Landracing Forum
Tech Information => Technical Discussion => Topic started by: A2WindTunnel on November 18, 2008, 09:10:19 AM
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If anyone is interested in Bicycle Aerodynamics, here is a recent article about A2 + Specialized and a collaboration we did with wind tunnel data and how it correlates with on-track data. Pretty interesting aero article weather your into bikes or not. But it can illustrate the time and power savings by optimizing the rider into a more aero position while allowing them to produce efficiant power, and while they measure power in watts, it is the same as how much HP they are saving by reducing the drag (1HP = 746 Watts). 70-90% of the power these riders a putting out is just to overcome the air resistance, and any reduction in drag adds up to big time savings over a x-distance race. By optimizing the position of this rider, his reduced drag and added speed would cut off 24min-58sec over an Iron Man distance race which are won by seconds (180.2km or 112miles).
This post is just intended to help people understand a little more about how wind tunnel testing could be beneficial and how reducing the aerodynamic drag is like adding HP. I know that bicycles have nothing to do with what you guys are doing (so please don’t blast me), but AERODYNAMICS have everything to do with what you guys are doing and the records you are trying to set. I am working on more stuff that would directly relate to LS racing and hope to have a video up of a wind tunnel test (A2 in house study) to show changes, and data with instruction to demonstrate what a typical wind tunnel test is and how we view at the data to see what is helping and what is hurting the vehicle.
http://www.bikeradar.com/news/article/how-aero-is-aero-19273 (http://www.bikeradar.com/news/article/how-aero-is-aero-19273)
(http://mos.futurenet.com/bikeradar/images/news/2008/11/12/IMG_6607-500-90.jpg)
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Do they have one of those helmets with snell rating/ :-D
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Fred-
Well, the Snell folks would probably take issue with the pointy thing in the back, don't you agree? Maybe if we submit the helmet to the rules and the safety committees -- and then also promise to wear a back protector and even maybe fashion the aero pointy part out of a breakaway material -- then perhaps. . .
I've ofter seen those bike helmets and wished there was a motorcycle racing version. Not yet, I'm afraid.
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Yeah, they are funny looking but if it was good for a mph or 2 I would wear it.
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And make the back protector into a tail...
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Believe it or not, all helmets are very specific to each bicycle rider and is the same on motorcycle riders as well. This is because of body size and shape and positioning on the bike. The bike and rider are a system working together and the air interacts with both. One helmet might work well for one rider but not another. Just look at all the different back shapes. One guy might have a flat horizontal back while another has a curved hump on his back.
For Motorcycles, a helmet and or a back protector in the right position and configuration for bike and rider would have great benefits in drag reduction if you could minimize the gap from the helmet and the back and also help transition the air down your back to try and keep the separation from the helmet to a minimum. You would also need the windsheild to transition on to the helmet well.
Here are 3 different back types you can see for yourself the difference and how it could apply to motorcycles and positions.
(http://a2wt.com/images/A2web/TeamType1%2001.JPG)
(http://a2wt.com/images/A2web/Nathan%20O'Neill%20Wind%20Tunnel%2005.JPG)
(http://a2wt.com/images/A2web/Broad%20Band%20Racer%20A2WT.JPG)
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How do butt cracks figure into this?
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Creates whistling in the wind.
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I still like Rollie Free's full layout and speedo.
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Stan, those are vertical smiles or rear cleavage :-D :evil: :cheers:
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the windscreen has to stop at the front of the helmet and can not wrap around the sides
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I wonder if Butt Crack Putty is allowed for additional streamlining and stops the whistling????? :evil:
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Seems to me, if the speedo's are tight enough, canyons would be welded together with no chance of wind velocity.
Lynda
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Fred-
Well, the Snell folks would probably take issue with the pointy thing in the back, don't you agree? Maybe if we submit the helmet to the rules and the safety committees -- and then also promise to wear a back protector and even maybe fashion the aero pointy part out of a breakaway material -- then perhaps. . .
I've ofter seen those bike helmets and wished there was a motorcycle racing version. Not yet, I'm afraid.
Maybe you could pack a parachute into it? :evil:
Kidding... :wink:
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I know that there is a rule on where the windshield ends, but you want the shape to match your helmet the best you can or have a smooth transition. I other words, you don't want there to be 4" of windshield sticking out from each side of your helmet and you don't want a helmet sticking 4" above your windshield. Plus, you do have to have your head in a position to see where you are going.
PS: The butt crack whistle is not as bad as you might think. :-D
Good smooth transition from windshield to helmet
(http://a2wt.com/images/A2web/Motorcycle%20wind%20tunnel%2001.JPG)
Head could be lower
(http://www.evworld.com/images/diesel_motorcycle.jpg)
This guy alone could benifit from a better position. Small HP means Aero is VERY important for his top speed.
(http://www.ecta-lsr.com/Gallery/albums/uploads/2008/May2008/normal_IMG_4269-1401.jpg)
windshield appears too short for that rider
(http://www.ecta-lsr.com/Gallery/albums/uploads/2008/May2008/normal_IMG_4377-1058.jpg)
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A2 --
Please address the spinning wheel situation -- a lot of us are curious.
Stan
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In case you didn't understand Stan Back's query -- the "spinning wheel" situation is our thoughts that there might be turbulence caused by the spinning wheel (mostly front). We've got some rules about the size and shape of the front fender -- so the question is mostly one of whether we should use a custom front fender to achieve best aero efficiency, and, if so -- what aspects should we try to design in to maximize the gain in efficiency.
Thanks -- and Stan, maybe he knows what you meant -- but I thought that as the head handlebar holder of this site I should make it clearer (I hope I did so!) to be sure that the casual reader/lurker/surfer would know whatcher talkin' 'bout.
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Actually Seldom, I was just reinforcing Rex's inquiry on another thread concerning Lakesters (and Roadsters). See what your biker mentality got you.
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Yeah, maybe -- but I've got the biker babe to go with it, so I'll take the abuse -- as long as I get to keep Nancy.
And now I guess I've got to go through the other topics and look for Rex's writings. But - Maybe A2 didn't see that post. Yeah, that'll be my excuse for posting as I did -- I wanted to save A2 all the work of clicking around.
Yeah.
(about two minutes later)
Dang -- I found Rex's comments, already addressed to the A2 folks. There goes my caveat.
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the wheels the wheels....ah yes....
there are some fairly complicated (relative term) interactions
going on at the back of the wheels where the air is trying to come
out of wheel...around wheel...and its interaction with components
in close proximity..ie fairing........of which we would need rolling
surface...and spinning wheels...........
Pork Pie.....where are ya........he has the hands on knowledge base
with this (in some cases) critical area of aero....
Joe :)
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Bike is at the bodyshop as we speak getting aero improvements as Dave and the tunnel suggested. Next to the chassis shop to implement the balance solutions. Then to the software additions. Things sure have changed in the 30+ years from when I first started doing this. Oh and doesn't every rider have beans for breakfast before record runs? Oops just gave away a speed secret. :lol:
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Actually Seldom, I was just reinforcing Rex's inquiry on another thread concerning Lakesters (and Roadsters). See what your biker mentality got you.
Yes I sure would like to know the typical Cd of an open wheel/tire like say a 26 inch good year. I've heard all different figures and the one that sticks in my head, maybe not good, is about .40.
Thanks,
Sum
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Thanks for posting the article A2. I'll be going over it a few times to see if I can get some inspiration for my over sized bicycle.
(http://www.wildbros.com/sitebuilder/images/naked246-600x361.jpg)
I am pedaling as fast as I can :-D
Bill
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Rollie Free:
(http://murdercycles.com/v-web/gallery/albums/miscellaneous/Rollie_Free01.jpeg)
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Ilove it. Use to do that on my Triumph, no speedo. :-D
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Rollie Free:
(http://murdercycles.com/v-web/gallery/albums/miscellaneous/Rollie_Free01.jpeg)
Dean,
That picture looks familiar.
(http://img.photobucket.com/albums/v629/1i1i1i/Newalbum2067.jpg)
J
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(http://img.photobucket.com/albums/v629/1i1i1i/Newalbum2068.jpg)
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Freud can make those guys look like wimps :-o
Come on Freud what you waiting for?
JL222 :evil:
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do ya really wanna see Freud in his bathing suit?
kent
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Kent,
Not after the last time... :cry:
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do ya really wanna see Freud in his bathing suit?
kent
Its not a bathing suit :-o
JL222
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do ya really wanna see Freud in his bathing suit?
kent
Its not a bathing suit :-o
JL222
Yea, the last time I saw it the suit had something to do with one's birthday,
Sum
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do ya really wanna see Freud in his bathing suit?
kent
Its not a bathing suit :-o
Yea, the last time I saw it the suit had something to do with one's birthday,
And it really needed ironing..... :roll: :cheers:
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Oooh, good comment, Stainless. I wonder if Freud will enjoy it, though...
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Since I am deaf and dumb, it all seems like compliments to me.
If I keep my mouth open as I ride, the inflation factor will remove the wrinkles.
FreuD
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Since I am deaf and dumb, it all seems like compliments to me.
If I keep my mouth open as I ride, the inflation factor will remove the wrinkles.
FreuD
Thats good stuff......and this kid thinks your attitude is GREAT stuff!
Thanks for 'reminding' how to think today and in 40 some years!!
Mark
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Mark, Freud is the most fun "legend" you will run into on the salt. If you get a chance to get into a little trouble with him it will be worth the night you might spend in jail :roll: Stop at the long course timing slip station, you will find him there often, with another troublemaker Bret Kepner...
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Stainless and other readers.......
It is my hope that Stainless is either misinformed or inclined to exaggerate.
Approaching this Holiday Season, I do not need to have any more of Glenn's
Bonneville antics brought to my attention.
I have concluded, he will never grow up. Just don't open up another can of worms
regarding his "behavior away from home."
Isn't it marvelous that the Salt season doesn't start for another 9 months !!
I enjoy my time when he is gone but I always wonder if he will come home in a body bag
or worse than that, a hopeless cripple that I have to care for for the remainder of his life.
Doris
wife of FREUD
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Doris
I want you to know that the antics Freuds "cohorts" refer to never slop over into how he treats me and my crew at Lands End. Contrary to what you hear from the guys, he's just being one-of-the-guys!! See if you can't get him to tell you about some of the antics the rest of them do!! He's only trying to keep even with all of them! He also is doing an excellent job in that regard!! :evil:
Please don't let the guys stop him from letting you allow him to come play with us!! And, I'd love to see you out on the salt too! If you've been waiting for an invitation, here it is! Gotta love the little critter!!
Lynda
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Sure glad she's talking about the other Glenn, I don't have time to get in trouble at speedweek.
The Glen in Utah. :cheers:
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Doris keeps my Living Will in her purse all the time I am away.
She's so ready.
FREUD
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Doris...Doris...Doris...
Glenn is one of my greatest friends and of course we exaggerate about his antics at Bonneville.... (How was that Freud? worth the $20 you promised)
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The only word she keyed on was exaggerate.
FREUD
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I have been really busy last few weeks at A2 so I have not had time to write about the front fender question. My #1 priority is A2, and I enjoy getting on landracing.com when I'm not busy to help give you guys some information about aero and inform about wind tunnel testing. I will try to get something up this week in the other thread that was asked about the fender to help address the question.
There are 2 new videos featuring AeroDYN on ESPN (?quality?) on youtube if anyone is interested.
http://www.youtube.com/watch?v=MTeNgtweC_o (http://www.youtube.com/watch?v=MTeNgtweC_o)
http://www.youtube.com/watch?v=xuHNgV5eKFw
Dave
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WARNING!! coming soon Freudian aerodynamics :-o
JL222 :-D
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I think Freud needed some duct tape. :-D
(http://i162.photobucket.com/albums/t246/bvillercr/IMG_2234.jpg)
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Great, I just lost 10,000 more brain cells....I couldn't afford that, ya know!! :roll:
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Wonder if he had a cell phone with him, :roll: :evil:
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Wuz gonna jealously compliment Freud on his generous endowment until I looked closer and saw it was the tailight hanging low under him!
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Wuz gonna jealously compliment Freud on his generous endowment until I looked closer and saw it was the tailight hanging low under him!
IB, Freud told me he had to put a hole in the seat to keep from being blown off the bike at speed.... something about the faster he went the better it worked... :roll:
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Any old hole when you're in heat..........
FreuD
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i would like to mount a lsr type fender on conventional mc front end. what are pros and cons between fenders that only provide coverage forward of the fork tubes and those that cover both forward and rearward(within rules)? thanks.
franey
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I haven't yet done it -- but I'm told over and over that enclosing the front wheel as much as possible is good. There's air being moved around by the rotating wheel, and since some of that air is being forced in the direction you're traveling (forwards) you've guaranteed yourself some excess drag and turbulence by having that dirty air there. Cover the wheel as much as the rules will allow.
Then there's the difficulty that was presented by the rules -- stating that no streamlining is allowed in front of the front axle; and that the front fender may cover the top half of the front wheel (I generalize -- the rules are a little more specific). The difficulty is/was that the front fender covering the wheel is de facto streamlining, but streamlining de jure describes the bodywork, nose piece, etc, and does not include the fender. There was a whole heck of a lot of discussion on that -- and maybe a rule change, too, to clear up the cornfusion.
Anyway -- cover that front wheel!
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am looking for a fender from different sources. might have a problem because of size of front end, and homemade isn't an option right now.
red wing front end sliders have inside width of 4.75" ; outside- 8.625" ; tire is a 110/70-17.
hope to come up w/ something.thanks again.
franey
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In case you haven't seen these already;
http://www.airtech-streamlining.com/landspeed/landspeed.htm (http://www.airtech-streamlining.com/landspeed/landspeed.htm)
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thanks,
called thurs.
franey
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Sam Wittingham @ approaching 80+ mph (all human powered)
(http://images17.fotki.com/v8/photos/4/43175/149033/samwork-1-vi.jpg)
This is aero!
(http://images17.fotki.com/v9/photos/4/43175/149033/varna-vi.jpg)
This bike was SO tiny! even compared to the other contenders. Something to think about.
David
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Just imagine that "bike" with a 100 cc engine in it. If it goes 80 with at best 1 1/2 hps think what it would do with 25!! That is AERO!!!
Rex
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Just imagine that "bike" with a 100 cc engine in it. .........Rex
Don't forget all the safety stuff that would also have to fit in there :cry: . John and Eric have done about as good as it is going to probably get with the required items.
c ya,
Sum
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Then there was the guy who came from Europe couple years ago that pedalled just under 75mph lying on his back facing backwards in his 'liner.
The Varna 80 mph plus bicycle record holder, as yrs truly posted a couple years ago on a similiar topic, looks incredibly like one of the NSU record bikes of the '50s. One that even raced around corners!
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that NSU bike looks about twice the width of a Varna . . .
A lot of the bike guys ride enduros - but the bikes must have a provision for cooling that the Varna does not. Even bikes w/ multiple riders presented more frontal area could not match that bike's speed.
Lots to learn there, I believe.\\cheers,
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that NSU bike looks about twice the width of a Varna . . .
A lot of the bike guys ride enduros - but the bikes must have a provision for cooling that the Varna does not. Even bikes w/ multiple riders presented more frontal area could not match that bike's speed.
Lots to learn there, I believe.\\cheers,
Yep, all the frontal area you don't have is 100% streamlined... :-D CD=0.0 :-o CDA 0.0 :roll:
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Here's a cutaway of the NSU MOTORCYCLE the Varna similarity was only comparing form, not CdA.
Another shot is a BICYCLE built for the one hour McCready prize that will have rider cooling , radio, nutrients supply. etc in a pretty compact package
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Just imagine that "bike" with a 100 cc engine in it. If it goes 80 with at best 1 1/2 hps think what it would do with 25!! That is AERO!!!
Rex
yes its aero, for 80mph..... i think it would be very lucky to go 160 with 25hp... ya see the aero is way screwed up for faster speeds... there would be mad separation on the tail do to the crazy convergence angle.... yes it was designed for 50,60 ,70 mph but over 1 buck things start getting very different
kent
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Kent, do you have the long tail version of the Can Am bike?
FREUD
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no not yet... i started to build a replica of the complete bike last spring and got side tracked.... i will probably get back to it this year
kent
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I am interested in what the consensus is in regards to wheels for M/C applications. Specifically for 'naked' classes and for the front, as a solid wheel is disallowed by rule. What wheel type represents the best attainable aero? Does a spoked wheel act as a solid wheel in regards to aero at speed (from headwind not side wind), do mag type wheels act as paddles against the wind, etc?
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Kent,
I think that I have to disagree with you regarding your thinking that the Varna would suffer from unattached air flow above 100 mph. Looking at the pictures the angle that the body converges at is certainly less that the accepted 11-14 degrees maximum also the bike has a very small surface area which minimizes skin friction which is probably the largest component of drag for the bike. There is no doubt that all of the air flow on the VARNA is attached and probably laminar,due to the low speed, so its pressure drag is only the area of the boundary layer from both sides as they converge at the tail and being pretty short and probably laminar flow the boundary layer is probably pretty thin at the rear of the bike.
Just a note: On the JCB liner over 50% of the total aero drag was skin friction, which is why on vehicles that have limited power you want to keep them as short as possible.
Rex
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The Can-_Am with the long tail...it was O.K. up to 80mph after that it was not safe.
It looked great in the wind tunnel but did not work on the salt.....................................................
Also the Can-Am first ran with wheel covers on both wheels (solid wheels looked good in the tunnel) but if I recall the front wheel covers were removed for the record runs....again it was not safe to ride on the salt............................................
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I'm thinking both Rex and 1212 are right- to a point -there is a relationship to finess ratio and speed -(Reynolds number?-help A2).
I was told many years ago that the Goodyear blimp is pretty close to a perfect 60 MPH shape- but looking at the WW2 drop tanks -300 mph tops -they are a bit stretched out!
Food for thought.
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bak189, what day of the week did Can Am set the record?
I'll see what my fotos show for that day. I should also have a foto from right to left for
the return record run. Then we will know if he used the discs during the record runs.
I have fotos both ways.
The bike ran in several classes. That is shown by the number plus the letters A and C.
As 89 C it has no wheel fairing. In my opinion, the wheel discs had no bearing on class.
Dolan would know.
FREUD
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In case you haven't seen these already;
http://www.airtech-streamlining.com/landspeed/landspeed.htm (http://www.airtech-streamlining.com/landspeed/landspeed.htm)
just want to say that kent and krew did a great job on my 2 pcs.
the 2kr7501 is a real beauty along w/lsr front fender. thanks also to dutch.
franey
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In regards to Dr. Freud question on which day the 125c.c. Can-Am set the record back in the 1970"s..........I may be wrong... but wed. comes to mind. About the "solid" front wheel..........as noted before it did not work back then.......and it did not work when I ran one on my Rotax 125c.c.
in 2001 (with special permission from Tom Evans)
But we have to remember that the 125.c.c. is a very light and short bike.....it may not be so bad on a bigger bike..........but then the rules say NO....
and I think this is a good thing...............................
Bak189
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I am interested in what the consensus is in regards to wheels for M/C applications. Specifically for 'naked' classes and for the front, as a solid wheel is disallowed by rule. What wheel type represents the best attainable aero? Does a spoked wheel act as a solid wheel in regards to aero at speed (from headwind not side wind), do mag type wheels act as paddles against the wind, etc?
Everything I have seen is that there is probably not a wheel out there that is worse than spoked wheels.
Ideally you would want them to have airfoil shaped and minimal, like hayabusa factory wheels.
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I'm thinking both Rex and 1212 are right- to a point -there is a relationship to finess ratio and speed -(Reynolds number?-help A2).
I was told many years ago that the Goodyear blimp is pretty close to a perfect 60 MPH shape- but looking at the WW2 drop tanks -300 mph tops -they are a bit stretched out!
Food for thought.
Yes, there is a relationship between separation potential and Rn- the other way.
At low Rn, the boundary layer is very thin and has little energy in it. This allows it to separate MORE easily than a thicker, more energetic boundary layer that we get at higher Rn.
The lowest drag fineness ratio is actually about 2.5:1. However, this is almost impossible for any practical vehicle because the very abrupt pressure recovery is too sensitive to other effects, especially intersections with wings, tails, and wheels. Wave drag and shock-induced-separation account for the large drag rise approaching Mach 1, but most wheel driven LSR will never get above 500+ mph where this is a factor. We discussed this before on another thread, and based on the practicalities of axle intersections, decided that a body fineness ratio of 4 to 5 would be about optimum for a lakester. A streamliner could be another 20% shorter. Using this short of a design, I would add a tail aft of the main body for better stability.
Low fineness ratios allow less wetted skin area. At subsonic speeds, this is the dominant drag besides separation. The fact that only half of JCB's drag came from skin friction indicates a need to fix the separation that accounted for the other 50%! Low fineness ratios also provide for more laminar flow as a percentage of wetted area; this is the next most dominant effect after separation and total wetted area. I worked this out from a pile of laminar flow research I have copies of and a streamliner with a fineness ratio of about 5 and the maximum cross section back about 60% of its length would have less than half of the drag of the current crop of 400 mph designs.
I hate to disappoint the streamliner crowd, but short and fat is better than long and skinny.
Beyond Mach 1 the rules go the other way. Wave drag is:
D/qwave = (9pi/2)(A/L)2(EWD)
Where,
D/qwave = flat plate equivalent wave drag
A = maximum cross section
L = total length
EWD = variation of the volume distribution vs. ideal
So beyond Mach 1, long and thin is better than short and fat. But only beyond Mach 1.
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Good read, Blue. In working on drag reduction for commercial aircraft, my favorite aspect is "fast paint." The project has the potential to reduce aircraft drag with or without the expense and engineering issues of passive/active riblets, or shark skin simulators. It's a matter of the nature of the chemistry of the coating, a challenge being low pressure application of small particulate paint with a quick drying time to a desired mil as opposed to large particulate mediums such as Imron with a slow drying time. The issue of reducing drag over solid surfaces in high velocity flows is about money more than speed. A 1% reduction in drag might save an airline company 25,000 gallons of fuel per year per aircraft. We expect a number much higher than 25% (in skin friction, I was remiss in not clarifying that in the unedited post) in certain applications.
And my most entertaining subsonic models for testing all wind up looking like round-nosed pub darts.
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k.h., Very interesting reading on the airplane "fast paints".
When we were racing in IMSA, I remember there was some pretty interesting work going on early to mid-90’s with some Lockheed (Marietta, GA) engineers trying to develop some race car stuff on the side. While in Atlanta we went and spoke to them and looked at a presentation of their project. If I recall correctly how it worked was they were essentially pumping air through a porous skin by letting air bleed from one pressure area to another. We had spoken previously about the fact that pressure pumps or reservoirs were completely banned for us. Later they came back with some "fuzzy" skin. In the end, they were starting to get to something that might have actually worked (on wings) and had really impressive lift/drag figures. But then Rahal bought the rights to what they were doing (that’s what the Lockheed guys told me) and I never heard or saw anything of it again.
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that NSU bike looks about twice the width of a Varna . . .
A lot of the bike guys ride enduros - but the bikes must have a provision for cooling that the Varna does not. Even bikes w/ multiple riders presented more frontal area could not match that bike's speed.
Lots to learn there, I believe.\\cheers,
to understand how big the NSU Baumm III was, it was less than an inch wider than the Varna.......when you see them in reality you will surprised how small this streamliner is and will not believe that a normal adult will match into this vehicle.....but there was still enough space to get a ashtray into the racer for the rider H.P. Mueller.
By the way - this was not a speed record streamliner....this was a economy attempt.....around 195 mpg............no this is no typing mistake....they run this attempt at old Hockenheim course
The streamliner is unfortunately not anymore complete.....some years ago someone stole the front suspension :roll:
The shape comes very close to perfect water drop shape.
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When you talk of the fast paint, it reminded me of the US attempts to win the sailing challenge maybe in the late 70's. Someone developed a vinyl decal wrap for the hull that simulated fish scales and it worked to reduce drag, and was banned immediately. I suspect the same ban would be true in motor-sports. Interesting concept, though. Doug
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Buick. Look up www.dimpletape.com Things I would look for in impounds..........when I worked there for DW
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The tape was from 3m. A few years ago they still listed it on their website, I forget the name of the tape. Found the article.
http://www.nasa.gov/centers/langley/news/factsheets/Riblets.html
3M under the type designation 3M 8691 Drag Reduction Tape (Riblet Tape)
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Buick. Look up www.dimpletape.com Things I would look for in impounds..........when I worked there for DW
JD or Dan, Curios why a car or bike covered with this stuff wold be illegal. Some of the body warps that are used have a interlocking pattern to them, and what about a paint job with a uniform "orange peel." I have seen good painters (and some very bad painters LOL) purposely do this to a car by playing with the air. Just like like to know where the line is drawn. Tony
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Back in the late 1990's early 2000's Mike Corbin
raced a new type Triumph Triple with success using a fairing with a surface like a golf-ball
at SCTA/BNI events......................................................
Mike has always understood "aero" and was a great help to us on our 1990 sidecar streamliner.
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Hey Blue,
Just curious about the shape of the streamliner. Trying to visualize it in my head. Is there a naca number that describes the shape of the streamline body that you are talking about. I have a list of all the naca shapes.
Thanks Willie Buchta
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Tony,
To answer your question, "Just like like to know where the line is drawn."
There is no rule against employing paint strategy on an LSR Car. Just interesting to see.
DW
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Blue,
Could you clarify this for me ? "...short and fat is better than long and skinny..." that would be with the same frontal area, right ?
thanks
roy
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Tony,
To answer your question, "Just like like to know where the line is drawn."
There is no rule against employing paint strategy on an LSR Car. Just interesting to see.
DW
OK, you guys caught me.... the extra MPH we needed came from the bad paint job I gave the bike last year... :roll: I just didn't know it would work that well :-o
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Did someone mention Golf balls :evil: oops! well hush my mouth.
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Only orange golf balls are allowed on the salt. Steel keeps losing the white ones. :? :cheers:
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Blue,
Could you clarify this for me ? "...short and fat is better than long and skinny..." that would be with the same frontal area, right ?
thanks
roy
Nope, that's one of the big misconceptions. Taking the same volume from a long and skinny streamliner and rearranging it in a short and fat profile creates more frontal area, less wetted area, more laminar flow and as little as one-forth the drag (presuming neither car had any separation).
Willie,
As airfoil sections for wheel driven LSR, we need to look at NACA 66-018 and 021 sections. If we have a body of revolution, we can go even fatter. A "body of revolution" is when we create a body from a profile like turning it on a lathe. A body of revolution can be much fatter than a wing profile for the same peak velocity and pressure recovery.
One of the more important things we can learn from these profiles is the reflex in the pressure recovery. This is where we close the back of the vehicle very abruptly and then reduce the closure angle. This reduces length, wetted area, and is much lower in drag than a straight taper. Not to criticize LSR too much, but the idea of this straight, "7 degree" closure has got go away. It died in aerodynamic science over 70 years ago. On my last drag reduction project, I closed the fuselage at a peak of 18 degrees to PREVENT separation. Along the wing trailing edge vortex sheet (the actual streamline), the angle peaked at almost 30 degrees. Tufting showed no separation where the more gentle profile had previously separated. I do not recommend these angles, each application requires analysis.
With no turbos, a lot of detail work by Mountain Air Aviation and the owner, and the described drag reduction, the aircraft is now 55 mph faster than stock: 343 vs. 287 mph on the Reno Sport course.
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the 021 would probably move the cp farther back but i like the NLF (1)-0414f much better... it has about 10% better laminar flow.... but i wouldn't use either in a 2D design...
Kent
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the 021 would probably move the cp farther back but i like the NLF (1)-0414f much better... it has about 10% better laminar flow.... but i wouldn't use either in a 2D design...
Kent
I'm not a fan of the 0414, it's thin (less room for structure) and has a sharp leading edge radius. This radius makes the profile very "peaky": the laminar bucket is very deep, but only for a narrow range of alpha. With the crosswinds that I saw at Bonneville, I would prefer a profile that didn't slam into a wall of drag at higher alpha.
Other than F-1 air racers, where the wing area is fixed, every trade study comes out against the 0414. The sharp leading edge makes the stall hard and prevents the use of large flaps. This forces more wing area, so the total drag is more, the stall higher, and the weight more than a thicker wing that is lighter and can use bigger flaps.
Remember that when looking at airfoil data in reference books, that data is for a 2D "infinite wing" and not applicable to bodies of revolution. These can be much fatter for the same recovery as a 2D airfoil.
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So, is there much abrasion to the frontal area of salt racers in any diverse or given environmental conditions? Just looking for an outlier observation that is separate from the wind tunnel data numbers. Looking to test some paint in 2010. Thnx.