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Aerodynamics of Russian R-77 guided missile....

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Patrick

Thu May 05 2011, 05:36AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ive been reserching John Boyd, missile control, rockets, and air to air weapons. Toward that end I have found the Russian R-77, which is roughly used as we Americans would use the AIM120 missile.

wiki, for background.

My question is in reguards to the "mesh" fins on the back of this missile. How are they moved to control the weapon in flight? are they rotated about a shaft independently or are they folded back to adjust drag? are they also generating a vortex behind each fin, at mach flight?

On a related note, suppossedly a seperation of supersonic flow, is not a problem with this design. as it would be with a normal flat fin. This corporation also claims that it takes less force on the motors to acheive the same turn rate then a traditional fin!

Any physics people out there who can explain this?

The Russians are so clever sometimes it scares the hell out of me.

See the back of the missile? Ive also seen the same type of fins on the MOAB. Still researching that one though.

EDIT: Ive just been told there called "Grid Fins", my google'ing will be easier now that i know what there called!

I think this source was what I needed to see before posting here. But didnt know what they were called before posting here.

TY

tarakan2

Fri May 06 2011, 06:06AM

Registered Member #3859 Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179

Interesting. I am Russian and I never thought about that before.
I am college student so my thought is not worth anything but what if those grids direct the currents of air that pass around the fins?
At supersonic speeds air shows its viscosity.

So grids work the way ailerons work on an airplane. At supersonic speeds, the vortex behind the wing will call for a very heavy aileron and maybe the aileron control couldn't be fitted into this missile in that specific place.
Very likely it takes smaller servos to turn the grids than to pivot the ailerons.

Also ailerons tend to vibrate as the air on the edge of the wing forms vortexes. Here those vortexes get "polarized" like the air in the wind tunnel, by passing through a grid so vortexes are suppressed.

If non of that is right than say thanks to American education system because I live in States.

tarakan2

Fri May 06 2011, 06:09AM

Registered Member #3859 Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179

What if they cool of the jet engine or some fluid in the system of the rocket.
Those run on solid fuel?
What if all of the above?

Patrick

Fri May 06 2011, 07:03AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

tarakan2 wrote ...

At supersonic speeds air shows its viscosity.

So grids work the way ailerons work on an airplane. At supersonic speeds, the vortex behind the wing will call for a very heavy aileron and maybe the aileron control couldn't be fitted into this missile in that specific place.
Very likely it takes smaller servos to turn the grids than to pivot the ailerons.

From my further research after making this post, I believe what I have qouted from you is accurate.

tarakan2

Fri May 06 2011, 03:24PM

Registered Member #3859 Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179

Thanks.
I wouldn't be surprised that there are several reasons for those grids to appear on the rocket.
Notice how they are in line with the stationary fins.

klugesmith

Fri May 06 2011, 04:46PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

The bit about flow separation (and clever new ideas, and force reduction)
reminds me of something I saw for the first time about 4 weeks ago.

Shovels full of holes, for digging very wet dirt and mud.
Normally a heavy chunk of mud sticks to the shovel after each stroke,
and is hard to shake off.
It slides right off the new shovel, whose holes break the suction.

ref:

James

Fri May 06 2011, 05:30PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Hey now that's clever! It ought to make the shovel quite a bit lighter too.

Now if only they could figure out something better for digging in rocky soil. Shovels are practically useless around here.

klugesmith

Fri May 06 2011, 06:39PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

James wrote ...
Now if only they could figure out something better for digging in rocky soil. Shovels are practically useless around here.

We are getting pretty far from guided missile aerodynamics,
but have you worked with a straight steel digging bar?
Commonly one end is widened to a chisel form, and the other is either a blunt tamper or a point
(like a rocket nosecone, now we are OK for this thread).

Also handy for moving large rocks:

Patrick

Fri May 06 2011, 06:49PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

tarakan2 wrote ...

What if they cool of the jet engine or some fluid in the system of the rocket.
Those run on solid fuel?

Yes on the solid fuel.

No on the cooling comment, at 1500mph I doubt they'ed cool anything, also there meant to fold up along the body when not in flight. This would mean high thermal resisitance. The grids appear to be high temp nickel-chromium stainless steel-(from a source)

hboy007

Fri May 06 2011, 08:03PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374

interesting topic. Can anyone imagine this turbulent flow

being blown through an array of horizontal blades? If they are meant to eradicate the curl of the turbulent flow behind the guide fins, I wonder where the advantage lies, especially when adding the massive exhaust jet to the picture (or are they significant once the fuel is burnt up?)

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