Engine Efficency

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moocrew

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Alright heres my questions/idea.
Im not rocket scientist so im not quite sure what would work..or what is even sensible to try.

But I've wondered if there is a possible way to increase the effecieny of a solid propellant engine.
Obvioulsy the first thing would be to use the lightest/strongest materials and then cram it with a **BIG** engine. But there has to be a better way....
like putting some type of nozzle on the butt end near the nozzle(s) of the engine(s) to "pressurize" the gases.
Kind of like those Jet nozzles for your garden hose works. The same amount of volume of "stuff" (i.e. water/air) only being pushed through a smaller outlet.
Is there some type of material that would be able to withstand the pressure and heat?
or make some type of verticle "catapult" that pushes the rocket off the pad so that so much of the burn time isn't wasted while trying to lift.
Im pretty sure this is an already thought of and used idea...referred to as a piston?

im sure there are other options.
These may not be the most intelligent things you have ever heard but this is part of one of my soon, very soon upcoming rocs to push the super sonic or even sound barrier with different size of engine.

In a nut shell im trying to push the super barrier with the smallest engine possible...like an I size.
 

solrules

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Wow. Bunch of questions:

As for nozzles, the most efficent is the Aerospike nozzle. It looks like a conical nose cone pointing down at the aft end of the motor. For smaller motors, the increase in ISP (efficenty of a motor, measured in seconds) is very small. Once you get to large motors past O, there is a pretty good increase (not sure the exact number). CTI makes the O5100 motor that uses an aerospike to increase efficency. For smaller motors, it is much more cost effiective to put a bigger motor in the rocket.

Graphite is the nozzle material of choice for larger motors, it is very heat resistant and erodes slowly.

Yes, there is such thing as a piston launcher, explained in the handbook of model rocketry. The motor, on ignition, pressurizes a piston which pushes the rocket upward. This harnesses the gasses released on ignition to greatly increase the liftoff velocity. This works very well with small models estes-sized, but for larger rockets/motors, there is a very small increase.

The best thing you could do to get the highest effiency is to find the highest ISP (sepecific impulse) motor that you could fly. ISP is measured in seconds, and is the ratio of Newton-Seconds (total impulse) over Newtons (weight of propellant), leaving you with seconds. The higher the ISP is, the 'cleaner' the propellant burns. For example, a BlackJack motor has about 155 seconds for ISP. A BlueThunder motor has about 210 seconds. Therefore, the blue thunder is much more effiecent than the blackjack.
 

Ryan S.

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people have tried something like this with a burst disk, so the engine has to pressurize before any gas escapes. It could work but you need to do it just right because if your plate is too thick you will have overpressurization.

You could put a smaller nozzle on a motor (like you said same material smaller hole, this would also make the motor experiemental) but you agian, run the risk of overpressurization. As you decrease the nozzle size you increase the Kn and the PSIs in the motor. As you increase the PSIs the size of the diffusion zone decreases and the propellant burns much much faster.

if you want to break the sound barrier use a propellant such as blue thunder (I300, I357, I435) This will punch your rocket off the pad and it will really move. Also Kosdon fast would be great for this. Either way you want a propellant that is fast burning and effeicant.

The best way to make this work would be to make a composite rocket (like Shadow composites' Shock value) You can make a 38mm rocket weigh like a pound with electronics if you build it out of CF. Stick and I motor in that and it will be gone
 

iGGiE

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A good way to improve the performance of a solid motor (or any for that matter) would be to tube launch it, that is, to launch it out of a tube, sealed at the bottom, that is only marginally greader in diameter than the body of your rocket. However this introduces numerous problems such as the problem of the fins in the tube and ignighting the rocket whilst in the tube.

iggie
 

Ryan S.

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if you want to use an I use a medium speed propellant for a case like this
 
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