So, maybe I'll try a three-stager

JimJarvis50 said:

Here's the recorded tilt data up to the point of the Raven signal. The tilt around 1 second is obvious in the video as is the wobble from 2-3 seconds. The big increase at 4 seconds is after burnout. Wonder if this is an N5800 thing? The tilt critical angle was set at 15°.

Jim

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Wow that is crazy. I really dont know if it has much to do with the N5800 motor. I am sure it is something else. I really can't say much since I have no experience yet.


Alexander Solis

TRA - Level 1
Mariah 54 - CTI RedLightning- I-100 - 6,345 Feet

So, Balls is about 12 weeks off. Time to start preparations for the flight (it takes a while). As was the case last year, this will be an N5800 to N2501 to M745 three stager (two of the three motors are leftovers from last year). You may recall that the booster motor lit, but the second stage didn't, and then all parts were recovered safely. In looking at the data, the tiltometer received the signal for second stage ignition, but didn't pass along the signal to the igniter, and indeed, became inoperable. In looking closer at this, we have discovered that the reason the tiltometer didn't work is that I hooked it up incorrectly. I can't bring myself to admit exactly what I did, but let me just say that if you're using a tiltometer, and you think a pull-up resistor is something that goes around your ankles, then you should probably ask a few more questions.

On to this year!

The two main changes for this year are the use of stabilization and a new rail setup. The stabilization spool will go between the first and second stages and is designed to straighten the rocket during the coast before the second stage motor lights. The new rail setup is shown in the drawing and the pics. The rail is intended to be more of an I-beam design, and it is much stiffer.

The first pic is the booster with the fin crowns (remember those?). The stabilization spool is just below the second stage fins.

The second pic is the second stage. The large bolt under the pipe support is the lifting point to winch the rocket into a vertical position.

The third pic is the third stage. The contraption in the lower left of the pic is what holds the guide wires and is also the ladder support. With the extra 2 feet from the stabilization spool, it's not going to be possible to get to eye level to arm the electronics. So, my current activity is to figure out how to arm these switch at arms length (i.e., reaching up to the switch area). I have a plan.

Jim

Excited!

Wow...wish I was going to BALLS just to see this amazing build fly. Amazing work, Jim.

Hey Jim,

Good luck on the flight. Does your new pad setup require the T-bar you loaned me in March? We haven't crossed paths since then - let me know if you need me to ship.

Best,

Steve

prophecy said:

Hey Jim,

Good luck on the flight. Does your new pad setup require the T-bar you loaned me in March? We haven't crossed paths since then - let me know if you need me to ship.

Best,

Steve

Click to expand...

I just need the eye bolts, but I ordered a couple of replacements, so don't worry about it (until it's time to order me a beer - then I'll remember).

Jim

JimJarvis50 said:

I just need the eye bolts, but I ordered a couple of replacements, so don't worry about it (until it's time to order me a beer - then I'll remember).

Jim

Click to expand...

Sounds like a plan.

-s

Guess I need to go to Balls this year.

Joe

This is something I can only dream off. UK doesn't have the room to fly not do we have a system that would let you. Good luck with the project. Amazing effort

Pyropetepete said:

This is something I can only dream off. UK doesn't have the room to fly not do we have a system that would let you. Good luck with the project. Amazing effort

Click to expand...

I'm lucky to be able to do this each year. Hopefully, I won't make a single mistake this year, because that's all it takes.

But, you can still help me plan my flight if you want to, even if you can't do the flight yourself. You have to catch me doing something wrong, but that's not all that hard. If you check back on this thread, you will see I incorporated many suggestions into the flight last year, and even more into the flight this year.

First step is to do the flight profile. The first pic shows a diagram of the rocket, with the stabilization spool, and the second pic shows the overall RockSim simulation. The projected altitude is about 117K (RasAero, with the approach I use for multi-stage flights, is a little more generous at 128K on the same overall timing). After burnout of the booster motor, the booster will be separated, and then the stabilization spool will provide active guidance for a while. At a time to be proposed here, the stabilization section will be separated and then the second stage motor will light. This is the separation sequence that I tested in the last stabilization test flight.

https://youtu.be/umoduWiQb-o

Fortunately, I have the 2014 data (the rocket without the stabilization section) to help formulate the plan. The third pic shows the actual altitude profile for the 2014 flight and the corresponding simulation. The configuration here is to drop the booster after burnout and then the second and third stages coast together. The 2015 simulation is also shown (it goes a little lower because of the weight and drag of the stabilization spool). The 2014 simulation is pretty good, particularly given that it wasn't perfectly vertical.

The fourth pic is the velocities from the 2014 and 2015 simulations. I'm not showing the actual data because the accelerometer data is affected by errors in the accelerometer calibration, and velocity calculated by altitude is noisy. However, it should fall just below the 2014 simulations based on the altitude data. The pic shows that the maximum velocity reaches about Mach 1, and that I am proposing to light the 2nd stage motor (having it up to pressure) at 15.4 seconds. This is at a simulated velocity of around 550 ft/s. The actual velocity is likely to be a little lower because the simulation doesn't fully capture the drag from my canards.

Here is the logic for picking that velocity. I want the velocity to be reasonably low in order to keep the top speed during the second stage burn as low as I can. From the simulation in the second pic, the 2nd/3rd stage stack will reach about 1,900 ft/s. That would be the fastest that I've ever run a stack, and this is the point of maximum risk I think. On the other hand, staging at a bit higher velocity doesn't have much of an altitude penalty, and would reduce the weather cocking that will occur in the time between when the stabilization spool is separated and the motor lights.

So, that's the plan for the first segment of the flight.

Jim

Hearing no objections, the plan will be to light the second stage at the point shown in the overall flight profile below.

The second segment of the flight will be an N2501 going to a maximum speed of 1900 ft/s. The issues with this segment are when to separate the stages and when to light the 3rd stage motor.

The second and third stages will be pinned together so that the 3rd stage doesn't drag separate on first stage burnout (that would be bad). After the second stage burn, though, I think the parts need to stay together until the velocity slows down a bit. On a similar flight ....

https://youtu.be/j2Q1TeNx6SI?list=PLEISeVEqORmyQ_SWUlpwt-U4INlmn0PNj

... the booster was separated at about 1400 ft/s, and I think the booster almost came apart. I don't know for sure if this was due to the velocity, or instead, dropping back through Mach (opinions?). I don't really want to separate at 1900 ft/s (my feeling is that exposing an interstage coupler at this high velocity just can't be good). I could separate at a lower velocity, and even as low as 700 ft/s where I plan to light the 3rd stage.

Jim

That last graph is so cool.

s6

I'm planning on flying my two stager on a N2501 to a M685 at Balls and will be around 1400 ft/s at burnout. My plan is to keep the stack together until I drop back under Mach 0.9. My only reasoning for doing this is to mitigate unknown risk.
However, in my opinion, the higher altitude you are at, the chances of bad things happening above Mach 1 seem decrease.

Per Kip's last sentence - what altitude was the booster at in the video when it separated at 1400ft/s vs when the 2nd stage is done on the current project?

Zebedee said:

Per Kip's last sentence - what altitude was the booster at in the video when it separated at 1400ft/s vs when the 2nd stage is done on the current project?

Click to expand...

The booster in the video would have separated at roughly around 5 or 6K. For the current flight, it would be much higher - somewhere between 20K and 40K depending on when it is released. I have initially programmed the release at 6.5 seconds after burnout, 1300 ft/s at around 30K, but lots of time to change that.

For some reason, I am suddenly glad there are no trees at BlackRock. Why is that??

Jim

JimJarvis50 said:

Hearing no objections, the plan will be to light the second stage at the point shown in the overall flight profile below.

The second segment of the flight will be an N2501 going to a maximum speed of 1900 ft/s. The issues with this segment are when to separate the stages and when to light the 3rd stage motor.

The second and third stages will be pinned together so that the 3rd stage doesn't drag separate on first stage burnout (that would be bad). After the second stage burn, though, I think the parts need to stay together until the velocity slows down a bit. On a similar flight ....

https://youtu.be/j2Q1TeNx6SI?list=PLEISeVEqORmyQ_SWUlpwt-U4INlmn0PNj

... the booster was separated at about 1400 ft/s, and I think the booster almost came apart. I don't know for sure if this was due to the velocity, or instead, dropping back through Mach (opinions?). I don't really want to separate at 1900 ft/s (my feeling is that exposing an interstage coupler at this high velocity just can't be good). I could separate at a lower velocity, and even as low as 700 ft/s where I plan to light the 3rd stage.

Jim

Click to expand...

It might be a worthwhile effort to conduct a few simulations to see whether or not it is useful to delay the separation of both the first and second stages until you are ready to ignite the next stage. The reason to keep the stack together would be for greater retained momentum versus potential drag reduction which would be the purpose of the tradeoff study.

Rationale. Drag force does not depend on the rocket mass but rather the shape of the rocket. Deceleration of the rocket due to drag depends on the retained momentum of the rocket so a heavier rocket will decelerate slower than a lighter one experiencing the same drag forces. (That's the same reason why heavier bullets travel farther and decelerate slower than lighter bullets of the same caliber.)

The additional reason for keeping everything together is to reduce the potential for shredding the ejected stage. If there is a solid transition piece to act as a NC for the ejected stage, I think there is a lower probability of shredding. Without an effective NC if the airframe turns sides at high speed, the chance for column buckling of the airframe and stall buffeting flutter of the fins is enhance, probably as the Mach number squared or possibly as the Mach number cubed...

Food or fodder for thought.

Bob
Bob

bobkrech said:

It might be a worthwhile effort to conduct a few simulations to see whether or not it is useful to delay the separation of both the first and second stages until you are ready to ignite the next stage. The reason to keep the stack together would be for greater retained momentum versus potential drag reduction which would be the purpose of the tradeoff study.

Rationale. Drag force does not depend on the rocket mass but rather the shape of the rocket. Deceleration of the rocket due to drag depends on the retained momentum of the rocket so a heavier rocket will decelerate slower than a lighter one experiencing the same drag forces. (That's the same reason why heavier bullets travel farther and decelerate slower than lighter bullets of the same caliber.)

The additional reason for keeping everything together is to reduce the potential for shredding the ejected stage. If there is a solid transition piece to act as a NC for the ejected stage, I think there is a lower probability of shredding. Without an effective NC if the airframe turns sides at high speed, the chance for column buckling of the airframe and stall buffeting flutter of the fins is enhance, probably as the Mach number squared or possibly as the Mach number cubed...

Food or fodder for thought.

Bob
Bob

Click to expand...

The first stage has to be separated rather quickly. Until that happens, the stabilization system (connected below the second stage) won't do much (although there is an appreciable lever arm even in that configuration). There is roughly a 10-second coast period. Another reason to separate quickly is that the booster is draggy. I am sure having the first stage attached would hurt performance. On the other hand, when the booster separates, there will immediately be a significant turning force from the canards. If the rocket is at an angle, it could oscillate. I have set the gains where I think they need to be based on the testing, but the three stage is quite a bit longer and heavier than the test rocket. I plan to do a few calculations yet to look at this, but I'm not sure if I have the technical capability to work out a solution.

For the second/third stages, I have done the simulations, and there isn't much effect of separating them or keeping them together (i.e., the tendency to drag separate is pretty neutral). One issue here is which is the better configuration for avoiding weathercocking going through the jet stream?

The interstage coupler that would be exposed is 4" x 3", and it is sealed (i.e., the open tube is not exposed). It is the same interstage coupler as in the video.

Jim

I would check the NWS and the weather balloon sounding out of Reno the morning of the launch. The jet stream or any offshoot of it could be well north or south of Black Rock. I would hold off if winds were moving up high.
20 deg lock out on staging is a narrow window to hit. I'm nervous for my simple 2 stage flight. About the only thing any of us can do to lessen the impact of gravity turning, weather cocking, etc. is to shorten the coast.
At this point you will have burnt though $2k of propellant. I would go for it, separate after burnout allow a second for the stage to clear and light the third.

Incredible thread. Good luck with everything.

Without any simulations or tests for setting the gain of the stabilization unit for the longer rocket configuration, I'd suggest reducing the gain by half compared to what was tested to work with the shorter configuration. It should then likely not overcontrol or overstress the interstage coupling during maneuvering for trajectory correction. If it does not fully correct to vertical in the available time that is not a tragedy. Even a moderate correction is good! Overcorrecting at high speeds though would be stressful to the airframe and increase drag due to the maneuvering and possibly control induced oscillations.

Gerald

Kip_Daugirdas said:

I would check the NWS and the weather balloon sounding out of Reno the morning of the launch. The jet stream or any offshoot of it could be well north or south of Black Rock. I would hold off if winds were moving up high.
20 deg lock out on staging is a narrow window to hit. I'm nervous for my simple 2 stage flight. About the only thing any of us can do to lessen the impact of gravity turning, weather cocking, etc. is to shorten the coast.
At this point you will have burnt though $2k of propellant. I would go for it, separate after burnout allow a second for the stage to clear and light the third.

Click to expand...

I have seven upper level winds sites. They seem to be able to predict what will happen there, and the forecasts don't change that much. That's something I look at before even getting in the car. Most years have had an acceptable window, but you never know.

20 degrees is a bit tight, particularly given gyro drift with time and acceleration. That's what worries me - the time after launch before the 3rd stage. Not sure allowing a second between stages would be a good idea though. I think the rocket needs to slow down a bit or it won't survive.

Jim

G_T said:

Without any simulations or tests for setting the gain of the stabilization unit for the longer rocket configuration, I'd suggest reducing the gain by half compared to what was tested to work with the shorter configuration. It should then likely not overcontrol or overstress the interstage coupling during maneuvering for trajectory correction. If it does not fully correct to vertical in the available time that is not a tragedy. Even a moderate correction is good! Overcorrecting at high speeds though would be stressful to the airframe and increase drag due to the maneuvering and possibly control induced oscillations.

Gerald

Click to expand...

I think you're exactly right.

Jim

So, here is the electronics configuration for the flight. I'm somewhat constrained by the electronics I happen to own and the existing designs and electronics bays of the sections. So, it isn't exactly as you'd draw it up on a fresh sheet of paper, but it could work. Obviously, there has to be an approach for the nominal flight plan, but there also has to be consideration for what happens in case there is a problem or if one of the motors doesn't light. This is quite complicated, so I'm not sure it can easily be reviewed, but if you spot something you don't think is correct, please speak up.

Jim

JimJarvis50 said:

So, here is the electronics configuration for the flight. I'm somewhat constrained by the electronics I happen to own and the existing designs and electronics bays of the sections. So, it isn't exactly as you'd draw it up on a fresh sheet of paper, but it could work. Obviously, there has to be an approach for the nominal flight plan, but there also has to be consideration for what happens in case there is a problem or if one of the motors doesn't light. This is quite complicated, so I'm not sure it can easily be reviewed, but if you spot something you don't think is correct, please speak up.

Jim

Click to expand...

Preparations for my three-stage flight at Balls are continuing. Here are a few posts with updates.

Zebedee came over a few days ago and we looked over the electronics strategy. Made a few changes just trying to anticipate everything that could happen.

Jim

If you recall, I added some "fin crowns" on top of my 1st stage fins before the flight last year. This year, with the addition of the stabilization section (making the rocket still longer), I decided to increase the stability just a bit more. So, I have added wing tips to the crowns. This increases the stability (according to RockSim) from about 3.5 to 5.2. Sounds like a lot, but the rocket is pretty tall and skinny. The current stability just fits my eye a bit better.

Jim

And last, I have made a new shipping container for the rocket. The one I have been using was getting a bit frayed, and the new one will be a little easier to use. For the trip out, the case will be set on its side (to make room for lots of other rockets this year). More importantly, it will let me transport the rocket to the pad with the pieces assembled (instead of having to install all of the shear pins at the pad). I did it this way last year (transporting the stages in my Uhall, assembled and laying flat) using an assortment of straps, blankets and pillows. This will be much easier.

Jim

Jim, I know I have said this before, but you sir are a craftsman. Just beautiful stuff.

Nice Box

Zebedee said:

Nice Box

Click to expand...

I added pad slave handles!

Jim

So, I did the flight Friday morning. Been spending lots of time trying to find the pieces. Got the first stage and stabilization section back on Friday, and today, we found the third stage. The second stage is still AWOL. The flight was certainly not perfect. Got 130K altitude, which was good, and I have lots of interesting data and videos. Unfortunately, the first stage didn't separate from the stabilization section, so the vertical stabilization system couldn't work. I don't know why that happened, and it's too bad because it was a big focus for the flight. I'll post more data when I have time.

Jim