"Finless" Rocket Design - Ram Air Intake Stabilization?

Your journey to the dark side is almost complete and there are many watching your career with much interest.

I've been to rocket launches from one side of the State to the other, seen lots of strange things, but nothing leads me to believe there is an all powerful Force that can make fin-less rockets fly.

The thing to say to the oddroc flyer who is alone and pushing the launch button on the prototype: "Where are your rebel friends now?"

The oddroc flyer has only a half dozen or so friends. They only show up with calm weather and a long launch rod:

1. No good, stinking, performance robbing nose weight.
2. Plenty of thrust: Trust in Thrust.
3. Canted motors.
4. Forward mounted/recessed motors.
5. Base drag.
6. GDS/air induction.

Hey, six friends isn't bad, and the list may grow. May the Force be with you.

Totally random thought. What about using a slight spin to increase stability, much like a bullet?

Daddyisabar said:

Your journey to the dark side is almost complete and there are many watching your career with much interest.

I've been to rocket launches from one side of the State to the other, seen lots of strange things, but nothing leads me to believe there is an all powerful Force that can make fin-less rockets fly.

The thing to say to the oddroc flyer who is alone and pushing the launch button on the prototype: "Where are your rebel friends now?"

The oddroc flyer has only a half dozen or so friends. They only show up with calm weather and a long launch rod:

1. No good, stinking, performance robbing nose weight.
2. Plenty of thrust: Trust in Thrust.
3. Canted motors.
4. Forward mounted/recessed motors.
5. Base drag.
6. GDS/air induction.

Hey, six friends isn't bad, and the list may grow. May the Force be with you.

Click to expand...

Sorry DIAB, but I am not falling to your temptations over to the dark side (yet). Mine uses the light side of the force!

1. No excessive nose weight. However on this one I think this design may do better with more, WD (Well DeFinned) flew with just a nose cone full of clay.
2. I would agree that more thrust is good; however my test used a 1/2A3 and got I'd guess 400' from looking at the video.
3-5. Not really a factor.
6. Air induction...yes! It's oddball!

Note that in WD flight #3, the wind was fairly brisk...you can hear it in my ground video and see it in Camera2 video...the rocket actually still went straight and just shifted over with the wind. Wow. :eyepop:

MTFBWY!

mbecks said:

Totally random thought. What about using a slight spin to increase stability, much like a bullet?

Click to expand...

Others have talked about spin stabilization and there are actually some rockets out there which use this (going back to Centuri kits even).

Once I get more tests down and the shroud "optimized", I will try other modifications & variations. One such as spinning may actually suit this one well since I think I can add it in a few ways:
1. Angled outlets...slanted outlets I think would produce spinning...probably not much, but it should be present
2. Angled inner vanes. just angling the vanes should make the air coming out go a bit more to the side than straight out
3. Offset outlets...having the outlets up against one vane should also case air to exit more at an angle
4. Rather than cut out the outlets, cut just the top, bottom and one side, push in (or pull out) and the air exiting should come out with much more sideways motion. I think this one is a winner! I want to try it right away!

So many ideas going on with this, so I'll likely solicit other people's help. I'll post directions on how to make WD very soon and see if others can help verify and improve this design.

Of note is that the performance of Well DeFinned is much, much better than I was expecting. The more I review the video, the more it surprises me how fast and straight WD flew. I've been carefully reviewing flight #2 and it looked arrow straight and very fast.

Despite many guesses that this would go unstable on coast (myself included), it actually did the opposite...it continued up very straight and didn't seem to lose much speed on coast...so straight that I initially thought the delay phase was still part of the boost phase!

Some snapshots of the coast phase...you can see where the boost stopped by the gap in exhaust smoke...

WD Flight #2:


WD Flight #3 (shows coast up until ejection starts):

*2/5/16 Update: Sorry, I'm pulling the build instructions for now...I'd like to test the design some more before releasing to the masses. I'm leaving some of the pics & instructions showing the modular build though.


Shroud Stop
This is one item which you'll have to McGyver. It is the item which the shroud sits on and stops it from slipping off. Set it about 1/8" from the end of the bt (you may want more for better taping; however this was my first attempt and I wanted the shroud low) and glue in place...make sure to add fillets for strength.


I used a black fiber centering ring (BT5 hole in the middle) and cut most of it away until I had a ring about 1/8" wide. I think you can use an 18mm thrust ring; however maybe cut it thinner to save on weight and so you have more bt on the end for the masking tape to grab onto. You can even try string and Elmer's Glue or CA.



Additional note: Before any mods, ensure the current model is stable and has good flight characteristics, then apply one small mod and check with a string test first, then flight if it passes (make sure that no one else is around or that it is a heads-up flight as a precaution).

KenECoyote said:

"Well De-Finned" Launches #2 and #3 (1/2 A3-2T):

I've saved the best for last! :grin:

Launch #2 was beautiful! I didn't video it myself, but got a look from under as it rose straight up, over on the delay and ejection and came back down not too far away. Very nice launch!

Video Link: https://www.youtube.com/watch?v=Cp0HLCHuFGs&feature=youtu.be

Launch #3...tried again to make sure...judge for yourself.

Video Links (note the wind sent it over to the right; however the rocket didn't noticeably weathervane and instead drifted to the right):
https://www.youtube.com/watch?v=qycwPCPfZPw&feature=youtu.be
https://www.youtube.com/watch?v=xrgaIUVnC8w&feature=youtu.be

I would consider "Well De-Finned" to be a successful design! I'll have to do more tests with the others; however it seems to be a very difficult mix to figure out successfully. Given that the ice will likely be gone after today, I'll have to launch elsewhere and this will be a bit on the back burner for now.

One thing no one picked up on was the modular construction I had on these rockets. I don't recall having heard/seen anything on this other than an article in Sport Rocketry where there was a very expensive modular rocket. With this method, I can readily switch shrouds and such (can add an exhaust nozzle or even switch to odd fins for testing). I'll likely make a separate thread on this part of my construction method since I think it works extremely well and is extremely convenient.

Thanks for following this far everyone! I think it's a great first start on this design!

Click to expand...

I've been away so haven't given this much thought, but this version's dimensions probably are making it act like a ring fin of sorts, as indicated by the 'what-if' Rocksim that I did. I was surprised it didn't outperform the others on the first set of flights. Anyway, press on!

rstaff3 said:

I've been away so haven't given this much thought, but this version's dimensions probably are making it act like a ring fin of sorts, as indicated by the 'what-if' Rocksim that I did. I was surprised it didn't outperform the others on the first set of flights. Anyway, press on!

Click to expand...

Thanks Dick!

IMHO this isn't a tube fin...the bottom is blocked, so it doesn't work the same as a tube fin. I would say it's a mix of tube fin, cone base and air fins. I think it's funny that we have two opposing camps...those that think it's nothing really new (although I haven't seen a tube fin rocket like this yet...let me know if I'm wrong) and those that think this is very dangerous and won't/can't work. Again, more testing is needed, but I can't right now...maybe in a week and a half.

The next set of tests should be having a similar bt5 rocket, but without the shroud bottom in place to see how it behaves with the tube fin and vanes alone (I was actually already planning this) and then also another where the shroud is replaced with conventional fins to compare performance/flight (see pic below).

If you follow the build I've done, you'll see that the modular nature if fantastic for testing. I can add a longer or shorter shroud or even a shroud extension (working on that next). I can even swap out the shroud with just the extension, which means it's a tube fin. finally I can swap out for conventional fins.

One problem for me is that I'm out of some of the bt5 items. I'll have to get more nose cones and bt (or find where I've stashed them after going HP). I may also make the 18mm match the same scale dimensions as this WD mini to try to replicate and see if upscaling works in the same way. Lots of stuff on my list right now and I'm loving it, but having trouble finding the time given a demanding full time job.

Check out "Well De-Finned" in "Everybody Relax" mode (fin can not pushed all the way down since I was lazy): :wink:

Also note...

KenECoyote said:

...I've changed to plan to start with less "RAIS" effect and more of the other known designs and slowly adjust. Likely nothing above an A8 motor until I can come up with a design that doesn't skywrite and then has repeated safe flights.

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I think mission accomplished on this part!

A few updates on RAIS'n Heck...

Started working on the adjustable outlet system! Plus I delivered on the earlier note about using TP tubes. LOL

TP tube actually fits nicely over the larger BT-60 shroud (this shroud may actually be too large for the 18mm bt, but for now I'll continue and we'll see later).




Full Vent Mode!


Half Vent Mode!


Lower Half Vent!


Also I made a nozzle since nozzles are cool.

Ken, anything that sits away from the central body acts as a fin. Including things blocked on both ends.

rstaff3 said:

Ken, anything that sits away from the central body acts as a fin. Including things blocked on both ends.

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I think this is different since the tube in this case acts to redirect the air to the side to create "air fins", so the shroud may actually be considered to be part of the central body. The "Mostly Harmless" design shows just that. Generally the function of ring and tube fins is to allow the air straight through them to stabilize the rocket in flight (at least for all the tube and ring fin designs I'm aware of). I would argue that the redirection of the air going in (induction) creates the air fins in flight, so basically it's finless since without it in motion, there aren't any air fins.

If anything, I would think that it's more of a cone base (like the New Way Spike) with the air redirected and narrowed; however I think that just that base alone would be woefully insufficient for keeping the rocket stable and straight. I think it's a combination of things going on to make it work when it doesn't look like it should work.

I'll revisit this after more testing...let's see if I can take RAIS to the point where it is clear whether it can work or not.

KenECoyote said:

I think this is different since the tube in this case acts to redirect the air to the side to create "air fins", so the shroud may actually be considered to be part of the central body. The "Mostly Harmless" design shows just that. Generally the function of ring and tube fins is to allow the air straight through them to stabilize the rocket in flight (at least for all the tube and ring fin designs I'm aware of). I would argue that the redirection of the air going in (induction) creates the air fins in flight, so basically it's finless since without it in motion, there aren't any air fins.

If anything, I would think that it's more of a cone base (like the New Way Spike) with the air redirected and narrowed; however I think that just that base alone would be woefully insufficient for keeping the rocket stable and straight. I think it's a combination of things going on to make it work when it doesn't look like it should work.

I'll revisit this after more testing...let's see if I can take RAIS to the point where it is clear whether it can work or not.

Click to expand...

Semantics. While clearly not a classic ring fin design, the outer tube will provide some stabilization, plugged or not, with or without the air fins. Maybe not enough stability by itself, which is what you are shooting for.

rstaff3 said:

Semantics. While clearly not a classic ring fin design, the outer tube will provide some stabilization, plugged or not, with or without the air fins. Maybe not enough stability by itself, which is what you are shooting for.

Click to expand...

Agreed. I think of my design almost like a "cheat" of sorts. It can blur the lines since my goal it to make the induction system internal to the body, therefore it would no longer sit away from the central body. I'm aiming to create stabilization without conventional fins that are visible or attached in the normal sense. Again, many comments about how this won't work or is unstable based on looks/design just supports that I am going in the right direction (go figure).

rstaff3 said:

Ken, anything that sits away from the central body acts as a fin. Including things blocked on both ends.

Click to expand...

Actually, thinking this over some more, wouldn't that argument mean that Gas Dynamic Stabilization (which I believe was noted to be finless) has a ring fin in the form of the aft body tube since it is basically extending beyond the main body tube and attached/extending from it and uses the airflow to maintain stability?

I'll give you the wishy washy answer...no and yes. The amount a fin affects stability is related to both area and how far the fin protrudes from the body. The further out, the more correction. I can't grab a photo but I've seen numerous rockets with smallish fins that sit on the end of struts (or dowels). So the fact that the lower section is the same diameter as the top, it doesn't help much. The bigger the diameter the more help it would be.

The yes part is that the water rocket folks sometimes use a minimum diameter ringtail that sits on struts below the 'motor'. But then fireworks guys use one stick. I don't exactly know what mechanism is in effect with those water rockets.

The prior ramble is why I always expected the longer version would work better. That's not saying your air fins aren't working. IMO, the perfect air fin rocket would be neutrally stable (or slightly unstable) without the fins and totally stable with them. An adjustable version should be able to prove how they are working.

rstaff3 said:

I'll give you the wishy washy answer...no and yes. The amount a fin affects stability is related to both area and how far the fin protrudes from the body. The further out, the more correction. I can't grab a photo but I've seen numerous rockets with smallish fins that sit on the end of struts (or dowels). So the fact that the lower section is the same diameter as the top, it doesn't help much. The bigger the diameter the more help it would be.

Click to expand...

Actually, I would argue against that in the case of GDS since for that design it appears that the motor plume is being used to suck the air in from the sides so that the air is funneled through the rear bt/tube fin. This is almost the same as I'm trying to do...redirect air. However in my design I'm trying to redirect the air from the front to actually form "air fins" on the sides which I think is the big difference.


How's this? :grin:



Or this?

rstaff3 said:

The prior ramble is why I always expected the longer version would work better. That's not saying your air fins aren't working. IMO, the perfect air fin rocket would be neutrally stable (or slightly unstable) without the fins and totally stable with them. An adjustable version should be able to prove how they are working.

Click to expand...

Just remember that this is still a work in progress. I think the key is figuring out the ratio of shroud inlet to bt to shroud outlet. I wanted to scale back to a good stable design and work off that, which I've done. I can now add on the extension (shown in the first pic above...the brown tube which actually has vanes inside) and see if that works the same. I can also use just the extension and compare the shroud (closed end) vs. tube fin (open end). Finally I have that red "open transition" which serves a few purposes including holding the shroud in place and also acting a bit like a larger nosecone and serving as a streamlined inlet. Quite a lot on my list!

I'm interested in seeing how the shroud extension affects the performance. I would think that it may perform almost the same since while it may shift the CP slightly forward, it also brings the CG forward. We'll see. If it works well, then it likely shows that the key is the inlet/outlet/shroud size ratio as mentioned earlier.

I get it but a larger tube at the bottom of that rocket will have some restorative effect. In GDS, a larger tube may not work as well. I forget if Dean tried that but his only attempt to provide a reference design did not cover that case. More room for experimentation.

Looking at THIS, this is clearly an annular finned missile. You can't call this "finless". Now if you can make an airframe all of the same diameter fly without lateral or annular fins, then you have a finless rocket.

David Bucher
TRA 829
NAR 47674
California Dave from the freezing Midwest!

rstaff3 said:

I get it but a larger tube at the bottom of that rocket will have some restorative effect. In GDS, a larger tube may not work as well. I forget if Dean tried that but his only attempt to provide a reference design did not cover that case. More room for experimentation.

Click to expand...

GDS - specifically Induction Tube Stabilization (ITS), from what I read as well as my understanding of it doesn't need to have a larger tube since you're using the engine exhaust to pull the air/airstream over to the rear tube/"fin". Having a larger tube would only add drag when it is unnecessary. Because this rear tube extends from the main body tube and (I would also argue) it is getting air pulled over to/through it, it acts like/as a fin.

IIRC "ITS" induces the air into the rear tube to provide stabilization...there is also the effect of the air almost wrapping itself around the rear motor area since it is being pulled in and the rear tube is a stabilizer of sorts. So in a nutshell as I see it, the motor exhaust power is being used to pull air over to what acts as a fin to stabilize the rear of the rocket. This is why ITS often goes unstable or tumbling right after boost...the engine power to pull air over the rear tube is gone, so the rear tube no longer acts as a stabilizer/"tube fin".

My design uses Ram Air Intake (I think I may change "Induction" to "Intake" in the name) to bring air into the system/chambers inside the shroud and send it out on the side. It is arguable as to when the shroud stops being an extension of the outer body and becomes part of the body, but my end goal is to figure out how I can get to the point where it is clearly part of the body...if I can get there (lacking a wind tunnel, I have to do incremental testing).

Here's the original pic I drew of my system in airflow and one I've drawn up of my interpretation of what is going on with ITS airflow (a simplified view since the air flow rate is much, much higher):



Sorry, but to be honest, I'm a bit confused. My OP on this thread showed a rocket (which you were helping me with earlier) almost the same as the one you're questioning...what changed?

Glideroc said:

Looking at THIS, this is clearly an annular finned missile. You can't call this "finless". Now if you can make an airframe all of the same diameter fly without lateral or annular fins, then you have a finless rocket.

David Bucher
TRA 829
NAR 47674
California Dave from the freezing Midwest!

Click to expand...

IMHO - Nope. Wrong. Incorrect. Please read the OP. :wink:

What you're calling "annular fins" aren't fins. They are "chamber separators" and also serve to support the outer shroud. If I wanted to,I can even leave them out and I don't think it would affect performance that significantly. Remember that the bottom is blocked, so they don't act as fins in the air stream in the conventional sense . I'm using them to keep air within 3 chambers to separate out the different sides so that if the rocket pitches over, more air will go to the chamber in that outer side of the arc to push the rear of that side outside the arc for additional stabilization.

This model is the first I'm working on and my goal is to eventually have the entire system well included within the rocket.

Ken this really has been a very interesting thread to follow! Keep pushing the envelope!!

kcobbva said:

Ken this really has been a very interesting thread to follow! Keep pushing the envelope!!

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Thanks for the support Kevin! Very much appreciated! :grin:

The annular fin he referred to is the larger tube, as I have been saying. The pilons on ring fin rockets don't help much anyway...its mainly the ring.

rstaff3 said:

The annular fin he referred to is the larger tube, as I have been saying. The pilons on ring fin rockets don't help much anyway...its mainly the ring.

Click to expand...

Apologies to David and thanks for clearing that up Dick! What happened was I wasn't familiar with the term "annular finned missile" so I selected just that and did a Google search (select and right click on that choice) and went directly to images and got this: https://www.google.com/search?q=ann...9h4KHev7DvAQ_AUIBygB&biw=1455&bih=694#imgrc=_

Additionally, when searching Google for that term ("annular finned missile") with quotes, nothing comes up.

However just now I searched for "annular fin" and see the disk type fin which you're saying he is referring to...now I understand the argument more. So, again my apologies for my misunderstanding that part.

Going back to this being a type of annular fin...it may be; however I did imply earlier when I said that this is more of a hybrid system with a combination of things including tube fin, "cone base" (which I think is more similar to annular fin) and wind deflection.

Just an update that I've changed the title to "Finless" (with quotes) to avoid arguments and confusion.

I just did a google search on "annular fin". Almost everything that came up had to do with radiators and heat transfer, not areodynamics. Gotta poke through my NACA files collection and see if there's anything there. Another way to look at this, fin or nofin is as base drag.

sooner.boomer said:

I just did a google search on "annular fin". Almost everything that came up had to do with radiators and heat transfer, not areodynamics. Gotta poke through my NACA files collection and see if there's anything there. Another way to look at this, fin or nofin is as base drag.

Click to expand...

Thanks SB and good note! CrazyOB actually also noted the same to me on a side discussion yesterday.

I would consider it in the same group as cone based such as the "finless" one GlenP noted on post #10 of this current thread.



Despite what others have stated earlier, I would still say that my design is neither a ring/tube fin alone nor annular/cone/base drag design alone. There's a lot of blurred lines with this one and it seems many have different interpretations of what it is.

For the record, M. Dean Black (author of the Apogee Peak of Flight article on GDS) noted "Finless rocket design has long been a subject of debate among rocketeers wishing to build and fly true scale models of space launch vehicles and large military rockets which do not normally possess prominent fins typical of tail heavy model rockets."

...I hope there is more progress this weekend...