Definitely interested to see how that looks with a bigger motor and a longer delay.
Horizontal Spin Recovery - with Magnus Effect?
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My launch partner and videographer just returned from a month in Europe, and now urgently needs to attend to matters in Oregon. But we'll get out to 60 Acres ASAP and work through C6-3, C11-3 and D12-5.
Our stats of HSR ejection events from the side of the nose in some models seems to predict a ballistic landing about one in ten times. That is not satisfactory for me. So the point of the retro rocket is more reliability in the transition from apogee to HSR. Other objective criteria might include elapsed time from apogee to landing, or maybe better would be slowest rate of descent. But right now maximum reliability of achieving routine HSR without accident either in flight or landing is my goal. Then, it might be worth a kit.
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Looks great!
Good motor choice for first flight.
Now the challenge of “how high do I really want to go?” And “what’s the optimal delay”?
Wish I could text with a Clint Eastwood voice.
“do you feel lucky, punk? Try a C6-5.”
Different motors are going to induce a shift in the CG, introducing another variable. Many possible ways to find the limits of success.
Another research agenda might involve blocking the ports and seeing what happens then. Just now effective are those nozzles? Is most of the ejection event coming out the back of the rocket and not the front? What happens when the ejection event is confined to a small closed chamber?
Can I continue to make meaningful experiments at a smallish field? Those drives to 60 Acres on crowded, competitive freeways are much less enjoyable than cruising to the launch site along the fashionable boulevards of north east Seattle. The girls are now in their summer clothes.
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I had my doubts initially about the retro fire rather than right angle. But you were already thinking way ahead of me, if you fire BEFORE apogee while rocket is nose up (assuming anything short of severe weathercocking), you are guaranteed to NOT be in the dreaded “nose straight down” (aka BALLISTIC) position.
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negative, Ghost Rider.
Assuming ejection charges fires BEFORE apogee, the empty casings of 18mm motors will be pretty much the same.
Unless you are concerned about the boost. I suspect however most of your rockets have more calibers of stability than would be comprised by going from an B to a C.
Another cat skinning technique: paper nose cone with medium short Kevlar thread and a good bit light weight snap swivel. Obviously not glue in.
Intentional early ejection (so rocket nose up vertical)
Ejection kicks rocket body backwards.
Goes into Horizontal Spin, the nose cone is light enough it doesn’t pull the nose down. My main concern is whether the swivel could keep up with the spin . My mind sim says probably not, cord would twist up, then I am not sure what would happen.
Aha, it hit me. Nerf darts could make could disposable nose cones. Could even put a streamer on them for retrieval if you don’t want to litter the field. But that does violate the “purist” them of “no moving parts” which makes HSR and Back Slide Recovery so cool.
What is a caliber on a rocket with three different diameters?
With D12-5 (less 5" of tape), the CG is 33.5" from the nose of a 39.5" rocket.
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I meant calibers of stability. And I think you are right, maybe @neil_w can correct me, but for a rocket with transitions not sure which one you use for open rocket (maybe the program averages them for the length of the rocket?)
In any case, there is a term “overstable”, which I think is nebulous. Presumably most “stable” rockets are actually somewhat “overstable” as (perhaps outside competition) you want a hedge against wind gusts or motor variances. But your rockets eyeball to me like you could put a moderately heavier motor in and get away with it.
My asymmetric fin birds are probably stable BECAUSE they are so “overstable”. They may avoid weathercocking (the bane of reeeeaaallly overstable rockets, particularly stagers) BECAUSE they corkscrew in flight (usually).
I believe Stine wrote that parasite boost gliders should have some intentional “roll “ on boost to avoid that problem, but it’s been a while since I read that and I don’t have book handy.
The largest diameter is used.
Whether that actually makes sense for when there is only a small section of larger diameter at the back of the rocket is... debatable. But for now the rule is applied in a very simple way.
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Okay I am slow to appreciate the nuances here.
So you have gone to 8 fins, with shorter hemispans.
A++ in the cool department.
Not as much in the KISS compartment.
The shorter hemispan should definitely improve stability on impact. You lose at least a little effectiveness in HSR induction and maintenance.
But could you get same stability AND HSR effect with FOUR fins, just double the chord length (basically combining the 6 shorter chord fins into 3 longer chord fins?)
I’ve read that for staged rockets with potentially “mated” sustainer and booster fins (meaning that when “in-line” they look like a single contiguous fin), that when positioned “in-line” you get less drag (booster fin is leeward of sustainer), but booster fin is less effective for same reason. Rotate the sustainer 1/2 the fin interval (like your set up here, except you aren’t staging) and you get MORE drag but also MORE stability.
My gut (FWIW) says 3 longer fins would be easier to build and stronger than 6
But my eyes say 6 looks much classier!
Edited to correct from 8/4 to 6/3
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I'll confess my fin arrangement for Retro Rocket is based almost as much in fantasy scale modeling as in rocket science. Beyond dubious aesthetics, the fins here have mainly a twofold purpose: induce maximum spin on descent and resist breakage on landing. Obviously these are contradictory so a compromise must be reached, actually a jumble of compromises.
So reliability of the ejection event to initiate HSR, and continuous repeatability of use without repairs are the goals right now. I will continue launching on B6-2 until I get to 10 consecutive successful flights. We plan to do that Tuesday unless scuppered by the heat dome and/or thunderstorms.
So reliability of the ejection event to initiate HSR, and continuous repeatability of use without repairs are the goals right now. I will continue launching on B6-2 until I get to 10 consecutive successful flights. We plan to do that Tuesday unless scuppered by the heat dome and/or thunderstorms.
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What time Tuesday?
Right now the plan is to arrive at Warren G Magnuson Park at about 8:20 AM and stay for a couple of hours or so. Weather etc. could alter the plan.
Getting to this park is essentially quite easy. Take I-5 north and exit at the NE 65th Street Exit in Seattle. Drive east on NE 65th until you get to the park. There is a potentially confusing downhill S-bend as you get to the end of NE 65th St. After entering the park at the NE 65th St. entrance, turn left at the first main intersection. You will immediately see a vast field to your right. When you come to the Sanicans, park in the 2 hour lot up the hill to your left. There is an RC airplane runway in the center of the field. We will be near there.
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Rockets to be tested to failure this morning at Magnuson Park - weather permitting.
Three-Side puffer on left, Retro-Rocket on right.
Current status: 4/0, 2/0
Three-Side puffer on left, Retro-Rocket on right.
Current status: 4/0, 2/0
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Hope the flights were great.
Can you re-describe the three sided puffer? How are the ports positioned? Seems like equilateral would be self defeating.
Can you re-describe the three sided puffer? How are the ports positioned? Seems like equilateral would be self defeating.
This is a four sided puffer in work, pointing down. Note that the very edge of the 3/16" holes are partially occluded by the transition. This section will be joined to a fin can and upper tube such that the holes are located at about the 20/80 point of the CG. Someone very clever with 3D printing could make this puffer work such that spin is initiated with the ejection event, making the transition to HSR ever more certain.
The tests this morning were disappointing, as the JB Weld for Plastics failed on the retro rocket's fins, eventually one by one as the flights went on. The join to the styrene failed, even though they were carefully cleaned and abraded prior to application, and well-cured afterward. I intend to abandon styrene even though the styrene itself is not breaking. As long as the rocket had 4 of the 6 fins, the HSR portion of the flights went well. The side puffer rocket was also going well...until it finally went ballistic. The fin can and puffer section were undamaged. We speculate the ports were too far forward. A new round of tests on new and rebuilt rockets will be conducted in a few days. Magnuson Park is turning out to be very convenient, only 20 minutes drive to a 750' x 750' field.
The tests this morning were disappointing, as the JB Weld for Plastics failed on the retro rocket's fins, eventually one by one as the flights went on. The join to the styrene failed, even though they were carefully cleaned and abraded prior to application, and well-cured afterward. I intend to abandon styrene even though the styrene itself is not breaking. As long as the rocket had 4 of the 6 fins, the HSR portion of the flights went well. The side puffer rocket was also going well...until it finally went ballistic. The fin can and puffer section were undamaged. We speculate the ports were too far forward. A new round of tests on new and rebuilt rockets will be conducted in a few days. Magnuson Park is turning out to be very convenient, only 20 minutes drive to a 750' x 750' field.
“We shall not cease from exploration. And the end of all our exploring. Will be to arrive where we started. And know the place for the first time."
- TS Eliot
Figure 13
https://www.apogeerockets.com/education/downloads/Newsletter447.pdf
After 21 pages of exploration, I humbly return to the very first post and very first image in this thread. I've alway envied those 135 degree fins, and now I shall model them.
Lacking the interest and skills to wet form balsa, I've made a tool which enables me to cut a sheet of 1/8" balsa such that a stout 135 degree butt joint results perfectly from the two pieces when one is flipped. A fillet on the inner side and papering the outer should result in a very serviceable fin. I'm looking forward to getting away from plastic fins, and getting back to the basics for a while. I'll be away at my fishing cabin for a few days. Pix next week.
- TS Eliot
Figure 13
https://www.apogeerockets.com/education/downloads/Newsletter447.pdf
After 21 pages of exploration, I humbly return to the very first post and very first image in this thread. I've alway envied those 135 degree fins, and now I shall model them.
Lacking the interest and skills to wet form balsa, I've made a tool which enables me to cut a sheet of 1/8" balsa such that a stout 135 degree butt joint results perfectly from the two pieces when one is flipped. A fillet on the inner side and papering the outer should result in a very serviceable fin. I'm looking forward to getting away from plastic fins, and getting back to the basics for a while. I'll be away at my fishing cabin for a few days. Pix next week.
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“We shall not cease from exploration. And the end of all our exploring. Will be to arrive where we started. And know the place for the first time."
- TS Eliot
Figure 13
https://www.apogeerockets.com/education/downloads/Newsletter447.pdf
After 21 pages of exploration, I humbly return to the very first post and very first image in this thread. I've alway envied those 135 degree fins, and now I shall model them.
Lacking the interest and skills to wet form balsa, I've made a tool which enables me to cut a sheet of 1/8" balsa such that a stout 135 degree butt joint results perfectly from the two pieces when one is flipped. A fillet on the inner side and papering the outer should result in a very serviceable fin. I'm looking forward to getting away from plastic fins, and getting back to the basics for a while. I'll be away at my fishing cabin for a few days. Pix next week.
@Rktman has a great technique for this. He does a partial cut through the balsa, I think he may even cut out a wedge, and then folds the balsa over. I suspect he will jump in since I tagged him and hopefully send a link.
that said, first enjoy the fishing.
second, there is a reason you haven’t seen the picture built, I can just about guarantee you will get one and only one flight. Those fins are going to be spinning like mad, and they stick out so far, they are gonna break off either at the root (better) or through the balsa (worse).
I still think either an external tough ring that can take the landing shock, or increase number of Fins and longer chord length with short hemispan and flexible fins is the way to go.
the challenge with HSR is figuring out how to bleed off the incredibly high rotational kinetic velocity in a way that doesn’t break the fins off.
I found some of that plastic tubing you gave me a while back. Wish it was slightly smaller diameter (but since I got it free, please don’t consider that a complaint!) and I may see what I can come up with.
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Time for me to rejoin the good fight and actually build something rather than firing off ”suggestions.”
base of unit one.
got your 2 inch plastic tubing, cut two 3” lengths into three 120 degree segments. So 6 fins, I guess using 3.14 as approximation for Pi , each 2.1” “hemispan” although given curvature not sure if that is the correct term.
I am laying down a base of 1/8” balsa, strips are 2.75” long, 1 cm (sorry, mixing metric and standard) cheaters/guides. They are MUCH taller (or hemispanned) than my usual cheaters. The cut is transverse for strength, which ended up being a bit of PITB as they tend to curl up, I’d be better off with three 1” segments each. Oh well, as @lakeroadster has exposed me, I kind of freehand stuff.
base of unit one.
got your 2 inch plastic tubing, cut two 3” lengths into three 120 degree segments. So 6 fins, I guess using 3.14 as approximation for Pi , each 2.1” “hemispan” although given curvature not sure if that is the correct term.
I am laying down a base of 1/8” balsa, strips are 2.75” long, 1 cm (sorry, mixing metric and standard) cheaters/guides. They are MUCH taller (or hemispanned) than my usual cheaters. The cut is transverse for strength, which ended up being a bit of PITB as they tend to curl up, I’d be better off with three 1” segments each. Oh well, as @lakeroadster has exposed me, I kind of freehand stuff.
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Okay, possible Epiphany vs dumb idea. I will be interested in @Dotini opinion on this, but also @sr205347d , @Rktman , @lakeroadster , @neil_w (effect of tip less nose cone on drag, stability, and altitude), @jqavins , @Daddyisabar and anybody else that wants to chime in.
at first I thought the idea of forward ports was dumb, now I think it’s brilliant. But I am also a lover of the KISS principle, and I am also a bit on the lazy side.
so as I understand it, the forward puff ports are used in conjunction with an intentionally short delay (you want the ejection event to occur while the rocket is at or near vertical, crossing our fingers not too much weathercocking.)
@Dotini is going to a lot of work to create those forward ports, and just by definition they must impart some component of extra drag. Which is okay, we really don’t want these to fly beyond visual range
the Enemy of both Back Slide Recovery (BSR) and Horizontal Spin Recovery (HSR) is a nose down vertical position of the rocket post ”ejection puff”. For the standard side port “puff”, the final rocket orientation is random, nearly but not all the time it is something OTHER than nose down vertical, and in those majority of cases it works, but on those rare occasions when the ”roulette wheel” (really in this case a sphere) lands on green, NOSE DOWN VERTICAL, the rocket falls in a STABLE Ballistic Trajectory. @Dotini’s FORWARD puff initiated with rocket vertical or near vertical nose up by pre-apogee delay timing should come as close to guaranteeing the ball never lands on green.
but is there an easier way?
I propose build the rocket essentially the same as any other BSR or HSR rocket with two exceptions.
1. No side port
2. Hollow plastic nose cone, glued (or externally taped) onto the forward end of the body tube, base bulkhead REMOVED (so the hollow center is fully open to the ejection charge) and cut the tip off the nose cone so you have a hole the same size as @Dotini ‘s forward port.
the rocket still has no moving parts (this is dogma for the purists of BSR and HSR.). Okay, it’s not the prettiest or most elegant solution, but it’s pretty darn simple (may want to coat the inside of the cone with JP WELD, as long as you don’t block the hole, to protect the plastic.). It’s gonna cost a bit in drag and stability (Neil, any guesstimates? is it that big a deal?) For best hope of success, needs to be teamed with a short delay motor to initiate transition prior to apogee (while at or nearly vertical), although I theeeeeeenk even if you are late it will be at least as reliable as a side port, so it goes from guaranteed to probably.
the only real problem I can think of is that the obvious name (“One Eyed Rocket”) might be a bit uncouth.
an advantage is it is probably somewhat safer. If somehow it still manages to come in ballistic, the cut off cone has a broader effective impact surface than the point of a cone. Not that I’d want to get hit in the head with it, but of the two options the cut off cone is probably less harmful,
at first I thought the idea of forward ports was dumb, now I think it’s brilliant. But I am also a lover of the KISS principle, and I am also a bit on the lazy side.
so as I understand it, the forward puff ports are used in conjunction with an intentionally short delay (you want the ejection event to occur while the rocket is at or near vertical, crossing our fingers not too much weathercocking.)
@Dotini is going to a lot of work to create those forward ports, and just by definition they must impart some component of extra drag. Which is okay, we really don’t want these to fly beyond visual range
the Enemy of both Back Slide Recovery (BSR) and Horizontal Spin Recovery (HSR) is a nose down vertical position of the rocket post ”ejection puff”. For the standard side port “puff”, the final rocket orientation is random, nearly but not all the time it is something OTHER than nose down vertical, and in those majority of cases it works, but on those rare occasions when the ”roulette wheel” (really in this case a sphere) lands on green, NOSE DOWN VERTICAL, the rocket falls in a STABLE Ballistic Trajectory. @Dotini’s FORWARD puff initiated with rocket vertical or near vertical nose up by pre-apogee delay timing should come as close to guaranteeing the ball never lands on green.
but is there an easier way?
I propose build the rocket essentially the same as any other BSR or HSR rocket with two exceptions.
1. No side port
2. Hollow plastic nose cone, glued (or externally taped) onto the forward end of the body tube, base bulkhead REMOVED (so the hollow center is fully open to the ejection charge) and cut the tip off the nose cone so you have a hole the same size as @Dotini ‘s forward port.
the rocket still has no moving parts (this is dogma for the purists of BSR and HSR.). Okay, it’s not the prettiest or most elegant solution, but it’s pretty darn simple (may want to coat the inside of the cone with JP WELD, as long as you don’t block the hole, to protect the plastic.). It’s gonna cost a bit in drag and stability (Neil, any guesstimates? is it that big a deal?) For best hope of success, needs to be teamed with a short delay motor to initiate transition prior to apogee (while at or nearly vertical), although I theeeeeeenk even if you are late it will be at least as reliable as a side port, so it goes from guaranteed to probably.
the only real problem I can think of is that the obvious name (“One Eyed Rocket”) might be a bit uncouth.
an advantage is it is probably somewhat safer. If somehow it still manages to come in ballistic, the cut off cone has a broader effective impact surface than the point of a cone. Not that I’d want to get hit in the head with it, but of the two options the cut off cone is probably less harmful,
lakeroadster
When in doubt... build hell-for-stout!
I like it. But instead of tape why not a flapper, like a check valve has, see diagram below? The air can't come into the fuselage during flight, but the ejection charge can leave the fuselage. Might even be able to make that work with a Bomarc ramjet style nose cone.
I thought the side ports are needed to nudge the rocket sideways... not sure your "punch it in the nose" (PIITN) idea would have the same effect.
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Interesting idea. If concerned about drag, retain the pointy tip that's cut off and anchor it with a short piece of kevlar and elastic to the inside of the nose cone. (The elastic will absorb the shock so that a shorter overall length of shock cord can be used). It will need a short piece of shoulder to keep it in place (piece of cork with end protected by epoxy?). Since it's so tiny, the trailing tip and cord would be insignificant in terms of drag negatively affecting HSR/BSR functioning on the way down.
If that violates the KISS principle, a sacrificial tip can easily and quickly be formed from plasticine modeling clay.
If the rest of the body is sealed then no air will come in. Should act like a blunt nosed cone.
Not sure it’s any more “safe” then a rounded nose cone, though.
Not sure it’s any more “safe” then a rounded nose cone, though.
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I initially thought the same.
But with a side port puff or punch, the rocket orientation regardless of orientation at time of activation is I believe completely random. Only thing required by BSR and HSR is that when the imparted rotation STOPS, the only UNACCEPTABLE orientation is nose down, or more technically at an angle of attack far enough OFF straight nose down that the rocket due to its long length IS now unstable for given angle of attach. Yup, you read right, we WANT it to be unstable. My experience has been far more limited than @Dotini , but HSR seems much more forgiving at near vertical nose down than BSR.
What @Dotini came up with was that if you do a FORWARD puff, pre-apogee while the rocket is nose UP vertical, it just about guarantees (I theeeenk) the rockets final apogee orientation while NOT be nose down.
Timing may be critical , as too soon before normal ideal apogee and the forward puff may be insufficient to slow down or stop the rocket, I.e. continues upward and noses over and almost certainly returns ballistic.
For both designs, once the rocket is unstable it STAYS unstable, for HSR settles into a horizontal attitude and just comes down sideways, the “slowing” is simply due to high drag horizontal orientation. In a sense, it is optimized tumble recovery. For BSR it settles into a horizontal glide. I am not sure it generates much left, but at least it gets the horizontal drag.
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You guys are challenging my moral fiber!
Above ideas would likely work, in fact the easiest is just to eject the cone and have it come down by chute. I did that with a parachute jumper figurine “standing” on the nose cone base. Lost the nose and jumper at NSL a couple years back.
I likely will try these ideas, although one of the “elegances” of HSR and BSR is the concept of “no moving parts” and “single piece”.
I have seen numerous streamer recovery models where the streamer balanced the nose weight, and the body of the (still attached) rocket recovered horizontally. It may have also been (unintentionally) spinning, seemed more likely to be backsliding.
I have successfully used HSR for recovery of an 18” long gap booster on a two stage, and it works well. It just hit me last night that this PROBABLY would work for a backslide recovery of a long gap booster. I have been thinking for years of a reliable way to get a glide recovery on a booster. With an asymmetric fin can, I think it might work, especially as with no nose cone the sustainer should be easier to make unstable.
A recent HSR model dubbed "Hexaflex" has completed 20 HSR flights without a failure of any kind. Motors include B4-4, B6-4, C6-5 and C11-5.
The development that makes success almost a certainty is the "retro-jet" ejection plan combined with a very particular CG and correct motor delay.
Four 5/32" ejection ports angled as seen above are formed in a 1.2" balsa plug in the section immediately above the fin can. A six fin can has been mainly employed on the premise that the model will land on two fins and spread out the landing load. However, the model operates even better on 3 fins.
Four 5/32" ejection ports angled as seen above are formed in a 1.2" balsa plug in the section immediately above the fin can. A six fin can has been mainly employed on the premise that the model will land on two fins and spread out the landing load. However, the model operates even better on 3 fins.
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Superb!
sorry if I missed the build on this (maybe gimme a thread number if it is here, we are on page TWENTY-ONE!)
I mentally pooh-poohed the retrojet idea purely due to “tunnel vision” on my part. Now of course it seems brilliant.
if I understand it right, delay is targeted for pre-apogee (so rocket is up vertical or near up vertical prior to event) and since evenly distributed (also something I initially misunderstood) post event somewhere between up vertical and horizontal, definitely shouldn’t be able to have any nose down vector at all.
questions.
are fins through the wall?
can this carry an altimeter and if so, where?
can the retrojets be built into a minimum diameter? And in any case how do you get the angled “pipes” or “nozzles” ?
is that a standard or extra light balsa or vacu-form nose cone?
in any case, congrats!
sorry if I missed the build on this (maybe gimme a thread number if it is here, we are on page TWENTY-ONE!)
I mentally pooh-poohed the retrojet idea purely due to “tunnel vision” on my part. Now of course it seems brilliant.
if I understand it right, delay is targeted for pre-apogee (so rocket is up vertical or near up vertical prior to event) and since evenly distributed (also something I initially misunderstood) post event somewhere between up vertical and horizontal, definitely shouldn’t be able to have any nose down vector at all.
questions.
are fins through the wall?
can this carry an altimeter and if so, where?
can the retrojets be built into a minimum diameter? And in any case how do you get the angled “pipes” or “nozzles” ?
is that a standard or extra light balsa or vacu-form nose cone?
in any case, congrats!
