Anyone tried this?

[Bullet]

Having a little fun last week trying some new ideas...anyone ever try something like this? Thinking about sending it in as third experimental car in May race for fun. /images/boards/smilies/wink.gif

This car has about area 30-35% pass-through, or body frontal area reduction, as compared to a standard 1/4'' x 1-3/4" and has a COM of about .66". Its fairly rigid also. Paint job and front fenders are weak and quickly done though! lol

 

[pony express]

Have not tried that yet. It looks promising. Good luck.

 

[Kinser Racing]

Looks cool! I'm curious how it will run.

 

[Guest]

SWEET!!!!!

 

[Chief]

Thats way COOL! Cant wait to see it run

 

[Bullet]

Will be hard to tell if the body design works, it will be covered up by the other things I'm probably doing wrong at this point! It has a tick in one of the wheels I cant get out of it. Will give it a shot though!

 

[Guest]

Fella,

That car is totally awesome!

Talk about a great experiment for wind thru a constriction!

Congrats!

 

[GravityX]

Interesting design! Can't wait to see it roll down the track this month.

 

[IAE Racing]

cool plan!

 

[down4derby]

I too can't wait to see it run, nice car!

 

[Bullet]

Thx. Was concerned that the path down the middle would be about the same drag as going over. The bottom is open but has mono over it now. If the rest of the car construction runs ok, may take off the bottom and try it again.

Would sure be nice to have a track, instead of only having one shot a month to try things out...seriously considering a track if I can talk my wife into parking outside for a week or two a month when its set up!

 

[ChrisF]

I've been working on pinewood aerodynamics, and came up with a tunnell design not unlike yours to reduce the turbulence at the trailing edge, but set it aside in favor of the classic aero foil because it was easier to weight up. Have you considered shortening your axles for better flow through your channel? I'm very interested in how she runs! Great work.

p.s. you might be able to test if it adds benefit by running it covered with a piece of cardstock or plugged with a piece of shaped balsa etc as a comparison.

 

[Bullet]

Good thoughts, I did cut the axle length down but still have some nubs sticking out. I narrowed the side rails while building and didn't take the time to cut axles again. The main thing I was trying to do was make sure the exit end of the tunnel was the same size or bigger than the intake side so there was no restriction. The thing I don't know is how much longitudinal drag there is versus cross-sectional drag. Was thinking these cars are not traveling at jet-type speeds so any air with a straight path should help. Have a couple things to try with this like you mentioned, cover/uncover front end and also with bottom open/covered. Just hope the prep and alignment is good enough to tell if there's any difference. /images/boards/smilies/wink.gif

 

[Chief]

Thx. Was concerned that the path down the middle would be about the same drag as going over. The bottom is open but has mono over it now. If the rest of the car construction runs ok, may take off the bottom and try it again.

Would sure be nice to have a track, instead of only having one shot a month to try things out...seriously considering a track if I can talk my wife into parking outside for a week or two a month when its set up!

Dont give yourself time restrictions...a week or two...I would think you would want more time than that, and she will hold you to your words!!! just my opinion based off my own Xperiences.

 

[ChrisF]

The convention I'd seen floated by so called Pinewood experts is that aerodynamics doesn't matter at Pinewood velocities (12-15 peak mph). I've seen enough empirical data to refute that, with fenders being the obvious case in point. I've been researching low vel aerodynamics of late. There is much more in the area of low vel hydrodynamics, but there are enough differences in the fluid behaviors to matter. Pinewood is quite the departure from the scale in velocity and distance I'm accustomed in dealing with (similar it seems with you).
Have you considered an NACA style duct to try to "reorganize" that boundary layer? Where did you hide all the weight?

...also with bottom open/covered.

Please report your findings. Wayne Scmidtt did this and had some surprising results.

 

[Bullet]

I was thinking the same, if fenders can get .015, then a 35% area reduction in the body should help some anyway. I was just planning to go the empirical data route with this so far, need to dust off my college fluid dynamics books and do a little more research I guess. Not familiar with NACA but should look into it. The weight is in plates across the top back and between axles plus four cubes each side behind axle...was able to balance load on wheels and still have a .66" COM. May will be my first real race so hope the prep and alignment is good enough to tell something. I have some other ideas to do this concept better, but this is a "fun" experiment anyway! I know I should work on the basics first, but cant help myself, I used to work in an R&D design group years ago and still like thinking outside the box! Sending in two other "standard" cars besides this one. Not so concerned with winning at this point, just having fun (winning and having fun would be the best I guess!). Definitely need to get a track for this kind of thing. lol

 

[OPARENNEN]

I tried this pass through design on a couple of SR cars last year. It didn't work for me. When I covered up the front end opening as well as the back bottom exit opening, both cars picked up time. IMO the tunnel effect creates more drag.

 

[B-4 Racing]

In a previous life I pulled a flatbed trailer over the road. If I had a load of pipe, either a few large diameter pipes or many smaller diameter pipe the results were the same. Better fuel mileage if the front of the pipe was covered with a tarp instead of leaving it open for air to flow through. With the center open, you have a bunch more surface to build friction with air flowing over it. Just my thoughts../images/boards/smilies/wave.gif

 

[The Iceman]

I tried this pass through design on a couple of SR cars last year. It didn't work for me. When I covered up the front end opening as well as the back bottom exit opening, both cars picked up time. IMO the tunnel effect creates more drag.

It might be 4 times the surface area for it to go over??

 

[ChrisF]

I can't speak for aksnowfun, but when I was reasoning through this design, my hope was that the increased frictional drag from almost twice the "skin" area (inside and outside the tunnel) would be offset by a reduction in the turbulent drag that comes with reducing the frontal area, and as importantly reducing the turbulence off the rear of the body. B4 Racing's and Oparennen's real world experiences are evidence that it might not. For myself, I went forward with a different design that I'm hoping will accomplish the latter without the toll of the former. Of course it got shelved temporarily during scout season.

Speaking of a truckIoad of open pipes...the more i think about this, the more I think I have to break the news to my wife that I'm building a wind tunnel!