Rounded corners vs. Straight edges on kammback

[MTrenk]

Here's a nice visualization of what will happen with the full Kammback:

http://www.youtube.com/watch?v=6b36ZP3PGis

And here's what you get with a full boat tail: (and I have a lot to say about how this design works not just by modifying the top, but the bottom of the car as well)

http://www.youtube.com/watch?v=cPQS2...feature=relmfu

[2000neon]

The flow off that boattail is impressive, of I didnt have to parallel park the car at school that would be a serious consideration.

I was thinking about this more today at work and revised my plan a bit. Instead of hinging a small section of the kammback to open to the trunk. I am now leaning towards making the kamm one solid piece, and allow the whole thing to hinge upward. Doing this allows for much easier building of the structure, and should be easier to make much more solid. I can also then taper the sides in farther, and have the sides of the kamm go overtop of the trunk. That should allow to gain more plan taper, and round off the back of it as much as possible.

Overall, I think that this will be easier to build, be sturdier and function better. I can then use a simple pin system at the back to keep it centered, and keep it down when I don't need in the trunk.

MTrenk, as for this idea, I am thinking if I use some thin (1/8th or 1/4") by about 1.5" aluminum to build the base of it, that will sit on top of the trunklid, and get me the basic shape at the bottom. Then I will be able to build the vertical transverse ribs to get the rest of my shape, and build sufficient support and a hinge at the top of the rear window to allow the whole thing to pivot upwards to get into the trunk.

I should be able to use some adhesive foam or rubber strips to prevent squeaking and help seal the kamm to the car.

[2000neon]

What I am thinking for the hinge is two hinges spaced reasonably far apart at the top of the window. The two problems I see with that is that they will be in the airflow, and since the roof is bubble shaped, and is curved across the top of the rear window. I am afraid that with two hinges spaced apart, they will both be slightly curved different directions and may bind against eachother? Or I could just be overthinking things, this may even be a case where have "sloppy" hinges may be better and allow some wiggle room between them.

[MTrenk]

You could use two Heimz joints as your hinges, then binding wouldn't be an issue.
Sounds like you are brainstorming quit a bit on this! Keep going, and don't be afraid to draw anything thing out to sort your brain out. Even if you think you suck at drawing, still draw what you're thinking.

I've got pressing Formula SAE matters to take care of tonight, so maybe drawings tomorrow. :P

[2000neon]

That would definitely work, but would complicate finding parts to use, and possibly budget.

Thats cool, I appreciate any help, whenever you could do it. I am trying to brainstorm as much as possible, I always like to at least work through things in my mind one step at a time and see what problems I run into. It has already helped out a few times in the planning of this kamm already. Its easier to fix something as an idea in my mind than when its metal on the car.

[freebeard]

Are the junkyards still full of cars from the 40's? The tulip panel on those probably had more curve than your Neon, and external, chrome teardrop trunk hinges.

[drmiller100]

on the pics of the boattail, the second pic shows the bottom angle is much too steep. The air is not staying attached to the bottom. Study after study has reported 10 degrees is about maximum on the bottom of the car - not as much energy below the car.

As to the previous study, I'm having troubles keeping up. First we were talking about angles of sides to top, and the study provided shows sharp angles don't hurt anything. Then we were talking about kammback to body, and study provided shows angles there don't matter much up to at least 18 degrees. Then we were talking about angles of kammback, and study showed 18 degrees stays attached.

Then we got switched around to a specific case which showed there is a possibility too much angle doesn't have the correct trailing vortices, and if you have STRONG vortices, in just the right place, you can have less overall drag because the vortices fill teh wake better. Predicting the lateral vortices is more than I can do off the top of my head, but the fact is they exist, and the fact is if you do things just right, you can use them.

[ChazInMT]

Originally Posted by drmiller100

on the pics of the boattail, the second pic shows the bottom angle is much too steep. The air is not staying attached to the bottom. Study after study has reported 10 degrees is about maximum on the bottom of the car - not as much energy below the car.

As to the previous study, I'm having troubles keeping up. First we were talking about angles of sides to top, and the study provided shows sharp angles don't hurt anything. Then we were talking about kammback to body, and study provided shows angles there don't matter much up to at least 18 degrees. Then we were talking about angles of kammback, and study showed 18 degrees stays attached.

Then we got switched around to a specific case which showed there is a possibility too much angle doesn't have the correct trailing vortices, and if you have STRONG vortices, in just the right place, you can have less overall drag because the vortices fill teh wake better. Predicting the lateral vortices is more than I can do off the top of my head, but the fact is they exist, and the fact is if you do things just right, you can use them.

Lateral Vortices are bad in almost every case.

[MTrenk]

drmiller100 said part of the study constituted 'proof'.
If you made it past Geometry, you know that the only real proof that exists belongs in mathematics. Science provides evidence, and by gathering this evidence, we obtain knowledge and understanding. You merely have one reference point and have not expressed any desire to further your understanding of the subject matter. There are certain aerodynamic principles that can be used for eyeballing and brainstorming. Vortices do not belong in this category. This forum is supposed to be about learning, and instead of learning, you read something that barely gives you want you want and treat it like gold. The only gold here comes from the people who have dedicated their time to learning, and sharing what they have learned. You have learned how to read a graph and make what you want out of it; statistics can be manipulated very easily.
I suggest you take a positive learning approach to this, instead of arguing with people who have the knowledge you should be seeking.

[aerohead]

Originally Posted by freebeard

While it's entertaining to watch people come at each other on Internet, I have been wondering about why nobody invokes the Coanda Effect, named by Theodore von Kármán after Henri 'my tails on fire' Coanda: Coand

Maybe it's because it can't be invoked passively; the main aero example being blown flaps. If only there was a car with handy supply of hot, pumped engine cooling air in the tail.

I looked into Coanda's work.It appears that none of his aircraft were capable of flight.His work is associated within the UFO community with respect to secret Luftwaffe projects.
Coanda did go on to make contributions within the aeronautical community,however none were associated with the 'effect' which bears his name.
Suction slots can do wonders with aft-body flow attachment,but so far,they require more energy to operate than they save.I believe that Georgia Tech is currently investigating this field of study.