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Carbon disk wheel DIY, pancake wheels
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Yanto View Drop Down
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Points: 1521 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2017 at 8:14am
I think using "vacuum" is the wrong word, lets call it a "lower pressure area" I disagree with Roy to some extent, it is side wind pressure and low pressure on lee side.

I think what you need to do is determine the operating parameters that you wish your machine to operate in, I have used my velomobile in wind speeds up to about 30 mph, which is pretty extreme, and can be an entertaining ride, i think above that then aerodynamics is a lesser concern when compared to mass of vehicle v side area exposed to wind, i.e. it's not heavy enough to remain stable. 

There are talks of 15kg (approx) velomobiles, coupled with a rider of say 80Kg that is less than 100kg, I don't know off hand what the side aspect ratio of my Df is, maybe 2 to 2.5 sqM?

You said you are aspiring to a car like stability, well for that you may need a car, but as a comparison a small car weighs about 1000kg and has something like 5-6 sqM side area, you can see where I'm going with this.
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runcyclexcski View Drop Down
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Points: 63 		Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2017 at 2:11pm
Ian --

I was thinking further regarding sidewind stability, the shape, the area, and 4 wheels vs 3 wheels. Almost all velos have a taper towards the tail, with the tail oriented vertically. At the same time, the tail is the part that is supported by the single wheel (in a tadpole design). Thus, a single wind gust (to which the vertical tail is more sensitive than the 'head') lifting the single wheel off, or a bump, would turn the velo into a Segway. For a fraction of a second, at least. If one had 2 wheels there, the chances of both wheels lifting simultaneously are lower (if there is independent suspension). Is this a reasonable thought? If yes, 4 wheels might be the No 1 design point for a lightweight vehicle which one wants to be wind-resistant
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Points: 981 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2017 at 8:00pm
Yes vacuum is an exaggeration as the forces involved never allow this situation, but the greater the air flow speed involved the more extreme the difference in air pressure. The tower block was 23 stories and in Black Prince Road in Lambeth London, but just a regular storm no hurricane forces involved thank goodness. Newspapers aren't really interested unless someone dies. You could always feel the block swaying at that height even on a mildly windy day. Because of the height and the fact no lifts are installed while construction is going on inspection was poor when the clerk of works had to walk up 23 stories and the brickies probably thought to save a few pence on each wall. I found all the walls on the upper floors had no wall ties install so they all had to be rebuilt. No one in their right mind would go out onto their balconies in a storm I would have thought, but the estate did not have balconies on the tower blocks. I can't remember seeing balconies on the very high tower blocks at all. 
 
The Dutch say that the type of Velo with a channel down the middle like the DF or the bumps on the Milan SL are less susceptible to side winds than the Quest as the side wind airflow is broken up to some extent so fills in the low pressure side faster.
 
There is a lot of design information here. http://www.recumbents.com/home/
 
All the best.
 
Roy 


Edited by RoyMacdonald - 17 July 2017 at 8:15pm
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Yanto View Drop Down
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Points: 1521 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 17 July 2017 at 7:46am
I can't say I've noticed any difference in characteristics of behaviour between my 3 velomibiles (full size Quest, Quest XS and Df), but of course I haven't done any comparative tests and memory is totally unreliable Wacko

One thing that hasn't been mentioned is the positive side effects of wind, in that if there is wind hitting the velo from the 3/4 front to 3/4 rear there is a "sail effect", the most prominent I've felt it is racing at what was called Fowlmead in Kent, and accelerating (being pulled) up the the hill on the long straight to mid 30's mph.
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Yanto View Drop Down
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Originally posted by runcyclexcski runcyclexcski wrote:

Ian --

I was thinking further regarding sidewind stability, the shape, the area, and 4 wheels vs 3 wheels. Almost all velos have a taper towards the tail, with the tail oriented vertically. At the same time, the tail is the part that is supported by the single wheel (in a tadpole design). Thus, a single wind gust (to which the vertical tail is more sensitive than the 'head') lifting the single wheel off, or a bump, would turn the velo into a Segway. For a fraction of a second, at least. If one had 2 wheels there, the chances of both wheels lifting simultaneously are lower (if there is independent suspension). Is this a reasonable thought? If yes, 4 wheels might be the No 1 design point for a lightweight vehicle which one wants to be wind-resistant

I have only limited experience of a 4 wheel velomobile riding in cross winds, this at race speeds of 30 mph plus, again it was one of Miles' amazing creations http://www.kingcycle.co.uk/page8.htm and was bloody scary, worse than my Quest.  It did have rather sensitive 4 wheel steering which due to my lack of riding time with it made me over correct though.

I've never lifted the rear wheel in any circumstances to make it a Segway, although on rough ground  at speed or those raised speed awareness strips on the approaches to roundabouts can make the rear end "patter" which isn't nice as it feels like it's going to spin, the softer and more responsive rear spring rates/damping help keep the rear tyre in contact.

It's a shame the few owners (in the UK) who have Quattrovelo's are not readers of this forum for input as to real life riding experience. 


Edited by Yanto - 17 July 2017 at 8:00am
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RoyMacdonald View Drop Down
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Points: 981 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 17 July 2017 at 8:35pm
Originally posted by Yanto Yanto wrote:

Originally posted by runcyclexcski runcyclexcski wrote:

Ian --

I was thinking further regarding sidewind stability, the shape, the area, and 4 wheels vs 3 wheels. Almost all velos have a taper towards the tail, with the tail oriented vertically. At the same time, the tail is the part that is supported by the single wheel (in a tadpole design). Thus, a single wind gust (to which the vertical tail is more sensitive than the 'head') lifting the single wheel off, or a bump, would turn the velo into a Segway. For a fraction of a second, at least. If one had 2 wheels there, the chances of both wheels lifting simultaneously are lower (if there is independent suspension). Is this a reasonable thought? If yes, 4 wheels might be the No 1 design point for a lightweight vehicle which one wants to be wind-resistant

I have only limited experience of a 4 wheel velomobile riding in cross winds, this at race speeds of 30 mph plus, again it was one of Miles' amazing creations http://www.kingcycle.co.uk/page8.htm and was bloody scary, worse than my Quest.  It did have rather sensitive 4 wheel steering which due to my lack of riding time with it made me over correct though.

I've never lifted the rear wheel in any circumstances to make it a Segway, although on rough ground  at speed or those raised speed awareness strips on the approaches to roundabouts can make the rear end "patter" which isn't nice as it feels like it's going to spin, the softer and more responsive rear spring rates/damping help keep the rear tyre in contact.
 
It's a shame the few owners (in the UK) who have Quattrovelo's are not readers of this forum for input as to real life riding experience. 
 
I did find that I had a similar issue with the Wasp on certain surfaces but to my surprise one day for some reason I went for a training ride with my rear carbon race wheel on and the effect virtually vanished. So much nicer. I was tempted to use it all the time but it had a racing tub on it so a puncture miles from home would have been a disaster. The wheel a Rev X and was all carbon with 8 spokes, 4 each side in the shape of an X. the spokes were less than a millimetre thick. The damping properties of the carbon were remarkable. The UCI banned them in 2001 because they could cause vibration related injuries! and felt the spokes were too thin! although they are not as thin as bladed conventional spokes that they have not banned, but there are still lots of 15 year old ones around still being used.
 
All the best.
 
Roy
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runcyclexcski View Drop Down
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Points: 63 		Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2017 at 1:19pm
You may laugh, but I am wondering now how a diamond-arrangement of the 4 wheels would handle. The front wheel steers. The backwheel drives. Won't be very responsive to turning, I would guess, but may be less twitchy, too...
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AlanGoodman View Drop Down
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Points: 8036 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AlanGoodman Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2017 at 1:22pm
Originally posted by runcyclexcski runcyclexcski wrote:

I am wondering now how a diamond-arrangement of the 4 wheels would handle.

My guess would be it wouldn't... 

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Points: 1025 		Post Options Post Options   Thanks (0) Thanks(0)   Quote atlas_shrugged Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2017 at 1:29pm
I really like the idea of diamond wheel layout. Most people in the know say this would be a daft idea but I would love to know if anyone has tried a diamond layout for providing stability at low speeds as well as a smaller turning circle ability for manoeuvring on narrow streets.
 
I know there have been Swiss and US motorcycle designs where training wheels come down automatically. It would be good to add a turning capability to this as well.
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Points: 981 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2017 at 5:42pm
Look at a kid riding a bike with training wheels on and you will see the problems if you attempt to do any thing other than walking pace.
 
Roy
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