Landracing Forum
Tech Information => Aerodynamics => Topic started by: sofadriver on November 16, 2014, 10:16:55 AM
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I know that if a streamlined shape tapers too quickly it will cause drag. I think I read 7 degrees of taper from centerline is about the optimum. Is that correct?
I've searched and can't find anything to confirm. If you can expand on this subject, I'd appreciate it
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I know that if a streamlined shape tapers too quickly it will cause drag. I think I read 7 degrees of taper from centerline is about the optimum. Is that correct?
I've searched and can't find anything to confirm. If you can expand on this subject, I'd appreciate it
What I've read and what I used (a little under) for the rear of the lakester's body.
I've also had it from someone I really trust on the subject that sometimes it is important to intentionally trip the air so that it reattaches but I've stayed away from trying to do that since I think now we are into needing a wind tunnel or Woody to make sure what we are doing is going to have the desired results,
Sumner
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Have a look over on ecomodder.com.
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Can i ask why you removed the last fairing, i thought it looked like a very good starting point ?
have heard 7 deg also, but tend to use naca shapes as more info is available online esp for laminar flow or detach points
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The racer with the best non wind tunnel designed fairing is Tom Borcherdt "Koncretekid" ... a lot to be learned from his project.
http://www.landracing.com/forum/index.php/topic,9341.msg152684.html#msg152684
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Can i ask why you removed the last fairing, i thought it looked like a very good starting point ?
have heard 7 deg also, but tend to use naca shapes as more info is available online esp for laminar flow or detach points
It was indeed a good starting point and a lot was learned. Mostly I learned that converting a fully functional road racing bike to an LSR bike is not the way I need to go to accomplish my goals. I began to realize it halfway thru the first build. So after returning from BNI I decided to go all the way. I cut up the fairings to cement my commitment. A new chrome moly frame is being built and a great engine builder (and past BNI record holder) is on board and excited about the project. Height at top of riders helmet will be 32" and width of 20" giving a total frontal area similar to the Buddfab streamliner.
I've seen pics of Koncretekid's beautiful bike. I'm taking the whole concept a few steps further. However, our color choice will remain the same since I've still got a half gallon of Rustoleum Safety Yellow paint and some rollers left! :-D
Seems to me that the "optimum" 7 degrees might depend on airspeed with more taper allowable at lower speeds (I'm not shooting for 200mph here). Any thoughts?
Sum........who's Woody?
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The book "The Racing Motorcycle" Volume 1, by John Bradley has quite a bit about bike streamlining. He recommends no more than 10 degrees included angle to the rear of the point of maximum cross section. I am not sure if this is the angle between one side and centerline, or both sides together. The 7 degree maximum taper you are planning to use seems to be reasonable.
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Michael,
Take aerodynamic lessons from nature (actually hyrodynamic). The sailfish is the fastest fish in the world, so trying to duplicate that shape is one way to get good aero. I know you are constrained by width and length, but perhaps getting the fairing to emulate the shape as much as possible would not be a bad way to go ( I don't think you need the sail or bill).
Don
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Michael,
Take aerodynamic lessons from nature (actually hyrodynamic). The sailfish is the fastest fish in the world, so trying to duplicate that shape is one way to get good aero. I know you are constrained by width and length, but perhaps getting the fairing to emulate the shape as much as possible would not be a bad way to go ( I don't think you need the sail or bill).
Don
If I remember right....
(http://purplesagetradingpost.com/sumner/b-ville%20meets/2006%20BUB-9.jpg)
http://purplesagetradingpost.com/sumner/b-ville%20meets/2006%20BUB-4.html (http://purplesagetradingpost.com/sumner/b-ville%20meets/2006%20BUB-4.html)
... Dennis said that for the BUB liner he was inspired by the salmon but maybe it was another fish or no fish at all :-),
Sumner
P.S. Who is Woody........look no further than this board for WOODY@DDLLC .............
http://www.landracing.com/forum/index.php?action=profile;u=3763 (http://www.landracing.com/forum/index.php?action=profile;u=3763)
http://www.designdreams.biz/ (http://www.designdreams.biz/)
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I believe that Sam Wheelers streamliner used the Salmon.
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They all look fishy to me! :-D The BUB-7 is a NACA profile from the top and a salmon from the side. Denis likes to say, "The BUB-7 has a very low Coho-efficient of drag!" :cheers:
http://en.wikipedia.org/wiki/Coho_salmon
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Bert Munro had the fishy look back in the 50s. Who copied who?
http://www.motorcycleclassics.com/black-side-down/munro-special-at-pebble-beach.aspx#axzz3JMmTvHCk
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I believe that Sam Wheelers streamliner used the Salmon.
I was guessing sardine based on the driver compartment size :-D
:cheers:
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I believe that Sam Wheelers streamliner used the Salmon.
Yep. There's a metal salmon on the wall of my shop for inspiration! :-)
How's the healing coming along, Don?
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My Triumph is fully partially streamlined as per FIM rules with a tail that sticks 7 inches back from the tire. The wheelbase is three inches longer than standard. I am 5'-11" tall and sorta wide in the shoulders. It was not possible to get 7 degrees of taper behind the widest point and to have a reasonably narrow tail end.
The nose was made as blunt and rounded as practical so the wide part was as far forward as I could get it. This allowed for a longer tail taper. The sides gradually transition back at an increasing taper rate with the greatest taper, 10%, being right near the tail end. I figure, what the heck, it is too much taper but it is doubtful the air would be attached at the tail that far back, anyhow. Along the sides and forward part of the tail the taper rate is less than 7 percent.
The idea is, it is impossible to get correct taper everywhere on the tail of a short bike. The excess taper is put towards the back where it does the least harm.
Look at the pix on the DLRA website. Note Brett DeStoop's Suzuki water buffalo. That is a good starting point.
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Google Brett and look at images for several pictures of his bike. :cheers:
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The nose was made as blunt and rounded as practical so the wide part was as far forward as I could get it. This allowed for a longer tail taper. The sides gradually transition back at an increasing taper rate with the greatest taper, 10%, being right near the tail end. I figure, what the heck, it is too much taper but it is doubtful the air would be attached at the tail that far back, anyhow. Along the sides and forward part of the tail the taper rate is less than 7 percent.
Exactly.
I guess I'm not the only one to have this little dilemma.
I still wonder, though. Is 10% too much at, say, 200mph but acceptable at 130mph?
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Google Brett and look at images for several pictures of his bike. :cheers:
I just did and the shape of that tail is fantastic! My problem is that my feet are very close to the rear of the rear tire leaving a pretty short distance to the end of the body. Even with a 10 degree taper, that's going to leave a pretty large Kamm tail. It's not too late to extend the wheelbase at the rear. That would lengthen the distance from my feet to the end of the tail. I'll check it out tomorrow
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Tunnel testing that Can-Am did on their 125c.c. effort in the early 1970's.....showed 7 degrees on the back end worked best......( 136mph...125cc.....22hp)
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NACA 66-021 wing section tapers over 16* per side and is one of the lowest drag drag shapes .
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NACA 66-021 wing section tapers over 16* per side and is one of the lowest drag drag shapes .
Interesting. I wonder though if you can't make the whole car that shape as viewed from above would the 16* work as well as say 7*?
In most of our cases trying to make the top view of the car a true NACA profile just won't work considering all of the stuff we have to package in the car. There are lots of compromises that have to be made. My car has gotten quite long trying to stay at the 7* though so now has more wetted surface :cry:. Still it looks like I'll end up filling the whole works and need all of that length....compromises compromises :cry: :cry:.....,
Sumner
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You can fit all the internals in a NACA-66 from plan view. I have seen it somewhere..... ;)
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You can fit all the internals in a NACA-66 from plan view. I have seen it somewhere..... ;)
I'm not saying impossible but still going to depend on what you have and what you will except for a total width. If you increase the width (frontal area) to get what you want in the car (wheels/tires if a streamliner) then the overall length might be shorter but with more frontal area. Still if the Cd is better it might make up for it. Lots of options one just needs to consider as many as possible.
In the smaller engine classes, say bike motors, this is easier. If you are in the larger engine sizes and running blown gas and have turbo/turbos, intercoolers, intercooler ice-water tanks, plumbing, main water tank, maybe a rad-in-a-box and so forth then I think you are ahead with a longer narrower car with the 7* taper at the back and a teardrop shape at the front vs. a wider car just to maintain the NACA profile, but that is just my opinion :-). One thing I love about the lakester/streamliner (and some degree comp coupe) classes is we have a lot of leeway to mess around and at worst go home with egg on our face :-).
I had the lakester set up with a teardrop shaped nose and an expanding width to just behind the driver and then it went to a 7* taper from there back. Now that I'm switching to a car engine I have to add 3 feet and will have a 3 foot length now just behind the driver (firewall) that will be a constant width/height. Not what I originally wanted but will now have :cry:,
Sumner
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The packaging of the #496 Carbiliner is the example I was referring to. That is a twin turbo, 540 cid, ice water intercooled full size car. It is a series of NACA-66 foils where the maximum width of the fuselage is roughly 30 inches while the length is 28 feet.
Testing shows that the airflow is highly laminar through the first 33% of the chord and very still through the last 66%. Oddly enough, there is very little penalty shown if the fuselage was shorter and wider.
I know that goes against what most people say about aero, but the numbers are there. The "fineness ratio" we have could be tweaked to shorten the length and widen the fuselage and there would be negligible change in the disruption of the air beyond the 30% chord mark. Meaning no drag penalty for that adjustment.
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From the things I've see at 300 mph skin friction is 70% of total aero drag . That says within reason adding width to reduce surface area pays off .
The 16* thing may be true for the motorcycle body we were talking about but not a roundish 4 wheeler body . Somebody said to equate 2 dimensional (wing) information to 3 dimensional body shape add 50% to the length . That would change a 66-021 to about 11* per side .
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Just want to see if the degree sign shows up here -- Option Zero on my keyboard -- ººººº.
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°°°
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The packaging of the #496 Carbiliner is the example I was referring to...
I figured it was :-), but you don't have the back wheels packaged in that shape and if someone wants to do that it is going to be hard. You guys might be on the right track :cheers: only time will tell,
Sumner
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It would be difficult to pull them in unless you adjusted the fineness ratio. If you went shorter and wider you would have a chance. I think the issue is the rears would need moved farther forward which would wreak havoc on cg.
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The best chance of doing this (NACA profile) with a larger car is John's front wheel drive where the back whee/tires could really be sucked in. John do I remember seeing a rendering of you car before?
Also the front drive Salttarus lakester approach is headed in the right direction so I think it could be done but unfortunately us lakester guys still have the wheels/tires hanging out there in the wind. But hard with a rear-wheel drive car or 4 wheel drive car.
If I was starting from scratch and at my age won't be, I'd go frontwheel drive even though there are some things that have be be carefully considered doing that and it is going to be more expensive,
Sumner
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A look at the photo galleries on Scooter Grubb's Smugmug website shows what folks are doing with their feet. Most have them forward in the wider part of the body and they scrunch up during their tuck. It is difficult. Remember to go pee just before you leave the line.
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You might also be able to pull it of by running a pair of wheels in tandem and a pair offset slightly. Balance would be tricky and I would worry about cross-winds. You basically would be running a 4 wheeled motorcycle.
If you went side-by-side, you would have a car with a wheel track that is only 10 inches wide if you ran the wheels 4 cornered but close. Then you have the conversation in your head that a chain drive slipped between the drive wheels takes up the least room width wise and things really get crazy from there!
I think in could be done but it won't be without lots of critical thinking and testing to make sure it is stable. Width is going to be limited by either the diff diameter + offset + wheel width or coming up with a staggered drive wheel setup that works. Electric motor might be the best way to pull that off. Might as well make it 4x4 if you are going that route.
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Lots of good thoughts from you guys.
I finally realized that the real problem here is not body shape or length. It's simply that my feet are too far apart with the current design. So we came up with a new footpeg location that moves my feet inward far enough to solve the body taper problem.
Only nine more months to Speedweek!
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That's what I like about brainstorming. You may not get the answer directly but it makes you think and often in another direction. Brainstorming works. :-o :-o :-D
Pete
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John Parham (J&P Cycles) said. " If you give a problem to 10 Bonneville racers, you will get different solutions and they will all work."
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That's what I like about brainstorming. You may not get the answer directly but it makes you think and often in another direction. Brainstorming works. :-o :-o :-D
Pete
Exactly!
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....been agonizing over this, ever since I cut the bike in half a couple weeks ago and made it longer and lower. I'm going to try an experiment and we'll see what happens.
I think we might have two aero forms to deal with. The front half with the rider, and how to get a decent aero release off of that mess, and a rear section that must take what airflow it gets and do something with it. That rear section will be its own streamlined form as much as possible. I think I will just give it a similar form as a nose shape, followed by clean tapers to a proper Kamm location tail.
Not much to lose with this experiment....clear out of horsepower and absolutely "long term unemployed!" :lol:
JimL