Some Mechanical and Structural Aspects of the Smolensk Crash By Dr. Gregory Szuladzinski, Ph.D., MSME
SCND2014GS
Appendix I. Collision of the Wing with a Tree (birch)
The issue has somewhat wider aspect than was previously considered. Namely, the results of such collisions depends inter alia on the impact speed. If the speed is high, say 100 m/s or more, the wing would cut trees and other objects stronger than wood. If the speed is low, say 10 m/s, the wing will probably be broken by a tree. If the case is still of interest, it can be resolved quite accurately, using the Finite Element Method, as described below.
Dr. Wieslaw Binienda Comments:
Since the time Dr. Szuladzinski published his first report, new important findings have been obtained. Dr. Szuladzinski himself built his own wing model of Tu154M and conducted several simulations. His results confirmed my results that the wing cuts through the birch tree under the conditions described in the official reports. His simulations also show that the wing with the same speed of 75m/s cuts through even medium size steel poles. It is important to know that steel is 3 times stronger than aluminum while a birch tree is 30 times weaker than aluminum. Also, the speed is the essential factor in assessing the ability of any aluminum structure to cut through other material. Dr. Cieszewski investigated available photographs of the birch tree, studied the sample from the tree to determine material characteristic of this particular birch tree, and investigated satellite images made between January and April 2010. He concluded that the physiology of the birch tree and satellite images of the tree crown show that the birch was broken at least five days before the Smolensk Crash. Finally, experts Jorgenson and Kowaleczko independently have shown through aerodynamic analysis that Tu154M had to fly above the birch tree in order to fall into the location of the crash site. Hence, all of the above work as well as parallel investigation of the fragmentation of the airplane on the crash site and the analysis of the debris prove that the airplane had no contact with the birch tree and crashed due to the explosions in the wing and fuselage at a low altitude. Accordingly, all independent scientist analysing the birch tree scenario from various fields of expertise, come to the same conclusion that the birch tree could not cut a fragment of the left wing of Tu-154M on April 10, 2010.
- Dr. Wieslaw Binienda, Ph.D., F.ASCE, March 25, 2014
The most important aspect of an aircraft wing colliding with a tree is a local phenomenon, namely, which of these two objects causes more damage to the other in the vicinity of the collision. It is therefore sufficient to build a small FEA model with a relatively short segment of the wing and a tree. Such a model should be inexpensive to prepare and execute, in terms of time needed for the task. In subsequent repeats of simulation, one must also reduce the impact speed, until a certain critical speed is reached when the wing is weaker than the tree.
There is also something more important about such a collision. A typical "cross" collision of two slender objects end up breaking or shearing only one of them. There is a very little chance that the two objects become broken. This means that if the tree was cut, the wing survived (with superficial damage) and vice versa. This should close the discussion on the possible role of the birch in this case.
Even if the MAK is right and contrary to recent research there was contact between the birch and the wing, neither the change of course was not noticeable, nor wing did not suffer much, so the role of the birch should be completely removed from consideration.
Despite a protracted discussion about which was stronger, the birch or the wing, no one has done a simple calculation based on the nominal static strength. Both for the birch and the wing the strength is the product of the effective cross section and the shear strength of the material.
The analysis should begin at this point, before using advanced methods. The difference in strength of these two elements may be so large that the dynamic approach may prove unnecessary. It should be noted that the velocity makes the cross section of the wing stronger.
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