Accepted Method for Air Starts or Staging Functions

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Dave A

Well-Known Member
TRF Supporter
Joined
Jan 21, 2013
Messages
1,263
Reaction score
220
Location
Fort Myers, FL
I have seen discussion of the safety involved in starting motors after liftoff.
IMO (just mine)

1) If the main engine is more than sufficient to lift the vehicle to apogee, then it should not matter what type of electronics light the air-started outboards. If it works it will happen on que, if it doesn't, no harm.

2) When igniting another stage, then it is important the event happens when the vehicle is vertical so it can continue on the correct path.
Is there a ruling from NAR or TRA (at their own sanctioned events) that successive stages cannot be fired by basic timers? (that have no way of knowing which direction the nose is pointed)
 
1) is perhaps a bit of a miswording? If the initial motor is sufficient to lift the rocket then just on that motor there is the potential for one apogee range. If it is not sufficient of course it should not be launched! Now for all the airstart motors, any combination of them could light, in any order, with any timing. The collection of those possible events defines where the rocket could go - each with its own apogee and trajectory range. Obviously bad things can happen with uneven starting or late firing, etc. Airstarted motors are not usually axial which adds additional consideration over simple staging. Having the airstart motor - singular - be at the center, moves the location where many of the bad things can happen to at the tower instead of in flight. Which is safer might be debatable. But in any event, airstarts which happen incorrectly can result in a great many hazardous scenarios. It is far from harmless.

Gerald
 
I would say that it is good to have a timer that senses and is activated by the lift-off. For example, some timers need to sense 2.5 g's for about 0.5 seconds. This removes the chance of an accidental upper stage firing.

I have been saved twice now on two different mid-power models by having a first stage parachute large enough to bring down both stages without damage. In both models there was a second stage coupler that was connected to the first stage shock cord and parachute. One model was the Nike Hercules with a cluster of four D12 motors in the first stage and the other model was a standard missile with a G78 in the first stage. In both cases the second stage failed to fire, but the whole model descended soft enough that there was no appreciable damage.
 
Last edited:
TRA has just placed a requirement on HPR staging electronics that it must have some kind of mechanism that ensures (at least in theory) that an airstart won't happen in a non-vertical orientation. No more simple timers. This could be some kind of IMU, a time-to-altitude, or a minimum-velocity-at-time function. For a successful airstart you need to model the flight carefully so you have a very good idea what the flight is going to look like, and pick a booster motor with a high enough average thrust so that it gets the rocket moving well to prevent it from weathercocking or otherwise going off-vertical.

Your sustainer's electronics should be able to bring the whole thing back in one piece if the motor doesn't fire, and of course you need to be able to disarm the airstart electronics if that happens.
 
Cris-you know we are leading you on for: A) fully sealed stand alone gyroscopic stabilization units and/or B) a G switch w/a 4th dimension sensor package for airstarts. I'm sure you'll think about it for 5 minutes, scribble a schematic on the side of a Top Ramen cup and then proceed with production units that cost three pieces of bubble gum and a licorice whip. I'm not in any rush, so tomorrow is good for me.
 
TRA has just placed a requirement on HPR staging electronics that it must have some kind of mechanism that ensures (at least in theory) that an airstart won't happen in a non-vertical orientation. No more simple timers. This could be some kind of IMU, a time-to-altitude, or a minimum-velocity-at-time function.

Can you point me to where this new rule is published? I wasn't aware Tripoli was doing this!
 
Can you point me to where this new rule is published? I wasn't aware Tripoli was doing this!

That's what I have been told by a TRA prefect. If it's not in fact a rule, I stand corrected. However, even if it's not a requirement, it would be prudent to treat it as such; timers and G-switches have no way of determining your orientation either directly or indirectly.
 
I too am hoping that by the time I finish the big monstrosity I'm working on that Cris has an Eggtimer air starter. I absolutely love my two Eggtimers and my TRS. Great stuff, and plan on ordering a few more.
 
The last discussion I remember about this in which any action was taken by the TRA board was when the mercury and roller switches were added to the "not allowed" list. Not sure when that was.

The subject does come up from time to time and I think there have even been a couple of tilt detectors manufactured and used but do not know if any are still available.
 
This was posted on my club (a Tripoli Prefecture) website:

Two Stage Rule #1 - This rule applies to multi-stage flights with one or more "I" 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 "combined impulse
of an I" and above multi-stage rockets will be required to complete and submit the PARS High Altitude Project
Submission Template thirty (30) days in advance of the launch (the form can be E-mailed to you upon request) 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.

Two Stage Rule #2 - There will not be any drag races of multi-stage rockets regardless of impulse installed. When you consider the complexity of each flight with the number of events that must occur for a successful and safe flight, the club is not willing to subject our spectators, guests and members to that level of risk.

If you have any questions or concerns, please contact our prefect.

Sooooooo, I take that would mean if using an H or below, it would be acceptable to do a timer. Anyone from TRA or NAR hierarchy feel free to correct me if that's not the case.

Kurt
 
Last edited:
The last discussion I remember about this in which any action was taken by the TRA board was when the mercury and roller switches were added to the "not allowed" list. Not sure when that was.

The subject does come up from time to time and I think there have even been a couple of tilt detectors manufactured and used but do not know if any are still available.

Joe,
The Tripoli BoD did indeed recently look into trying to put in a rule that would make some sort of "smart" ignition devise a requirement but we found that quantifying what would and what would not be allowed was too onerous on the local clubs and their RSO's so we did not take any action.
However, with that said, there is no doubt that the risk of a multi-stage rocket is significantly higher than a single stage. Simply put, there are many more failure modes that can occur with a staged rocket. With this in mind, we as a hobby community should use the best technologies available to minimize risk. Right now, there are several altimeters that have the ability to inhibit the ignition stage unless the rocket has met either a time/altitude threshold or can check for verticality. At this point, to continue to use a simple timer just adds to the overall risk of your flight which puts the hobby at risk.
Years ago we all used launch rods for guidance. With the advent of rails, our ability to launch straighter was increased significantly. Now, at any major launch, the number of high power flights that fly off of rails greatly exceed the number of flights off of rails. From time to time at one of our launches, a flyer will show up with a large rocket looking for a large diameter rod. When I ask them why they don't put buttons on their rocket I normally hear "I'm old school!" It took me a while but I finally figured out what "old school" meant. I've come to the conclusion that it means "I'm too lazy or cheap to put $3 worth of buttons on it."
Folks, if you are into staging, I challenge you to go take a look at the newer altimeters out there. Most are quite capable and many are reasonably priced. Don't go "old school" just because you have a timer or don't want to go through the effort to upgrade your avionics.

Bob Brown
Prefect, Kloudbusters Inc.
Tripoli Member
 
This was posted on my club (a Tripoli Prefecture) website:

Two Stage Rule #1 - This rule applies to multi-stage flights with one or more "I" 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 "combined impulse
of an I" and above multi-stage rockets will be required to complete and submit the PARS High Altitude Project
Submission Template thirty (30) days in advance of the launch (the form can be E-mailed to you upon request) 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.

Two Stage Rule #2 - There will not be any drag races of multi-stage rockets regardless of impulse installed. When you consider the complexity of each flight with the number of events that must occur for a successful and safe flight, the club is not willing to subject our spectators, guests and members to that level of risk.

If you have any questions or concerns, please contact our prefect.

Sooooooo, I take that would mean if using an H or below, it would be acceptable to do a timer. Anyone from TRA or NAR hierarchy feel free to correct me if that's not the case.

Kurt

Kurt,
I'm not Tripoli "hierarchy" but what you are referring to is a local club rule not a national organization rule. Our club implemented a similar rule back in 2013. Any club can put additional restrictions in place for their launch sites above and beyond what the national organization requires.
Bob Brown
Prefect, Kloudbusters Inc.
Tripoli Member
 
I do believe that the TeleMega is one of the ones that can stop ignition if the rocket goes x degrees from vertical

  • Recording altimeter for high power model rocketry
  • Supports dual deployment and 4 additional pyro events.
    Pyro events are configurable and can be based on time and various flight events and status, including angle from vertical (for safety in staging and air start flights).
 
Joe,
The Tripoli BoD did indeed recently look into trying to put in a rule that would make some sort of "smart" ignition devise a requirement but we found that quantifying what would and what would not be allowed was too onerous on the local clubs and their RSO's so we did not take any action.
However, with that said, there is no doubt that the risk of a multi-stage rocket is significantly higher than a single stage. Simply put, there are many more failure modes that can occur with a staged rocket. With this in mind, we as a hobby community should use the best technologies available to minimize risk. Right now, there are several altimeters that have the ability to inhibit the ignition stage unless the rocket has met either a time/altitude threshold or can check for verticality. At this point, to continue to use a simple timer just adds to the overall risk of your flight which puts the hobby at risk.
Years ago we all used launch rods for guidance. With the advent of rails, our ability to launch straighter was increased significantly. Now, at any major launch, the number of high power flights that fly off of rails greatly exceed the number of flights off of rails. From time to time at one of our launches, a flyer will show up with a large rocket looking for a large diameter rod. When I ask them why they don't put buttons on their rocket I normally hear "I'm old school!" It took me a while but I finally figured out what "old school" meant. I've come to the conclusion that it means "I'm too lazy or cheap to put $3 worth of buttons on it."
Folks, if you are into staging, I challenge you to go take a look at the newer altimeters out there. Most are quite capable and many are reasonably priced. Don't go "old school" just because you have a timer or don't want to go through the effort to upgrade your avionics.

Bob Brown
Prefect, Kloudbusters Inc.
Tripoli Member

Thanks Bob,

I understand and agree with everything you are saying here. As a TAP member i try to stay abreast of the rules and I knew this has been a hot topic in the past. Wanted to make sure that no "new rules" had been created that I missed.

I agree that staging is something not to be approached lightly. I remember when L3 flights were using timers to deploy the main at apogee and we just hoped that the rocket would come down close to being inside the radius listed on the waiver. Some of those recoveries were real adventures. With the avionics we have now dual deployment is cheaper, safer, easier, and more dependable than a timer. Hopefully, staging will soon become as easy and more importantly, as safe.

I've noticed that the term "old school" often comes from folks who have been away for a while and are not aware of the advances that have been made in the hobby or sadly, don't care.
 
I've succesfully used Rocksim and the Raven altimeter to stage (and prevent staging) on a two stage rocket, as well as someone else's airstart. I simply program the 3rd output on the Raven using time and altitude.

I sim carefully in Rocksim for a flight at 0 degrees, then another at 20 degrees (the maximum allowable angle to stage under CAR rules). I pick my time where I want staging, then compare the distances. On a 0 degree angle flight, at 4 seconds I'll be 1000 ft. At 20 degrees and 4 seconds I'd be at 825 feet. So I program the output to only fire if the rocket is over 825 at 4 seconds. Any less altitude or time, and it knows something isn't quite right and won't fire.
 
The altimeters that I'm aware of that can do an altitude check are the Raven 2 or Raven 3, the Eggtimer, the RRC3, the Telemetrum line, the Marsa54L and the GWiz HCX.

Jim
 
The time altitude method can not work if you consider motor variations, or non predictable flight events, like motor cato, loosing a fin, getting unstable, drag separation, premature ejection ....

Is there any reason why one should not use an altimeter which can determine the tilt angle?

Sure the calculation of the angle might be worng, but if you combine it with the time altitude method you will have a larger security.
 
The time altitude method can not work if you consider motor variations, or non predictable flight events, like motor cato, loosing a fin, getting unstable, drag separation, premature ejection ....

Is there any reason why one should not use an altimeter which can determine the tilt angle?

Sure the calculation of the angle might be worng, but if you combine it with the time altitude method you will have a larger security.

Time/altitude works very well if you sim it properly, because if you go off-center/cato/etc. it's not going to be reached, therefore no airstart. You need the right booster motor though, preferably one with a relatively flat thrust curve and a nice fast dropoff. Something like a CTI 54mm 1266J760... White Thunder is a good propellant for boosters.
 
The time altitude method can not work if you consider motor variations, or non predictable flight events, like motor cato, loosing a fin, getting unstable, drag separation, premature ejection ....

Is there any reason why one should not use an altimeter which can determine the tilt angle?

Sure the calculation of the angle might be worng, but if you combine it with the time altitude method you will have a larger security.

^^ No one method guarantees success. Airstart and staged flights accident probability is reduced by layering protection.

This Tiramisu can combine many elements.
Layer 1: A well design stable rocket that has been test flown in booster flight only with sustainer inhibited to test stability and stage separation. Data recording altimeter on board to confirm simulation points for time at altitude.
Layer 2: Time at altitude lockout used, this is ubiquitous on most recent altimeters now.
Layer 3: Tilt
Layer 4: Ground command to inhibit ignition or command to blow all laundry in case above layers do not protect the flight.

In short air-start safety best practice is not just applying a single electronic gadget on your rocket.

L
 
Kurt,
I'm not Tripoli "hierarchy" but what you are referring to is a local club rule not a national organization rule. Our club implemented a similar rule back in 2013. Any club can put additional restrictions in place for their launch sites above and beyond what the national organization requires.
Bob Brown
Prefect, Kloudbusters Inc.
Tripoli Member

Right Bob, I discovered this posting after I heard a warning went out to the prefects about some staging mishaps from TRA HQ. Nobody routinely flies two stage flights above modroc size anyways but prefect felt it appropriate to put a rule in place
to avoid what happened at the last MWP. Since we are a small group and no one does large two stagers it was enacted in case of the rare event of a visiting flier. Single stage rockets can be "hairy" enough. I saw one on an ex-motor that made that
two stager from MWP look like kid stuff. Kurt
 
I typically don't use an altitude check for the purpose of aborting a flight due to too much tilt. Sure, it's possible to do a simulation to predict the time and/or altitude associated with different angles. However, in practice, you have to consider errors in the simulation, allowed differences in the performance of the motor, biases in your sensors, and the nature of the calculations being done within the altimeter (i.e., is altitude filtered and is the time value used by the altimeter exactly zero at launch). Trying to inhibit a motor based on detecting a tilt less than 20 degrees is pretty difficult, and for a more complex flight, it is not possible. In my opinion, an altitude check, which I always use, is for the safety of the folks near the launch site. In contrast, a tilt check is primarily for the purpose of staying within the waivered radius (i.e., for the safety of the folks not near the launch site).

The tilt check can also provide a measure of safety for folks at the launch, but be a little careful about that. The only unit that is currently available looks at the tilt angle at the instant that ignition of the secondary motor is called for. The rocket at MWP might have "passed" the tilt check, and then launch horizontal when the motor actually came up to pressure. Since the unit that allows the tilt check also supports an altitude check, there is no reason not to use it.

Jim
 
Been reading this, but haven't seen anyone name the electronics that TRA would accept for a two-stage flight. Anyone?
 
I believe the Raven, Marsa 4 can do the altitude checks. No one can criticize one's choice of using a Tele-Mega or Easy-Mega that can also do a tilt check and ignition inhibit. The out of production Rocket Tilt-O-Meter also did what the name implied.
Those were off the top of my head. Anyone else chime in if there others.

I would suspect if one brought flight data or proof of a previous flight done with altitude checking on a given pair of motors would go a long way to convince an RSO/LSO of the ability to fly successfully. But one's mileage might vary there.

Kurt
 
On my 7.5" BumperWAC I hit the boost hard with a Loki J-820 motor, it allows for a pretty long coast phase. I learned that 2nd stage motors like a F-50 or any other fast propellant light everytime. I had a 50% success rate with the slower F-25. Although it has a long coast time of the J820 I initiate the 2nd stage 1 sec after burnout, gives ample time to come up to pressure and go. When the F25s would not light, the V-2 apogee charge would sling off the upper stage and all came back under dual deploy safely. It did that at TARC years ago and gave Tripp a heart attack when the 2nd stage headed towards the crowd. It all came back safely under all the chutes.
 
Been reading this, but haven't seen anyone name the electronics that TRA would accept for a two-stage flight. Anyone?

As stated earlier, TRA chose not to implement a rule, so their acceptance isn't required. I put a list of altimeters that have the capability to do a check in Post #16. (Please let me know if I have missed any)

Jim
 
As stated earlier, TRA chose not to implement a rule, so their acceptance isn't required. I put a list of altimeters that have the capability to do a check in Post #16. (Please let me know if I have missed any)

Jim

Ok, Thanks Jim but it behooves a flier to find out what is expected at an unfamiliar launchsite as additional restrictions may apply. Local additional cautions will trump headquarter based minimums so saying it's not in the rule book will not help.

Kurt (I'll ask the local prefect because in our case I thought he had received from HQ a cautionary note at least even though there was no official rule enacted.)
 
I agree with the above and Jim Jarvis's point that tilt and other airstart safety measures need to protect that rockets do not fly out of the required perimeter of the launch site. The latter is the real requirement and "requirements" on electronic capability is just a tool. If you can't satisfy the first then satisfying the 2nd doesn't get you a pass.

At our club's launch site we do not allow staging at all because we have rather valuable property and a population center at or outside the perimeter. Each local case is different and I applaud TRA caution on advancing a national or international rule.
 
Dual deploy is a MUST IMHO for all stages.
I disagree. Some kind of electronic deployment is needed for the upper stages as they may not have their motors ignited and wouldn't recover safely otherwise, but the first stage can use motor ejection safely unless it's going so high that dual deploy is needed just to keep it on the field.
 
Back
Top