Swamp Thing 3 Propulsion

Research for Swamp Thing 3 Propulsion (until we think of a better name for the sub)

Variable pitch on wikipedia
http://en.wikipedia.org/wiki/Controllable_pitch_propeller


we need to research:

the number of blades we want. probably 2 or 3.

the hydrofoil. This can probably be done with a computer program.

the length of the blades.

Here's the hydrofoils and propellers class FREE at MIT that Marcos posted. His link doesn't work anymore.

http://ocw.mit.edu/courses/mechanical-engineering/2-23-hydrofoils-and-propellers-spring-2007/

Are we leaning towards having the pilot adjust the pitch or have it done automatically somehow?

The variable pitch is an automatic control system (ie heavily electrical). It automatically adjusts the pitch depending on the speed. I'm sure there's some sort of formula that gives the best angle of attack to produce optimal thrust, which is a function of speed.

For other non-aero types, here is a simplified version of propeller efficiency.

http://www.aerospaceweb.org/question/propulsion/q0039.shtml

things to consider for prop design

http://www.mh-aerotools.de/airfoils/jp_propeller_design.htm

Instructions on how to CAD an airfoil (sent from Chris Neal)


Here are those websites that show how to cad an airfoil:

http://www.dur.ac.uk/g.l.ingram/download/SolidWorksAerofoilGuide.pdf

http://www.ae.illinois.edu/m-selig/ads/coord_database.html#S


For Solidworks to properly read in the data from the airfoil website you have to add a third column of data full of 0s to the .txt airfoil file. The coordinates are x,y,z.

Thanks for sharing those propeller design considerations that we have to take into account. This stuff is making much more sense now.

I'm not really sure how we would be able to have it adjust the pitch automatically. I have been reading up on propellers and it seems that most constant speed propellers are for aircraft and use a hydraulic system to automatically adjust the pitch. I am not really sure why, but it seems that most marine propellers are controllable pitch.

If we went the controllable pitch route, we could probably go with 2 pitch setting and have the pilot switch between the two. I am not really sure how fast the sub will be going, but 2 different pitches could be all we need. It would also probably be a lot easier to design.

Neil, It is a control system. It will be controlled by computer programming. It will have an infinite number of possible pitches, which will be decided by the computer program. so what we have to do is get a linear actuator, and have that push something that is attached to the blades. So the linear actuator pushes the blades proportionally, depending on what the computer program tells it how far to push. Then the blades turn.

Does that make sense? I didn't understand it at first either, but Blue showed me a picture. I'll look for it some more later.

Neil - I found those pictures.

Here's how it works: The metal rod on the left side is a linear actuator. It moves linearly depending on how much signal/power or whatever it is given. We can find the current angle
by using the current length of the linear actuator and doing some trig. We will have a microprocessor generate a desired angle of attack based on some aero formula in a computer program.
Then we create an error signal by subtracting the desired angle from the actual angle. The error causes the linear actuator to move. When the error is below a specific tolerance, the elevators stop. Since the angle of attack depends on velocity, the microprocessor will also have the velocity sensor input. when the velocity changes, so that the optimal angle of attack changes, so will the elevators.

If you don't understand most of this, that is ok. Listen, we don't have to reinvent the wheel. We just gotta see how other people have solved these problems in the past. I have a CD with lots of pics and every team's paper from the competition.

http://www.mh-aerotools.de/airfoils/jp_propeller_design.htm

different kind of props
http://en.wikipedia.org/wiki/Voith_Schneider

here's a demo. check it out!!

http://www.voithturbo.com/545950.htm

www.mh-aerotools.de/airfoils/javaprop.htm
then the applet

under options
rho=.997
viscosity=1.004x10^-6
a=1482

rho should be 997 not .997

The linear actuator just showed up on my doorstep minutes ago. this one
http://servocity.com/html/heavy_duty_linear_servo__25__l.html

We paid $300 for it.

I just found these for $75. I can return the one I got and buy 2 of the $75 ones.

(type this into google: surplus center 1.96 stroke 107 lb 12 vdc linear actuator)

I asked the EEs if the cheaper one will work.

metal ball and socket joints for the variable pitch hub

http://www.mcmaster.com/#ball-sockets/=b4vnsv

CIMAR is letting us use rapid prototype for free! Dr. Crane said that you can only buy them in 5 packs, and they are $700.