a fair fairing?

Recumbents and all feet forward machines

a fair fairing?

Postby froodh » Mon Dec 14, 2009 12:41 pm

Hi All,

After riding my 'bent for a year, I've finally got around to building a fairing. Its only a cardboard mockup, held together with masking tape at the moment. I'll build a proper corflute one next.

Image

So far it hasn't helped me reduce my ride time to work (normally 35-40 minutes) averaging ~25kmph.
Maybe since my bike is a 20/26 USS bike and not a low racer, the fairing doesn't help much. My shoulders and arms stick out either side of the fairing as I don't ride a begging hamster OSS bike.

Maybe I need to work on the engine instead :p

What do you think?

cheers,
Jeremy
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by BNA » Mon Dec 14, 2009 12:49 pm

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Re: a fair fairing?

Postby }SkOrPn--7 » Mon Dec 14, 2009 12:49 pm

Nice work and good results on time saving I look forward to the corflute finished product thanks for sharing plus a nice ride too I really like the colour. :D
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Re: a fair fairing?

Postby bradwoodbr » Mon Dec 14, 2009 3:20 pm

Nice work indeed and good mock up.
Can I suggest:
:) Making the front down along the seat, behind the seat and all joins completely airtight.

:) Ensure the width of the mock up at your shoulders is at least one cm wider than your shoulders.
Your hands will still be wider than the fairing but you will get better airflow around and behind your body.
:) Riding to work may not be a fair test as there are many uncontrollable variables.
Perhaps rolling down a particular hill, measuring time/speed or both, with and without the fairing.
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Re: a fair fairing?

Postby raptordesigns » Tue Dec 15, 2009 6:54 am

I've played with a fairly aero tail fairing on a similar bike (with OSS though)
Image

In my experience, the improvement you can expect from the tail fairing, assuming that you've done it right is only in the region of a couple of km/hr extra in the 30km/hr cruise zone, and drastically less as your speed decreases. (drag is roughly proportional to the square of speed)

The general consensus seems to be that to work properly to get that extra couple of km/hr, the fairing needs to line up with your body... the test being that viewed from the front, an observer shouldn't be able to see the fairing behind you, and viewed from the rear, an observer shouldn't see any part of your body outside the fairing. If you look at my pic above you can see that I've sealed the fairing to my body shape using soft expansion joint foam. (the grey bit), and have included a shoulder bulge and even so I still have some issues with my upper arms and elbows creating drag thanks to the way the steering is set up.

If you have under seat steering with your shoulders and arms blocking the airflow and creating massive turbulent flow, the fairing is going to be of minimal use except as a box to keep gear in.

Other design factors include assuring that the bottom of the fairing is enclosed/sealed as closely to the wheel and other hardware as possible. If it's left mainly open, you're hauling an open drag bucket.
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Re: a fair fairing?

Postby froodh » Fri Dec 18, 2009 2:12 pm

Thanks for the comments guys!

"open drag bucket" is right! I rode yesterday, left home while it was sprinkling but halfway through the ride, it was pouring down.
My cardboard fairing got a little wet and sagged. Since the bottom is open, it made the aero worse, not better. On my way home it felt like I was riding through mud!

I'll have to redesign my construction & attachment method. The current design hangs off the seat with three strips of cardboard, held in place with the seatpad's velcro onto the FRP seat base. Its not even attached to the rear rack beyond touching it at a couple of points. If the fairing is to be wider than the seat, to cover my arms & shoulders, and also completely sealed, the attachment will need to be better.

Also, the angle of the sides was exactly 13 degrees, which is a figure that I read somewhere was the optimum angle. This was by pure luck - I didn't calculate or measure the cardboard at all, just used the length of card board I had available. The 13 degrees from the longitudinal axis, so right at the back there is 2x13 = 26 degree angle between the two side. Is that right? Will it need to be longer to get the 13 degrees?

The corflute sheet I have is bright yellow, even sexier than brown cardboard and will go with the fluoro yellow or fluoro orange t-shirt I normally wear when riding!

Do I need a sexy aero helmet like John's as well?

Would I get more benefit with lower profile tyres?
I have 1.5" x 20" & 26" Kenda 65 psi tyres. Would I get more of a speed increase with 1.3" 100 psi tyres like Continental Sport Contacts?

cheers,
Jeremy
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Re: a fair fairing?

Postby bradwoodbr » Sat Dec 19, 2009 12:32 pm

froodh wrote:Thanks for the comments guys!

The corflute sheet I have is bright yellow, even sexier than brown cardboard and will go with the fluoro yellow or fluoro orange t-shirt I normally wear when riding!

....

Would I get more benefit with lower profile tyres?
I have 1.5" x 20" & 26" Kenda 65 psi tyres. Would I get more of a speed increase with 1.3" 100 psi tyres like Continental Sport Contacts?

cheers,
Jeremy


I think bright yellow is the perfect colour for a fairing.
You will get a real benefit with the narrow, harder tyres (less resistance) at all speeds.
Do they give more speed than a fairing?? I think the faster the headwind, the more the fairing works with headwind speeds above 30km/hr.
I use 28 x 406(20) and 29 x 559(26) at 120psi and they work extremely well.
The ride may be a little harsher but I have gotten used to it. My bike is very comfortable.
Anyway the faster you ride the smoother the bumps Eh? :roll:
I am sure putting a fairing and narrower harder tyres together, there would be a big advantage. That is what I am working on.
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Re: a fair fairing?

Postby raptordesigns » Sat Dec 19, 2009 3:46 pm

bradwoodbr wrote:I am sure putting a fairing and narrower harder tyres together, there would be a big advantage. That is what I am working on.

Depends on what you mean by "big". A good tail fairing and hard tyres is unlikely to net you more than about 3km/hr improvement on your normal cruise speed.

A full fairing (front and rear combined), even a fairly crude one like the one I'm using, will improve your cruise by 10km/hr plus (if you were cruising at 30-35) and more if you cruise at a higher speed - and that's extremely noticeable when you're out mixing it with other bikes....
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Re: a fair fairing?

Postby bradwoodbr » Mon Dec 21, 2009 1:03 pm

I was thinking 10% was a big advantage. I had not considered the 10km/hr advantage of a full fairing.

Good on you. That is awesome. So what gearing issues if any arise and how have you solved them?
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Re: a fair fairing?

Postby just4tehhalibut » Mon Dec 21, 2009 9:17 pm

Possibly my post is old news since the last poster did his tomorrow (Raptordesigns date stamp Tue Dec 22, 2009 3:15 am ). How does he do that?

Anyway, in looking at full fairings wouldn't a front and possibly tailbox plus easy-to-install bodysock be a better way to go? It has to be lighter, easier to use with a SWB, more adaptable to wind conditions (as in you can remove when the crosswind is too slap-happy with the fairing and wheels), more likely breathes better and doesn't hold in noise like a drum. Possibly also cheaper to make. Here's one at the Hostel Shoppe
http://www.hostelshoppe.com/cgi-bin/rea ... 1261081012
Note that this version doesn't have a tailbox, instead they employ a simple strut framework behind the seat to take the bodysock back to a tail.

So it probably isn't quite as aerodynamic as a full fairing but it might be more practical and more comfortable in the heat.
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Re: a fair fairing?

Postby raptordesigns » Tue Dec 22, 2009 5:15 am

bradwoodbr wrote:I was thinking 10% was a big advantage. I had not considered the 10km/hr advantage of a full fairing.

Good on you. That is awesome. So what gearing issues if any arise and how have you solved them?


The gearing issues are only that given any decent downhill or in a sprint, I spin out at about 55km/hr (That's more me than the bike - it's a 53-11 on a 26inch rear wheel, so I should have a bit more cadence in me!). Mind you, I have realised that I start to feel a bit vulnerable and worried about my safety at that speed anyhow.

The real issues are crosswinds, a tendency to overheat in the plastic box, and indicating.

The up side is being able to comfortably, at cruise, blast past most road riders at a speed they can only maintain in a sprint. :-)
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Re: a fair fairing?

Postby raptordesigns » Tue Dec 22, 2009 4:54 pm

just4tehhalibut wrote:Possibly my post is old news since the last poster did his tomorrow (Raptordesigns date stamp Tue Dec 22, 2009 3:15 am ). How does he do that?


I guess I'm just ahead of my time. Unappreciated, too... ;-)

just4tehhalibut wrote:Anyway, in looking at full fairings wouldn't a front and possibly tailbox plus easy-to-install bodysock be a better way to go? It has to be lighter, easier to use with a SWB, more adaptable to wind conditions (as in you can remove when the crosswind is too slap-happy with the fairing and wheels), more likely breathes better and doesn't hold in noise like a drum. Possibly also cheaper to make. Here's one at the Hostel Shoppe
http://www.hostelshoppe.com/cgi-bin/rea ... 1261081012
Note that this version doesn't have a tailbox, instead they employ a simple strut framework behind the seat to take the bodysock back to a tail.

So it probably isn't quite as aerodynamic as a full fairing but it might be more practical and more comfortable in the heat.


Steve Nurse has an arrangement like this (above). It's definitely not as aero as my coreflute version, and interestingly, it's easier to get in and out of mine and to install/uninstall than his unit is. (the tailbox section slips over the rear rack and is held down with some straps, and the front part slots into an extended bottom bracket boom with one quick-pin.) I'm only using 2.7mm coreflute, so weight is moot. My whole fairing is about 5kg.

As for cost, it cost me $40 in coreflute, $15 in gaffer tape, $3 for velcro and the rest is oddments from the scrap bin. I'd estimate it cost less than $100 all up.
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Re: a fair fairing?

Postby bradwoodbr » Wed Dec 23, 2009 12:28 am

Would a fairing with more rounded sides reduce the effect of sidewinds?
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Re: a fair fairing?

Postby raptordesigns » Wed Dec 23, 2009 5:44 am

bradwoodbr wrote:Would a fairing with more rounded sides reduce the effect of sidewinds?


I suspect so. I'm going to have a shot at making a more rounded version sometime soon.
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