View Full Version : zero g's flight,how is it done?
giorgino
5th Mar 2007, 21:06
Hi guys
I've seen a very intresting footage in Euronews not very long ago of an
Airbus that its interior was converted to a surgery for an inflight
experiment.
The purpose was to fly in zero g's condition and at the same time a group
of doctors would operate a volunteer with a hand trauma,which they did.
The purpose behind that was to check if an operation in space shuttles
would be possible.
It was pretty amazing to see that everything inside the aircraft was
floating but what really impresses me and I don't have a clue how it's
done is what the pilots did in order to have zero g's.
The footage showed for a very short period of time a view of the aircraft
flying,where it appeared flying in an extreme high nose up attitude.
If this is how it's done I'm still wondering how they achieved to fly like
that for the duration of the whole operation(which even if I can't
remember the exact duration it couldn't be less than 10 min?)
Any ideas?
Happy ldgs
BackPacker
5th Mar 2007, 21:41
In essence very simple. You dive to gain as much speed as possible. Pull up sharply into a very nose-high attitude and then let the aircraft describe a ballistic arc (zero g) until you are back to a very nose-low attitude again. At the top of the arc your airspeed will be almost zero if you timed it well (and that's no problem since you can't stall with zero g), and at the 2nd half of the arc your airspeed builds up again. At the end of the ballistic arc you pull up sharply again and repeat the whole process.
Obviously the characteristics of the flight depend on the exact airplane involved, but a flight would, I guess, typically be 30 seconds of zero g followed by 30 seconds of two g. Very sickening. I think NASA calls the airplane with which they do this the vomit comet.
What I remember from reading about that surgery is that the actual cutting was done during the periods of zero g, then they had to down their tools for the two g period, and so on. Ad nauseum (literally, probably).
A neat trick I heard from an aerobatics pilot was the following. To maintain zero g, he would just put his pencil in the air and chase that as if it were his artificial horizon.
ahramin
5th Mar 2007, 21:42
Mods??? Is this the right forum?
The "Vomit Comets" in the US average just over a minute of zero G time. No way to stretch this by 10 times.
This works by flying a parabolic arc. The aircraft pitches up to a high nose up angle then slowly pushes over in a ballistic arc. The zero G starts when the aircraft first pushed over and continues as long as the aircraft continues to push over. Obviously this cannot continue for very long. Once the aircraft is in a steep dive the plane must be pulled up again, and the Gs will be more than one.
If you wanted 10 minutes of zero G time you would have to do this ten times.
llondel
5th Mar 2007, 21:42
The aircraft is flying a parabolic path. Go and look up the "vomit comet" for more information.
nimbostratus
6th Mar 2007, 07:28
:ugh: It's not 'zero G'.
You will still be subject to the same 'G' as you would if you were outside the aircraft.
giorgino
6th Mar 2007, 09:53
Thanx backpacker for your detailed answer:ok: :ok: ,and the rest of you!!
Hey nimbostratus sorry for not having your level of knowledge:ugh: :ugh:
A neat trick I heard from an aerobatics pilot was the following. To maintain zero g, he would just put his pencil in the air and chase that as if it were his artificial horizon.
:eek:
Followed no doubt by a very short period of intense g after he falls out of the sky with a pencil lodged in the control lines!
(I know it could depend on the aircraft but I just remember it being imprinted on my brain that nothing is loose when doing aeros!).
Gargleblaster
6th Mar 2007, 12:29
This is a must-see, IMHO one of the funniest aviation videos ever: http://www.youtube.com/watch?v=CtnXWwzn368
Wizofoz
6th Mar 2007, 12:59
It's not 'zero G'.
You will still be subject to the same 'G' as you would if you were outside the aircraft.
Yes, it is and no, you won't.
Because you are in an aircraft with engines and flight controls you are able to control the arc so that your vertical acceleration is exactley that of gravity. Similarly you can use power to match drag so that your lateral acceleration is also zero.
In freefall (e.g skydiving) you are always under positive G (less than one initially, but 1G once you reach terminal velociy),because you are creating drag in the vertical axis (which is therefore a form of lift), but in the aircaft you are able to put the wing at an angle of attack that is exactley zero G.
Think of it this way, push any harder and you will be under negative G, don't push at all and you be under 1G, so somewhere in the middle must be- 0G.
nimbostratus
6th Mar 2007, 16:21
What you are experiencing is apparent weightlessness. This is similar to that which you would experience if you were dropped out of a plane in a container. Ok, I accept that in a free-fall situation there would be drag on the container to consider, and this will affect the rate if acceleration and terminal velocity, but surely you are not actually experiencing a situation where there is no gravitational effect? I'm not a physicist, just a pilot, but although I do sometimes become weightless, I never thought that this was due to a lack of gravity. :confused:
Wizofoz
6th Mar 2007, 17:35
Nimbo,
We are getting into semantics (and relativitey!!) a little here, but there is no such thing as "Apparent" weightlessness. You are either under one G or you aren't, and wherever you are in the universe, it is because of the sum of all forces acting on you at the time.
If you are subject to acceleration due to gravity, and an equal acceleration due to being in a plumenting aircraft, your net acceleration (in relation to the aircraft which is your current local environment) is zero.
Astronaughts experience zero G for exactley the same reason. They are in a parabolic trajectory, it just happens to have a radius bigger than the earth. Whether their weightlessness is "Apparent" or not is irrelevent. It has exactley the same effects on them as if they were in intersteller space (including relativistic effects such as time itself running faster!).
sir.pratt
6th Mar 2007, 18:05
Followed no doubt by a very short period of intense g after he falls out of the sky with a pencil lodged in the control lines!
(I know it could depend on the aircraft but I just remember it being imprinted on my brain that nothing is loose when doing aeros!).
#shivers# loose objects in the cockpit.....
Zero G isn't a "lack of gravity". You'll always be in gravity.
Zero G is a lack of acceleration in your frame of reference. As your bodily frame of reference is the aircraft, nz=0 is indeed zero G.
PieterPan
6th Mar 2007, 18:28
As a student of an Aerospace university we have the opportunity to fly (as passengers) in the university's Cessna Citation 550 (PH-LAB) to experience the motions that are characteristics of the airplane. Phugoid, short period, dutch roll, spiral dive and aperiodic roll. Once the educational part was over we were treated to a 10-15 sec (seemed like forever) of parabolic flight (0 g). I took some pictures (http://pieter.panman.eu/index.php?q=image/tid/9&page=2) of floating pencils etc.
Surely an awesome experience. All 6 students were able to hold their breakfast :)
Stop using "G", it's "g"...........and if you don't know the difference you need to get your Physics notes out again.....
edited to add - sorry for the rant -night out of bed..however for those not in the know "G" is the recognised symbol for the Universal Gravitational Constant and should never ever be confused with "g" , which is used ( usually) as the symbol for acceleration due to gravity.
Clarence Oveur
7th Mar 2007, 10:24
For an answer to your question giorgino, have a look at the ESA A300 Zero-G (http://www.spaceflight.esa.int/users/index.cfm?act=default.page&level=11&page=1048) and ESA parabolic flight users guide (http://www.spaceflight.esa.int/users/downloads/userguides/chapter_4_parabolic_flights.pdf).
giorgino
8th Mar 2007, 12:11
Clarence Oveur this is a great site,thanx:ok: :ok: :ok: :ok:
The 0g segment doesn't last for long, others above describe it as between 30 and 60 seconds. So when you see video of the weightless conditions inside (the film Apollo 13 for example was shot inside the NASA 0g aircraft) it is only for short segments, the film makers then cut them together to make it look like longer.
It's similar to all those photographs of effortless relative (formation) work by skydivers, they always are shot at about 6,000 feet. Jump from the plane at 12,000 feet, it takes half the descent to get into position, the cameraman has just a few seconds to get their shot, then it's all break apart again to deploy canopies. But all you are shown is those few stable seconds.
Wizofoz
8th Mar 2007, 17:55
WHBM,
A bit of a general statement there regarding skydiving. A good 16 way team will come out of a large aircraft (sat a Twin Otter) already gripping (i.e already in a formation) and begin turning points immediatley.
The current record for an 8 way team is 32 formations in 60 seconds.
Larger formations do take longer to build, but I've been in a 32 way that exited at 14 000' and was complete by 10 000'.
Wizz :
Yes it was a generalisation but just to get the point over. Good to hear you are better than my shambles out of a Turbolet. At our club we tried 4-ways out of the C206 from 8,000 ft and we really just didn't have the time to come together. It's a bit difficult operating out of a farm strip in a 206 with no external handholds !