Front + Tail Fairings for bicycle - RC Groups
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Oct 18, 2017, 10:39 AM
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z-matrix's Avatar
Discussion

Front + Tail Fairings for bicycle


Hello my friends!

I want to ask your opinion about using a tail fairing combined with a front fairing

i assume the front fairing needs to be smaller than the tail fairing in diameter/width/height to let the flow reattach to the tail fairing right?


Z
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Oct 18, 2017, 01:33 PM
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z-matrix's Avatar
illustration
Oct 18, 2017, 01:52 PM
Registered User
Examine the design of the windscreen in these (bipe & car), I have been in both at approx the same speed (somewhat faster than a bicycle) and experienced ZERO wind on me (the flow going over & around)

surprisingly small windscreen (note pilot's head size & position) https://wikipedia.org/wiki/Bücker_Bü_131








Boxter windshield/headrest combo prevents backlash turbulence, creates smooth flow
Oct 18, 2017, 02:03 PM
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z-matrix's Avatar
Quote:
Originally Posted by xlcrlee
Examine the design of the windscreen in these (bipe & car), I have been in both at approx the same speed (somewhat faster than a bicycle) and experienced ZERO wind on me (the flow going over & around)
Boxter windshield/headrest combo prevents backlash turbulence, creates smooth flow
Thank you for the tip,
i only have one problem that prevents me from enclosing the entire bicycle in a shell, that is to enter/exit and put down foot when stopped!


Z
Oct 18, 2017, 03:54 PM
Registered User
https://wikipedia.org/wiki/BMW_C1

aerobike





MonoTracer






Crossbow

Oct 18, 2017, 08:54 PM
just look at it smokin'
z-matrix's Avatar
Quote:
Originally Posted by xlcrlee
https://wikipedia.org/wiki/BMW_C1

aerobike





MonoTracer






Crossbow

The C1 is a joke, the MonoTracer is interesting thanks
So if i were to put 2 retractable landing gears on 2 sides in theory i would be fine most of the time with a door on a 2 wheeler, only minor issues when there is something in the landing gear's path, or it fails to deploy fast enough.
the Crossbow is an interesting design too, now i need to start making something


Z
Last edited by z-matrix; Oct 18, 2017 at 09:04 PM.
Oct 19, 2017, 08:27 AM
Registered User
for some reason RCGroups often refuses to display the above posted (often not shown) aerobike pic
so from

http://aerobikeenclosedmotorcycle.bl.../?view=sidebar

http://aerobikeenclosedmotorcycle.bl...?view=snapshot



Why bicycles do not fall: Arend Schwab at TEDxDelft (17 min 56 sec)
Oct 19, 2017, 09:20 AM
An itch?. Scratch build.
eflightray's Avatar
I vaguely remember cycling speed records being carried out in a modified railway coach, with the rail track covered to give a smooth surface.

I bit limiting though.

Wiki shows some cycling speed records -- https://en.wikipedia.org/wiki/List_of_cycling_records

I particularly liked the ---
172 km/h (107 mph) Downhill on a volcano, on a prototype bicycle

Obviously not an active volcano then, and being chased by the pyroclastic flow

As for a fairing shape, I would have thought the shape shown would also create a lot of drag. Do these give a better idea ---

https://motoredbikes.com/threads/get...d-gains.37010/


Or is this one of the 'hypothetically ...... ' questions, more about aerodynamics ?
Oct 19, 2017, 03:31 PM
B for Bruce
BMatthews's Avatar
Two wheeled powered pods aside for the moment (cool as they are!) for your bicycle the key element for aerodynamics is the rear portion. A while back I was all interested in HPV's in general and bicycle lowriders in particular. Still have building a lowrider as a project on the list in fact.

Anyway, aerodynamic drag is a funny thing. It is more important to close the air BEHIND the object smoothly than it is to split it apart smoothly in the first place. So if you really have to limit the amount of added weight it is best to use the tail fairing.

The others such as the windscreens on the plane and sports car are not to reduce drag but to increase pilot/driver comfort by shielding them from the wind blast. And in fact they are LESS aerodynamic. Ever driven in a sports car or other convertible? The air rolls over the windscreen and around and smacks you in the back of the head.

Speed skier's fancy "Star Wars" helmets are tapered back like they are for this same reason.

The sharp cutoff "Kamm" style tail is better than a shorter and blunter angle to the fairing but it's not as low a drag as a full length fairing that ends in a sharp line.

OK, so back to your linked fairing combination.

You asked about the front being smaller or larger than the rear. Keep in mind that there is a BIG gap between the two. The air is going to roll inwards off the rear edge of the front fairing heavily. So it matters little that it's a little bigger in frontal area than the rear fairing. And in line with the above I'd suggest that the front fairing is more about room for the rider's legs and weather protection than it is about drag. At least in this case where there's a big gap between the two.

And in fact on one web page an enterprising sort took the time to make up stretchy fabric "door panels" that closed off the gap. I don't recall if he then slithered down through the head opening or if the panels were able to open and close much like a proper door. But the report was that it did make for better speed at a given heart rate. Or a lower heart rate at some given speed. So the closer you get to a full airfoil shape the better it is. And if you can't do that then at least close the gap with SOMETHING. As I recall you could see the rider's shoulders bulging out the stretch fabric slightly. And it may also have bulged upwards somewhat during the upper limits of his knees when pedalling.

So ranking things would be at the lower end no fairing. Next up would be a front fairing. More effective is a rear with no front. Better yet front and rear. Going up from that close in as much of the front to rear gap as practical and possible. And finally there's the full clamshell airfoil shaped pod options.

At least one such full pod was done in a very lightweight manner using formers, stringers and Ceconite aircraft covering. I don't recall the materials used other than the Ceconite. But if ultralight boat building with that same idea is anything to go by a decent full fairing could be done within 10 to 15 lbs for the frame, covering and mounting bracketry.

One thing few think of though is how a full fairing would shield you from the cooling properties of the wind on a hot day. I don't know about you but during summer rides I rely on that 25 to 30 kph "air conditioning" to keep things tolerable. Put a fairing around me and I think it would be like cycling in a sauna! ! ! So if I were to go with a fairing I'm thinking I'd be looking at the tail trunk idea both as a way to carry home the packages from the errands as well as for the aerodynamics and leave the forward area open. Although if I were still all weather commuting to work and back I'd likely add a front fairing just for the weather protection on the cool days of winter. And possibly with some stretch fabric side covers if I could figure out how to easily and rapidly use them.
Oct 19, 2017, 03:46 PM
B for Bruce
BMatthews's Avatar
I didn't watch the video on why bicycles don't fall. But the reality is that any two wheel vehicle is ALWAYS trying to fall down. And in fact to stop it from falling over it requires a series of constant corrections. The geometry of the front wheel steering setup provides some of this positive correction and certainly the gyroscopic forces of the front wheel also helps. But in the end a two wheel vehicle does not fall over simply because the operator is constantly turning into the undesired falling as they ride down the road. When in a straight line for some moments it just says that the balance is such that the turn radius happens to be infinity for that moment. But soon enough it'll change. Any two wheel vehicle is always in the process of turning. It's how we maintain our balance and yet can also turn on demand.

And in fact to start a turn on a bike we actually induce a fall towards the direction desired with a slight kick of the front wheel AWAY from the desired turn. Then we catch and balance that fall by turning in. And finally we rise back up by turning further into the turn to move the bike back under the CG. All of this has been given the name "counter steering".

Not understanding how this works has led to many a motorcycle crash by newer riders. Riders that did fine with bicycles where the forces for all this were so slight that they didn't realize what they were doing to ride well. But when on a heavier motorcycle that required a firmer hand how it all came out to bite them in the backside.

Back when I was racing motorcycles for a while there was a chicane near the end of the main straight at my local track. I'd be up around 120 mph by that time and to perform the jog to the right to aim through the "gate" it would require around a 40 pound push on the RIGHT hand grip to roll the bike over enough that I would hit the path needed. And then another 40 lbs on the left side to lift up from the right bank and over to the left to turn down the straight chute towards turn 1.

Yet if I didn't need to turn that tight so rapidly I could be zooming along on the freeway at the same 130mph and do a long lazy lane change with just a few ounces of force. But it would still be a PUSH RIGHT TO GO RIGHT or PUSH LEFT TO GO LEFT. This push to go thing applying regardless of if I'm upright and want to turn or if I'm in the turn and want to get back upright.
Oct 19, 2017, 04:47 PM
Registered User
Bruce, the rear headrest fairings on the Boxter work GREAT: I experienced zero "backlash" and no mussed hair at high speed! (I'd always owned ragtops, but this one, driven by a rich competent German who knew his car [factory-painted Ferrari-red Porsche] AND the cops, on the backroads between Stuttgart & Tübigen at illegal speeds was quite different)

and you really should watch that video, shows some new facts and the experimental proof
Oct 19, 2017, 05:50 PM
B for Bruce
BMatthews's Avatar
It's not uncommon to see deflectors on the tops of some convertible wind screens so that when the air does come back down it lands far enough back that it doesn't hit the occupants. And while I don't doubt that the head fairings help that a lot I can't see the fairings removing all the cockpit buffeting on their own. I'll bet there's a spoiler/deflector up on the wind screen. Or the angle of the windshield was tested and set to provide that same degree of air control.

Not so on the old A-H bug eye Sprite I had for a while. One time the cap I was wearing blew FORWARD off my head and came down on passenger floor after spiralling around in my lap for a few circuits....
Oct 19, 2017, 07:07 PM
Registered User
Oct 20, 2017, 01:13 AM
I bail out, anywhere, anytime
Taurus Flyer's Avatar
My fairing-less recumbent, own design own construction.

Taurus Flyer
Oct 20, 2017, 06:17 AM
just look at it smokin'
z-matrix's Avatar
Quote:
Originally Posted by BMatthews
Two wheeled powered pods aside for the moment (cool as they are!) for your bicycle the key element for aerodynamics is the rear portion. A while back I was all interested in HPV's in general and bicycle lowriders in particular. Still have building a lowrider as a project on the list in fact.

Anyway, aerodynamic drag is a funny thing. It is more important to close the air BEHIND the object smoothly than it is to split it apart smoothly in the first place. So if you really have to limit the amount of added weight it is best to use the tail fairing.

The others such as the windscreens on the plane and sports car are not to reduce drag but to increase pilot/driver comfort by shielding them from the wind blast. And in fact they are LESS aerodynamic. Ever driven in a sports car or other convertible? The air rolls over the windscreen and around and smacks you in the back of the head.
I have read that in the front there is pressure drag and in the back there is friction drag on an airfoil, assuming if i were to put a streamlined body behind me i would cause large pressure drag, would it be better if the gap between me and the tail is minimized so no air is curving inside and causing turbulence?
It will probably help to add a front fairing but ut us not clear yet, still many options, i guess i need to test some.

Quote:
Originally Posted by BMatthews
The sharp cutoff "Kamm" style tail is better than a shorter and blunter angle to the fairing but it's not as low a drag as a full length fairing that ends in a sharp line.
I read that this is the case in front fairings too because if you were to curve inside the attached flow would follow the edge and cause larger drag

Quote:
Originally Posted by BMatthews
OK, so back to your linked fairing combination.

You asked about the front being smaller or larger than the rear. Keep in mind that there is a BIG gap between the two. The air is going to roll inwards off the rear edge of the front fairing heavily. So it matters little that it's a little bigger in frontal area than the rear fairing. And in line with the above I'd suggest that the front fairing is more about room for the rider's legs and weather protection than it is about drag. At least in this case where there's a big gap between the two.

And in fact on one web page an enterprising sort took the time to make up stretchy fabric "door panels" that closed off the gap. I don't recall if he then slithered down through the head opening or if the panels were able to open and close much like a proper door. But the report was that it did make for better speed at a given heart rate. Or a lower heart rate at some given speed. So the closer you get to a full airfoil shape the better it is. And if you can't do that then at least close the gap with SOMETHING. As I recall you could see the rider's shoulders bulging out the stretch fabric slightly. And it may also have bulged upwards somewhat during the upper limits of his knees when pedalling.

So ranking things would be at the lower end no fairing. Next up would be a front fairing. More effective is a rear with no front. Better yet front and rear. Going up from that close in as much of the front to rear gap as practical and possible. And finally there's the full clamshell airfoil shaped pod options.

At least one such full pod was done in a very lightweight manner using formers, stringers and Ceconite aircraft covering. I don't recall the materials used other than the Ceconite. But if ultralight boat building with that same idea is anything to go by a decent full fairing could be done within 10 to 15 lbs for the frame, covering and mounting bracketry.

One thing few think of though is how a full fairing would shield you from the cooling properties of the wind on a hot day. I don't know about you but during summer rides I rely on that 25 to 30 kph "air conditioning" to keep things tolerable. Put a fairing around me and I think it would be like cycling in a sauna! ! ! So if I were to go with a fairing I'm thinking I'd be looking at the tail trunk idea both as a way to carry home the packages from the errands as well as for the aerodynamics and leave the forward area open. Although if I were still all weather commuting to work and back I'd likely add a front fairing just for the weather protection on the cool days of winter. And possibly with some stretch fabric side covers if I could figure out how to easily and rapidly use them.
Thank you for ideas
Yeah it is a funny thing, it doesn't make a huge difference in drag if i get in front of a streamlined body? The streamlined body leading edge will cause backpressure to cancel out some of the airflow around me?
I am not worried about weighteven if it is 30 kg heavier, it will be faster. Slower uphill, but faster on flat, and downhill.
btw.: I do not need fairings to go 30-40 km/h, in my opinion, 25-30 km/h is where the fairing will start to help, under that it doesn't matter.
I would cut a ventillation hole that is adustable in the full fairing, i can even put a fan in it that is temperature regulated if needed., but now it will be winter so it won't be needed.


Z


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