Acceleration question

[javfn 0]

Hello!I

[WarpD 824]

Acceleration is nothing more than velocity change for a given moment.There are three values:VELOCITY BODY XVELOCITY BODY YVELOCITY BODY ZThese are returnable in feet per second. To convert the values to acceleration you simply need to measure the time between each set of readings.As example, let delta_x1, delta_y1 and delta_z1 be your prior reading. When you obtain your next values let them be delta_x2, delta_y2 and delta_z2. Variable time1 is the time value for the prior reading and time2 is the time value for the current reading. A variable, total_time is time2-time1.Your resulting acceleration values of accel_x,accel_y and accel_z would be derived from an equation like accel_x = (delta_x2-delta_x1)/total_time.

[Murmur 3,941]

Each of the two formulas for calculating drag is specific to a different flight regime.Precisely, the first formula ( D = W * sin(gamma) ) is valid only for a = 0 ( steady flight ) and T = 0 ( no thrust ). In other words, it is valid for steady gliding.The second formula instead ( D = T cos (alpha) ) is valid under the hypotheses of, again, a = 0 ( steady flight ) and gamma = 0 ( zero vertical speed ). In other words, it is valid for steady horizontal flight.Marco

[javfn 0]

Hello!Thank you guys for your replays.EdI've trayed mesuring change in TAS using the low pass filtering Ron kindly posted in this forum, but realized the final value has a delay (unless I'm making a mistake), I take the value of TAS twice one second apart each other and then filter that diference to avoid the jumps betwen changes, where I suppose the delay is added. Do you have another method to messure the diferential equation you posted?MarcoDo you know what equation can be used to calculate accelration no matter the flight conditions?, I've being serching but that formula is the only one I could find so far, and some documents say it can be used for any flight condition, no matter if there's constant TAS or not, let me check, maybe I'm mistranslating.RegardsJavier

[WarpD 824]

I gave you the name of three variables and the methodology to use them. I'm not certain what more you need. Those three velocity variables are far more accurate than TAS.

[Guest Ron Freimuth]

>................>Ed>>I've trayed mesuring change in TAS using the low pass>filtering Ron kindly posted in this forum, but realized the>final value has a delay (unless I'm making a mistake), I take>the value of TAS twice one second apart each other and then>filter that diference to avoid the jumps betwen changes, where>I suppose the delay is added. Do you have another method to>messure the diferential equation you posted? In my XML code, I gather 'V', etc. every tick (1/18.2 sec), then divide successive differences by delta t (=1/18.2) to get an unfiltered 'Vdot'. That variable has sampling errors in Magnitude and Phase. Mainly in Phase. Since there is an average delay of (1/18.2)/2 in the sampled datums. To smooth Vdot, I added a low pass filter set with a Time Constant of typically 0.5 seconds. That adds a further delay to the Vdot variable, but the result is still very useful. I display Vdot as something like "5.25 ft/s". Note 32.17 ft/sec^2 is "1 G", so I can easily estimate acceleration in G's during TO, in flight, or landing. In fact, Vdot is negative if power is cut on the ground, and the value gives a direct indication of 'rolling coefficient of friction', mu. In FS9 (and earlier), Vdot will display about 32.2*0.05 = -1.6 ft/sec^2 if the thrust is cut to zero at lower runway speeds (where only rolling drag is significant). A more reasonable value for mu, consistent with actual hard surface drag, is indicated when the 'fixed for rolling friction' sim1.dll is being used.>Marco>>Do you know what equation can be used to calculate accelration>no matter the flight conditions?, I've being serching but that>formula is the only one I could find so far, and some>documents say it can be used for any flight condition, no>matter if there's constant TAS or not, let me check, maybe I'm>mistranslating.>>Regards>Javier I eventually calculated Fnx, Excess Thrust, in my Jet Test gauge. Fnx = Fn - Fdrag, and is 0 in unaccelerated, level flight. Later, I resolved Fnx (in lbs) into Fvs (vertical speed) and Fac (acceleration), so I could see how much of the excess was available for climb, and how much was used to accelerate the AC. Fac is simply (W/g)*Vdot, while Fvs involves no more than a basic consideration of forces on a frictionless, inclined plane. A screen shot of my Jet Test" Window taken on a Concorde test flight gives some details. 60% down the window, in 'light blue' I see: Fnx 29.67% 15887 lb Fvs 3602 Fac 12001 lb | 0.6% The last '0.6%' is a calculation of the error, which can be over 10% in dynamic conditions. Ron

[javfn 0]

Good day!RonI'm using a factor of .01 for L:Airspeed diference and .99 for L:Airspeedfiltered, Do you think that's why I see the delay in the final value?. Do you use a factor .5 for each var? Since I messure TAS every second I don't have to multiply for nothing the filtreted value, I suppose 18.2 times Airspeedfiltered is the value of dv/dt for one second using tick 18.2 .I think calculating acceleration using the F=ma equation could be some how better if i don't have to filter, but ofcourse it requires to caclulate the net force along the flight path, that's why i posted the F=T cos(alpha)-D-W sin(gamma), but i'm not sure if that's the right one.Javier

[Guest Ron Freimuth]

>Ron>>I'm using a factor of .01 for L:Airspeed diference and .99 for>L:Airspeedfiltered, Do you think that's why I see the delay in>the final value?. Do you use a factor .5 for each var? Since I>messure TAS every second I don't have to multiply for nothing>the filtreted value, I suppose 18.2 times Airspeedfiltered is>the value of dv/dt for one second using tick 18.2. I'm not sure what "L:Airspeed diference" and "L:Airspeedfiltered" relate to. My XML code is based on simple minded intuition and verification. Displayed values are consistent with Newton! You can't get FS variables over time differences of exactly one second. However, the DOS Tick, close to 1/18.2 seconds, is the time difference between XML Parameter. Note FSX appears to make accelerations directly available. >I think calculating acceleration using the F=ma equation could>be some how better if i don't have to filter, but ofcourse>it requires to calculate the net force along the flight path,>that's why i posted the F=T cos(alpha)-D-W sin(gamma), but i'm>not sure if that's the right one.>Javier I think I simply used gamma(in radians)~sin(gamma) to approximate the vertical component of thrust; saving the overhead of a sin(gamma) calculation. So, if 'flight slope' is 11.46 deg (0.20 rad), the vertical component of thrust increases mgh (potential energy due to height) by 0.20*Fn*VS ft-lb/sec. I display the vertical component of Fn (thrust) as Fvs. Ron

[javfn 0]

Well, if acceleration is going to be available in the next version of FS this is very good news, that parameter and alpha channels on 0,0,0 areas have been on my whishing list.Javier

[javfn 0]

Hello!Regarding the alternative method to find the acceleration value I don

[WarpD 824]

I already replied with a method that works.

[javfn 0]

Hello Ed!Sorry, but I can't see the diference betwen yours and what Ron's Low pass filter does. Or am I ignoring something in your first reply?Javier

[WarpD 824]

Let's put it this way... I can calculate drag accurately with it. I'm taking the velocity values and quantizing them based on time between samples. It gives a fairly accurate value for the 3 acceleration axes. I'm not using TAS, I'm using velocities.I have no idea what Ron's doing, to be honest. The only 'low-pass filter' I've ever had knowledge of is in electronics.

[Guest Ron Freimuth]

>Hello!>>Regarding the alternative method to find the acceleration>value I don

[Guest Ron Freimuth]

>Let's put it this way... I can calculate drag accurately with>it. I'm taking the velocity values and quantizing them based>on time between samples. It gives a fairly accurate value for>the 3 acceleration axes. I'm not using TAS, I'm using>velocities.>>I have no idea what Ron's doing, to be honest. The only>'low-pass filter' I've ever had knowledge of is in>electronics. I'm an EE and am quite familiar with RC LP filters. The challenge was to come up with an algorithm that did the same thing, but digitally. All previous values of a variable are in the current reading, but the farther back in time they are, the less they add to the total. I was able to combine various parts of the calculations in compact XML code. However, it gets tricky to understand what is going on. This is a much better approaching than the 'running averages', etc. used in market, etc. analysis. JSBSim source code has many kinds of filters written in C. It's on the WEB at sourceforge. Ron