Measuring takeoff distance

Vitus · 13 May 2018

Hello again,
I'm not really sure where to post this, since the topic expands to various aspects of the aircraft design.

In short: I need a way to easily measure the takeoff distance. Does anyone know if there's a simple gauge available that I can use, or can you think of a different, easy method?

I am compiling the performance data for the Vega to compare to it to the sparse information I got. I'd like to gather the typical information:
takeoff speed under various loadouts, takeoff distance, distance to clear a 50ft obstacle, speed when reaching 50ft. And all that at different pressure altitudes. This will be fun!

Ronald · 13 May 2018

How about this (quick?) solution:

1. Create a ruler-runway texture (see image above) and add it to your test airport's runway
2. Position your Vega and the beginning of the ruler-scale.
3. Take off with your Vega (of any other aircraft you would like to test)
4. When having achieved the "Vr Speed", pause you flight-simulator.
- https://www.baatraining.com/did-you-know-about-aircraft-take-off-speeds-v1-vr-and-v2/
5. Switch to a top-down / satelite-view and .. tadaaah.. instantly read your required take-off distance

.

No extra gauges needed and you can re-use this runway-texture to measure for other distances / planes too.

Roy Holmes · 13 May 2018

I use AFSD. For take-off runs you select Ground Dynamics which gives you a load of details while still on the ground and the ground run which appears when the wheels break ground. Print screen will capture the data but capture screenshot will not because the AFSD display is not part of the sim windows.
Incidentally Engine Data will display everything you ever wanted to know about engines but were afraid to ask.
For props this includes indicated power, which is a function of engine capacity, pressures and RPM. Friction loss. Indicated power minus friction loss gives shaft power. Prop efficiency times shaft power gives thrust power which is what's available to pull the airplane. it also gives RPM, Beta, J, Prop Efficiency and shaft RPM.
AFSD and a lot of other good stuff is available on http://www.aero.sors.fr/
Roy

Vitus · 13 May 2018

Thanks for your answers guys. I never, ever tried any scenery work and I didn't want to get into it just to get some takeoff data. Therefore I spent the morning coding a small XML gauge that provides me with all the data I need.

After lining up with the runway, you press the "BEGIN TAKEOFF ROLL" button and the gauge takes a reading of your position. Once the aircraft reaches 2ft above ground read the second set of coordinates and remember the speed. At 52 ft I take the third reading. I use the Latitude/Longitude of the three points to approximate the distance traveled. The formula I use is quite rough, but since we're talking very small distances the result is acceptable.

@roy: Thanks for the link. Unfortunately I only saw it after I was done programming

But I installed the program you suggested to have a look. Unfortunately it looks like it crashes after connecting to the sim. No idea whats causing this...

Ronald · 14 May 2018

Nice gauge Vitus

Vitus · 14 May 2018

Thanks Ronald. I actually ended up spending the whole day adding to it. It can now record performance data for all parts of the flight. It's a bit crude but will get the job done

Ronald · 22 May 2018

It can now record performance data for all parts of the flight.

So you build your instant flightrecorder / blackbox gauge on-the-fly? That sounds interesting Vitus.

Vitus · 24 May 2018

It's really a very quick&dirty solution to my problem. The only thing that was a bit tricky was to find the distance between two coordinates for the takeoff and landing distance. But since we're talking about a very short length I didn't use spherical trigonometry but rather a simplified approximation. If anyone is interested:

Code:

        (L:PERF DATA ACQUISITION,enum) 1 ==
        if{
          (A:PLANE ALT ABOVE GROUND,feet) (L:PERF P1 HEIGHT,feet) - 2 &gt;
          if{
            (A:PLANE LATITUDE,radians) (&gt;L:PERF P2 LAT,radians)
            (A:PLANE LONGITUDE,radians) (&gt;L:PERF P2 LON,radians)
            (A:AIRSPEED INDICATED,mph) (&gt;L:PERF SPEED LIFT OFF,mph)
            (A:PLANE ALT ABOVE GROUND,feet) (&gt;L:PERF P2 HEIGHT,feet)
           
            (L:PERF P2 LAT,radians) (L:PERF P1 LAT,radians) - d s0 (&gt;L:PERF S0,number)
            (L:PERF P2 LON,radians) (L:PERF P1 LON,radians) - d s1 (&gt;L:PERF S1,number)
           
            (L:PERF P2 LAT,radians) (L:PERF P1 LAT,radians) + 0.5 * cos l1 * d s2 (&gt;L:PERF S2,number)
            l2 sqr l0 sqr + sqrt 6371000 * (&gt;L:PERF DISTANCE LIFT OFF,meters)

            (L:PERF FUEL 1,gallons) (A:FUEL TOTAL QUANTITY,gallons) - (&gt;L:PERF FUEL USED 1,gallons)

            2 (&gt;L:PERF DATA ACQUISITION,enum)
          }
        }

(L: PERF DATA ACQUISITION,enum) is the variable that gets set to "1" when the user clicks on the button to start the data acquisition. The code above is wrapped in the <Update> script of the gauge. The code is checking for the height above ground to work out if lift-off occurred. I'm setting the (L: PERF P1 HEIGHT,feet) variable to the plane's altitude when clicking the button - that is to offset the fact that (A: PLANE ALT ABOVE GROUND,feet) is measuring the height to the reference position. I give it another 2 feet to allow for the decompression of the gear's suspension. For the actual calculation of the distance, I need to calculate the angle between the two coordinates and then multiply it with the earth's radius. (L: PERF P1 LAT,radians) and (L: PERF P1 LON,radians) contain the coordinates, recorded when the user presses the data acquisition button. Besides the distance, the gauge also calculates the fuel used by comparing tank quantity.

The performance data for climb, cruise and descent are much easier, since the distance is irrelevant. Activated by a button in the gauge, it records the tank quantities of two points in flight and takes the average of the two indicated airspeeds. It also calculates the power setting of the engine (HP, manifold pressure, rpm), the density altitude and temperature. Easy-peasy.

Ronald · 26 May 2018

Thanks for sharing the code Vitus. This helps me to gain a better insight on how to build my own gauges for my own YF16-project in the future.

Roy Holmes · 26 May 2018

(A:SIM ON GROUND,bool) changes from 1 to 0 when you get airborne
Roy

Vitus · 27 May 2018

Roy Holmes said:
(A:SIM ON GROUND,bool)

I always tried to get around the sim on ground variable. Wasn't there some problem with that variable in multiplayer?

Roy Holmes · 27 May 2018

Wasn't there some problem with that variable in multiplayer?

Never heard of that and I use it a lot. However, who cares if it works in single player?
Anyhow it was just a suggestion to simplify your code.
Roy

Vitus · 27 May 2018

Yeah you're right. I really don't know why I care in the first place. The Vega is a single-pilot aircraft and it's not even equipped with a radio. It's utterly useless in multiplayer :laughing: