Do red propellants burn at higher temperatures..?

Curiosity question: I had a great flight yesterday with a CTI J355 RL - but noticed that the thrust plate was scorched afterwards. This has happened every time I've used Red Lightning above H impulse, but not with any other propellants. Do reds burn hotter?

I don't know the answer, but I do have a quick question. In the above photo, is this after just one flight or multiple flights? And what material or type of epoxy "was" covering the centering ring?

This was this particular booster's first flight on a red, but it's flown on blues and smokies before no problem. The CR was painted with several coats of Hammerite.

Are you using a standoff to minimize blowback off the blase deflector? Kurt

ksaves2 said:

Are you using a standoff to minimize blowback off the blase deflector? Kurt

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Yes - and the deflector is angled at 45°. The first time it happened I thought of blowback too - but if so, why does it not happen with other propellants launched in the same way, from the same type of rail? Hence my question re temperature..

While I have never flown CTI reds, I have flown numerous AT Redlines and can definitely tell they burn much hotter.

Compare a spent nozzle and liner from a Black Jack or White Lightning and a Redline and you'll see the difference especially in the nozzle throat.

Same with the Mojave Green loads, those burn just as hot or maybe even a bit hotter.

However I have never scorched a rocket with a red load.

Effects propellants will burn cooler than most properly designed performance propellants. The difference can be quite substantial. But the hobby motor propellants are not usually engineered for top performance (for instance I get an extra grain's worth of total impulse out of one of my motors in the same case, say, 7600 size for reference). Ease of manufacturing and being easy on the hardware are likely greater concerns.

A good red can be obtained in two main ways. One does burn a lot cooler than the other, with the hotter one having better ISP and better density ISP.

Gerald

"Butt-Burns" like that usually are more a function of slow ignition and sitting on the pad cooking a bit....often seen with reds.

@Donaldsrockets, @G_T - thanks both for your insights. It so happens I have two similar spent nozzles, both from 54mm 3 Grain motors here - as you say, Donald, the Red (on the left - the one fired yesterday) is considerably more pitted than the one on the right (a Smoky Sam).

FredA said:

"Butt-Burns" like that usually are more a function of slow ignition and sitting on the pad cooking a bit....often seen with reds.

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Thanks - yes - that also makes sense. I sensed when I pressed the button it took a moment longer to come up to pressure than some other motors. The plywood isn't actually charred - it's just the paint stripped, as if with a blow torch. I'll sand it, and give it a coat of JB Weld this time before repainting

don't know why you want to do it. Burn marks on the aft end is a mark of a well used rocket....

cbrarick said:

don't know why you want to do it. Burn marks on the aft end is a mark of a well used rocket....

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A good point, well made. My only concern is if I keep using reds (and I do like red motors, so that's a given) I'll end up with a charcoal thrust plate, with the attendant structural risks that would entail.

What does the thrust curve of the red motor look like compared to other motors you've flown in this rocket? Is it possible that the red had a lower initial thrust and the rocket spent more time near the blast deflector while building enough thrust to move?

FredA said:

"Butt-Burns" like that usually are more a function of slow ignition and sitting on the pad cooking a bit....often seen with reds.

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Here's a video showing the flames licking out before and after the motor pressurizes. Makes a good "whoop" coming up to pressure too.


It's worth noting the motor in the video is a 98 mm. The 54mm CTI motors have a pyro pellet that makes ignition and pressurization almost instant, but the 98 mm don't. I had a cardboard Madcow AGM 33 Pike come back from a flight with a roasted tail. When I get home I'll have to look through my flight logs and see if I noted it. If I did, I'll see if it was a red motor. I never knew for sure, but suspected it might be due to the flames licking out after burnout.

Smoky Sam and other smokies are effects motors. They have lots of extra binder or rubber or plastic additives and generate a lot of dark smoke. The binder is a mediocre fuel and the burn is run oxygen starved. It is a very cool burn for APCP. They are also low on metals so they will be low on slagging.

Gerald

Keisling said:

What does the thrust curve of the red motor look like compared to other motors you've flown in this rocket? Is it possible that the red had a lower initial thrust and the rocket spent more time near the blast deflector while building enough thrust to move?

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Thanks - yes, a good point. I've posted a selection of screenshots , courtesy of the excellent Thrustcurve.org, including a 38 J425 flown with an adapter. The K630 cato'ed before the burn finished (this is a 'well used' rocket), but is included here as despite the damage there was no scorching on the backplate (just everywhere else)

3.4s suggests to me one of the cooler reds and that your retainer and butt plate may be getting toasted by recirculation.

dhbarr said:

3.4s suggests to me one of the cooler reds and that your retainer and butt plate may be getting toasted by recirculation.

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Thanks for the input, and excuse my ignorance - what is 'recirculation' exactly?

You've seen pictures of a cannon blowing a smoke ring? Think about it sitting right at the base of the rocket.

Gerald

G_T said:

You've seen pictures of a cannon blowing a smoke ring? Think about it sitting right at the base of the rocket.

Gerald

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Ah - I understand, thanks. Would it be visible, or too defuse to see? The reason I ask is that since I last posted a fellow club member sent me this image obviously taken just after it cleared the rail, which shows the portion in question already blackened. A similar angle shot from another flight (using a blue), shows the rear plate silver. I'm thinking this suggests that the back end was 'cooked' before it left the rail in the manner described by FredA.

Donaldsrockets said:

While I have never flown CTI reds, I have flown numerous AT Redlines and can definitely tell they burn much hotter.
Compare a spent nozzle and liner from a Black Jack or White Lightning and a Redline and you'll see the difference especially in the nozzle throat.
Same with the Mojave Green loads, those burn just as hot or maybe even a bit hotter.
However I have never scorched a rocket with a red load.

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2 L1150 Rs flown on the same day. These had medusa nozzles just befor ethe switch to single-throat. That is the way they looked when pushed out of the case, scorched the case slightly but was easily buffed-out.

Tim51 said:

Curiosity question: I had a great flight yesterday with a CTI J355 RL - but noticed that the thrust plate was scorched afterwards. This has happened every time I've used Red Lightning above H impulse, but not with any other propellants. Do reds burn hotter?

View attachment 363497

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I usually cut a cover plate out of 1/16" to 1/8" aluminum and attach it to the base of the rocket before I attach the Aeropac retainer. I make the outer OD bt diameter so it helps slightly in the strength department...makes clean up a snap and you don't scorch the rear CR