topic mainly says it all. If we built a car in the shape of a wing with the flat side up would it produce lift? Would the lift be pushed down toward
the trac? Would the lift combine with gravity to increase the speed of the car? :puzzled:
I think we will build 2 cars and test it out. Any of you engineers out there with ideas are welcome to add them.fletcht - 9-1-2012 at 05:52 PM
Ah pine wood derby, where kids get to compete against engineers and those that own machine shops. Brings back memories.MikeDobbs - 9-1-2012 at 06:09 PM
technically speaking, anytime air is deflected from a straight path (which is essentially what a wing does) there will be some transfer of force to
the wing. However, at the speeds involved with a Pinewood Derby car, and the limitations on the size of the wing, I would expect the effect to be
negligible.
Let us know how it turns out : )snowspider - 9-1-2012 at 08:50 PM
Way back when , I was studying human powered vehicles and came across charts and diagrams for various bicycle fairings both real and theoretical. The
results indicated a rider lying prone in a torpedo shaped vehicle required the least amount of horse power. Your gravity is your horsepower that is
trying to overcome the resistance of the air, bearings and wheel friction. I think any wing is going to eat into your horsepower to take the load off
those bearings and wheels. Frictionless supermagnet bearings will solve the bearing issue , wheels? , allignments super critical , fairings check
NASA. It all sounds like fun ,got to google pinewood derby now.cheezycheese - 9-1-2012 at 09:26 PM
Quote:
Originally posted by snowspider
Frictionless supermagnet bearings will solve the bearing issue , wheels? , allignments super critical , fairings check NASA. It all sounds like fun
,got to google pinewood derby now.
Patty, it's a two inch car....Jaymz - 9-1-2012 at 09:26 PM
As Mike pointed out, at the slow speed these cars go, Aero and the shape of the car really isn't a factor.
We had a good 4 year run in our Cub Scout pack a few years ago. Three 1st's and a second vs. 32-38 cars.
In the District finals we never won, but there was a winning car using the square wood block UNTOUCHED.
IMHO, what makes a fast PW Derby car, is more weight, less friction........NOT more taste, less filling as you were thinking
Our Cub Scout District rules were.....
Use ONLY the parts in the "official kit", (wood block, wheels, axle pins).
Weight, decoration, wings, spoilers, driver, etc. can be added.
Precut wheelbase in wood block can not be altered,
The car must be 5ozs or under,
Use only DRY graphite lubricant.
You want the car at the 5oz max and weight in the BACK to "push" the car. Weight in the back also gives gravity a car length advantage.
Wet sand the wheels smooth and camber the wheels a few degrees to keep them from rubbing against the car. Sand the burrs off the axle pins. Use plenty
of graphite on the wheels and axles right before you weight in.
That's about all I can say about that ;-)
Have fun!soliver - 9-1-2012 at 09:28 PM
it seems to me that a wing shape in its expected position (flat side down) would reduce friction on the wheels therefore lessening frictions
resistance against the "horsepower."
Though,... I'm not an engineer, my undergrad was in art,... maybe I'm dumber than I think.snowspider - 9-1-2012 at 09:43 PM
Wow just got back from google , special weights, cog , packed graphite, offset wheels, camber , obviously pinewood isn't the same as soap box. So no
super magnets eh.stetson05 - 10-1-2012 at 02:02 AM
Good responses! I was thinking about having the wing shape upside down to turn the lift into downward force. I agree the speeds might not be right.
Just playing with some ideas. I am one of those dads that makes the kid work on it themselves. It is a good chance to spend time with him. Show him
how to do things and the importance of attention to detail.jimbocz - 10-1-2012 at 06:54 AM
My first, and hardest lesson in the school of hard knocks came courtesy of the Pinewood Derby. After I won the first race, the loser picked up my car
and handed it to me. It never occured to me that he was also pushing the axle pins all the way in, binding the wheels.PHREERIDER - 10-1-2012 at 07:13 AM
considerable threshold limits there, velocity mass and size of foil.
down force is what is desired(upside down wing) . IF speeds exceeded the basic design resistance to stay on the ground and REQUIRED MORE down force
then a wing would be helpful.
a big ULTRA light foil could produce effective force but its drag and pressure would be the "brakes" and look funny with a big wing.
when power, and velocity are higher effective use of a small wing would work but who's gonna do soap box at 50mph+
if the total materials where very light i would think around 60-100mph some effective "reasonably" foils would be considered ...think like a wing suit
..., the pilots mass, the terminal velocity by gravity and the size of the tiny foils. ...with less POWER (and less velocity) the effective wing
just has to be decently size..like one meter(2)/10kg to produce effective power at low speeds.....like hangglider or KITE!mdpminc - 10-1-2012 at 07:52 AM
For these type of vehicles, rolling resistance of tires and bearings would be the biggest factor to consider.
Steering geometry and stiffeness of the wheels and chassis is also very important.
Air resistance would be secondary at these speeds
Spend your money on tires, wheels and bearings first, then on stiffening of the body (vibrations do reduce speed) loose body will also slow you down
on turns (smooth turns=minimum speed reduction)
Body should have the minimum air resistance rounded cardboard nose would be enough
Now: go to your Physics handbooks and do some math :puzzled:
Vehicle+driver mass, length of the course, angle of downhill and sharpness of turns will determine your overall speeds and side forces on turns.
It will also tell you at what point of your race you should avoid crashing into anything; (speed x mass) / crash distance = level of pain you will
endure BeamerBob - 10-1-2012 at 08:11 AM
Many are confusing pinewood derby with soapbox derby. These are unmanned 5 oz 5 inch long cars that run down a hotwheels like track.
My sons car was untouchable in his boy scout den of about 50 cars. Max weight, sanding block shape, polished and graphited axles with burrs removed.
We also sanded the burrs off the edges and flat surfaces of the wheels and graphited the running surface of the wheels. With the shape we chose,
there was no room for weight in the back so ours was centered between the axles. We also epoxied the axles in place so they would run true. Black
paint with yellow racing stripes were the real factor though.
As mentioned above, the wing is using air resistance in one vector to apply force in another. The application of the air resistance will slow the car
and it will all be over.snowspider - 10-1-2012 at 11:03 AM
Historicaly black and yellow has been some of the fastest colors available in any type of racing.PHREERIDER - 10-1-2012 at 12:58 PM
Patty, it's a two inch car....
