Sorry for the short reply I dont have time right now to type out a long one. But its would be best to have the only airfoil be the body. every time you are detaching and reattaching flow you are causing drag.Ciro Pabón wrote:=D> This could be called Bazanaius Inverted Shark Fin...bazanaius wrote:just thought, if you're looking at vertical rudders, why not hang your nozzle off the bottom of an extended (rearwards) rudder? the rear wing then sits on top of the cannister as you have now, without having to have an additional support below the wing.
I haven't thought about CG. The body acting as a stabilizer is also a good idea.
The following comments apply only if ballast is not enough to nullify the torque caused by the CG being below the canister axis (that is, if the car tries to do a wheelie, even with the front end loaded with ballast):
What if instead of using only the body of the car for stability, and given the rules restrictions, you use the front wing as the "primary" stabilizer?
I mean, if you use the whole surface of the car, don't you create more drag than if you use a smaller NACA section at the front to achieve the same effect?
I suppose this question is hard to answer: the "continous" small push from the front wing must be compared with the "haphazardly" push of the body. If the car is inherently unstable, that is, if the body is continously pushing down throug the whole run, perhaps it's better to use the front wing.
I think bazanaius is right: the body has to be flat, for added stability. But perhaps the "minimum" stability can be provided by the front wing (pushing downwards to avoid the car from flipping up).
If the variations in push (or in friction or in "whatever happens") overcome the "primary" stabilizer (the front wing), then the body "kicks in", keeping the car on the track and minimizing friction with the guidelines under the car.
Now, I´d presume that smaller drag of a wing as compared with a body is one of the reasons for having stabilizers in airplanes whose body is also stable...
Actually, perhaps you could use both wings to stabilize the car in the XY plane: front one with a "regular" NACA and rear one with an inverted profile, so you can use "flatter" profiles with smaller lift.
So I have another question to test bazanaius and flynfrog patience: what's better, two profiles, one profile or none (that is, only the body)?
Or, to put it in other terms, what's better at this speed, a flatter profile with more area or a steeper one with less area? What's the best wing load, if that's the proper term? I repeat, the previous discussion only applies if there is a need to use the car surfaces to stabilize it. It's always about ballast, I guess...
Well, of course a laval nozzle should be laying right at the edge of the hole in the container. Good point. The whole idea of the nozzle is that it's more efficient than having just a "combustion chamber" (in our case, the hole in the canister). For the nozzle to work as a Laval you have to adjust the nozzle against the hole with some kind of seal.flynfrog wrote:You are forgetting the nozle is the hole the pin punches in the co2 container. Also MEPs pump still wont have more energy than the CO2 contains it may move more air but at a lower speed. The pesky laws again.
However, if you don't have a good seal, like when you use a fairing, or part of the CO2 flow to impulse a propeller, you are "sucking" more air into the CO2 flow, isn't it? That's why we talk about the "proper speed" of air.
I don't think that considerations about that "proper" speed of the "impulsed" air are a "perpetuum mobile" idea. What I've understood of what I've read is that you have different efficiencies depending on the speed of the craft.
At low aircraft speeds it's better to use a larger volume with low air velocity than at higher craft speeds, where you want a faster flow with less volume (if I'm not mistaken, flynfrog), even if the total push is the same in those two situations.
Of course, the turbofan idea is a bit crazy, it's better to use a fairing, as mep and myself have suggested (if we're not mistaken, again).
For example, I think that the reason for smaller passenger planes to have turbofans instead of turbines is that propellers are are more economic at their relatively low speeds.
On the turbine Idea this is a rocket not a turbine. A turbine you are heating and expanding air with a fuel. In this case the best use of the fuel is to throw it out the rear of the car and push the car forward. Doing anything else with it is wasting energy.
One thing you could control is the size of the impulse this would be done by controling the size of the hole in the co2 tank. But I belive that this is controled by track not the teams.
When I built these cars we would take the C02 tank out to the shop and heat it with a lighter before putting it in the car
I also found a loop hole in our rules that didnt say we had to use the spec CO2 so I found some 12 gram ones for paint ball guns.
Ill try to go into more detail after work.