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Post by acourt on Sept 9, 2011 23:03:30 GMT
I've noticed the same "nose low" effect on all my DC-9s. I think a potential problem lies in weight and balance. Looking at the standard loading, I think the airplane is loaded with a center of gravity WAY too far forward. The aircraft.cfg I have for the DC-9-10, installed without modification, shows the following weights... 10 x 160 lbs first class 30 x 160 lbs forward coach 30 x 160 lbs aft coach 2940 lbs forward cargo 1500 lbs aft cargo I can't speak for a true DC-9, but on the 717, a load like this would probably cause CG problems. Cargo/bags is almost always loaded aft. It's not uncommon to have all the bags loaded in the aft bin, with only strollers and gate checked bags--if anything at all--in the forward bin. I've found that if I intentionally load the HJG Nine's and 717s with a CG further aft (putting all the cargo in back is usually enough), the airplane sits more realistically, trims properly for takeoff, and actually flies more like the real airplane. If you load too far aft, however...watch out! Bad things happen The long term fix I came up with on my own setup involves removing all the loading stations, save for one. I then compute the entire load (pax, bags, cargo, crew) and put the total in that station. I put the station right on top of the empty weight CG. For example, on the DC-9-10... station_load.0 = 13550.0, -4.0, 0.0, 0.0, Payload I love the Nine's! I'm always surprised how much they fly like the real airplane, including having to push through the flare (holding it off and continuing to flare to touchdown usually results in a less than stellar arrival). Keep up the great work!
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Post by Mike Monce - HJG on Sept 10, 2011 12:35:56 GMT
Well, when we work on the FDE, we try to keep the parameters as close as possible to the real values. Unfortunately, due to limitations of FS that's not always possible. In the case of the -9's the cargo loading is not realistic, BUT the ratio of the forward and aft loading is close.
If you go to the FAA TCDS, it lists the cargo loading for the DC9-10 as max 5600 forward and 3400 aft.... we ended up reducing those values to get the overall loading we want, but note that the real values also have more loading in the forward bay.
to get back to Bill..... if you want to play with the strut stiffness it's the 9th entry in the line, just after the steering angle. The lower the number the stiffer the strut will be. Related is the next entry which is ratio of compression static/dynamic of the strut.
Mike
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Post by acourt on Sept 10, 2011 13:54:57 GMT
Mike,
Sounds good. I understand the TCDS shows a higher capacity in the forward bin, but I think that's more a function of its much greater size (according to the station numbers, on the -10, for example, the forward bin is almost ten feet longer than the aft bin).
There's nothing wrong with the numbers HJG used. They reflect a maximum possible loading. I'm just saying that the airplane normally isn't loaded in that manner. I can remember only one time when we carried more weight in the forward bin than the aft. And even in that case, the bags in the forward bin were stowed as far aft in the bin as possible.
I normally plan for a load something like this...
Normal crew (two 190 pound pilots, and two 140 pound FAs), 65 passengers (@ 190 pounds), 65 bags (one 25 pound bag per customer), and no cargo. Fuel is planned for 6,000 pounds per hour of flight to the destination and alternate, plus a 4,500 pound reserve. I load all the bags in the aft bin. Sometimes I'll through in some cargo, like 300 pounds of parts, or a 50 pound liquor kit. I'll put the cargo in the forward bin. When I load the airplane in this manner, it sits in more of a normal attitude.
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Post by aerofoto - HJG Admin on Sept 10, 2011 14:11:35 GMT
Thanks Mike ! A couple of comments I'd also like to add .... 1. When Mike & I worked on the DC9 FDE's we never moved the COG position from that which was originally supplied to us. We increased weights .... either at each of the stations provided, or, for each of the the fuel tanks provided .... to get as close as we could to the certified weight of each individual DC9 TYPE aircraft we represent .... with a nominal overload (the end user is expected to reduce fuel, or payload, or both, in order to set these aircrat at or below their certifed MGTOW's) in order to avoid aircraft loading into FS underweight as so many other simulations often do. We learned that if we attempted to move the COG position to where we calculated it should best be placed (COG positons are not necessariliy perfect calculations in FS) then it resulted in something along the lines of what "BILLA" has already reported .... and much worse .... so .... we avoided doing this and left the originally calculated COG values alone/as was originally provided to us. 2. I presented a selection of line profile images displayig how each of our DC9 TYPE aircraft appear to sit, on the ground, in FS9/2004 .... but .... these are should not be interpreted as an absolutely accurate indication. For each of the images presented I set the FS9/2004 VIEW HEIGHT position to +1 FT (to get as near to ground level as possible without falling below the actual scenery tiles) .... but .... when a value of + 10 FT, or more is applied, which then raises the VIEW HEIGHT sligtly, then more of the NG wheel seems to be revealed (I've noticed this with a number of other FS aircraft too and not just ours). What I've presented "HERE may, to some extent, just be an illusion creatted by FS9/2004) according to the VIEW HEIGHT settings I've applied .... particularly in the case of the DC9-50. This's what I'm seeing of the NG from a slightly higher VIEW angle .... again with the DC9-50 .... and once again without any weight adjustments .... Mark C AKL/NZ
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Post by acourt on Sept 11, 2011 14:21:57 GMT
Mark,
I understand what you're saying about not modifying the CG on HJG's models. I only modify the aircraft.cfg to my own personal preferences (I've done this with all my HJG models). I'm very pleased with the HJG DC-9s. Again, I'm not saying there's anything wrong with it, and I hope I haven't given the impression of complaining or nit-picking!
All I'm saying is that, when end users adjust the loading, they should strive to load the aircraft with a further aft CG than the default.
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Post by BillA on Sept 11, 2011 19:34:43 GMT
I checked my 50 series, and yes its fine, wheel never sinks bellow the gear door. Its just like your pic. Thanks for the pics Mark. How does one attach a jpg on this forum? I would like to show my DC-9-30's nose gear
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Post by BillA on Sept 11, 2011 19:57:24 GMT
Ok, I downloaded a fresh DC-9-30 and put 50% fuel on both right and left tanks and zero fuel on the center. Did not adjust any weight on the plane. Here is what the nose wheel looks like and its totally compressed. The top part of the wheel is behind the doors. Again, tried it stock on the DC-9-50 and I don't have this issue
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Post by aerofoto - HJG Admin on Sept 11, 2011 20:12:12 GMT
No problem "ACOURT" I was really only commenting in regard to the NG tire observations .... and then just explaining a litle of what we did and didn't do and why. Bill .... just out of curiosity ..... What particular base pack are you using with your AERO CALIFIFORNIA DC9-30 ? You should be using it with the "DC9-30 JT8D-15" pase pack .... and then adjusting the fuel loading (at least) to reflect that which appears in my following flying guide for this particular version in order to set this simulation at/near it's MGTOW .... Mark C AKL/NZ
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Post by BillA on Sept 11, 2011 20:42:26 GMT
Hi Mark, yes this is the DC9-30 JT8D-15 version plus i had a lighter load of fuel.
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Post by aerofoto - HJG Admin on Sept 11, 2011 22:35:27 GMT
I've had another look at my own installation of that particular DC9-30 base pack version .... There "IS" slightly more compression of that NG strut on this particular version than is evident with some of the others .... and the same possibly applies to the even heavier DC9-30 JT8D-17 version too. I'm not overly concerned by this though .... because I do think any discrepency is a "relatively minor" issue. In the interest of providing accurate weights for each these aircraft then its perhaps also got to be expected .... to some extent too. It's also possible that the "models natural COG position" may be fractionally out .... and that may also be contributing to what's being seen .... BUT .... adjusting that now (model data we're talking about and not CFG data) is a much more complex issue than it actually sounds. In any case .... we've all become busy with other projects here now and don't really have time to give this a more serious look. "IF" we look at resolving this at all .... then it's something perhaps best left until we're well into 2012 .... maybe Mark C AKL/NZ OH and BTW Bill .... "FELIZ CUMPLEANOS" amigo/"HAPPY BIRTHDAY my friend !
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Post by BillA on Sept 12, 2011 0:14:48 GMT
Muchas gracias mi amigo...no worries, the nines are great to fly and I enjoy them. Maybe down the road it can be looked at, but just thought I would mention it again.
Saludos Mark
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