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  #11  
Old 03-12-2017, 10:42 AM
frognbuff frognbuff 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.


Sadly, neither of us has that level of interest in the topic. Sounds like you do, however! Go for it and add to this thread. Research has been done on the duct sizing - Blackshire has the reports if you want them. No "rocket head" judges to worry about - this is a small scale event.

Recessed motors, ducted motors, etc, in my experience, result in short-lived rockets due to scorching. Yes, you can add a certain amount of thermal protection, but you still get bubbled paint and burn damage. I did a finless rocket that was destroyed (burned through) after just three flights. A true ducted rocket fared much better.
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  #12  
Old 03-12-2017, 11:15 AM
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blackshire blackshire is offline
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Quote:
Originally Posted by frognbuff
Sadly, neither of us has that level of interest in the topic. Sounds like you do, however! Go for it and add to this thread. Research has been done on the duct sizing - Blackshire has the reports if you want them. No "rocket head" judges to worry about - this is a small scale event.

Recessed motors, ducted motors, etc, in my experience, result in short-lived rockets due to scorching. Yes, you can add a certain amount of thermal protection, but you still get bubbled paint and burn damage. I did a finless rocket that was destroyed (burned through) after just three flights. A true ducted rocket fared much better.
Although it is a "specialty niché" in model rocketry, the ducted rocket is interesting and can produce a scale-realistic wide smoke trail, as well as generate greater thrust due to the air augmentation. There are--and have been--several air-augmented rocket (and integrated rocket-ramjet) missiles and target vehicles which would make attractive flying scale models, and they could utilize the ducted rocket principle. Three of them are:

[1] The MBDA Meteor air-to-air missile (see: www.google.com/#q=meteor+ramjet+missile&* );

[2] The Orbital Sciences Corporation (OSC) GQM-163A Coyote supersonic target (see: http://www.google.com/#q=gqm-163a+c...rget+vehicles&* ), and:

[3] The LTV ALVRJ (Advanced Low-Volume Ramjet [sometimes called Air-Launched Low-Volume Ramjet]), see: www.google.com/#q=Vought+ALVRJ&*

I hope this material will be helpful.
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Last edited by blackshire : 03-12-2017 at 08:24 PM.
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  #13  
Old 03-12-2017, 02:25 PM
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rocketguy101 rocketguy101 is offline
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There was an article in the Nov 1969 issue of Model Rocketry magazine about this...those old MRm contained a lot of useful technical articles!!!
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  #14  
Old 03-12-2017, 07:55 PM
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Jerry Irvine Jerry Irvine is offline
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Not a believer in ducted rockets below 18" ID. The effect of putting the motor inside the bottom (or top on retro boost) has observable effects with minimal damage (Centuri Saturn V and this project's coupler concept).
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  #15  
Old 03-12-2017, 11:02 PM
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Jerry Irvine Jerry Irvine is offline
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Quote:
Originally Posted by rocketguy101
There was an article in the Nov 1969 issue of Model Rocketry magazine about this...those old MRm contained a lot of useful technical articles!!!
Ad for RDC E!

11-69 Damon Engineering precursor.

Absolute altitude record.

Krushnnik P 37+
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