Another finless rocket

[KenECoyote]

I'm extremely embarrassed to report that due to my age (72) and Paleolithic nature, I do not possess the technology to take and send a picture. I've asked my fellow Boeing retiree Blair, a knowledgeable engineer and close friend, to teach me how to send pictures. I'm going to do this thing!

The good news, all three of my ringtail models are complete, with finish and decals, and are ready for launch. I hope to accomplish that, with Blair's help, sometime in the next 10 days.

No shame in not knowing or being unfamiliar! I've actually been learning to use TRF on my phone and it's a learning experience as well, but it has the advantage of easily taking a picture to post.

 

[Rktman]

Very cool project! Question though: from what I can tell from the photos regarding the relative spacing of the tail cone, struts and ring fin, wouldn't it be difficult to get the motor in there? Also noticed there's no motor-retention hardware?

 

[Mike Haberer]

https://www.apogeerockets.com/education/downloads/Newsletter379.pdf

Attached is another write-up on GDS. It's a good complement to the Apogee article. I think it explains it better, while Tim's formula helps with the design and build aspects to ensure a stable design if you are using GDS alone without an induction tube.

 

[KenECoyote]

Attached is another write-up on GDS. It's a good complement to the Apogee article. I think it explains it better, while Tim's formula helps with the design and build aspects to ensure a stable design if you are using GDS alone without an induction tube.

I remember the post and testing the PDF is based on! I read up on GDS back in 2016 when I was working on a new finless idea (I think the OP started this thread as an offshoot to some of the things discussed there):

"Finless" Rocket Design - Ram Air Intake Stabilization?

(Note that updates are at the bottom of this first post.) GOAL: To create a "finless" rocket similar to that defined by M. Dean Black (author of the Apogee Peak of Flight article on GDS) "Finless rocket design has long been a subject of debate among rocketeers wishing to build and fly true...

www.rocketryforum.com

My experiment got very far, but not as well performing as I would've liked.

 

[Mike Haberer]

I remember the post and testing the PDF is based on! I read up on GDS back in 2016 when I was working on a new finless idea (I think the OP started this thread as an offshoot to some of the things discussed there):

"Finless" Rocket Design - Ram Air Intake Stabilization?

(Note that updates are at the bottom of this first post.) GOAL: To create a "finless" rocket similar to that defined by M. Dean Black (author of the Apogee Peak of Flight article on GDS) "Finless rocket design has long been a subject of debate among rocketeers wishing to build and fly true...

www.rocketryforum.com

My experiment got very far, but not as well performing as I would've liked.

I've always liked the lines of the Polaris A3, so that's in my build pile, starting with a 13mm motor design and working my way up (18mm, 24mm, 29mm) as I get it dialed in (IF I can get it dialed in....). Goal is a 1/10 sport scale, 5.5" diameter, 39" tall, 38mm or 54mm motor. I've simmed it with fins to see how high it would go (since Rocksim just cart-wheels without them); about 4,000' on a 38mm J435. It will be less than that, however; once thrust is gone, it will become unstable and slows down quickly, will likely be more like 2,000'. (I've seen this happen on my nephews Estes Saturn V. It has the engine significantly recessed with small'ish clear fins. Once thrust ended, it floundered.) On a 54mm K76WN (20 sec long burn) it sims to 8,000, legit. I will likely do HED with an Eggtimer Apogee or Quark in the NC for apogee ejection (and an Eggfinder!).

 

[Sooner Boomer]

Very cool project! Question though: from what I can tell from the photos regarding the relative spacing of the tail cone, struts and ring fin, wouldn't it be difficult to get the motor in there? Also notice there's no motor-retention hardware?

You are correct on all points. Plus, I'm going to have to attach "extender" leads to the igniter to hook up to clips. There's a risk the clips could hang up on something.

I've thought of all these problems. I couldn't easily use something like a motor clip due to the tail cone. I think tape will be enough to hold it in place. It's not too difficult to put a motor in, you can reach through the struts. Getting it back *out* again...

 

[jqavins]

Will you be able to push it out from the top?

 

[Rktman]

Will you be able to push it out from the top?

I believe there's a top glued to the forward end of the baffle that would probably prevent it...

 

[Rktman]

Getting it back *out* again...

Use a motor puller made from a coat hanger with a bent tip that just fits through the clay nozzle?

I've had to use this method with hard-to-reach motors when they get jammed due to motor mount thermal expansion or ejection crud (especially during humid summers when I don't remove the motor right away).

 

[Sooner Boomer]

Use a motor puller made from a coat hanger with a bent tip that just fits through the clay nozzle?

I've had to use this method with hard-to-reach motors when they get jammed due to motor mount thermal expansion or ejection crud (especially during humid summers when I don't remove the motor right away).

Oh, yeah. Estes (I think) used to sell these, back in the day.

 

[Sooner Boomer]

Will you be able to push it out from the top?

no. There's an ejection baffle sealing off the top of the motor tube.

 

[Sooner Boomer]

There's a launch scheduled for Sunday. Winds forcast up to 20mph. I'll have to wait for better conditions for the first flight, 3 or 4 more weeks.

 

[Rktman]

Oh, yeah. Estes (I think) used to sell these, back in the day.

Really? Haha and here I thought it was just another ad hoc home-brewed remedy that I came up with.

 

[Sooner Boomer]

Really? Haha and here I thought it was just another ad hoc home-brewed remedy that I came up with.

It's a great idea, and you're showing ingenuity. Just because someone thought of it before you, doesn't mean your idea lacks value.

 

[Dotini]

I'm going to have to attach "extender" leads to the igniter to hook up to clips. There's a risk the clips could hang up on something.

I too may have to do this to launch a pair of ringtails I've made. The motor is at the top of the rocket in a small pod, and to attach to the igniter means feeding up through the ring and its connecting structure. Is there a photo, diagram or description available which shows a preferred method for these "extender leads"?

In other news, I'm planning on purchasing a digital camera this morning. With some help from my pal Blair I may be able to post pix of my three ringtail odd rocs. We plan to launch them all this week.

 

[Sooner Boomer]

I just twist the ignitor leads to some scrap piece of wire, I only need to extend the leads about 6" or so. I strip about 1/2" to 3/4" of insulation from each end. I don't think it matters if it's solid core or stranded wire. I've also seen a rig, used for front-motor boost/rocket gliders that use a dowel to extend the clips to the motor. A pair of wires is taped or zip-tied to the dowel, leaving a few inches free at each end. Clips are attached at the top, and bared wires at the bottom for the "regular" clips to attach to. The idea is for the dowel to carry the weight of the clips/wiring, so that it's not hanging from the engine.

 

[Dotini]

The Animist

die Glock (18mm)

 

[Sooner Boomer]

The Animist
View attachment 454374

die Glock (18mm)
View attachment 454376

Those look pretty sweet! How fragile is the one on the bottom? What are the struts made from?

 

[Dotini]

Those look pretty sweet! How fragile is the one on the bottom? What are the struts made from?

The struts are of high end Birch dowel, manufactured in Canada, 1/8" diameter. The "canards" are basswood, the ring a shortened section coupler, the flange on the bell is 65 lb cardstock. It's been dropped and mishandled a bit, but so far no damage. I don't think flight stresses or landing are going to harm it. But, as always, I could be wrong.

It weighs 0.77 oz without motor. I intend to launch it on 1/2A6-2, A8-3 or A8-0. The purpose of this rocket is to experiment with descent characteristics. By changing the shape, size and trimming of the flange, lip or "Gurney flap" in racing car parlance, I hope to refine and ultimately slow the descent. The relationship of the small canards to the ring in terms of stability I do not yet understand. I need to do a swing test before this experiment goes any further.

 

[Dotini]

I just twist the ignitor leads to some scrap piece of wire, I only need to extend the leads about 6" or so. I strip about 1/2" to 3/4" of insulation from each end. I don't think it matters if it's solid core or stranded wire. I've also seen a rig, used for front-motor boost/rocket gliders that use a dowel to extend the clips to the motor. A pair of wires is taped or zip-tied to the dowel, leaving a few inches free at each end. Clips are attached at the top, and bared wires at the bottom for the "regular" clips to attach to. The idea is for the dowel to carry the weight of the clips/wiring, so that it's not hanging from the engine.

How is this?

I expect the dowel to get scorched. But I can soak it in borax, and it is easily replaceable.

 

[Sooner Boomer]

How is this?

I expect the dowel to get scorched. But I can soak it in borax, and it is easily replaceable.
View attachment 454418

I bet that will work great! I don't see how it could catch on anything. I generally consider parts like that to be consumable. I don't know what you used, but something like a bamboo skewer is minimal cost.

 

[jqavins]

die Glock (18mm)
View attachment 454376

I didn't know Glock made anything as big as 18 mm. That's a huge round!
They're both great looking birds.

I don't know what you used, but something like a bamboo skewer is minimal cost.

Y'know what's even cheaper, and easier to setup? Why not clothes pin the leads to the launch rod?

 

[Dotini]

I didn't know Glock made anything as big as 18 mm. That's a huge round!
They're both great looking birds.

Thanks!
FYI, die Glock translates to "the bell" from German. The tube and flange vaguely resemble a bell - and I hope I can get it to swing like a bell on the way down.

 

[jqavins]

Ah. And hench glockenspiel, I see.

 

[Charles_McG]

Y'know what's even cheaper, and easier to setup? Why not clothes pin the leads to the launch rod?

From the pictures, he has the launch lugs on the ring and canard, not on the body tube. Clipping the leads to the rod would put them in the way.

 

[jqavins]

There's no face palm emoji. Don't ask me how I know this.

 

[Mike Haberer]

From the pictures, he has the launch lugs on the ring and canard, not on the body tube. Clipping the leads to the rod would put them in the way.

Zip tie. Snip it off after the flight.

 

[Dotini]

I launched these three odd rocs today. All successful, no damage. All very fun to see perform in their unique ways.

I now have new ideas about what to build next!

From left to right:
die Glock (1/2A6-2), Estes Blender (A10-0T), Animist (1/2A3-2T)

 

[BABAR]

Hmmmmm.....regarding the tube launch issues.

1. Sealed vs unsealed, how will pressure affect thrust INSIDE THE TUBE?
if sealed, possibilities are dependent on tube volume. With a piston launch, the tube is I think the motor diameter, so the nozzle gas plume not only accelerates the rocket the same as for a launch lug or tower or rail rocket (every reaction has an equal and opposite reaction) but the build up of pressure in the tube forces piston up. With a sealed bazooka tube not sure if the volume may be greater than the ejection gas as rocket moves upward, so I am not sure whether a sealed tube and near sealed ring would be a plus or minus. I think safest course of action would be unsealed tube

2. How will tube traveling in a sealed (or unsealed) tube affect ring fin or gas dynamic stability? I don’t think it matters. The tube itself will keep the rocket on trajectory (just like a rod or rail) until they exit the tube, at which point the ring fin or GDS or whatever will have a chance to kick in (or not!). This is not that different from a rod or rail, the fins aren’t effective until a certain velocity is reached, presumably a during portion (1/2, 3/4?) of the trip up the rod the fins aren’t doin much of anything, but they don’t need to kick in until the rocket leaves the rod.

 

[jqavins]

Since it seems like you're speculating, I'll join in. If anyone knows, I will withdraw all such speculation.

On the first point, I'd be surprised to find sealing the tube is a negative, since the plume continues to fill the volume behind the rocket as said volume increases.

But if the tube is sealed at the bottom end and not completely filled by the rocket the flame will precede the rocket out the front; we've all seen pictures of that, I'm sure. So I would think the finish would be badly scorched. One might consider using a sabot to fill the tube and protect the rocket until it emerges. Which would increase the pressure behind the rocket and any gun barrel effect, as well as protect the paint.

Regarding the second, I think you've got it right, 99%. The difference with a rocket that's on a guide and also in free air is that the fins or GDS (or whatever else) begin operating, as you said, before the end of the guide. The two means of assuring straight motion overlap. With a tube launch there is a hand off from one to the other with no overlap. Is there a moment after emerging from the tube that, even though there's enough speed for the fins or whatever to work, the necessary air flow geometry is not yet established? A hand-off transient? And if so, does it last long enough to do any mischief? (If it's scant milliseconds then simple inertial will keep the rocket going straight enough.)