2 Stage Flight

[gkieley]

I flew my PML Thunder & Lightening (unsuccessfully) last April and am getting ready to try again. I did not get ignition of the sustainer and yes I had the timer section labeled “nosecone” facing forward. Any thoughts on igniter vs. dipped ematch?

 

[WillMarchant]

Did you try lighting that same type of motor (in a single stage rocket) using that same type of motor initiator?

Did you try that same sort of motor initiator with the electronics to make sure it would start it?

In the failed flight, when you recovered the rocket, had the starter been started?

 

[gkieley]

Did you try lighting that same type of motor (in a single stage rocket) using that same type of motor initiator?

Yes, not problems in the past.

Did you try that same sort of motor initiator with the electronics to make sure it would start it?

Yes, the AT igniter worked fine.

In the failed flight, when you recovered the rocket, had the starter been started?

Unfortunately, no.

 

[WillMarchant]

Did you try using that AccuFire and the same battery to fire that same initiator after the flight?

The https://stores.whatsuphobby.com/-strse-178/Public-Missiles-Ltd.-Accufire/Detail.bok page strongly urges only e-matches. And that 1.25A firing current seems *really* low for a standard Aerotech motor starter...

 

[gkieley]

Did you try using that AccuFire and the same battery to fire that same initiator after the flight?

No I did not... good idea for future analysis.

The https://stores.whatsuphobby.com/-strse-178/Public-Missiles-Ltd.-Accufire/Detail.bok page strongly urges only e-matches. And that 1.25A firing current seems *really* low for a standard Aerotech motor starter...

I will look at link. Thanks for the reference.

 

[bobkrech]

From https://stores.whatsuphobby.com/-strse-178/Public-Missiles-Ltd.-Accufire/Detail.bok

IMPORTANT CUSTOMER ALERT:
For the AccuFire to function as a 2nd stage ignition device, you MUST use:
1) BlackSky HiRMI Standard electric match (preferably dipped in pyrogen) or
2) DaveyFire N28F (preferably dipped in pyrogen).

For the AccuFire to function as an ejection charge initiator the following electric matches could also be used:
3) 1 or 2 above (without the pyrogen dip),
4) BlackSky HiRMI - Sensitive,
5) DaveyFire N28B, or
6) Oxral.

Other ignition devices WILL NOT FUNCTION PROPERLY with the AccuFire.

Motor manufacturer supplied APCP igniters will not function with this device. If the igniter does not have an all-fire current rating, or if the all-fire current rating of the igniter exceeds 1 amp, it will not work with this device.

Regardless, you should ground test your chosen ingiter several times before you put on in your motor and launch to insure that the electroniics will initiate the igniter.

Also from https://blastzone.com/pml/images/AccuFireTimerInstructions.pdf

The AccuFire uses a 9VDC Alkaline battery. We do not recommend use of NiCad or other rechargeable batteries, as many do not provide a full 9 volts (they are actually 7.2 or 8.4v).

The AccuFire uses very little current from the battery. It may be left installed between flights, but the AccuFire should be turned Off to prevent draining the battery when not in use. Of course, you should NEVER leave an igniter, electric match or other ignition device attached to the AccuFire at any time when it is not in use, whether you leave the battery in or not.

It is VERY important to use a fresh, good quality battery with the AccuFire to ensure plenty of power to operate the onboard computer, sensors, and pyro circuits. PML recommends using a fresh, new battery after no more than about 5 hours of total On/flight time. When in doubt, use a fresh battery. A 9VDC battery is very inexpensive compared to a damaged or destroyed rocket that did not work properly due to a low battery!

Bob​

 

[hardinlw]

Public Missiles currently recommends the M-Tek electric match from MJG Technologies since the Oxral and Daveyfire are no longer available. The minimum all-fire current for the M-Tek is 0.5 Amps. This would need to be dipped in pyrogen as we did with the old Daveyfires to get a long, hot, flare as required to ignite an engine. Note that electric matches are designed to ignite materials like black powder which are relatively easy to ignite. Lighting engines takes a longer, hotter flame, so you dip the electric match in the same pyrogen you would use to make an igniter and use the e-match to light the pyrogen which then lights the engine.

 

[gkieley]

Thanks Larry. It was my first attempt at staged flight. I do have the Mteks at home and some Quick Burst quick dip pyrogen. I will do some testing this weekend.

 

[JimJarvis50]

You probably already know this, but with CTI motors, you only need to use an ematch. Easiest way to light a sustainer. Another option, if the motor is large enough, is to use a pyrodex pellet just as CTI does. I believe that an ematch with a pyrodex pellet (or two) is more reliable than a dipped match. I glue a pellet to the smoke grain and have a second attached around the head of the match.

Jim

 

[bobkrech]

You probably already know this, but with CTI motors, you only need to use an ematch. Easiest way to light a sustainer. Another option, if the motor is large enough, is to use a pyrodex pellet just as CTI does. I believe that an ematch with a pyrodex pellet (or two) is more reliable than a dipped match. I glue a pellet to the smoke grain and have a second attached around the head of the match.

Jim

Jim

CTI manufacture a black powder starter pellet for all their Pro motors.

If you use an e-match initiated Pryrodex(R) pellet to start a APCP or hybrid motor, you should inhibit the central bore of the pellet to double the length of the pellet burn and to prevent over pressurization of the motor by making the grain a regressive burner. Here's why.

An uninhibited Pyrodex(R) pellet has about 30 ms burn-time with a neutral burn geometry. Both the inside and outside bores burn so the surface area doesn't change as a function of time. By filling the pellet center with wax, grease or another inhibitor, the burn time is doubled to about 60 ms with a regressive burn geometry. The pellet burns from the outside in and the surface area decreases with time. When inhibited, the pressure generated by the Pyrodex(R) decreases with time as the pressure generated from the motor propellant is increasing. This provides optimum heat transfer to the propellant without over-pressuring the casing.

Bob

 

[highpowerrocket]

As mentioned previously by others I also consider a Pyrodex(R) pellet to be essential in all critical ignition (stage and cluster) situations. Even with the pellet(s) I do not rely on a low current e-match alone, I still dip the e-match in pyrogen. With dozens of multi-stage launches I've never had an ignition or overpressure problem. Also make sure that your booster motor is providing sufficient g's for more than the time required (0.5 sec?) to activate your timer.

 

[gkieley]

Looking at the Pyrodex web site... what caliber and grain size do you suggest?

 

[JimJarvis50]

Jim

CTI manufacture a black powder starter pellet for all their Pro motors.

If you use an e-match initiated Pryrodex(R) pellet to start a APCP or hybrid motor, you should inhibit the central bore of the pellet to double the length of the pellet burn and to prevent over pressurization of the motor by making the grain a regressive burner. Here's why.

An uninhibited Pyrodex(R) pellet has about 30 ms burn-time with a neutral burn geometry. Both the inside and outside bores burn so the surface area doesn't change as a function of time. By filling the pellet center with wax, grease or another inhibitor, the burn time is doubled to about 60 ms with a regressive burn geometry. The pellet burns from the outside in and the surface area decreases with time. When inhibited, the pressure generated by the Pyrodex(R) decreases with time as the pressure generated from the motor propellant is increasing. This provides optimum heat transfer to the propellant without over-pressuring the casing.

Bob

Bob, thanks for the clarification and the idea on adjusting the burn time of the pellet. That wouldn't have occurred to me. They do seem to burn very quickly and slowing them down a bit makes sense, as does changing the shape of the burn.

Jim

 

[bobkrech]

Looking at the Pyrodex web site... what caliber and grain size do you suggest?

The recommended method is to use a pyrogen coated e-match and coat some of the inner bore of the upper propellant grain with pyrogen as well, however if you use a Pyrodex(R) pellet as an ignition booster in an APCP motor, use the smallest ones that work. I'd start with (1) 30 grain equivalent pellet with the central bore inhibited in L2 motors and (1) 60 grain equivalent in L3 motors. I would not use Pyrodex(R) pellets in most L1 APCP motors because the bore volume and/or nozzle area is too small.

Bob

 

[gkieley]

Thanks Bob. I suspected that the pellet would be too large for most Hs & Is.