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neil_w

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Greebles, @neil_w , Greebles.
Nope, my fleet is 100% greeble-free. Not that I have anything against them, just not my thing (or rather: I don't really know how to do them). My decorative crap of choice is pointlessly complex fin/tube/ring arrangements.
 

BABAR

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Nope, my fleet is 100% greeble-free. Not that I have anything against them, just not my thing (or rather: I don't really know how to do them). My decorative crap of choice is pointlessly complex fin/tube/ring arrangements.
One man's crap is another man's gold.
 

Mike Haberer

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Note, the total area of my fins and ring is about 17 square inches. That is about the equivalent area of 4 fins, 2" x 2.13".
The square inches of the fins is relevant to calculating the center of pressure, but not the drag on the rocket. The drag is based on the frontal area going into the airstream. The includes the nose cone and the leading edges of the fins. You have six fins and the entire ring as leading edges, several times the frontal area of a simple 3 fin design.

I have a very draggy rocket where the it flew 213' on a C5, 246' on a C12 and 317' on a D16, all measured with a Fightsketch Mini altimeter. Total impulse did not make a big difference in altitude, drag won the day...
 

Dotini

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The square inches of the fins is relevant to calculating the center of pressure, but not the drag on the rocket. The drag is based on the frontal area going into the airstream. The includes the nose cone and the leading edges of the fins. You have six fins and the entire ring as leading edges, several times the frontal area of a simple 3 fin design.

I have a very draggy rocket where the it flew 213' on a C5, 246' on a C12 and 317' on a D16, all measured with a Fightsketch Mini altimeter. Total impulse did not make a big difference in altitude, drag won the day...
Please don't be too quick on your assumptions, Mike. My ring is only 0.020" in thickness. If my calculations are correct, the ring is 0.188 square inches in frontal area. My fat but rounded edge 1/8" fins are 0.83" in length, so total frontal area for them is 0.623 square inches, giving a total ring + fin frontal area of 0.81 square inches. If that were distributed over 3 1/8" thickness fins, that would require fins of 2.16". Please check my calculations.

But guess what? I possess the technology and the materials, if not the need, to now make my fins .020" in thickness. Just for fun, I will do this on my next model.
 
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BABAR

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Please don't be too quick on your assumptions, Mike. My ring is only 0.020" in thickness. If my calculations are correct, the ring is 0.188 square inches in frontal area. My fat but rounded edge 1/8" fins are 0.83" in length, so total frontal area for them is 0.623 square inches, giving a total ring + fin frontal area of 0.81 square inches. If that were distributed over 3 1/8" thickness fins, that would require fins of 2.16". Please check my calculations.

But guess what? I possess the technology and the materials, if not the need, to now make my fins .020" in thickness. Just for fun, I will do this on my next model.
I am far from an expert, but it is a bit more complicated than just the surface area of the fins and the thickness of the fins and ring.

don’t get me wrong, thinner is generally better, but I don’t think the drag reduction between thin and REALLY thin fins (or rings) is directly proportional to the change of thickness.

your design is elegant (and cool), but may have another disadvantage. The 6 fins in combination with the ring divides the air stream into “channels” each bordered by a segment of the ring, two fins, and a segment of the body tube. This may also create an unintended “tube fin” effect. Tube fins definitely work, but the are known to be generally less efficient than regular fins (reference Larry Brand’s page for detail, especially


my biggest concerns for your design are two fold, both based on my experience with BackSliders AND Horizontal Spin.

first and most definite, pure BackSliders when they work come in at a mild to moderately steep glide. The effect on flight duration is not the issue (nobody expects these to be competition duration models and you and I both are fans of small field recoveries, we don’t WANT rockets if any sort to have a long “hang time”, we want them back safe, sound, and NEARBY!). What IS an issue with these is that in the process of descent hey develop a significant linear forward trajectory, TWO of my stable of my THREE SUCCESSFUL BackSliders (hey, I only built 4;)) have been arrow straight on descent, I would estimate their lateral travel was about equal to their apogee altitude, so they were moving laterally (literally speaking “Backward “) as fast as they were descending. This is gonna literally impact on you fin can, and in this case the “Ring” won’t help as much as it does with HORIZONTAL spin, although it may help simply because a ring with 6 fins will certainly be tougher Than one or two fins alone. This IS a solvable problem, one solution being Asymmetric fin attachment which I believe I have proved works well, at the cost of at lest a minimally squirrelly but completely same boost (which if you are like me, is no cost at all:bravo:!)

the SECOND one, which I will post in more detail separately, is that unfortunately I think PURE UNASSISTED BackSlide (no streamer or other physical rocket configuration change at apogee, just a forward eccentric port ejection charge which transiently “stalls” controlled Barrowman flight Trajectory) is not 100% reliable. While nothing else is 100% either, my experience has been 80%, and the 20% failures have been I believe random. Meaning I am not convinced it is truly fixable. I hope I am wrong. I will explain in a separate post. As opposed to reliability of traditional methods of chutes and streamers, which I expect experienced rocketeers would put at may 95%, and of the 5% failure rate I’d guess experienced HONEST rocketeers would attribute 95% to operator error (poor packing) and most of the rest to equipment failure (broken shock cord, bad ejection charge, electronic Gremlin) with a very small percentage (if any) being truly random. I think @Steve Shannon would agree, in the vast majority of chute recovery failures, the Flyer messed up. For parachute and presumably streamer rockets, ballistic recoveries should be close to a “never” event.

so earlier I may have “dissed” your chute or streamer idea, now I think it is a good idea, first with a full chute to test stability of the rocket on boost (although your design easily passes my “mindsim” analysis, it’ll fly straight and true as long as you have a decent thrust to weight ratio and appropriate delay.). Second, I think a small streamer may indeed be required to get to 100% (or at least practically 100%, which is where a non experimental rocket must be. In other words, I can’t recommend to friends or a kit manufacturer to build a design that lawn darts 80% of the time, the Estes Cosmos Mariner, Estes MIRV, and the Holverson foamy Swinger aside:angiefavorite:.)

on the good side, the exception of one of my four models which was unstable on boost (for the record, I launch these is isolation, start with small motors, and nobody is within 300 yards), all the other FIRST flights were good.

so looking forward to your flight report!
 
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Dotini

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I am far from an expert, but it is a bit more complicated than just the surface area of the fins and the thickness of the fins and ring.

don’t get me wrong, thinner is generally better, but I don’t think the drag reduction between thin and REALLY thin fins (or rings) is directly proportional to the change of thickness.

your design is elegant (and cool), but may have another disadvantage. The 6 fins in combination with the ring divides the air stream into “channels” each bordered by a segment of the ring, two fins, and a segment of the body tube. This may also create an unintended “tube fin” effect. Tube fins definitely work, but the are known to be generally less efficient than regular fins (reference Larry Brand’s page for detail, especially


my biggest concerns for your design are two fold, both based on my experience with BackSliders AND Horizontal Spin.

first and most definite, pure BackSliders when they work come in at a mild to moderately steep glide. The effect on flight duration is not the issue (nobody expects these to be competition duration models and you and I both are fans of small field recoveries, we don’t WANT rockets if any sort to have a long “hang time”, we want them back safe, sound, and NEARBY!). What IS an issue with these is that in the process of descent hey develop a significant linear forward trajectory, TWO of my stable of my THREE SUCCESSFUL BackSliders (hey, I only built 4;)) have been arrow straight on descent, I would estimate their lateral travel was about equal to their apogee altitude, so they were moving laterally (literally speaking “Backward “) as fast as they were descending. This is gonna literally impact on you fin can, and in this case the “Ring” won’t help as much as it does with HORIZONTAL spin, although it may help simply because a ring with 6 fins will certainly be tougher Than one or two fins alone. This IS a solvable problem, one solution being Asymmetric fin attachment which I believe I have proved works well, at the cost of at lest a minimally squirrelly but completely same boost (which if you are like me, is no cost at all:bravo:!)

the SECOND one, which I will post in more detail separately, is that unfortunately I think PURE UNASSISTED BackSlide (no streamer or other physical rocket configuration change at apogee, just a forward eccentric port ejection charge which transiently “stalls” controlled Barrowman flight Trajectory) is not 100% reliable. While nothing else is 100% either, my experience has been 80%, and the 20% failures have been I believe random. Meaning I am not convinced it is truly fixable. I hope I am wrong. I will explain in a separate post. As opposed to reliability of traditional methods of chutes and streamers, which I expect experienced rocketeers would put at may 95%, and of the 5% failure rate I’d guess experienced HONEST rocketeers would attribute 95% to operator error (poor packing) and most of the rest to equipment failure (broken shock cord, bad ejection charge, electronic Gremlin) with a very small percentage (if any) being truly random. I think @Steve Shannon would agree, in the vast majority of chute recovery failures, the Flyer messed up. For parachute and presumably streamer rockets, ballistic recoveries should be close to a “never” event.

so earlier I may have “dissed” your chute or streamer idea, now I think it is a good idea, first with a full chute to test stability of the rocket on boost (although your design easily passes my “mindsim” analysis, it’ll fly straight and true as long as you have a decent thrust to weight ratio and appropriate delay.). Second, I think a small streamer may indeed be required to get to 100% (or at least practically 100%, which is where a non experimental rocket must be. In other words, I can’t recommend to friends or a kit manufacturer to build a design that lawn darts 80% of the time (the Estes Cosmos Mariner and the Holverson foamy Swinger aside:angiefavorite:.)

on the good side, the exception of one of my four models which was unstable on boost (for the record, I launch these is isolation, start with small motors, and nobody is within 300 yards), all the other FIRST flights were good.

so looking forward to your flight report!
Thanks for your extensive post! Altho ready to launch, my flight and report will have to wait, as my able assistant is vacationing in Montana until nearly Father's Day.
 

BABAR

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Hoping to see a flight report soon!
 

Dotini

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Hoping to see a flight report soon!
First launches of the 6th Observable and freshly minted Magnus X-4 are scheduled for Saturday morning, reports to follow.

Sneak preview of Magnus X-4. Patriotic Sharpie blue tube accents for 4th of July family party on Camano Island.
DSC00270.jpg

Model weighs 0.74 oz with 1/2 A3-2T, is 29" length, BT-5, and built in very close accord with Alway design (excepting the 4 "curly" fins).
 
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BABAR

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First launches of the 6th Observable and freshly minted Magnus X-4 are scheduled for Saturday morning, reports to follow.

Sneak preview of Magnus X-4. Patriotic Sharpie blue tube accents for 4th of July family party on Camano Island.
View attachment 470231
Model weighs 0.74 oz with 1/2 A3-2T, is 29" length and built in very close accord with Alway design (excepting the 4 "curly" fins).
Very good use of color for nice pattern without much weight.

so you downsized to BT-5. Did you scale the fin area down as well?

what’s the reinforcement on the fins?

my predictions

1. horizontal? Check

2. Glide? Not sure, I am guessing no, just horizontal.

3. Magnus? Yes, I think your long graceful experience curved fins generate much higher RPMS than may “Shirley Temple” short curls. I think you will get a great lateral Magnus deviation, a combination of your design with the SuperRoc length.

4. Survivability? Not sure. If pure horizontal spin, fin impact will be RPM kinetic energy plus 1/2 mass x (vertical velocity ) squared. If it GLIDES, It will be the former PLUS the effect of a 90 degree force 1/2 mass (longitudinal [glide] velocity) squared. IIRC correctly, @PeterAlway. Models that spun did so only transiently, they didn’t make it all the way to the ground, so you are quite literally breaking new ground!

hope for a soft grassy landing spot!

good luck!
 

BABAR

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Is your CG with a spent engine casing in line with the Alway report?
 

Dotini

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Very good use of color for nice pattern without much weight.

so you downsized to BT-5. Did you scale the fin area down as well?

what’s the reinforcement on the fins?

my predictions

1. horizontal? Check

2. Glide? Not sure, I am guessing no, just horizontal.

3. Magnus? Yes, I think your long graceful experience curved fins generate much higher RPMS than may “Shirley Temple” short curls. I think you will get a great lateral Magnus deviation, a combination of your design with the SuperRoc length.

4. Survivability? Not sure. If pure horizontal spin, fin impact will be RPM kinetic energy plus 1/2 mass x (vertical velocity ) squared. If it GLIDES, It will be the former PLUS the effect of a 90 degree force 1/2 mass (longitudinal [glide] velocity) squared. IIRC correctly, @PeterAlway. Models that spun did so only transiently, they didn’t make it all the way to the ground, so you are quite literally breaking new ground!

hope for a soft grassy landing spot!

good luck!
For a ~38" BT-20 model, Alway gives (3) 1"x 1" or (3) 1.5" x 1.5" fins, with CG 28" - 30" from the nose tip, or 7" - 9" from end of main tube.
My 29" BT-5 model has (4) 1.2" x 1.2" fins, with CG 21" from short nose cone, or 7.5" from end of main tube.

I do not expect good durability with this particular model, as I greatly dislike the superglue I'm using to attach the fins and I currently have no brace or ring to reinforce the fins. I expect the very light weight of this model to help durability of the fins once I get them attached properly.

Subsequent build editions (if any) of the X-4 (BT-5) Magnus rocket will have a different fin adhesive system with big fillets, and if required, some additional reinforcement. Also it will receive refined visibility accents, and a longer nose cone.
 

BABAR

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Looks like you have a motor hook, which is good. My SQuirt just succumbed to failed motor retention. I just used tape around the back of the motor and a section of body tube. Usually works, but do to venting system on both horizontal spin and Back Slider, I suspect the pressures are very high.
 

Dotini

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Looks like you have a motor hook, which is good. My SQuirt just succumbed to failed motor retention. I just used tape around the back of the motor and a section of body tube. Usually works, but do to venting system on both horizontal spin and Back Slider, I suspect the pressures are very high.
No, no motor hook. I will apply masking tape to the motor for a snug fit inside the tube, then black tape the motor to the outside of the tube, which will be protected by yet another piece of (heat resistant mylar) tape. This will all add up to a small amount of weight, but less than a steel hook.
 

BABAR

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No, no motor hook. I will apply masking tape to the motor for a snug fit inside the tube, then black tape the motor to the outside of the tube, which will be protected by yet another piece of (heat resistant mylar) tape. This will all add up to a small amount of weight, but less than a steel hook.
You should be fine.

suggestion.
Sounds like you have a short extension of your motor mount below the fins, which for no-hook designs is good.

BEFORE you put the motor in, take a piece of cellophane or Mylar tape and do a wrap around that protruding end. Do the wrap in the OPPOSITE DIRECTION that you plan on doing the post motor placement wrap. I tend to use Mylar cause it looks pretty, but if you have a nice paint job cellophane works just as well and the paint color shows through

why? If you don’t do this, when you do the external tape motor wrap, there is a good chance that when you peel it OFF after the flight, it will take either paint (bad) or outer layer of body tube (really bad) with it.

why opposite direction? If you go the SAME direction it is possible when you pull the tape you used to wrap the motor in place it will pull up the underlying tape with it, since both are wrapped in the same direction.

I do suspect the optimal solution to the fin breaking problem with your design is an integrated 3D Fin and Can construction, where the fins are durable and flexible enough to “bounce” but not break on landing, but stiff enough that they function fine as fins on boost.

or your Brace option.

or the mixed curvy fin with outside ring construction.

I don’t have and am not planning to get a 3D printer, I don’t know if @cwbullet or any other other guys or gals on this forum with such devices would find this worth playing with.
 

Dotini

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You should be fine.

suggestion.
Sounds like you have a short extension of your motor mount below the fins, which for no-hook designs is good.

BEFORE you put the motor in, take a piece of cellophane or Mylar tape and do a wrap around that protruding end. Do the wrap in the OPPOSITE DIRECTION that you plan on doing the post motor placement wrap. I tend to use Mylar cause it looks pretty, but if you have a nice paint job cellophane works just as well and the paint color shows through

why? If you don’t do this, when you do the external tape motor wrap, there is a good chance that when you peel it OFF after the flight, it will take either paint (bad) or outer layer of body tube (really bad) with it.

why opposite direction? If you go the SAME direction it is possible when you pull the tape you used to wrap the motor in place it will pull up the underlying tape with it, since both are wrapped in the same direction.

I do suspect the optimal solution to the fin breaking problem with your design is an integrated 3D Fin and Can construction, where the fins are durable and flexible enough to “bounce” but not break on landing, but stiff enough that they function fine as fins on boost.

or your Brace option.

or the mixed curvy fin with outside ring construction.

I don’t have and am not planning to get a 3D printer, I don’t know if @cwbullet or any other other guys or gals on this forum with such devices would find this worth playing with.
I've ordered some styrene T sections, 1/8 x 1/8 x 14". These are of .047 wall thickness. I will try using these to mount a set of fins, eliminating the need for root fillets on a very thin fin. I will try using Foam Tac adhesive for PETG fin (.020 flat or curved) to styrene T section to paper tube.
 

Dotini

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Not too high. Six fins and the ring tail will be pretty draggy. I mocked up a quick equivalent in Rocksim. 130' with an optimal 1.8 sec delay. Stability margin is 5.67 with engine loaded, seriously overstable. Don't fly this in windy conditions.

Let us know what you actually get. Rocksim doesn't do the best sims with ring tails and tube fins....
Actual achieved altitude for the 6th Observable - flown this morning for the first time - was 492'.

Very good use of color for nice pattern without much weight.

so you downsized to BT-5. Did you scale the fin area down as well?

what’s the reinforcement on the fins?

my predictions

1. horizontal? Check

2. Glide? Not sure, I am guessing no, just horizontal.

3. Magnus? Yes, I think your long graceful experience curved fins generate much higher RPMS than may “Shirley Temple” short curls. I think you will get a great lateral Magnus deviation, a combination of your design with the SuperRoc length.

4. Survivability? Not sure. If pure horizontal spin, fin impact will be RPM kinetic energy plus 1/2 mass x (vertical velocity ) squared. If it GLIDES, It will be the former PLUS the effect of a 90 degree force 1/2 mass (longitudinal [glide] velocity) squared. IIRC correctly, @PeterAlway. Models that spun did so only transiently, they didn’t make it all the way to the ground, so you are quite literally breaking new ground!

hope for a soft grassy landing spot!

good luck!
Magnus X-4 was flown twice his morning, once on 1/2 A3-2T and once on 1/4 A3-3T.
Both flights were a great success in every respect. Hopefully video tomorrow in the Horizontal Spin with Magnus Effect thread.
 
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Dotini

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Super!
grass field?
Yes, Dahl playfield is mostly grass, 500 x 500 being 4 baseball fields with dirt infields. An adjoining 500 x 300 grass field contains the hazardous concrete skateboard facility. There is an Osprey nest with 4 occupants atop one of the tall lamp standards surrounding the field. After we launched the thunderous C-11 high into the vapor, a notorious local lady dogwalker asked us to move our launch pad a bit further from the Osprey nest. Naturally, being responsible citizens and representatives of model rocketry and NAR, we politely complied with her request. :rolleyes:
 

BABAR

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Actual achieved altitude for the 6th Observable - flown this morning for the first time - was 492'.


Magnus X-4 was flown twice his morning, once on 1/2 A3-2T and once on 1/4 A3-3T.
Both flights were a great success in every respect. Hopefully video tomorrow in the Horizontal Spin with Magnus Effect thread.
So, describe the descent. Was it more a glide, tail first along the longitudinal axis, or a horizontal fall with or without lateral Magnus effect?

i can tell you that true Back Slide is unreal to watch, it just looks like you are violating the rules of physics. With one exception my successful Back Slides have come down just about arrow straight (which is something I DON’T Think you usually see with REAL gliders, caveat being most experienced non-RC Rocket Gliders intentionally put a bit of weight on a wing or something to make the come down in gentle circular trajectory to keep them on the field.)

the other “unreal” rocket behaviors I have see are my Air Brakes, when they work well with no rotation or “toddling” it looks like someone is lowering them from the sky on a pair o balanced wires. They drift with the wind but they look like a bad sci if special effect scene, they are just too stable to be real, even though they ARE real,
 

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So, describe the descent. Was it more a glide, tail first along the longitudinal axis, or a horizontal fall with or without lateral Magnus effect?

i can tell you that true Back Slide is unreal to watch, it just looks like you are violating the rules of physics. With one exception my successful Back Slides have come down just about arrow straight (which is something I DON’T Think you usually see with REAL gliders, caveat being most experienced non-RC Rocket Gliders intentionally put a bit of weight on a wing or something to make the come down in gentle circular trajectory to keep them on the field.)
Thanks for your question, although I don't want to get too far ahead of the definitive video(s) which hopefully will be posted in the "Horizontal Spin with Magnus Effect" thread tomorrow.

To my recollection, the two flights differed somewhat. On first flight with the more powerful (hah!) 1/2A motor, the rocket descended absolutely 100% horizontal, tail first, describing very long, slow spirals, but spinning furiously. Eventually, it deigned to delicately alight to Earth about 100' away, much as a feather would, at 0.67 oz. The 2nd flight on the 1/4A motor involved less in the way of spiraling, but was also exactly horizontal with mad spin. It came to Earth bare feet from the pad. (note: wind 3mph). This particular flight firmly establishes (for me) that horizontal spin recovery does not necessarily lead to lost rockets, and gives me great confidence to fly it in my brother's backyard 4th of July party!
 

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A new iteration of the 6th Observable is in work, this one with larger BT-60 fuselage and the same 3" ring fin and 24 mm motor mount. There are now only four fins instead of six, and in place of balsa they are assemblies of polystyrene T-sections and flat PETG plastic, 0.020" thickness. It has a payload section for the altimeter, and recovery is by conventional parachute. This will be flown on C11 and D12 motors, and I can barely wait for the smoke and thunder!
DSC00315.jpg


DSC00314.jpg
 

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Nice. I’d start a new thread
 

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Thanks for posting the specifics on this rocket. I've been goofing around trying to get a realistic flight simulation of a rocket with a ring fin in Open Rocket. If I build a quick model of your 6th Observable in Open Rocket and then run a flight simulation, the only way I can get the nearly 500 ft. altitude you posted is to model the rocket without the ring fin.

Which flies in the face (no pun intended) to an article that was written up in an Apogee Peak of Flight Newsletter Issue 27

But I'm guessing about some things... a lot of things actually. Could you help me to clarify the design?
  1. BT-55 Body Tube 1.325 OD x 1.28 ID x 30.875 long
  2. Ellipsoidal Nose Cone 4-5/8" long plastic. No ballast in the nose cone, correct?
  3. Fin Size: 1.5 Root length, 1.5 Tip length, 1" high, .18 Thick - Is the leading edge square, rounded or airfoiled?
  4. Motor Mount Tube: BT-50 .976 OD x .95 ID x 2.75 long - Does this hang out the back of the body tube 0.50"?
  5. (2) centering rings: 1/4" thick
  6. Launch lug: .176 OD x 0.15 ID x 1.25 Long
  7. 18" parachute
  8. Overall length = 37"
  9. mass, including C11-3 motor, 5.07 ounces
  10. are the avionics attached to the nose cone
  11. how thick is the ring fin? What is it's O.D. and Length?
 

Dotini

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Thanks for posting the specifics on this rocket. I've been goofing around trying to get a realistic flight simulation of a rocket with a ring fin in Open Rocket. If I build a quick model of your 6th Observable in Open Rocket and then run a flight simulation, the only way I can get the nearly 500 ft. altitude you posted is to model the rocket without the ring fin.

Which flies in the face (no pun intended) to an article that was written up in an Apogee Peak of Flight Newsletter Issue 27

But I'm guessing about some things... a lot of things actually. Could you help me to clarify the design?
  1. BT-55 Body Tube 1.325 OD x 1.28 ID x 30.875 long 34.375 long
  2. Ellipsoidal Nose Cone 4-5/8" long plastic. Balsa nose cone, 2.25. No ballast in the nose cone, correct?
  3. Fin Size: 1.5 1.0 Root length, 1.5 1.0 Tip length, 1 0.9 " high, .18 0.125 Thick - Is the leading edge square, rounded or airfoiled?
  4. Motor Mount Tube: BT-50 .976 OD x .95 ID x 2.75 long - Does this hang out the back of the body tube 0.50 0.375"?
  5. (2) centering rings: 1/4" thick 2 plywood centering rings, about 0.112".
  6. Launch lug: .176 OD x 0.15 ID x 1.25 Long Two launch lugs, .233 x 1" and .233 x .25", ID about .210"
  7. 18" parachute 15" parachute.
  8. Overall length = 37"
  9. mass, including C11-3 motor, 5.07 4.80 ounces, plus a few scraps of black tape and wadding
  10. are the avionics attached to the nose cone Yes. There is 1/4" hole punched in the payload bay.
  11. how thick is the ring fin? 0.020" What is it's O.D. and Length? 3.0" x 1.25"
I'm very happy to help get improved and more realistic sims of my rocket flight. :)
I have struck out wrong answers and bolded correct answers within your quote. Check for any edits.
 
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Dotini

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If I build a quick model of your 6th Observable in Open Rocket and then run a flight simulation, the only way I can get the nearly 500 ft. altitude you posted is to model the rocket without the ring fin.

Which flies in the face (no pun intended) to an article that was written up in an Apogee Peak of Flight Newsletter Issue 27
Heh heh! Now you are beginning to understand why I call it the 6th Observable!! We are dealing with a phenomenon that is not entirely within the bounds of current human knowledge and understanding.

On the other hand, since I have made the ring fin clear and near-invisible, you are free to ignore it in your material calculations. :rolleyes:
 

Dotini

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Conjecture: This ring fin gathers up detached or turbulent flow, reconnecting it as more laminar flow, thus greatly reducing drag.
 

lakeroadster

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Conjecture: This ring fin gathers up detached or turbulent flow, reconnecting it as more laminar flow, thus greatly reducing drag.
If that were true... most real finned rockets would have ring fins.

My theory as to why the simulation shows a lower altitude than your altimeter showed during actual flights is that the actual motor thrust is higher than the thrust used in Open Rocket. If you look at the spec's, motor thrusts can vary by a pretty wide margin.
 

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