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P3D v2 Cannot get Floats to take hold?

lionheart

lionheart

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us-arizona
Hey all,

Does anyone see a issue here with my contact points?

I have included floats in my contacts for doing belly landings. For some reason, they arent working. Tested in the water, and the crash as well there. I have raised and lowered them, nothing is working.


[contact_points]
point.0 = 1, 0.90, 0.00, -2.85, 1500, 0, 0.5, 22.0, 0.25,2.5, 0.7, 5.0, 5.0, 0 // nose gear
point.1 = 1, -4.70, -4.50, -2.92, 3500, 1, 0.5, 0.0, 0.3, 2.5, 0.7, 5.0, 5.0, 2 // main gear
point.2 = 1, -4.70, 4.50, -2.92, 3500, 2, 0.5, 0.0, 0.3, 2.5, 0.7, 5.0, 5.0, 3 // main gear

point.3 = 2, -10.0, -21.4, 1.70, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 5 // wingtip
point.4 = 2, -10.0, 21.4, 1.70, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 6 // fx_navgre // wingtip
point.5 = 2, -7.90, -15.0, 0.20, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 5 // fx_navred // wing underside
point.6 = 2, -7.90, 15.0, 0.20, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 6 // fx_navred // wind underside

point.7 = 2, 3.48, 0.0, -1.10, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4 // fx_navred // belly scrape
point.8 = 2,-10.00, 0.0, 1.60, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4 // fx_navred // tail top
point.9 = 2, -2.00, 0.0, 2.50, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4 // fx_navred // roof
point.10 = 2, 3.20, -9.5, -1.10, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 5 // fx_navred // wing underside
point.11 = 2, 3.20, 9.5, -1.10, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 6 // fx_navred // wind underside

point.12= 4, 4.90, 0.0, -2.20, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0 // fx_navred // float
point.13= 4, -6.90, 1.5, -2.40, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 2 // fx_navred // float
point.14= 4, -6.90, -1.5, -2.40, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 3 // fx_navred // float
 
shot in the dark. try 4 points in a rectangle for floats like Beaver.

point.12= 4, 4.90, 1.5, -2.20, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0 // fx_navred // float
point.13= 4, 4.90, -1.5, -2.40, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 3 // fx_navred // float
point.14= 4, -6.90, 1.5, -2.40, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 2 // fx_navred // float
point.15= 4, -6.90, -1.5, -2.40, 1800, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 3 // fx_navred // float

get rid of 7 to 11 temporarily
 
He lionheart, I'm having the same problem with a Volmer Sportsman. I have to keep full forward stick after touching down (until it slows down to under 20mph), or while taking off, or I get a crash. I'm keeping the plane on the backburner until I figure it out. Please let me know how that four-point works out for you. Thanks.

A short (humorous?) video of my Sportsman
 
Bill,
Does it happen with the landing rear retracted?
I have a helo that has a retractable landing gear and built in fixed floats.
If I land it on the water with gear down it crashes. If I land it with gear up it is fine even though the wheels are submerged.
Roy
 
Nope, on water its fine (with gear up). Planes will usually flip forward when they land on the water with gear down, (real planes, real world). On this, landing on the grass, gear up, it starts sparking. I think I figured it out though. My scrape points are below the floats, or even with them. I cant use floats as my RG as then the floats will have the plane hovering in the air when she belly lands in... I think. Maybe I should try that. :S (They have to sit at waterline. That might be enough to have her sitting in the grass at the right height).
 
FSX float points are weird for sure; way different than FS9. The scrape points really confuse the issue of setting float points so you are better off setting up floats and gear first. then setting any scrape points. Scrape points will definitely alter the way she sits in water without telling you, so I do not use them for the hull, just for wings and upper nose and tail. This allows the craft to lean to the side and sit on a wing float as it should. Be careful with wing float position as that will disrupt your normal hull points. Set them last if you can.

Generally, it seems FSX wants your rear float points much farther back than FS9 did. Get your weight distribution right, CoG at/near 25% MAC and below the engine weight, and the task should be easier. Also be sure that the engine positioned thrust line is at or slightly below the engine spinner thrust line. This will pull the nose down on your takeoff run, and allow for easy flare upon pulling off power before touchdown.
 
Hi Lionheart,

Did you get the floats issue resolved? If so, what was the culprit? Although I have usually managed to adjust the contact points for the pilotable boats I make such that they work fairly well in FSX more or less by trial and error, the same aircraft.cfg file used in P3D often results in a crash, or no apparent contact with the surface. I had started with the FSX DHC2 float contact points along with the static CG height and datum offset, etc, but after a few mods the result sometimes does not work in P3D and I'm trying to figure out just why.

Because there are so many interrelated factors I've made a spreadsheet that calculates the distance between each contact point and the surface with static compression and with the maximum compression. The results from the functional floatplanes I've checked seem reasonably consistent, but not always! And I've found a couple of errors with it too, like periods instead of commas, or vise versa. They are otherwise almost impossible to spot. (I'll run your contact points through the spreadsheet when I get home if you can post the static CG height, datum offset, static pitch and empty weight CG values.)

But at this point I still don't know exactly how the datum offset, the empty weight CG and the static CG height all work together other than the rather cryptic notes in the SDK. Does anyone have any info on the relationship?

Here's my suspicion of the moment: the model itself just goes along for the ride (provided it does not have a crashbox I would guess) : it can be moved up or down using a datum offset and via MCX.

If what amounts to the struts are unequal in length fore and aft, the angle from fwd to aft with respect to the horizontal should match the static pitch. The amount the strut moves up or down as a result of the pitch is based on its fore and aft distance from the for and aft datum location perhaps modified by the empty weight CG location. Without accounting for this when the static pitch is significant, calculations of the distance to the surface don't make sense.

The static CG height is critical and the acceptable range seems to be about plus minus 0.1 feet based on what my spreadsheet says.

What's not clear are the relationships between the datum offset if any and the static CG height and empty weight CG. And I'm puzzled by the use of a different vertical contact point position and perhaps static and dynamic compression values on one strut, say the right forward one as in the DCH2. I'm trying to figure out *exactly* how the sim uses these values. Thoughts anyone?
 
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As you have discovered, the visual model has no relation to the dynamic behaviour of the model in the sim. As you also note, many models have odd, or syntactically wrong contact point sections.

The model's behaviour in FS is governed by the reference centre, which is at 25% MAC – 25% back from the leading edge, that is. This is where FS places the empty weight CoG. Good modelling practice is to place the model's centre at this point, but not all do. Reasons for this include inexperience, but also include manufacturers' data which may be measured from the very front of the aircraft: the datum offset is included in aircraft.cfg to account for this. When the reference datum is not at the empty CoG, the contact points must be adjusted to reflect the reference data position.

Contact point positions for landing gear are for the gear when fully extended and ought to be measured on the model in Gmax, 3ds Max or Blender; not guessed at once the model is compiled. Now the fun bit. Static compression is how much the gear has compressed when the empty aircraft is at rest on the ground. Ratio of maximum to static compression tells the sim how much more the strut or oleo can compress. But if the model has struts which compress by fully 15 inches, while the static value is 3 inches and the max/static ratio is 3.0, the sim thinks the maximum deflection is only 9 inches. Thus is confusion sown.

Static CG height only tells FS at what height to load the model into the sim: after that simulated gravity takes over. In FSX you really only see errors in static CG height in Slew mode where the height the model starts at in slew is set directly by that.

I hope this helps.
 
I must add that a through search here will yield many, many discussions on this subject. Numerous comprehensive explanations have been advanced in the past.
 
Hi Tom,

Yes, your information is very helpful! It confirms how I set up my spreadsheet calculation, and explains some things that are not directly considered when making a boat model, like MAC. I had assumed that the sim placed the cg at my chosen datum assuming no datum offset but I was never absolutely sure. Shifting the empty CoG to account for a datum offset is likewise something I had guessed at, but now it makes perfect sense. (I often move the empty weight CoG a little upwards to induce a little outward heel when ferries alter course.)

And amusingly enough, I had just now come to the conclusion you noted regarding the static CG height, and the problems I had attributed to it were in fact caused by something else. And not only was my comment about the static CG height above not right, the static pitch should likewise not be critical to behavior in the sim I would assume, other than initially positioning the vehicle or in slew mode. It turns out that in modifying and re-using the same basic contact point values, a number of errors crept in over several years, some of which FSX may not be as fussy about as P3D. Here's a short list of embarrassing errors: two contact point lines by the same name, commas instead of periods and vice versa here and there, values intended for one column get accidentally shifted to an adjacent one, accidentally giving both front and aft contact points a steer angle, etc. The funny thing is that I've stared at these errors over and over and simply not seen them.

Your comments also have bearing on the problem of wakes, both for boats as well as floatplanes in P3D. At least as of P3D v2.5, wakes are attached at the level of the model datum. The datum of a floatplane is well above the surface so the wake and spray effect displays there, whereas the datum for a boat can be close enough to the surface to cause z fighting with the wake. In that one would not want to change the datum, the only solution appears to be including offsets in an effect specifically for the vehicle in question. (Using attachpoints to attach wake effects does not work if you want the wake to turn off when the plane takes off or when a boat stops.)

So thanks for clarifying things Tom! And I hope this note is mostly correct….

And thanks Bill, I'll look more.
 
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