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Side-wind resistant streamliner.

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Topic: Side-wind resistant streamliner.
Posted By: Balor
Subject: Side-wind resistant streamliner.
Date Posted: 23 January 2019 at 3:58pm
I am contemplating a 'streetable streamliner' (as in - streetliner), because I participate in brevets and just like long-distance cycling. I am affected by blood pressure drop in elevated legs and high BBs just don't work for me, and fairings is one of possible means of solving relatively low speeds that I experience on a bent.
It is supposed to be something like Traylor's Critical Mass or Picuponcho no Torq - basically, a small step up from a combination of a nose cone and tail fairing, not a true 'flying coffin' type of a racing streamliner, likely even less extreme than Rotator Coyote.
 
Still, I intend to ride on all sorts of roads and in all sorts of conditions, hence susceptibility to side winds and 'truck suck' is extremely important (plus I'm relatively clumsy and just like making weird stuff, admittedly).
 
When it comes to 'side winds' only, when you lean into the wind on a streamliner so not to be blown over, your form gets not unlike an airfoil with significant angle of attack and start to generate lift. Given strong enough wind and light enough rider, especially if your bent is low (ekranoplan effect) you can generate enough lift for takeoff... not good in our case. I'm not a light rider, but I don't want even a theoretical possibility of this.
 
So, what can be done about it, beside minimisation of lateral area and Cd, obviously (which is an other project)?
 
1. Make CG as high as possible, while CP as low as possible.
Kills two birds with one stone - you don't have to lean into wind as much, and tilting moment of inertia is increased, making you a wider window for steering corrections.
 
Of course, you cannot make CG higher than CP... without some technical ingenuity.
For instance, one can take something heavy and prop it up as high as possible, maybe even on a mast - think 'bulb keel', but a 'bulb mast' instead... say, a lead-acid battery.
 
Given than moment of inertia goes up with a square of radius, same mass two times as high will affect your moment of inertia 4 times as large.
 
This 'bulb' can serve as a place to mount DLR lights for visibility as well, serves much better than a flag for a fraction of a drag penalty.
 
2. A refinement of the idea above.
 
Make this 'aerodynamics device' in form of a wing, or, better yet, a lenticular shape.
Something like this:
 
 
This way, when leaned into a wind, this 'wing' will generate downforce, as opposed to sides that will generate lift, somewhat cancelling out this effect.
 
Of course it will generate more lateral drag, with L/D ratio that gets worse the higher lean angle is... not sure how much of a 'refinement' would that be, maybe I should play around with CFD.
 
3. An other idea that makes sense, but not sure how much it works in practice:
 
Make the pressure-recovery 'tail' be somewhat flexible laterally, for it to reorient itself for side wind load, somewhat reducing lateral CdA. I think latter may even add to 'sail effect' in crosswinds.
Anyone tried that before?



Replies:
Posted By: russellbridge
Date Posted: 23 January 2019 at 9:00pm
I think you’re fighting against the natural form that a human and two wheels take up too much - it’s impossible to minimise the side area. Have you thought about building a three wheeler with electric assist - stable and very fast...
See Geoff Bird’s amazing Vulcan trike for what’s possible by a (very talented) home builder.
Russ


Posted By: Balor
Date Posted: 23 January 2019 at 10:43pm
Yea, that is indeed an aerospace-grade project! Way out of my reach, so far I'm experimenting with a nose cone on my MBB and some small stuff like composite headrests...

https://pp.userapi.com/c845521/v845521202/188ef3/QlUUx_cE7UM.jpg

Electric assist is out of the question though - brevets are purely HPV, even though any conceivable HPVs are allowed (a kickbike once successfully completed PBP... I bet he did not have any 'saddle sores' either :)).
Plus, there is no way it would be able to fit into my elevator, I don't have a garage and live on 7th floor, not to mention that full suspension that is required for any faired apparatus (especially out there) is an extremely complex affair on a trike.

I'll be experimenting with other means of getting around my physiological limitations like a combined arm/leg drive and adjustable geometry, to attack it from different angles and adopt the most successful one.


Posted By: atlas_shrugged
Date Posted: 24 January 2019 at 9:45am
Have you considered 'storm strips' - these are placed length-ways along the top of an HPV and are said to disrupt sideways laminar flow over the top of the HPV.
 
I have no personal experience of using these storm strips.
 
I wonder in the future if we will use hybrids with bikes turning into trikes/quads when the need arises. This will compromise weight and simplicity but may improve safety.
 


Posted By: Balor
Date Posted: 24 January 2019 at 11:27am
Makes total sense - basically, like a turbulator wire in a classic experiment with spheres (or golf ball dimples)... provided, of course, the air is not already turbulent over the top, depends on reyonold's number (and other factors) obviously.


Posted By: Balor
Date Posted: 24 January 2019 at 11:46am
Originally posted by atlas_shrugged atlas_shrugged wrote:

 
I wonder in the future if we will use hybrids with bikes turning into trikes/quads when the need arises. This will compromise weight and simplicity but may improve safety.
 

Not likely without heavily adjustable geometry.
Best-behaving two-wheelers are high.
*Safe* 3+ wheelers are very low.

Simply having a few wheels lowered will not work... and tilting trikes do not combine 'best of two worlds' - more like 'worst of two worlds' if you ask me, once you get to truly analyse how they work :(.


Posted By: Balor
Date Posted: 24 January 2019 at 6:51pm
By the way, if you think about it, having a set of 'training wheels' of sorts that ONLY get engaged during relatively significant lean might be a good compromise - otherwise they hover a few cms from the ground (which allows for suspension to work on main wheels as well).

They can be extremely small (say, 10cm polyurethane skating wheels) and castering  - hence it will not affect your efficiency much even when engaged. I think I saw something like that before...

It gives you passive stability, tip-over protection, yet for all intents and purposes your bent is two-wheeled with some (not much) aero penalty if you use wheel spats like on some aircraft with unretractable landing gears.

Making them if not 'retractable' (way too much complexity), but at least somewhat 'storeable' or quickly removeable may solve the 'size' problem as well. Hmm.


Posted By: Balor
Date Posted: 24 January 2019 at 7:52pm
Hmm... it would lead to rather confusing dynamics though - some curves could be negotiated leaning into them like on a bike (before inner wheel contact), but in others you'll have lean out of the turn and ride outer wheel instead like on a trike. Tricky...


Posted By: Balor
Date Posted: 25 January 2019 at 5:50pm
Ok, it seems everything is invented already :))
 
http://www.autocycles.org/" rel="nofollow - http://www.autocycles.org/
https://barnfinds.com/flying-low-pulse-autocycle/" rel="nofollow - https://barnfinds.com/flying-low-pulse-autocycle/


Posted By: Balor
Date Posted: 25 January 2019 at 6:51pm
http://www.autocycles.org/pulseoutrigger.html" rel="nofollow - http://www.autocycles.org/pulseoutrigger.html
Problems encountered with outriggers on this design suggest it might be suboptimal for a HPV unfortunately :(.
High tire wear sound like a lot of rolling resistance.


Posted By: RoyMacdonald
Date Posted: 06 April 2019 at 2:51pm
What's wrong with a Kingcycle with all the fairings and a bit of padding on the seat? 

Roy


Posted By: JDub
Date Posted: 08 April 2019 at 10:01am
In general, bikes with a more cylindrical shape behave better in side winds, and are more aero. Obvious really. I think the reverse bulb keel is unlikely to handle well. It will be more stable, but you may have to fight it. Any extra devices are more likely to add to problems, though a lift dumper under the bike might work.
A surprisingly important part of handling is the relation between CP and trail. If it is fairly forward, and you have considerable trail, the bike will castor with the wind and get blown around. I had to moderate the trail on Oscar. With less the steering was very light, but the bike was only gently pushed away from the wind, and naturally corrected itself. This makes sense with the work Matt Weaver did. Next version (if I ever build it) will have the front wheel a bit further forward and should be able to cope with a bit more trail. 


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jdub... Got the T-shirt
http://s1127.photobucket.com/user/Protobikes/library
http://protobikes.org.uk/
https://www.flickr.com/photos/150386999@N02/



Posted By: JDub
Date Posted: 08 April 2019 at 10:26am
I think Glen Thompson was proposing the conforming tail on one of the later Bluebell variant. Could work, but assumes wing shape rather than torpedo.

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jdub... Got the T-shirt
http://s1127.photobucket.com/user/Protobikes/library
http://protobikes.org.uk/
https://www.flickr.com/photos/150386999@N02/



Posted By: RoyMacdonald
Date Posted: 08 April 2019 at 10:30am
I rode 50,000 miles on the Wasp, in all weathers, and side wind was just was not an issue on a bike that low. Truck suck was though, in London on the South Circular where the lorries would pass at speed and very close while waiting to turn in to Dulwich Park and I used an exaggerated amount of lean while waiting to turn. I weigh nothing of course and traction with FWD was a bigger issue for me than side winds.

Roy


Posted By: Balor
Date Posted: 05 August 2019 at 1:17pm
Originally posted by JDub JDub wrote:

In general, bikes with a more cylindrical shape behave better in side winds, and are more aero. Obvious really. I think the reverse bulb keel is unlikely to handle well. It will be more stable, but you may have to fight it. Any extra devices are more likely to add to problems, though a lift dumper under the bike might work.
A surprisingly important part of handling is the relation between CP and trail. If it is fairly forward, and you have considerable trail, the bike will castor with the wind and get blown around. I had to moderate the trail on Oscar. With less the steering was very light, but the bike was only gently pushed away from the wind, and naturally corrected itself. This makes sense with the work Matt Weaver did. Next version (if I ever build it) will have the front wheel a bit further forward and should be able to cope with a bit more trail. 

Missed that reply...
Where I find about that 'work' Matt Weaver did or pictures of your HPV?
I simply don't follow how 'trail' can affect wind steer on 'streamlined' HPV. Was the wheel open or covered? How much trail was before and after? Was trail reduced by steepening the steering angle or increasing offset?
May it be that it was not due to forward CP, but forward CG and hence more due to camber torque (steer into lean force) that indeed grows proportionally with trail?


Posted By: JDub
Date Posted: 05 August 2019 at 2:49pm
Really? You should find some pics of Matt Weaver's machines on recumbents.com
A fairly forward CoP was his discovery. The bike corrects itself. Does not matter how you achieve the trail balance. Except for extreme shallow the head angle is irrelevant. I don't know what camber torque is. Nothing to do with CoM, (not G). My bike is on protobikes.org.uk. Circuit racer.




-------------
jdub... Got the T-shirt
http://s1127.photobucket.com/user/Protobikes/library
http://protobikes.org.uk/
https://www.flickr.com/photos/150386999@N02/



Posted By: Balor
Date Posted: 06 August 2019 at 11:44am
Originally posted by JDub JDub wrote:

Really? You should find some pics of Matt Weaver's machines on recumbents.com
A fairly forward CoP was his discovery. The bike corrects itself. Does not matter how you achieve the trail balance. Except for extreme shallow the head angle is irrelevant. I don't know what camber torque is. Nothing to do with CoM, (not G). My bike is on protobikes.org.uk. Circuit racer.


I've seen Matt Weaver's machines of course, it just relation of trail to wind steer I am not familliar of. I am familliar with CoP in front of CoM not being good and I've recall reading that some designers actually extended their fairing 'tail' to shift CoP back a bit.

I am also familliar that bikes with full disk wheels and negative offset actually behave better in windy conditions as compared to bikes with positive offset, because with negative offset you have a sort of 'positive aerodynamic trail' effect where wind resistance on a disk wheel actually adds to trail 'return-to-center' force.

I've tried full disk with a monocote film on this bike (similar to rear wheel):

It did just fine in windy conditions (though required leaning into the wind, of course), but disk wheels are good with narrow tires, and our roads (and my weight) do not agree with them, even with suspension.
But unless you have steering close to 90 deg and even above, negative offset imply lots of trail, hence your statement conflict with my experience.

This is Oscar you are talking about, I presume?

https://protobikes.org/my-bikes/

You front wheel is hardly covered so would interact with the wind, but would interact with wind off the fairing as well, that greatly complicates things... so, where can I find that 'trail vs CoP location on the fairing" bit explained in particular? I'd really like to understand it better.

As for camber torque - if you ever rode a 'conventional' fat bike with low pressure on solid cambered surfaces you'll surely know :).
https://en.wikipedia.org/wiki/Camber_thrust

The net camber thrust is usually in front of the center of the wheel and so generates a camber torquetwisting torque, or twisting momentThe orientation of this torque is such that it tends to steer a tire towards the direction that it is leaned. An alternate explanation for this torque is that the two sides of the contact patch are at different radii from the axle and so would travel forward at different rates unless constrained by friction with the pavement.

My (FS MBB pictured) bike has 60mm of trail and heavily loaded slick wheel, hence a ton of traction and I also experience it a bit on roads where asphalt was 'rutted' by combination of heat and heavy traffic.


Posted By: Balor
Date Posted: 06 August 2019 at 11:59am
P.S.
I really like your bikes, especially HPB - very creative!

Concentric front cranks solve a lot of problems with crank height, wheelbase and weight distribution.
One Russian inventor actually went for a 'sort of' centerless front wheel instead of hub steering for that (They are not MBB like Kervelo):

https://imgsrc.ru/totmih/47916804.html

FWD version:
https://imgsrc.ru/totmih/a1117410.html

In theory you can make a lowracer like your HPB out of it, but with much less limited steering lock - but you lose 'no head tube' benefit, of course.


Posted By: Balor
Date Posted: 15 December 2019 at 7:58am
Hmm, when it comes to truck suck in particular, it is possible to make entirely passive system - add lift-generating wings (may be relatively stubby) to the sides, with large lift to drag coefficient to prevent them from adding too much drag.

Truck suck is due to Venturi effect of air speed getting greater as it is forced into a relatively small opening between you and overtaking vehicle, accelerated and the side facing the truck getting a drop in relative pressure compared to freestream velocity due to Bernulli principle.
So we get 'sucked' towards the truck and hence develop a roll moment into the truck depending on your CP height (and steering moment depending on location of CP along the wheelbase).

Now, since the wing in Venturi effect will also develop more lift compared to wing in freestream, it should provide a counter-roll moment, and if you balance wing lift with lateral area, the arrangement might cancel this effect out completely (though this is highly unlikely).


Posted By: Balor
Date Posted: 27 January 2020 at 9:36am
I've somehow missed this article:
https://motochassis.com/Articles/Aerodynamics/AERO.htm" rel="nofollow - https://motochassis.com/Articles/Aerodynamics/AERO.htm

Now I finally understand WHY a lot of trail is bad for a fully-faired single-track vehicle - it has to do with side force!

DYNAMIC DIRECTIONAL STABILITY.

The above refers to the steady state conditions of a constant side wind. In practice, this is rare and gusty conditions are more usual. Apart from varying wind, gaps in hedgerows and the wakes and bow waves of lorries on motorways all contribute to our problems. The full dynamic effects of all this on a bike is extremely complex but we can look at some of the main features. As I have pointed out in previous articles, roll or leaning motions of a bike are intertwined with yaw or steering motions. This can lead to destabilising effects under gusty conditions. Consider a sudden blast of air from the left hand side, the bike will respond by a sudden roll movement away from the wind to the right, this in turn, through precessional effects, will cause the steering to turn to the right, and hence the bike will tend to steer away from the wind rather than into it as we would like. But this turning tendency to the right will, through centrifugal force, try and make the machine lean to the left which is what we need to maintain balance. ----- See what I mean by saying that this whole business is very complicated!

In 1986 I converted a Gold Wing from telescopic forks to one of my "hub centre" front ends, for its owner, Wayne Boys. After he had had it for a while we discussed the various effects that he noticed in normal riding, many observations were as I had expected but I was a bit surprised when he pointed out that it was far more stable in gusty side winds. At first I thought that this was probably just due to the greater lateral stiffness of the new suspension, which is generally more stable anyway. But a bit more thought as to the differences between the two setups, shed a bit of light on why they should behave so differently under these conditions. There seemed to be three main differences, in addition to the stiffness already mentioned ;----- 1. 16" wheel instead of 19", 2. Less trail, 3. A 17 rake angle which needed zero offset between the steering axis and the wheel centre-line to achieve the desired trail. It can be argued that all three of these changes work toward improving the performance in gusts.

Smaller wheel;----- The precessional forces will be reduced in line with the reduction in weight close to the wheel/tyre circumference. This will reduce the coupling between yaw and roll movements.
Less trail;----- The component of the wind side force, acting at the front of the machine is passed to the road surface through the tyre via the steering axis, but the steering axis is in front of the tyre contact patch by the amount of the trail, and hence the sideways force on the bike will tend to steer the wheel with the wind. Exactly the situation that we might wish to avoid.
Zero offset;----- With normal steering geometry with about 1-2" of offset, the bulk of the wheel side area is forward of the steering axis, this combined with the effect of today's large tyres and discs means that a considerable steering force can be generated by the action of a side wind on the wheel. But with the zero offset geometry used on the hub-centre arrangement, this wind force is balanced about the steering axis and no turning effect is produced.


Zero offset bit is complicated.

While the steering moment produced is 'right' one, out of the wind (self-correcting), it may be too much of a good thing for starters, and it gives the wheel 'negative aerodynamic trail' - turning it into a reversed weathervane, that amplifies steering disturbances and reduces control over the steering.


Posted By: Balor
Date Posted: 03 July 2020 at 6:56pm
Ok... I think I've solved the wind steer problem given positive trail for good.

https://imgur.com/a/ytuaU50" rel="nofollow - https://imgur.com/a/ytuaU50

If you flip the VPS steering (like that on Horn's bike) upside down, instead of getting virtual positive offset in turns (due to virtual steering axis inclination), you get virtual negative offset, a ton of return to center force yet close to zero 'trail' in conventional sense - as seen from the side, hence SIDE force has no leverage to steer you, and when you brake in a turn the wheel will try to self-right instead of going to full lock.

The problem is, you need a ball joint with rigid connection to the frame somewhere *inside* the wheel... or above it and you still get what amounts to a head tube and the effect of lateral steering axis tilt gets greatly aimplified.

I thinik it will work just wonderfully with a bogie forks with wheels spaced wide enough apart, and you can have suspension in a similar fashion like on Horn's bike too (but, again, flipped upside down).


Posted By: Balor
Date Posted: 05 October 2020 at 10:08pm
OK, here is my take on it so far:


Zero trail geometry and a steering damper for stability... maybe I should add a wee bit more trail after all, but I'll need to do actual experiments with a fairing... which is getting severely delayed due to Covid-related (and work-related) stuff :(

It's is quite fine at speed up to about 50 kmh, but could not make it go faster yet w/o a fairing, but I think I want more stabilty after all (not to mention it is quite flimsy due to 3d printed connectors).

Maybe I should go with the way of Matt Weaver and DIY myself an electronically controlled steering damper - should not actually be hard, just need to find a way to actuate the damping setting on existing damper with, say, a simple servo...

Other than that, side wheels with steering damping should take care of strong unwanted toppling moments.


Posted By: RoyMacdonald
Date Posted: 06 October 2020 at 6:50am
I'm impressed that you can get it to 50kph unfaired.Clap 

All the best.
Roy


Posted By: AlanGoodman
Date Posted: 06 October 2020 at 7:26am
Interesting choice of front tyre...

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Posted By: Balor
Date Posted: 06 October 2020 at 8:29am
Techically, nothing prevent me from hitting a steep hill, but here are not much of those around... so yea, that was on the flat, but accidentally with a different front wheel :)
https://imgur.com/CkD1Lg3" rel="nofollow">

I've also experimented with installing low-power e-assist, it's a great help for starting and uphill boost.
Ultimately, I want to install no less than two motors - a geared crank drive and dedicated regen brake, but I need to have it 'clutched' and this is not that easy.

Offroad setup is, well, because I'm using it for offroad for now. Great fun actually :)



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