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Old 04-07-2014, 11:49 PM   #11 (permalink)
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Interesting thoughts about the vortex due to uneven pressure. I may look further into that.

The soap box cars were very helpful. The picture shown is similar to what I have in mind. The only major difference is a piece behind my head to streamline and match up with the end of the tail. for bad weather i plan on a top to fully enclose it. Other points I noticed were that flat and level to the road bottom was best, as well as the rounded nose and sharp tail. All points I had planned on. I'm shooting for a very similar shape to the middle wing section posted above.

No trike farm made yet, still in the planning stages. I finished an 18v lithium power wheels for my son over the weekend. Have a turbo motorcycle that really should be finished before I start buying materials for this project

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Old 04-07-2014, 11:50 PM   #12 (permalink)
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The volvo looks slick! But seems too long and wide at the back. I'm planning on a single rear wheel, so I can go much closer to a sharp tail end.
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Old 04-08-2014, 02:05 AM   #13 (permalink)
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Start with a 3ft diameter cedar billet and remove everything that doesn't look like a Velomobile.

To answer your question, as pointed out the sharp edges are a liability. Even a 4" radius would help, but there goes your buildability. For examples look to the 1912 Trophenwagen:



Notice the beltline bevel and how it curves down in the top front. Compare with the Airstream Basecamp:



There's also the Stanley Steamer that went 127mph in 1907.
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Old 04-08-2014, 09:38 AM   #14 (permalink)
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Vortex Energy Recovery - Innopedia

I'm trying to determine a couple of things. 1. Is a drag causing vortex really an issue at this speed?
2. If I built the design as is, how would I test the existing vortex, then eliminate it?

The picture above answers part of the question. I could mount a small turbine and let it spin freely to see the effect of the vortex. I could then make small adjustments to the body to improve it. If the vortex generated seems insignificant, then I won't even mess with it. I've been studying Wingfield of aircraft since they're the same shape and have tips specifically designed to eliminate this problem.

I also learned that the vortex created is inversely proportional to the aspect ratio.
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Old 04-08-2014, 10:09 AM   #15 (permalink)
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Quote:
Originally Posted by k-vette View Post
Wow, I've never seen that vortex tip recovery system before - nice find.

One thing I've picked up by posting over a hundred images in the "Wind Tunnel Pictures" thread is that any smoke wand point just a few inches off centerline draws the air off to the side of the vehicle canopy, not over it's roof.

There are a few shots where the air rolls over the tops of the doors (where they used to put raised rain gutter lips) at the plane intersection of roof and side window glass. This is one of the potential major vortex starting areas, yet I have yet to see a vortex here which is non-CFD generated. There are images of smoke tunnel vortexes, but only in fairly extreme case studies.

My suggestion is to go ahead and plan on building this bulbous nosed canoe shape, keeping in mind that the larger you can radius the corners (top to side planes), the better off you will be.

Also, I would not put anything unguarded and rotating within arms rear of curious hands.

NOTE: One way to avoid the complexities of building a radius corner on a compound curve is to build this shape like I did on the acoustic absorber, but use 4-inch (in lieu of 1/2") foam on the top piece. You will now be able to sand down the corner with an almost 4-inch radius. Internal fillets for strengthening can also be used to reinforce this right angle connection.

If loss of internal volume or foam weight are a concern I suppose you could always hot wire the excess material out.

Another option is stacking material layers at the corners or getting involved with a bunch of bevels or smaller pieces.

Just using the KISS Method here, thicker foam is silly stupid simple - my style.

If you build this before I build my small boat please post the construction details and shoot me a PM in case I miss it.
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Old 04-08-2014, 02:11 PM   #16 (permalink)
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Quote:
I've been studying Wingfield of aircraft since they're the same shape and have tips specifically designed to eliminate this problem.
Wut?

The F-173 was basically all wingtip. What made it work was the propwash from the counter-rotating props ahead of the wing.



Also, consider the construction of this:



All simple curves and no longitudinal edges.

If you cut the gores lengthways you wind up with more seams.



Edit:
Quote:
I could mount a small turbine and let it spin freely to see the effect of the vortex.
I notice the Airbus example uses a 'feathered' prop. It wouldn't need to be much more than a tachometer on a forward-reaching arm [or tentacle] that can be adjusted around. No vortex would equal zero RPM.


Last edited by freebeard; 04-08-2014 at 02:35 PM..
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