# FLOWN! appropriately post 13. Devil's Triangle Backslider moved

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#### BABAR

##### Builds Rockets for NASA
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Would help if I had put it here to start

Will continue here

Marker black to fins

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#### BABAR

##### Builds Rockets for NASA
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Motor mount, for people too cheap to buy centering rings.

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#### BABAR

##### Builds Rockets for NASA
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Fin can

Sanding down the contact points

This will allow me to use the long tube for multiple projects

#### BABAR

##### Builds Rockets for NASA
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The ventral side contributes little to stability and a lot to drag, it's coming off.

Sanded smooth

Covered with black mylar tape.

Also some around forward edge of tube as a base for taping to the multipurpose tube which will be used for Horizontal Spin and Magnus experiments

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#### BABAR

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Probably didn't need to color the paper straw ( got like 144 for $5 online 7 years ago, still at least 1/2 left) The dowel holds it in place until glue dries. Also did a coupler, it's two layers to take more stress #### Dotini ##### Well-Known Member TRF Supporter This is not intended to spin, yes? Does this have the same fin area as the tube-fin spinner? My limited experience with backsliders is that, upon landing, they are murder on their fins and the tube section immediately in front of the fins. #### BABAR ##### Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter This is not intended to spin, yes? Does this have the same fin area as the tube-fin spinner? My limited experience with backsliders is that, upon landing, they are murder on their fins and the tube section immediately in front of the fins. This is a non-spinner on descent, although I anticipate a pronounced corkscrew on ascent. I will have better pics tomorrow when I hope to launch. IF (and it is a reasonably big IF) it works correctly, the asymmetric fin design should place ALL the fins dorsal on descent, so it should land on either the motor casing or the body tube, depending on how shallow (or steep!) the glide angle is. It has about a 37 to 1 length to caliber ratio. Planned for my first launch tomorrow, I will bring some spare tubes if necessary, otherwise the same tube will go for my Magnus and AntiMagnus twins, probably will go with the Magnus fin can (figure a spinning fin can will probably work if Devil's Triangle works). Then will try the non-spin tube fin can. Then I will try the ebay with a dummy payload altimeter on board. That lengthens the rocket a couple of inches, but it also adds about 11 grams of nose weight, I am NOT certain that won't cause a ballistic reentry. For those watching this, I will be flying at a local park, but will only try these attempts if it is empty, which on a Friday morning it generally is. #### BABAR ##### Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter corrected a typo on post 5, somehow got "central" instead of "ventral". In any case, this rocket has NO ventral fins, so it falls into my growing family of asymmetric fin rockets. Most of these have a corkscrew pattern of boost, although this one is so long that it may be minimal. This is the first time I have tried it on a Back Slider, to me it makes sense as @Dotini noted, Back Sliding is rough on fins. The real question is going to be balance, hopefully enough fin area to be stable on boost with near zero angle of attack, but unstable when ejection charge flips the angle of attack way outa wack. Stay tuned. #### Dotini ##### Well-Known Member TRF Supporter This is a non-spinner on descent, although I anticipate a pronounced corkscrew on ascent. I will have better pics tomorrow when I hope to launch. IF (and it is a reasonably big IF) it works correctly, the asymmetric fin design should place ALL the fins dorsal on descent, so it should land on either the motor casing or the body tube, depending on how shallow (or steep!) the glide angle is. It has about a 37 to 1 length to caliber ratio. Planned for my first launch tomorrow, I will bring some spare tubes if necessary, otherwise the same tube will go for my Magnus and AntiMagnus twins, probably will go with the Magnus fin can (figure a spinning fin can will probably work if Devil's Triangle works). Then will try the non-spin tube fin can. Then I will try the ebay with a dummy payload altimeter on board. That lengthens the rocket a couple of inches, but it also adds about 11 grams of nose weight, I am NOT certain that won't cause a ballistic reentry. For those watching this, I will be flying at a local park, but will only try these attempts if it is empty, which on a Friday morning it generally is. What do you think of ejecting the altimeter with the nose cone to come down on a streamer? #### BABAR ##### Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter What do you think of ejecting the altimeter with the nose cone to come down on a streamer? Definitely Do-able! Thing is, I am trying to measure descent rate of the rocket body itself with and without Magnus effect. So this gets me altitude but not descent rate. also, since I frequently fly by myself (I am a bit more daring this way, as if there is fecal turbine interaction I am the only potential target to hit, and I definitely AM watching the rocket), having more than one thing to track can be problematic, especially when they go significantly different ways! #### BABAR ##### Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter @Dotini , I want to thank you for getting me on this track. I can't compete with you on Magnus. This DID however divert me back to BackSlider recovery, and I think I am about as pleased with this as I was with the Gyskelion in 2011 https://www.rocketryforum.com/threads/gyskelion-helicopter-rocket.25862/ jump to post 11 for the flight and practical details, if you don't want to click the links on post 1 I remember reading about Back Slider rockets, I think in Tim Van Milligan's book, where I also read about horizontal spin and Magnus recoveries and Air Brake recovery. Interesting thing was that I don't know if ANY commercial kits used these techniques, and could find very little on the Rocketry Forum or online about them. The articles on BackSlide made it sound pretty hard to do, requiring a 30 to 1 length to caliber ratio and small fins. And I did try it a few weeks ago, it worked great but one of the fins broke off, pretty much to be expected the way this glides in for a landing. Then I thought about some of my asymmetric fin models, and some of my models which had streamers or chutes and recovered with the nose cone hanging off the chute and the body of the rocket just kind of falling horizontal next to it, since the drag of the fins was enough to balance the rocket even with the motor weight in the tail. I had launched rockets which had NO fins at all on one side of the rocket, I will have to submit one to @Neil and play with it in Open Rocket (had it and RockSim for years, never used them.) But I haven't seen and kits or even any scratchers on the forum that had ZERO fin surface on one side of the rocket (exception, @Flyfalcons 2 fin Guitar rocket, THAT was mega cool, posted at end here for those interested*, you know those guys that are just really nice and really bright and really talented and can make rockets that are both engineering marvels and works of art? yeah, those guys you just want to hate and can't because they are so darn good. Yeah, he's one of them) Anyway, this one came out just the way I wanted to. No, it's not art, my excuse here (although the real reason is I lack to the patience for good finishing skills) is keeping the weight down, so all the color is with markers. The Asymmetric fin design WORKS. Yeah, there's a little corkscrew action (not sure if that reduced weathercocking or not), but net trajectories are STRAIGHT. At apogee, the ejection charge vents out the side ports just behind the nose cone and kicks it off a normal stable trajectory, it goes into freefall. At that point, Barrowman, RockSim, and OpenRocket all go out the window. At this point I am not sure what happens, but it DOES happen consistently, the rocket's heaviest part is the tail (makes sense, that's where the motor is and all the fin weight), it comes down that way first, but the fins cause enough drag to keep it level. And because the fins are predominantly on the DORSAL side of the rocket, it tends to come down dorsal side up. Since there are NO fins on the ventral side of the rocket, the rocket lands either on the motor casing or the ventral body tube, neither of which is prone to breaking. Had four great flights, rare for me to fly a rocket at one outing more than twice, this one was just so much fun. Can't beat the prep. Remove old motor. Stick in new motor. Tape around the end of the motor mount and the protruding end of the motor. Install an igniter and go. No chute, No streamer. No wadding. No burn string. No rubber bands. This rocket has NO moving parts, even the motor stays right where it is. The only thing that moves is the ejected propellent and the rocket as a whole. Here's the pics.. here is the best flight, although I am not the best videographer, you can see it at the lower 1/4 of the screen at 38-40 seconds. By the way, the corkscrewing portions of the flight are ABSOLUTELY expected with this design, I have decided that while they cost me a bit in altitude (which is not my goal anyway) they are part of the "devilish" cool factor in these rockets. At least on the boost phase, these are NOT on the "straight and narrow" pathway (sorry @Peartree ), although the descent is surprisingly straight. few more flights Here you will see it again at 38-40 seconds, just below 1/2 down on the screen and just to the left of mid screen. I used the same tube for my Magnus and AntiMagnus rockets, the Magnus flight was weird, I will post that later, but it did put a crimp in the tube that I was sharing between rocket fin cans. After the AntiMagnus had an unstable flight, I wasn't sure whether it was due to the repair crimp (which may have had a bit of a bend to it) so I just cut off the crimped tail end, crossed my fingers and hoped the Devil's Triangle would still be both STABLE on ascent with the shorter tube and BACKWARDLY STABLE on descent, again with the shorter tube. Peter Always discussion made it seem like CG was of critical importance, I am NOT sure that is really true. In any case, it worked just fine with a couple inches cut off, so experimentation will have to go on with how short I can build these. Anyway, elected to go with a C6-5. Wondered if it would cause stability issues. Was NOT a problem, net trajectory was an Arrow Straight vertical boost (okay, the rocket corkscrewed AROUND that net trajectory) but I was plenty happy with the altitude I got. Unfortunately I lost it in the sun after seeing it establish a horizontal glide. I went looking for it (I had started the launch at one end of the park, unfortunately for me apparently a youth soccer group was out of school this day and took over my area of the field, so I moved a few fields down. The glide was HEADED toward their end of the field. As I was walking that way, a gentleman waved at me and pointed me in a different direction. I went ahead and spoke to him and he pointed out my rocket two fields away, it was 90 degrees from where I expected it to go, but I found it! This shows a great launch, with straight portions and corkscrewing, don't bother to watch after that, I lost it in the sun. * build thread here #### BABAR ##### Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter thinking about submitting this to Apogee Rockets. Not too many designs out there with no moving parts. #### Flyfalcons ##### Well-Known Member BABAR you are too kind, and that Devil's Triangle design of yours is way cool! #### rklapp ##### NAR# 109557 thinking about submitting this to Apogee Rockets. Not too many designs out there with no moving parts. From @neil_w experience, they will take your design and modify it for whatever reason. I think it’s worthwhile as long as you don’t mind a few changes. The video’s great. Just needs a little bit of zoom to see the rocket at apogee. That’s why I don’t use the GoPros as a handheld because the zoom is rather clumsy and difficult to operate while tracking the rockets. #### Dotini ##### Well-Known Member TRF Supporter thinking about submitting this to Apogee Rockets. Not too many designs out there with no moving parts. I think you should. Your design and result are nothing short of both brilliant and practical. And not least because it is simple, robust by design, and reusable on a number of different motors, virtues lacking in my Magnus series of rockets. The only potential drawback could be any tendency to drift and get lost. Do you think it would work on a B4-2? Do you think it would work with a variety of other fin configurations so long as they were all on one side of the rocket? In summary, most impressive! #### BABAR ##### Builds Rockets for NASA TRF Lifetime Supporter TRF Supporter I think you should. Your design and result are nothing short of both brilliant and practical. And not least because it is simple, robust by design, and reusable on a number of different motors, virtues lacking in my Magnus series of rockets. The only potential drawback could be any tendency to drift and get lost. Do you think it would work on a B4-2? Do you think it would work with a variety of other fin configurations so long as they were all on one side of the rocket? In summary, most impressive! B4-2 should work, ejection might be early, but this may be the penultimate rocket for tolerating early or late ejection. I need to post the A8-3 flight, it was successful but a bit disappointing, it takes the rocket a moment or two [email protected];$ perhaps 75-100 feet) to “find” its “horizontal legs.”

I think you should send in your Magnus series, a key on that is the plastic fin can which resists fin damage.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
From @neil_w experience, they will take your design and modify it for whatever reason. I think it’s worthwhile as long as you don’t mind a few changes.

The video’s great. Just needs a little bit of zoom to see the rocket at apogee. That’s why I don’t use the GoPros as a handheld because the zoom is rather clumsy and difficult to operate while tracking the rockets.
Yeah, I need to subcontract @burkefj ‘s videographer ([email protected]). Clearly using a video camera with a view finder and a good zoom. And either a really steady hand or a monopod (or both.) Those I think are consistently the best ground based rocket videos I have seen.

if someone on the ground (well away from the launch site) hadn’t seen the rocket land, I never would have found it. Part of that was trying to video it with my cell phone and tracking it with my eyeballs. I don’t suppose your son has any burning to desire to visit Tennessee any time soon?

it’s a bit like some of my AirBrakers, the flight pattern is so weird it just looks unreal.

#### Dotini

##### Well-Known Member
TRF Supporter
B4-2 should work, ejection might be early, but this may be the penultimate rocket for tolerating early or late ejection. I need to post the A8-3 flight, it was successful but a bit disappointing, it takes the rocket a moment or two [email protected];\$ perhaps 75-100 feet) to “find” its “horizontal legs.”

I think you should send in your Magnus series, a key on that is the plastic fin can which resists fin damage.
Alas, even my curved plastic fins are subject to eventual damage. One fin snapped off, and another loosened up, both necessitating repairs. And the paint always wears off. So I'm now experimenting with (a) adding stiffening struts like on X-1, or (b) adding a small doubler to the fin, or (c) adding a ring at the back. Or all three. Plastic fins made form ultra-thin shipping tubes are no panacea. Also I will round off the corners.

Your solution of keeping the fins off the ground is genius!

EDIT:
They say imitation is the sincerest form of flattery. So I've dropped everything and started my own version of your fins-all-on-one-side backslider.

Also, I've ordered an altimeter and decided to research and buy a proper video camera.

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#### neil_w

##### Doldrum dweller
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Alas, even my curved plastic fins are subject to eventual damage. One fin snapped off, and another loosened up, both necessitating repairs. And the paint always wears off. So I'm now experimenting with (a) adding stiffening struts like on X-1, or (b) adding a small doubler to the fin, or (c) adding a ring at the back. Or all three. Plastic fins made form ultra-thin shipping tubes are no panacea. Also I will round off the corners.
I was thinking a very narrow ring front and back, to protect the exposed corners of the fins, to prevent anything from catching on them at landing. Hard to know for sure how much it would help.

#### Dotini

##### Well-Known Member
TRF Supporter
And because the fins are predominantly on the DORSAL side of the rocket, it tends to come down dorsal side up.
Question: Why does it work this way? Why do the fins not hang down instead of up? Could you achieve the same results by taking a four fin rocket and cutting one fin off?

#### BABAR

##### Builds Rockets for NASA
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I was thinking a very narrow ring front and back, to protect the exposed corners of the fins, to prevent anything from catching on them at landing. Hard to know for sure how much it would help.
This is very close to what I did with Bail out Bill

@neil_w may be doing it one better.

Integrating an outer ring fin set, one forward and one aft, will spread the impact load to ALL three fins (or 4 or 5, even more structural support)

Larger Hemi Spans are also a potential structural weakness, as when the rocket falls horizontally, the fin can (with or without the ring) hits first.

Okay, here is waaaaay outside the box.

4 big tail fins, your shape, with an extension ring at the forward and rear ends (there’s a reason these are big fins.)
the ring solidifies the unit and spreads the impact stress.

put a FORWARD CANARD ring fin maybe midway up the fuse. This is much shorter. It’s only purpose is to take up some of the bending stress at impact.

regarding your “why does it work”, it’s basic drag. If you took of one of four fins, it would PROBABLY fall finless side down, but it would totter a bit. If you took out one of THREE fins however, it would almost definitely fall finless side down.