New Boeing 737-800

[GabrielYV]

@jwocky Thanks

[jwocky]

Ooookay ... I finally found the time to take a quick look at the FDM and found ... Michael Soitanen!

- His GC refers actually to a document version, Boeing has pulled back because it had a print error ... in the section with the GC.

- His 25% MAC would be reasonable, only if you look where it is and compare it to where the middle of the plane is, it seems, here sneaked a -700 in, instead of an -800

- He used for his GC calculation a value with a total of 7 crew members on board as empty weight ... which makes aboutish 1400 lbs on the maximum of leverage ... then he calculated the positions of the tanks backwards via trim sheets (I don't know for which model exactly).

Sooo, now we have the x-position of the engines at 715.6 inches from the nose (his engines have thruster position and engine position equal???) while the tank x-positions are at 767.01 inches with a drain location of 703 inches (and if I am not entirely mistaken, that would be somewhere in front of the wings ... which doesn't matter, his feed pipes are 15 inches in front of his engines anyway.) The center tank is, omg, at 675 inches.

Soo, all of this adds up to plane that is in most load situations extreme rear heavy. Now, here is the rub, usually, in most airlines, if the plane is loaded for a short flight, bags go in the forward compartments first (because the real one is a little ass-heavy with small fuel loads) and if she is loaded for longer flights (means fuel load in the center tank), bags are preferably loaded in the rear compartment because the forward positioned center tank makes her then nose-heavier. So, airlines use actually some load and balance software to figure out how to load the birds correctly to get the best attitude out of them. Obviously the scream for "authenticity" combined with some weird backward engineering has led here to a bad balance situation and we have basically a plane that needs for every flight and load situation a balance calculation but we have not the software integrated to do so.

Long story short, for most situations, we can get her better by moving the CG aft, but there will be extreme load situations possible in which she will be somewhat bitchy and the AP has all the time to correct with trim. However, that would be the more "make her sim flyable" approach and probably, Michael Soitanen will jump me again for even thinking that.
The other thing is, someone who is fit in Blender can check all the positions of tanks, engines and compartments. For my impressions, the wing tanks are a little too far aft and the center tank maybe too far forward.

On another side note, for my feeling, she is a bit low on lift and way low on drag?

Please let me know, what you want to do: Just move the CG? Recheck all positions? Integrate a load balance software?

[Octal450]

Recheck all positions would be good for now.

Please also fix what you fixed in the A320, engines have to much effect on PITCH.

Rgds
Josh

[jwocky]

That is because they sit so badly out of the axis, Josh. So, well, who is the Blender specialist on this one? I take the positions in inches, meters, centimeters, whatever ...

[Octal450]

Uhh... not me... I use AC3D. So the coords might not match...

[IAHM-COL]

Uhh... not me... I use AC3D. So the coords might not match...

The coordinates from AC3D should be fine too.

[Octal450]

They don't line up with Blender or FGFS, you have to swap around, and I can't just select a point a get position, I have to select a vertex or object. Gabriel uses Blender, maybe he has them.

In the mean time:
I have just completed to push an update to the 737, which includes the latest autopilot version, LNAV waypoint transitions should be alot better now., and a bunch more fixes and updates that the 737 missed, due to my absence.

[GabrielYV]

@jwocky Hi Dont Worry about soitanen.
Now the person in charge of this project is me And my other colleagues who help me in the updates.
Do what you have to do and over time will be improving I use a lot of blender and ac3d But I do not think I change what you want, Can i get some help..
By the way, you already have permission to push changes in my branch https://github.com/YV3399/737-800
Sorry for my english.
@jwocky I have some manuals that can help yo. You can communicate with me privately and with pleasure send the file.
Thank you for taking the time to review the 737 800
Regards Gabriel Hernandez

[jwocky]

Got the invitation, but no time before Sunday to go for the FDM. I think, I do some quick repairs first to make her stable, then grind it down more in the details. Anyway ... the Blender-question is not to change anything, but Blender gives positions in meter (at least Israel gets always meters out of it). The trick is to load the plane, get the Blender positions of nose tip, tail end, engines, tank positions and so on (should work also in AC3D) because since I know the real length between nose and tail end, I can recalculate all other positions in between them in the same relation. The problem is, if I touch a 3D program, weird things happen.
Alternatively, if you have some real good blueprints ... I can calculate from there as well.

[jwocky]

I just pushed a changed FDM. Admittedly, a lot of estimation work, but I think, she is better now. However, keep in mind, the -800 is due to the stretch a bit iffy anyway. For short flights (means, no center tank fuel) bags go in the front, for long flights (center tank fuel) bags go in the rear because without weight in the center tank she has for real a tendency to pitch up if not countered by trim. So, that is dampened now but not entirely gone.

The pitch/throttle problem: The engines hang low, under the CG. Sooo, yes, she gets some hefty impulse. It is better now since she is otherwise less rear-heavy and if the load is dispersed ok, yeah, well, better but not good. I couldn't find anything how long the CFM56's need to spin up, but they seem pretty fast, that means, the impulse comes quick and hard, so maybe there is a root of the problem. Now I haven't studied the IT-Autoflight, but why is the elevator slower than the engine spin up anyway? Because to a degree, even not that extreme as a 737, all commercial liners nowadays have those low hanging engines to begin with?

I try to bring my Blender to run and to understand it, then I get me better positions out of the model. Some things appear still a little fishy there to me.