Wing it

[War Eagle River]

[Perrotoro]

I'm sure many can poke holes in the calcs below, but my calcs would indicate no effective down force.

A boat sail force was given in a reference to be 0.00256 x the square of the velocity in mph-squared. For a first run, I assumed the Spoiler to be vertical - not applying a downforce at all - rather applying a braking or full drag force. Then I assumed the spioler to be at a 45 degree angle.

I assumed the greatest downforce (or braking in first case) would occur in the 16' straight where top speeds occur. This will obviously be a higher force than in the curves, where down force is needed - but for the sake of the calc, I went with this. For a range of calcs, I assumed the cars traverse the 16' straight in 1/32, 1/16, 1/8, 1/4, 1/2, 1, and 2 seconds. The associated top averge speed to traverse the straight would thus range from 349 to 5.45 mph. I like to think the real traverse time is 1/4 to 1/2 seconds yielding 21.8 and 43.6 mph, respectively. It's squirrely beacuase average speed is not the top speed, but I did enough velocities that I think the top spessd is taken is encompassed.

I assumed a spoiler size of .25" High x 6" Wide - overly conservative but yielding 0.001042 ft2.

The drag forces in grams were calculated to be:

0.030249 - 5 mph
0.120997 - 10.mph
2.304321 - 44 mph (= 16' straight in 1/4 second)
12.099668 - 100 mph
48.398672 - 200 mph
108.897012 - 300 mph
193.594688 - 400 mph
302.491700 - 500 mph
435.588048 - 600 mph


For the second case using the sin of 45 deg and using the same velocities, the down force in grams would be:

0.021389 - 5 mph
0.085557 - 10 mph
1.629385 - 43.4 mph
8.555675 - 100 mph
34.222701 - 200 mph
77.001077 - 300
136.890804 -400
213.891881
308.004308

So if the 43.4 mph average speed is a close approximaton of the top straight speed, 1.63 grams of down force is applied in the straight at top speed. 1.6grams is 2% the weight of a 75 gram car and 1.55% of an 110 gram car. Again the oversized spoiler and the use of top speed in the straight exagerates the calulations of the downforce in the curves where it is needed.

Would you want to assume 100 mph? 8.56 grams downforce is over 10% of a a 75 gram car - maybe appreciable. But rememeber, this force on teh rear of the car might do more to lift the guide from the rail than applying proper downforce.

In summary, negligible force in my opinion.

That's my best try - throw darts if you like.

[Kevan]

Just give it up war eagle, if you think it makes your lap times quicker then crack on :hand:

[War Eagle River]

So in essence what your saying Perrotoro, is that we should turn the wings vertical, and use the guide flag as a keel. :clap:

[War Eagle River]

[War Eagle River]

Oh wait...one last thing...this about covers it!

[mattb]

I thought the whole subject of this post was did wings help speed. I guess I've been discussing the wrong thing.
Personally I don't like hot wings. Regular old fried is fine with me!

[slothead]

Perrotoro - thanks for doing the calculations. For many of the things we wonder about (in general) there is a way to resolve it with basic math and physics. I was nearly inspired to do what you did using the size of the wing on the MRRC Chaparral 2F, but no longer needed.

In your case I think the speed you cited as an approximation, 44 mph, is too optimistic for a home track straightaway. I doubt a slot car could stay in the slot at that speed. Any sort of bump or vibration would lift it out of the slot. But your calculations show that even at this speed the down force effect is negligible.

This thread has been fun and is the sort of thing we should banter about, and let science have it's say. I'll also admit I'd like to see someone with a very accurate scale do a test both with a fan blowing air over a car and also with it being held out the window of a car driving down a street. But, in the latter case vibrations would probably make it impossible to get a steady reading.

By the way, that kid whose face expresses the sheer joy of speed and lift reminds me of myself in my PF Flyers!

[War Eagle River]

“By the way, that kid whose face expresses the sheer joy of speed and lift reminds me of myself in my PF Flyers.”

And that’s what it’s all about!

[mattb]

I remember when I painted my track, I did scientific testing. All I had ever used was gloss latex applied by roller. I wanted to see if flat finish would be better or maybe even porch and floor paint. I took an unfinished piece of routed track and painted it with each kind of paint. I sat a typical car with silicone tires in the slot then tilted the track till the back of the car started sliding downhill. I used the semi gloss as the car held to it t was nearly vertical.

That was the extent of my science and physics. I did brush with the grain of the track this time and didn't roll the paint on.

[ra7c7er]

Back when I first started in slot cars I worked with a kid who was in college to be an engineer (start the jokes) and he asked me if the wings did anything on the cars. I told him I doubted it since they weren't exactly setup or anything. (Remember fly wings they used to be angled the wrong way to even do anything good for your car). He took one of my cars and put it in wind tunnel he made out of a fish tank. After hours of playing with a Fly M3 GTR in the tunnel and on the track I had at the time 10x3 straight was 8.5ft. He concluded the wings did nothing because the cars couldn't go fast enough and the magnetic strength was so much higher then any down force created which at maximum even after he cut up and adjusted the wing on the car was negligible.

Wings and louvers on scale slot cars are for accuracy they don't actually do anything on the track and even if they did even on the biggest fastest tracks the gain would be barely above none.

[Rastas]

I reckon wings work , I remember Australia winning a certain cup with wing

[Perrotoro]

Thanks for the aprrecaition Slothead. I would say the assumptions and calcs were fun, but I'd further expose myself as the engineer I am - ha! Kevan - you gotta be an engineer too - right? The "I stayed up all night wondering where the sun had gone - then it dawned on me' is idealistic engineering humor. If you guys think my wife has not for the last 40-years, applied of the enginnering humor on the open market to me, try one. I'm sure all are very tired - ha!.

The assumptions for the calcs are sketchy - I still will not stamp em! Ha.

ra7c7er - I ran with heavy magnets for a while. With these heavy weights and high curve speeds, my great nephew did so much body damage I decided to go to stock magnets only - with a trim magnet here or there - for more scale speeds like others suggested on this site. I'm happier - may go to no magnets.

I did notice on several occaisons when I put minimal magnet force behind the rear axle, the tendency to lift the guide out of the slot caused the need for more magnets in the front or positoning the magnet closer to the rear axle. That's essentially in itself, proof that if the slot car wings did apply appreciable downforce at a location - even further back than the magnets behind the rear axle - the downforce here would be adverse. Nothing appreciable as on real - state of the art racing vevicles - where the wing downforce is a well calculated force that is distributed as perfectly as possble to press the car to the road.