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Ramjet pod functionality and design

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RocketTree

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Adding decorative ramjet engines to a jet style design. I would like to model them to look "realistic".



Jet front-view with two ramjet pods:

1611240976234.png




Would this design act similar to a smaller tube fin?

Ramjet Pod design:

1611241318911.png





What happens when we add an internal compression cone, and force the air around it through the gap? At higher velocities, would it lead to high pressure within the ramjet and possibly self destruct?

Ramjet pod with compression cone:

1611241888621.png

1611241970366.png



Interested to hear some thoughts on this pseudo-ramjet idea...
 

Nytrunner

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What happens when we add an internal compression cone, and force the air around it through the gap? At higher velocities, would it lead to high pressure within the ramjet and possibly self destruct?
If you get to the speed where that would happen, I think it's highly likely your rocket will be experiencing other problems too.

@Wally Ferrer was it you that I modified the ramjet intake files for? May be a fun addition here
 

BABAR

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@K'Tesh and @neil_w are among the OpenRocket masters. I know that simple open tubes beyond a certain width to length ratio stop functioning as tubes and function aerodynamically as closed cylinders. I suspect given the small openings around your central spike these are going to be a real drag.

But a COOL drag!
 

neil_w

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@K'Tesh and @neil_w are among the OpenRocket masters. I know that simple open tubes beyond a certain width to length ratio stop functioning as tubes and function aerodynamically as closed cylinders. I suspect given the small openings around your central spike these are going to be a real drag.
You won't get any proper simulation of this sort of thing in OR. I would tend to agree that these will behave more like tubes with full nose cones, passing very little air through in flight and mainly offering drag.

Hey @Nytrunner, feel like firing up your CFD?
 

Nytrunner

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You won't get any proper simulation of this sort of thing in OR. I would tend to agree that these will behave more like tubes with full nose cones, passing very little air through in flight and mainly offering drag.

Hey @Nytrunner, feel like firing up your CFD?
How big, what speed?
 

neil_w

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How big, what speed?
The OR screenshots in the original post give dimensions (or close enough, anyway). As for speeds, @RocketTree can chime in, but I would be curious to see a few different subsonic speeds, maybe 100, 300, 500 mph?

If that's not enough I would be happy to make more work for you, just ask. :)
 

RocketTree

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Great feedback so far! Here is an update & accurate spec (except weight) OR file for the ramjet I have built. Should I go with an internal compression cone or without?




1611249388357.png


(It shows max diameter 1.85", but that is the internal transition diameter). The outside tube is 2.170"

How big, what speed?
These pods could experience around 300mph on a G80.


1611249457714.png
 

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RocketTree

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On a similar note - if I were to block off the tube completely, would these two tubes act the same during flight? One blocked in front, the other blocked at the rear. I would think the rear blocked tube would experience added stresses from buffeting, while the other would not.
1611250120100.png
 

shockie

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I think you would get a lift/drag functionality over the open ramjets........they would allow air to flow past the intakes, and while the air flow might not compress fully and become supersonic there might be some compressibility effects. I think they would probably essentially act like tube fins.....if you where to place 3 at 120 degree angle on small struts it would probably fly straight. Now of course what would make this design idea even more interesting is if you had engines in each pod......the high subsonic airflow might act as an additive to the thrust .....
 

shockie

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you might get a ramjet effect out of them or at least they will function as ring/tube fins with some slight high subsonic compressibility..... I've attached some articles from 1982 by Chuck Rogers you might find interesting. what I's like to see is those ramjet pods have an engine in them.....now you're talking!
 

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jqavins

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Should I go with an internal compression cone or without?
If you consider the open cross section and figure the diameter of a simple tube with the same area, then compare your to the flow cut-off length for the simple tube, I just bet you've got no flow through this. Which means that internal compression cone would make no difference for all practical purposes.

On a similar note - if I were to block off the tube completely, would these two tubes act the same during flight? One blocked in front, the other blocked at the rear.
I would again bet that it makes no difference for all practical purposes.
 

K'Tesh

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@K'Tesh[/USER] and @neil_w are among the OpenRocket masters. I know that simple open tubes beyond a certain width to length ratio stop functioning as tubes and function aerodynamically as closed cylinders. I suspect given the small openings around your central spike these are going to be a real drag.

But a COOL drag!
Thanks for the shoutout, I appreciate it.

However, my specialty is making things look accurate... I'm only surface level accurate. I don't have any mastery of the math that underlies the sim. But I'd agree with what Neil said, OR probably doesn't have the gumption to do that kind of sim.
 

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MadRocketer

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I know the OP said these are decorative, however, they might as well be useful as well as attractive. If you are looking to have air flow through these babies, scramjet might be the way to go! If you have an air compressor, try blowing air through the tube to see what kind of results you get.
1611269059513.jpeg
1611269059513.jpeg
 

Nytrunner

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At risk of being pedantic, scramjet is for supersonic flow regimes.

At your speeds, you want a ramjet
 

MadRocketer

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Yea, yea. I just wanted to funnel more air down the tube.

I’ll just scram now... 😬
 

RocketTree

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Got the ramjets all finished. They look the same externally as the last pictures I posted, so will leave it at that. I reduced the diameter of the internal cones to allow more air to flow through the tube. So best of both worlds.
 
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MadRocketer

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Got the ramjets all finished. They look the same externally as the last pictures I posted, so will leave it at that. I reduced the diameter of the internal cones to allow more air to flow through the tube. So best of both worlds.
Let us know how it soars!
 

BABAR

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Thanks for the shoutout, I appreciate it.

However, my specialty is making things look accurate... I'm only surface level accurate. I don't have any mastery of the math that underlies the sim. But I'd agree with what Neil said, OR probably doesn't have the gumption to do that kind of sim.
I dunno, I’ve always been impressed by Chuck Norris.....

of course, the rockets I built for NASA were for Earth Day celebration and made out of recycled text books, so it is possible my sub avatar text may be somewhat exaggerated! ;)
 

BABAR

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One word: fuel.
Yup. A ramjet OR a scramjet with no fuel burning is the rocket equivalent of a cylindrical brick. It ain’t a tube fin.
 

BABAR

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I don't car what you say, that is a calk tube with fins.
View attachment 447347
And spiffy paint job and decals!

hmm, if I can make a rocket out of a toilet tank float, a caulk tube (minus caulk) would make a pretty good imitation ramjet rocket......

maybe a Jedi theme, SkyCaulker?
 
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neil_w

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And spiffy paint job and decals!

hmm, if I can make a rocket out of a toilet tank float, a caulk tube (minus caulk) would make a pretty good imitation ramjet rocket......

maybe a Jedi theme, SkyCaulker?
Well if you're going to do it, then do it right:
1611418146109.png
 
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