Tweaking the mains

Willy

Willy

Administrator
Staff member
I'm wanting to see if I can do a little adjustment on a fixed gear aircraft that's in my hanger.

Here's the contact points:

point.0 = 3, -10.3202, 0, -2.8016, 1968.503937, 0, 0.2, 10, 0.3, 2.5, 0.85, 0, 0, 0, 0, 0
point.1 = 1, 0.722, -3.0999, -5.36693, 1850, 1, 0.87, 0, 0.35, 1.5, 0.75, 0, 0, 2, 0, 0
point.2 = 1, 0.722, 3.0999, -5.36693, 1850, 2, 0.87, 0, 0.35, 1.5, 0.75, 0, 0, 3, 0, 0

IRL, the aircraft had 6" of travel on the springs/shocks on the mains. In FS, it rips the wheels off on touchdown if you're lucky. If not, it's an automatic crash.

How would I get that 6" into this and strengthen up the mains? It doesn't have flaps and has to be flown in a bit hot to land.
 
Hey Willy,

I am going to let uncle Milton do this as he is the landing gear expert. But.. For when you are going into a landing gear adustment, rule number one is to simplify and line up the numbers into rows (vertically) so that you can quickly see all the settings. On those that have 5 or more digits in the distance, you can safely lower that to 2 digits, such as 5.67843 could be 5.67 or 5.68. After that, in distance, you really cant see the settings.

You can also adjust the weight if it seems to be crashing the landing gear. The impact weight might be too low.

Here are the numbers squared up as I would start out to work on them.

point.0 = 3, -10.32, 0.0, -2.80, 1968, 0, 0.2, 10, 0.3, 2.5, 0.85, 0, 0, 0, 0, 0
point.1 = 1, 0.72, -3.09, -5.36, 1850, 1, 0.87, 0, 0.35, 1.5, 0.75, 0, 0, 2, 0, 0
point.2 = 1, 0.72, 3.09, -5.36, 1850, 2, 0.87, 0, 0.35, 1.5, 0.75, 0, 0, 3, 0, 0


Note, your tail wheel is showing only 10 degrees of travel either way. A bit tight.

Note 2, your first gear is noted as being a skid type, (3).

The 3 sets of digits per section/string are your primary suspension sections. Note that if you know of a plane that has a similar suspension and weight layout, you can try copy/pasting in those sections. They follow the rudder degrees input, so its easy to track where they are. Breaks mapping is the 1,2,3, then you have rudder with the mains being a setting of 0 degrees.

If this is a hefty tail dragger, try the DC3 (stock FS) suspension settings and see if that works. (Sometimes you can really luck out with a different planes suspension setting).

Hope that helps..


Bill
 
Hello Willy-looks like you are up for some 30's racing type flying ! Fragile landing gear really doesn't work with these (any?) planes. This 'landing gear made of glass' problem is made worse by the fact that we land with 'blinkers' on in terms of peripheral vision.

This web page for the Gee Bee R1/2 http://www.geocities.com/dgraves549/geebeer2.html describes the landing gear as-

"This type of landing gear proved not only to be of very low drag, but had fine shock absorbing and ground handling qualities, as well as the ability to withstand a terrific load in rough landings at high speed on rough fields."

With all that in mind I try to set up a really strong and well damped gear by increasing the Impact Damage Threshold (5th column) to 5000-10000 and the Damping Ratio (11th column) to 0.99.

If the plane is freeware I would like to try it out too. Cheers
 
I've added a bit more to the cfg descriptors for myself to help understand what they do...

/Classes...What type of point 0=Unused or Ignore
// 1=Wheel
// 2=Scrape point
// 4=Float
// 5=Float Rudder
//0 Class
//1 Longitudinal Position (feet)
//2 Lateral Position (feet)
//3 Vertical Position (feet)
//4 Impact Damage Threshold (Feet Per Minute)
//5 Brake Map (0=None, 1=Left, 2=Right)
//6 Wheel Radius (feet)
//7 Steer Angle (degrees)
//8 Static Compression (feet) (0 if rigid,smaller=less bounce travel=harder landings, or strut compression length on ground contact or nose dive on braking)
//9 Max/Static Compression Ratio
//10 Damping Ratio / Water Rudder Effectiveness (0=Undamped, 1=Critically Damped) / 1.0 = normal
//11 Extension Time (seconds)
//12 Retraction Time (seconds)
//13 Sound Type
//14 Airspeed limit for retraction (KIAS)
//15 Airspeed that gear gets damage at (KIAS)

Moments of inertia also affect ground handling.

Hope this helps. What is the aircraft?
 
It's Wozza's Gee Bee Z. Great flyer, but touching down it's like you've got 50lb bombs attached to the wheels. The default DH 88 Comet is easier to land.
 
I'd by happy to check this out but probably can't until tomorrow or the next day. Just glancing at the numbers those last bold ones seem high,0.85, 0.75, 0.75. These run between 0.01 say and 0.99 with higher numbers being stiffer landings. Undamped looks like a car without shocks, each bump will have the car bouncing for miles. Critically damped looks like a flea on a skillet. You could try changing the last two to something like 0.50 for a start. The effect these numbers have also depends on the designers initial 0,0,0 point which can vary.
I'm sure Milton has got this in hand and will have the 411 for you soon. Most of what I know about this stuff I learned from him.

BTW my post with the descriptors.. I don't remember where that 1=normal thing came from but suspect it has something to do with the water rudder.
 
Yours is set up like mine, with 4.2 inches compressed on the ground (.35 foot), and 1.5 times that amount for a max of 6.3 inches. The damage threshold is 1850 feet/minute on the mains and a little more on the tail skid. The 0.75 damping ratio allows for some rebound, but I don't think it's too much for that time period (though I could be wrong).

That said, sitting with the mains compressed to almost two-thirds total compression seems a little much. Here's a possibility for a set of mains with less less static compression (stronger springs) and tighter damping:

point.1 = 1, 0.72,-3.09, -5.36, 1850, 1, 0.87, 0, 0.25, 2.1, 0.85, 0, 0, 2, 0, 0
point.2 = 1, 0.72, 3.09, -5.36, 1850, 2, 0.87, 0, 0.25, 2.1, 0.85, 0, 0, 3, 0, 0

This gives you only 3 inches of static compression, the same 6.3 inches of total travel, and a little tighter damping for less rebound.

All that being said, a short and stout little tail dragger like that will still have a quite a bit of rebound on landing. When the mains hit, the tail dips, which suddenly increases your angle of attack, sending you right back into the air. Stiffer gear may actually hurt your cause. I've always flown the "Z" like it was a much bigger plane, requiring higher landing speeds and a longer roll. If I try to "land" it, I usually find myself right back in the air staring at the sky. But if I fly it all the way to the ground and let it roll out long, I can avoid putting any more dents into frame!:isadizzy:
 
Well I tested it at Hana, Maui with my mods and it lands fine. It still bounces a bit and you have to watch the braking and get the stick back as soon as you are below flying speed. I used 50% fuel and it seems a bit slow. It should do around 270mph flat out but struggles to top 250mph. Cheers
 
I took a page from Lionheart's book and with the exception of the contact points locations, I used the rest of the data from another aircraft that landed well (Tom Eads' Gee Bee R-6). Went for a quick test hop at the local airfield (KTGC) and it landed so beautifully, I had to do it six more times :d.

Here's the revised contact points section from the aircraft.cfg:

[contact_points]
max_number_of_points = 13
point.0 = 3, -10.3202,0,-2.8016,1968.503937,0,0.250,45.000,0.343,2.501,0.900,5.000,5.000,0
point.1 = 1, 0.722,-3.0999,-5.36693,1850,1,1.250,0.000,0.719,2.000,0.900,5.000,5.000,2
point.2 = 1, 0.722,3.0999,-5.36693,1850,2,1.250,0.000,0.719,2.000,0.900,5.000,5.000,3
point.3= 2, -0.750, -17.250, 0.060, 1575, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 5
point.4= 2, -0.750, 17.250, 0.060, 1575, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 6
point.5= 2, -17.250, 0.000, 1.000, 1575, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 9
point.6= 2, 8.860, 0.000, -4.700, 750, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 4
point.7= 2, 10.000, 0.000, 0.000, 3000, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 4
point.8= 2, -14.600, -6.000, 0.900, 1700, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 9
point.9= 2, -14.600, 6.000, 0.900, 1700, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 9

static_pitch= 16.9
static_cg_height= 4.78
gear_system_type = 4
tailwheel_lock = 0

It has no flaps and a stall speed of 59kts, so I played with approach speeds. I did best between 75 and 85 with a 33% fuel load.

Woo Hoo! :ernae:
 
Awesome! Glad its landing smoothly for you Willy.

Thanks for posting the settings.

:ernae:

Getting a plane to land just right (realistically) is one heck of a difficult thing to do. Soooo many variables.



Bill
 
You must log in or register to reply here.
Back
Top