Some Stability!
 

A lot of you will have probably seen these...
Attachment 56257
These seem to be the latest fad in RX, with all the 2013 Bulldog shells coming with one. They work in real life, they seem to be be working in RX, so will they work in 1/10 off road? I am intrigued by this, so every week I will be reporting the effects on stability when using one of these and on the adjustments I have made each week. Just as a note, the base car will be a Cougar SV2. Here's to an interesting project:)

To make any aerodynamic surface work you need smooth (Laminar) air flowing over them. I have not seen any other examples other than the one you have attached. But the air coming over the cab in this example would be turbulent as hell, completely useless in generating any aerodynamic effect. Plus I'm pretty sure these fins are primarily designed for drag reduction with control over air flow over the rear wing not stability.

If you look at the modern Le Mans cars (and old F1 cars) the cabs and bodies channel smooth air over these dorsal fins making them a lot more effective.

A gimmick i'm afraid. Any gain in performance would be purely psychological.

They are for increased rear downforce, therefore more stability. Also drivers have noted that it seems more controlled in mid air and easier to pitch. They do nothing at low speed, just high speed; the idea is it splits the airflow into 2 clean paths, rather than a big turbulent mess over the shell, which means that in theory more air will be channeled onto the wing. However, if the fin extends over the rear wing, around 3% of the wing would be stalled, making it worse effectively. I will not be using a cab forward, but the kit rear cab shell. I am doing this to see A) if it works B) if there is notably more downforce or stability, how will the fin size/positioning affect this.
EDIT - the mandatory LMP fins are to stop them flipping if they spin sideways, similar to what i'm trying to achieve with this - it isn't about the front aero, but the side, which makes me think what the guys running these new shells are telling us is true.

I genuinely wish you all the best with your discoveries. A good experiment is always worth the time :)

Yours sincerely

Mark Spencer -BEng Aerospace Engineering (Hons) ;)

The placebo effect is very strong in R/C, I genuinely do think it's a good thing.
Tell me a time when you have a new car, new shell or new gizmo that does not make you feel good, and therefor race good?

Look at a 10th off road car front-on and ask yourself if anything other that the front tower/shocks/wheels or rear wing has any realistically useful aerodynamic affect?

Is there any confusion in this thread about which area we are discussing ? The fins on top of the cab ? Or the new idea of the clear (in this shot) upright bit next to the motor For cornering stability ?

The fins as seen in that pit probably has nothing to do with strait line stability, probably most side draft then anything, the same reason for dish wheels, it makes the side profile of the car bigger making it lean on more air

I'm going to make a stab here and say it has nothing to do with aerodynamics or stability at all.

I'd go more along the line that the shape of the body without the airdamn created a low pressure area in the well where the engine sat so created minimal airflow of the bottom of the cooling head - by putting the damn in place air is forced through.

Just to clarify, I am talking about add-on fins that go anywhere on the shell. There are many things I want to try with it, I have three different ones in mind...
offset (left and right) which will help with predominantly left/right hand circuits. This is to do with offset tracking - i.e a turning aid. The third is both in one, a 'double' fin, aiding straight line tracking and also doing what I mentioned in an earlier post. No racing for me this weekend, but more time to get these made.

You'd think the massive cylinder head sticking out of one side of the body would have more of an effect than a skinny bit but of lexan !!!

True, so these fins could be helping the aero issues that could cause. We actually don't know what effect they will have on another off road category (as i'm testing mine on 1/10 off road), but we are seeing more 'inbuilt' fins.