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 Delta vs tadpole velomobile
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Dubya
Starting Member

USA
16 Posts

Posted - 12/27/2012 :  20:02:13  Show Profile  Visit Dubya's Homepage  Reply with Quote
I am new here, and am looking to scratch build a velomobile. I researched the aerodynamics and saw that the rear end matters more than the front. My question is: If the teardrop tadpole shape is supposed to be more aero than the longer delta missile shape, what if they both had the same shape in the rear? Wouldn't the pointier delta be more aero with the same rear end? Like if you took a Quest with 2 different front ends.

warren
human power expert

USA
4902 Posts

Posted - 12/27/2012 :  20:37:35  Show Profile  Visit warren's Homepage  Reply with Quote
I think the main issue with the Delta is not the aerodynamics it's the handling. Secondly that wide rear end makes it hard to close with a nice aerodynamic tail shape.

Warren
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Dubya
Starting Member

USA
16 Posts

Posted - 12/27/2012 :  21:01:08  Show Profile  Visit Dubya's Homepage  Reply with Quote
I am saying that if the body aft of the seat was identical, would it matter much if the front was different? I am talking about straight line speed.
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Dubya
Starting Member

USA
16 Posts

Posted - 12/27/2012 :  21:08:52  Show Profile  Visit Dubya's Homepage  Reply with Quote
I should have mentioned, the wheels will be outside the body with discs or wheel pants. The fairing will be shoulder width at the widest part. The tail can extend past the seat.
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warren
human power expert

USA
4902 Posts

Posted - 12/28/2012 :  05:40:36  Show Profile  Visit warren's Homepage  Reply with Quote
A large part of a faired bike's speed has to do with frontal area. You have the right idea with keeping it a minimum (shoulder) width. The nose shape does need to be aerodynamic. Pointier is faster up to a certain point, and rounder means less susceptibility to crosswinds. Have you see Raymond Gage's Orion speedbiike? It's a delta trike.
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nerdmobile
New Member

USA
61 Posts

Posted - 12/28/2012 :  07:00:30  Show Profile  Reply with Quote
It would seem to me that a delta design wth a tapered tail would be excessively long. Also that excess weight behind the rear wheels would effectively unload the front wheel and reduce steering response.

jeff garrett
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warren
human power expert

USA
4902 Posts

Posted - 12/28/2012 :  08:26:14  Show Profile  Visit warren's Homepage  Reply with Quote
Here's the Orion speedtrike:


This design was plenty stable up to 70 MPH.

-Warren.

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raymondg
recumbent guru

865 Posts

Posted - 12/28/2012 :  10:08:49  Show Profile  Reply with Quote
Dubya,

You don't mention what the purpose of the vehicle is. At first you say it's a velomobile, implying something relatively utilitarian and road worthy. Then you mention straight line speed, implying a race or record vehicle, with road worthiness as secondary. You would want different details for those different approaches. Since my background is mainly with record attempt vehicles, that’s what I will discuss.

My experience is that both the nose and tail are important. If you look at the pic above of my trike, you will notice that the nose is much pointier than most velomobiles. This was a decision to try and improve laminar flow over the vehicle, at the expense of cross wind sensitivity. If you look at the rear of the vehicle, you will notice that the main fairing needs to close up sharply to keep the length down, but creates a diffusion zone between the two external wheels, which can cause a lot of drag. That effect was mitigated by raising the main fairing higher off the ground, and spreading the rear wheels quite wide. This is good for improving aerodynamics, but would be bad for a road vehicle, as it won't fit in most shoulders, bike lanes, or between access limiting poles, and the height makes it much more likely to tip when cornering hard. Also, to get the geometry to fit and keep the front wheel as far from the nose as possible, I chose a Short Wheel Base (SWB) approach, which ends up putting most of the weight on the front wheel. Again, OK for a record vehicle, but not good for a road vehicle, due to increase tipping risk. That said, the delta config would lend itself very nicely to being a tilter, like many people have been doing recently with their unfaired trikes.

I should note that going with external wheels and wheel fairings (pants) is a nice way around adding excessive frontal area on a streamlined trike, but adds a lot of complexity. If you are the kind of builder who can turn out good quality work quickly, this is not a problem. If you work slowly, like I do, it can end up taking a huge amount of the overall project. For me, I estimate that the rear wheel assembly took about as much work as a whole other streamliner. This is because you have most of the same problems to solve and hardware to build as a simple two wheeled streamliner.

The Tri-Sled Completely Overzealous showed that a more conventional tadpole velomobile config can be very fast and stable. The trick was a very clean simple design, and ridiculously narrow front track. I forgot to ask Ben and Gareth what the max steering angle was, but it wasn’t much. So again, it comes down to the details of what you want to accomplish with the design.

For my next trike I’ve chosen to go with a wheel in main fairing tadpole config. This is to avoid the extra work of external wheel fairings, and because Completely Overzealous has pointed us in the direction of what might be possible with that config. I believe there are improvements that can be made to the config to bring it up to the level of the top bikes in the sport. But I’m talking record vehicles now, and that may not be relevant to you if you are more interested in a road going velomobile.

Regards,
Raymond

Edited by - raymondg on 12/28/2012 14:51:05
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Dubya
Starting Member

USA
16 Posts

Posted - 12/28/2012 :  13:23:46  Show Profile  Visit Dubya's Homepage  Reply with Quote
Thank you Raymond. That gave me a lot to think about. I wanted the delta design for simplicity but I also want a pretty good speed. It will be a street vehicle. I envision it to be a bit like that Russian Dragon velo from Velodreamers. Forgive my newbie questions. I am a great fabricator and auto body repair man, but I am new to aerodynamics and trike design.
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Dubya
Starting Member

USA
16 Posts

Posted - 12/28/2012 :  17:06:32  Show Profile  Visit Dubya's Homepage  Reply with Quote
http://www.recumbentblog.com/wp-content/uploads/2010/09/2256.jpg
This is what gave me the delta velo idea.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 12/28/2012 :  21:36:12  Show Profile  Reply with Quote
If you're scratch building you might consider a two wheel drive delta, with individual freewheeling hubs instead of a differential. It would have better traction on every surface other than dry pavement. Keep it fairly low and with the weight heavily biased on the two back driving wheels that will allow building it with a narrow track and still maintain acceptable stability. Deltas are great for turning on a dime. Another thing to consider is the fixed gear trick riding scene has brought very heavy duty deep profile 700C rims to the market, might as have a great variety of low rolling resistance tires. 20mm thru axle mountain bike front hubs with a sprocket on the brake disc mount, for the two back wheels on solid rod 20mm axle, for no alignment problems. Stanton Inc.com has thread on freewheel carriers for mounting freewheels to a jackshaft. My 2 cents on velomobile design, albeit unconventional.
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Dubya
Starting Member

USA
16 Posts

Posted - 12/28/2012 :  23:52:15  Show Profile  Visit Dubya's Homepage  Reply with Quote
The 2 freewheel thing makes it harder to turn because it puts the powered wheel on the inside of the turn. Other than that, yes, I was going to make it low like the Kettweisel. Based loosely on the Atomic Zombie Aurora delta.
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OpusthePoet
recumbent guru

USA
678 Posts

Posted - 12/29/2012 :  14:06:20  Show Profile  Visit OpusthePoet's Homepage  Reply with Quote
2 wheels connected by freewheels makes for easier turns in both directions because the outside wheel is free to turn faster than the inside wheel, while giving better straight-line traction in bad conditions. It works like a locker rear in a car, except without the ability to back up under power. It also prevents pulling away from the side of the single powered wheel in single wheel driven deltas. This can be very bad when climbing a hill with right side drive in the US as the trike will tend to pull in front of motor vehicle traffic. I installed a lower gearset in a trike for a handicapped woman and had this exact problem, while she could now climb hills that were much steeper than before, the trike would pull sharply to the left as the front wheel would get light and lose traction. While I was doing testing after altering the frame to install the triple crank (derailler post, front derailler, and additional controls) I did a 180 in my driveway. Driving both wheels through freewheels prevents this.

Opus

My gas is up to $0.99 a burrito, $5.99 for premium and I'm only getting 10 miles to the regular burrito. Dang $0.99 burritos are smaller now.
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Dubya
Starting Member

USA
16 Posts

Posted - 12/29/2012 :  15:54:06  Show Profile  Visit Dubya's Homepage  Reply with Quote
I know the outside wheel can freely turn with 2 freewheels. But the inside wheel is receiving the power no matter which way you turn, which makes it harder. A car differential powers the outside wheel. I will be riding it in dry conditions and where I live (Long Island, NY) it is very flat. One wheel drive should be Ok. I want to keep it light as possible. It will be for fair weather fun.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 12/30/2012 :  09:21:25  Show Profile  Reply with Quote
The double freewheel arrangement automatically wants to track straight under power as the slowest wheel is always driven. My brother and I cooked up a custom trike for one of his neighbors with this arrangement, an upright with effective 11 inch chainstays and a large caster welded to a steel suspension seat post as a wheelie bar. When we were testing it it worked awesome, you could feel the mechanical voodoo action of the double freewheels doing their thing, while doing standing on the pedals power wheelies. I've spliced a one wheel drive trike rear end end to a full suspension mountain bike and it was pretty limiting in all the ways Opus out lined, plus the traction was really poor hill climbing off pavement.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 12/30/2012 :  09:48:00  Show Profile  Reply with Quote
It sounds like you're on the right path with an Atomic Zombie design, nice and solid, nothing fussy. Best of luck with the project. The delta steering will allow it to turn around on a dime, and not have to use "wheel chair style reverse" on tadpole front wheels to perform 3 point turns. Light, nimble and easy rolling; equals a fun vehicle that begs to be ridden.
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Dubya
Starting Member

USA
16 Posts

Posted - 12/31/2012 :  14:02:41  Show Profile  Visit Dubya's Homepage  Reply with Quote
OK, I was thinking about the 2 wheel drive thing and now I want it. I will not be carving corners with it most of the time anyway. I'm trying to design a body that is sleek but with a little steampunk/retro/Flash Gordon thrown in and is able to carry a 12 pack. I am looking to make the thing pretty fast and a lot of fun. As a 25yr auto body repairman, I think I have the skill to pull it off. If it works, the next one will be a tadpole design or maybe something based on the infamous MASA Slingshot.
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warren
human power expert

USA
4902 Posts

Posted - 12/31/2012 :  15:11:18  Show Profile  Visit warren's Homepage  Reply with Quote
Maybe something like Greg K's velomobile then.

http://www.adventuresofgreg.com/RocketMain.html

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Dubya
Starting Member

USA
16 Posts

Posted - 12/31/2012 :  19:45:01  Show Profile  Visit Dubya's Homepage  Reply with Quote
I saw Greg's in my research, but the tilting thing is more than I want to tackle right now. The styling is kind of what I was thinking, but I want to use stitch and glue construction with flat panels for simplicity. Maybe a little carved foam. The whole project will sacrifice some speed in exchange for ease of construction. I can't really explain my idea well because I cannot draw well or use CAD so I will post pics when I build the test model.
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mikeatlbch
recumbent enthusiast

USA
200 Posts

Posted - 12/31/2012 :  20:51:11  Show Profile  Reply with Quote
Look at the Aurora velomobile.
http://velomobiles.ca/Aurora.html
I saw steve's work at pir some 4 years ago. Very practical.
Maybe some of the owners can let you know about their experience.

Then Garrie and Richard can let you in on 55/55 or is it 65/65 now?

Edited by - mikeatlbch on 12/31/2012 20:53:39
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Dubya
Starting Member

USA
16 Posts

Posted - 12/31/2012 :  21:50:38  Show Profile  Visit Dubya's Homepage  Reply with Quote
I will never buy a velo. I will homebuild to my own crazy ideas.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 01/01/2013 :  07:02:53  Show Profile  Reply with Quote
stanton inc for threaded on freewheel adapters for a jackshaft.

As I remember Utah Trikes has a freewheeling 2wd back axle kit for $600 or so, if you're not into doing the custom machine parts thing to achieve 2wd.

I think it's a bad rap that freewheeling 2wd is hard to turn, as one drive delta trikes can turn right OK under moderate pedaling loads.
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OpusthePoet
recumbent guru

USA
678 Posts

Posted - 01/01/2013 :  14:08:49  Show Profile  Visit OpusthePoet's Homepage  Reply with Quote
Also the AZ delta trikes use a solid axle with both wheels tied together and that really causes a bad push/no turn condition. But by weighting the outside rear wheel while leaning to the inside you can get one to turn reasonably well. You just have to learn how to make a trike ride on 2 wheels when you turn.

Opus

My gas is up to $0.99 a burrito, $5.99 for premium and I'm only getting 10 miles to the regular burrito. Dang $0.99 burritos are smaller now.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 01/02/2013 :  02:47:22  Show Profile  Reply with Quote
Atomic Zombie trikes are one rear wheel drive. 2 pillow block bearings per split axle.
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Tom Schneider
New Member

59 Posts

Posted - 01/02/2013 :  03:59:25  Show Profile  Reply with Quote
I have started on a 2 wheel drive low carbon delta. After many sketches, I came up with using a disc brake rear hub as a jackshaft. Bolting 2 cogs with a spacer between to the disc mount on the hub, with 2 chains running forward to 2 freewheels on the axles. I can then have the drive between 2 short chainstays keeping the rear end clean for better aero. A 9 or 10 speed cassette on the rear hub with a single chainring up front completes it.
Now to build a wood mockup to see how I fit on a 7.5" high seat with a 15 degree seatback delta.

Edited by - Tom Schneider on 01/03/2013 03:13:06
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Dubya
Starting Member

USA
16 Posts

Posted - 01/02/2013 :  18:03:22  Show Profile  Visit Dubya's Homepage  Reply with Quote
Atomic zombie now has parts for the 2wd double freewheel thing. I think he uses it on the new Aurora racing trike. That is the one I am baseing my creation on.
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