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Side-wind resistant streamliner.

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Balor View Drop Down
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    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 :)

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote AlanGoodman Quote  Post ReplyReply Direct Link To This Post Posted: 06 October 2020 at 7:26am
Interesting choice of front tyre...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 06 October 2020 at 6:50am
I'm impressed that you can get it to 50kph unfaired.Clap 

All the best.
Roy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post 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

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).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 27 January 2020 at 9:36am
I've somehow missed this article:
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.

Edited by Balor - 27 January 2020 at 9:36am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post 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).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JDub Quote  Post ReplyReply Direct Link To This Post 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.




Edited by JDub - 05 August 2019 at 2:50pm
jdub... Got the T-shirt
http://s1127.photobucket.com/user/Protobikes/library
http://protobikes.org.uk/
https://www.flickr.com/photos/150386999@N02/

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