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  #1  
Old 03-09-2017, 08:51 PM
frognbuff frognbuff is offline
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Default Krushnic Effect Science Fair Project

My daughter needed a science fair project idea, so we opted to explore the Krushnic Effect. An excuse for daddy-daughter rocket time in some ways, but I've also never observed the effect first hand. I'll post some photos of our approach soon.

In the meantime, any first-hand experience out there? How far recessed does the motor have to be? (I could Google, but what fun is that?). I'm guessing something around 1 to 1.5 body diameters.
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  #2  
Old 03-10-2017, 02:20 AM
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mwtoelle mwtoelle is offline
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You need to go more than one body diameter. In 1993, I launched an Estes Hercules (1377) on B6-0/A8-5 combo. The flight was fine until staging, when the booster motor was spat out, but the booster stage remained attached the rocket. The A8-5 burnt out the motor tube of the booster and coasted until the sustainer burnt out. Fortunately, I got the rocket back with only a burnt out motor tube in the booster. I have seen pictures of another Hercules burn out the booster body tube with a longer burning sustainer (either a B or C motor).

If you don't want to burn too many body tubes I would try ST-20 or BT-70 size tubing. This is assuming the use of 18mm motors. BT-55 or BT-60 would work with 13mm motors.
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  #3  
Old 03-10-2017, 08:03 AM
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Jerry Irvine Jerry Irvine is offline
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The Centuri Saturn V was intentionally recessed for stability purposes and the noise was different as well.
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Old 03-10-2017, 11:28 PM
olDave olDave is offline
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Default Use the google

I recommend that you get all the info you can (reasonably) find, and start from there.

No point re-inventing the wheel. Plus, you never know if one of the judges happens to be an old-time, knowledgeable rocket-head. You don't want your project getting DQd for plagiarism.

Instead of "researching" just plain old Krushnik effect, how about demonstrating a baseline configuration (such as, recessed 4 diams deep) and then experimenting with ways to CANCEL the effect? Side inlets of various sizes? Internal diverters or mixing vanes? Asymmetric positioning of nozzle (within a larger diam body tube)? Some original work would be better, and could be of benefit to the rocketry community as well.
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  #5  
Old 03-11-2017, 10:10 PM
frognbuff frognbuff is offline
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So, here are the Krushnic rockets. Generic models. The white one is BT-60, the blue one is BT-80. Rather than build many rockets with motor mounts at varying depths, or engineering a way to move the mount in or out, we opted for a tube coupler at the end so we could add "tail stock" to effectively move the motor further inside the tube.
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  #6  
Old 03-11-2017, 10:14 PM
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Jerry Irvine Jerry Irvine is offline
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Quote:
Originally Posted by frognbuff
So, here are the Krushnic rockets. Generic models. The white one is BT-60, the blue one is BT-80. Rather than build many rockets with motor mounts at varying depths, or engineering a way to move the mount in or out, we opted for a tube coupler at the end so we could add "tail stock" to effectively move the motor further inside the tube.
Good idea. I will publish the report if you want.
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  #7  
Old 03-11-2017, 10:16 PM
frognbuff frognbuff is offline
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The motors are even with the ends of the tube couplers. The add-on tubes are designed to add multiples of the body diameter to the tube length (length = length of the coupler plus the add-on length). The multiples are 0.5x, 0.75x, 1.0x, 1.25x, and 1.5x.

As expected performance started to dive around 1.0x body diameters added. Performance was WAY down at 1.25x diameters. The white one basically flew too low and crashed with the 1.5x diameter addition. The blue one, flying only on C11s, crashed with 1.25x diameters.

My Estes altimeter was really balky. The only serious glitch with the experiment. I expected to crash at some point. Actually, I hoped we could reach the point the models didn't budge, but instead they flew just high enough to crash! Oh well.....
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Old 03-11-2017, 10:17 PM
frognbuff frognbuff is offline
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Quote:
Originally Posted by Jerry Irvine
Good idea. I will publish the report if you want.


Publish it where?
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  #9  
Old 03-12-2017, 01:26 AM
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blackshire blackshire is offline
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Quote:
Originally Posted by olDave
I recommend that you get all the info you can (reasonably) find, and start from there.

No point re-inventing the wheel. Plus, you never know if one of the judges happens to be an old-time, knowledgeable rocket-head. You don't want your project getting DQd for plagiarism.

Instead of "researching" just plain old Krushnik effect, how about demonstrating a baseline configuration (such as, recessed 4 diams deep) and then experimenting with ways to CANCEL the effect? Side inlets of various sizes? Internal diverters or mixing vanes? Asymmetric positioning of nozzle (within a larger diam body tube)? Some original work would be better, and could be of benefit to the rocketry community as well.
I concur--air-augmented rockets (ducted rockets, which are related to ramjets) and gas-dynamic finless stabilization (which utilizes air vented inside the body tube, working in concert with a very forward-mounted motor) are both concepts that represent "extreme"--and useful--solutions to the Krushnic Effect. A project of this type could be used to demonstrate how problems in engineering can, if addressed thoughtfully, actually be turned into advantages.
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  #10  
Old 03-12-2017, 08:59 AM
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Jerry Irvine Jerry Irvine is offline
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Quote:
Originally Posted by frognbuff
Publish it where?
On a permanant website, and if desired in a published report available by mail order. Old school.

http://v-serv.com/usr/kits.htm
Under the heading "Tech"

http://www.v-serv.com/crp/
Probably under monographs
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