rocketry equations

[crashforce]

First off hi all and great forums, ive been skulking in the background learning a hell of a lot for a while now and finally decided to register.

I hope someone on here will be able to lend an ear to the problems im currently facing.

although i have no previous experience in the aerospace sector i thought this would be the best place to start asking.

All my previous experience has been with 4stroke and rotary engines running various fuels and some ram jet engine and jet prop work. Nothing at all rocketry so i decided to seek some proffessional advice.

Ive got a project on the go at the minute that requires the use of 4 rocket engines to drive 4 seperate turbines under load. The rockets will be monopropellant hydrogen peroxide with the possibility of a bipropellant conversion afterwards to kerosense or methanol -cant let all that o2 go to waste can we!

Im not entirley even sure what it is im looking for so if anyone with experience in this field is willing to have a chat or pass on any relevant documents i they would be gratefully recieved.

ideally i need to know- the expansion qualities of h2o2 in a perfect world when all molecules have been perfectly catalysed- a base thrust per pound of h202 figure if you like- although im not sure i this can be done given the variables in rocket and nozzle design

also any equations relating to pressures before and after the catalyst packs, thrust remaining after the gasses have passed the turbine etc etc and any documents covering pressurized nitrous oxide against pumps for supplying h202 etc

As i say i wont hide the fact that i have no previous experience in this field but as everything in life tis a learning curve that i hope someone can help me with.

Thanks in advance,
regards, Harry

 

[IRstuff]

Is this for school?

What is the end goal here? Turbines are designed for specific operating conditions. Changing the input conditions drastically could simply mean failure to function, or catastrophic failure.

One thing that you need to do when posing such questions is to delineate the requirements of the actual problem, not steer the solution.

TTFN

 

[crashforce]

haha no its not for school, i apologise if it came across that way. Im a bit to proud for letting other people in on subjects and tend to keep things very vague-a bad habit i must get rid of.

The turbines will drive 4 axles underload via speed reduction gearboxes with a maximum axle speed of 8000rpm.
on a 1/4 mile car im currently developing. The primary power coming from the turbines powering the 6 wheels with any acceleration coming from the exhaust gasses being a bonus.

As i say above im new to the rocketry concept (this a personal project btw nothing commercial) and with so little on rocket driven turbines out there im just trying to clear a few things up i.e turbine positioning in the exhaust stream (will it produce more torque in a low velocity high pressure or high velcity low pressure area), And how much flow can the turbine block without stalling the gasses and causing a blow out or a massive pressure spike at low operating speeds?

Im sure itl end up being a try it and see project as thats were most of the fun comes in anyway but theres some fantastically clever chaps on this forum that are to good waste on things like satelites and spaceships

 

[rb1957]

let's see if i've got this straight ...
you're building a type of jet engine, but instead of combusting a fuel/air mixture you want to use a rocket. and like a jet engine you're going to have turbines in the exhaust flow to power some wheels.

a very creative way of using rocket thrust and i'd expect pretty inefficient. Forget the problems about turbine discs in a very hot (really hot) so you might be looking at powered metalurgy for the disc, aren't you going to have significant losses first with the turbine then with the gearbox ...
why not use the rocket like all the other land speed "cars" do ... and power the "car" from the rocket thrust alone ?

 

[crashforce]

rb1957- kind of like a jet engine only take the compressor away and attach the exhaust turbine to the gbox.

From my little experience with jet engines and what ive found on rockets, as a propulsion system they are pretty ineffecient as they have no solid mechanical connection with the surface their trying to move along.
To my mind the first split second or so of engine power creates a highpressure area behind the vehicle and the rest of the power uses this 'wall' of high presure air to propell the engine forward.

The clearest way to explain my thoughts are stand in an empty space and punch your fist out in front of you- you might rock backwards slightly but in generally the air presents very little resistance.
Now go and push your arm out into a wall- youl push your elf backwards (obviously) because the wall limits the direction the force can go in.

Although the conversion of power from exhaust gases to mechanical energy will as you say be fairly low i have a strong feeling that the acceleration/thrust ratio will be much higher.

My to main problems at the minute are how high is the backpressure behind the turbine going to get when launching from a standing start? i.e will the sudden increase in pressure just smash the turbine to pieces (i guess only expensive experimentaion will tell)
And is at a certain speed the engines propulsion from the exhaust going to create more thrust than the turbine is supplying to the wheels/over rev the turbine by dragging the tyres along the ground when the turbines at maximum rpm due to the gbox?
The second one could be solved with a simple clutch although finding a clutch to take 10000lb+ of torque is not quite so simple and fitting it in a small weight reliant vehicle is even less simpler.

Thanks for your comments

 

[rb1957]

pretty much like i thought

why drive the wheels ? why not let the rocket thrust directly power the vehicle ?

 

[IRstuff]

Your comments about rocket thrust are completely off the mark. There is nothing to "push" against, because there is no need to "push" at all. Otherwise, rockets would need wheels. Your description of what you think the problem is demonstrates a lack of understanding of basic physics.

Rockets work because of conservation of momentum, PERIOD. The momentum of the exhaust is directly applied to the drag resistance of the rocket and its momentum.

A real rocket has a output velocity well exceeding several times the speed of sound, while a standard turbine is limited to around the speed of sound. Any higher input velocity simply goes into heating up the blades and breaking them.

Your concept is woefully inefficient, because you now have aerodynamic losses in the turbine, coupled with energy conversion losses, coupled with mechanical linkage losses.

The rocket, by itself applies its entire thrust to the objective of motion.

I suggest that you review Newton's laws of motion more carefully and read your physics books more carefully.

TTFN

 

[MechanicalChef]

Out of curiosity, did you have a particular body/shell in mind?

 

[crashforce]

frames being made at the minute with the final bracing for the engine to be sorted once the final engine dimensions are sorted.

Aerodynamics dont really interest me and this is after a project so i think il hand the green stuff over to a proffesional there and let them sort nose lift at 300+mph lol

38lbs weight - 1500bhp at 95000rpm
they can be as inefficient as they want but imho youl struggle to beat that power to weight ratio

http://www.swissrocketman.com/images_gtre/41.gif