DSB final report doubts: no drift angle

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In determining the location where the missile exploded plus determining  the angle of the missile relative to the aircraft it is important to understand the position of the aircraft relative to the missile at the time of the explosion.

The modeling of the damage pattern and matching the location of the missile was performed by TNO. TNO however failed to include the drift angle of the aircraft. This does have an effect on the modeling.

Terms

There are four  important terms to understand:

  • displayed heading of aircraft
  • Magnetic declination at position
  • drift angle of aircraft
  • track course  of aircraft

Displayed heading (aka magnetic heading)
DSB describes the displayed heading as “Angle in degrees between the longitudinal axis (where the aircraft is pointed) and magnetic north
as displayed on the primary flight display (1 x per sec).

The Flight Data recorder showed a displayed heading of 115 degrees.

Magnetic declination
Magnetic declination or variation is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the direction of the Earth’s magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole). This angle varies depending on position on the Earth’s surface, and changes over time.

Magnetic declination in Torez is 8 degrees.

Drift angle
The difference between the track and heading is called ‘drift angle’. Drift angle is caused by wind.

The drift angle of MH17 because of the South/southwesterly wind at 10km alititude was 4 degrees.

Drift angle according DSB final report was  – 4 degrees. The table below was taken from the DSB final report page 111 of 279.

Almaz Antey showed the drift angle of  4 degrees in their presentation as shown below.

track course 
The track course is the actual ‘heading’ of the aircraft relative to the meridian of a map.

The track course of MH17 was 115 + 8 -4 = 119 degrees.

No drift angle used for TNO missile azimuth calculation

The remarkable fact is that TNO, who did the modelling of the warhead damage, did not use the drift angle of the aircraft in the calculations. Split X software was used to model the damage pattern. If parameters in Split X matched damage to MH17, the location, azimuth and elevation was determined.

Page 13 of Appendix Y written by TNO clearly states:a possible roll angle, angle of attack and drift angle of the airplane have been assumed to be negligible.

TNO was informed by Dutch NLR via an email dated January 28 2015 that there was no need to use drift angle in the calculations.

Dutch NRC on April 16 published an article about the angle the BUK missile hit the aircraft. NRC concluded there was a large difference between the expected angle (azimuth) from a launch near Snizhne compared to the calculated azimuth of 27 degrees.  NRC did use the drift angle in the calculations.

Modelling on software only

One of the most remarkble facts of the DSB investigation is the lack of a full scale, complete reconstruction of the cockpit and business class section during the investigation. The 3D model we saw at the October 13 presentation of the final report was made for that purpose.

NLR and TNO had to use the limited number of wreckage which was attached to a temporary wooden construction. Read this pressrelease for more information.

 

 

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12 Comments on DSB final report doubts: no drift angle

  1. DSB/NLR/TNO seem to be talking about the effect on speed, rather than angle, when they say that the “drift angle of the airplane have been assumed to be negligible”. A difference of four degrees (MH17’s drift angle) would have very little effect on the speed at which a missile or its fragments approach a target.

    But those few degrees are very important if you’re trying to figure out the exact direction of the missile towards the aircraft. In that calculation, what’s important is the plane’s heading, not its track (the track is the direction that the aircraft is actually travelling, but the heading is where it’s pointing in order to compensate for the effect of the wind.)

    So the drift angle should be taken into account when calculating the exact direction, but it’s almost insignificant as far as speeds are concerned.

    • To put it another way, I think that the DSB is using a slightly simplified model where they assume that the aircraft is travelling exactly in the direction of its longtitudinal axis (ie. its heading). In reality, the wind is also pushing it a bit to the side at the same time. This component of the velocity is tiny, and even more so if you consider that the missile and its fragments were moving much faster than MH17.

      Unfortunately the DSB/TNO don’t explain in what way the drift angle was assumed to be negligible.

      The diagram above by Almaz Antey is also confusing because it shows the aircraft rotated by 4 degrees from its real orientation. Its longtitudinal axis would actually have been along the red line, at 115 degrees from magnetic north, as read from its onboard compass. The dashed line is actually the track, or direction of travel, which results from the southwest wind pushing the aircraft to its left.

      The illustration in the NRC article shows the correction direction of the heading angle. However the article itself is confusing because it mentions lots of different angles without making it clear what they are referring to (at least the Google translation is unclear to me).

  2. sotilaspassi // April 19, 2016 at 12:47 pm // Reply

    Now I’m littlöe puzzled… Boeing777 nose was pointing to 119′ (according to earth magnetic field) while the plane was moving to 115′ (according to earth magnetic field).

    Then, to match with geographic map, one needs to add another 8′.

    • sotilaspassi // April 19, 2016 at 12:49 pm // Reply

      “one needs to add another 8′.”

      Correction: one needs to minus 8′ from magnetic compass values.

    • No, the Boeing 777 nose was pointing to 115 deg according to earth magnetic field. 115° was the last displayed heading, which is defined in p.33 of the September 2014 Preliminary report:

      “Displayed Heading: Angle in degrees between the longitudinal axis (where the aircraft is pointed) and magnetic north as displayed on the primary flight display (1 x per sec).”

  3. Don’t hang me if I’m wrong 🙂

    http://www.whathappenedtoflightmh17.com/dsb-final-report-doubts-no-drift-angle/#comment-16886

    Karel Knip:

    http://www.nrc.nl/nieuws/2016/04/16/boekraket-had-mogelijk-ander-doel-dan-mh17-1609314

    Ultimately calculated in subsequent exercises azimuth value rise from 17 to 35 degrees, with 27 as the most likely value.

    http://tinyurl.com/jcprrd2

    On this basis, the launch site can be calculated as the position and direction of the Boeing are known. The last position of the Boeing is shown by the Flight Data Recorder

    http://tinyurl.com/z8gvtqt

    The drift was caused by approaching from the right side winds which forced the plane to a somewhat oblique position in its orbit.

    http://tinyurl.com/jymjxxx
    http://tinyurl.com/jdjfc3c
    http://tinyurl.com/hblvymm

    and the aircraft position can be calculated. Magnetic heading ( ‘heading’) was, according to a table: 115 degrees and ‘drift angle’ 4 degrees.

    http://tinyurl.com/hupfsy9
    http://tinyurl.com/zf2bx87

    The drift was caused by approaching from the right side winds which forced the plane to a somewhat oblique position in its orbit. In the area (Donetsk) has a compass deviation of 8 degrees in an easterly direction. The true heading (relative to the meridians) of the Boeing was therefore 119 = (115 + 8-4) degrees. This is reflected exactly as drawn in the OVV illustrations and are thus suitable for further analysis. Recall that a rocket-azimuth of 27 degrees relative to [course of] the Boeing manifests itself due to the drift as an angle of 31 = 27+4 degrees with the route flown.

  4. sotilaspassi // April 20, 2016 at 12:52 pm // Reply

    Hmmm… what would be the drift angle of BUK missile coming from south of snizhne? (I imagine with 3x speed vs MH17 the drift angle would be 4 deg / 3 )

    Then, how much upwards missile nose must be, for it to stay in air with tiny wings, at 600ms…700ms speeds? (I imagine only a few degrees.)

    ((TOW missile also has small wings and very low 300m/s max speed.
    Here we see 7 deg angle for it to keep on flying, in the photo the speed is perhaps 200m/s coming closer to max range.
    https://drive.google.com/file/d/0BxNz0P5oVk2wNjVGR0VQR29MejQ ))

    • “Hmmm… what would be the drift angle of BUK missile coming from south of snizhne? (I imagine with 3x speed vs MH17 the drift angle would be 4 deg / 3 )”

      I would expect it to be that much lower too, at least at that altitude and wind velocity. Looking at it in the form of vector addition, the same wind would have a relatively smaller effect because of the far greater speed of missile. The drift angle (between track and heading) will therefore be smaller.

      I don’t know if anyone has tried to work out the drift angle of a missile from either Snizhne or Zaroshchenske. For that calculation, the wind from roughly the opposite direction at lower altitudes on 17 July should be taken into consideration:
      “The winds at the surface were north or north-easterly, and tended to gradually veer with height, eventually settling on a south-westerly direction from around 23,000 feet, after which they increased in speed with height …”

  5. DUTCH HEADING, GROUND TRACK AND TRUE TRACK

    Literally an aircraft’s heading is the direction that the aircraft’s nose is pointing. It is the true track. But true track is not always the right course. Just as ground track for sailing boats not always leads to sinking on a sandbank. Anyway, in a narrower sense the heading of an aircraft is into the direction of the X-axis:

    http://tinyurl.com/jcprrd2

    Heading (in a general sense)

    EN: heading NL: koershoek (course angle)
    EN: magnetic heading NL: magnetische koers (magnetic course)
    EN: change heading NL: koers/richting veranderen (change of course/direction)
    EN: compass heading NL: kompaskoers (compass course)

    http://tinyurl.com/zj4lk92

    Relationship between course and heading

    The heading will differ from the course depending on (1) the forward speed (speed [not] parallel to the heading) of the vehicle in its medium (air for an aircraft, water for a vessel), (2) drift speed (speed orthogonal to the heading) in its medium (only for vessels, especially for sail boats at close points of sail), and (3) wind speed and wind direction (only for aircraft) or current speed and current direction (only for vessels). In the event of a headwind or tailwind, heading and course in an aircraft are the same. For a ship at sea, if a current is running parallel to the heading, then the course is the same as the heading.

    Koers (richting)

    De koers van een vaartuig of luchtvaartuig is de hoek tussen een noordrichting en de koersrichting. De koersrichting is die van het vlak van kiel en stevens richting het voorschip. Er zijn meerdere noordrichtingen en daarmee meerdere koersen. De koers kan worden afgelezen van een kompas.

    Track (direction)

    The track of a vessel or aircraft is the angle between the north direction and course direction. The course direction is given by the plane of keel and hull towards the bow (true track). There are several directions north and with multiple rates. The course can be read from a compass.

    Ground track and true track

    Grondkoers (GrK) = track, ground track, track angle. It is the direction in which the ship is moving. If the ship is off course, for example by drifting, than it can run on the ground or on sand banks. That’s why they speak of ground track.

    Ware koers (WK) = true track = course direction, the position intended by the board compass and given by the X-axis of the airplane. If there are no disturbances for vessels true track is the way through water. Else true track must be changed to avoid ground track and sink on sandbanks.

    Ware koers en grondkoers

    De ware koers (WK) wordt gegeven door de koersrichting, de stand van het vaartuig. De grondkoers (GrK) is de richting waarheen het schip zich beweegt. De afwijking tussen deze twee wordt drift genoemd. Drift wordt veroorzaakt door stroom en wind. Vooral bij zeilschepen kan de afwijking aanzienlijk zijn. Ook vliegtuigen hebben te maken met koersafwijking ten gevolge van de wind.

    The true track (WK) is given by the course direction, the position of the vessel. The ground track (Grk) is the direction in which the ship is moving. The deviation between these two is called drift. Drift is caused by wind and current. Especially when sailing the error may be significant. Also, aircraft have to do with deviations as a result of the wind.

    [The vessel aims at the desired course direction by its board compass. That is the intended true track visible from the keel line of the vessel towards the bow. But in case of drift the resulting course direction deviates and we say ground track is taking quite a different path.

    http://tinyurl.com/zd7vv6j

    Hence, with drift the true track given by the direction of the X-axis of the plane is still correct but leads to the wrong course. By landing in heavy winds, the course (the true track) must be over corrected and further than the desired course track (the runway), so the X-axis of the plane lands askew with strong side winds. Only if there is no drift then true track (direction of the X-axis of the plane) given by the board compass is in line with the desired course direction. Then true track and ground track are the same.]

    http://tinyurl.com/jp2qol8

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