The P5: What Would You Change?

[Bert]

If you're asking how the square back end is better than a rounded one that isn't appreciably longer, that's a lot more involved. The best brief description I can give is that a properly designed flat end tends to create a stable bubble of turbulent flow behind it that is smaller than the one you would have with a rounded design on average. The key is to make the shape of that bubble taper aftward, using it as a sort of virtual fairing. This picture describes the effect fairly well:

Yup, what he said! LOL

 

[slinches]

Yes, but I cheated and found a diagram.

 

[HonestTex]

Here's why, Airplane wings are designed to "lift" the plane. if you turn it upside down, it would firmly plant that same plane hopelessly on the ground.

OK Bert, I completely understand how lift overcomes gravity and planes fly. What I don't get is how planes fly upside down. With lift and gravity working in the same direction, why doesn't the plane slam into the ground??
(I've been lost on this for years.)

 

[Rob Croson]

Can someone please explain to me how having a square rear end of the vehicle and the wheel fenders is aerodynamic. I have been told this is aerodynamic by the tour people.

Slinches has a good diagram. Wikipedia has a good explanation. (I underlined the salient part.)

https://en.wikipedia.org/wiki/Kammback

Aerodynamics
While the realities of fluid dynamics dictate that a teardrop shape is the ideal aerodynamic form, Kamm found that by cutting off / flattening the streamlined end of the tear at an intermediate point, and bringing that edge down towards the ground, he could gain most of the benefit of the teardrop shape without incurring such a large material, structural, and size problem. The airflow, once given the suggestion of the beginning of a turbulence-eliminating streamlined teardrop tail, tended to flow in an approximation of that manner regardless of the fact that the entire tail was not there. This is called the Kamm effect.[9]

There is controversy about the proportions of a true Kamm tail. According to the classic definition the tail should be cut off where it has tapered to approximately 50% of the car's maximum cross section,[10] which Kamm found represented a good compromise—by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds. Thus a minivan is not a Kammback, and neither are numerous cars that have truncated tails.​

Essentially, the full aerodynamic tail may be best, but the Kammback is "close enough". Get the air moving in the way you want it, and it just keeps going that way, even though the rest of the tail isn't really there.

 

[Rob Croson]

OK Bert, I completely understand how lift overcomes gravity and planes fly. What I don't get is how planes fly upside down. With lift and gravity working in the same direction, why doesn't the plane slam into the ground??
(I've been lost on this for years.)

http://physics.stackexchange.com/questions/15981/how-can-airplanes-fly-upside-down

In short: They keep the nose pointed higher toward the sky, causing the wings to deflect air toward the ground. The shape of the wing doesn't work quite as well, but it still works.

 

[Mel]

http://physics.stackexchange.com/questions/15981/how-can-airplanes-fly-upside-down

In short: They keep the nose pointed higher toward the sky, causing the wings to deflect air toward the ground. The shape of the wing doesn't work quite as well, but it still works.

Also aerobatic aircraft don't have quite the same airfoil as, say a Cessna. Aerobatic aircraft have a symmetrical or semi-symmetrical airfoil that helps. By using this type of airfoil the aircraft can fly inverted with a smaller angle of attack. i.e. The nose doesn't have to be held as quite as high.

 

[floydv]

Slinches has a good diagram. Wikipedia has a good explanation. (I underlined the salient part.)

https://en.wikipedia.org/wiki/Kammback

Aerodynamics
While the realities of fluid dynamics dictate that a teardrop shape is the ideal aerodynamic form, Kamm found that by cutting off / flattening the streamlined end of the tear at an intermediate point, and bringing that edge down towards the ground, he could gain most of the benefit of the teardrop shape without incurring such a large material, structural, and size problem. The airflow, once given the suggestion of the beginning of a turbulence-eliminating streamlined teardrop tail, tended to flow in an approximation of that manner regardless of the fact that the entire tail was not there. This is called the Kamm effect.[9]

There is controversy about the proportions of a true Kamm tail. According to the classic definition the tail should be cut off where it has tapered to approximately 50% of the car's maximum cross section,[10] which Kamm found represented a good compromise—by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds. Thus a minivan is not a Kammback, and neither are numerous cars that have truncated tails.​

Essentially, the full aerodynamic tail may be best, but the Kammback is "close enough". Get the air moving in the way you want it, and it just keeps going that way, even though the rest of the tail isn't really there.

So basically Elio is the Kammback Kid?

 

[Bamdalam]

If you're asking how the square back end is better than a rounded one that isn't appreciably longer, that's a lot more involved. The best brief description I can give is that a properly designed flat end tends to create a stable bubble of turbulent flow behind it that is smaller than the one you would have with a rounded design on average. The key is to make the shape of that bubble taper aftward, using it as a sort of virtual fairing. This picture describes the effect fairly well:

Thanks for the diagram. I (apparently) have a kammback, but never really knew what that meant.

http://motortalk.co.za/car-news/47-...oster-turbo-korean-on-the-kammback-trail.html

 

[Frim]

I like it, too. It's different, like the Elio, and I like that Paul is basically dedicating this vehicle to his Dad. How many car companies have done that? He's on a personal mission, and this car is clearly personal to him.

As long as it has appropriate increments, I'm fine with it. I suspect the Elio won't be a speed demon, so changes in the speedometer should be relatively gradual and easy to read.

The Edsel was named for a son.

 

[Frim]

OK Bert, I completely understand how lift overcomes gravity and planes fly. What I don't get is how planes fly upside down. With lift and gravity working in the same direction, why doesn't the plane slam into the ground??
(I've been lost on this for years.)

Because the pilot "chickens out" and puts the plane back into a flying attitude. I am not an engineer I am a psychologist.