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Cluster air starting. A few answers from the experts needed.

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stevethecontractor

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Prepping my 12ft modified Pterodactyl for a cluster launch. Weighs 20lbs

I have the ability to hold 3 motors. one 54mm and two 38mm.

I want to launch on a large 54mm K and then air start a pair of I motors.

I have flown many 2 stage rockets and I have always set my air start around the burn out time of the booster engine plus 1/2 second.

In this case I am wondering if I should set the air start about 3+ seconds after main engine cutoff as the rocket will still be climbing. Or should I time it for right when the main engine burns out?

Also, since I am air starting two engines, would you suggest I use Cesaroni reloads since I can use electric matches to ignite instead of relying on a dipped aerotech ignitor or it does not really matter?

Lastly,
Moon burner or warps for my airstart motors? or just stay with a standard?

Thanks
Steve
 

markkoelsch

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The timing depends on what the goal is. If it is to achieve the max altitude I suggest building a sim of the rocket, and running some sims with varying ignition times.

If you are airstarting two motors I would stick with something quick to light- maybe Blue Thunder. Again, depends on the goals. Some folks airstart smokers for effect.
 

Rocketjunkie

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I fly a lot of air started clusters. IMO, the best time to light them is shortly after burnout of the main motor. Use a high thrust main motor to maximize the velocity when the outboards are lit. Best motors for the outboards are propellants that produce a lot of smoke (White Lightning, Imax, Smoky Sam, BlackJack, Skidmark, Dark Matter). I usually build the igniters into the outboards to prevent them from pulling out early. Do not use extremely high thrust outboards. If they don't light together, the rocket will be thrown off course.
 

Dave A

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The timing depends on what the goal is. If it is to achieve the max altitude I suggest building a sim of the rocket, and running some sims with varying ignition times.

If you are airstarting two motors I would stick with something quick to light- maybe Blue Thunder. Again, depends on the goals. Some folks airstart smokers for effect.

X2 on
1) Faster burning propellant light more reliably for me
2)Initiate the air starts at main motor burnout, it takes a few for the air starts to light.
3) Make sure none of the igniters can't move or fall out under thrust.

Coming to BattlePark, VA this weekend

Patriot-Rear.jpg

I made some plugs to protect the ends of the outboard tubes when not in use.
 
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stevethecontractor

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Thanks for the replies.
As far as making sure the ignitors for the outboards do not move, what do you do to insure that does not happen? How do you secure or build them into the engine?
 

Nick@JET

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I'm wanting to do the same thing with a LOC Magnum - a K711 and 2 H115DM. I'm going to still coat the igniters with some blue thunder shavings and secure to the smallest wooden dowels and tape those to the OD of the nozzle.

This will be my first so I am Not an authority just sharing my thoughts. Altitude is not what I'm going for only effect so I'll light 1 sec after burnout since it will be coasting for several seconds.
 

rms

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I used CTI motors and motors were light at 1 second after prior motor/s burn out. L800 classic- 2xI180 skids to 2xH100 IMAX. I used the supplied nozzle caps and taped them on with aluminum taps to hold igniters in.
35lb 7.5' rocket with central 75mm and four 38mm holes
[video=youtube;F98_EduqTqw]https://www.youtube.com/watch?v=F98_EduqTqw[/video]
 

jrkennedy2

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Nice movie.
How much delay did you use and what do you wish you used?

I like your launch field? Where is it?

I used a Minitimer 4 and set it to .9 seconds after burn-out. I think an additional second would have looked cool. Didn't want it to coast too long as the Bruiser is not the most efficient flyer. My profile image is that rocket. I was not sure how long the delay was going to be from Minitimer trigger-start until actual up-to-pressure so I kept it short. Apparently the 3cell Lipo lit things pretty aggressively as my guess is that they were up-to-pressure in under .5 second (or less).

The club is S.C.O.R.E. southwest of Pueblo CO. http://scronline.net/
 

stevethecontractor

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I used a Minitimer 4 and set it to .9 seconds after burn-out. I think an additional second would have looked cool. Didn't want it to coast too long as the Bruiser is not the most efficient flyer. My profile image is that rocket. I was not sure how long the delay was going to be from Minitimer trigger-start until actual up-to-pressure so I kept it short. Apparently the 3cell Lipo lit things pretty aggressively as my guess is that they were up-to-pressure in under .5 second (or less).

The club is S.C.O.R.E. southwest of Pueblo CO. http://scronline.net/
Thanks for the info. I just emailed that club with a few questions. I will happen to be in Colorado springs for a few weeks next spring and I happen to have another large stretched Pterodactyl, 60lb rocket, in my motor home for LDRS or Balls that I would consider launching at your club. That is my profile picture.
 

markkoelsch

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Are there not rules in place now pertaining to the impulse of the cluster, and having an ignition inhibit to deal with the angle from vertical?
 

georgegassaway

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Are there not rules in place now pertaining to the impulse of the cluster, and having an ignition inhibit to deal with the angle from vertical?
Uh...... that would have to be a rule assuming and requiring all models that ignite a motor after liftoff, to have an onboard Flight Computer that knows where the rocket is pointed at any given moment.

Some individual fliers have chosen to do that for their own reasons, with their choice of very advanced electronics / guidance.

But to make that into a rule would really have a chilling effect on all staged and air-started models. Might as well go the next step and just require guidance on all "complex" models to begin with, and what a can of worms that would be to make it required rather than optional.

Heck, I know how to get a commercially made Autopilot to make a rocket fly vertically. I do NOT know of an easy way to make a rocket lock out firing an upper stage or air-starting if it exceeded some specified tilt angle. I know the road to doing that would be to have custom programming in some Arduino type controller with the same kind of sensor that "drone" flight controllers use, but that's not an easy/simple code to create. So ironically, it's easier to use existing off the shelf components to fly with vertical guidance than it is to come up with a tilt lockout feature for a custom programmed flght computer for ballistic rockets.

At least AFAIK for now, there is certainly room for a "Smart Ballistic Rocket Computer" that could have lockout options and other features for when a rocket exceeds a certain tilt angle and programmed options as what else to do in such cases. The homemade Arduino rocket Altimeter (I do not recall the name of it) might be ripe for such upgrade/expansion, though to be widely used someone would need to produce finished ones for sale as most are not into building electronics.

Now to jump tracks a little bit, do your best to design and use an air-start system that minimizes the chances of an accident. Same goes for any electronics that "fire" something, such as Ejection Charges, or stages.

Especially to avoid ignition on the ground.

And even so, ALWAYS treat it like it's going to accidentally ignite anyway (hard to think up every possible complexity.... file it under "STUFF" happens rather than assume it is 100.00% safe and be complacent). So if it ever did ignite, it would not have the engines pointed at anyone, and not have the nose pointed at anyone or towards an occupied area if it fired and took off while being prepped, carried, moved, or loaded onto the pad. Making the power-up and arming procedures as safe as practical and again treating like it can go off at any moment.

- George Gassaway

 
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jrkennedy2

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I am intrigued when opinions are offered as "fact" and/or practices, even good ones, are presented as "rules"...
 

cerving

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There's no requirement for any off-axis ignition inhibit, but it's prudent to model such a flight carefully and use a big enough booster motor so that the stack is moving vertically at a good clip before the airstart kicks in. I don't know how many 2-stagers I've seen where the booster motor obviously didn't have enough kick, and the rocket started to arc over well before the sustainer started. Ignition inhibit won't keep the rocket from arcing like that if you make a bad choice of booster motors, but at least it won't go horizontal on you and you won't be driving for miles looking for your rocket.
 

ksaves2

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I am intrigued when opinions are offered as "fact" and/or practices, even good ones, are presented as "rules"...
Ummmm, Local sites can formulate requirements to suit them. It doesn't have to be written in a national organizations rules. The below is from a club website though it pertains to 2 stage operations:

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; (I believe that would be something like a Raven and perhaps a Marsa) A.K.S annotation

(B) An altimeter that checks for vertical trajectory of flight prior to sustainer ignition. Flights of all "combined impulse (The TeleMega/Easy Mega or OOP Rocket Tilt-o-Meter) A.K.S annotation
of an I" and above multi-stage rockets will be required to complete and submit the 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 group 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.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

There is nothing to prevent a local club from instituting rules to prevent the loss of a launchsite and keep a landowner content. It "behooves" a guest flier to seek out what is expected of them before they arrive to a launch they have not attended before.
If a straight timer situation is prohibited, don't expect to be allowed to fly it otherwise.

The above was a two stage rule. The site I took this from says nothing of airstarts which makes sense as the 1st round motor generally is selected to provide a safe lift off and flight. If the outboards fail, the electronics will go through their recovery sequence and a nominal, albeit lower flight will result. I don't think there is anything official concerning airstarting except that the first fired booster motor has to be
sufficient for flying the rocket. Straight timers for outboards are prefectly doable and acceptable in this case. Although, if a local group has their reasons for saying otherwise, it's their prerogative and not an official pronouncement.

There are many videos of clusters where "all" the motors coming up to pressure at the same time is needed for a stable flight. It's these situations that get very dicey with terribly off vertical flights if things don't go as planned.

Kurt
 

MaxQ

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X2 on
1) Faster burning propellant light more reliably for me
2)Initiate the air starts at main motor burnout, it takes a few for the air starts to light.
3) Make sure none of the igniters can't move or fall out under thrust.

Coming to BattlePark, VA this weekend

View attachment 303907

I made some plugs to protect the ends of the outboard tubes when not in use.
Dave:
which day is this going up?
 

Lowpuller

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George,

I thought guidance systems were prohibited?
 

georgegassaway

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George,

I thought guidance systems were prohibited?
I am intrigued when opinions are offered as "fact" and/or practices, even good ones, are presented as "rules"...
JR Kennedy, you and me both.... :)

Sorry Lowpuller, not trying to pick on you. :)

It's just that this is stated so often and is so wrong. Seems like it's been only a month or so since the last time someone posted on TRF that guidance was banned, so I'm a bit cranky abut seeing it repeated so soon after the last time (again, not trying to pick on you, it's just how often this keeps happening in general, now weeks apart rather than many months).

So many people post often that there is a rule against guidance, or it's prohibited or whatever. When they either do not know but would rather assume so, or misinterpret something, and post it as though fact. Or repeat bad info from someone else who made the same mistake.

NOT TRUE!

Nope. Guidance IS ALLOWED. We really need a FAQ or permanent Sticky.

What is not allowed is TARGETING. To fly a model in a manner that could try to hit a target, and THAT can be done even with a ballistically launched rocket with no guidance, as many old-school "dumb" military rockets have done.

Guidance that does NOT make a model try to fly at a target is allowed. Most certainly guidance that makes a model fly straight, or vertical, unable to home on a target, is allowed.

We've had successful onboard guidance since at least 1988 (Sun-seeking), and Forrest Mims III was experimenting with guidance methods at least as early as 1969 (I'm sure he could have gotten servo-based steering to work, though servos and batteries to power them were big and heavy at that time. But he was trying out some unique forms of steering like Ram-Air, which if it had worked, it would have been incredibly minimal and light. But the mechanism had a fatal design flaw that prevented the neat concept from working).

Many many hobby models using onboard guidance the last 28 years, from literally homemade spinning disc gyros working much like the old V-2 guidance (David Gianokos' team), to today's microcomputers and Smart Phone sensors and "drone" Controller/sensor technologies.

See my animated Avatar in the upper left of this post? That's a multiframe repeating cycle of my original 1988 Sunguidance model (using nose steering fins), on a flight in 2004. And then this below.

- George Gassaway

[video=youtube;I6ZFSSBQNT0]https://www.youtube.com/watch?v=I6ZFSSBQNT0[/video]
 
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Lowpuller

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I don't view as picking on me but rather educating me, and in fact I have posed the question twice in the last month, so thank you for the clarification.
 

ksaves2

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Ummmm, When guidance is confused with targeting, it's what gets people to soil their shorts. I propose the more "politically correct" would be stability augmentation just to keep the thing flying straight up.
Nothing wrong with that.

What "really" starts a gray area are R/C steerable chutes and the technique of a GPS guided steerable parachute. Technically, if one is flying an R/C chute and "aiming" for themselves, could call that targeting.
Same thing if one would perfect a GPS guided descent. Get it to land at one's feet and some trolls could call that "targeting".

Soooooooooo. Shouldn't jerk anyones chain if a small rocket can fly home but anything larger...............That's when there would be cause for concern.

Heck, I remember seeing a launch video of a sounding rocket from a small aerospace concern with the camera trained on the pad. Rocket goes up, camera stays on the pad and with editing, one sees the same rocket land very close to the pad under autonomous GPS control. Kurt
 

soopirV

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X2 on
1) Faster burning propellant light more reliably for me
2)Initiate the air starts at main motor burnout, it takes a few for the air starts to light.
3) Make sure none of the igniters can't move or fall out under thrust.

Coming to BattlePark, VA this weekend

View attachment 303907

I made some plugs to protect the ends of the outboard tubes when not in use.
What do you have written on your retainers? Can't make it all out...
 

cerving

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"Guidance" is most definitely NOT allowed. "Active Stability" is. The difference is which way you're going... Guidance implies that you're sending the rocket to a particular location, Active Stability just means that you're keeping the pointy end up. With Active Stability, the path is still ballistic, i.e. guided primarily by gravity and other natural forces (i.e. wind).
 

georgegassaway

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"Guidance" is most definitely NOT allowed. "Active Stability" is. The difference is which way you're going... Guidance implies that you're sending the rocket to a particular location, Active Stability just means that you're keeping the pointy end up. With Active Stability, the path is still ballistic, i.e. guided primarily by gravity and other natural forces (i.e. wind).
That is a load of.....

PLEASE CITE THE EXACT RULE you are "most definitely" basing your claim on?

GUIDANCE is guidance. STEERING. A course change, or keeping course.

Not TARGETNG.

TARGETING is what is not allowed. TARGETING is where it ends up hitting (or trying to hit) a ground TARGET or an object in the air. And targeting can be done by ballistic rockets as used by the military for hundreds of years, up until the V-2 in WW-II when an improved way of "targeting" became possible. In war there have even been planes and helicopters shot down by "dumb" ballistic rockets, like a Bazooka (no guidance) that had a lucky hit (lucky for the one firing it, not for those onboard)

The difference between a Titan-II Missile and Titan-II flying NASA Astronauts during Gemini was not that one used a guidance system and the other used some fictionally labeled "Active Stability System".

The Titan-II used the same guidance method for both - the Missile was PROGRAMMED to hit a TARGET, the Launch Vehicle was PROGRAMMED to fly into ORBIT. BOTH used "guidance", difference was HOW it was programmed and used.

As I said, there have been dozens of model projects since the late 1980's that have used onboard GUIDANCE. NAR and TRA have no problems with such models, there have been articles about the systems in magazines of both groups, flown at both organizations' national level launches, and as subjects for first place R&D projects at several NARAMs.

With the rare exception of FINLESS rockets using gimbaled thrust, that may have been unstable otherwise, none of the rest have been using "active stability". They have been STABLE rockets that used GUIDANCE to make them fly in a non-ballistic manner (Well, for that matter all the above flew in a non-ballistic manner, if the system worked).

BTW - R/C "guidance" (Steering) has been used in this hobby since the late 1960's, with R/C Rocket Boosted Gliders. I guarantee no "unstable" R/C RBG has ever been "activity stabilized" by the pilot!

STOP SPREADING THE BIG LIE that GUIDANCE is not allowed.

- George Gassaway
 
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cerving

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NFPA 1122 states:

4.7 Model Rocket Flight Paths.

A model rocket shall not be launched on a flight path aimed at a target.

That sure sounds like a prohibition of "guidance" to me. Along with the NAR/TRA rules regarding launch angle, it's pretty clear that the intent is to make the rocket go as vertically as practical, thus Active Stabilization vs. Guidance.
 

boatgeek

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[leaving guidance vs. stability aside] I've seen a bunch of recommendations here for airstarts a short time after booster burnout. Why not have the airstart while the booster is still burning? It seems like that would pretty much guarantee that the rocket was still largely vertical which would be safer. You could also use a longer-burning booster and still have the airstart at an altitude where you can see the start. Is there something I'm missing?

Also, is there a rule of thumb for how high you need to be to safely light a sparky motor and not cause fires on the ground?
 

Nick@JET

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Thought was about clusters guys, back on track - maybe a new thread for guidance is in order. That could be quite a target rich environment
 

Titan II

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Thought was about clusters guys, back on track - maybe a new thread for guidance is in order. That could be quite a target rich environment
There are several already. All one has to do is look.
 
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Dave A

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What do you have written on your retainers? Can't make it all out...
Some of my rockets I had starting building them a while back but only finished recently, namely this Patriot here and my all FG 4-finned Ultimate Endeavor.
I had used some older Aeropak retainers. They had thin retainer caps and not deep enough seat for a snap ring motor to satisfy me. Those were comments to my machinist to open the holes on the caps so the rear of the case would fit through the cap and then the cap could be tightened all the way down.

The Patriot has a custom motor mount I built..
I designed the motor mount myself. It has a 98mm retainer for the bigger motors.
The 75mm-98mm adapter has a retainer made on the end. You slide into the main motor mount. The 98mm cap locks the adapter in, then you slide in your 75mm motor and screw that cap down. The tip of the 75mm case protrudes out the cap slightly.
98mm retainer.jpg

Thinking about wiping them off and write:
"If you can read this...you're about to get burned!"
 
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