static. In the above case, the 4th parameter -3.38' needs to be adjusted to lower the aircraft to the new tire height. Adjust it .2 at a time to get close then tweak the number.

The nose gear numbers above look okay for suspension.

The second reason an aircraft will dance around on the runway is that the MOI's are too low for the weight of the aircraft. It is usually the Yaw MOI but if that one is off, they are all suspect.

An aircraft of this size and weight with two engines would likely have Yaw MOI's in the 12000-14000 range, and roll moi around 5000 and pitch moi around 7000 because of inline engines.

You can check your MOI's with similar aircraft weights keeping in mind the differences in engine configurations and affects on pitch and roll.

EDIT: I might add that since in-flight handling was tuned to existing MOI's, that the pitch and roll may have to stay the same, but and increase in Yaw may be called for.

[pfflyers]

Thanks a bunch Milton! Your numbers gave my Skymaster a miracle cure. I modified the contact points and the MOIs at the same time, so I'm not sure which had the bigger effect, but I don't care. It's like a whole new plane. I didn't realize the part the MOIs played in this equation. Thanks again.

I was typing my post while you were editting yours so I went back and restored the pitch and roll MOIs and set the yaw at 13000, seems to taxi and fly just fine.

[Milton Shupe]

Thanks a bunch Milton! Your numbers gave my Skymaster a miracle cure. I modified the contact points and the MOIs at the same time, so I'm not sure which had the bigger effect, but I don't care. It's like a whole new plane. I didn't realize the part the MOIs played in this equation. Thanks again.

I was typing my post while you were editting yours so I went back and restored the pitch and roll MOIs and set the yaw at 13000, seems to taxi and fly just fine.

Ah, great! Glad it helped.