Landracing Forum
Tech Information => Aerodynamics => Topic started by: sofadriver on January 01, 2015, 10:48:39 PM
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Wheel discs (similar to Moon hub caps) on a motorcycle rear wheel. Is it worth it? Any pros or cons?
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Wheel discs... no
tail Fairing as described in special construction... 10 inches behind tire, 4 inches off the ground... yes, major reduction in drag as compared to the tail in your avatar
:cheers:
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Wheel discs... no
Fair enough. I really didn't want to jump thru all the hoops to do 'em anyhow.
The avatar pic shows my A/G tail with the APS fairing. I was planning to run both classes. Didn't want to change it just for a pic in front of the sign.
Here's a (bad) pic of the APS tail.
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I'm a simple lad and rocking the boat isn't my thing but how will you
know if you don't try?.
R&D is a big part of racing so I'd say do a back to back and get your answer that way.
How many bikes do you know of that run wheel discs?.
Someone came up with the wheel disc idea and they are still around.
Try them and see what you get. :wink:
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In 2012 I ran the 500 APS PG record at 134 mph. For 2013 I added rear wheel discs, a modern 3 spoke front wheel, a few changes to the motor (length of intake and exhaust), and ran the same record to 143 mph. This was at AMA/BUB before the fully enclosed tail was permitted. I almost think the wheel discs were part of the 9 mph increase in speed, but you know, change 4 or 5 things and then try to decide which change made the real difference.
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Here's a quick tangent/hijack:
I was looking through the rules to find what they say about discs covering the wheels -- and found the page where we're told that fronts must be "cross ventilated" but rears are okay for discs. At the end of that rule (7.B.10) is a comment that the installation of the disc must be of "...a workmanship like manner". The word workmanship has baffled me for a while since workmanship (the word) is a noun. It means something like "the degree of skill with which the job is done". It isn't an adjective - so the use here (7.B.10, for instance) could easily be interpreted as "...a crappy manner" or a "...a super-duper manner" or anything -- and still be correct to the letter of the rule.
Next -- look one word above workmanship in the dictionary to find the adjective "workmanLIKE" (emphasis mine). This one means "showing efficient competence", and that's probably what the rule-writer had in mind.
Being pedantic sometimes is a good thing*. I wonder what it'll take to get the word changed throughout the rulebook? :-)
*Ask me how I know, but be ready for a story.
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Jon, submit a rule change request...
back to subject...
Maybe that is a bad pic, it looks a little like a closed scoop... is there an opening in the back for trapped air to get out?
does it end up 4 inches from the ground with the rider mounted?
Does your fairing bellypan go back close to the rear tire?
Hey, not being critical, I am not a bike aero guy, I know what worked for us before the long tail was allowed, we met our goal and decided not to build a long tail and stay in the fight. Building to the limits of the long tail put 10 to 25 MPH on bikes at Bonneville
It is a discussion... look at the A fairing pictures that have been posted.
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A few changes were made last year including rear wheel covers. A 7 mph gain was made and all of this cannot be attributed to the 5 hp power increase. There were a few aero changes and it is hard to attribute the increase to the wheel covers.
Last year was a wetter one and salt accumulation was an issue on some days. The covers kept salt from accumulating on the rear wheel rim and the wheel stayed in balance. The covers stay on the Triumph for this reason.
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back to subject...
Maybe that is a bad pic, it looks a little like a closed scoop... is there an opening in the back for trapped air to get out? (YEP - cellphone pic at a bad angle)
does it end up 4 inches from the ground with the rider mounted? (Nope - poor execution of a mediocre design :oops:
Does your fairing bellypan go back close to the rear tire? (YEP - but not nearly as close as the new design will) :evil:
The new version will use only the wheels, fork and transmission from the first bike. It's a whole new build. Much was learned.
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The new version will use only the wheels, fork and transmission from the first bike. It's a whole new build. Much was learned.
That is the important part... Experiment, change, try to go faster.... it is what we do :cheers:
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"How did you make the wheel covers?" I was asked this today. This looks like a good place to put the photos.
Several bikes go real fast without much horsepower and they use wheel covers. Rocket scientist logic told me that wheel covers couldn't hurt. They might help aero a little bit. They keep salt from accumulating on the rim and they look cool. These are enough reasons to use them every year.
The covers were made using what I had on hand. The wheel rims are covered with tape so they will not be scratched by the covers. Blue duct tape was used in the photos. It peeled up from the rim after sitting in place for a few weeks. Now I use two layers of contractor's grade very sticky masking tape. The good quality American made stuff. It stays where I stick it.
The pix shows the first cover. The inner circumference fits between the spokes and the spoke flange. The cover is made from two halves that are pop riveted together. Three aluminum spools attach one cover to the other using flat head stainless steel screws.
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The wheel cover shown in the previous post is shown on the bike. The edges are taped to the rims. There is a little hatch to provide access to the valve stem.
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The second wheel cover is shown. It is all one piece. It is taped to the rim. The paint marks near the screws tell me they have been tightened and I do not need to recheck them.
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Pretty cool Wobbly, but let me make sure I'm gettin the concept here.
You cut the discs then you cut a hole for the hubs. The three screws simply hold the two discs together but do not act as locators, is that right? (locating is done by a VERY close fit of the disc over the hub, correct?)
What keeps the discs from rotating around the hub? I can see that they couldn't rotate very far before being stopped by the spokes but is that the job of the tape? And being taped in place is OK with tech?
Did you have those discs water cut/ laser cut?
How do you apply wheel weights?
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That first cover is two pieces riveted together so the inner circumference will fit inside the gap between the spokes and the spoke flange. The Triumph is sorta weird in this way. The spokes on the back wheel on that side are all "inside" style spokes.
The three spools stick through the spokes and they are located so the cover is positioned exactly right. The spokes keep the spools fixed so the covers will not turn.
The wheel is balanced without the edges being taped to the rim. There is enough room for me to squirrel the weights inside and to stick them to the rim where needed. The edges are taped after the wheel is balanced.
Tech would be a problem if the tape held the covers on. They are securely locked in place without the tape. It is simply there to keep the salt out of the space inside the covers.
I do not know anything about water or laser cutting. The covers are cut using tin snips and pounded flat on an anvil with a rubber hammer. Do not use a metal hammer. It will spread the aluminum out when hit and the dang covers will never fit.
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OK, I get it now.
I'll give it a try on my spare wheel.
Like Tauruck said - how will I know if I don't try it.
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I've been working on some wheel discs for 15" car wheels.
They will be Carbon fiber examples, light weight, no corrosion
and will look good.
Maybe you should do something similar using glass/epoxy?.
I know there is very little similarity between bicycle racing
and LSR but it says something when they use disc wheels
for better aero.
Prof. Joe Katz wrote in his book Race Car Aerodynamics" that covered wheels work best
but were not always the answer for auto racing due to brake temps.
He says wheels discs reduce drag by 16%.
From some of the posts above disc wheels work but you have to make
"one" change at a time. With a totally new bike how will you really know???.
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I've been working on some wheel discs for 15" car wheels.
They will be Carbon fiber examples, light weight, no corrosion
and will look good.
Maybe you should do something similar using glass/epoxy?.
My buddy told me I should stop into the local bicycle shop. They do all that hi-end road racing bicycle stuff. Those guys are really into wheel discs. I'll check them out on Monday
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It would be easy to test the aero on these things. Put the bike on the center stand. Run it in fifth gear and hold a peacock feather near the wheel. Do it with and without the covers. The setup that produces the least feather flutter is the best.
Keep in mind that the bottom of the wheel travels at 0 mph compared to the ambient air. it is the friction drag that is manifested by turbulence around the spinning wheel that is a concern.
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it is the friction drag that is manifested by turbulence around the spinning wheel that is a concern.
Exactly.
Since my wheel is inside the tail there's not much aerodynamic drag on it (air coming past it) so reducing the drag generated by the (6) spokes could really conserve some power. Remember the old stationary exercise bikes that used air for resistance? I'll work on this.
Now I'm thinking about streamlining the front 6 spokes, too.
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I'd set it up just like the "9mph" bike. Set everything on kill and go get the record. I would look for EVERY aero advantage I could get, unless you're just going out for fun! :-D
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I'd set it up just like the "9mph" bike.
I think I agree (but I'm not real sure)
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That first cover is two pieces riveted together so the inner circumference will fit inside the gap between the spokes and the spoke flange. The Triumph is sorta weird in this way. The spokes on the back wheel on that side are all "inside" style spokes.
The three spools stick through the spokes and they are located so the cover is positioned exactly right. The spokes keep the spools fixed so the covers will not turn.
The wheel is balanced without the edges being taped to the rim. There is enough room for me to squirrel the weights inside and to stick them to the rim where needed. The edges are taped after the wheel is balanced.
Tech would be a problem if the tape held the covers on. They are securely locked in place without the tape. It is simply there to keep the salt out of the space inside the covers.
I do not know anything about water or laser cutting. The covers are cut using tin snips and pounded flat on an anvil with a rubber hammer. Do not use a metal hammer. It will spread the aluminum out when hit and the dang covers will never fit.
Lots of people plastidip wheels just for looks. I suppose that plastidip would hold up to the salt longer than the tape if it can hold up on daily drivers.
Just another way to skin the cat.
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wobbly: how thick (thin?) is the aluminum on those covers? I like 'em!
thanks,
Frank
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Hey Sofa
I had an aero guy from the local university come round and have a look.-- I could only get him once.
He said-- If the wheel was closely and totally enclosed it would be better with spokes.The disks will have more drag due to
the surface area
Discs will work better in our case with the wheels being as open as they are.
I'm going to put discs on the rear of the busa engined bike.
cheers Bones
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Hey Sofa
I had an aero guy from the local university come round and have a look.-- I could only get him once.
He said-- If the wheel was closely and totally enclosed it would be better with spokes.The disks will have more drag due to
the surface area
Discs will work better in our case with the wheels being as open as they are.
I'm going to put discs on the rear of the busa engined bike.
cheers Bones
I'll be interested to see your method.
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There are a few topics on this forum about enclosing the rear wheel. One asks me the gage of aluminum I used for the covers. I cannot find the topic. The answer will be here. It is 0.020 inch aluminum from Ace Hardware. This alloy is in the 2000 series, I think, and it is susceptible to salt corrosion in the form of pitting. Right after I get home from the race I untape everything and wash the wheels, covers, etc with lots and lots of cold water. No pits at this time. There are aluminum alloys with more corrosion resistance. One of my future project is to get 0.020 thick sheets in them for this work.
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There are a few topics on this forum about enclosing the rear wheel. One asks me the gage of aluminum I used for the covers. I cannot find the topic. The answer will be here. It is 0.020 inch aluminum from Ace Hardware. This alloy is in the 2000 series, I think, and it is susceptible to salt corrosion in the form of pitting. Right after I get home from the race I untape everything and wash the wheels, covers, etc with lots and lots of cold water. No pits at this time. There are aluminum alloys with more corrosion resistance. One of my future project is to get 0.020 thick sheets in them for this work.
How did you go about fabbing the discs themselves? This is something I am interested in too, and there is an Ace Hardware 1 mile from my house. :)
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Wobbly wrote:
It would be easy to test the aero on these things. Put the bike on the center stand. Run it in fifth gear and hold a peacock feather near the wheel. Do it with and without the covers. The setup that produces the least feather flutter is the best.
Keep in mind that the bottom of the wheel travels at 0 mph compared to the ambient air. it is the friction drag that is manifested by turbulence around the spinning wheel that is a concern.
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Reading Wobblys' comments made me wonder if applying a scraper near the bottom rear of the fairing (think automotive crank scraper method) would eliminate some turbulence and keep the salt build up less? Scraper angle and possibly a 3/8" of soft foam attached to the ground side of the scraper would keep salt build up off the scraper or to a minimum. Foam velcro'd to our motocross helmet and visor helps shed the mud buildup when riding/racing in wet conditions. Just a thought......
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Posts 11, 12, and 13 show the covers being made. The big circles were marked on the aluminum using a carpenter's trammel. Google "General No.520 Precision Trammels." These are a good tool for any fabricator. They clamp onto a 3/8 x 3/4 bar so use of a long bar will allow a big circle to be scratched out on the metal. The outer edge of the cover is just large enough to overlap the wheel rim so the tape will attach to both the cover and the rim.
In my case, the covers were made along with a spat in front of the rear wheel and some changes to the front of the fairing and the tail skirting was also cleaned up, aerodynamically. It is hard to say if the wheel covers did anything for aero. Too much other stuff was done, too.
My guess is if the wheel has aerodynamically inefficient spokes, like some one piece wheels, it might make a significant difference.
That scraper idea, or a brush alongside the wheel, might work, too.
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I have seen aluminum pizza pans used as wheel disc, Dzus fasteners and all.
If the builder hadn't told me I wouldn't have guessed.
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I'd go online and find someone close to you who does aluminum spinning, then make them one piece and the crown the the exact height and taper you need. Make 3 then you have 1 extra.