Simviation Forums

When I load up my POSKY 767-400 the nose gear collapses and sinks into the ground up to the fuselage. The mains stay on the ground however.

Here are the contact points:

point.0 = 1.000,  76.500,   0.000, -15.500, 2181.102, 0.000, 1.541,  65.000, 0.350, 0.650, 0.850,  9.000,  9.000, 0.000, 280.000, 300.000
point.1 = 1.000,  -4.000, -13.750, -15.750, 2574.803, 1.000, 1.916, 0.000, 1.500, 1.200, 0.550, 11.900, 11.900, 2.000, 280.000, 300.000
point.2 = 1.000,  -4.000,  13.750, -15.750, 2574.803, 2.000, 1.916, 0.000, 1.500, 1.200, 0.550, 13.100, 13.100, 3.000, 280.000, 300.000

What variable in point.0 would help fix the collapsing nose gear?

Thanks for your help.
Scott

Scott,

Not as simple as that, I'm afraid. The points are usually OK. Collapsing nose gear can mean that the balance of the plane is wrong or that there's another fault with the flight dynamics, and there's too much weight on the nose gear. One of the culprits is often the fuel tank locations; for example from the Posky 767  aircraft.cfg:

[fuel]
Center1= 0.000, 0.000, 0.000, 11896.000, 3.000
LeftMain=  0.000, -5.000, 0.000, 6122.000, 3.000
RightMain= 0.000, 5.000, 0.000, 6122.000, 3.000
fuel_type=2.000000
number_of_tank_selectors=1
electric_pump=0

The bold figures are the horizontal locations of the fuel tanks in the model - as you can see, the wing tanks (in red) are actually situated in front of the wings, as the wings sweep backwards. If you adjust these figures back by say 10 feet or so (make them -10 instead of 0) then this might solve the problem. If not, look for other areas where weight might be too far forward. Another area of potentially bad weight distribution (and not only with Posky FDs here) are the passenger and cargo weights, stated as station loadings in the [weight_and_balance] section. In these cases, the total payload weight is often placed at the zero reference point which is usually towards the forward end of the wing chord, which puts a lot of the weight (which is normally at the back of the plane or in the rear cargo hold) too far forward.

Another way of checking whether it's the fuel loadings is to set the plane up for zero fuel when you start the 767 up from the initial screen, and see if it still does it. (Assuming that the plane does a nose dive when you start up with 100% fuel?)

Some Posky FDs suffer from some of these issues - I've had similar problems with some of their 747s.

Make a backup of your original aircraft.cfg and make the amendments above via Windows Notepad, and let us know how you get on.

Here is my POSKY 767-400 fuel tank location:
_____________________________________________
Center1   = 0.000,  0.000, 0.000, 7440.000, 3.000
LeftMain  = 0.000, -5.000, 0.000, 8350.000, 3.000
RightMain = 0.000,  5.000, 0.000, 8350.000, 3.000
fuel_type = 2.000000
number_of_tank_selectors=1
electric_pump=0
_____________________________________________

I guess I could try to move the tank location back a few feet and see what happens.

Also here is my weight and balance section:
_______________________________________________
reference_datum_position= 0.000, 0.000, 0.000
empty_weight_CG_position= 0.000, 0.000, 0.000

empty_weight     = 198443.000
max_gross_weight = 700000.000

max_number_of_stations = 6

// New FS2004 Numbers
// Max Structural Payload Per Boeing - 96,557 lbs
// Max Structural Payload Opensky    - 55,500 lbs

// Actual Total PAX  - 38,150 lbs
station_load.0 =4200.000000, 20.000000, 0.000000, 0.000000, 1st Class - 24  
station_load.1 =8050.000000, 40.000000, 0.000000, 0.000000, Bus Class - 46  
station_load.2 =25900.000000, 0.000000, 0.000000, 0.000000, Econ Class -148

// Total Opensky Cargo - 17,350 lbs
station_load.3 =8175.000000,  45.000000, 0.000000, 0.000000, Lwr Dk Cgo Fwd
station_load.4 =8175.000000, -50.000000, 0.000000, 0.000000, Lwr Dk Cgo Aft
station_load.5 =1000.000000, -70.000000, 0.000000, 0.000000, Lwr Dk Cgo Bulk

// Moments of Inertia
empty_weight_roll_MOI= 4378085.000
empty_weight_pitch_MOI= 7971735.000
empty_weight_yaw_MOI= 12879901.000
empty_weight_coupled_MOI= 0.000
___________________________________________________

There are allot of numbers in this section. Perhaps I should try and set all the weight values in this section to 0. (An empty plane) It looks like the plane is set up for full gross.

Keep the ideas coming. Something must work.

Thanks for your help.
Scott

I have to say that something looks a little odd with those station load numbers:

// Actual Total PAX  - 38,150 lbs
station_load.0 =4200.000000, 20.000000, 0.000000, 0.000000, 1st Class - 24  
station_load.1 =8050.000000, 40.000000, 0.000000, 0.000000, Bus Class - 46  
station_load.2 =25900.000000, 0.000000, 0.000000, 0.000000, Econ Class -148

// Total Opensky Cargo - 17,350 lbs
station_load.3 =8175.000000,  45.000000, 0.000000, 0.000000, Lwr Dk Cgo Fwd  
station_load.4 =8175.000000, -50.000000, 0.000000, 0.000000, Lwr Dk Cgo Aft  
station_load.5 =1000.000000, -70.000000, 0.000000, 0.000000, Lwr Dk Cgo Bulk

The weights (first figure in the line) represent in total a half-empty plane. This is OK I guess. Horizontal locations (in red) look odd though. They have the business class passengers sitting 20 feet in front of first class and ALL of the economy section located at the reference point. (No wonder there's too much weight in the nose!) The cargo locations look better.

Try relocating the fuel tanks back around 5 feet (not too far as if you do, then they'll then be located behind the main gear which may cause the plane to tilt upwards!), reverse the locations of first and business, and move the economy location to read -20 or so - or even further if necessary. Then you can adjust the nosewheel until it's resting on the ground:

point.0 = 1.000,  76.500,   0.000, -15.500, 2181.102, 0.000, 1.541,  65.000, 0.350, 0.650, 0.850,  9.000,  9.000, 0.000, 280.000, 300.000

Decrease the negative figure (to say -14.5) to lower the wheel towards the ground.

Almost there!

I think I fixed the problem. First I had to adjust the Static Compression of the nose gear. This at least stopped it from bouncing and dropping through the ground. So now I had a nose gear that was stable, but two feet off the ground. So then I adjusted the Vertical Position and managed to get the tires on the ground. Then I had to adjust the Dampening Ratio so it would compress ok when braking.

So far it seems to be working. I did not modify the Weight and Balance section, but I might later.

Once again, THANKS for all your help microlight. I think I will print your comments out and save them for later use.

Scott

Scott,

I am having awful trouble with this bird, any chance you can post the details of the adjustments you made. (I am having the bouncing and plane sitting off the floor problem you described above)

Thanks,
Phil

Here is the post that tells how I fixed the problem with my POSKY 767.

http://www.simviation.com/cgi-bin/yabb2/YaBB.pl?num=1181311475

I had to adjust the [glow=yellow,2,300]static_cg_height[/glow] (See the second to last post at the bottom). When I adjusted this value (it was too low) the plane now does not sink into the ground when taxing, slewing or loading.

Scott