I’ve done the Stokes flow calculations and even a 10 micron droplet stays aloft for 12 minutes. I presume an ebola virus can bend since every picture I’ve seen shows that they do indeed bend. I’ll do the vaporization calculation too, but I can guarantee you it’s not fast enough.
I had to wait to answer this, because most of my references are at work. There are quite a few studies on droplets and droplet nuclei generated by coughs and sneezes; the three foot (1 meter) rule for avoiding droplets has been used for a long time now.
My statements regarding the Ebola virus presence in droplets are based on a number of facts. As described in this study (pdf here), the majority of particles emitted during a cough are less than one micrometer. In fact, figure 3 from that paper shows that the majority of particles are 0.74 micrometers and smaller, with the largest peak of the distribution at 0.34 micrometers.
I do not know if Ebola viruses naturally bend, or if they have straight rod-like structures and the bending is an artifact of the process used to prepare the samples for electron microscopy. One of the challenges of doing studies in electron microscopy is that the preparation process is harsh, and the imaging takes place in a vacuum, in which samples are bombarded with an electron beam. I had electron micrographs taken of ciliated cells, in which the cilia were bent every which way and appeared to entangle each other, but cilia in cells normally stand up and wave in unison, like grass in a breeze.
Ebola viruses have a diameter of 80 nm, and a variable length between 970 and 14,000 nm. Clearly, a rigid rod-like virus will not be contained in a sphere that has a diameter less than the length of the rod. But if the virus bends, then the number of viruses that can be contained within a particle is limited by their flexibility; even in the electron micrographs showing bent virus, there is a lot of space in the loops and so forth. Assuming that the virus can be fully compressed for the sake of calculation, then the quantity of virus that could be contained within a sphere of 400 nm (selected for the ease of calculation; the bulk of the cough particles are, in fact, smaller) would be between 55 (based on smallest virus volume) and 4 (based on largest virus volume). The actual number would, of course, be less, since the viruses most likely cannot be compressed without destroying them. In any case, I doubt that an infectious dose can be contained within such a small particle.
Another consideration is that the viruses are environmentally unstable. Changes in temperature, hydration, and pH, as well as exposure to UV or various oxidants or enzymes in the environment, will destroy them. The only thing protecting them is the material making up the droplet--and since it evaporates rapidly, changing salt, pH, and so forth--the particles are not very friendly to virus.
A third consideration is that the viruses must be present in respiratory secretions in order to be able to exit via a respiratory route. Although Ebola can enter the body through contact with mucous membranes of the respiratory system, it does not infect those cells. It infects certain blood cells and the connective tissues of organs. Since it does not infect respiratory cells, those cells do not secrete it into the mucous. Thus, in order for Ebola virus to be present in mucous, the mucous must be contaminated with blood.
I've seen coughing described as a late symptom of Ebola--meaning that it occurs when the patient is highly infectious. Yet airborne transmission of Ebola has never been documented. The Ebola treatment centers are not high-containment facilities--often, they are just tents, open to the surroundings. In pictures, you can see Ebola patients sitting outside. Family members can go within a few yards of Ebola patients, within aerosol (but not droplet) range. Many instances have been documented where people living in the same house as an Ebola patient remained healthy, if they were not directly involved in patient care.