Horizontal Spin Recovery - with Magnus Effect?

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Model in work of new HSR equipped with PETG shipping tube fins reinforced with small PETG ring tail. The goal is improved durability upon landing.

DSC00831.jpg

Since in my experience painting embrittles this plastic, the fins will be skinned in sticker paper, already colored in gloss black and fluorescent yellow.
 
Model in work of new HSR equipped with PETG shipping tube fins reinforced with small PETG ring tail. The goal is improved durability upon landing.

View attachment 563859

Since in my experience painting embrittles this plastic, the fins will be skinned in sticker paper, already colored in gloss black and fluorescent yellow.


Those clear fins look cool as is..
 
Those clear fins look cool as is..
Yes! There may be an unadorned primal geometry with the 3 curved surfaces joined by rings that even Archimedes might have enjoyed. But I think skins of sticker paper would improve stiffness and durability of the empennage (and fuselage), but also aid in visual observation, an area where the old man needs all the help I can get.
 
Yes! There may be an unadorned primal geometry with the 3 curved surfaces joined by rings that even Archimedes might have enjoyed. But I think skins of sticker paper would improve stiffness and durability of the empennage (and fuselage), but also aid in visual observation, an area where the old man needs all the help I can get.

But you won't be able to see Wonder Woman... ;)

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Two new fin cans are under construction in which the fin roots are reinforced by gussets, or doublers, made from Apogee product's BT-50 tube sleeve.

DSC00835.jpg
Fin is captured and aligned by slotted sleeve rings, tacked in place with CA. Rings are fastened with wood glue. Next step, epoxy fillets.
 
When a fin breaks off... where does that usually happen?
Is it a failure of:​
  • the fin material,
  • the glue joint, or,
  • the body tube outer skin?
Have you tried drilling a series of small holes through the plastic fins to allow the epoxy to flow through those holes to create "epoxy rivets" to increase the strength of the joint?

Or maybe try the technique shown below where 50% of the body tube is sliced to create body tube fillets to hold the fin? Or maybe try both where you use a hole through the fin at each slice?

TRF-161479-16-1.jpg
 
  • the fin material,
  • the glue joint, or,
  • the body tube outer skin?
Over the course of over a hundred HSR launches I've experienced all these failures. The PETG material eventually fails by what I believe is paint/solvent induced embrittlement and cracking, so I no longer paint this material. Otherwise, no fin material failure in PETG.

The glue joint to the fin seldom has any problem. I've used CA, epoxy and original Gorilla glue with PETG fins. Sometimes I use an angle or tee section as part of the fin root design. Using styrene in this part has proven to play a role in failures.

Failure by delamination of the tube, usually starting at one end of the fin root, the problem I'm addressing in this experiment, is addressed by means of doubling the skin thickness at each fin root end. They also align the fins and avoid the need for a fin alignment jig or other tool. Exploiting this handy aftermarket product seems like a good technique to add to the pile.DSC00833.jpg
Fins are tacked with CA while aligned with slotted rings, then rings are removed and replaced with white glue.

After fillets, coupler and paint for the paper tube is added, total weight of the fin can should be under 1/2 ounce.
 
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Over the course of over a hundred HSR launches I've experienced all these failures. The PETG material eventually fails by what I believe is paint/solvent induced embrittlement and cracking, so I no longer paint this material. Otherwise, no fin material failure in PETG.

The glue joint to the fin seldom has any problem. I've used CA, epoxy and original Gorilla glue with PETG fins. Sometimes I use an angle or tee section as part of the fin root design. Using styrene in this part has proven to play a role in failures.

Failure by delamination of the tube, usually starting at one end of the fin root, the problem I'm addressing in this experiment, is addressed by means of doubling the skin thickness at each fin root end. They also align the fins and avoid the need for a fin alignment jig or other tool. Exploiting this handy aftermarket product seems like a good technique to add to the pile.View attachment 568962
Fins are tacked with CA while aligned with slotted rings, then rings are removed and replaced with white glue.

After fillets, coupler and paint for the paper tube is added, total weight of the fin can should be under 1/2 ounce.

I wonder... :dontknow: is the CA making the fins brittle, thus contributing to premature failure? I'm not a fan of CA.. it seems to create as many problems as it solves. About the only thing I use CA for is sealing the exposed edges of papered fins.
 
I wonder... :dontknow: is the CA making the fins brittle, thus contributing to premature failure? I'm not a fan of CA.. it seems to create as many problems as it solves. About the only thing I use CA for is sealing the exposed edges of papered fins.
I agree it's possible, so I will now only use CA for tacking (and edge sealing).
 
Fin can complete less paint on tube only. We're hoping to be at 60 Acres about Thursday.
DSC00842.jpg
Fin can weighs 0.35 oz, has 15.7 square inches of fin area.

For a long time I've been charmed by the notion of building the "bulletproof, sure-fire, can't miss, never fail" fin system. Is this it? Probably not, but looks pretty good for a BT-50. I'll be making two of these for long-term testing starting next week.
 
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In an hour or so I'll be on the road to 60 Acres, with several experiments planned. The first tests will be with the ejection ports located very near to the CG when the motor is expended. Two different models will be participating.

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BT-50 model with altimeter weighs about 3.5 oz depending on motor. All sections are replaceable and overall length is adjustable in the field.
 
Very interesting results have been obtained from this morning's launches at 60 Acres in the effort to test ejection ports located behind an altimeter bay located just ahead of the CG.

The rocket depicted above in post #582 had three consecutive failures (ballistic), while the rocket depicted below had three consecutive 100% successes, spiraling very nicely. No fin was damaged.

DSC00849.jpg
Above successful model is 51" long, weighs 4.7 oz with expended D12-5 as show above. CG is located about 40.5" from tip of nosecone, about 80%. It went a long way, straight up, on a D12-5. No altimeter was aboard during this session.

The model which repeatedly failed, shown in the post above this one, is 47.5" long, with CG 31" from tip of nosecone, about 65%.

Another interesting photo of ejection ports appears to show ejection blast marks seemingly directed forward(!), against the airstream. Note, the transition is immediately forward of the ports, and slightly eclipses the holes.
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Three 3/16" ports are used on this model.
 
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Congrats on the successes, and hoping lessons learned on the less than optimal flights.

I have questions.

what has been the most reliable port placement? Forward, mid, rear?

if it is as far forward as possible, has this even been a failure mode? (has the side port “puff” ever convincingly “bent” the rocket?)

why the transitions? Seems like a wider body tube would increase Cross-sectional Lateral Area (CLA, or Cardboard Cut Out surface) with minimal if any increase in net boost and coast drag compared with transitions. i am NOT sure how it would affect stability. In any case, greater lateral surface area should increase drag in DESCENT, which IS desirable. the Greater diameter would also increase Magnus effect (i theeeeenk), although that seems to be a “coolness” effect which has little cost or benefit to recovery.

has too large a diameter full length tube ever caused a “puff” failure due to “too much volume” to pressurize to achieve an effective destabilizing “puff.”? This failure mode is well known in standard rockets (too much volume for ejection charge to blow the laundry), but the standard solution of a “stuffer tube” or “chimney” may cause too much CG shift for HSR.

Is there an optimal fin chord to hemispan ratio? Per surface area wider span fins are definitely more efficient, but shorter spans should be more robust, especially if longer chord.

apologize if I have missed it, but have all your flights been STABLE? I am wondering if you could use shorter fins which might be more durable. Put another way, have you explored the minimum diameter of fins required to routinely achieve HSR? Your fins are dual role (pun unintended but interesting), on boost for stability, at ejection to initiate horizontal spin. At least in one aspect I expect there is a limitation from the boost stability standpoint, the shorter the fins, the longer the rocket needs to be to achieve boost stability. As you approach “SupeRoc” extreme length to diameter ratios you get structural failure issues.

My Mind Sim keeps predicting the simplest most reliable HSR would be one
1. with the highest structurally sound length to diameter ratio (not as extreme as required for Back Spin) ,

2. greatest Diameter the chosen rocket motor can handle (so go as long as you can and then within max take off weight as WIDE as you can) with

3. the smallest diameter fins that achieve both stable boost AND initiation of HSR.
 
Congrats on the successes, and hoping lessons learned on the less than optimal flights.

I have questions.

what has been the most reliable port placement? Forward, mid, rear?

if it is as far forward as possible, has this even been a failure mode? (has the side port “puff” ever convincingly “bent” the rocket?)

It's all a work in progress with port placement. Looking back, my most reliable designs have been the BT-5 and BT-20 diameters, particularly the X-8, with dozens of flights and zero failures. It's very light with disproportionately large fins which have luckily never broken. These two models have a forward port just behind the nosecone. I'm now building in larger sizes to make more visible and carry an altimeter.

We have determined that four 3/16" diameter ports spaced circularly at the same station line on a BT-50 confer a definite weakness in that section of the tube. We won't be doing that again.

why the transitions? Seems like a wider body tube would increase Cross-sectional Lateral Area (CLA, or Cardboard Cut Out surface) with minimal if any increase in net boost and coast drag compared with transitions. i am NOT sure how it would affect stability. In any case, greater lateral surface area should increase drag in DESCENT, which IS desirable. the Greater diameter would also increase Magnus effect (i theeeeenk), although that seems to be a “coolness” effect which has little cost or benefit to recovery.
has too large a diameter full length tube ever caused a “puff” failure due to “too much volume” to pressurize to achieve an effective destabilizing “puff.”? This failure mode is well known in standard rockets (too much volume for ejection charge to blow the laundry), but the standard solution of a “stuffer tube” or “chimney” may cause too much CG shift for HSR.
The transitions serve a dual, even triple purpose to us. Firstly, to replace a major length of BT-60 tube with a transition and a BT-50 or BT-20 tube of the same length results in a measurably lighter model. Secondly, they form a bulkhead which can protect both the ports behind or any cargo such an altimeter in front of it. Nextly, and most importantly, we feel the Magnus effect is enhanced resulting in the wondrous spiraling effect on the descent, keeping the landing nearer to the pad. Also, we are very concerned with the strength and reliability of the ejection event, so wish to reduce internal volume as well as use 24mm motors in lieu of the 18mm.

Is there an optimal fin chord to hemispan ratio? Per surface area wider span fins are definitely more efficient, but shorter spans should be more robust, especially if longer chord.

Your astute questions make you a highly desirable correspondent!

The ratios you speak of are of considerable interest to me. Each of my designs considers this issue both in practical and philosophical ways. There are trade-offs. My next build will incorporate the Golden Ratio in the fin design, believe it or not.

apologize if I have missed it, but have all your flights been STABLE? I am wondering if you could use shorter fins which might be more durable. Put another way, have you explored the minimum diameter of fins required to routinely achieve HSR? Your fins are dual role (pun unintended but interesting), on boost for stability, at ejection to initiate horizontal spin. At least in one aspect I expect there is a limitation from the boost stability standpoint, the shorter the fins, the longer the rocket needs to be to achieve boost stability. As you approach “SupeRoc” extreme length to diameter ratios you get structural failure issues.

My Mind Sim keeps predicting the simplest most reliable HSR would be one
1. with the highest structurally sound length to diameter ratio (not as extreme as required for Back Spin) ,

2. greatest Diameter the chosen rocket motor can handle (so go as long as you can and then within max take off weight as WIDE as you can) with

3. the smallest diameter fins that achieve both stable boost AND initiation of HSR.

Instability with my models does not seem to be an issue at all. Today we had steady winds 7 mph gusting to over 10. The only rocket which appeared to head into the wind (weathercock) was the one of post #582. The model of post #584 went up straight as a laser. We made many other flights this morning in addition to those pertaining to the subject models. We are exploring length to diameter ratios between 40 and 50 to one for HSR. Some of our models with larger fins areas spin to to 420 rpm. Those with smaller fin areas don't spin as rapidly. The faster the spin, the greater the Magnus effect, we think.

So far, the simplest and most reliable HSR I know of is the BT-20 Magnus X-8. Launched on C6-5, you get 4 beautiful spirals and land close to the pad. But also limited visibility and no altimeter.
 
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It's all a work in progress with port placement. Looking back, my most reliable designs have been the BT-5 and BT-20 diameters, particularly the X-8, with dozens of flights and zero failures. It's very light with disproportionately large fins which have luckily never broken. These two models have a forward port just behind the nosecone. I'm now building in larger sizes to make more visible and carry an altimeter.

We have determined that four 3/16" diameter ports spaced circularly at the same station line on a BT-50 confer a definite weakness in that section of the tube. We won't be doing that again.


The transitions serve a dual, even triple purpose to us. Firstly, to replace a major length of BT-60 tube with a transition and a BT-50 or BT-20 tube of the same length results in a measurably lighter model. Secondly, they form a bulkhead which can protect both the ports behind or any cargo such an altimeter in front of it. Nextly, and most importantly, we feel the Magnus effect is enhanced resulting in the wondrous spiraling effect on the descent, keeping the landing nearer to the pad. Also, we are very concerned with the strength and reliability of the ejection event, so wish to reduce internal volume as well as use 24mm motors in lieu of the 18mm.



Your astute questions make you a highly desirable correspondent!

The ratios you speak of are of considerable interest to me. Each of my designs considers this issue both in practical and philosophical ways. There are trade-offs. My next build will incorporate the Golden Ratio in the fin design, believe it or not.



Instability with my models does not seem to be an issue at all. Today we had steady winds 7 mph gusting to over 10. The only rocket which appeared to head into the wind (weathercock) was the one of post #582. The model of post #584 went up straight as a laser. We made many other flights this morning in addition to those pertaining to the subject models. We are exploring length to diameter ratios between 40 and 50 to one for HSR. Some of our models with larger fins areas spin to to 420 rpm. Those with smaller fin areas don't spin as rapidly. The faster the spin, the greater the Magnus effect, we think.

So far, the simplest and most reliable HSR I know of is the BT-20 Magnus X-8. Launched on C6-5, you get 4 beautiful spirals and land close to the pad. But also limited visibility and no altimeter.
Regarding
“Instability with my models does not seem to be an issue at all. Today we had steady winds 7 mph gusting to over 10. The only rocket which appeared to head into the wind (weathercock) was the one of post #582.”

If I read that right, you haven’t had any UNSTABLE rockets, and the worst you have had is OVERSTABLE. So from a BOOST stability standpoint, you haven’t reached the lower limit of effective size of fins.

From HSR standpoint, regarding your ballistic or other failures, have any been secondary to insufficient fin size?

So the Transitions are used to
1. Reduce mass

2. Reduce forward diameter, which reduces Magnus forward, so the rear Magnus overwhelms forward Magnus, and induces rotation. And

3. Gives you a bulkhead to protect the altimeter. Altimeters are a problem, on a standard rocket putting their mass as forward as possible is win-win, but for HSR that same forward weight favors ballistic over HSR.

FlightSketch Mini is
  • 3.16g (0.11oz) ready to fly with CR1225 battery (included)
But currently and commonly out of stock.

It does fit inside a BT-20 coupler.

PNut is 0.26 oz. including battery (7.37 grams), also fits inside a BT-20. And is in stock.

$65. http://www.perfectflite.com/pnut.html

Apogee has a vac-formed lightweight BT20 nose cone that weighs 1gram.

Compares with standard BT20 plastic nose cone Weight: 5.9 g (0.21 oz)

Best of all worlds? Pass through transition To allow ejection charge to go through, small forward BT-20 payload bay with altimeter, lightweight cone, puff port just behind payload.

Of course, if it goes ballistic you lose at least the nose cone, maybe altimeter.
 
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From HSR standpoint, regarding your ballistic or other failures, have any been secondary to insufficient fin size?
I don't think so from a ballistic standpoint. But I have made HSR fin cans that don't spin well and become backsliders. Typically these are too small in fin diameter.

Best of all worlds? Pass through transition To allow ejection charge to go through, small forward BT-20 payload bay with altimeter, lightweight cone, puff port just behind payload.

Of course, if it goes ballistic you lose at least the nose cone, maybe altimeter.
I'm in general agreement with your other observations, and will purchase one of these small diameter altimeters and Apogee nose cones as well. Thanks for the tips!

Please revisit the photo of the stained ejection ports. What is going on here? Can the forward aimed ejection discharge from a 24mm motor help ensure a light, rather tail heavy rocket never goes ballistic by stopping it in the sky while still pointed up? If so, that suggests that certain transitions may be suitable to have ejection ports drilled though the outer sloping periphery to vent more or less forward. I'll investigate this and report back.

During the recent launch session we evaluated numerous fin cans for durability. One of several designs emerged worth a second look, a funny looking thing we call the Bank Vault. It emerged from several flights without a scratch and spun well enough to achieve HSR. It's very strong, definitely not too light, has truly massive fin area, and is made of fairly low cost, quickly assembled materials - styrene angles.

DSC00852.jpg

The Bank Vault
 
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I don't think so from a ballistic standpoint. But I have made HSR fin cans that don't spin well and become backsliders. Typically these are too small in fin diameter.


I'm in general agreement with your other observations, and will purchase one of these small diameter altimeters and Apogee nose cones as well. Thanks for the tips!

Please revisit the photo of the stained ejection ports. What is going on here? Can the forward aimed ejection discharge from a 24mm motor help ensure a light, rather tail heavy rocket never goes ballistic by stopping it in the sky while still pointed up? If so, that suggests that certain transitions may be suitable to have ejection ports drilled though the outer sloping periphery to vent more or less forward. I'll investigate this and report back.

During the recent launch session we evaluated numerous fin cans for durability. One of several designs emerged worth a second look, a funny looking thing we call the Bank Vault. It emerged from several flights without a scratch and spun well enough to achieve HSR. It's very strong, definitely not too light, has truly massive fin area, and is made of fairly low cost, quickly assembled materials - styrene angles.

View attachment 571518

The Bank Vault
With a different paint color this could easily become... The Borg Cube

Borg Cube.jpg
 
During the recent launch session we evaluated numerous fin cans for durability. One of several designs emerged worth a second look, a funny looking thing we call the Bank Vault. It emerged from several flights without a scratch and spun well enough to achieve HSR. It's very strong, definitely not too light, has truly massive fin area, and is made of fairly low cost, quickly assembled materials - styrene angles.
That one is genuinely novel and interesting. 👍
 
Following the successful tests with three 3/16" ejection ports located at the CG and ejecting laterally, a forward ejecting "retro rocket" setup is prepared. This has four 1/8" nozzles aimed directly forward.

View attachment 576117
If nothing else... that looks bad ass!
 
The model is now in rough mock up condition. With loaded C11-5, CG is is currently just behind the retro jet nozzles. No altimeter is aboard. I know there will be changes to the tubes. One of the goals is to test various locations for the nozzles relative to CG.

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Model balanced at CG with expended D12-5.

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This sort of model you don't see very often - possibly for very good reasons! We'll found out after a bit more paint and better weather. Weight is 2.6 ounces as she sets. A Pnut altimeter could be installed just ahead the retro jets, but I would have the vent at the other end of the tube.
 
It was a beautiful morning at Warren G Magnuson Park on the shores of Lake Washington in Seattle. Winds were in the 2-3 mph category. Consecutive successful HSR flights were achieved with the new "Retro Jet" rocket. No damage at all was sustained. Stable lift offs on B6-2's culminated in an ejection event while the model was still rising, well before apogee. Immediately the rocket reversed course, tail first, then promptly transitioned into HSR, turning left into a half spiral before landing horizontally, both on grass and astroturf. Video was taken and hopefully be posted later today. More powerful motors will be installed for flights at 60 Acres.

DSC00863.jpg
Retro Jet/HSR rocket on the launch tower at Magnuson Park, Seattle.
 
Congrats! No damage?
No damage. None. Zip. Zero. But my admittedly rather harsh self-imposed standard is 10 consecutive flights with no damage. Testing does not stop.

The current model has styrene angles tacked on with Testors Red and filleted with JB Weld epoxy for plastics. IMHO, the model is very light relative to its fin area. If I had the skill, I'd definitely try balsa fins wet formed to a 135 degree angle, then papered.
 
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