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Steven Challenge Posted - 05/22/2012 : 07:49:54
I've been lurking on this forum for a while, to find a way to create fairing on my Challenge Hurricane. What I've seen so far is the "surfboard" approach. Foam mold, chaped and sanded. Then fiberglass cover, then remove the mold. From an enviromental point of view (and financial and time to) I think this could be better.
Why not use the approach the old airplane builders did. A wooden frame, covered with air tight fabric. With a good choice of wood you can make a firm, lightweight structure. I'm thinking of using 3mm poplar plywood, cut in 1" strips. Two strips glued together (with PE construction glue) in the correct shape can withstand a lot of force. Think about the laminated wooden chairs.
I could use a fabric that is air tight by itself, but most of those are non-stretch. Therefore I need to cut parts in strips and sew them together, creating a seam (that can cause drag). I'm thinking about a stretch fabric to cover the frame, then put a coat of resin over that, to make an air tight top.
So that's basically the idea. I'm going to start with the rear fairing, because this looks easier. After that, front fairing.

Now for some questions:
#1 For what I could understand from several builds, you first have to trace the shape of the person sitting in riding position. From that shape it's gradually move towards the back ending in a vertical line. This move towards the back, does it matter how it flows towards the vertical line? I guess, start parallel to the frame and about half way bend towards the center.
#2 What happens underneith, where the rear wheel is situated? Is it just a hole that fits the wheel or is this airodynamic shaped?
#3 Do I need to keep the front fairing in mind when designing the rear fairing? Do they have to line up aerodynamically?

I'm going to draft some pictures soon to elaborate my design.
25   L A T E S T    R E P L I E S    (Newest First)
TrikeMakto Posted - 08/01/2012 : 07:44:08
Ive been thinking about trying a pre-fab tail box for the rear -- like one made by NovoSport -- their Fujinbox -- then using my curved tube idea to make the forward portion

that particular tail box has a nice aero shape and its cut to fit a bike with a rear suspension and wide tubes -- which my QNT also has -- it may pr may not be a compatible fit -- has anyone tried it?
Steven Challenge Posted - 07/27/2012 : 10:27:47
Not at all LongJohn, I've managed to take off about 45 minutes from the two hours I started with. I weighed about 105kg when I started, now 97kg and getting more pounds off. Right now it's with every kg off, about 1km/h faster. A couple of days ago I lowered my suspension. It might be a placebo effect, but it seems to increased my speed. It seems to ride better for me.
Not being an expert (far from it) on aerodynamics, but using common sence: When you ride a bike, at a certain speed, you feel the wind in your face. This would be the speed where fairing would have effect, am I right? The faster you go, the more the airodynamics would take part. There is a sertain speed and aditional weight where the both would be equal. The best way to find out this ratio is by precise calculations and airodynamic testing. The alternative way is trail and error.
I could go for a standard box fairing, but that wouldn't give me the pleisure to express myself in making my own fairing.
To end this with a question: is there a minimum speed for a box fairing to have any effect on the preformence? Given the bike is a Challenge Hurricane (midracer, two-wheeled, steering above.) Person riding 1,85meter, 97kg.
LongJohn Posted - 07/27/2012 : 02:23:47

Not to be funny; but judging from your average speeds in the other threat, your goal to have a fairing make you faster will not work....
The speeds you are riding just don't justify using a full fairing to go faster. The added weight of the fairing would increase rolling resistance making you actually go slower....
I would look for a nice box fairing (try Elan in Nijmegen) that you can close and keep all your stuff dry.
Going faster would require simple training, ride your bike more often to work you should be able to shave some time off the two hours it takes you to do 36km.

Hope you don't feel offended,

Steven Challenge Posted - 07/27/2012 : 01:06:48
I just browsed thru the website you mentioned, TexasTuff. This is the structure I want to go for:
Thank you for the info.
TexasTuff Posted - 07/17/2012 : 07:30:33
I too have been lurking for sometime. You may find some answers here.
I've been gathering information on skin on frame construction for awhile in anticipation of adding a velo body to my delta trike. http://texasrecumbents.wordpress.com/skin-on-frame/
Hope this helps.

alevand Posted - 06/29/2012 : 04:34:14
You have to dope the fabric, as they do on aircraft, to keep them from flapping.

Tony Levand
Speedy Posted - 06/28/2012 : 16:25:52
the tent pole concept has been tried, perhaps not well enough ....
tents are designed to be stationary
fabric flapping in the wind can serve to slow the vehicle
TrikeMakto Posted - 06/28/2012 : 15:07:39
Thanks for the tent pole suggestions -- I agree those would require more lateral hoops not just the nose to tail ribbing -- definitely a second choice option

seems like using the rigid curved shower curtain rods should also provide enough tension for a fabric covering -- probably the easiest way to go

doesnt sound like its ben tried before.....could be breaking new ground

I'm also looking at joining the curved rods at their ends front and back using the rings that hold patio umbrella ribs together in a circular fashion near the top of an umbrella
Steven Challenge Posted - 06/18/2012 : 03:27:43
I haven't made a decent draft jet, but I do have some ideas to incorparate into the design. The best design for airodynamic tailfairing would probably go all the way down to the bottom of the seat, and back to the tail of the fairing. However sidewinds would influence the ridability on a full tailfairing. I'm thinking of making the bottom and top half of the tailfairing detachable, so I could ride full tailfaired when there is little to no wind, but half tailfaired when there are sidewinds. Perhaps a structure where the bottom half can be stored inside the top half.

at TrikeMakto: welcome to the forum. I guess the problem with licra is that it is stretchy. Without propper support it might flutter and cause drag. Also if it isn't 100% airtight, it works as an airfilter. Not flowing all the air around the bike, but letting some thru.
A (iglo) tent structure works on the ridgidness of the fabric in two dimentions(X and Y). Fixing the third dimention (Z) with flexible rods. So you need basically a bag in the right shape with tunnels to keep the rods. The rods have to bend in order to keep tention on the fabric, so it keeps the desired shape. Rods placed along the length of the bike, wouldn't provide that much of tention. Better would be to put them perpendiculair to the length of the bike. If you are able to put tention to the fabric, in the length of the bike, your structure would be good.
Something like this:

this tent is held into place by putting tention on the front and in the back. Removing either side would collapse the tent.

this structure:

is self supporting. The crossed poles and the shape of the fabric prevents it to collapse.

How to transfer this into a full fairing, I don't know. This is just the general idea.
TrikeMakto Posted - 06/15/2012 : 14:17:11
I'm with Stevn on this...there's got to be a thinking-outside-the-box better way

Ok I'm new to forum, but here's my two cents worth of crazy ideas....

similar to the old airplane construction idea....

I was thinking of trying a few of those curved shower rods laid from nose to tail -- since they are rigid and will hold their gently curved shape -- then covering with stretchy fabric like lycra -- has anyone tried this? it should give a lovely dirigible look

I also considered using tent poles (the camping tent kind) laid from nose to tail the same way covered with stretchy fabric, but I'm guessing they won't be as rigid and will flop around alot

someone mentioned PVC tubing, which I tried once before for a cheap solar car project -- but they didn't seem rigid enough
Grant-53 Posted - 06/14/2012 : 20:03:44
Yes, chicken wire fencing. I use a cone or ellipsoid shape to minimize side wind effects. Sail planes have very sleek shapes and the seating is similar to a recumbent.
alevand Posted - 05/30/2012 : 05:08:27
Yes, I know the feeling, Warren, its kinda like OH NOOOOO!*#&@ ~ a tail box alone shouldn't be a problem.

Tony Levand
warren Posted - 05/29/2012 : 08:55:13
I stopped using my full coroplast fairing for commuting on my full suspension SWB bike because on some days we have very strong and gusty winds, and I would get pushed around. That's fine if you are riding on empty roads or in a trike, but I was feeling like I may get pushed in front of a car.

alevand Posted - 05/29/2012 : 04:41:54

Tony Levand
Steven Challenge Posted - 05/29/2012 : 04:09:31
Sidewinds is one of my concerns. The road I travel is partly thru acres, flat with often sidewinds. I could make a tailfairing that goes all the way down to the bottom of the seat, what would be more airodynamic. Or I could make the tailfairing go as far as the top of the rear wheel, making it less infuenced by sidewinds.
I have some disc wheels laying around, I guess I'm going to try that some time.
Patrick Bateman Posted - 05/29/2012 : 00:26:34
I've messed around with fairings a bit. Their advantages depend a LOT on where you ride. For instance, I live in a very hilly area. A fairing will increase my top speed on the flats, but it really won't help me much on the downhills, because I'm simply not comfortable bombing down a hill at 70 kilometers per hour. And the big problem for my area is that a fairing will slow me down on the hills, and is a bit dangerous in traffic, due to sidewinds pushing you into traffic.

IMHO, a nice compromise is the use of aero components. For instance, disc wheels.

If speed is not your goal, but avoiding rain IS, then a fairing can be very useful.

IMHO, one of the nicest compromises of weight and aerodynamics is the F40 recumbent. It's faired, but the fairing is removable, and the use of lycra keeps weight to a minimum. HTH
Steven Challenge Posted - 05/23/2012 : 22:54:25
@Pugzcat: I got the Challenge Hurricane for about $500. I'm thinking about spending 1/8th of that price for my fairing.
@Grant-53: hex mesh? As in chicken fence?
Grant-53 Posted - 05/23/2012 : 20:06:36
I laminate 1" hex mesh between two layers of 0.005" tarp plastic and use stiff nylon tubing for ribs.
PUGZCAT Posted - 05/23/2012 : 16:25:42
An Electrathon race parts company had fiberglass bodies on sale awhile back, the smaller of the two would have been ideal for a lowracer if 14 inches in height was added to the belt line of the body so there would be a big enough foot box to pedal the cranks. It seems like a quick, low mess, fuss, time, labour, expense, way of enclosing a lowracer in a body. $500 or so as I recall. I'm thinking rivets and thin lexan sheet to add height to the belt line.
Steven Challenge Posted - 05/23/2012 : 12:02:59
Thank you Victor, your answers has helped me a lot. I think I'm going to make a cardboard mock-up for the basic shape and way to mount to the bike. Pics and probably more questions later. It might take a couple of days before I make the mock-up, because I'm using the bike to go to work tomorrow. I'm riding on tuesday's and thirsday's to work, so building the fairing should be in such a way that I can keep riding while working on it. No second recumbent and no car on the two days I ride.
Victor Ragusila Posted - 05/23/2012 : 07:38:53
I will do my best to answer your questions. Generally, i have never faired an existing bike, but started from an aero shape and then figured out how to fit the person inside.

1) I dont understand what you are asking. The idea with the rear fairing is to make the airflow unite again without any separation. If one keeps the angle of the fairing w.r.t. the centerline under 15-17 deg, generally separation will not occur. A tuff test will prove whether that is the case or not. The shape should be as simple and smooth as possible.

2) The wheel fairing is very important. Generally, the hole for the wheel should be as small as possible, just big enough to let the tire thru.

3) Yes. Generally, you want your fairing to create 0 lift/downforce. Also, you should create the front and rear such that they create 0 downforce themselves. An issue we had before (with Vortex) was that the front creates lift, and the rear downforce. This doesnt cancel out, but makes the induced drag quite important.

I would suggest looking at a few of the fast streamliners out there. ACE (our first streamliner) had a decent shape, and is big enough that it might allow a bike inside. Also, "The leading Edge" by Goro Tamai is a great aero reference. If you read that and understand why the fast streamliners are fast, you will have a good basis for your fairing.

There is a streamliner with exactly the same construction method as you describe, we race against it in Waterford. It is quite fast and good looking, but a bit heavier (50lb) than i would have expected. You can see a pic of it here http://www.flickr.com/photos/fa2din/7249306332/in/pool-1898048@N24/



PS the streamliner in the pic uses metal ( i think aluminium) tubes to create the fairing structure, not plywood. It did survive a drop without any issues, not sure how it would do in a high speed crash.
Steven Challenge Posted - 05/23/2012 : 06:35:57
I've read the "build/tech" pages before, but I've just re-read them again.
Question #2 "What happens underneith, where the rear wheel is situated?" has been answered (Seen the pictures, got the idea).
So is #3 "Do I need to keep the front fairing in mind when designing the rear fairing?"
As for question #1 about aerodynamics, I guess it depends on the bike and rider and the way I'm going to use it. Basic aerodynamics (from the top of my head) is to let the air flow as smooth as possible. The faster I go, the more influence the airflow will be. For relatively low speed, I won't need a long, close to parallel, tailfairing.
I've found a website and a picture of a guy that has about the same idea. Difference is, he used a foam rib structure, I want to use plywood. Basically, this is what I'm going for.
alevand Posted - 05/23/2012 : 04:37:28

Tony Levand
Steven Challenge Posted - 05/23/2012 : 01:38:05
2 reasons, in no particular order.
Right now I put a small backpack on my bicycle rack to carry my wallet, phone, raincoat and sometimes food. When I want something out of it, I have to remove the bungee cord, open the backpack and dig in. A tailfairing with custom made pockets/shelves might organise it a bit more and keep it dry in the rain.
I also think I could go faster when the bike is more aerodynamic. I've noticed the rather dramatic difference bitween an upright bicycle and a recumbent. At a certain speed, I can hear the wind behind me creating drag. This might be psycological, but it feels like it is holding me back to go faster.

The reason I want to make my own fairing is because I like to DIY. I also like to think outside the box and find the conventional way of fiberglass and carbonfiber to labor intensive and pricy. Cardboard and coroplast seems to be to sketshy. (No offence to all creations.)
Plywood strips covered with fabric seems to me easier and less expensive. I've worked with plywood before and find it remarkably strong and easy to work with.
JMvD Posted - 05/22/2012 : 23:33:57
Originally posted by Steven Challenge

50+ viewers but no reply. Either the concept is to alternative or I didn't make myself clear. ;)

Here's a picture of what I'm talking about:
Look at the tail part of the airplane. That would be the structure for the fairing. Lightweight but strong.

The big question is:
Why do you want a fairing on your Hurricane?

There are a couple of different tailfairings on the market. Or you can build a (tail)fairing yourself with cardboard, coroplast, fiberglass, carbonfiber.
You could make a body sock.
You could. . .



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