Howdy again,

Turbofandude, adding weight is a placebo for changing drag but still doesn’t address the issue. Download AFM 51-9 at http://www.c141heaven.us/handbook/afm51-9.pdf.  Computationally aircraft weight is not considered in the lift-drag equation, but derivatively it is. In the eyes of performance, increase in weight=increase in induced drag via an increase in lift requirement, thus a higher weight aircraft will require more thrust (higher fuel flow) to maintain a given airspeed at a set altitude. Hence the most efficient cruise profile being a cruise-climb in which the aircraft is allowed to accelerate and climb naturally as fuel burns off.

CoolP, in regards to EPR, that was my point.

Sooo, 2 more cents
The Stratofortress was original built with bladder style fuel tanks in all positions, with the H model a wet wing was incorporated, greatly increasing fuel load. For comparisons sake we will look at the F, G, and H and Captain Sim H.

(no weapons)    
Total Fuel Quantity      Zero fuel      ZFW+Fuel      Max Flight      Weight Difference
F         271,053          184,000      455,053      450,000      (-5053)
G        312,997          184,000     496,997      484,000      (-12997)
H        312,997           184,000      496,997      484,000      (-12997)
H(SIOP) 312, 997       184,000      496,997      540,000+      43003
CS H    301,000      185,000      486,000      488,000      2,000

This simply illustrates, as I stated in my first post, mission planning requires the decision of range to weapons vs air refueling; due to limiting weight. Only the SIOP mission was critical enough to over-gross the aircraft to ensure mission accomplishment even with multiple A/Rs. The difference; SIOP was a mission that would only be accomplished once.

As a fun aircraft, Captain Sim set up the weights so that you could just start up and fly. That is a smart way to procedurally simplify a VERY complex fuel usage model. This thread is to discuss flight model changes for the fun model. I would love to see a systems heavy, crew required accurate model of this aircraft, but in the mean time I will settle for an accurate fun model that I can user tweak for more realistic operation. The point is, fun doesn’t have to mean playschool. In fact, I would hazard to guess that most users would consider realistic flight in MSFS more “fun” than a 747 that can do Mach 2. This is why I’m endeavoring to illustrate these tests.

Sooo, I tried adding a weapons station at station 0, 0 for 70,000 lbs, then reduced the fuel load in the body and ctr wing to the max flight weight of 488,000 lbs, and dropped the acft.cfg thrust to 29100 and RPM to 10200. The results were the same as before, climbing at 4500+ fpm, passing 380knots as if it was speed trap. The absolute best WAG numbers I could come up with form the 1-1 was 3500fpm. I then altered the tank positions and set real life correct fuel loads, and executed the same takeoff at a SIOP load of 535,000 lbs. The results: the aircraft still climbed at 4000 fpm, and with the RPM gauge at the end of the green arc, I made 36,000 feet at 310 knots. A little closer to charted, but still to hot. I decended to 30,000, flew at .85M (roughly 310 Kias) and ran some numbers. I was WAY above best endurance and best range, and should see a total fuel flow of about 35,000 lbs per hour. The aircraft gauge showed total FF of 12,500lbs/hr. The deck angle was almost 5 degrees up in level flight. (Now I’m having KC-10 flashbacks). RPM was just tickling the bottom of the green cruise arc. Best range in the charts is at 290ish or .765m. Charted fuel flow was 22500lbs/hr, and actual 9500. After multiple trials, I adjusted the “fuel_flow_scalar   = 1.66” and now the fuel consumption is much more in line, with 22,400lbs/hr at 78% RPM.

This just leaves the “hot” takeoffs and the climb and cruise deck angle. I think this is basically two issues in the flight dynamics, a mismatch between CL and CG causing the attitude issues, and a lift/Drag issue causing the “hot” speed and climb performance.


Nose down on takeoff:
Watch these three videos:
http://www.youtube.com/watch?v=Cq6Hpxyrhyo
http://www.myspace.com/video/vid/12032621
http://www.youtube.com/watch?v=wJ7niLYSVFo

You will notice that the aircraft must be rotated into flight, then transitions to a near level attitude during climb out. The C-141 did the exact same thing. I think when the cg solution is reached, this will be corrected. The real issue with takeoff performance isn’t nose down attitude as much as the acceleration rate. I am convinced that the issue lies in the lift-drag correlation in the .air file.

Tweaking .air files is like juggling plates while balancing on a ball. I enjoy GMAX, textures are no problem, and even gauge coding is doable, but deep .air file editing is a place where angels fear to tread. I will do surface tweaks and peak at values using airwrench, but beyond that, I leave the .air file to the experts. I enjoy flying this jet immensely, but I have reached the extent to which I am going to mess with the flight model, I hope the masters at Captain Sim will look into this further. I am happy to assist with real world data computation, scenario analysis and mission planning, just PM or email.

--Dan