3 Two Stage Questions: Shear pins, Flyaway rail guide, and Sustainer igniter installation

[strider07928]

I'm in final stages of prepping my first big 2-stage I'll be launching at Airfest next week (I am giddy with excitement).
4" Wildman Argonia (11'9") L1090 in the booster and K250 in the sustainer
I have three questions and would love input. I already tried searching but didn't find answers.

* Do I use shear pins to secure the aft sustainer airframe?
Seems like I should to avoid drag separation in both sustainer sections, but figured I'd ask to make sure this is correct.
Planning for 4 4-40 shear pins in each (maybe this is overkill, might leave one out and go with 3. Trying to figure out the math now)

* I'm using a Flyaway rail guide. Is a single Flyaway Rail Guide placed on the Booster OK? Or do I need two rail guides? Or should one be placed on the Sustainer?

* When setting up at the pad, what is the best order of operations for installing the sustainer igniter?
Given the size of the rocket it will be tough to install the sustainer igniter when it is upright, and should the flight computer already be armed? (Blue Raven)
Seems a bit scary to be installing the igniter into an armed sustainer if it isn't upright on the pad.

Here is what I am thinking for at the pad:
Install and secure the igniter into the sustainer (dowel and tape).
Load the rocket onto the rail and point upward
Arm the flight computers
Install the booster igniter

Thanks!
Jason

 

[Titan II]

* Do I use shear pins to secure the aft sustainer airframe?
Seems like I should to avoid drag separation in both sustainer sections, but figured I'd ask to make sure this is correct.
Planning for 4 4-40 shear pins in each (maybe this is overkill, might leave one out and go with 3. Trying to figure out the math now)

* I'm using a Flyaway rail guide. Is a single Flyaway Rail Guide placed on the Booster OK? Or do I need two rail guides? Or should one be placed on the Sustainer?

Here is what I am thinking for at the pad:
Install and secure the igniter into the sustainer (dowel and tape).
Load the rocket onto the rail and point upward
Arm the flight computers
Install the booster igniter

I use shear pins on all points of separation, and always use a separation charge at the ISC.

I do not use flyaway guides, so no comment. However, I only use rail guides on the booster.

Pad sequence looks good.

Have fun.

 

[jderimig]

"Drag "separation in a 2-stage is good (unless your sustainer ignition electronics are in the booster). But sustainer separation during boost is bad,

 

[StreuB1]

Unless you absolutely need to hold onto the booster during coast, I would ditch it immediately. A separation charge at 0.5sec after burnout of the booster is good to allow deacceleration to set in. A very close fit on the sustainer to interstage with a separation charge is what I would plan for.

I would not use flyaway's on a 2-stage or anything with a substantial amount of weight. Its not what they were designed for. Rail buttons on the booster is what I would suggest or a tower.

Please don't take this the wrong way, but shouldn't all of this be worked out at this point if you are flying this at Airfest?? IIRC you need to be approved by Kloudbusters for a rocket like this.

Two Stage Rule #1 - This rule applies to multi-stage flights with one or more "K" or greater impulse motors installed. The ignition of the sustainer motor must controlled by one of two types of electronics: (A) An altimeter capable of inhibiting the ignition of the sustainer unless a specific time/altitude threshold is met, or; (B) An altimeter that checks for vertical trajectory of flight prior to sustainer ignition. Flights of all "K" and above multi-stage rockets will be required to complete and submit the KLOUDBusters High Altitude Project Submission Template thirty (30) days in advance of the launch (the form can be found here: http://kloudbusters.org/images/HiAltApp.doc) regardless of the altitude the rocket will attain. A description of the electronics used to comply with this rule and of the time/altitude threshold or other means of inhibiting sustainer ignition in the event of a not nominal booster flight will be required.

 

[ChuckH]

I've used flyaway rail guides on the 3" minimum diameter two stage in my profile pic. Two sets, one on the booster and one on the sustainer. It worked fine but this is a sample size of one so take it for what it's worth.

Your planned order of operations for igniter installation and arming looks good to me:

Here is what I am thinking for at the pad:
Install and secure the igniter into the sustainer (dowel and tape).
Load the rocket onto the rail and point upward
Arm the flight computers
Install the booster igniter

 

[JimJarvis50]

My quick opinions ....

You should shear pin everything except for the sustainer separating from the interstage coupler. In particular, the IC should be pinned to the top of the booster as a nose cone would.

I would personnally never use flyaway guides for a larger two-stage. Put 1515 buttons on there. I would suggest two of them closer to the bottom of the booster, perhaps 24" apart. A third button can be put at the top of the booster or on the sustainer.

You should really have a switch to disconnect the igniter from the altimeter. This switch gets closed last after powering up the altimeter.

For your Raven, I assuming you are using tilt inhibition. In addition to that, there should be a minimum altitude or time threshold. To be honest, I'm not sure how the Blue Raven should be programmed. With Ravens before the Blue Raven, the strategy was to have the motor light at some preselected altitude as long as the time was less than T. So, you would determine the time at the altitude where you want the igniter to fire, and then set a T< value a few seconds after that. The Blue Raven may be different, and in particular, allow a T= trigger. If you'd like to post a pic of the program screen, we could take a look.

Jim

 

[rfjustin]

I like and use the 1515 rail suggestion @JimJarvis50 mentioned above. I'm flying a two stage 3", same motor combo as OP, both the booster and sustainer have (2) 1515 rail buttons. Overkill, yes, but I like the rigidity of 1515 for anything 25+ pounds on the pad.

Good luck OP, I hope your flight was pre-approved by the BOD, if not this is going to require some serious attention on site...

Best,

 

[rocketace]

Good luck on your flight!

Here are my comments: (I have only flown 3 two stagers so take it with a grain of salt)

I do not use sheer pins on the Booster/Sustainer connection, nor would I recommend it. If you want it to stay together, just make sure it's a snug fit, just like the other joints. And either way use a separation charge.

I'll ignore the flyaway guides question as I have no experience and do not plan to use them for anything.

As far as arming sequence for the Blue raven, see below for a simplified version of my check list. I highly recommend making your own with more detail. If anything it will help you walk though it in your head and get it right before you are at the field.

Big note: If you are using the custom output feature on the BlueRaven, make sure you program the primary and secondary logic for that channel. If you never look at the secondary, it could ignite before you want it... They can be programed the same as the old ones, but also have multiple new ways to program. The logic I used on my most recent 2 stage flight for the Blue raven can be found Here, but basically is to ignite when the rocket slows to a specific velocity (if vertical enough).

 

[strider07928]

I use shear pins on all points of separation, and always use a separation charge at the ISC.

I do not use flyaway guides, so no comment. However, I only use rail guides on the booster.

Pad sequence looks good.

Have fun.

Thank you!

 

[cerving]

I know your launch is pretty close, but a tower would be a much better option than flyaway rail guides. My experience with them for heavy/fast rockets (including 38mm 2-stager and a 54mm MD with a K2050) has not been good... I think the only one of several that I have bought that's still intact is a 29mm. If you ARE going to use them, definitely put one on each stage, and don't expect to get them back in re-useable condition... they tend to break on landing. I wish somebody would come up with an aluminum rail guide... I like 3D printing, but it's not suitable for every use case.

 

[strider07928]

two

My quick opinions ....

You should shear pin everything except for the sustainer separating from the interstage coupler. In particular, the IC should be pinned to the top of the booster as a nose cone would.

I would personnally never use flyaway guides for a larger two-stage. Put 1515 buttons on there. I would suggest two of them closer to the bottom of the booster, perhaps 24" apart. A third button can be put at the top of the booster or on the sustainer.

You should really have a switch to disconnect the igniter from the altimeter. This switch gets closed last after powering up the altimeter.

For your Raven, I assuming you are using tilt inhibition. In addition to that, there should be a minimum altitude or time threshold. To be honest, I'm not sure how the Blue Raven should be programmed. With Ravens before the Blue Raven, the strategy was to have the motor light at some preselected altitude as long as the time was less than T. So, you would determine the time at the altitude where you want the igniter to fire, and then set a T< value a few seconds after that. The Blue Raven may be different, and in particular, allow a T= trigger. If you'd like to post a pic of the program screen, we could take a look.

Jim

Thank you Jim. I’ve attached a pic of the Blue Raven configuration. You can set a minimum altitude, maximum velocity, max gyro angle, and maximum tilt angle.
I’m also overnighting 1515 rail buttons that I’ll epoxy on as well as see about adding a disconnect between the sustainer ignition.

Thanks for your suggestions.

 

[strider07928]

I know your launch is pretty close, but a tower would be a much better option than flyaway rail guides. My experience with them for heavy/fast rockets (including 38mm 2-stager and a 54mm MD with a K2050) has not been good... I think the only one of several that I have bought that's still intact is a 29mm. If you ARE going to use them, definitely put one on each stage, and don't expect to get them back in re-useable condition... they tend to break on landing. I wish somebody would come up with an aluminum rail guide... I like 3D printing, but it's not suitable for every use case.

Thank you!

 

[strider07928]

Good luck on your flight!

Here are my comments: (I have only flown 3 two stagers so take it with a grain of salt)

I do not use sheer pins on the Booster/Sustainer connection, nor would I recommend it. If you want it to stay together, just make sure it's a snug fit, just like the other joints. And either way use a separation charge.

I'll ignore the flyaway guides question as I have no experience and do not plan to use them for anything.

As far as arming sequence for the Blue raven, see below for a simplified version of my check list. I highly recommend making your own with more detail. If anything it will help you walk though it in your head and get it right before you are at the field.

Big note: If you are using the custom output feature on the BlueRaven, make sure you program the primary and secondary logic for that channel. If you never look at the secondary, it could ignite before you want it... They can be programed the same as the old ones, but also have multiple new ways to program. The logic I used on my most recent 2 stage flight for the Blue raven can be found Here, but basically is to ignite when the rocket slows to a specific velocity (if vertical enough).

View attachment 600441

Thank you! I’ll have shear pins at all connection except between the booster and sustainer. I’ll just friction fit that (not tight) and will separate via a charge.

 

[strider07928]

Unless you absolutely need to hold onto the booster during coast, I would ditch it immediately. A separation charge at 0.5sec after burnout of the booster is good to allow deacceleration to set in. A very close fit on the sustainer to interstage with a separation charge is what I would plan for.

I would not use flyaway's on a 2-stage or anything with a substantial amount of weight. Its not what they were designed for. Rail buttons on the booster is what I would suggest or a tower.

Please don't take this the wrong way, but shouldn't all of this be worked out at this point if you are flying this at Airfest?? IIRC you need to be approved by Kloudbusters for a rocket like this.

Two Stage Rule #1 - This rule applies to multi-stage flights with one or more "K" or greater impulse motors installed. The ignition of the sustainer motor must controlled by one of two types of electronics: (A) An altimeter capable of inhibiting the ignition of the sustainer unless a specific time/altitude threshold is met, or; (B) An altimeter that checks for vertical trajectory of flight prior to sustainer ignition. Flights of all "K" and above multi-stage rockets will be required to complete and submit the KLOUDBusters High Altitude Project Submission Template thirty (30) days in advance of the launch (the form can be found here: http://kloudbusters.org/images/HiAltApp.doc) regardless of the altitude the rocket will attain. A description of the electronics used to comply with this rule and of the time/altitude threshold or other means of inhibiting sustainer ignition in the event of a not nominal booster flight will be required.

Thank you! Appreciate the feedback. I’m installing 1515 rail buttons and I sent the application.

 

[JimJarvis50]

Thank you Jim. I’ve attached a pic of the Blue Raven configuration. You can set a minimum altitude, maximum velocity, max gyro angle, and maximum tilt angle.
I’m also overnighting 1515 rail buttons that I’ll epoxy on as well as see about adding a disconnect between the sustainer ignition.

Thanks for your suggestions.
View attachment 600537

I haven't used the Blue Raven before, so take several grains of salt with what I say here. On the minimum altitude, I would typically select a value that is perhaps 60% of what you expect based on a simulation at the time you want the igniter to fire. A gyro angle of 7° is pretty tight. Unless you're flying over 20K, 15° is fine. I think you want burnout number to be greater than or equal to 1 (not two). It surprises me not to see the ability to set a time. If you can do that, you should set a time-less-than value to be a few seconds after you expect the motor to light. This "closes the window" so that the motor can't light at some later time if the criteria just happen to be met.

With two stagers, your job is to keep the sustainer motor from lighting on the ground (by accident) or in the air if the conditions are not met. The altimeter does the job in the air, but the disconnect switch to the igniter is important as well. There are various ways to do this. The lowest approach is a switch that disconnects one lead. Next level is a switch that disonnects both leads. Above that is a switch that disconnects the leads but also shunts the leads with the switch in the off position. Even higher is the previous switch but make-before-break.

The other thing that I would suggest you consider is to perform an all-up test at the pad. In an all-up test, you set the rocket vertical and then turn everything on, except that the igniter is outside of the motor. This includes all of the deployment electronics and gps equipment. A successful test is where the igniter doesn't fire. Then, you turn everything off, put in the igniter (horizontal) and then put the rocket on the rail and finish the prep, just as in the all-up test. The all-up test is your insurance that the motor won't light while your next to it turning on the switches. The pic is from a high altitude flight I did a few years back. You can see the sustainer upright on a little stand that I use (so that the wires don't get damaged under the rocket).

Jim

 

[rocketace]

The preset "Airstart" settings are fairly limited. If you switch it to custom, you have a lot more options.

 

[AllDigital]

Thank you Jim. I’ve attached a pic of the Blue Raven configuration. You can set a minimum altitude, maximum velocity, max gyro angle, and maximum tilt angle.

Jason, make sure you have a MINIMUM velocity lock-out set in the staging logic, in addition to the booster burn-out detect, tilt angle lockout, and minimum altitude. We had a team out at FAR last weekend with a two-stage vehicle ready to go to 180K feet and a few seconds after launch they lost the nosecone. The rocket turned into a skywriter, hit apogee, and then both sustainer and booster came down under their own drogues. Once their sustainer was upright (under drogue) the motor lit, because they didn't have a velocity lock-out and all the other staging rules had been met.

 

[JimJarvis50]

Jason, make sure you have a MINIMUM velocity lock-out set in the staging logic, in addition to the booster burn-out detect, tilt angle lockout, and minimum altitude. We had a team out at FAR last weekend with a two-stage vehicle ready to go to 180K feet and a few seconds after launch they lost the nosecone. The rocket turned into a skywriter, hit apogee, and then both sustainer and booster came down under their own drogues. Once their sustainer was upright (under drogue) the motor lit, because they didn't have a velocity lock-out and all the other staging rules had been met.

I think this is a good example of why it is important to set a T< value. It's hard to light a motor if there is the combination of a minimum altitude with a T< value because there is only a small window where the two criteria can be true. You have to close the window.

Jim

It appears that this team didn't go through Tripoli Class 3 review since they were going to FAR. The review process catches this sort of crap.

 

[jderimig]

Speed calculation by accelerometer integration likely goes out the window after skywriting and apogee deployment. The speed inhibits would be unreliable at best. A good altimeter algorithm could detect flight anomalies like this and cancel airstart events instead. One obvious solution to this use case is not light a sustainer after an apogee was detected.

 

[AllDigital]

Yeah, seems obvious to me. In this case the university team was using a commercial flight computer (I don’t recall which one), but confessed they only had a few lockouts selected (altitude and angle?). When the sustainer nose ripped off it damaged the sustainer forward closure, so when the computer fired the sustainer igniter (under chute), both ends lit up like a pinwheel. There were multiple failures for the team to diagnose and learn from. Here is video of that crazy flight:

 

[Neutronium95]

Yeah, seems obvious to me. In this case the university team was using a commercial flight computer (I don’t recall which one), but confessed they only had a few lockouts selected (altitude and angle?). When the sustainer nose ripped off it damaged the sustainer forward closure, so when the computer fired the sustainer igniter (under chute), both ends lit up like a pinwheel. There were multiple failures for the team to diagnose and learn from. Here is video of that crazy flight:

I heard that they were using a Telemega, which has had one or two other notable failures where it lit the sustainer when it really shouldn't have.

 

[JimJarvis50]

I heard that they were using a Telemega, which has had one or two other notable failures where it lit the sustainer when it really shouldn't have.

It's always possible that there could be a hardware failure. However, it is far more likely that there was simply poor programming. There is a proper way to program a Telemega (with minor variations on the theme) and those that fly high altitude regularly know what that is. I have reviewed easily 50 large two-stage projects for Tripoli or Spaceport, and at least two-thirds of them were Telemega's. The initially proposed program is seldom correct, and part of the review process is to try an educate the team or flyer where the holes are in what they proposed. Unfortunately, over time, teams lose that knowledge, and when their projects are not reviewed, stuff happens. I don't have specific information on this flight, but I suspect this is what happened.

Jim

 

[strider07928]

Thanks everyone for all your suggestions. I ditched the Flyaway rail guide and installed 2 1515 buttons on both the booster and the sustainer (2 on the sustainer because I'll want to fly that solo, too). I also installed an extra disconnect between the sustainer ignition and the flight computer. I'll dig into the Blue Raven setup and custom configurations when I get to the hotel. I'll be looking for guidance to make sure the setup all looks good before I fly it. Leaving tomorrow morning for Wichita. See you at Airfest!!! Thanks again! This was definitely my most ambitious project yet.

 

[JimJarvis50]

I'm planning to be at AirFest, hanging out with the Texans. I have a small two-stage flight in the works (a couple of J motors). I can take a quick look at your rocket if you'd like. Otherwise, good luck on the flight!

Jim

 

[Adrian A]

I haven't used the Blue Raven before, so take several grains of salt with what I say here. On the minimum altitude, I would typically select a value that is perhaps 60% of what you expect based on a simulation at the time you want the igniter to fire. A gyro angle of 7° is pretty tight. Unless you're flying over 20K, 15° is fine. I think you want burnout number to be greater than or equal to 1 (not two).

Agreed about the above, especially the burnout counter. Setting the burnout counter to 2 is what you want for ignition of a 3-stage flight (which I forgot to do on my 3-stage flight attempt at last year's BALLS)

It surprises me not to see the ability to set a time. If you can do that, you should set a time-less-than value to be a few seconds after you expect the motor to light. This "closes the window" so that the motor can't light at some later time if the criteria just happen to be met.

The "custom configuration" screen can be used to add this if you want.

Jason, make sure you have a MINIMUM velocity lock-out set in the staging logic, in addition to the booster burn-out detect, tilt angle lockout, and minimum altitude. We had a team out at FAR last weekend with a two-stage vehicle ready to go to 180K feet and a few seconds after launch they lost the nosecone. The rocket turned into a skywriter, hit apogee, and then both sustainer and booster came down under their own drogues. Once their sustainer was upright (under drogue) the motor lit, because they didn't have a velocity lock-out and all the other staging rules had been met.

The "custom configuration" screen can be used to add this if you want.

I think this is a good example of why it is important to set a T< value. It's hard to light a motor if there is the combination of a minimum altitude with a T< value because there is only a small window where the two criteria can be true. You have to close the window.

There are several ways to skin the cat of preventing an ignition for the failure case shown in the video. The Blue Raven's default airstart setup shown earlier does it using the check I call "nominal ascent" which is the one labeled with the "Do not ignite if tilt angle exceeded this value at any time during the flight". If the rocket goes up and does a loop-de-loop, the nominal ascent check will latch false and will stay false even if the rocket goes perfectly vertical again later.

A time < X check wouldn't hurt, though at the moment I can't think of an off-nominal scenario that wouldn't be caught by the other checks. I might be missing one though.

Adding a velocity > X check could be important. An example where this could come in handy is a booster CATO. The burnout counter won't get to 1 unless the booster provided at least 40 feet/second, so in effect there is already a (very low) minimum velocity. But that threshold check is much lower than you would want for a sustainer ignition check, since usually you want at least 45 feet/second coming out of a tower, and at those slow speeds the rocket can pitch over pretty quickly due to ignition delays even if it's within limits after the booster burnout.

Speed calculation by accelerometer integration likely goes out the window after skywriting and apogee deployment. The speed inhibits would be unreliable at best. A good altimeter algorithm could detect flight anomalies like this and cancel airstart events instead. One obvious solution to this use case is not light a sustainer after an apogee was detected.

If the rocket is skywriting, then the nominal ascent check would be effective. The minimum velocity check would cover a case where the sustainer is still going straight but the booster just didn't do its job, for example if it CATOs. In that case, the velocity estimate should be accurate.

 

[pugachu]

^ This type of functionality is why I bought my Blue Raven. Also, the high fidelity data logging is awesome. I had a 2-stage sustainer light on the pad while I was next to the rocket setting it up 20 years ago. It happened because it was a simple timer with break wire launch detection, and I bumped the break wire cord. Don't even get me started on mercury switches for staging

 

[cerving]

And that's why both of those ignition mechanisms are no longer allowed. There are too may other options available that have built-in intelligence to know what a nominal flight should look like.

 

[Titan II]

And that's why both of those ignition mechanisms are no longer allowed.

Tripoli rules state that a mercury switch shall not trigger the ignition of a rocket motor. Do you happen to have a citation showing where Tripoli does not allow a breakwire? Thank you.

 

[cerving]

My mistake... it's "roller switches" that are banned. Using a breakwire (alone) to ignite a motor is probably not a very good idea, though... I doubt that you'd get that past an RSO with any experience.

13-11

A mercury switch or roller switch shall not trigger the ignition of a rocket motor.

 

[pugachu]

Tripoli rules state that a mercury switch shall not trigger the ignition of a rocket motor. Do you happen to have a citation showing where Tripoli does not allow a breakwire? Thank you.

I thought timers were still allowed, the breakwire 20+ years ago was just to trigger the timer, and was what the timer manufacturer recommended using at the time. In any case, there weren't tilt lockout devices that I knew of when my 'incident' happened. I'm just glad it happened out on the range, while vertical, and it was 'only' a G64. I still never load the starter until I'm at the pad.

The mercury switches was back in the days of using sheathed thermalite to do airstarts and such.

I'm working on piecing together a complex cluster / 2 stage Nike Hercules (4x 29mm's + 1x 38mm in booster, 1x 54mm in sustainer). But rest assured, there won't be a simple timer or breakwire for staging or airstarts on that.