streamliner designs

[LittleLiner]

Quote from: Howard on March 26, 2007, 10:13:53 PM
" . . . . . We were the first 60 inch car in the two club . . . . . ."

Question:  What is a 60 inch car??   Does it refer to the approximate displacement of 1 litre?  Or is there some other reference?

[PorkPie]

Quote from: Howard on March 26, 2007, 10:13:53 PM
" . . . . . We were the first 60 inch car in the two club . . . . . ."

Question:  What is a 60 inch car??   Does it refer to the approximate displacement of 1 litre?  Or is there some other reference?

61 ci = 1 litre class = I/BFS in SCTA

[Rex Schimmer]

The Reynolds number is a little more that velocity X length also included is the the kinematic viscosity which is the dynamic viscosity of the fluid, air in our case, divided by the density of the fluid, again air in our case. So when you multiply the length by the velocity and divide by the kinematic viscosity, and if you get your units right, you end up with a dimensionless number that is the Reynolds number for that length. Now you can use any length dimension on your car and what you get then is the Reynolds number for that point, and obviously as you go farther to the rear of the car the length dimension increases of the Reynolds number increase porportionally. So far what we have is just a number that doesn't really mean anything without some extra information that typically is found out in a wind tunnel or testing. What we want to know is at the point that the length is picked and at the velocity that we have used, is the boundry layer laminar or turbulent? If, thorough testing, we can find the velocity at our selected length, at which the boundry layer becomes turbulent then we can calculate the Reynolds number for that point on the car and know for any Reynolds number above that we will have turbulent flow. So what has this really gotten us, not much unless we start comparing different car shapes then we can use the calculated Reynolds number to compare the efficiency of the shapes. Also if we happen a pile of money and can do wind tunnel testing with a scale model, obviously a 25% model will reguire either a higher velocity or more dense fluid (air) to be able to have the same Reynolds number at the selected point as a full size car. So when wind tunnel testing the Reynolds number is very  important so that we can "scale" the information from the model in the wind tunnel to the real car.

As the speeds of landspeed racing vehicles is pretty fast I doubt that there is any place other that right at the very nose of the car that the boundry air flow is laminar, so we are typically working with turbulent flow and the real trick is to keep it attached.

Rex

[PorkPie]

I was NOT the first one with a narrow liner. Not trying to make that claim.  I don't spend much time on forums. Peace. Have your own heroes. I knew I could stir things up but I read all the chatter about motorcycle engined streamliners and not one mention of one of the most successful ones to date.
We raised a three year old record by 110 MPH so I thought it was worth pointing out.
I will go away now.
Howard

Howard,

may be my English was to bad.

What I liked to say was that you was (I say now may be) the first who used a so package - slimline streamliner with a very small displacement (60 ci) so successful - your 259 mph was a real good number nearly 20 years ago.

[sockjohn]

Rex is pretty much right on with this, note I used a ~ not an = (typically ~ means proportional to)

One way to look at is to start with a vehicle length and intended speed, and find an airfoil that is low drag at that Reynolds number.
If you're designing a vehicle from a blank sheet of paper you need to start working out some basic dimensions.

I've briefly brought up this point before, but any wheeled vehicle will never retain a true airfoil shape, since there will be holes for wheels, air intake, parachutes and exhausts.
Anything in the rear is mostly irrelevant as the flow is probably non-laminar long before it reaches the back.
I think you're better off using a non-laminar flow airfoil than a laminar airfoil due to this, but I don't have a wind tunnel to prove this.

This is where I disagree with him, I don't think it's a matter of fast, it's a result of holes, projections and a not entirely smooth surface causing the flow to be non-laminar not the speed.
After all, there are lots of composite aircraft that maintain laminar flow at high speed, at least up until the wings are covered in bugs or it starts to rain.

Some of the recent motorcycle streamliners did an excellent job of dealing with these issues, trap doors for parachutes and doors to cover landing gear.

I've seen water tunnels before, and there are lots of issues with them to keep the flow laminar to even be able to test a scale model, but since water is denser than air makes a good medium to keep the Reynolds number correct for a scale model.

[interested bystander]

The mysterious Reynolds number!

How I somewhat got a grasp of it is when I read that the bumblebee is swimming in MOLASSES when he flies- relative to us in the same environment.

"WETTED AREA" is another item one needs to keep as small as possible-if there is a flaw in Coslella's designs it may be too much of that. (Don't get me wrong, the guy's a wizard).

Rex's comment on laminar flow is right on (probly nil). In a conversation with Top Fuel aerodynamic wing guru Mike Mageira a couple weeks ago he made the same comment.

[Harold Bettes]

Good Comment string,

Howdy Howard - been a long time! Ya still live in AZ? I am often in contact with Tom Monroe and he is in NC.

Roger the comments that Rex shared on laminar Vs turbulent flow. Laminar airflow is something that we might call it at times, but it is as elusive and believeable as the Easter Bunny, the Tooth Fairy, or Santa Claus.

The attachment oh the attachment of airflow is the key to the kingdom.

Unfortunately too many folks interchange the words "laminar" and "attached" or substitute clean and attached for laminar. 

Regards to All,
HB2

[seatacartist]

  Geeze Rex, Ouch!! tryin to understand that....man, my head hasn't hurt this much since 9th grade Algebra.

Pat

[stayt`ie]

g`day Howard, could you or somebody please post a photo of your streamliner , as we down under can have a look at it,,

 thankyou in advance,  stay`tee....

[Loose Goose-Terry#1]

  Correct me if I?m wrong. But, doesn?t ground effects come into play in the design? Round bottom verses flat bottom? If you have a narrow round bottom (streamliner) you wouldn?t have the air compression factor (otherwise known as air drag). The liner that is wider and has a flat bottom  would seem to be at a disadvantage from the unwanted ground effects. Also, would it not matter that you could conceivably design a 2 ft tall x 3 ft wide w/frontal area of 6 ft2 and a 3 ft tall x 2 ft wide with the same frontal area. All other things being equal, the second design would be faster than the first design. Right?

[LittleLiner]

Terry

Honest answer - I really don't know.  Concerning ground effects - I haven't seen any design that can do away with those pesky wheels and tires.  No matter how wide/narrow or low/high you make it there seems to always be wheels and tires sticking out the bottom.  My guess is a flat bottom (think Neb Therom II and III) gives a  better chance of covering the tires.  Or . . maybe not . .

I have run across some interesting streamliner aero info about a little liner build in Sweden a few years back.  Google it at Dreamliner III.  Somewhere in their web site they have an engineering paper concerning stuff I can't even pronounce let alone understand . . .

[sockjohn]

Correct me if I?m wrong. But, doesn?t ground effects come into play in the design? Round bottom verses flat bottom? If you have a narrow round bottom (streamliner) you wouldn?t have the air compression factor (otherwise known as air drag). The liner that is wider and has a flat bottom  would seem to be at a disadvantage from the unwanted ground effects. Also, would it not matter that you could conceivably design a 2 ft tall x 3 ft wide w/frontal area of 6 ft2 and a 3 ft tall x 2 ft wide with the same frontal area. All other things being equal, the second design would be faster than the first design. Right?

Absolutely beautiful sidecar by the way!  I'm working on drawings for a streamliner and want to run a sidecar first before having to deal with landing gear, yours makes me not want to put a wheel on a stick!

In theory what you propose would be a better design to avoid the effects of the ground.  If you look at the evolution of HPV (human powered vehicles)  they started out as attempts to get as low to the ground as possible, and then started realizing the headaches with this approach and evolved to a higher body and streamlined wheel pants. When I get home I'll show links to make this clearer.   All other things equal is often difficult to do in reality, especially if it's for a practical vehicle and not a wind tunnel model.

What you  proposed would be a good university project, so if you have a mechanical engineering university with a wind tunnel, may be worth pitching it to them.  I would not be suprised if this has been covered in a masters thesis somewhere, so maybe if I get a bit of time will try to sort it out with solid data.

[Rex Schimmer]

Terry,
Most of the present day publications on aero that I have give information relating the ground clearance of a streamlined vehicle and it is a ratio of the height above the ground to the length of the vehicle. What you will find is that the Cd, based upon the frontal area of the car, actually increases as the ground clearance decreases once you get below a minimum height. If you look at these numbers you think that Costello'd Neb Therom cars are obviously in violation of this minumum ground clearance height, but damn they are fast!!

I have my own idea why Jacks cars can violate this "rule" and be so fast and one day I will get a chance to see if it is right. Got to get my street roadster done first!!!!

As far as your question regarding two cars with the same frontal area and Cd but one is wide and the other is high it would depend on ground clearance as to which one is the most affected by ground affects. Get the book  "The Leading Edge" by Goro Tamai, a little deep in some place and it is about solar powered cars but it is very applicable to land racing cars.

Rex

[PorkPie]

 If you look at these numbers you think that Costello'd Neb Therom cars are obviously in violation of this minumum ground clearance height, but damn they are fast!!

I have my own idea why Jacks cars can violate this "rule" and be so fast and one day I will get a chance to see if it is right. [/quote]

There is no trick behind and the reason is known - this car is simple not effect from the bouncing (airflow) wave.

[Sumner]

...........What you will find is that the Cd, based upon the frontal area of the car, actually increases as the ground clearance decreases once you get below a minimum height. If you look at these numbers you think that Costello'd Neb Therom cars are obviously in violation of this minumum ground clearance height, but damn they are fast!!..................

Small frontal area, no air under the car, low Cd, and good HP works good as long as the course is good.  Rough course equals a parked car.

c ya,

Sum