The Finless Rocket Flies Again

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To wake up this thread...and to answer Daddyisabars "where are the rocket scientists", look at the article in Apogee components peak of flight newsletter number 379.
I am a total novice, and it looks to me that to get finless rockets mainstream, you need rule changes!
At the very least you could have an experimental category like you have with small aircraft. Doing that could then give you the ability to fly weird ****, but only off far away launch pads, on low attendance days, or nutters only days at the club, with obligatory sheets of Lexan!
 
When I was a kid I built this Superman model. When I grew tired of it I taped an Estes D12 onto him. My friends and I experienced 1.7 seconds of bliss and terror as that SOB circled us in an incomprehensible blur. It was like he was everywhere all at once.

MitchellAuroraSuperman.jpg


My next bad-idea rocket was when I took an Estes V2, carved out the nose cone to make it lighter and faster and then, based on a photo in a book, made scale wings so that it would fly.
The pic in the book looked like this:

3i.jpg

I'm borrowing that photo of Supes to post on another website about comics. Just sayin'....:cool:
 
This got me LOLing at work. :^)

I once built a rocket using one of those Designer Special kits. It was short, fat, and had a box section tail like a bomb. It flew great on a C6. My Dad thought it would be more fun to try it as a two stage and taped another C motor onto the end of it (chad staged?). Anyway that little bastard scared the bejesus out of me. It made it about 15' off the rod, spun around like a pinwheel, staged into cruise missile mode and then cratered in about 100' away. By far the most exciting model rocket flight of my childhood.

My friend and I once went to a park to launch some rockets. He had brought along his Estes Helicat along with a B4-4 and C6-5 motor. For some reason the rocket was unstable, even though he built it according to stock. The flight on the B motor was a bit weird, and it looked like watching a video in slo-mo. The rocket took off the pad and coasted up to 25-30 ft at barely 5 mph, and then the parachute popped open and it floated down to the ground. We took this as a bit weird, but nevertheless we loaded it up with a C6-5 and pressed the button. The rocket shot off the pad, went 15 ft up, then angled on to its side and took off like a blur. It disappeared behind a grove of trees where some unfinished houses were being constructed and then we heard a loud thud. It turned out that the ejection charge had gone off just before the rocket hit the ground, and that thud we heard was the sound of the rocket's nose cone hitting the wood wall of the house. Anyway, the rockets tube had lawndarted into the ground and was bent and broken so the rocket was in a unflyable condition.
 
I like the concept of a finless rocket, but why would you severely damage the aerodynamic capabilities of your rocket just so it sounds unique? If you're aiming for innovation finless isn't the way to go.
 
I like the concept of a finless rocket, but why would you severely damage the aerodynamic capabilities of your rocket just so it sounds unique? If you're aiming for innovation finless isn't the way to go.

Yes, you have a point. It is a lot of work for something that is unique, but only offers the same stability at best as a standard model. There are at least two considerations in favor for a finless design. The first is that it may be possible to make scale models of real finless rockets or rockets with small fins without resorting to clear plastic fins. The first Navy Polaris SLBM design and the early Air Force Thor IRBM are examples. Secondly, there is the aspect of validating the Gas Dynamic Stability (GSD) theory that says this concept will work. (The conventional model rocket design with fins suggests that this design should not work.) This past summer we discussed on a different thread the fluid dynamic control volume analysis of this concept. It was one thing to discuss the theory. It is another thing to see the concept work in action. David Hall shows his model and design features on post no. 1 and No. 29 of this thread. I am glad that someone bumped this thread recently, so I could see David's model, again. I keep thinking that I would like to go back and build this model, but I just have too many other model rocket projects at the moment.
 
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I keep thinking that I would like to go back and build this model, but I just have too many other model rocket projects at the moment.

I should add that to my sig! :wink:

I've pondered finless design as well. I love cup rockets and figured a finless rocket would be a cool variation of it; however if you make the tube straight, you likely need some other way to make it more stable with less wobble (which is what fins normally help with). I figured maybe air inlets in the nose/sides with internal ducting leading out at the aft section (possibly thin vertical slots) at an angle downwards and sideways...invisible air fins. Way beyond what I'm willing to start right now, but maybe one day.

BTW - Just a guess, but I would think the full scale finless missiles you mentioned have sophisticated guidance controls which likely includes vectored thrust/articulated nozzles.
 
Maybe this method could be used to make a multi-staged Saturn V! :D
 
I've pondered finless design as well. I love cup rockets and figured a finless rocket would be a cool variation of it; however if you make the tube straight, you likely need some other way to make it more stable with less wobble (which is what fins normally help with). I figured maybe air inlets in the nose/sides with internal ducting leading out at the aft section (possibly thin vertical slots) at an angle downwards and sideways...invisible air fins. Way beyond what I'm willing to start right now, but maybe one day.

I spoke too soon! I've been losing some sleep thinking about this one. I'll likely make a few test samples and right now I'm thinking of using an Estes Converter or Converter XL (luckily they've been on clearance recently and I picked some up...the smaller one for just $1.65!). I've included a drawing below and I figure I'll first use the converter with the test shroud added only to the bottom of the three sections since this one would be very difficult to sim and I don't want it unstable right off the bat. Also with the shroud only on the bottom of 3 sections, it looks and should behave more like a conventional rocket and would be less of a concern for RSOs. If that works, I may then try two of 3 sections and then after that remove the top 1/3 and replace with a nose cone. I'm guessing there is also some magic ratio of width to length since if it is too narrow, the air induction wouldn't be significant enough to send enough out the slots for stabilization. Additionally, this is complicated by having the right size of outlet hole/slot. Maybe short & squat when slow and narrower if faster is better since you need significant air flow to make a difference. Design is such that if the rocket arcs off vertical (assuming no wind), the outer side of the arc gets more wind, which then pushes the bottom back to vertical from what I'd guess.

Really rough sketch:
2016-01-15%2008.21.59.jpg


If the prototypes work, there is possible future versions with perhaps an inlet cover around the shroud (using a large conical nose cone with most of the top cut off), so it looks like the intakes of a Bomarc or the front of a Talon missile. Also depending upon how big the inlets need to be, it may be possible to use a large nose cone and drill inlet holes vertically down into it so the inlets are in the nose cone itself.

Thoughts? :)
 
So what is going to be your first try? I would recommend a BT50 inside a BT60, that way you can use a centering to block the bottom and it is not a lot of surface area. You should be able to get reasonable performance, fin less rockets require a lot of air flow. Also, if you build it light enough tumble recovery would be a good first try. Less weight and not a lot of stuff to fool around with.

Please test without a lot of people around!
 
...fin less rockets require a lot of air flow. Also, if you build it light enough tumble recovery would be a good first try. Less weight and not a lot of stuff to fool around with.

Please test without a lot of people around!

For those reasons, I'm thinking shorter and wider than originally envisioned. Almost like the drawing, but the shroud at half length first. Good idea with the tumble recovery! Thanks!
 
I spoke too soon! I've been losing some sleep thinking about this one. I'll likely make a few test samples and right now I'm thinking of using an Estes Converter or Converter XL (luckily they've been on clearance recently and I picked some up...the smaller one for just $1.65!). I've included a drawing below and I figure I'll first use the converter with the test shroud added only to the bottom of the three sections since this one would be very difficult to sim and I don't want it unstable right off the bat. Also with the shroud only on the bottom of 3 sections, it looks and should behave more like a conventional rocket and would be less of a concern for RSOs. If that works, I may then try two of 3 sections and then after that remove the top 1/3 and replace with a nose cone. I'm guessing there is also some magic ratio of width to length since if it is too narrow, the air induction wouldn't be significant enough to send enough out the slots for stabilization. Additionally, this is complicated by having the right size of outlet hole/slot. Maybe short & squat when slow and narrower if faster is better since you need significant air flow to make a difference. Design is such that if the rocket arcs off vertical (assuming no wind), the outer side of the arc gets more wind, which then pushes the bottom back to vertical from what I'd guess.

Really rough sketch:
2016-01-15%2008.21.59.jpg


If the prototypes work, there is possible future versions with perhaps an inlet cover around the shroud (using a large conical nose cone with most of the top cut off), so it looks like the intakes of a Bomarc or the front of a Talon missile. Also depending upon how big the inlets need to be, it may be possible to use a large nose cone and drill inlet holes vertically down into it so the inlets are in the nose cone itself.

Thoughts? :)

I'll be very interested on seeing your results. I have successfully made several versions of rockets, one totally finless, that rely of 'Gas Dynamic Stabilization' and have one on the bench that will basically have a large tube fin. If the air was to just flow through, I'd say this wouldn't fly. However, your idea of ducting the air out the sides is interesting. Motor choice will also be interesting. I'd guess that high average impulse would provide more stability, but in my experience they give boring, low flights on finless designs. That's because even if this works it will tend to go unstable during the coast phase. I'd put in a 24mm mount and go for a C11 for the first flight. Then try an E12 :eek:

Mindsims rule :)
 
I'll be very interested on seeing your results. I have successfully made several versions of rockets, one totally finless, that rely of 'Gas Dynamic Stabilization' and have one on the bench that will basically have a large tube fin. If the air was to just flow through, I'd say this wouldn't fly. However, your idea of ducting the air out the sides is interesting. Motor choice will also be interesting. I'd guess that high average impulse would provide more stability, but in my experience they give boring, low flights on finless designs. That's because even if this works it will tend to go unstable during the coast phase. I'd put in a 24mm mount and go for a C11 for the first flight. Then try an E12 :eek:

Mindsims rule :)

Mindsims rule! :D

Good points! Yes, low flights may be boring; however that is probably safer (slower so you can run away in time - lol) and if it works, I can go smaller and faster. I think the hardest part is figuring out the combination of inlet and outlet as well as width and diameter. At the most "slow & wide" extreme, it would act almost like a rocket with a flat base or even similar to a saucer.
 
Yes, a stubby version would tend to have some base drag benefits. One good thing about these experiments, when they go wrong they are so unstable and lose so much speed that they don't have the energy to mount an assault on the spectators. I fly mine at MDRA where the LCO is pretty far from the flight line and then go off a high power pad.
 
Ken, would not the length x width x # of slots equal the area of the hole. For example, a BT80 is 2.56" ID and a BT50 is 0.976 OD. So figure the area of both, subtract the inner tube. This gives you the area of the ring or air inlet, which you use to guesstimate length, width, and number of slots. I would think these values would have to be identical so you are not generating unnecessary back pressure.

As I stated earlier, you could just use a centering ring to make a quick and dirty build. Obviously, this will take a few tries to get right so don't spend a lot of time on the first few.
 
Ken, would not the length x width x # of slots equal the area of the hole. For example, a BT80 is 2.56" ID and a BT50 is 0.976 OD. So figure the area of both, subtract the inner tube. This gives you the area of the ring or air inlet, which you use to guesstimate length, width, and number of slots. I would think these values would have to be identical so you are not generating unnecessary back pressure.
As I stated earlier, you could just use a centering ring to make a quick and dirty build. Obviously, this will take a few tries to get right so don't spend a lot of time on the first few.

Good point, but not necessarily because you don't have to have the same amount of air going out that you have going in. In fact, you can't get that due to the shroud itself causing some capture of air and the resistance of the captured air to funnel through a hole smaller than the inlet. Additionally, I'm not sure how much air is needed to be funneled or even what pattern of outlet is most effective. Wide slot for more air flow or thin slot to more closely replicate a fin? The weight of the shroud supports may also be an issue, but we'll see.

I was already thinking about using a centering ring on the bottom when I first dreamed this up, so I think that's a great idea! :wink:
 
If the rocket tilted, would the change in airflow cause positive or negative feedback in the pattern of air jetting out the sides? I have no intuition how this would behave. Looks cool.
 
Upon further thought, it does *seem* like it would provide a good negative feedback loop. Would be interested to see how it actually behaves.
 
I am thinking that the flow out of a hole that is opposite the direction of pitch might damp the motion. But my mindsims are often GIGO.
 
Upon further thought, it does *seem* like it would provide a good negative feedback loop. Would be interested to see how it actually behaves.

I am thinking that the flow out of a hole that is opposite the direction of pitch might damp the motion. But my mindsims are often GIGO.

From what I figured, I think both would be true. If the rocket strays from vertical/straight, as it leans over in an arc, the outer side of the arc gets more air/higher pressure, which would force more air through the bottom slot on that side and pushing it back to a straighter path. One possible negative here is that this same characteristic it may make it more prone to weathervaning since the side with higher wind pressure would be pushed into the wind until the pressure evens on all sides of the inlets.

I think. ;)
 
I really need the updated version of mindsim that at least runs on windows. An upgraded processor would help too. My 60's vintage machine running on punch cards and vacuum tubes just doesn't cut it these days. It is all about the Pentiums baby! And that is so 90's!

How far up are you going to mount the motor?

Are you going to paint it like a candle? And say to the LCO "Let's light this candle!"

A flying organ pipe would be cool.
 
You could try round holes initially and convert to slots once you figure how large they need to be.

I originally thought of round holes; however I later decided that it would be more effective to have the outgoing air as much like a fin as possible...the same way a rocket with short dowels as fins wouldn't be as efficient/stable as one with flat fins/"air fins". Plus I think a vertical slot in itself would be more efficient in allowing more air to be pulled out as the rocket moves faster upwards...with higher pressure at the bottom of the slot and lower pressure at the top of the slot (MindSim v.2K16).
 
How far up are you going to mount the motor?

Are you going to paint it like a candle? And say to the LCO "Let's light this candle!"

A flying organ pipe would be cool.

Good question! I initially considered recessing the motor mount to allow for GDS (Gas Dynamic Stabilization - as noted in Apogee newsletter on finless rockets); however now I think I'll have the motor flush with the bottom so I can see the results of the design separate from other stabilization factors.

Still thinking of names...I think you have an upper hand on this one! Candle would be an amusing possible design, but I'm thinking more like the front end of this :):
images
images
 
Your concept can't be GDS since the base is solid. It might benefit from a recess less than one caliber. Or not.
 
Your concept can't be GDS since the base is solid. It might benefit from a recess less than one caliber. Or not.

Correct! Mine isn't GDS...I was responding to Daddyisabar's inquiry about how far the motor mount would be recessed and I noted I wouldn't be going with GDS ("I initially considered recessing the motor mount to allow for GDS...however now I think I'll have the motor flush with the bottom so I can see the results of the design separate from other stabilization factors."). :)

Also just to be clear, "flush" means the rear centering ring is pretty much level with the bottom of the tube. I may use a retainer on the end, but I'll see.

Maybe this is GES _ gas expulsion stabilization?

Good thought; however in this case, I don't know if that is correct either since "gas" in GDS also refers to exhaust gases. This design has more to do with airflow alone...Air Flow Stabilization?

Just dug up my $1.65 Estes Converters (what a find!)...I thought it had 3 sections, but it has 4. Those screw connectors alone are like gold to me and will allow me to swap out different parts of this design for testing. Awesome. :)

Here's a pic I took last night of one version I'd love to get working (likely 2nd version once I determine if it works at all and then if the front flow can be a bit smaller.

2016-01-16%2001.16.37.jpg
 
Nice. As for the gas in GDS being exhaust, air is still a gas. But, since you thought it up you should name it ;)
 
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