-  [WT]  [Home] [Manage]

[Return] [Entire Thread] [Last 50 posts] [First 100 posts]
Posting mode: Reply
Name
Email
Subject   (reply to 7005)
Message
Captcha
File
File URL
Embed   Help
Password  (for post and file deletion)
  • Supported file types are: 7Z, GIF, JPG, PDF, PNG, RAR, SWF, ZIP
  • Maximum file size allowed is 5120 KB.
  • Images greater than 300x300 pixels will be thumbnailed.
  • Currently 551 unique user posts. View catalog

  • Blotter updated: 2017-02-04 Show/Hide Show All

Patches and Stickers for sale here



No. 7005 ID: 9bee81
  So, is this stuff bullsit or not? Also is there a way to produce supercavitation effect in the air, so the bullet flies farther and retains more energy?
Expand all images
>> No. 7006 ID: 369bd6
File 142273529111.jpg - (483.08KB , 1400x996 , a0041278_4f315e1e67ff8.jpg )
7006
> So, is this stuff bullsit or not?

Bullshit? Probably not, supercavitating projectiles are not exactly new. RAMICS comes to mind, using a helicopter mounted cannon to fire supercavitiating projectiles to neutralize sea mines. I am a little skeptical on their claims about the terminal effects but I would need to see more information.

>is there a way to produce supercavitation effect in the air
Strictly from the definition of supercavitation...no. Supercavitation is caused by changing a liquids phase to a vapor via pressure changes. This creates the 'cavity' part of cavitation. I think supercavitating torpedoes typically use ejected gas as well.
>> No. 7007 ID: 9bee81
>>7006
>Supercavitation is caused by changing a liquids phase to a vapor via pressure changes.
How about supercavitating air into plasma? :3
Seriously though, what about significantly reducing drag by applying the same ptinciple. Would it work?
>> No. 7008 ID: 052639
Water is a fairly non compressible fluid, air is a gas

>>7006
RAMICS is still in water though
>> No. 7009 ID: 052639
>>7007
>How about supercavitating air into plasma? :3
That's called a reentering MIRV
>> No. 7010 ID: 7188a3
File 142276326254.gif - (42.24KB , 450x349 , flameaerospike.gif )
7010
>>7007
Closest I've ever seen to something like that are the experiments into flame-injection aerospikes. The flame is supposed to reduce flow separation of the spike-induced shockwave and do other stuff that's way too high above above my pay grade for me to understand.
http://www.tfd.chalmers.se/~valeri/Ajax/stAIAA02.pdf

Aerospikes in general are really only feasible for powered bodies since they need a very low angle of attack to work.
>> No. 7011 ID: a6b004
>>7006
>>7008
Air functions differently at supersonic and subsonic speeds. Supersonic air can't be compressed, it functions as a liquid for the purposes of aerodynamics.

Subsonic air, however, can be compressed, as it functions like a gas.

All supersonic aircraft require a way to slow down engine inlet air to subsonic speeds so that it can be compressed, this is normally done with ducts that expand enough after the inlet to cause the air to slow down to subsonic speeds before it hits the first compressor stage.


Now, that's *most* aircraft. Some, namsly the SR-71, are going so fast that a divergent duct alone can't slow the air down enough, so they have rines that create a very precise shock wave. This shock wave, ideally, hits the inlet just outside of the duct, with the inner (radially speaking) area being low-pressure and subsonic, while the outer area is still supersonic.

In effect, it works very much like a supercavitating torpedo, which utilizes a shock wave to produce a low-pressure and thus low-friction area.

Incidentally, one of the three "speed limits" for the SR-71 comes from the fact that the tines cannot keep the shock wave balanced on the inlet above roughly 3.3 Mach. The faster the Sled goes, the narrower that cone gets, and if that shock wave enters the inlet, it will "unstart", which basically kills that engine.

I once read a man's Master's thesis in which he talked for 50-something pages about possible redesigns of the SR-71's inlets, he stated that it would be possible to get the engines to run at roughly 6.6 Mach with variable-geometry inlets and tines. Impressive.

The other two "spped limits", of course, are the heat limits for the turbine inlet, which has to handle thecompressive heating of the air AND the inadditional heat from the flame itself, and the structural limits of the airframe, which has to handle hitting air at thousands of miles an hour. Without melting, peeling, or bending.
>> No. 7013 ID: d7c33f
>>7011
>SR-72 V2.0
>Mach 6.6
I want this to be a thing.
>> No. 7014 ID: d7c33f
>>7013
71*
>> No. 7015 ID: 052639
File 142280710398.jpg - (55.91KB , 500x667 , usns_shepard03.jpg )
7015
>>7011
>SR-71
While air is non compressible at supersonic speeds the speed, simply going supersonic is not enough to create cavitation
Think about it, once you go supersonic and meet non compressible air, you're basically experiencing a medium equivalent to something boats see the moment they start moving in water

The king of shockwaves SR-71 deals with is simple wake that even slow boats deal with, and the kind of shockwave managing shapes on SR-71 are equivalent to wake managing shapes on boats like pic related

Supercavitation means that the speed is so incredibly high in a non compressible medium that it goes beyond what is needed to force compression, and instead of compressing the medium reacts by changing phase and turning into a less dense medium
This reduces friction on the traveling body, improves accuracy and range

Which isn't the case in OP

The only time that can happen in air is in the case of hypersonic (mach 5+) travel, this is why the hypersonic boundary exists
Reentering nuclear warhead, teardrop shaped landing craft, and possibly scramjets can hit the atmosphere at a high enough speed to turn air into far less dense plasma
>> No. 7017 ID: 369bd6
File 142283273596.png - (810.73KB , 2000x1688 , 2000px-Phase_diagram_of_water_svg.png )
7017
>>7008
>>7015
I don't know if you noticed but thought I should clarify, I am pretty sure OP meant that question about supercavitating through the air as a secondary thought not related to his video or initial question. The video is about projectiles intended to supercavitate thought WATER to go further without bleeding off energy as quickly. (which is why I mentioned RAMICS which operates on the same idea) Once again, entering water before it supercavitates.



Phase diagram of water.
>> No. 7018 ID: a6b004
>>7015
I should have clarified, the ONLY part of the SR-71 that has any kind of shockwave cavitation is the engine inlet.

The hypersonic scramjet tests haven't been promising. Laminated composites don't hold up to the forces very well.

>>7013
me too.
>> No. 7019 ID: 052639
>>7017
Oh my bad, yeah undersea bullet cavitation is a thing
http://en.wikipedia.org/wiki/SPP-1_underwater_pistol
http://en.wikipedia.org/wiki/APS_underwater_rifle
>> No. 7020 ID: de0bec
  >>7017
>> No. 7023 ID: fb83e7
>>7015
Supersonic air is quite compressable.
[Return] [Entire Thread] [Last 50 posts] [First 100 posts]


Delete post []
Password  
Report post
Reason