I could use just a little guidance

CarVac said:

That's not that fast, and also by the time you hit apogee, it has slowed down a lot. When you simulate a really really high performance rocket like Jim's staged rockets or Bare Necessities (which could definitely have benefited from spin stabilization) with half a degree of fin cant, it ends up spinning extremely quickly, and since the air thins out a lot, it no longer has any friction slowing the spin.

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And the lateral mass has to be perfectly balanced or you will get a washing machine effect and the rocket will come apart.

Sounding rockets are spin balanced like a tire.

CarVac said:

That's not that fast,

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It is fast in the context of reducing dispersion which is what I thought this thread was about.

UhClem said:

It is fast in the context of reducing dispersion which is what I thought this thread was about.

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I do acknowledge that it's probably fast enough, but if you put practically any intentional cant on something going as fast as Jim's rockets, it's going to be spinning much faster.

I have pretty much completed the initial hardware assembly for the vertical stabilization system. Over the weekend, I ordered the parts for my test rocket. It'll be a simple, 10-foot fiberglass rocket with four large fins (that can be made smaller as testing progresses). It pains me to have to build a fiberglass rocket, but I need something to test with.

On a more interesting note, it looks like I will be fortunate enough to equip the system with a UDB5 board and an OpenLog board.

https://www.sparkfun.com/products/11703
https://www.sparkfun.com/products/9530

With these, I can acquire and record the PWM signals from the Guardian, the rocket orientation and the raw gyro and accelerometer data. This will make evaluation of the system much easier. More details on this to come. At some point in the future, I would expect to retire the Guardian in favor of the UDB5 or its successors.

Jim

It sounds a lot like our current projects are about to collide.

Ravenex said:

It sounds a lot like our current projects are about to collide.

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Please continue to monitor my progress (and help me stay out of trouble). If you develop something that you would like me to use or test at some point, just let me know.

Jim

JimJarvis50 said:

In a typical flight, I would separate the booster shortly after burnout and then coast for perhaps 15 seconds. So, only the sustainer would be guided during that period and there is lots of time to get vertical. Even a minor correction back towards vertical will be an improvement.

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What about the option of keeping the control system in the head end of the booster? It would have to correct the attitude of the whole stack, but the mass would not be carried along in the sustainer.

jsdemar said:

What about the option of keeping the control system in the head end of the booster? It would have to correct the attitude of the whole stack, but the mass would not be carried along in the sustainer.

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Do you mean have the control system separate from the servos (which would be at the head end of the sustainer)? I don't think that would save much weight.

Or, do you mean have the control system in the top of the booster and keep the stages connected through the coast? I think the cannards would be close to the CG and perhaps not much use? Worth looking at a little closer though.

Or, perhaps you mean keep the control system (only) attached to the bottom of the sustainer during the coast, and then eliminate it when the sustainer motor lights? Hmm.... Minimum diameter fin tabs with no control linkage issues, and the mass goes away. I may have to think about that one.

Jim

Hey Jim,

Nice work as usual! How did you make the canards? Also, how are they mounted to the servos? A little hard to see in the video,

Jerry

JimJarvis50 said:

Please continue to monitor my progress (and help me stay out of trouble). If you develop something that you would like me to use or test at some point, just let me know.

Jim

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I would be honored I'd you would be willing to fly my system.

JimJarvis50 said:

Or, do you mean have the control system in the top of the booster and keep the stages connected through the coast? I think the cannards would be close to the CG and perhaps not much use? Worth looking at a little closer though.

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Yes, that one. The CG would be quite a bit forward in the 2-stage stack after burnout. You could put the complete control system section with canards at the head end of the booster motor with the recovery section for the booster above that. I think the canards would have a lot more control authority moving the empty booster around while keeping the heavy sustainer pointing up. Pointing the loaded sustainer (after separation) using forward canards would have less control authority. Different dynamics and inverted pitch deflection between the two options.

Carrying the booster along during coasting would have drag penalty, but carrying the canards along in the sustainer might have more penalty in mass and drag.

vahpr said:

How did you make the canards? Also, how are they mounted to the servos? A little hard to see in the video,

Jerry

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The canards are just from some scrap G10. The actual fin is mounted on another piece of G10 (with the holes). The metal piece attaches to the servo (in place of the typical plastic wheel) and then the canard screws into the metal piece. Pretty simple.

Jim

I got the forward canard system done. However, thinking about John's post, I have decided to pursue something different. My next big flight is a repeat of the three-stager, which is planned for Balls. I'd like to make that rocket go a bit straighter. What I'm leaning toward is putting the stabilization system at the top of the 1st stage. After the boost, the 1st stage would separate from the 2nd and 3rd stages, but the stabilization section would stay attached to the bottom of the second stage. In this location, the system would have about 10 seconds to bring the 2nd and 3rd stages to vertical. When the second stage motor is lit, the stabilization package would drop off (via a separation charge) and then recover under its own chute.

The advantages of this approach are numerous. First, guidance is applied when it's needed most (after the initial boost). Second, the canards can be a bit larger since they would be operating at Mach 1.2 and below (rather than Mach 3). This might actually improve overall stability. Third, when the 2nd stage motor lights, the weight and drag of the stabilization system are gone.

I still need to make my test rocket, which would now fly motor-less (or with the 98mm case included as a coupler). But, I need to add a short booster to get the stabilization/test rocket parts moving.

Jim

Jim, your build is looking really good. It will be great to see the outcome and resulting data. I noticed you mentioned my retractables awhile back in the thread, what do you need?



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JimJarvis50 said:

What I'm leaning toward is putting the stabilization system at the top of the 1st stage. After the boost, the 1st stage would separate from the 2nd and 3rd stages, but the stabilization section would stay attached to the bottom of the second stage. In this location, the system would have about 10 seconds to bring the 2nd and 3rd stages to vertical. When the second stage motor is lit, the stabilization package would drop off (via a separation charge) and then recover under its own chute.

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Would the attitude control system be active from liftoff or after first stage burnout?

You can minimize the drag of the canards with shape optimization and drag minimization. I think that you would get more altitude advantage with the canards keeping the second stage going vertical all the way to apogee than you would with the second stage on it's own doing a gravity turn for 60 seconds.

Bob

UhClem said:

It is fast in the context of reducing dispersion which is what I thought this thread was about.

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A 4"-4.5" spin stabilized sounding rocket use ~20-25 Hz spin rates at max velocity. A 14" diameter sounding rocket use ~4 Hz spin stabilization rate at max velocity.

Source: NASROC Sounding Rocket Handbook - 2001

Bob

Eyesinthesky said:

Would the attitude control system be active from liftoff or after first stage burnout?

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For the three-stage configuration, the canards at the top of the 1st stage would be close to the CG. Since they wouldn't be doing much, I would expect to have the system off until after burnout and dropping the first stage. Then, there is a coast period with velocity dropping from roughly 1400 ft/s to perhaps 500 ft/s (depending on how low I dare to go). Then, the stabilization package would drop off as the 2nd stage lights. It might be good to wait a second or two after burnout before turning on stabilization. This depends on how the Guardian reacts to acceleration and then deceleration, which is yet to be measured.

I could accomplish a similar outcome putting the canards midway on the 1st stage and then just keeping the stages attached. My first stage is pretty draggy (remember those fin skins). Of the two options, I think dropping the first stage would be better.

Jim

Man this thread is gettin' good.

op:

bobkrech said:

You can minimize the drag of the canards with shape optimization and drag minimization. I think that you would get more altitude advantage with the canards keeping the second stage going vertical all the way to apogee than you would with the second stage on it's own doing a gravity turn for 60 seconds.

Bob

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The interesting thing about this approach is that it seems that there are a lot of options for exactly where you put the stabilization. The first thing is to try to figure out if the Guardian can be used in this service. Need to look at the effects of acceleration, gyro drift over time, etc. Once that's done, then there are the goals for the flight to consider and the specific equipment limitations that I have to deal with. Listing all of those considerations would be boring, and there are a lot of things that will come up that I don't know about yet. So, for the short term, I'd like to be able to test both forward and rear canards and see how they work. Then, we can pick the best approach with all things considered.

Jim

bobkrech said:

A 4"-4.5" spin stabilized sounding rocket use ~20-25 Hz spin rates at max velocity. A 14" diameter sounding rocket use ~4 Hz spin stabilization rate at max velocity.

Source: NASROC Sounding Rocket Handbook - 2001

Bob

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I did look through the handbook and what I saw was that the spin rate at booster motor burnout was typically around one to two rps. Which is what I thought was most applicable to this thread.

UhClem said:

I did look through the handbook and what I saw was that the spin rate at booster motor burnout was typically around one to two rps. Which is what I thought was most applicable to this thread.

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The spin rates are linearly proportional to max V and inversely proportional to the velocity. https://hyperphysics.phy-astr.gsu.edu/hbase/amom.html

You comments are apply to Nike or Terrier boosted vehicles which are ~14" OD. In these cases the spin rate at booster burnout is 2 Hz and the final second stage burnout spin rate is 4 Hz.

The Super Arcas and the Viper Dart are more analogous to Jim's rocket. Both are about 4" O.D. The Super Arcas and the Viper Dart are both launched from spin rail launcher with a rail spin rate of ~6 Hz. At burnout the Viper booster spin rate is ~20 Hz and the Super Arcas is ~25 Hz.

View attachment VIPER DART LV - SRPHBK 2001.pdfView attachment Super Arcas -SOUNDING_ROCKET_PROGRAM_HANDBOOK_(JULY_2001).pdf

Since Jim's rocket will not be traveling as fast or as high as the sounding rockets, the spin rates would be lower (~12 Hz) for equivalent stabilization however it requires energy from the motor to spin up the rocket. I'm guessing that with today lightweight canard stabilization system you will get a higher apogee with active vertical stabilization (including drag loss) than you would with spin stabilization and a minimum launch angle of 5 degrees of vertical. The more forward the canards, the longer the lever arm and the smaller the fins for the same torque. I'd like to see someone do the calculations for the trade-off for properly profiled fins.

Bob

The closer the canards are to the CG, the less effective they will be. You'd need to make them bigger. And too close to the CG, they won't be worth having.

Would you mind posting a sketch if the various staged configurations with the expected CG for each configuration and where you are talking about having the canards located for each?

If I was doing a real 3-stager, and wanted the 2nd stage to have the guidance system, to point the 3rd stage vertical, I would have the control surfaces on the fins at the back of the 2nd stage. But that is a more complicated thing to do, of course, never mind issues with landing damage, so I am not seriously suggesting that. Only that canard guidance in the "middle" of the rocket, closer to the CG, is not good.

Same thing for a 2-stager, control surfaces on the lower fins.. Unless the lower stage was VERY big and tall and the upper stage was pretty small and light (and not too long), that is the only reasonable way I can see canards on the "not upper stage" being able to control the vehicle and point the upper stage vertical.

- George Gassaway

georgegassaway said:

The closer the canards are to the CG, the less effective they will be. You'd need to make them bigger. And too close to the CG, they won't be worth having.

Would you mind posting a sketch if the various staged configurations with the expected CG for each configuration and where you are talking about having the canards located for each?

If I was doing a real 3-stager, and wanted the 2nd stage to have the guidance system, to point the 3rd stage vertical, I would have the control surfaces on the fins at the back of the 2nd stage. But that is a more complicated thing to do, of course, never mind issues with landing damage, so I am not seriously suggesting that. Only that canard guidance in the "middle" of the rocket, closer to the CG, is not good.

Same thing for a 2-stager, control surfaces on the lower fins.. Unless the lower stage was VERY big and tall and the upper stage was pretty small and light (and not too long), that is the only reasonable way I can see canards on the "not upper stage" being able to control the vehicle and point the upper stage vertical.

- George Gassaway

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I have to spend a little flying rockets, but I'd be happy to post the configurations I plan to fly. Although I will keep an open mind for a while, my current best option is to put the canards below the second stage, just as you have suggested. They would come off, though, when the motor lights, so this probably isn't what you have in mind, but I'll post the plan shortly.

Jim

Jim, have you considered doing this in smaller, or at least lower performance setup? I think that make a lot of sense- maybe something that goes 10k'-20k'. This way you might actually get some experience with the system without having to risk the big rocket to an totally unknown and untested guidance system.

Heck do it first with a normal 4" glass rocket, single stage, pointed 10 degrees of vertical and see if it corrects.

It seems smart to me to test more before trying it on the über carbon three stage of doom.

markkoelsch said:

Jim, have you considered doing this in smaller, or at least lower performance setup? I think that make a lot of sense- maybe something that goes 10k'-20k'. This way you might actually get some experience with the system without having to risk the big rocket to an totally unknown and untested guidance system.

Heck do it first with a normal 4" glass rocket, single stage, pointed 10 degrees of vertical and see if it corrects.

It seems smart to me to test more before trying it on the über carbon three stage of doom.

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Sure, it will just be a test rocket for initial testing. The first test will probably just be a flight where the output from the Guardian is acquired but with no guidance applied. I think with a couple of flights like that, we'll know whether the unit will work or not - getting the data is the key. First flight probably not more than 5K or so.

Jim

JimJarvis50 said:

Sure, it will just be a test rocket for initial testing. The first test will probably just be a flight where the output from the Guardian is acquired but with no guidance applied. I think with a couple of flights like that, we'll know whether the unit will work or not - getting the data is the key. First flight probably not more than 5K or so.

Jim

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Good, I figured you were, but it crossed my mind so I thought I would mention it.

Here's a pass at the stability calculations for the three-stage configuration. The first pic shows the N5800 to N2501 to M745 rocket that flew at Balls last year, but where only the first stage fired (crap!). For the rocket as shown, the stabilities of the three configurations are 3.56 (all three) to 1.53 (sust & 2nd) to 1.45 (sust).

The second pic below is what it would look like with the stabilization package below the second stage. I'm not sure of the weight yet. It will need to be pretty strong in that location. I've assumed 5 pounds for this analysis. For the canards I currently have (2" root cord, 1" tip cord, 1.5" span), the stabilities are 3.61 to 1.46 to 1.45. It might make sense to increase the size of the canards just a little.

The flight profile would be to drop the first booster after motor burnout (going to the configuration in the third pic). The rocket would glide for about 10 seconds in this configuration, hopefully, going vertical. The stabilization section would drop off as the 2nd stage lights.

It could work ....

Jim

A two-stage sustainer might glide for quite a while in the attached configuration.

Jim

Now that I see the size of those controlling fins, I'd be worried that if they are ever used when they are not the farthest aft fins, you might get control reversal. I think Armadillo Aerospace ran into that problem when they tried canards?

Basically, you may have to disable them until the stage behind them has separated.

In that vein, I'd imagine that they'd be best behind the second stage, so that they can right the stack before the second stage really gets it going.