flybynite1526

I'M HELPING MY GRANDSON PUT TOGETHER A WIND TUNNEL EXPERIMENT. WE ARE STILL IN THE INITIAL DESIGN PHASE, AND I KNOW ALMOST NOTHING ABOUT ELECTRIC R/C.
It must be constructed using electric r/c components.
The objective is to move the largest volume of air through a 12.5" plastic tunnel, using brushless motors, (2, one at each end) and r/c propellers. Battery power plant.
This experiment is judged by total airspeed achieved and total air volume moved in 1 minute.
I would think that a 12' prop and the largest motor possible would be the way to go, but have read blogs from others on this experiment which suggest otherwise.
Can anyone suggest motors, props, batteries,etc.?
Thanks!

KidEpoxy

What are some more details of the test?

Are they suplying the motor?
You are correct, that given no restriction or evaluation of how much power can be used, obviously a 8horsepower motor will move far more air much faster than some 1/10 hp motor. Without restriction, or even adjusting the score for how much power it takes, it certainly will just be a matter of spending $1000 to completely spank the kids with $40 setups.

The other side of this is the battery.
While some will choose $200 LiPo batteries, and others will get $60 NiCad batteries, you should go to Walmart & get a car battery for a 72 Buick that will again stomp all over the other kids. In RC Aviation, we cant do this because of the very high weight of the Buick battery, but without a restriction on weight, you can run way outrageous battery.

Can you get more details as to the restrictions on what can be used?
If there are limits or other givens, please let us know.


As for moving air thru a tube,
the inlet needs to guide the air as to pick up speed as it gets near the propeller, rather than just trying to pull in air from all over the front of the tube. Without a propper inlet nozzle, it will suck in the air that is just infront of the tube, and air from all around that will try to move into where you just pulled the air.... from the sides as well as from infront. This means that for the air that was to the side, it has to accellerate sideways, then in the next moment it will be sucked into the tube at a 90degree turn. Thats bad. We want to pull from a kinda cone shaped pool of air infront of the tube so the air 4' out front will want to mosey toward the tube, and as it gets closer it gets more & more speed approaching the tube... before the prop even touches it.

Also, you should look at how much the motor blocks the tube flow.
Consider running a papertowel tube thru the center of the tube, so the air wont try to whip behind the blocking motor and then have to get shoved back to the side as it gets to the exit blocking motor. Nose cones in front of the in & after the out motors will help greatly too.

vicarh

My Feedback: (1)

I always remeber when my daughter was in grade school where she always placed among the top in the science fair. Her experiments were not the most sophisticated or the most colorful but she always placed among the top. My wife and I wondered why this was until one of the judges told us that she was always able to explain her work and discuss it which was the difference between the kids whose aldut relatives did the work for them and those that worked on the project. My wife was in charge of this department so I take very little credit for my daughters success...

I urge to continue looking into this but please do not do the project for your grandson. He may end up being an engineer if he finds the beauty of science. Guide him to gain the knowledge instead of figuring it out for him.

flybynite1526

Hi & thanks for the response... this is my May 08 advanced physics project and my gramps is helping me but not with the $$$... That's provided by a special school grant and the limit is $400.00 for this project.
None of us (5 total) have been informed as to the actual purpose(s) for this project... (makes it interesting) only that we are to,
"Be as VGER and learn all that is learnable" from it. (my teacher has a weird sense of humor)
That's straight off the sheet and we are also supposed to find the meaning of the above in quotes. The VGER is not a typo, and we think it's from an old star trek movie but haven't tracked that down yet.... working...

The experiment is:

1. Achieve the max airspeed possible, in a 12.5" diameter & 12" length tube, using ONLY electric r/c parts.
This includes up to 2 motors, and ANY necessary hardware, including (but not limited to) batteries, props, gears, mounts, etc.,
with the ONLY stipulation being that ALL component parts MUST be suitable and standard ELECTRIC r/c components. (that includes batteries
and also the props must not exceed 12" diam. The motors can be brushless or not)

2. Achieve the max airflow volume possible in 60 second, 180 second, & 300 second time periods, per the above specs.

3. Learn and document all that is learnable from the above. Multi discipline rule applies. (Any and all fields of physics)


In other words... Blow as much air, as fast as you can, through a 12" pipe, using ONLY electric r/c components.
Then, document all you have learned as it pertains to any branch of physics applicable. (ie. aerodynamics, thermodynamics, etc.)
We are also supposed to document any general lessons learned in the areas of electric r/c aircraft operation and practical mech eng.
For instance, will counter rotating the props effect total volume output or should both spin the same direction? and so on.
(THIS STUFF IS GREAT THOUGH AND I THINK I'VE JUST FOUND A LIFE LONG HOBBY!)

The example drawing on our sheet shows a basic cut-out of a tube which contains a center mounted motor & prop at each end. Pretty simple design... Presumably a push-pull (vacuum/pump) sort of airflow mechanism.

The only other rules are that the Motor(s) and props MUST be INSIDE the tube, (although exact placement, sizes or configuration of the components is not exactly specified... we're supposed to make those decisions) and that the air speed will be measured INSIDE the tube, while the total air volume moved will be measured at the end of and OUTSIDE the tube. We are not required to provide any of the measuring equipment such as an air speed indicator, etc.
My understanding from another student, is that they take your mech and hook it up to a pressurized tube that recirculates the air.
Essentially, I guess we're building an air mover.

That's it... we have 1 week to research and provide a component parts list and design spec. Research CAN include advice from r/c enthusiasts.
We also have to list the reasons why we chose the component parts we choose, as later we will have to justify those choices based on performance. (OR LACK OF!) That's really the biggest part of these projects we get... to see what we came up with and why. Why this design and not some other... why this motor... this prop... basically, why did you accept one recommendation and dismiss another, etc.
The only other caveat I would mention is that we all suspect that a large part of what we are probably expected to report on will be the thermodynamic aspects of small electric motors on moving air volumes. (how heat from an electric motr causes the surrounding air to expand and the effect that has on the ability to continuously move that same volume of air as it heats up and expands)
Hope this answers any questions you may have had.
Any ideas on a, "super tunnel" would be greatly appreciated and I thank you in advance.

ALEX

PS. from Alex's Grandfather. In case anyone's interested, my grandson just turned 11 years old. I never tell him the answers or do his projects for him. He earns everything he learns.
I also say, "Thanks!!" to all of you for keeping knowlege alive with this forum!! Keep on!!

Glacier Girl

My Feedback: (4)

Not much help here except as a Trek geek. VGER was the alien's misinterpetation of the word VOYAGER. Debris covered the rest of the word. VGER became all powerfull or some crap like that.

Was from one of the movies not the series, I just happen to remember the bald headed girl in the movie. She was kinda cute.

As Kid had mentioned intake will be one of the biggies along with elimination of any turbulance to air flow.

For simplicity I'd go with a single motor set up, you are building a ducted edf unit.
Running twins means having to compensate on the second motor/fan unit for the increased air speed from the first one. You would end up designing a duel compressor unit. Lot of calcs needed to do that.

Exhaust end size will also be involved in determining speed and thrust(airflow volume)
smaller exhaust to intake ratio will tend to speed up the air, but reduce volume, and visa versa.

I would think you should be looking at as mentioned before, and edf unit verses a prop.

For ideas look at something as simple as a vacumn cleaner set up, it's nothing more then a modified edf.

KidEpoxy

In the spirit of learning by research rather than direct teaching:

Glacier Girl <who is a guy named after the plane> mentioned the EDF: Electric Ducted Fan.
Alex, look up what is inside a jet turbine, what Rotor & Stator blades are & how they work together as Stages in operation. This might lead to ideas to incoroprate into your design.

How much electric theory do you have an understanding of? Do you know about Volts & Amps, and resistance/load? This would be important when looking at the motor & batteries.

When you say it has to be standard RC equipment, does that mean you are looking at using a RC transmiter to control the motor by a reciever, or can you use a simple on off switch? The expense of a high power Electronic Speed Control (ECS) could be avoided if you can use just a simple ON switch... and you could spend that money on bigger motor & batts


All of the RC plane stuff is aimed at keeping it light.
you may be interested in using some of the RC Car equipment too... especially the car batteries. They use heavier & cheaper NiCad & NiMh where we generally use LithiumPolymer these days. The heavy RC car batteries might be the better power source for high output vs cost, leaving more money for a bigger motor.



Glacier:
I dont know if he will be able to find a 250-300mm EDF rotor cheap [&:]

mjsas

Jet engines or turbines are designed to move the most air through a pipe so you should consider something like that.

I would look for a high capacity fan and model the turbine from that.

Fans are anything from the cooling fan on your computer to the cooling fan on an automobile. However, most cooling fans are designed to be quiet, not move maximum air.

Glacier Girl

My Feedback: (4)

Kid, (who's not a terrorist gopher by the way) yeah, a 12" pipe is a pretty big opening.
And sticking with r/c only, would almost have to funnel down to the biggest fan unit and motor combo they could get.

Just cause it's a 12.5" pipe, I didn't see any mention of how big an area had to be used for exhaust. A set up with a 12.5" intake and much smaller exhaust almost sounds like the way to go. Use the rules to your advantage.

KidEpoxy

GWS 10x8 Fourblade?
Pull the 5mm shaft from a 1000w outrunner, and have it setscrew down onto a foot long threaded rod,
use stators to hold carrier bearings,
and run 10 of them fourblade props on the threaded rod supported by bearings at prop # 4 & 8, with the stators to make sure we dont just spin air in the tube

Dorsal

My Feedback: (17)

My suggestions:
Get a 12" diameter SonoTube for setup and testing, if the plastic tube isn't supplied. These are used in construction to pour concrete columns and are smooth internally.
Buy a large motor like this one: http://www.hobbycity.com/hobbycity/s...idProduct=3889
Get one of these ESCs (or larger) http://www.hobbycity.com/hobbycity/s...idProduct=3727
Get a 12X10 to 12X12 prop for it. If needed, get a 13" prop and cut it (and balance it)
Power everything with 2 12V Gel-Cell batteries, in series, to give you 24 volts. (Weight is not an issue here, just voltage and amperage supplied) These have often been used onboard 1/4 scale models.
Get a Wattmeter and use it, 'cause you're gonna be pushing a lot of power! http://www.hobbycity.com/hobbycity/s...idProduct=6380

Glacier Girl

My Feedback: (4)

And don't forget safety equipment. Especially safety glasses.

KidEpoxy

I'm still thinking 2000w motor will move more air than 700w

brunobl

Don't forget other fans. So they may go from the CPU cooling fan, to the fan on a large airliner turbofan engine!