Finless Vent-channel Design?

Has anyone tried this? Its an idea that I have for a finless rocket, where there are intake vents under the nosecone which lead to channels through the body tube, allowing the air to exit around the motor housing?

Imagine a “Tube Fin” rocket wherin the fin tubes were the same length as the main airframe.
I do not think it would be stable and what you are describing sounds essentially the same.

A novel idea to be sure but I'm not gonna give it a vote of confidence. That said, I'm only imagining what your doing--plans/drawing would be helpful. You'll still have to deal with the same cp/cg challenges of any other rocket. There are other challenges as well--low speed/launch--you have no exterior fins for dynamic control--AOA would be a huge concern as well--intakes being blocked by airflow/turbulence. One other thing to think about, turn the design inside out, you may find that the design has pushed the cp WAY forward---that sorta oversimplifies the challenge , but you get the point. If your just trying to build one without fins the best bet is a light rocket with a ton of nose weight and a honking big fast burner in the rear, even then you gotta play with it and you can't launch in wind--any wind! As is always the case, everything we do is a trade off. It would be a cool build though and I'd like to see you try it, it might work, I'm no rocket scientist for sure. Hell, I figure I'm more lucky than good with my stuff anyway----H

A friend tried something like that, his idea being to put the fins on the inside of the tube. No it didn't work, the Cg is still right at the front, and it skywrote 10' off the pad.


Richard

MAD said:

Has anyone tried this? Its an idea that I have for a finless rocket, where there are intake vents under the nosecone which lead to channels through the body tube, allowing the air to exit around the motor housing?

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Before everyone blows your imagination candle out, consider showing a drawing of sorts. Using vents in the proper place could act as a replacement for tube fins IMHO. I ain't skeert to try something. At least if it works, all of those that said it wouldn't fly will be eating their words.

MAD said:

Has anyone tried this? Its an idea that I have for a finless rocket, where there are intake vents under the nosecone which lead to channels through the body tube, allowing the air to exit around the motor housing?

Click to expand...

Though my mind could think I still was a mad man
I hear the voices when I'm dreamin', I can hear them say

Carry on, my wayward son....or in other words..go for it.
I have a few wacked out ideas Ive glued together and gave it a shot..or at the least ,a swing test.






Read more: Kansas - Carry On Wayward Son Lyrics | MetroLyrics

MAD said:

Has anyone tried this? Its an idea that I have for a finless rocket, where there are intake vents under the nosecone which lead to channels through the body tube, allowing the air to exit around the motor housing?

Click to expand...

I say go for it!

I did my 'finless' rocket a while back - spin stabilized. While I wouldn't want to use it for manned flights, I had a lot of fun building and testing it.

Innovate and have fun!

Krusty

Alright, this is what I had in mind. The engine's thrust being used like a jet-pump to start airflow across the channels. The green areas are the vents in the rockets BT. Blue is the airflow, red is the thrust. the circle with the cross is a view of the rocket from the bottom, with the vertical MMT supports shown in black. The channels are closed off from the rest of the inside of the body tube, so the ejection charge will not leak through them.

Is it possible to sim this in open rocket?
(And if this isnt viable I can always put a gyro in the payload bay)

MAD said:

Alright, this is what I had in mind. The engine's thrust being used like a jet-pump to start airflow across the channels. The green areas are the vents in the rockets BT. Blue is the airflow, red is the thrust. the circle with the cross is a view of the rocket from the bottom, with the vertical MMT supports shown in black. The channels are closed off from the rest of the inside of the body tube, so the ejection charge will not leak through them.

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I wouldn't say no at this point, because I don't know. I would, on the other hand, say that external vent chambers could work.

MAD said:

Alright, this is what I had in mind. The engine's thrust being used like a jet-pump to start airflow across the channels. The green areas are the vents in the rockets BT. Blue is the airflow, red is the thrust. the circle with the cross is a view of the rocket from the bottom, with the vertical MMT supports shown in black. The channels are closed off from the rest of the inside of the body tube, so the ejection charge will not leak through them.

Is it possible to sim this in open rocket?
(And if this isnt viable I can always put a gyro in the payload bay)

View attachment 142963

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If you extend the 'ring' portion down below the exit point of the motor, you may create more of a venturi effect and 'suck' air through the side vents.

I think it's a neat design External launch lug or tube launch??

Krusty

I have extra rocket parts. Ill just make a mock-up, tie a string to it, and spin around in circles and see what happens. *shrug*

MAD said:

I have extra rocket parts. Ill just make a mock-up, tie a string to it, and spin around in circles and see what happens. *shrug*

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Sounds like Science to me... Rocket Science!

Krusty

There was a big conical rocket with vents on the side. However, I think this was to avoid the Krushnik effect, a problem of the motor recessed up in a tube, allowing the motor to be further forward, closer to the CG purposes. I doubt any additional stability from the vents themselves was relied upon. The stability increase is allowing the cone to still be there, the vents were only near the CP.

With finless, aerodynamic forces are weaker relative to the size (dia.) of the rocket, but if it is lightweight compared to the size also, the aero forces can be good relative to the weight. That is one reason why launching needs to hit a certain speed, so that aerodynamic forces become significant compared to other forces such as thrust. And finless and other unusual designs can be better in wind due to reduced CP shift at an angle of attack. Usually high drag though.

Just remembered, there's a paper by a high school kid back in the '50s-60s on conical rear ejection rockets. He found the drag coefficient lower than normal rockets, and an attempt to vent air through the internals resulted in increased drag, though could probably be improved.

This is a cool idea. Without throwing around much theory, look into some papers on inlet duct designs, esp the 'naca' duct which creates a low pressure area and uses existing (however transitory-our birds are in and out of laminar flow rather quickly-if ever) boundary layer pressure to assist in the 'ram air' principle indirectly. Think 'hood/brake scoops' in the glory days of muscle cars or Nascar. Ancillary to this may be the ring fin design problems approaching mach. Whole lotta stuff going on in the air column there-esp. shock wave reverberation and subsonic exit chaos showing as base drag. It would be hard (for me at least) to calculate what stability that may add. Too late (or early for some of you) to think/type rationally. Best of luck in your endeavours!

Heads up flight?

cwbullet said:

Heads up flight?

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:lol:

This is like the old Estes Little Augie design except without the fins. It is probably not stable.

aerostadt said:

This is like the old Estes Little Augie design except without the fins. It is probably not stable.

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Was that a typo? Shouldn't that have been "Little Auger" ???

Now that I can actually look at it, its not really "finless" at all. look at the motor mount, supports. they run the entire length of the motor housing, so this thing is more or less "Recessed Internal fins", similar to a torpedo etc...

I'm gonna build it, and if it fails stability tests I will just mount some external fins. Win-Win either way

I say go for it. Post a build thread and flight videos please.

I would say no this would not work. The purpose of fins is to generate correction force due to airflow. The moment your angle of attack changes, the airflow will start to be restricted by the "reduction" of the duct inlet area versus airflow direction. This would reduce the correcting force which is the opposite affect you would want. Also, instead of venting straight out the bottom, I think you would need to vent out the side to try to create a correcting force to push the rocket back.

falingtrea said:

I think you would need to vent out the side to try to create a correcting force to push the rocket back.

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Hmmmm, that gives me another idea =)

This is the principal used in ducted cone rockets (see: https://www.rocketryforumarchive.com/showthread.php?t=7016). Many of these of all shapes and sizes have been done over the years. There was a nice design article done in Extreme Rocketry IIRC about a dozen years ago that went through the aerodynamic principles and parameters.

I suspect the ducted cone rocket in the link would be stable without the ducts (tape them over). It is essentially a cone which has very nice stability properties. My suspicion is the original idea in this thread would not be stable at all since there would be no restorative force. All the forces (from the motor and the ducts) are pointed straight backwards and the vacuum force of the ducts is evenly distributed around the circumference.

dixontj93060 said:

This is the principal used in ducted cone rockets (see: https://www.rocketryforumarchive.com/showthread.php?t=7016). Many of these of all shapes and sizes have been done over the years. There was a nice design article done in Extreme Rocketry IIRC about a dozen years ago that went through the aerodynamic principles and parameters.

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MAD said:

Alright, this is what I had in mind. The engine's thrust being used like a jet-pump to start airflow across the channels. The green areas are the vents in the rockets BT. Blue is the airflow, red is the thrust. the circle with the cross is a view of the rocket from the bottom, with the vertical MMT supports shown in black. The channels are closed off from the rest of the inside of the body tube, so the ejection charge will not leak through them.

Is it possible to sim this in open rocket?
(And if this isnt viable I can always put a gyro in the payload bay)

View attachment 142963

Click to expand...

If I am interpreting your picture right, this could also be considered a ring fin located just below a transition. The ring fin is the same diameter as the "main" body tube above it, but larger than the diameter of the lower body tube. You also indeed have four "internal fins" as pictured attaching the outer ring to the smaller lower body tube.

I believe this COULD work depending on the size of the "gap" between the the forward edge of the transition and the forward edge of what I am calling the ring fin. In other words, if the airflow around the upper larger body tube remains laminar enough to hug the transition you may have enough flow over the ring and internal fins to make them effective in shift your CP backwards. As a bonus, in Lil' Augie style, you can actually shorten your lower body tube and recess your motor mount forward which will move your CG FORWARD. The position within your vent chamber should prevent the Krushnik effect. I do NOT know if the jet effect of the engine blast really helps with the the airflow effectiveness.

Again, the effectiveness will depend on airflow. The wider the gap and the longer the transition segment, the more likely you will have enough flow to "effectuate" the ring and internal fins. Of course, the wider the gap and the longer the transition the less "unique" the rocket looks.

As mentioned, I THINK this could work. May not simulate well on any of the available programs. Swing test and first flight test as a heads up flight with as few spectators as possible recommended for obvious safety concerns.

The more I think about it the less viable it "feels". Think about this:

Grab a rocket with no fins by the BT just under the nosecone, and swing it around sideways. It will cut right through the air.
Grab a rocket with traditional fins in the same manner, and the sideways air action on the fins will make the rocket try to right itself.

This design would fall somewhere in between. Yes you would have some effect on the internal fins via the vents, but the "ring" fin would shield the rest of the internal fins and lessen thier effect. If the ring fin was box shaped (Similar to the Fat-Man and Little-Boy weapons from WWII) then MAYBIE...

BABAR said:

If I am interpreting your picture right, this could also be considered a ring fin located just below a transition. The ring fin is the same diameter as the "main" body tube above it, but larger than the diameter of the lower body tube. You also indeed have four "internal fins" as pictured attaching the outer ring to the smaller lower body tube.

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I agree; as long as the gap between the larger upper tube and the ring fin is large enough, it should be fine.

BABAR said:

Of course, the wider the gap and the longer the transition the less "unique" the rocket looks.

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Also true, but even if you lost some of the unique look, you would still have the ability to launch it out of a tube.

Check out the design of the "Flyin' Stovepipe", Estes Rocket Plan #56, 1968. Similar to what you're describing.

sooner.boomer said:

Check out the design of the "Flyin' Stovepipe", Estes Rocket Plan #56, 1968. Similar to what you're describing.

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What? Nah! The Flyin' Stovepipe is more like an offbeat version of the Sprite. MAD's rocket is the same size up & down.