Horizontal Spin Recovery - with Magnus Effect?

[Dotini]

Tests comparing HSR and backslider recovery will resume tomorrow morning at 60 Acres.



From left, 4 interchangeable fin cans and Magnus Veritas, center is X-8, right is new model CHAD Magnus.

 

[BABAR]

Hope they all look that purty at the end of the day!

 

[Dotini]

Interesting evidence is being obtained that there may be a statistical difference between HSR and BSR (Backslider) enough to validate a Magnus force. However, there is not yet enough data to rigorously support such a conclusion. So more testing will have to be done. As it happens, my launch partner is off to Europe for a month, so I will be doing more building than flying for the next month.

The distilled flight data so far:

1. HSR...........27 seconds descent time
2. BSR...........25 seconds
3. BSR...........26 seconds
4. HSR...........28 seconds
5. HSR...........27 seconds
6. BSR...........21 seconds
7. BSR...........24 seconds
8. HSR............25 seconds

HSR average: 26.75
BSR average: 24

Random observations: The wind was almost dead calm, no more than 1, 2 or 3 max mph. Reliability of the ejection event does not seem to be helped by very calm winds aloft. Reliability of painted and/or Sharpied PETG fins is fragile. Joints of Gorilla glue to paper is not great. The Gorilla glue does not penetrate well. Same problem for CA. Two ejection ports are probably not optimal, at least in the sizes and locations we used. We may be shifting to epoxy for joints involving plastic to paper.

Importantly, we are on the verge of confirming that a rocket which is kinked is much more likely to spiral on the way down.

Edit: We now are working on the explanation of how the Magnus effect acts vertically as well as horizontally in the spiraling HSR model rocket.

 

[BABAR]

Edit: We now are working on the explanation of how the Magnus effect acts vertically as well as horizontally in the spiraling HSR model rocket.

depending on how kinked it is, it may be more likely to spiral on the way up, too !

jokes aside, congrats on successful HSR And BSR (is this your first BSR? I found BSR to be just as “alien” to watch as HSR, it is just supercool To watch.)

where are the failure points in your PETG fins?

Are the fins breaking or is the joint failing or both?

How are the tubes holding up to the landing?

would increased number of shorter fins provide the same stability on boost and the same success in conversion to HSR or BSR? Say 6 smaller fins, which may because they are shorter be less likely to break?

i will continue to play Devil’s advocate on Magnus Force relating to slowing descent on HSR. I have an alternative theory as to why An HSR rocket might fall slower than BSR.

Two rockets, identical except for fin orientation (your reversing the curve on two fins to convert HSR to BSR in otherwise identical rockets was pure genius, by the way), fly to same altitude and perform the ejection. They have same mass. At this point, they have same POTENTIAL ENERGY based on altitude and mass, and the same surface area.

phase 1 is transition from random orientation (following ejection “puff” i theorize there is no way to predict the orientation of the rocket, you just HOPE it isn’t nose down) to either horizontal spin or backslide recovery. I don’t think this is calculable, I suspect it is pretty quick in either case, but I do not know if it is faster for one or the other, though if I had to guess I would say it is faster for BSR. In any case, I am going to take a leap and say that it is negligible.

Start with BSR

the BSR rocket finally gets horizontal and falls horizontally, with drag being the main component of energy loss as it drops, the rest is kinetic energy. So the initial potential energy is converted to drag based on transverse surface area and the kinetic energy it develops when it hits the ground. The kinetic energy is based on mass and fall velocity. Mass is the same for both rockets, so velocity is our target measurement, we want it as slow as possible. Hang time is altitude divided by velocity. We want long hang times.

but key is the POTENTIAL ENERGY for BSR at apogee is converted to TWO components,

kinetic energy and

energy lost to drag, which is increased because of horizontal orientation.

now for HSR

the HSR rocket finally gets horizontal. But in the process, it starts spinning (developing ROTATIONAL kinetic energy) AND the MAGNUS FORCE, while lateral to the fall vector, IS generating lateral acceleration (which may be straight lateral or spiral, and which is reaches a peak when lateral acceleration is countered by wind resistance.) Here’s the point:

with HSR the initial POTENTIAL energy has To be dispersed to FOUR components

drag component from horizontal orientation of rocket (presumed same as BSR)

PLUS rotational kinetic energy

PLUS the lateral force/velocity generating by MAGNUS FORCE (so in my theory Magnus Force vector is still not UPWARD, but it IS bleeding off potential energy)

and the rest of the energy is the kinetic energy based on mass (same as other rocket) and fall velocity.

this last component should be LESS for the HSR rocket, since as opposed to the BSR rocket, some of that original potential energy was bled of into rotational and lateral acceleration/velocity generated by Magnus Force.).

so HSR should fall slower.

caveats (and these are only the ones that I have thought of.) First is that the BSR rocket when it backslide does develop a considerable forward or rather backward velocity, which may be equal to or greater than the Magnus effect lateral velocity, so there is a potential for loss of potential energy via this route for the BSR rocket. I am also assuming that the fins on the BSR rocket are not generating any lift, and I am not sure if that is correct. (@Rktman have any ideas on this?)

also BIG assumption that time from ”puff” to full HSR or BSR orientation is either negligible or similar. If not negligible, it is likely considerably variable for HSR, as if at the end of the puff tweak, the rapidity of conversion to full HSR (time taken to rev up to max spin and horizontal orientation) is dependent on the how “horizontal” the rocket is at the end of the puff, which is I believe completely random. If you get lucky and it is horizontal to start with, it will spin up rapidly. If you are unlucky and it is well off horizontal, it will take a little longer. If you are REALLY unlucky and it is vertical nose down, it doesn’t happen at all and your rocket comes in ballistic.

summary: I still theorize that Magnus Force by laws of physics does not produce any direct “upward” lift, but perhaps the energy expended in GENERATING the Magnus Force DOES reduce the vertical kinetic energy developed and therefore INDIRECTLY slows the rocket descent. I further theorize however that the Magnus Force and energy “stolen” is likely minimal compared to the rotational kinetic energy “stolen”, which is considerable as demonstrated by your fin breakage issues.

 

[Dotini]

depending on how kinked it is, it may be more likely to spiral on the way up, too !

jokes aside, congrats on successful HSR And BSR (is this your first BSR? I found BSR to be just as “alien” to watch as HSR, it is just supercool To watch.)

where are the failure points in your PETG fins?

Are the fins breaking or is the joint failing or both?

How are the tubes holding up to the landing?

would increased number of shorter fins provide the same stability on boost and the same success in conversion to HSR or BSR? Say 6 smaller fins, which may because they are shorter be less likely to break?

i will continue to play Devil’s advocate on Magnus Force relating to slowing descent on HSR. I have an alternative theory as to why An HSR rocket might fall slower than BSR.

Two rockets, identical except for fin orientation (your reversing the curve on two fins to convert HSR to BSR in otherwise identical rockets was pure genius, by the way), fly to same altitude and perform the ejection. They have same mass. At this point, they have same POTENTIAL ENERGY based on altitude and mass, and the same surface area.

phase 1 is transition from random orientation (following ejection “puff” i theorize there is no way to predict the orientation of the rocket, you just HOPE it isn’t nose down) to either horizontal spin or backslide recovery. I don’t think this is calculable, I suspect it is pretty quick in either case, but I do not know if it is faster for one or the other, though if I had to guess I would say it is faster for BSR. In any case, I am going to take a leap and say that it is negligible.

Start with BSR

the BSR rocket finally gets horizontal and falls horizontally, with drag being the main component of energy loss as it drops, the rest is kinetic energy. So the initial potential energy is converted to drag based on transverse surface area and the kinetic energy it develops when it hits the ground. The kinetic energy is based on mass and fall velocity. Mass is the same for both rockets, so velocity is our target measurement, we want it as slow as possible. Hang time is altitude divided by velocity. We want long hang times.

but key is the POTENTIAL ENERGY for BSR at apogee is converted to TWO components,

kinetic energy and

energy lost to drag, which is increased because of horizontal orientation.

now for HSR

the HSR rocket finally gets horizontal. But in the process, it starts spinning (developing ROTATIONAL kinetic energy) AND the MAGNUS FORCE, while lateral to the fall vector, IS generating lateral acceleration (which may be straight lateral or spiral, and which is reaches a peak when lateral acceleration is countered by wind resistance.) Here’s the point:

with HSR the initial POTENTIAL energy has To be dispersed to FOUR components

drag component from horizontal orientation of rocket (presumed same as BSR)

PLUS rotational kinetic energy

PLUS the lateral force/velocity generating by MAGNUS FORCE (so in my theory Magnus Force vector is still not UPWARD, but it IS bleeding off potential energy)

and the rest of the energy is the kinetic energy based on mass (same as other rocket) and fall velocity.

this last component should be LESS for the HSR rocket, since as opposed to the BSR rocket, some of that original potential energy was bled of into rotational and lateral acceleration/velocity generated by Magnus Force.).

so HSR should fall slower.

caveats (and these are only the ones that I have thought of.) First is that the BSR rocket when it backslide does develop a considerable forward or rather backward velocity, which may be equal to or greater than the Magnus effect lateral velocity, so there is a potential for loss of potential energy via this route for the BSR rocket. I am also assuming that the fins on the BSR rocket are not generating any lift, and I am not sure if that is correct. (@Rktman have any ideas on this?)

also BIG assumption that time from ”puff” to full HSR or BSR orientation is either negligible or similar. If not negligible, it is likely considerably variable for HSR, as if at the end of the puff tweak, the rapidity of conversion to full HSR (time taken to rev up to max spin and horizontal orientation) is dependent on the how “horizontal” the rocket is at the end of the puff, which is I believe completely random. If you get lucky and it is horizontal to start with, it will spin up rapidly. If you are unlucky and it is well off horizontal, it will take a little longer. If you are REALLY unlucky and it is vertical nose down, it doesn’t happen at all and your rocket comes in ballistic.

summary: I still theorize that Magnus Force by laws of physics does not produce any direct “upward” lift, but perhaps the energy expended in GENERATING the Magnus Force DOES reduce the vertical kinetic energy developed and therefore INDIRECTLY slows the rocket descent. I further theorize however that the Magnus Force and energy “stolen” is likely minimal compared to the rotational kinetic energy “stolen”, which is considerable as demonstrated by your fin breakage issues.

Thanks for your many observations and questions. They are all greatly appreciated. I won't be able to address all of them in this one post, but will get to some of them. My colleague, a retired aeronautical engineer, is currently working on a formal explanation of the Magnus force as it applies to our Veritas model rocket. I have my own words, but we'll compare notes and get an explanation out pretty soon. Admittedly, we do not yet have enough data for a full academic proof, but the data so far suggest the HSR will descend about 10% slower in a very light wind. We are hoping for a 6 mph wind for our next test session.

To witness a good BSR or HSR flight is one of the most weird but also exhilarating experiences in rocketry. The BSR, after a successful ejection event, will slide gracefully down and backwards, and will level out in a nearly horizontal attitude. It does not spin. Much of the time, it will descend in a straight line with the wind, but I've seen quarter and half circles as well. It will land almost level but clearly on the back end and on the lower fin. Somewhere in this forum I have a photo of my BSR having completed a perfect "one-point landing", solidly impaling the earth with one fin and everything else clear of the ground! This particular model had a reversed Estes E2X fin can - very sturdy!

The HSR rocket by comparison, will spin rapidly and descend sideways, often perfectly level. It will almost never go in a straight line, but do up to 4 complete spirals, as if it is continuously seeking out the wind and trying to turn sideways into it. The spirals may appear somewhat "jerky", as though the model is alternately slowing and speeding up. At landing, the rocket will slow its spin and land slightly tail down, applying a torque on whatever fin hits first.

For convenience of construction, I've made heavy use of PETG shipping tubes to make my HSR fins from. These are only 0.025 wall thickness, and although they do not flutter, they do have reliability problems. Firstly, I fear they suffer from embrittlement from paint and Sharpie solvents. They will crack right in half on occasion. Other failure modes consist of coming off at the root, sometimes leaving the adhesive behind, and sometimes taking the adhesive along, leaving only bare or sometimes ripped paper behind.

Due to the possibility of ballistic events, we now go to the range with spare tubes and nose cones at the ready. Our newer rockets all break down into sections, including the nose cone, held together with tape for launch.

 

[lakeroadster]

Thanks for your many observations and questions. They are all greatly appreciated. I won't be able to address all of them in this one post, but will get to some of them. My colleague, a retired aeronautical engineer, is currently working on a formal explanation of the Magnus force as it applies to our Veritas model rocket. I have my own words, but we'll compare notes and get an explanation out pretty soon. Admittedly, we do not yet have enough data for a full academic proof, but the data so far suggest the HSR will descend about 10% slower in a very light wind. We are hoping for a 6 mph wind for our next test session.

To witness a good BSR or HSR flight is one of the most weird but also exhilarating experiences in rocketry. The BSR, after a successful ejection event, will slide gracefully down and backwards, and will level out in a nearly horizontal attitude. It does not spin. Much of the time, it will descend in a straight line with the wind, but I've seen quarter and half circles as well. It will land almost level but clearly on the back end and on the lower fin. Somewhere in this forum I have a photo of my BSR having completed a perfect "one-point landing", solidly impaling the earth with one fin and everything else clear of the ground! This particular model had a reversed Estes E2X fin can - very sturdy!

The HSR rocket by comparison, will spin rapidly and descend sideways, often perfectly level. It will almost never go in a straight line, but do up to 4 complete spirals, as if it is continuously seeking out the wind and trying to turn sideways into it. The spirals may appear somewhat "jerky", as though the model is alternately slowing and speeding up. At landing, the rocket will slow its spin and land slightly tail down, applying a torque on whatever fin hits first.

For convenience of construction, I've made heavy use of PETG shipping tubes to make my HSR fins from. These are only 0.025 wall thickness, and although they do not flutter, they do have reliability problems. Firstly, I fear they suffer from embrittlement from paint and Sharpie solvents. They will crack right in half on occasion. Other failure modes consist of coming off at the root, sometimes leaving the adhesive behind, and sometimes taking the adhesive along, leaving only bare or sometimes ripped paper behind.

Due to the possibility of ballistic events, we now go to the range with spare tubes and nose cones at the ready. Our newer rockets all break down into sections, including the nose cone, held together with tape for launch.

I looked online and the weight of PETG is 0.734 ounces/cu-in. If that weight is correct you could replace your 0.025 wall PETG with tri-papered balsa = 0.095" thick (2 pieces of 1/32 balsa & 3 pieces of 11 mil paper) and the weight would be nearly identical.

What's the diameter of the shipping tubes you are using?

 

[Dotini]

I looked online and the weight of PETG is 0.734 ounces/cu-in. If that weight is correct you could replace your 0.025 wall PETG with tri-papered balsa = 0.095" thick (2 pieces of 1/32 balsa & 3 pieces of 11 mil paper) and the weight would be nearly identical.

What's the diameter of the shipping tubes you are using?

Nominally they are 3" diameter. Measured by caliper, 3.2" is maybe a bit more accurate. I'm currently building up my inventory of balsa.

 

[lakeroadster]

Nominally they are 3" diameter. Measured by caliper, 3.2" is maybe a bit more accurate. I'm currently building up my inventory of balsa.

Then 3" PVC pipe should be good for your fixture.​

​

​

 

[BABAR]

I looked online and the weight of PETG is 0.734 ounces/cu-in. If that weight is correct you could replace your 0.025 wall PETG with tri-papered balsa = 0.095" thick (2 pieces of 1/32 balsa & 3 pieces of 11 mil paper) and the weight would be nearly identical.

What's the diameter of the shipping tubes you are using?

i will show my ignorance here.

two factors, strength and flexibility.

is that tri-papered balsa stronger?

is it stiffer? (Ideally you want stiff enough to avoid flutter but flexible enough to bounce)

Obviously you wouldn‘t suggest it if you didn’t think it would work better, I’d appreciate it if you would expound a little.

i am still thinking that shorter fins in greater numbers is one partial solution.

an other is an external ring that allows the rocket to slide/spin a bit longer, as the slower the energy is dissipated the lower the force at a given time. Seems like this worked with one of you recent creations for the booster.

another is to create a mount that easily accepts cardboard 1/2 body tubes. If they bend, you just replace them. Sort of what Ford did with the Brakes in Ford Vs. Ferrari. I liked that movie.

 

[Dotini]

i will show my ignorance here.

two factors, strength and flexibility.

is that tri-papered balsa stronger?

is it stiffer? (Ideally you want stiff enough to avoid flutter but flexible enough to bounce)

Obviously you wouldn‘t suggest it if you didn’t think it would work better, I’d appreciate it if you would expound a little.

i am still thinking that shorter fins in greater numbers is one partial solution.

an other is an external ring that allows the rocket to slide/spin a bit longer, as the slower the energy is dissipated the lower the force at a given time. Seems like this worked with one of you recent creations for the booster.

another is to create a mount that easily accepts cardboard 1/2 body tubes. If they bend, you just replace them. Sort of what Ford did with the Brakes in Ford Vs. Ferrari. I liked that movie.

To my mind, unquestionably six smaller fins woulds be preferred to 3 or 4 larger fins when it comes to damage resistant landings. But even if they had the same total fin area, my first concern would be, do they spin as fast as the longer fins? I've built several six fin normal rockets, and they look and fly quite well. So one of my immediate jobs will be to build a six fin HSR.

The ring reinforcement idea is a very good solution for damage limitation. The major drawback is that the area of the ring detracts from the spin-generating area of the fins while adding useless drag and weight. An inelegant solution? That is why I continue with small diameter dowels triangulating the fins into a rigid box structure. Replacing the round section rods with airfoil section bamboo RC airplane wing struts would be even better.

The cardboard body tube idea has merit, too. But no way would I use 1/2 tube per fin - 1/4 is much better, IMHO. Six fins 2" x 2" cut from a BT-80 body tube might serve very well.

 

[lakeroadster]

is that tri-papered balsa stronger?

is it stiffer? (Ideally you want stiff enough to avoid flutter but flexible enough to bounce)

In the plywood configuration, it's stronger, stiffer and lighter.

I tend to disagree about the bounce comment... hell-for-stout has always worked great for me.

 

[Rktman]

I am also assuming that the fins on the BSR rocket are not generating any lift, and I am not sure if that is correct. (@Rktman have any ideas on this?)

I don't believe BSR fins generate any lift per se, just drag resistance.

 

[BABAR]

The ring reinforcement idea is a very good solution for damage limitation. The major drawback is that the area of the ring detracts from the spin-generating area of the fins while adding useless drag and weight. An inelegant solution? That is why I continue with small diameter dowels triangulating the fins into a rigid box structure. Replacing the round section rods with airfoil section bamboo RC airplane wing struts would be even better.

concur with ring adding weight and drag. It DOES markedly increase boost stability, probably better than a dowel. But I think your rockets already have plenty of stability, so adding more stability is like reinforcing an area already strong enough, no benefit.

Aesthetics are completely in they eye of the builder, the dowel definitely adds uniqueness!

many people use clear fins especially on scale rockets which have insuffic inherent fin stability (Saturn V, for example) or rockets based on objects where visible fins detract from appearance (@neil_w SkyWriter Pencil, for sample). So I see little point in painting fins. It does make painting the body tube NEXT to the fin challenging. you are a craftsman as well as an engineer and inventor, so you insist your rockets look good (a “problem” I don’t have!). One compromise is to use a large black sharpie (sort of an oxymoron) to color the tube black PRIOR to fin attachment. As opposed to paint, my experience has been the pre attachment Magic marker coloring does NOT detract from adhesion. And IMO black sharpie over tan or white tubes actually looks pretty good (again my aesthetic standards are woefully behind yours.) A brief google search suggests that Epoxy dries clear to slightly yellow, although there are those that intentionally tint it for decorative purposes.

so at least for your swappable fin cans, if You like black, I think you can create a decent to good looking fin can with a black sharpie, clear fins, and epoxy glue. As a note, other marker colors like red leave a kind of ”bush league” appearance, and you need to use a white tube.

 

[Dotini]

concur with ring adding weight and drag. It DOES markedly increase boost stability, probably better than a dowel. But I think your rockets already have plenty of stability, so adding more stability is like reinforcing an area already strong enough, no benefit.

Aesthetics are completely in they eye of the builder, the dowel definitely adds uniqueness!

many people use clear fins especially on scale rockets which have insuffic inherent fin stability (Saturn V, for example) or rockets based on objects where visible fins detract from appearance (@neil_w SkyWriter Pencil, for sample). So I see little point in painting fins. It does make painting the body tube NEXT to the fin challenging. you are a craftsman as well as an engineer and inventor, so you insist your rockets look good (a “problem” I don’t have!). One compromise is to use a large black sharpie (sort of an oxymoron) to color the tube black PRIOR to fin attachment. As opposed to paint, my experience has been the pre attachment Magic marker coloring does NOT detract from adhesion. And IMO black sharpie over tan or white tubes actually looks pretty good (again my aesthetic standards are woefully behind yours.) A brief google search suggests that Epoxy dries clear to slightly yellow, although there are those that intentionally tint it for decorative purposes.

so at least for your swappable fin cans, if You like black, I think you can create a decent to good looking fin can with a black sharpie, clear fins, and epoxy glue. As a note, other marker colors like red leave a kind of ”bush league” appearance, and you need to use a white tube.

Here are some swappable fin cans we have been using on the Magnus Opum model. They are unpainted PETG attached to Sharpied tubes with Gorilla glue. So far, no failures.



Personally, I like to use the fin area for maximum visibility purposes, so we may end up adding reflective tape to these units.

 

[Dotini]

In browsing the literature/video of Magnus effect in common objects, we often encounter the baseball and the golfball. With these objects, seams and dimples are said to be required in the surface in order to bring the effect fully alive. In the HSR model rocket, we have only the fins down at the far end to provide serious rotational drag around an otherwise smooth body tube/fuselage. To begin to test extension of this principle on a model rocket, I filled the spiral on a BT-50 tube with Kevlar line. We can interchange this tube with a smooth one and measure any difference in altitude, descent time or change in flight characteristics.

This is the first time I've filled a spiral with something other than filler or paint! White glue holds the Kevlar into the groove. It will be trimmed, painted and taped where it joins the other sections.

 

[neil_w]

Interesting.

Just spitballing here (haven’t read any of the literature) but wouldn’t the maximum effect be obtained by running the protrusions parallel to the body tube?

 

[Dotini]

Interesting.

Just spitballing here (haven’t read any of the literature) but wouldn’t the maximum effect be obtained by running the protrusions parallel to the body tube?

Yes, I believe they would! But just for openers, I'm trying the easier and more convenient application process. Lazy guy gotta start somewhere. Occasionally you do see these barber pole strips in nautical and other Magnus applications.

 

[jhill9693]

I’m sitting on the couch trying to work up the gumption to put fins on this staff of a tube which will be a Backspin 125.

All 60.75” of tube is heavy wall Kraft identical in ID and OD to an LT-125 (now discontinued) using LT-115 commonly used as 29mm motor mounts as couplers.

These Kraft tubes were saved from packages of contact paper from my wife’s kitchen. I put a 24mm motor mount and will use 1/8” x 3” x 5” basswood pieces for fins in the interlocking triangle configuration.

 

[jhill9693]

Okay, I did it. Cut all edges at 30 degrees via table saw. First fin attached with thin CA, the rest with Titebond II. After watching the BT-5 prototype, I’m really looking forward to seeing this fly!

@Dotini how big does the vent hole need to be at this size?

 

[BABAR]

Okay, I did it. Cut all edges at 30 degrees via table saw. First fin attached with thin CA, the rest with Titebond II. After watching the BT-5 prototype, I’m really looking forward to seeing this fly!

@Dotini how big does the vent hole need to be at this size?

Can you run the lug in between the fins?

given length of rocket, you may need a second lug around the CG.

 

[BABAR]

Interesting.

Just spitballing here (haven’t read any of the literature) but wouldn’t the maximum effect be obtained by running the protrusions parallel to the body tube?

It’s a matter of efficiency. I love modifications that do two things at the same time. This covers the spirals and simultaneously breaks the boundary layer. Plus the Kevlar might stick better in the grooves than to the smooth rocket surface, and the wrap around will probably also help adhesion vs a lengthwise strip.

Law of unintended consequences (although certainly minimal and likely Undetectable.). This creates a very shallow “air screw” which may result in a small (likely negligible) forward or backward force (relative to long axis of rocket). Although, come to think about it, while likely minimal on descent, it may INDUCE a certain amount of spin on ASCENT. this could be a plus OR a minus, but you’d probably want to induce a spin that would compliment the spin direction the curved fins will generate.

an option, dye the Kevlar a color that contrasts with the rocket tube color, and attach it with clear white glue. Do NOT use CA, I believe it makes Kevlar brittle.

 

[Dotini]

Okay, I did it. Cut all edges at 30 degrees via table saw. First fin attached with thin CA, the rest with Titebond II. After watching the BT-5 prototype, I’m really looking forward to seeing this fly!

@Dotini how big does the vent hole need to be at this size?

Congratulations on your new HSR model!

I'd make the vent hole 1/4" and place it as close to the base of the nosecone as possible. I agree with @BABAR that a 2nd lug would be advisable.

 

[jhill9693]

Can you run the lug in between the fins?

given length of rocket, you may need a second lug around the CG.

Yes, agreed.

 

[Dotini]

Mock-up of Mississippi riverboat inspired paddle wheel model. A pseudo ring of intra-fin stiffeners will be employed to prevent the 3/32 balsa fin segments from snapping like twigs.

 

[neil_w]

It’s a matter of efficiency. I love modifications that do two things at the same time. This covers the spirals and simultaneously breaks the boundary layer. Plus the Kevlar might stick better in the grooves than to the smooth rocket surface, and the wrap around will probably also help adhesion vs a lengthwise strip.

The issue is whether the spiral orientation creates enough friction to measurably increase the magnus force. It might or might not. If the objective were strictly to test that particular effect, then pure longitudinal protrusions would be a better choice. If the object is to try something that *might* increase the Magnus effect but looks cool either way, then mission accomplished.

Although, come to think about it, while likely minimal on descent, it may INDUCE a certain amount of spin on ASCENT.

I really doubt that'll be enough to induce spin on ascent. The effect of crosswind on the paddlewheel fin can is likely to be stronger, and that is working in the opposite direction.

 

[lakeroadster]

The best way to see if a new concept helps, is to only change one thing at a time. You may fly this and see it spins on the way up. Is it because of the spiral wrap, or because a fin isn't exactly straight? You'll never know.
One thing I do know... that rocket looks cool.

I do have a question @Dotini . What are the items I circled in orange in the photo you posted?

 

[Dotini]

The best way to see if a new concept helps, is to only change one thing at a time. You may fly this and see it spins on the way up. Is it because of the spiral wrap, or because a fin isn't exactly straight? You'll never know.
One thing I do know... that rocket looks cool.

I do have a question @Dotini . What are the items I circled in orange in the photo you posted?

View attachment 536265

One of those things (upper left) is a bucking bar for a massive Boeing 757 wing assembly riveting tool once in daily use at the Renton plant. The others are hand held bucking bars commonly used in the factory. The round object under the 3-leg table is also a bucking bar. This table itself has a hole in the center to locate the fin can vertically on a planar surface. Here I've been using these heavy steel objects as tooling to locate loose parts during assembly.

 

[lakeroadster]

One of those things (upper left) is a bucking bar for a massive Boeing 757 wing assembly riveting tool once in daily use at the Renton plant. The others are hand held bucking bars commonly used in the factory. The round object under the 3-leg table is also a bucking bar. This table itself has a hole in the center to locate the fin can vertically on a planar surface. Here I've been using these heavy steel objects as tooling to locate loose parts during assembly.

Could you briefly explain what a bucking bar is used for?

 

[Dotini]

Could you briefly explain what a bucking bar is used for?

Sure. A bucking bar is used to install a rivet. More precisely, one side of the rivet is driven by a power tool, and the other side of the rivet is bucked by a strong, heavy metal bar held tight and square against the side of the rivet that is being deformed against the material.

 

[lakeroadster]

Sure. A bucking bar is used to install a rivet. More precisely, one side of the rivet is driven by a power tool, and the other side of the rivet is bucked by a strong, heavy metal bar held tight and square against the side of the rivet that is being deformed against the material.

Awesome! That explains the heavy mass.

Thanks for taking the time to explain.