Chuff / spit ignitor - impact on delay element?

[David_Stack]

Good Morning All;

Hoping for some feedback as a 'post mortem' for a problem experienced yesterday at a launch...

F40 White Lightning RM 29/40-120 reload. Date code 111504 08. 'Fresh' delay element from a new 3-pack of HDK-21's (purchased within the last 6 months) with 1 second drilled off, for a calculated 6 second delay. Rocket is an Estes PSII Nike Smoke; 540 grams empty weight.

First attempt saw brief smoke from the nozzle, a 'pop' and a spit igniter (FirstFire Jr. igniter). Pulled the igniter and installed a new one. Had to guess at the installation depth since the first attempt burned away the tape at the top of the propellant grain that is installed at the time the motor is built to ensure the igniter is not installed too far into the motor.

Second launch attempt again saw it slow to ignite/come up to pressure but eventually got off the pad. Next series of events were quick, but it appears that on the way up the ejection charge fired. Data from FlightSketch Mini:

Max Altitude: 217 ft.
Max Speed 308 ft/s
Time to Burnout: 1.3 s
Time to Apogee: 1.7 s

Is there any chance that on the first attempt, the delay element started to burn and was then extinguished when the motor failed to come up to pressure and spit the igniter; end result being that I no longer had a 6-second delay in the motor?

This is the second time in as many attempts that I've had problems with this rocket and F40's. The first was back in February and the manufacture code on that motor was 04221303. Then it was a series of chuffs prior to liftoff, and a flight that was well below what the simulation predicted (453 ft apogee per FlightSketch Mini, flight data at: https://flightsketch.com/flights/3347/). That motor was a F40-10 with the original delay element, drilled down to 6 seconds.

These motors (I have nine more along with 15 G64W's as well) were obtained from the estate of a deceased hobbyist. I was advised they'd been stored in a climate controlled environment, but after these two experiences I am beginning to question the reliability of these loads, or is it something that I am doing incorrectly which is resulting in these results...

Thanks in advance,
Dave

 

[UhClem]

Failed ignitions don't usually do much to delays. I had a G33 once that shrugged off several attempts including a sheathed thermalite ignitor that someone donated to the cause. After disassembly and cleaning up, it later lit with a Copperhead for a normal flight.

That first attempt with the tape in place almost certainly did nothing to the delay. The early deployment was caused by something else. Loose nose cone or you drilled too deep into the delay. (Modifications of model rocket motors, including delays, are still prohibited by NFPA 1122.)

The climate control isn't so important as humidity. Dead dry (In sealed container with desiccant) is best.

 

[3stoogesrocketry]

Good Morning All;

Hoping for some feedback as a 'post mortem' for a problem experienced yesterday at a launch...

F40 White Lightning RM 29/40-120 reload. Date code 111504 08. 'Fresh' delay element from a new 3-pack of HDK-21's (purchased within the last 6 months) with 1 second drilled off, for a calculated 6 second delay. Rocket is an Estes PSII Nike Smoke; 540 grams empty weight.

First attempt saw brief smoke from the nozzle, a 'pop' and a spit igniter (FirstFire Jr. igniter). Pulled the igniter and installed a new one. Had to guess at the installation depth since the first attempt burned away the tape at the top of the propellant grain that is installed at the time the motor is built to ensure the igniter is not installed too far into the motor.

Second launch attempt again saw it slow to ignite/come up to pressure but eventually got off the pad. Next series of events were quick, but it appears that on the way up the ejection charge fired. Data from FlightSketch Mini:

Max Altitude: 217 ft.
Max Speed 308 ft/s
Time to Burnout: 1.3 s
Time to Apogee: 1.7 s

Is there any chance that on the first attempt, the delay element started to burn and was then extinguished when the motor failed to come up to pressure and spit the igniter; end result being that I no longer had a 6-second delay in the motor?

This is the second time in as many attempts that I've had problems with this rocket and F40's. The first was back in February and the manufacture code on that motor was 04221303. Then it was a series of chuffs prior to liftoff, and a flight that was well below what the simulation predicted (453 ft apogee per FlightSketch Mini, flight data at: https://flightsketch.com/flights/3347/). That motor was a F40-10 with the original delay element, drilled down to 6 seconds.

These motors (I have nine more along with 15 G64W's as well) were obtained from the estate of a deceased hobbyist. I was advised they'd been stored in a climate controlled environment, but after these two experiences I am beginning to question the reliability of these loads, or is it something that I am doing incorrectly which is resulting in these results...

Thanks in advance,
Dave

When the rocket sits on the pad chuffing and smoking , it is in fact burning away fuel / delay element. It is 100 percent accurate that your delay probably burned away a couple seconds coming up to pressure. Next time you fly one , put your ignitor in , then put a couple pieces of masking tape over the nozzle to creat a burst disk . Then using a toothpick / ball point pen , poke one hole in the tape to allow a small amount of gas to escape before it hits full Pc

 

[OzHybrid]

For white lightning I get a sliver of compressed BP cut from a B or C motor grain and stick it in the slot at the top of the white lightning grain. Ive not had any chuffing since then. White lightning is notorgious for this problem.
Other methods will work, but this is what I use. The BP is very easy to get lit as a bonus.

 

[UhClem]

Something that just occurred to me...

There is a graph in Rocket Propulsion Elements by Sutton showing the relationship between igniter pyrogen mass and motor free volume. That being the space not taken up by propellant. (The data points for that graph are all for motors much larger than hobby motors, so I have no idea if the curve he fit to the data holds.)

An F40 (and E16) has a lot of extra free volume (the tape does nothing) so that would imply a need for much more pyrogen. If you have old Copperhead igniters around you can always use the head of one or two. Placed at the top of the propellant grain during assembly and held by the tape.

 

[David_Stack]

Good Afternoon Norm, David;

Thank you both for the suggestions on ways to 'augment' my current igniters (AT FirstFire Juniors) to assist with getting these stubborn, aged White Lightning motors burning.

These are old enough that of the three F40's and one G64 that I've launched to date, three of the four were packed with Copperhead igniters, so I've got a ready supply on hand if I choose to affix those to the grain (I suppose it was fortuitous that I didn't heed the advise of several and just tossed them out).

As for using the BP as Norm encouraged, I've a couple questions on how to do so, and sent Norm a PM accordingly.

 

[cls]

...assist with getting these stubborn, aged White Lightning motors burning.

I keep a nail file in the rocket range box, to scrub the oxidized propellant off old WL grains. Seems to help!

 

[Sooner Boomer]

When the rocket sits on the pad chuffing and smoking , it is in fact burning away fuel / delay element.

Or not. Last year, I tried to fly a rocket on an old G64 reload. I was stupid. I knew better than to fly using this grain. It had white powder on the surface, and the slot had swelled almost shut. It took two igniters to light off. It sat on the pad and chuffed and danced for several seconds before slowly lifting off. It arced over and fence-posted before the ejection charge went off. The problem was that while the motor chuffed on the pad, it burned off propellant before it came up to pressure enough to light the delay grain.

 

[OzHybrid]

Or not. Last year, I tried to fly a rocket on an old G64 reload. I was stupid. I knew better than to fly using this grain. It had white powder on the surface, and the slot had swelled almost shut. It took two igniters to light off. It sat on the pad and chuffed and danced for several seconds before slowly lifting off. It arced over and fence-posted before the ejection charge went off. The problem was that while the motor chuffed on the pad, it burned off propellant before it came up to pressure enough to light the delay grain.

https://www.rocketryforum.com/threads/clustering-composites-question.170547/post-2234372This will fix it. Difficult to NOT get a 10 year old G64 in OZ. This is how I do it. YMMV.

 

[Handeman]

I keep a nail file in the rocket range box, to scrub the oxidized propellant off old WL grains. Seems to help!

And leave all the dust (pixie dust) from the nail file in the slot. That seems to help even more.