Static Tests (Digital Audio/Video)

[botrobasi]

SHOOP DA WHOOP  *< =======================

[transslucide]

Nice ! 

[shaneseale]

S.I.C.K.!

[randyrox69]

i still dont under stand the point of having differnet grains like why not just have one long one? some one care to explain?

[PurintonSFC]

each grain burns from the inside out and from the ends inward, by using multiple grains instead of one long one, the burn rate is increased because each grain burns from the ends inward aswell meaning the propellent will be used up slightly faster. secondarily, it's also easier in preperation. if i happen to damage 1 grain during prep all is not lost

[randyrox69]

@PurintonSFC Thanks for the info buddy :) very nice motors btw (Y) keep up the good work

[Grundalizer]

Is there a monk in the background singing hohoho hohoho?

[PurintonSFC]

The 5 Grain Motor shown in these tests had the highest total impulse at 170 lb-sec for an average thrust of 106 lbs over 1.6 seconds of the burn.

[EgyptianKings6]

Ok my goal tell me if I am stupid, I know about kinetic constant energy. That it picks up massive speed as it goes. I want to mount a rocket on my mountain bike.,,,,get a good speed going then let the monster loose. I mean while I am like in traffic lmao, like I take off from a light pedal hard then hit the rocket and let everyone go WTF!!!!!!..Is that bad?

[PurintonSFC]

Yes, lol. National Fire Protection Agency regulated discharge of rocket motors in public.  In order to have a rocket motor that provides any sort of acceleration to you and your mountain bike you would need to have something that is beyond the limit for unlicensed use. I believe you would need a certification in order to fire one in public. If you did it on your own property, it's no problem.

[EgyptianKings6]

ah,,,hence the night test of the skateboard. So what kind of pound thrust does the engines you make have? And will adding a bit of baking soda give you a longer burst but (dramatically) lower the thrust?

[PurintonSFC]

to add baking soda you would have to take away fuel to add the inert ingredient, so you would get less total impulse than in these motors, and with the longer burn time a much lower average thrust

Without inert

170 lb-sec / 1.6 second burn = 106 lb avg thrust

150 lb-sec / 3.2 second burn = 47 lb avg

and of course less total impusle means less total force imparted on the object

[Gmc42082]

do it anyway,i've seen ppl do dumber things! and @ purintonSFC i'd be more concerned over a failed rocket exploding while riding the bike,rather than the National Fire Protection Agency, and laws. remember its not illegal if you don't get caught!

[EgyptianKings6]

OMG lol there is no leaves left for a 100 feet trail on the last blast..thats some blast.

[PurintonSFC]

Yea that last one was a little monster

[dashcommand]

It sort of looks like the nozzle is burnt away, as the exhaust diameter seems to grow.

Is this actually happening or is the nozzle staying put?

[PurintonSFC]

The washer which was the exit hole stayed put and eroded very little.

The reason for the exhaust plume changes is due to the change in inside chamber pressure. These were bates burners designed to have a nice round thrust curve.

[dashcommand]

Ah ok.

Besides the change in diameter of the exhaust, in the test that happens at 1:00 min, you can see the white nozzle piece, and then it almost looks as if it melted away. At the end of the burn you can only see black, which is what could give the impression that the nozzle piece is gone.

[EgyptianKings6]

Actually I notice there IS an object in the end at 1:00 and by 1:05 its 100% for sure not there. Maybe its just the part that is holding your ignition set up???

[vahe5790]

You lose A LOT of exit pressure by having that type of nossle. It is cheap but the performance can increase if you lower to exit area by making a small cone type exit.

Great job and I am using your motor creation video to make my own stuff. Keep it up.

[PurintonSFC]

I'm not sure what you mean. The nozzles used here had conical convergences and divergences. The throat diameter was provided by a flat washer held in place with hydraulic cement formed into a cone shape on the inside and out. Only the throat cross-sectional area influences the pressure. The nozzle design does not, it only influences effective thrust if it is designed with the proper expansion ratio.

[15Death15]

cool

[PurintonSFC]

thx

[IMconfused]

What was the actual outer diameter of the casing at its biggest point (the top and bottom caps). your grains were 38mm O.D right and you wrote that you used 40 sch pipe, I have no idea what that corresponds to in mm. Can you fill me in, thanks.