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This is all you, I have never done anything like that.
So, maybe I'll try a three-stager
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This is all you, I have never done anything like that.
JimJarvis50
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You are absolutely right. CarVac should check my entire calculation and then do a beam calculation.
Jim
PS - Kyle, an idea what a collinear constraint is??
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Haha! I have an idea of what it is but its only a guess. I still have years of school left before I have a degree, so no judgement!
A5tr0 An0n
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I forgot your rocket was around 20'+, nonetheless I think that idea helps in the elimination of pad slaves. I have only ever stared up at a rocket that was 13' tall so 25' is a lot higher, almost double that. I do agree with Kyle, in that the easiest way is to lift not at the CG and to reinforce the rails if need be, but I do understand your concern. I also think the easiest is to lift from the upper part of the rail. Frankly just guessing, I would think that the launch rail could momentarily support the lift, is this a real issue or just a concern that you might like to avoid?
Kyle,
On an off topic post, I just noticed that you had Euler's identity under your username! That is the most beautiful equation of all time. Amazing how [(2.71...)^(sqrt(-1))(3.14…
+1] = 0; it uses the 5 most important numbers in all of mathematics. Rant over.Beam Calculator:
https://www.engineeringcalculator.net/beam_calculator.html
The only thing I know about collinear constraint is that it is a tool used in some CAD software to align lines on the same plane. See the video.
[video=youtube;mSeaGY7lEK0]https://www.youtube.com/watch?v=mSeaGY7lEK0[/video]
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JimJarvis50
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The rail is segmented in pieces (4' + 6' +6'). They are aligned using a 1' pipe on the bottom and 1/4" by 2" by 12" plate steel on the sides (you can see these features in Post 17). The rail is quite strong, but if you do a dismount off the end of the beam, you can mess up the collinear constraint. The play in the rail is just due to the diameter of the screws that attach the plate versus the width of the channel in the rail. Making the 12" long plate sections 24" long instead would probably help, and add weight too, but we're still not ever going to pick up the rocket using the far end of the rail.
Jim
CarVac
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RE: collinear constraint: I meant that the 3 rail guides on your rocket are going to stay in a straight line relative to one another. Unless your airframe yields...
Give me the cross section of the beam, the material, the location of the 3 rail guides, the mass and CG of the rocket relative to the 3 rail guides...
JimJarvis50
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Well, it's apparent that one thing I need to do is to determine how much sag will occur if the rail/rocket is lifted at the CG. I went and got some 1/4" x 1.5" x 4' sections of steel, and I plan to replace my 1' supports with 2' supports. That should keep the sections aligned sufficiently. For this issue and for others, I will also do an "all up" test with the rail and rocket loaded in the pad. That will generate actual data on the rail deflection, and let us determine if the end of the rail needs to be supported more during the lift. So, I promise we will revisit this issue.
In the meantime, it would be great if a few of you could look over the static analysis in Post 50 and let me know if you agree with my conclusions. Ignoring beam deflection for the moment, the question is, does pulling on the rope in the configuration shown generate a force that would want to bend the rail between the CG and the fulcrum?
Jim
CarVac
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The tension in the rope itself is not doing the bending; it's the weight of the unsupported end and that of the rocket.
However, if there is significant compression in the bottom part of the rail, then that combined with the weight of the rocket can cause column failure (buckling). The risk will be greatest, however, when the rail is closest to horizontal, so make sure to have people holding it then.
JimJarvis50
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Yes, but ....
For the moment, assume all of the weight is at the CG (i.e., no bending of the rail when pushing up at the CG). Then:
If the rope is attached to the CG, there is compression but no bending of the rail. On the other hand, if the rope is attached at a point higher than the CG, then there will be compression plus a resulting force wanting to buckle the rail downward.
Now, if we distribute the weight of the rail such that the unsupported end of the rail is trying to buckle the rail upward (when pushing up at the CG), then perhaps we can determine a location for attaching the rope - higher than the CG - where these two forces would offset each other, at least at the point where the rail is closest to horizontal. We should be able to calculate this from the loads, right?
The actual curving of the rail is a separate issue. I can look at that by experiment.
Am I getting warmer?
Jim
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Are you using 1010 or 1515 buttons? The reason I ask is that when we did the Delta III, one of the guys did some math on 1530 rail. A 12 foot piece doesn't flex much at all, even with significant weight, as long as it's oriented such that the load is trying to deflect it on the 3" axis.
-Kevin (IT nerd, not Engineering nerd, so terminology may be wrong, but you get my point)
JimJarvis50
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The rail is essentially the 1515 rail (actually, MC sent me the 40mm rail, which is just slightly larger). It doesn't flex much either. The problem, which is really only a problem because of the weight distribution of the rail (i.e., the extra structure at the top of the rail), is the joints between the sections. I can strengthen those to some extent. Then, i just need to figure out where to pull on the rail to minimize column compression and buckling. I have access to some programs that can do that, or I can just set up a spreadsheet and figure it out. My homework assignment....
Jim
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Other than the logistics of getting it to you, and getting it back, I could probably get you some 12 foot long pieces of 1530 on loan, which would resolve a lot of that.
-Kevin
JimJarvis50
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Well, necessity would be the mother of invention. Let me work on the necessity part.
Thanks!
Jim
Sorry, I'm a bit late to the party, so the following will be partially redundant after Carlo mentioned it already. One thing that the crane folks use, especially on the really heave ones, is called a derrick boom.
https://www.google.com/search?q=derrick+crane&tbm=isch
This would be a simple way to handle the forces, while keeping bending moments in the rail low.
For the purpose of erecting the launch pad, you could use a variant where the rope is not fixed to the derrick, but only gets redirected by it, so that the rope gets "released" after the pad has been erected by a certain amount. Imagine a derrick boom with a structure looking like a two pronged fork on its end to guide the rope as long as necessary. The following graph hopefully illustrates the idea:
Assuming the rope is more or less horizontal between the derrick and the winch and that the CG is at the location where the rope is connected, the maximum force in the rope calculates to "force_rope = weight_cg * (length_load_boom / length_derrick_boom)", so if the derrick boom has a length of 5' we end up with about 361lbf. This is also about the force that the pad anchoring has to resist, to prevent dragging it over the playa. Under the same assumptions, the force in the fulcrum is in the neighborhood of "sqrt(weight_cg^2 + force_rope^2)", in this case around 418lbf. In real life, this force will be slightly higher because the rope will not be exactly horizontal and the winch will also pull it down. However, this is a reasonably good approximation for our purposes (unless you plan to build a fulcrum that fails at exactly 425.000lbf :wink.
Other forces: the axial force in the load boom will be "sqrt(force_rope^2 - weight_cg^2)" (about 294lbf) and in the derrick about 210lbf (the weight at CG).
Most of the involved forces can be reduced by making the derrick longer, but at a certain length it becomes inconvenient to handle. In theory, one could also have multiple ropes that get connected to different points of the rail with the forces distributed by some kind of pulley mechanism (see here if you're really bored). However, if this is necessary, this would probably be a sign that the rail is not strong enough.
One detail, that might be relevant: Where are the support points of the rocket on the rail (rail buttons and, if present, temporary support during erection)?
Reinhard
https://www.google.com/search?q=derrick+crane&tbm=isch
This would be a simple way to handle the forces, while keeping bending moments in the rail low.
For the purpose of erecting the launch pad, you could use a variant where the rope is not fixed to the derrick, but only gets redirected by it, so that the rope gets "released" after the pad has been erected by a certain amount. Imagine a derrick boom with a structure looking like a two pronged fork on its end to guide the rope as long as necessary. The following graph hopefully illustrates the idea:
Assuming the rope is more or less horizontal between the derrick and the winch and that the CG is at the location where the rope is connected, the maximum force in the rope calculates to "force_rope = weight_cg * (length_load_boom / length_derrick_boom)", so if the derrick boom has a length of 5' we end up with about 361lbf. This is also about the force that the pad anchoring has to resist, to prevent dragging it over the playa. Under the same assumptions, the force in the fulcrum is in the neighborhood of "sqrt(weight_cg^2 + force_rope^2)", in this case around 418lbf. In real life, this force will be slightly higher because the rope will not be exactly horizontal and the winch will also pull it down. However, this is a reasonably good approximation for our purposes (unless you plan to build a fulcrum that fails at exactly 425.000lbf :wink
.Other forces: the axial force in the load boom will be "sqrt(force_rope^2 - weight_cg^2)" (about 294lbf) and in the derrick about 210lbf (the weight at CG).
Most of the involved forces can be reduced by making the derrick longer, but at a certain length it becomes inconvenient to handle. In theory, one could also have multiple ropes that get connected to different points of the rail with the forces distributed by some kind of pulley mechanism (see here if you're really bored). However, if this is necessary, this would probably be a sign that the rail is not strong enough.
One detail, that might be relevant: Where are the support points of the rocket on the rail (rail buttons and, if present, temporary support during erection)?
Reinhard
JimJarvis50
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Sorry, I'm a bit late to the party, so the following will be partially redundant after Carlo mentioned it already. One thing that the crane folks use, especially on the really heave ones, is called a derrick boom.
https://www.google.com/search?q=derrick+crane&tbm=isch
This would be a simple way to handle the forces, while keeping bending moments in the rail low.
For the purpose of erecting the launch pad, you could use a variant where the rope is not fixed to the derrick, but only gets redirected by it, so that the rope gets "released" after the pad has been erected by a certain amount. Imagine a derrick boom with a structure looking like a two pronged fork on its end to guide the rope as long as necessary. The following graph hopefully illustrates the idea:
View attachment 175852
Assuming the rope is more or less horizontal between the derrick and the winch and that the CG is at the location where the rope is connected, the maximum force in the rope calculates to "force_rope = weight_cg * (length_load_boom / length_derrick_boom)", so if the derrick boom has a length of 5' we end up with about 361lbf. This is also about the force that the pad anchoring has to resist, to prevent dragging it over the playa. Under the same assumptions, the force in the fulcrum is in the neighborhood of "sqrt(weight_cg^2 + force_rope^2)", in this case around 418lbf. In real life, this force will be slightly higher because the rope will not be exactly horizontal and the winch will also pull it down. However, this is a reasonably good approximation for our purposes (unless you plan to build a fulcrum that fails at exactly 425.000lbf :wink
Other forces: the axial force in the load boom will be "sqrt(force_rope^2 - weight_cg^2)" (about 294lbf) and in the derrick about 210lbf (the weight at CG).
Most of the involved forces can be reduced by making the derrick longer, but at a certain length it becomes inconvenient to handle. In theory, one could also have multiple ropes that get connected to different points of the rail with the forces distributed by some kind of pulley mechanism (see here if you're really bored). However, if this is necessary, this would probably be a sign that the rail is not strong enough.
One detail, that might be relevant: Where are the support points of the rocket on the rail (rail buttons and, if present, temporary support during erection)?
Reinhard
I'm going to be tied up for a few days so I don't have time to comment on this idea (which is a good one). Let me re-attach the geometry I posted a while back, which is the position that the rail could be lifted to by hand. The clamshell rod shown is 4 feet long, so to a first approximation, a 5-foot derrick would just be releasing at this point. How much longer do you think a derrick would have to be to provide a significant additional advantage starting from that point? Or stated differently, would an 8' or 10' derrick help much? By coincidence, your 5' derrick and my 5-foot drawing are similar, and the forces you cited are about the same as what I listed. Good to see that confirmation.
Thanks for giving this some though!
Jim
Attachments
A longer derrick would decrease the rope force (~1/x relationship). At a certain length it will become awkward to handle. If it were 8.6' long, the force in the rope (between derrick and winch) would be about the same as your weight. A 10' derrick will get the force down to about 180lbf. While it is a minor improvement compared to the 260lbf from your example, the difference is not that big.
There is something that didn't jump at to me intuitively, when I first thought about it, but in the theoretical case where the rope section to the winch stays perfectly horizontal, the rope force stays constant. While the load moment decreases during erection, the derricks advantage also decrease by the same amount - so the force can only decrease after the derrick releases the rope. On the other hand, this also means that the rope force doesn't become absurdly big if the rail is close to horizontal, so you wouldn't need pad slaves for the initial phase of the erection in this case.
I think all discussed variants are viable in your case.
A) A ton of pad slaves. There is certainly no lack of willing hands for this kind of project. It will require some coordination, but it is also the most flexible approach.
B) Some pad slaves and a winch. As long as the rail gets erected to a sufficient angle by the slaves (your numbers look good to me), the forces should be reasonable.
C) Derrick and winch. After set up, all happens at the push of a button. It can be tested at home without a big crew. On the other hand, it requires a more preparation and there might be some smaller technical difficulties (no particular idea, but I have no experience).
Reinhard
JimJarvis50
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Well, I've spent a few days making some modifications to the rail setup. This is still a work in progress, but some modifications were needed. One of the nice things about starting this thread was that it prompted me to take a closer look at this.
A few pics are attached that show how the rocket will sit on the rail. The first just shows all three stages and how they sit relative to other parts of the rail.
The second pic from the pointy end of the rocket shows the upper support structure. This piece has several functions. The eye bolts on the corners hold the guide wires that support the top of the rail. These have to be arranged so that they don't apply a torque to the rail when the guide wires are tightened. The two bolts near the top of the structure support a ladder, which I get to climb to arm the electronics. Then, there are two t-rail extensions that will support the third stage while the rocket is being prepped and lifted, and these supports are also my handholds while on the ladder. We've piloted the ladder climbing part of this. It's exciting, but it can be done.
I made two modifications to strengthen the rail. The bottom part of the rail is now backed with a 1.25" pipe that is 10' long. This replaces the two sections of 1" pipe. With this change, there is minimal stress on the rail buttons and the rocket could be lifted from the top end of this pipe (roughly the CG) without any chance that the lower part of the rail will buckle. Thus, I could winch up the rocket if I end up going that way. I also added 2' side supports (replacing the previous 1' supports). The third pic just shows these features.
The fourth pic shows the rocket from the bottom end. Nice fin crowns, no? The blue buckets contain rocks that simulate the weights of the three stages. I'm using them to get a feel for the weight and response of the rail when it's being supported and then raised.
Jim
A few pics are attached that show how the rocket will sit on the rail. The first just shows all three stages and how they sit relative to other parts of the rail.
The second pic from the pointy end of the rocket shows the upper support structure. This piece has several functions. The eye bolts on the corners hold the guide wires that support the top of the rail. These have to be arranged so that they don't apply a torque to the rail when the guide wires are tightened. The two bolts near the top of the structure support a ladder, which I get to climb to arm the electronics. Then, there are two t-rail extensions that will support the third stage while the rocket is being prepped and lifted, and these supports are also my handholds while on the ladder. We've piloted the ladder climbing part of this. It's exciting, but it can be done.
I made two modifications to strengthen the rail. The bottom part of the rail is now backed with a 1.25" pipe that is 10' long. This replaces the two sections of 1" pipe. With this change, there is minimal stress on the rail buttons and the rocket could be lifted from the top end of this pipe (roughly the CG) without any chance that the lower part of the rail will buckle. Thus, I could winch up the rocket if I end up going that way. I also added 2' side supports (replacing the previous 1' supports). The third pic just shows these features.
The fourth pic shows the rocket from the bottom end. Nice fin crowns, no? The blue buckets contain rocks that simulate the weights of the three stages. I'm using them to get a feel for the weight and response of the rail when it's being supported and then raised.
Jim
JimJarvis50
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Tracking will be pretty conventional. The 1st stage will have a Marshall RDF tracker that is "revealed" at apogee (i.e., it comes out of the carbon airframe at apogee). This is a good way to know that the apogee event has actually occurred. Same for the 2nd booster, except a BigRedBee.
The third stage will have two RDF trackers (a BigRedBee in the cone and a Marshall in the drogue section) and two gps's in the nose cone (both BigRedBee's). I have a Yaesu handheld radio with Yagi to keep track of all the BRB signals and a separate ground station with UI-view to monitor the gps.
This is pretty much what I have done on my two-stage flights - just one more stage to keep track of.
Jim
pyrobob
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Man that looks nice.........
JimJarvis50
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Thanks Bob.
I introduced the first booster back in Post #27. Here's some info on the second booster. For the most part, it's the sustainer from the two-stager I flew at Balls last year.
The two pics below show the parts of the rocket in their approximate positions. In my next post, I'll cover some details on the key pieces.
I built a new 4x3 transition, and I'll discuss that more when I show the 3rd stage information.
The airframe for this rocket is an 8-wrap tube. It's pretty strong.
The altimeter bay is next, and the extended charge holder tubes that I use for high-altitude deployment are on the right side of the bay.
The zipperless coupler is a PML phenolic coupler tube. I use that because it's the tubing that I rolled the airframe on and it's a perfect fit. It's lined, though, with about 3/16" of carbon. The wires for the separation charge and the igniter will emerge from the top of this zipperless coupler.
The motor case has the Gecko/Taperwire cable that I use for the separation charge and the motor igniter.
The bottom of the motor case has a sleeve, which is a PML phenolic airframe tube. I use that tube because it's the tubing that I rolled the oversize 1st stage airframe on, and it's a perfect fit. The portion of the motor covered by the phenolic tube sits down within the top of the 1st stage.
The last small piece is essentially the nose cone for the 1st stage. It keys into the bottom of the 2nd stage motor (to help keep it from turning during flight) and it gets shear pinned into the top of the 1st stage airframe.
Jim
JimJarvis50
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Here are a few more pics.
The first shows the altimeter bay for this rocket as it was for the Balls two-stage flight. It was a bit crowded in there. For the three stage flight, there are less electronics and no camera. I've redone the sleds and rebalanced the bay.
The second pic shows the bottom of the sustainer. Again, this was from the two-stage flight, but it will be the same for the three stage flight. Once the igniter dowel is inserted, the nozzle is covered with a cap.
The third pic shows the cap that is the nose cone for the 1st booster. The cap keys into the bottom threaded closure of the 2nd stage motor. The separation charge sits in the base of the cap close to the nozzle cover. The cap sits on a ring inside the top of the 1st booster airframe, and the cap is shear pinned to the tube (as you would a nose cone). The other side of the cap has a lead weight to help pull out the pilot chute for the main chute deployment bag. The cap is designed so that it cannot become jammed in the top of the airframe no matter how it is turned.
The 2nd stage motor will light at around 10K at around 800 ft/s. So, I want to have a little extra fire in the motor to help get it lit. I will use a dipped ematch, similar to the CTI provides to light the motor on the ground. This will be supplemented by a pyrodex pellet and a longer-burning igniter (which will be lit by the pyrodex pellet). Selecting this combination is just guesswork, and this is what I've chosen.
Jim
The first shows the altimeter bay for this rocket as it was for the Balls two-stage flight. It was a bit crowded in there. For the three stage flight, there are less electronics and no camera. I've redone the sleds and rebalanced the bay.
The second pic shows the bottom of the sustainer. Again, this was from the two-stage flight, but it will be the same for the three stage flight. Once the igniter dowel is inserted, the nozzle is covered with a cap.
The third pic shows the cap that is the nose cone for the 1st booster. The cap keys into the bottom threaded closure of the 2nd stage motor. The separation charge sits in the base of the cap close to the nozzle cover. The cap sits on a ring inside the top of the 1st booster airframe, and the cap is shear pinned to the tube (as you would a nose cone). The other side of the cap has a lead weight to help pull out the pilot chute for the main chute deployment bag. The cap is designed so that it cannot become jammed in the top of the airframe no matter how it is turned.
The 2nd stage motor will light at around 10K at around 800 ft/s. So, I want to have a little extra fire in the motor to help get it lit. I will use a dipped ematch, similar to the CTI provides to light the motor on the ground. This will be supplemented by a pyrodex pellet and a longer-burning igniter (which will be lit by the pyrodex pellet). Selecting this combination is just guesswork, and this is what I've chosen.
Jim
TheAviator
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I wanted to quickly address your vertical staging concern. Let me preface this by saying that I am only L1, so I have never flown anything this big.
Many sounding rockets impart a 0.5-2.0 degree per second roll to help reduce landing dispersion. I personally use it on my competition altitude and duration rockets, along with a high accuracy fin fixture, to ensure an arrow straight boost, though the smaller ones have roll rates far in excess of 2*/s. So long as the launch guidance is sufficient and well performed, I have never had a problem, and I have very little deviation from vertical.
In light of that, why not take your "fin crowns" and do a slight asymmetric bevel in the leading and trailing edges. That should be enough to impart a slow roll.
Anyways, I am thoroughly enjoying your thread and looking forward to the flight report. Good luck!
Many sounding rockets impart a 0.5-2.0 degree per second roll to help reduce landing dispersion. I personally use it on my competition altitude and duration rockets, along with a high accuracy fin fixture, to ensure an arrow straight boost, though the smaller ones have roll rates far in excess of 2*/s. So long as the launch guidance is sufficient and well performed, I have never had a problem, and I have very little deviation from vertical.
In light of that, why not take your "fin crowns" and do a slight asymmetric bevel in the leading and trailing edges. That should be enough to impart a slow roll.
Anyways, I am thoroughly enjoying your thread and looking forward to the flight report. Good luck!
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MClark
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Spinning the rocket works better on paper than in reality.
For best result the rocket must be spin balanced, the upper stage motor is a moon burner and would be severely out of balance.
M
For best result the rocket must be spin balanced, the upper stage motor is a moon burner and would be severely out of balance.
M
CarVac
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Perhaps he could swap the M745 for the only slightly lower-impulse CTI L395 Mellow coreburner... 12 seconds of leisurely burn. It could potentially be lit sooner, too, because it's so slow.
A bonus, it fits perfectly in the same 75/6000 case as the M745 (with adapters).
bobkrech
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I think you will find that the roll rates for unguided sounding rockets is typically 4 Hz for 14" rockets to as high as 20 Hz for the 4" Arcas.
Bob
CarVac
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As will you find that no hobby rocket ever has less than 2 degrees of roll per second and they are perfectly capable of weathercocking anyway.
Perhaps you meant revolutions per second?
JimJarvis50
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I already have the M745 and I won't be spinning the rocket. But, for future reference, how does one know that this is certified for AMW/Gorilla hardware?
Jim
JimJarvis50
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I did give some thought a while back about spin stabilization. I tried to find a few references on the subject. I didn't have much luck with that and the urge went away (or rather, was replaced by the likelihood of active stabilization, which may be more practical for me). I have noticed that on many of my two-stage flights, the off-angle occurs shortly after leaving the rail. I'm not sure this is weather cocking, because it seems to happen well after it leaves the rail. This flight (LDRS where the sustainer didn't light) is a good example:
https://www.youtube.com/watch?v=B1NGe44Jjhc
This change in angle was enough to abort the flight.
I think the rocket would need to be spinning leaving the rail, and I don't have the technical ability to do that. I also don't know how to de-spin the various stages. And I've been sorta stuck with the moonburners up to now. If anyone does have a good reference on the subject, I'd like to learn more about it.
Jim
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