Hi patrix, glad you enjoyed this.patrix wrote: ↑Fri Dec 06, 2019 11:18 amLooking forward to that heniek and great post. It’s amazing how many people that when asked what will happen if you stand inside a vacuum chamber and releases a balloon, believes the balloon will fly away.In my next post I will share some ideas of potential test that I think could be done in a garage.
I was raised on a booked titled "Transport Phenomena" by Bird,Stewart and Lightfoot. In the case of "what is going on in vacuum" I can't quite throw everything out of the bathtub WITHOUT having done some testing/experimenting. Thought experiments are good but physical experiments are even better.
1) In the case of the water jet pack that was suggested by Simon
I see one way to do a test to see if the water surface/ground is needed to support the flyer. Have the flyer fly over a surface discontinuity, a water fall or a deep ditch where the water surface suddenly disappears . Then see what happens to the flyer when he finds himself over this. We have two possibilities not much or drops lower down toward the new horizontal surface.
Alternately we (where I am it is freezing) can take a garden hose and start the water at such a rate that if we hold the hose some distance from the water spray we will have the same situation as the water jet pack.
Water jet keeps the end at a constant height.
I have played this game in my younger days, a sort of "walk the dog" trick. Now do this except now over something that is around the house that rapidly goes below the ground level. Where I am we have small windows to the basement below the ground surface level and there is an opening area made of concrete (oil drum would also do the trick). Hence we could walk this "water dog" first on the ground then move the hose so as to locate it over the opening. If the flow rate is constant we should see one of two possibilities, nothing happens or it drops lower :-)
2) Rockets in Open Space. I am in the camp that what I know I know it because I have been told so. We on Earth (the little people) have no contact with this environment. Everything I have learned has been related to things working in our atmosphere. Did something go into Deep deep Space? I have no clue. I was told it did and that is it. Faith Baby Faith.
The experiments with rockets in vacuum on YT are BS. It looks nice but it misses on one fundamental aspect, Scaling Law. If you want to see how and actual rocket (potentially) will work in Open Space you need to scale everything such that the experimental environment will scale-wise come close to (I'm going to get hit here) Open Space. What I would do,
1) Make a tiny rocket
2) Lay it within a glass tube (little friction) with jet sticking out just outside of this tube.
3) Place this inside of a tank the size XXX. XXX would need to be calculated based on rocket size, jet/plume size, etc. so that boundary problems in the first ms of firing would not be an issue. This is where Scaling Law would come into play.
4 Evacuate to ... well as best a vacuum as you can get.
5) High speed cameras
6) Ignite it and observe the first ms of the burn. The rocket has one degree of freedom.
Moving or Not Moving?
3) Now a few words about the discontinuity air-vacuum. I will refer again to this article,
https://vacaero.com/information-resourc ... heory.html
This is not a trivial situation as some people in the Internet would like us to believe. Hell, just reading this should give anyone familiar with thermodynamics, fluid dynamic, mechanics and space communication a pause and a thought "will what I know work there?". Many without blinking say YES they believe that between 1960 and 1969 all issues with traveling to the Moon and back were figured out??? Wow, that is a lot to swallow. I don't buy it.
Now for an experiment. Back again to our water hose. Get a large oil drum and fill it with water. Set a table like surface next to the drum so that water level and the table surface are the same. Now get that hose and do as I said above, "walk the dog". Make sure the "dog" maintains a constant height for the given flow rate. Now walk it from the table to be above the water and then slowly push it toward water surface. What happens?
As I recall the "dog" will get sucked underwater. Like I said I can not do this experiment today but I recall doing this when filling a bucket. I recall always feeling a distinct pulling sensation when doing this. Hence, when in the air the thrust is enough to keep the "dog" at constant height but when contacting water the forces change. I would have to do this again as my memory could be wrong on this. But the experiment would be a good one to see if surface comes into play in the dynamics of the water jet.
Behavior at a "discontinuity" is often very abrupt. That's how ships disappear off the surface of the oceans. How abrupt is this when you are dealing with air-vacuum????