huh? i think this goes a little differently here, just knowing my fuel and oxigen flow rate gets me nowhere, i need to know the regression rate to design a fuel grain with the correct length, if my fuel grain is too short not enough fuel will vaporize resulting most of my N2O going out the nozzle without ever oxidizing anything. to satisfy my fuel flow rate needs i have to have sufficient port surface area, to calculate that i need regression rate.
i could do a educated estimate and make some kind of hybrid motor that will prolly work, but that not my goal here, my goal is to put together a good design method, a set of equations and a sequence of calculations that results in a rocket engine that can be expected to perform according to calculations, building the actual engine is only my goal so i could verify that my design is correct.
questions remains, is the above calculation correct? Rp - port Radius in in cm, ´r should be regression rate in mm/s, ´Wo is oxidizer flow rate, ´W is propellant flow rate, ´Wf is fuel flow rate
 
[edit]
whoa, a wealth of information http://www.sorac.org/  - somewhere there are probably answers to half my questions

okey here goes
thrust 100N
oxidizer flow rate 0.389 kg/s
nozzle diametre 6mm
max mach number in port 0.3
initial port diametre 8.6mm
initial oxidizer mass flux 6642
initial regression rate 2.305mm/s
port length 682mm
 
http://no.life.ee/rainer/h%fcbriid%20mootori%20disainin%e4idis%20v0.1/schematics /design%20example.pdf    <-- math
http://no.life.ee/rainer/h%fcbriid%20mootori%20disainin%e4idis%20v0.1/schematics /Nozzle%20dimensions.pdf  <-- reference to engine dimensions
 
please take a look and note when you see some mistake or verify it to be(mostly) correct
hmmzzz.... now hoping my calculations are correct, next step would be post and precombustion chamber lengths and injector calculations, there was a thread about injector diametre calculations, but the equation was for english units, and i havent seen any formulas or anything for pre- and post-combustion chambres, are there any? if there is no practical way to calculate pre and post combustion chambers i'll do the engine without them, should work nevertheless
after i do the injector calculations is it time to get down to actual plumbing? or is there anything else that needs attention first?

ok i took precombustion chamber length 2Xdiametre and postcombustion chambre 1Xdiametre, i'll see if i can find a comrade to help me buid and test it. and then get down to actual blumbing, would like to calculate nozzle diametre first. given chamber pressure 2.4132 MPa and supply pressure 5.85 MPa(vapour pressure at 20C). is it a good idea to look for injector nozzles at for example car shop?(fuel injection nozzles are these large enough?)
 
[edit]
hmmzz... would a CO2 extinguisher work as my N2O tank? that is, would any car shop sell me nitro when i go and ask for it with a fire extinguisher in hand, any other place to get a pressure vessel cheap?

well... rigth now i have no plans for a flight model, i'll think about that after i have build and thruoutly tested this static test design. will propably try lots of different fuels and grain/pre-/postcombustion chamber/nozzle configurations. i would rather purhashe the injector nozzle as that way i should get guaranteed proper oxidizer fog without much trial and error. i'll see where i can get a properly rated tank without breaking my bank, or maybe i can get nitro under the counter somewhere, will see. oxygen tank from welding setup would work i think but these are kinda too large and heavy.
too bad but we are kind of short handed on the rocketscientists over here, i'll be lucky to find anyone with high pressure systems exp
once the rocket engine itself is done, making a teststand will prolly be kind of a challange, besides thrust id also like to measure chamber pressure, supply pressure, prolly gonna have termocouplers all over the place. would love to take a thermal video of the firing, but i doubt anyone in their rigth mind would lend a thermal camera for use in explosion hazardous area - gotta do some investigation, maybe someone is foolish enough. luckily test systems are my speciality so test stand shouldnt me much of a problem to handle.
2 questions though:
calculationg nozzle diametre
should i make vertical or horizontal test stand, horizontal seems easier. but rocket engine will work in vertical setup so maybe there is difference in performance or smth? shouldnt be but i am no expert

Good to see you're still working on your project.  Commercial HPR hybrid motor designs are indeed useful as starting points because they're straightforward and have been shown to be workable and reasonably safe in normal/as-designed use.  They rarely incorporate pre- and postcombustion volumes as deliberate design elements (though you will see short grains with spacers used in some motor/grain combinations, but this is generally sinply to add more grain options for a given motor tube length rather than to incorporate pre/postcombustion volumes per se).  
 
You, on the other hand, have the option of designing your motor and grain lengths and using spacers to deliberately create appropriate pre/postcombustion "chambers".  The usefulness of these is well recognized and would be a good advance over standard commercial HPR designs.  
 
Best of luck in your efforts and keep us posted  

okay, got my 8g n2o cartridges and did some pressure testing, i have plenty polyurethane tubing lying around so i tried using that, 3mm OD, didn't work so well, blew with a bang in 3 seconds, looks like it has to be nylon tubing after all - that i don't have lying around, gotta go and buy some. at least i know a place where i can buy it by the meter not a whole 50m roll in once