59 replies to this topic

[digger]

thanks thats interesting! so it helps adding a metal powder , and whats the odds i cant make another chuffer again! most of the 1lb motors perform better than the 3lb,Er's i guess its the extra id of the bigger motors needing a lot more thrust, at the moment I'm just using normal bp rocket tooling( 1/3rd id core) so I'm going to try whistle tooling 1/2 id core on the bigger motors to see if the extra surface area of the wider core gives more thrust? I'm after a stubby hot motor about 1"x6" to lift a big payload how did the barium fuel work out nice and bright?

The Barium Nitrate fuel was a development I was working on but never finished. I will get back on it at some point in the future. The fuel was far more powerful than I was expecting it to be (I was looking for a low power fuel). There was a bit of a stability problem with the fuel, make and use and it was fine but wait a few days and it became hard to light and prone to CATO's. I have a few ideas for improving the fuel but that will have to wait for some day in the future when I have a bit more spare time.

Yep the fuel was bright, but they did disappear into the distance very quickly.

Edited by digger, 04 August 2008 - 07:40 PM.

[dr thrust]

hmm i had a Revelation today whilst trawling the net, looking for sexy propellants for my motors, fancying sulfur-less bp next, and there was an article on burn rates here bp burn rates check out page 4 of 7 where the burn rate a significantly reduced by extra tonnage on the press, me giving it a "good pressing" is doing more harm than good and would explain why two identical motors flew completely different!, the only difference being one motor got 1 ton the other 2 ton because i was trying to compact the perc bp better

on my video i state the harder pressed motor really flew, i wonder if i" mixed em up in dark" very scientific i know! looks like these motors are tricker than i thought , so back to testing identical motors different pressings see how they perform

[digger]

hmm i had a Revelation today whilst trawling the net, looking for sexy propellants for my motors, fancying sulfur-less bp next, and there was an article on burn rates here bp burn rates check out page 4 of 7 where the burn rate a significantly reduced by extra tonnage on the press, me giving it a "good pressing" is doing more harm than good and would explain why two identical motors flew completely different!, the only difference being one motor got 1 ton the other 2 ton because i was trying to compact the perc bp better

on my video i state the harder pressed motor really flew, i wonder if i" mixed em up in dark" very scientific i know! looks like these motors are tricker than i thought , so back to testing identical motors different pressings see how they perform

Interesting, however it would appear from the table on page 4 it is the linear velocity that decreases but the mass burning rate actually increases except for the last data point (which appears to be within expected experimental deviation). So you should get a faster rate of gas production with the higher pressing pressure.

Edited by digger, 09 August 2008 - 11:35 AM.

[dr thrust]

ho i see, all that text its a lot to swallow, but would this apply to potassium perc bp, it doesn't compress at all, even after 3 tonnes its just "spongy", as apposed to willow bp which has a good hard grain, i guess there's not a lot been published on it, or i just plain cant find any thing, all this fun has used up my "stash"of perc for now so back to willow bp, and sulfur less bp for the moment

ho yeah! I'm going to change the "binder" back to mineral oil from the Vaseline, has suggested on the original inventors site, i tried this before in nozzled motors and noted a very clean burn but was disappointed there wasn't a charcoal "tail" and shelved it, this isn't important now, and id like to get away from the James bond smoke screen that occurs with Vaseline

Edited by chris m, 09 August 2008 - 11:29 PM.

[dr thrust]

yeah me again, ," just doin a bit of readin" on bp burn rates, and it looks like( well to me anyway) this is what the text says, that with extra loading pressure of a composition in a tube this effects the efficiency of energy feed back by convective transfer, high loading pressure decreases the burn rate by decreasing gas permeability.

so.. the extra pressure is not allowing a higher temperature to form in the motor therefore you dont get a hotter more efficient burn, hmm so an additive( metal powder) should give you a higher heat of reaction and more power, irregardless of press load?, ho made my first batch of sulfur-less bp rp riced in baby oil dissolved?/ mixed in a acetone carrier, and it makes a lovely fluffy comp that presses into a good firm propellant grain, vid soon,

Edited by chris m, 14 August 2008 - 10:09 PM.

[knackers]

thanks chris, your work on different propellant additives has interested me very much, i have an r c model aeroplane and use 20% nitromethane fuel and thought this may be worth investigating as a ricing agent/ propellant additive,, has anybody tried this ? i`m not sure if the nm will disipate on drying and just leave the lubrication detergents or disolve/deposit the n/m in/on to the BP,, the additives are usually castor oil or some other synthetic oil (which wouldn`t hurt ?) i would try a static nozzle less end burn first 1"x5", then a core nozzle less,

[portfire]

I'm not sure mixing nitromethane with oxidizers will be behond the scope of the forum, as It's considered a HE. I know what it is, but never realized it was a HE, until I did some "digging" just now.

http://en.wikipedia....ki/Nitromethane

http://msds.chem.ox....tromethane.html

Maybe Mod/Admin approval is needed for further discussion on the subject? but hey, it get's those top fuel dragsters from 0-100Mph in 0.8 seconds

[digger]

yeah me again, ," just doin a bit of readin" on bp burn rates, and it looks like( well to me anyway) this is what the text says, that with extra loading pressure of a composition in a tube this effects the efficiency of energy feed back by convective transfer, high loading pressure decreases the burn rate by decreasing gas permeability.

Interesting what do you mean by burn rate? Conclusion 1 taken from the document says:-

(1) An increase in compaction produces a decrease in the
linear burning rate (cmls) but an increase in the mass burning
rate (gis). Similar observations(28) led to the conclusion that the
rate-controlling reactions of black powder occur in the condensed
(i.e. liquid and solid) phase. The maximum reaction
temperature (1250 °C) is, however, sufficient to cause the sublimation
or vaporization of most intermediates and products.

Hence the same amount of powder will burn in a shorter time in a rocket motor.

Looking at figure 1 in the paper, it shows a difference in the temperature when burning a pressed or rammed powder. This graph relates to a binary mixture. It would have been interesting to see this analysis continued through the paper. As assuming the total sample size was the same the integral of the two lines on the graph would show that the total energy output was lower in the pressed sample. This is interesting because it would mean that a different reaction stoichiometry is occurring under these different preparation regimes.

It would also have implications for developed thrust in a motor (ideal gas law PV=nRT).

However it would appear later in the paper they say that the calorific value of the fuels is identical (pressed vs rammed). In which case given their other results you would expect the lines on the graph in figure 1 to be reversed.

[/list]so.. the extra pressure is not allowing a higher temperature to form in the motor therefore you dont get a hotter more efficient burn, hmm so an additive( metal powder) should give you a higher heat of reaction and more power, irregardless of press load?, ho made my first batch of sulfur-less bp rp riced in baby oil dissolved?/ mixed in a acetone carrier, and it makes a lovely fluffy comp that presses into a good firm propellant grain, vid soon,

It is pretty much certain that the addition of metal powders will increase the temperature of the burning fuel. There is a high possibility that it would increase the heat of reaction (this can be checked using heats of reaction / heats of formation tables), but I am not certain without checking. From experience it does make for a powder with more thrust (except in the case of course powders which create nozzle erosion and burn mainly outside the rocket body), but this is probably due to the higher gaseous volume due to the higher temperature (PV=nRT).

As usual I am looking forward to seeing videos of your next test motors.

D

[knackers]

[quote name='portfire'
I'm not sure mixing nitromethane with oxidizers will be behond the scope of the forum, as It's considered a HE. I know what it is, but never realized it was a HE, until I did some "digging" just now.

http://en.wikipedia....ki/Nitromethane

http://msds.chem.ox....tromethane.html

Maybe Mod/Admin approval is needed for further discussion on the subject? but hey, it get's those top fuel dragsters from 0-100Mph in 0.8 seconds


i did do some research and arrived at your conclussion, as it was just a passing thought,, i understood it to be in the catergory you mentioned although in the liquid or slurry states,, i read the text on when it was discovered to be, and it was caused by a valve shut off hammer effect on oxygen pockets,,,, it doesn`t readily burn on its own ( 20%) but under pressure is a different game,,..
o-1oo mph in o.8 seconds is why i thought it may be beneficial in a proppellent,,,, point taken in regards to forum scope ( HE ) but it is, was, a rocket propellant

Edited by phill 63, 17 August 2008 - 08:39 AM.

[dr thrust]

ey up, nitromethanol eh?, yum last time i experienced that stuff was at the drag strip where they where running funny cars and top fuelers real bad stuff burns the skin on contact, and irritates the eyes as well, they blipped the throttle in the pits and the crowd around the car all disappeared rubbing there eyes rapid style.

rockets eh?, as you've all pretty much guessed rocket scientist i ain't! just your average Joe trying a few things out, so its hard to keep up with the technical bit! digger you've well lost me pal! i like pretty colors and sparkly things what did i mean by burn rate? that would be grams per second consumed in a motor i think?

"there's lots at lot happening in them there motors!" with many of different factors the choice of fuel, the ratio of the fuel, particle size,catalysts, core geometry and good old degree of consolidation!( loading pressure is a factor) im quoting from another source here not the tables i linked to,

quote ,"higher loading pressure decreases burn rate in a gas producing composition and convective transfer is the prevalent mode of energy feedback, higher loading pressure decreases the burn rate by decreasing gas permeability", make of it what you will, all i know is two rockets, the same size, same amount of fuel from the same batch, only difference loading pressure flew completely different, only way to prove this theory, practical experimentation coming to a dark field soon, so there!

Edited by chris m, 17 August 2008 - 10:24 PM.

[digger]

quote ,"higher loading pressure decreases burn rate in a gas producing composition and convective transfer is the prevalent mode of energy feedback, higher loading pressure decreases the burn rate by decreasing gas permeability", make of it what you will, all i know is two rockets, the same size, same amount of fuel from the same batch, only difference loading pressure flew completely different, only way to prove this theory, practical experimentation coming to a dark field soon, so there!

Ok, I thought you said that in your experiments that the rocket that you pressed harder flew more like a nozzled rocket. You say that you may have got them mixed up, did you get to the bottom of this?

Yep I agree that there will be a difference when loaded differently, as this is my experience too. I however press to a different pressure (7.5 tonnes per square inch of end grain). I will have to dig out some vids to see which is quicker. The main reason that I use a press is due to the consistency that can be given to the motors so they perform the same every time.

Who are you quoting on this passage? Interesting that they say that convective transfer is the predominant form of heat feedback, how did they prove that?

I would have thought that radiation/conduction would also have a significant heating effect due to the small distances involved between the flame and the grain along with the temperatures involved (Although I have done no work at all on this and it is a pure guess).

Edited by digger, 20 August 2008 - 05:53 PM.

[dr thrust]

ey up just got back from testing , i tried a 1lb sulfur less motor which had a slow ascent but nice loud whistle delay, which is a nice touch to add to these motors a little something extra next a 3 lb whistle to report much better ascent as i had finely milled the pot Benz, and pot perc to fine dust(separately of course) in dedicated milling drums.

next up 1lb perc bp 75,15,10 pressed 1 ton every slow takeoff and strange rasping noise, next up 1lb perc bp+10% german dark to test the heat of reaction theory and a slightly better takeoff but nothing to write home about, finally 1lb willow bp riced with baby oil, 10/10 very nice , so next time ill press the perc bp motor harder, should get the chuffing effect again which is quite cool! heres the vid nozzle less test

ho tested a whistle,bp hybrid fuel in a 1 lber and got a nice cato, i think they'll need a shorter core cato chris is back!

Edited by chris m, 02 September 2008 - 11:27 PM.

[digger]

Some more good rockets there chris. I do like to the perc bp rocket with the 10% German dark. It looks like it has a large flame at take off and then later in its flight starts to emit white sparks. I am looking for a fuel that looks somewhat similar to yours at take off, but without the sparks later in the flight (just perpetuating the long white flame tail). The application is for fixed line rockets, so a very short core would be in order to keep the thrust right down. Do you have any suggestions for the fuel?

[dr thrust]

thanks, the spark trail wasn't intentional i was hoping the al would be burnt up in the motor to help performance, ho well so much for that idea, the perc bp motors are a bit unpredictable with each one performing/ sounding different i wasn't after sound as such but its a bonus. they don't press well,

line rocket eh? i like those have you considered using a magnalium fueled motor, has found here on the creagan pyro site but shorten the core heres the link mag rockets ho just had a thought on an earlier vid on you tube i tried perc 70, willow 30 no sulphur( it says 40 willow but forget that its a typo) and this gives a bright flame,tail

Edited by chris m, 03 September 2008 - 08:55 PM.

[digger]

thanks, the spark trail wasn't intentional i was hoping the al would be burnt up in the motor to help performance, ho well so much for that idea, the perc bp motors are a bit unpredictable with each one performing/ sounding different i wasn't after sound as such but its a bonus. they don't press well,

line rocket eh? i like those have you considered using a magnalium fueled motor, has found here on the creagan pyro site but shorten the core heres the link mag rockets ho just had a thought on an earlier vid on you tube i tried perc 70, willow 30 no sulphur( it says 40 willow but forget that its a typo) and this gives a bright flame,tail

Cheers

Yep I had seen this site before, but completely forgotten about it. I think I will give those a go with a very wide nozzle to keep the thrust right down. I think I will use the red formula and substitute the strontium for calcium carbonate to get more of a flame coloured tail.