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-   -   Aero of teardrop on its side? (https://ecomodder.com/forum/showthread.php/aero-teardrop-its-side-28652.html)

 k-vette 04-06-2014 07:34 PM

Aero of teardrop on its side?

I'm considering building a velomobile and have a question about the shapes. Typically they are a 3 dimensional teardrop. I however am looking at building a 2 dimensional teardrop, so it would be aerodynamic from the top view, but essentially a rectangle from the side.

Do I lose anything by having the airflow go around the sides? The bottom would remain flat, which seems like it would be good against the ground plane.

The advantage of this shape would be two fold. 1, ease of construction. I could use flat aluminum plate for each side, top, and bottom.
2. I may add a motor and solar to the flat top side. Solar can recharge power for a velomobile in a few hours.

Any data on this? The templates all go the "wrong" way.

 kach22i 04-07-2014 11:00 AM

The problem is the air isn't going to go only where you want or decide it should go.

What's going to happen is the air on the sides will travel around this really sexy curve shape, the air above and below straight across.

It's going to take longer to go around (air at sides), the air on top will not be traveling at the same speed, there will be air pressure differences between each side and the top/bottom.

These pressure differences will cause air to be drawn to the low pressure areas, and as it does this it will be over distance which in turn causes a swirling or vortex.

The vortex is a funnel of twisting air which results in high drag once air flow further out from the body in motion contacts or interacts with it.

Your design sounds like an old soap box derby car, which I'm sure at the speed it operates at does okay as the vortexes are not too large or violent. However if you want to compete with the Velomobile, you are going to end up looking like the Velomobile.

I'd like to see a sketch or diagram of your design, the devil is in the details, and where your head is and it's treatment is rather important in the scheme of things.

 Frank Lee 04-07-2014 11:22 AM

Probably works quite well:http://i146.photobucket.com/albums/r...pse704b267.jpg

Mochet

1933:

http://i146.photobucket.com/albums/r...ps8452d6e2.jpg

 kach22i 04-07-2014 11:46 AM

Maybe a really aerodynamic helmet would help?

This Week in CFD | Another Fine Mesh

The S-Works+McLaren TT | RKP
http://redkiteprayer.com/wp-content/...Helmet-CFD.jpg

WIND TUNNEL TESTING IN TEXAS
Derby Tech - January/February, 1990
by Bruce Finwall
http://derby.mypalmer.com/techinfo/d...h/windtunl.htm
Quote:
 On January 2 and 3, 1990 some interesting observations were made during tests of soap box derby racers in the Texas A&M University subsonic, closed-circuit wind tunnel. Six of the top cars in the country (3 seniors and 3 juniors) were involved in a total of 48 separate tests. The following is a summary of what was found.
http://derby.mypalmer.com/techinfo/d...s/windtun2.jpg
Quote:
 Cody Robertson’s ‘88 racer had the least drag of all junior cars tested.
I like the stability of this design below.

SUNDAY, APRIL 02, 2006
Extreme Gravity Car!
http://photos1.blogger.com/blogger/2...ity_car_05.jpg
http://photos1.blogger.com/blogger/2...ity_car_10.jpg
Quote:
 Conceptually, not much has changed since the first event was staged in 1934: Build a small, simple race car according to tightly constrained rules, and coast down a racetrack powered by nothing more complicated than gravity. However, a lot has changed in the design of the cars, as evidenced by Volvo's "Aria", the car that won the latest extreme gravity car race!
http://www.swedespeed.com/news/publi...ticle_626.html
http://www.swedespeed.com/news/uploa.../gravity05.jpg
http://www.swedespeed.com/news/uploa...scaled_600.jpg

 kach22i 04-07-2014 12:07 PM

For context, these are some old posts on the topic I and others made in another forum back in 2010.

Random Picture Thread - Page 207 - Boat Design Forums
Quote:
 Originally Posted by kach22i (Post 365476) I saw a red and white striped one of these downtown Ann Arbor today, parked on the sidewalk with the regular bikes. It is so cool in person....bet it floats too, just needs an outrigger.:D Velomobile MikesBike.net http://mikesbike.net/wp-content/uplo...16317_7181.jpg http://mikesbike.net/wp-content/uplo...8632_thumb.jpg http://mikesbike.net/wp-content/uplo...5_30_thumb.jpg http://mikesbike.net/wp-content/uplo...7900_thumb.jpg

Random Picture Thread - Page 207 - Boat Design Forums
Quote:
 Originally Posted by Angélique (Post 365562) That velomobile is a Dutch designed Velomobiel.nl Quest built under license by the Canadian Bluevelo. They are HPV's (Human Powered Vehicles). Below some velomobiles from Europe.... http://en.velomobiel.nl/quest/img/quest.jpg Velomobiel.nl Quest http://www.velomobiel.nl/mango/img/xs.jpg - http://www.velomobiel.nl/mango/img/m...huinachter.jpg Here the designer working on the Velomobiel.nl Mango plug. This Quest is from Holland................. http://www.velomobiel.nl/image.php/haai1.jpg And here a Magazine cover.............. http://www.velomobiel.nl/nieuws/img/living.jpg --------------------------------------------------------------------------------------------------------------------------- This 214 MPG Super-Aerodynamic Modified Honda is from the same designer. Pay attention to the design process . . ! ! ! http://www.velomobiel.nl/allert/Recu...n/image081.jpg http://www.velomobiel.nl/allert/Recu...n/image082.jpg http://www.velomobiel.nl/allert/Recu...n/image083.jpg Here's an article about it. --------------------------------------------------------------------------------------------------------------------------- The Milan is German Velomobile (HPV). http://www.milan-velomobil.de/milan/bilder/intro.jpg [YOUTUBE][/YOUTUBE] http://www.youtube.com/watch?v=rN7W1I7YsMY --------------------------------------------------------------------------------------------------------------------------- The WAW is a Belgian Velomobile (HPV). http://www.recumbentblog.com/wp-cont...tser-waw-7.jpg http://lh6.ggpht.com/_WKfX4Oq0Qws/Ss...0/P1020663.JPG And see this WAW in Norway . . :) --------------------------------------------------------------------------------------------------------------------------- More velomobile companies are linked here. Cheers! Angel
Quote:
 Originally Posted by Angélique (Post 365567) No it rides over the water . . :D http://1.bp.blogspot.com/_cFao0zH2oM...0/IMG_0598.jpg Leaving port . . . . . . . . . . . . . . . . . . . . http://3.bp.blogspot.com/_cFao0zH2oM...0/IMG_0595.jpg http://1.bp.blogspot.com/_cFao0zH2oM...0/IMG_0587.jpg http://4.bp.blogspot.com/_cFao0zH2oM...0/IMG_0594.jpg [YOUTUBE][/YOUTUBE] http://www.youtube.com/watch?v=f4lGqoyJ_xc This one is in Norway. [YOUTUBE][/YOUTUBE] http://www.youtube.com/watch?v=O21bVeTChZE Cheers, Angel

 Frank Lee 04-07-2014 12:10 PM

You should help him fab it up then.

 kach22i 04-07-2014 12:18 PM

Quote:
 Originally Posted by Frank Lee (Post 419119) You should help him fab it up then.
No you should, aren't you are the one with the FWD bike, chainsaw powered wasn't it?

I'd like to see you put a skin on that thing Frank.

Seriously.:)

 Frank Lee 04-07-2014 12:22 PM

FWD, but no ICE.

OP wanted easy fab. That's a reasonable requirement, especially if it means a completed project vs a stillborn one.

The old Mochet quads were skinned with plywood.

 aerohead 04-07-2014 03:36 PM

2-D 'Template'

Here is a symmetrical wing section of minimum drag (center section).Any 'shorter' or 'longer' and drag goes up.
If anything,you'd go longer.

 kach22i 04-07-2014 03:58 PM

Quote:
 Originally Posted by Frank Lee (Post 419123) OP wanted easy fab.
This looks pretty easy (see below).

Endless-sphere.com &bull; View topic - Aerodynamics
http://recumbents.com/wisil/e-bent/e...bent_fair8.jpg

It would help to know if the original poster already has a Velomobile trike frame already fabricated up.

If not then the yellow recumbent above may be an option.

I found the comments below from the same page as the yellow one to be quite interesting.

Endless-sphere.com &bull; View topic - Aerodynamics
Quote:
 A body on a trike is good because you are not pushed around by side winds so much. IMO, Velomobiles are too low for in city commuting. A trike commuter with a taller stance (eyes at least at same height as the drivers of cars) would work well, but then you start getting more looks from the local authorities... I'm just sticking with the non-faired recumbent for now as that what seems like the best solution (for me!). -Warren.
K-Vette may find this little project of mine (see below) interesting, it's 1/2 of what he first proposed. You can skip putting all the holes in it.

Fireplace acoustic absorber for enhancement of the center stage

I've considered building a small one person fishing pontoon boat using the same form and techniques (+ covered in fiberglass cloth & resin). I might build a scale test model this summer to test the waters.;)

NOTE: Fan-Fold insulation is much thinner and lighter than what I used above (as used on my hovercraft). However even in the thickness shown above, scoring of the insulation was not necessary to bend or arc it. In addition, be weary of the weight of glues and fasteners.

 k-vette 04-08-2014 12:49 AM

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

 k-vette 04-08-2014 12:50 AM

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.

 freebeard 04-08-2014 03:05 AM

http://ecomodder.com/forum/member-fr...6-100-0041.jpg

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:

http://ecomodder.com/forum/member-fr...ture4984-a.jpg

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

http://images.gizmag.com/hero/4279_150705113152.jpg

There's also the Stanley Steamer that went 127mph in 1907.

 k-vette 04-08-2014 10:38 AM

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.

 kach22i 04-08-2014 11:09 AM

Quote:
 Originally Posted by k-vette (Post 419246) Vortex Energy Recovery - Innopedia
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.

 freebeard 04-08-2014 03:11 PM

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:

http://ecomodder.com/forum/member-fr...llmystery1.jpghttp://ecomodder.com/forum/member-fr...llmystery2.jpg

All simple curves and no longitudinal edges.

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

http://ecomodder.com/forum/member-fr...ticuda-tb5.jpghttp://ecomodder.com/forum/member-fr...lboxlayout.jpg

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.

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