Amateur aerodynamics
- Thread starter Jim Gerwing
- Start date
hamishbarker
Well-Known Member
the sides are probably
the sides are probably compressing because you have a big detached flow eddy on both sides. Perhaps the nose is too bluff. With a more pointy shape you might be able to bring the separation point further aft. If the flow is not separated, the sides will suck outwards due to low pressure flow on the outside, at least up near the nose.
Of course the hands outside is not helping.
One good experiment would be to put wool tufts on the nose fairing and on the skirt to see which way the flow is going. (would need someone to be able to photograph you from the side at speed - from the inside of a velodrome, or just with a telephoto lens standing a long way to the side of your road and panning the lens with you to avoid motion blur.
example tuft test - see the detached flow near the nose making a few tufts blow backwards in this picture:
the sides are probably compressing because you have a big detached flow eddy on both sides. Perhaps the nose is too bluff. With a more pointy shape you might be able to bring the separation point further aft. If the flow is not separated, the sides will suck outwards due to low pressure flow on the outside, at least up near the nose.
Of course the hands outside is not helping.
One good experiment would be to put wool tufts on the nose fairing and on the skirt to see which way the flow is going. (would need someone to be able to photograph you from the side at speed - from the inside of a velodrome, or just with a telephoto lens standing a long way to the side of your road and panning the lens with you to avoid motion blur.
example tuft test - see the detached flow near the nose making a few tufts blow backwards in this picture:
Eric Winn
Zen MBB Master
@BK - It isn't Jim, it is
@BK - It isn't Jim, it is probably the Drupal forum software.
Jim's photos are right side up when I'm using my iPad to view the forums and upside down when I view the forums from my desktop browser.
Pulling the image up in a separate browser tab or window displays them correctly on my desktop browser and if you look at the HTML source the IMG tag has the same filename as what displays correctly in a separate window or tab.
Drupal has a " feature " called autorotate that tries to read EXIF metadata to determine if there is orientation information present. Drupal has had a few documented and supposedly fixed bugs with this feature in the past.
Some cameras will embed some additional EXIF data indicating the camera may have been held upside down but the image should be viewed right side up. Think rotating an iPhone or iPad around and the image rotates so it is always facing up.
Something is possibly awry with Drupal, or Jim's camera, or maybe both. In either case it is awkward for Jim to be able to do anything about it if his photos look OK everywhere else he views them - suggesting it is more of a Drupal issue.
One experiment would be to take the same picture at different camera orientations and upload both and see if one is right side up and one upside down. If this works then that may tell Jim how to best hold his camera to work around the wayward EXIF processing Drupal is doing.
See http://cruzbike.com/some-uploaded-pictures-display-upside-down for more details.
-Eric
@BK - It isn't Jim, it is probably the Drupal forum software.
Jim's photos are right side up when I'm using my iPad to view the forums and upside down when I view the forums from my desktop browser.
Pulling the image up in a separate browser tab or window displays them correctly on my desktop browser and if you look at the HTML source the IMG tag has the same filename as what displays correctly in a separate window or tab.
Drupal has a " feature " called autorotate that tries to read EXIF metadata to determine if there is orientation information present. Drupal has had a few documented and supposedly fixed bugs with this feature in the past.
Some cameras will embed some additional EXIF data indicating the camera may have been held upside down but the image should be viewed right side up. Think rotating an iPhone or iPad around and the image rotates so it is always facing up.
Something is possibly awry with Drupal, or Jim's camera, or maybe both. In either case it is awkward for Jim to be able to do anything about it if his photos look OK everywhere else he views them - suggesting it is more of a Drupal issue.
One experiment would be to take the same picture at different camera orientations and upload both and see if one is right side up and one upside down. If this works then that may tell Jim how to best hold his camera to work around the wayward EXIF processing Drupal is doing.
See http://cruzbike.com/some-uploaded-pictures-display-upside-down for more details.
-Eric
billyk
Guru
another upside-down photo solution
Thanks, Eric.
One solution is to put the photos on another site and just post the link. That has the advantage of being able to put up higher-resolution images so we can see more details. I've done this for photos of my Quest fairing mounts (links reposted below). It means we readers have to click a link (remember to "open link in new tab"), but if we have to view Jim's photos separately anyway, no extra work is created.
Another low-tech, easy solution is to take a screen shot of the photo as it appears on your screen. That will get rid of all the EXIF data, and also - if you're viewing it small on your screen - make the file much smaller as it has to be for this forum.
Pics of an early version of the fairing/mounts:
https://picasaweb.google.com/108555949105733959248/QuestFairingMount?authuser=0&authkey=Gv1sRgCPzHn5Dr09y3cQ&feat=directlink
Some later pics:
https://picasaweb.google.com/108555949105733959248/QuestModsNov2012?authuser=0&authkey=Gv1sRgCLG95PPd8p7DvAE&feat=directlink
Yesterday I remade the upper mounts (for the "wings" that cover my hands) in aluminum. Much stiffer and better all around, but I haven't had time to take photos.
By the way, the fairing is mostly raingear for me, not for speed - I live in rainy Seattle and commute year-round - but it adds 10-20% to speed above 15-20mph. It keeps my hands and feet dry, and also keeps the drivetrain clean and dry. There's a dead air space behind the fairing that is considerably warmer in winter. However, in summer I take it off because it gets too hot under the "greenhouse".
BK
Thanks, Eric.
One solution is to put the photos on another site and just post the link. That has the advantage of being able to put up higher-resolution images so we can see more details. I've done this for photos of my Quest fairing mounts (links reposted below). It means we readers have to click a link (remember to "open link in new tab"), but if we have to view Jim's photos separately anyway, no extra work is created.
Another low-tech, easy solution is to take a screen shot of the photo as it appears on your screen. That will get rid of all the EXIF data, and also - if you're viewing it small on your screen - make the file much smaller as it has to be for this forum.
Pics of an early version of the fairing/mounts:
https://picasaweb.google.com/108555949105733959248/QuestFairingMount?authuser=0&authkey=Gv1sRgCPzHn5Dr09y3cQ&feat=directlink
Some later pics:
https://picasaweb.google.com/108555949105733959248/QuestModsNov2012?authuser=0&authkey=Gv1sRgCLG95PPd8p7DvAE&feat=directlink
Yesterday I remade the upper mounts (for the "wings" that cover my hands) in aluminum. Much stiffer and better all around, but I haven't had time to take photos.
By the way, the fairing is mostly raingear for me, not for speed - I live in rainy Seattle and commute year-round - but it adds 10-20% to speed above 15-20mph. It keeps my hands and feet dry, and also keeps the drivetrain clean and dry. There's a dead air space behind the fairing that is considerably warmer in winter. However, in summer I take it off because it gets too hot under the "greenhouse".
BK
Eric Winn
Zen MBB Master
The photo Hamish uploaded
The aero skin on the bike in the photo Hamish uploaded also uses similar contours to the Milan velomobile and probably for the same reason - very reclined so forward view is limited so instead of a smooth cigar shape that would occlude more of your road visibility there are "aero bumps", if you will, to give clearance to moving bits while keeping the rest of the nose as low as possible.
Foot clearance in this case? Looks too far forward to be his knees...
-Eric
The aero skin on the bike in the photo Hamish uploaded also uses similar contours to the Milan velomobile and probably for the same reason - very reclined so forward view is limited so instead of a smooth cigar shape that would occlude more of your road visibility there are "aero bumps", if you will, to give clearance to moving bits while keeping the rest of the nose as low as possible.
Foot clearance in this case? Looks too far forward to be his knees...
-Eric
Eric Winn
Zen MBB Master
Jim, you might want to take a
Jim, you might want to take a look at the Mosquito Velomobile construction for your aero skin. You are already doing something similar but with clear heat-shrink wrap.
A complete skin of clear heat-shrink might be quite an eyeball grabber.
See here: http://www.mosquito-velomobiles.com/index.htm
Play the vimeo video at the bottom of that page and check out the interior view at time mark 0:55.
Note the weight of this Mosquito prototype is 20kg. I and most of that is the wood frame and trike components. I wonder what just the shell weighs?
Here is one of their photos, click it to go to the page this photo is displayed on.
-Eric
Jim, you might want to take a look at the Mosquito Velomobile construction for your aero skin. You are already doing something similar but with clear heat-shrink wrap.
A complete skin of clear heat-shrink might be quite an eyeball grabber.
See here: http://www.mosquito-velomobiles.com/index.htm
Play the vimeo video at the bottom of that page and check out the interior view at time mark 0:55.
Note the weight of this Mosquito prototype is 20kg. I and most of that is the wood frame and trike components. I wonder what just the shell weighs?
Here is one of their photos, click it to go to the page this photo is displayed on.
-Eric
Jim Gerwing
Well-Known Member
Candy for my eyes
Eric, that mosquito was very similar to what I was imagining (short of going fiberglass).
what is that matrix made of?
very cool, very encouraging.
apparently, transparent pods are solar furnaces so it may look cool but cook.
JG
Eric, that mosquito was very similar to what I was imagining (short of going fiberglass).
what is that matrix made of?
very cool, very encouraging.
apparently, transparent pods are solar furnaces so it may look cool but cook.
JG
Eric Winn
Zen MBB Master
I believe those are thin wood
I believe those are thin wood strips along with the aircraft grade fabric. Do you remember building balsa wood model airplanes like that where you doped the "skin" of the wings and fuselage and then when it dried it shrinks everything taut leaving a sealed somewhat water repellent coat? In the case of the models the covering was some sort of paper rather than fabric.
I built a couple of model airplanes like that. They had little gasoline engines and propellers and you flew them around on the end of a guy wire. Or some that were just gliders that you launched by hand to see how far they could go.
Usually you painted the airplane skin so you could do the same thing with your Vendetta aero skin. Leave it clear until you were satisfied with shape, design, and function and then paint it to protect you from too much sun exposure.
Anyway, your tail is already constructed in a similar fashion so I thought this might provide some visual stimulus for you to get cracking.
-Eric
I believe those are thin wood strips along with the aircraft grade fabric. Do you remember building balsa wood model airplanes like that where you doped the "skin" of the wings and fuselage and then when it dried it shrinks everything taut leaving a sealed somewhat water repellent coat? In the case of the models the covering was some sort of paper rather than fabric.
I built a couple of model airplanes like that. They had little gasoline engines and propellers and you flew them around on the end of a guy wire. Or some that were just gliders that you launched by hand to see how far they could go.
Usually you painted the airplane skin so you could do the same thing with your Vendetta aero skin. Leave it clear until you were satisfied with shape, design, and function and then paint it to protect you from too much sun exposure.
Anyway, your tail is already constructed in a similar fashion so I thought this might provide some visual stimulus for you to get cracking.
-Eric
hamishbarker
Well-Known Member
From reading on the Mosquito
From reading on the Mosquito site, it seems to me that the diagonal strips are actually carbon, but most other stuff on the machine is wood, with a little aluminium here and there, and the two big carbon struts in the rear suspension.
Looks like a really nice machine and a labour of love!
From reading on the Mosquito site, it seems to me that the diagonal strips are actually carbon, but most other stuff on the machine is wood, with a little aluminium here and there, and the two big carbon struts in the rear suspension.
Looks like a really nice machine and a labour of love!
Jim Gerwing
Well-Known Member
Posted from my new iPhone
These pics always appear right side up to me. Does this new gizmo solve the problem?
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These pics always appear right side up to me. Does this new gizmo solve the problem?
Charles.Plager
Recumbent Quant
Yes!
Yes!
Yes!
Ivan
Guru
Jim, I am really enjoying
Jim, I am really enjoying your pioneering efforts! You may want to try uploading your pics to another site then just past the URLs. I find it MUCH faster than uploading jpegs to the cruzbike site and you don't have to add text to your pics! I use Google Plus for example. Since the uploading feature of these photo sites are very friendly, and you can rotate/edit/crop on these sites as you wish that would circumvent the unusual problem you are having. I just past the URL into the Cruzbike forum and decrease the width to 790 so the image is smaller and fits in the message window width.
Jim, I am really enjoying your pioneering efforts! You may want to try uploading your pics to another site then just past the URLs. I find it MUCH faster than uploading jpegs to the cruzbike site and you don't have to add text to your pics!
I use Google Plus for example. Since the uploading feature of these photo sites are very friendly, and you can rotate/edit/crop on these sites as you wish that would circumvent the unusual problem you are having. I just past the URL into the Cruzbike forum and decrease the width to 790 so the image is smaller and fits in the message window width.
Eric Winn
Zen MBB Master
I use Flickr and since they
I use Flickr and since they generate a few different sizes when you upload the original I try and set the main display link to a more suitable size for the forum "frames" and then set the hyperlink to open in an new page/tab and link in the full size or a larger size image.
-Eric
I use Flickr and since they generate a few different sizes when you upload the original I try and set the main display link to a more suitable size for the forum "frames" and then set the hyperlink to open in an new page/tab and link in the full size or a larger size image.
-Eric
Jim Gerwing
Well-Known Member
Thanks, Ivan and Eric
First, for the encouragement on these innovations (I have a tweak that I was working on during the week that is ready for a try if the wind dies down tonight).
i was visiting a blog last night where the blogger has analyzed optimal nose shapes in the 10-20m/s range. His virtual studies indicate more pointiness for speed. I'm going to have to incorporate that in next year's front fairing.
second, (and this includes Eric) Thanks for your suggestions here. My new iPhone has a better camera and, I think, doesn't flip my pics so I'll go with it for the next while. And the iPhone has some pretty awesome possibilities for data collection and analysis.
JG
First, for the encouragement on these innovations (I have a tweak that I was working on during the week that is ready for a try if the wind dies down tonight).
i was visiting a blog last night where the blogger has analyzed optimal nose shapes in the 10-20m/s range. His virtual studies indicate more pointiness for speed. I'm going to have to incorporate that in next year's front fairing.
second, (and this includes Eric) Thanks for your suggestions here. My new iPhone has a better camera and, I think, doesn't flip my pics so I'll go with it for the next while. And the iPhone has some pretty awesome possibilities for data collection and analysis.
JG
Jim Gerwing
Well-Known Member
Aero-booties
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John Tolhurst
Zen MBB Master
Pedal fairings were part of
Pedal fairings were part of Tom Traylor's arsenal.
Pedal fairings were part of Tom Traylor's arsenal.
Jim Gerwing
Well-Known Member
New project
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hamishbarker
Well-Known Member
front half fairing or both
front half fairing or both front and back with a lycra joint? Composite or moulded zotefoam?
front half fairing or both front and back with a lycra joint? Composite or moulded zotefoam?
Jim Gerwing
Well-Known Member
Front and back
Plus Lycra joint, probably of
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fibreglass.
Plus Lycra joint, probably of
hamishbarker
Well-Known Member
Interesting that your
Interesting that your templates seem to show a central dip with the pedal/toe clearance humps either side. Is your choice of this for better forward vision?
Hope it works out well. I think the moving bottom bracket format makes for really simple and solid frame/fairing connections. I have been thinking of making something similar to your new project fairing for a while, but have too many higher priorities. Good luck!
Interesting that your templates seem to show a central dip with the pedal/toe clearance humps either side. Is your choice of this for better forward vision?
Hope it works out well. I think the moving bottom bracket format makes for really simple and solid frame/fairing connections. I have been thinking of making something similar to your new project fairing for a while, but have too many higher priorities. Good luck!
