F1 in Schools Help - basizeland's project

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flynfrog
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Re: F1 in Schools Help

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Ciro Pabón wrote:
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.
=D> This could be called Bazanaius Inverted Shark Fin...

I haven't thought about CG. #-o 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... ;)
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.
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.

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.
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.

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 :twisted:

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.

REA
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Re: F1 in Schools Help

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Thanks! I have to admit here to being the author of these regulations. To all helping out Brett with his original questions - WELL DONE - this is exactly why we run F1 in Schools, so students can be inspired to take up technical careers by linking with experts! Thank you.... I have thousands more students just as enthusiastic and talented as Brett, eager to learn.

basizeland
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Re: F1 in Schools Help

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hey REA do you know whether AC Racing got docked any points for having their so called aspirator on the back of the car.

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flynfrog
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Re: F1 in Schools Help

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REA

Really cool I just had a chance to do through the regs and you have tied up most of my loop holes.

also is there other way we can help. I would be willing to be a real world contact but my company wont let me release there name.

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flynfrog
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Re: F1 in Schools Help

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I just realized that the cars have a min weight so the biggest gains will be through rolling resistance and aero drag.

out of bordem im working on my own car.

basizeland
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Re: F1 in Schools Help

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I have changed a few things on the car such as extending the canister housing so that the car complies with the rule 2j.

I have added an elliptical back wing with one vertical rudder in the center to help stabilize the car.

I also removed the cuts in the side pods and added a small one to the top and just curved the bottom of the sidepod because I remember someone saying that it would be better without it and it is giving the car lift the other way.

I haven't changed the front wing yet because im not sure what to do for it so if anyone any suggestions a picture of it would be great to go by.

Here is the pics of the new car. tell me what you think Better or Worse

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Mystery Steve
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Re: F1 in Schools Help

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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.
The way that a de laval nozzle works is that when air is flowing at less than the speed of sound it will increase speed as the nozzle area decreases, and vice versa. The opposite is true for supersonic flow (as the nozzle area increases, so does the speed). So a de laval nozzle is designed such that the flow is initially subsonic and the area is decreasing, which causes the speed to increase. As the the flow reaches the throat of the nozzle, the flow should be sonic (Mach number = 1) if the nozzle is designed correctly. The nozzle then begins to expand and cause a greater increase in velocity. The exit area of the nozzle should be such that the exiting gas is the same pressure as ambient (to reduce oblique shock waves at the exit of the nozzle).

This is great when you have several thousand pounds of rocket fuel being ignited and thrown out the back end because you have a large mass flow and very high pressures. However, with a small CO2 canister the mass flow might be so insignificant that the nozzle may need to be so small that it isn't worth the effort to make it. I have a MATLAB code already setup from my Compressible Flow course, if the original poster knows the mass flow that the cylinder is capable of providing, the temperature of the gas, and the pressure of the gas, then I can run the numbers through to see what a feasible size would be.

The mass flow can be an average; that is, measure the mass before it is used, set it off and measure how long it takes to empty and then remeasure the mass. Divide the change in mass by the time it takes to empty. The pressure may be trickier; you could possibly get a ballpark number using PV=RT, or do these things have pressure ratings? It's been over 5 years since I did a project similar to this. If these do have a pressure rating, the temperature is then easy as long as you measure the volume of the canister (Fill a graduated cylinder to a known mark with water, fill the cylinder with water and see how much water was removed from the graduated cylinder).

Not sure about the legality, to be honest I've been too lazy to dive into the rules. If they have a committee that organizes this event, you may want to contact them. Legal or not, however, I am curious to see how beneficial a nozzle could be.

basizeland
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Re: F1 in Schools Help

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I googled CO2 canister and found that the pressure of the co2 canister is roughly 7-8 MPa at a tempreture of 20-30ºC and the mass flow is 0.28 kg/s. This may not be correct but it was on a pyhsics forum so im guessing that it is correct.

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raceman
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Re: F1 in Schools Help

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basizeland wrote:Image

whoa! :o
attaboy, awsome design..... way to go!


no offence, but hey, had this car been real racer, where would the driver will sit??

Mystery Steve
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Re: F1 in Schools Help

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I googled CO2 canister and found that the pressure of the co2 canister is roughly 7-8 MPa at a tempreture of 20-30ºC and the mass flow is 0.28 kg/s. This may not be correct but it was on a pyhsics forum so im guessing that it is correct.
Given these numbers under the most favorable circumstances, this is the scenario:
a) Pressure upstream of the nozzle throat is 8 MPa.
b) Free stream pressure is assumed to be 101 kPa.
c) Mass flow rate is assumed constant at 0.28 kg/s
d) Temperature upstream of the nozzle is assumed 300 K
e) Fluid is carbon dioxide: specific heat ratio is 1.289 and the gas constant is 188.9 J/(kg*K)

At these conditions, the area of the nozzle throat (the point where the flow becomes sonic, transitioning from subsonic to supersonic) would be .1252 cm^2 for a radius of 1.997 mm. To ensure proper expansion of the fluid in the supersonic region of the nozzle (you want the pressure of the CO2 to reach the ambient pressure so you don't get shock waves forming at the exit of the nozzle and decreasing efficiency), an exit area of 1.0489 cm^2 for a radius of 5.778 mm would be required. This would result in an exit velocity of approximately 560 m/s of the fluid and an exit Mach number of 3.4.

Keep in mind that a major assumption here is that the "upstream pressure" before the nozzle is identical to the pressure of the CO2 cylinder. This will not likely be the case as the pressure will decrease when it leaves the cylinder. When changing the "upstream pressure" to 5 bar (505 kPa), the dimensions of the nozzle increase: throat radius becomes 7.947 mm and the exit radius becomes 9.438 mm. This is good from a manufacturing point of view. However, nothing is free and those pesky thermo laws reduce the exit velocity to 391.3 m/s for an exit Mach number of 1.7.

The actual design inputs (pressure and mass flow) should be checked prior to building anything as the nozzle is sensitive to under-expansion and over-expansion; the exit pressure should be the same as ambient for best efficiency. However, these numbers should at least give you an idea for the ballpark size of the dimensions you would be considering. I'll leave it to you to determine how feasible these dimensions would be to machine given your manufacturing capabilities and the material you're using.

bazanaius
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Re: F1 in Schools Help

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These are some cool ideas - I'd like to reiterate flynfrogs point:-) minimise drag and rolling resistance. Make sure it doesn't flip about instead of accelerating. Then look at clever tricks to augment thrust etc. :-)

Seems this is exactly what you've done! Looking good - I'd be interested to see any pictures of CFD, or the windtunnel smoke tests when you get some.

FWIW: on the thrust augmentation with nozzles - I'd be interested to see some tests with cold, solid fuel jets (effectively what the CO2 cannister is). I've only seen thrust augmentation with combustion processes included, and I wonder if it would work the same. The nozzle as described by me effectively entrains fluid by generating a vortex ring at the trailing edge of the rocket outlet. This vortex ring then moves onto the leading edge of the nozzle and sits there, drawing fluid in and forcing it through the nozzle (entraining). Whether this would occur in a relatively low pressure, RTP exanding gas is something I'd be very interested in!

Re. The turbofan, laval nozzle ideas - the same thoughts from above spring to mind. I'm honestly not sure there's enough energy in there to generate the thrust augmentation, especially given the offsets due to complexity and weight of the solutions we're describing. This is the reason I think the separated nozzle may be worth investigating - it's light, simple and could be easy to setup a black/white test (yes it works/no it doesn't) without having to tweak it too much. If it works, excellent, if not you've wasted maybe a week.

bazanaius
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Re: F1 in Schools Help

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oh and, why not make your rudder elliptic as well?
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basizeland
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Re: F1 in Schools Help

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bazanaius is this what you meant by the elliptical rudder

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bazanaius
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Yeah that's the idea - not sure how much of an effect it will have though. Not sure why, but I might have made it a bit bigger - although I can't say for sure whether it's worth it or not! A bigger vertical fin would give greater restistance to yaw, but would increase drag. The compromise depends on how much resistance to yaw you need!

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basizeland
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Re: F1 in Schools Help

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thats has high as i can go because that is as high as the balsa block is although if i get RP wings i could make it higher.