Reluctant Redlines

[uncle_vanya]

I've seen a couple of H268 Redlines flown recently that were not all that "fresh". I do not know the exact age of the loads but I know they are not young. They were HARD to light.

A lot of prep went into them - I know that the fliers had sanded the grains. One did not sand the cores the other did. Both had to take apart the motor and sand some more before these lit. Both motors took more than one igniter - one took 3 and the other took 2 - but we all expected it would take 3 since it huffed and puffed on the second one and almost did not get started.

While these loads chuffed a spat on initial ignition - once they kicked in they worked great.

Anyone with experience with lighting older redline reloads that could chime in with advice here? Standard igniter augmentation was attempted in multiple ways - so keep that info to a dull roar - the interest is in what steps to take to get old redlines lit.

 

[jj94]

I've never flown a redline before, but I do know that the strontium nitrate (I think that's it) absorbs moisture like a sponge. Maybe the sanding didn't do much because the moisture was absorbed throughout the whole grain instead of te surface only.

 

[Art Upton]

Originally posted by uncle_vanya
- the interest is in what steps to take to get old redlines lit.

Hi,

I've flown old 29mm redlines and used a quickburst ignitor to light them.

The one size between the twiggy and big one, I forget the name of it.

Thermite lights larger hard to lite older motors.

I had a 2-1/2 year old K670GG.

First a Pyrodex pellet. Bang like a gun, but no fire.

next, a pair of twiggys lighting a pair of thermalite wick.

A quick burst of green but no pressure up.

Next a Thermite straw and

Snap...Pressure up..Ignition

Edit: each of these is a method to get a hard to lite motor going'

 

[metalwizard]

another method, is to use a small sliver of blue thunder on your igniter.
For a 29mm reload make it really small (long and thin, rather than a chunk) you want it to pass through the nozzle easily. so there is no chance of blocking it.

Just curious, was the reload in a SEALED package?

 

[SpartaChris]

Try sanding the inside of the core just a bit to remove any oxidization.

Also, I second the use of a boosted igniter. Blue Thunder strips work great as does White Lightning.

 

[uncle_vanya]

Originally posted by metalwizard
another method, is to use a small sliver of blue thunder on your igniter.
For a 29mm reload make it really small (long and thin, rather than a chunk) you want it to pass through the nozzle easily. so there is no chance of blocking it.

Just curious, was the reload in a SEALED package?

Blue Thunder on a J420 recently completely failed to help. It simply was too fast. The J420 was 4 years old and it was sealed. The igniter flashed and blew itself out of the motor without any effect. This motor was eventually lit using the other augmentation (thermalite) method. This seems to burn more slowly and give the old redline a chance to get going.

 

[uncle_vanya]

Originally posted by SpartaChris
Try sanding the inside of the core just a bit to remove any oxidization.

Also, I second the use of a boosted igniter. Blue Thunder strips work great as does White Lightning.

See reply to similar post about blue thunder. It appears to be too fast for this old redline propellant. Thermalite (?) worked but that's hard to get now. I wonder if blackjack would be a better choice for these redlines? It burns more slowly and that seems to be important. We may try that or another slower burning propellant next time.

The motor grains were all sanded to remove oxidation and roughen the surfaces. This did not help. This was also done on the H268's I mentioned.

 

[jsdemar]

I wonder if any of the following applies to the problem you're experiencing?

From NFPA1125:
7.9 Motor Shelf Life.
7.9.1 When the performance of a solid propellant rocket motor or motor-reloading kit deviates from the sample test criteria and limits detailed in 7.8.6 within 5 years from the date of manufacture, it shall be withdrawn from commercial sale and redesigned to provide reliable operation when ignited within 5 years from the date of manufacture.
7.9.2 If the expected shelf life of a rocket motor or motor reloading kit is less than 10 years, the manufacturer shall imprint
a “use before” date on the package or motor casing.

 

[KermieD]

What are the sample test criteria and limits in 7.8.6? Rather difficult to speculate without that info handy.

 

[jsdemar]

Originally posted by KermieD
What are the sample test criteria and limits in 7.8.6? Rather difficult to speculate without that info handy.

For 7.9.1, the 7.8.6 tests are the standard requirements for NAR or TRA certification. 10% variation in total impulse, or 20% variation in delay, or ejection charge fails to operate properly, or the motor "malfunctions in any other manner that affects the safety of its shipment, storage, handling, or use." It's not a practical test because the manufacturer or the testing organization doesn't store away a batch of motors. It's done with newly manufactured motors of the same type (a sample per production batch by the manufacturer, and every 5 years by the NAR or TRA). It's up to the consumer to report these problem to TRA or NAR S&T.

For 7.9.1, the manufacturer is supposed to have an idea of what may happen to the propellant formula as it ages. If it oxidizes, swells from moisture, or 'something' migrates out, the shelf life is reduced.

I suppose it's an open question as to whether the ignitability problem "affects safety of its.... handling or use". Personally, I don't think that scraping a grain is a safety problem. But it is a fact that hard-to-light motors will cause short delays after eating away at the delay with misfires. And trying an oversized igniter may overpressurize the case.

-John

 

[uncle_vanya]

Originally posted by jsdemar
For 7.9.1, the 7.8.6 tests are the standard requirements for NAR or TRA certification. 10% variation in total impulse, or 20% variation in delay, or ejection charge fails to operate properly, or the motor "malfunctions in any other manner that affects the safety of its shipment, storage, handling, or use." It's not a practical test because the manufacturer or the testing organization doesn't store away a batch of motors. It's done with newly manufactured motors of the same type (a sample per production batch by the manufacturer, and every 5 years by the NAR or TRA). It's up to the consumer to report these problem to TRA or NAR S&T.

For 7.9.1, the manufacturer is supposed to have an idea of what may happen to the propellant formula as it ages. If it oxidizes, swells from moisture, or 'something' migrates out, the shelf life is reduced.

I suppose it's an open question as to whether the ignitability problem "affects safety of its.... handling or use". Personally, I don't think that scraping a grain is a safety problem. But it is a fact that hard-to-light motors will cause short delays after eating away at the delay with misfires. And trying an oversized igniter may overpressurize the case.

-John

So I'm seeing a lot of data here that says that what we all know (old motors are hard to light) isn't supposed to be accepted. What's the solution? Do we need to contact Aerotech and the S&T on each of these incidents?

The last thing I want to do is make it harder for motor manufacturers - I don't get the feeling that making them pull products and put expiration dates on them is going to help the costs or the availability. I also don't get the feeling that these situations are dangerous - just frustrating.

Am I wrong?

 

[KermieD]

Since delay kits are usually sold separately from motors in HPR motors, would the potential for the short delay apply to the motor certificatin with regards to NFPA in those cases, or was your reference rather that a delay grain must burn within +/- 20% of its manufactured burn rate?

 

[Art Upton]

Originally posted by uncle_vanya
So I'm seeing a lot of data here that says that what we all know (old motors are hard to light) isn't supposed to be accepted. What's the solution? Do we need to contact Aerotech and the S&T on each of these incidents?

The last thing I want to do is make it harder for motor manufacturers - I don't get the feeling that making them pull products and put expiration dates on them is going to help the costs or the availability. I also don't get the feeling that these situations are dangerous - just frustrating.

Am I wrong?

I only saw this on the hard to light issue. The rest is about impluse and delay varation.

John wrote: "I suppose it's an open question as to whether the ignitability problem 'affects safety of its.... handling or use'. "

I don't think hard to light is part of a safety issue IMHO

 

[KermieD]

Originally posted by uncle_vanya
So I'm seeing a lot of data here that says that what we all know (old motors are hard to light) isn't supposed to be accepted. What's the solution? Do we need to contact Aerotech and the S&T on each of these incidents?

The last thing I want to do is make it harder for motor manufacturers - I don't get the feeling that making them pull products and put expiration dates on them is going to help the costs or the availability. I also don't get the feeling that these situations are dangerous - just frustrating.

Am I wrong?

I don't see that statement being made at all. I think John is asking whether the issue affects performance enough or whether some of the steps that appear to be necessary to light the motors might raise enough safety questions to wonder whether these motors need to be looked at from that standpoint.

There's certainly not enough data out there to answer the question either way. Just enough to raise it.

I do agree with you that I don't see much of a safety issue as well, but I'm not an expert.

 

[uncle_vanya]

Originally posted by KermieD
I don't see that statement being made at all. I think John is asking whether the issue affects performance enough or whether some of the steps that appear to be necessary to light the motors might raise enough safety questions to wonder whether these motors need to be looked at from that standpoint.

There's certainly not enough data out there to answer the question either way. Just enough to raise it.

I do agree with you that I don't see much of a safety issue as well, but I'm not an expert.

Mea culpa... I didn't mean to imply that the direct statement had been made. My reading of the posts led me to think that this was what was being said.

I agree that I'm no expert either. How do we get the S&T to look into this without making this into a solution in search of a problem?

 

[KermieD]

That's a good question. Don't happen to have any old Redlines on me to send to S&T (nor would I give 'em up if I did ).

 

[uncle_vanya]

Originally posted by KermieD
That's a good question. Don't happen to have any old Redlines on me to send to S&T (nor would I give 'em up if I did ).

I know someone with several. But I guess that doesn't help unless he wants to give up about 5 of them for free to the S&T. Highly doubtful...

 

[jsdemar]

Originally posted by KermieD
Since delay kits are usually sold separately from motors in HPR motors, would the potential for the short delay apply to the motor certificatin with regards to NFPA in those cases, or was your reference rather that a delay grain must burn within +/- 20% of its manufactured burn rate?

Delays are tested as part of a motor reload system.