xml lift formula

[taguilo 33]

>Quite serious.>>Despite what ACES thinks... most of the civilized world does>not do math via reverse polish notation (RPN), as the XML>stack method is commonly refered to.I agree, Ed. However, I believe RPN is the only type of scripting that can be parsed from an FS XML file with an acceptable performance. In fact, the way it mainly works is such #### simple (so to speak) that I can't say anything but kudos to ACE's team developers!Tom

[Guest Ron Freimuth]

>Hi,>>The results of the units are of course visible in a gauge.>Like:>>weight: 380.000 lbs>speed: 250 ft/sec>density: 0.001 slug/ft^3>aoa: 0.1 radians>In the acft.cfg Wing Area: in sq ft (3050)>Also from Boeing data.> >Btw. The formula gives now exact the same results as AFSD of>Herve Sors, so it seems to be not so very wrong.>>Jan One needs to use AoAe, not AoA. Since CL = 0 at AoAe=0. One can find this in TBL 404. REC 1101, 'AoA at CL = 0' should agree. AoAe is then calculated as AoAe + alpha. One can multiply Weight by 'G' to get actual wing lift. That worked pretty good in my XML Test Gauges. Lift slope should be gotten from TBL 404, it is [delta CL]/[delta alpha]. Another complication is that lift slope varies with M. Set in TBL 401. Since I calculated Lift from G*W, I didn't have a problem with some of the other details. In any case, AFSD is very useful for checking that one's calculations are working correctly. AFSD3, for FS9 and FSX no longer requires the standard FS WX, any variation of temperature, pressure, etc. gives the correct values for everything. Ron

[WarpD 824]

Ok, something odd happening.I calculate lift correctly. I have correct values for Cl, Cdp. All confirmed by AFSD.I can not get the correct value for Cdi. I am calculating it with the following formula:Cl^2/(Pi*e*AR)It's off, not horrendously but off never-the-less. I have confirmed I have the same values for e and AR that are shown in AFSD. So why am I not coming up with the same value for Cdi that AFSD is calculating?

[hervesors 1]

Ed,At this time, I'm affraid nobody knows exactly how FS calculates induced drag. The classical formula you quote doesn't work correctly in many situations (it is the vortex drag associated with the untwisted wing). By now, AFSD Cdi is the residual drag obtained by substracting from total CD, all other drag components (parasite, compressibility drag,flaps, gear, spoilers,etc..). I named it CDi since, after numerous tests, we are rather on the safe side for all other drag components and the remainer "should" be the viscous and inviscid drag parts. This is still open to experimentation but clearly you will not fit the value with the classical formulaHerv

[WarpD 824]

Well, I'm even more confused at this point.Cdp is the summation of all the items you just listed. It is clearly less than Cd. So, where are you obtaining Cd from?I need to be able to accurately calculate drag, that's my ultimate goal.

[hervesors 1]

Ed,Total drag and Cd are obtained from 2DOF aerodynamical equations (acting forces along true air speed flight path), dynamic pressure and wing reference area. No assumption here about the participating drag componentsIf your aim is to calculate total drag and Cd during steady level flight only, you will need to assess simultaneously total thrust (and thrust angle in FSX), AoA, dynamic pressure and acceleration along the TAS axe and use the classical equations of motion for calculating total drag and therefore Cd.Calculation during climb and descent will request some additional data (slope angle and actual gross weight)Herv

[phjvh 0]

Hi,I feel like an intruder between the pro's, but i think i calculated Cdi (controlled by AFSD) with:(A:AMBIENT DENSITY,Slug/ft3) (A:AIRSPEED TRUE,feet/second) (A:AIRSPEED TRUE,feet/second) 3050 (L:Airfoil,number) pi 2 (A:INCIDENCE ALPHA,radians) * * + * * * * 2 / 100000 / 100 * (>L:LIFT,pounds) (A:TOTAL WEIGHT,pounds) (A:AMBIENT DENSITY,Slug/ft3) (A:AIRSPEED TRUE,feet/second) (A:AIRSPEED TRUE,feet/second) 3050 * * * / 2 * pi 2 (A:INCIDENCE ALPHA,radians) * * - (>L:Airfoil,number) (L:Airfoil,number) 2 pi (A:INCIDENCE ALPHA,radians) * * + (Cl)(L:Airfoil,number) 2 pi (A:INCIDENCE ALPHA,radians) * * + * (Cl) pi 0.69 * (eff.fact)156.083 (span, ft)156.083 * (span, sq ft)3050 (wing area, sq ft) / * / (>L:Cdi,number) Sorry for RPN, but "Translation" above.Jan"Beatus ille qui procul negotiis..."

[taguilo 33]

Jan et al,May I intrude as well? :-)I am eager to know the reason you need such "technical" values like Lift, Drag, Airforil, etc within a flight...Do you use them in FMC calcs maybe?Tom

[phjvh 0]

Tom,Nothing of the kind?, of course a big bit!I am always busy on long haul flights and that are the only flights i like because:1.Listening to or playing Mozart.2.Looking at the Mythbusters.3.Drinking Coffee.4.Talking to the wife.5.On call for duty, work.6.And....wrestling with aircraft stuff to develop a reasonable Thrust System.I still didn't succeed to set N1 in take off, climb, cruise and descent.I tried all kind of formulas without succes.And testing those, lift, drag, Cl etc. came along.And because of failures the question was born, see upstairs.Do you guys have good thrust, performance etc. stuff, so you can set thrust and derated thrust etc.?????Jan"Beatus ille qui procul negotiis..."

[Guest Ron Freimuth]

I'll continue.> One needs to use AoAe, not AoA. Since CL = 0 at AoAe=0. >One can find this in TBL 404. REC 1101, 'AoA at CL = 0' should>agree. >> AoAe is then calculated as AoAe + alpha. > .......... That should be AoAe = alpha - AoAo. Where AoAo is value where CL=0 (typ -0.033 rad). CL_alpha is slope of TBL 403 at low AoA. Typ 5.0 Cdi = [AoAe * Kf*CL_alpha]^2 * Cid Cid = 1/[Pi*AR*e; AR = sqrt(bw)/Sw Kf is a fudge factor, typically 0.985, ideally 1.00. I adjust it to get correct total drag at low speeds were Cdi predominates. One can also adjust Kf so Cdi agrees with AFSD. The above calculates Cdi very well, and automatically accounts for TBL 401, which modifies Oswald Efficiency as Mach changes. Add zero lift drag(s) to get total CD. Physical drag then equals CD * S * q. Dynamic pressure, q, should be calculated from V based on Mach, not 'True Airspeed'. FS9 and probably FSX give the wrong value for TAS, further, I had other problems using it to get q = 1/2 rho V^2. Ron

[WarpD 824]

Ron... I see no TBL 403 in any .air file... I'm assuming you meant TBL 404?As well... when you say CL_slope... are you talking about the slope of the line between any two points of TBL 404? I'm also assuming this is correct.You're saying AR is sqrt(bw)/sw... if AR is aspect ratio, I'm familiar with AR = sqr(wingspan)/wingarea... but not with what you've written. :(If AR is indeed aspect ratio... then I'll see what I can come up with for results.

[Guest Ron Freimuth]

>Ron... I see no TBL 403 in any .air file... I'm assuming you>meant TBL 404? Right, TBL 404, CL vs AoA.>>As well... when you say CL_slope... are you talking about the>slope of the line between any two points of TBL 404? I'm also>assuming this is correct. Yes. AFSD gives the slope in its Info window.>You're saying AR is sqrt(bw)/sw... if AR is aspect ratio, I'm>familiar with AR = sqr(wingspan)/wingarea... but not with what>you've written. :( bw = span_wing. Sw = Area_wing>>If AR is indeed aspect ratio... then I'll see what I can come>up with for results. I had to check my formulas against my XML Test Gauges, which give good values for Cd's and total drag. I set 'e' from the Oswald_efficiency in aircraft.cfg. Ron

[taguilo 33]

Jan,Long time since a did my last big iron's flight :-( Too busy with my gague programming task. However, I do listen Beethoven while working with code :-)Regarding your thrust question, I succeeded to model my 757 Thrust system as real as it gets. It includes EPR settings for different phases of flight, ECC Thrust control and ELP N1 protection, EPR Commanded indicator (throttle's position for a desired EPR), etc.I took me several months to finish the engine model (RR), where I had to work with engine tables of the .air file. The clue to obtain good thrust values is to find the proper relationship between those tables, use a set of polinomials to show proper values on the gauge's readings, and other tricky stuff.Tom

[Guest Ron Freimuth]

>Tom,>I am always busy on long haul flights and that are the only>flights i like because:>>1.Listening to or playing Mozart.>6.And....wrestling with aircraft stuff to develop a reasonable>Thrust System.>I still didn't succeed to set N1 in take off, climb, cruise>and descent.>I tried all kind of formulas without succes.>And testing those, lift, drag, Cl etc. came along.>And because of failures the question was born, see upstairs.>>Do you guys have good thrust, performance etc. stuff, so you>can set thrust and derated thrust etc.?????>Jan Again, I first get drags good by comparing fuel flow against FM's for different flight conditions. TSFC is set per turbine specs, it is constant in MSFS, but that's acceptable for cruise conditions. I may get actual drag coefficients from data in Roskam, etc. But, still have to adjust TBL 401. It changes Oswald efficiency as a function of Mach. After getting close fuel flow I adjust the turbine to get appropriate CN values. Intake area can be used to adjust Ram Drag, though one can adjust TBL 1507 to get appropriate air flow for a realistic intake area. The later can be figured as about 8% greater than the area of the intake compressor rotor. The nacelle bell mouth scopes in the extra air. I think Tom worked out a way to figure EPR directly from Thrust and Ram Drag. Better than the approach I used for a 727 with JT8D's. I got CN1 close for the correct thrust at a given flight condition, then used a table of EPR, EGT, vs N1 and N2 to model EPR and EGT. That came out close in cruise at Mach 0.80, but deviated some at approach conditions and other Mach numbers. If we understood turbine and compressor variations better I think a few formulas could be adjusted to model the AIR file turbine tables and the extra gauge code needed to get EPR and EGT without all the fooling around. The ratio of TBL 1507 to 1506 is especially important for low throttle descent. High air flow makes thrust negative above FL 100 or so; if one wants accurate descent performance thrust has to be appropriate for the flight idle setting. Incidentally, my Jet Test gauge pretty well shows me how to fly an accurately modeled jet transport. Don't need no FM tables! In fact, I think FM tables are created to give gauge readings that result from the kinds of engineering values I see on my gauge. With some adjustments from actual flight tests. I adjust climb IAS so Cdi/Cdp is about 0.33 (best range) and Relative Thrust to 90 to 95% of rating. A typical climb value. Actually, it may increase to 115% at cruise FL. I transition to constant Mach at the FL Mach for Best Range. After leveling out at appropriate FL I let M increase to (typically) LRC Mach. Then, reduce N1 or EPR to FM cruise value. "Relative Thrust" is based on Thrust/Delta, scaled to 100% at SL values. Delta is Pressure/Std SL Pressure. AFSD displays values than are similar to many of my Test Gauge readings. Including some things I can't display; other factors that would have be be calculated from what AFSD does show. Mainly 'Relative Thrust'. Descents are generally at a -3 deg slope, the AC should stabilize near normal descent IAS when the throttles are set for rated descent N1. The AC should be trimmable so it descends without autopilot (at least after M drops below 0.74 or so). After than I only have to retrim a bit every 10000 ft. Similar for Climbs before the M transition speed. Ron

[phjvh 0]

Hi,This goes a little bit much over my head of course.I tried with weight, temperature, altitude (density etc.), vert. spd., pitch etc.Then calculate a constant for the different flight stages and so a number to set the throttle-axis.But....not very reliable.At least can you say which factors i have to consider to come a little bit closer.E.g. influence of weight, temp., alt. etc.Jan"Beatus ille qui procul negotiis..."