Streamliner body design

[blackslax]

Hello everyone,

I have been thinking fora few years about building a MC streamliner.  I have a good fundamental understanding of aspect ratio, CP/CM relationships, etc.  (I tend to way overdo my homework up front and then eventually talk myself out of things.) The first question that I have is about air intake. 

The high pressure area on the nose would appear to be the ideal location for the intake, but what problems would that create? I read somewhere online that the open front was the "Achilles heel" of the E-Z Hook.
Will it move the CP? and if so I hope it would be backwards as the cp of the basic airfoil design with no tails is 33%.  (Fluid study not done yet)

Thank you for any help you can give.

[bbarn]

When you consider where to build your air inlet, keep in mind that the farther it has to travel, the less efficient the design is. If you use the nose, you will more than likely be tunneling the air close to 10 feet to get to the engine. That distance will cause turbulence and therefore flow loss within the ducting reducing efficiency.

Try to get your air in as close to the engine as possible to increase efficiency. Keep in mind that at the higher velocities, you can ram quite a bit of air into a scoop. In some engine applications, you will need to slow the air down before it hits the engine.

What type of engine are you thinking of building? (NA, Boosted, Turbo, Blown, Fuel, gas...)

[blackslax]

Great point on the ram.  I hope to be able to design in an air box to give the carbs more stable and hopefully pressurized air.

It will be NA gas and or fuel.

Body design is a very efficient NACA airfoil and I am trying to avoid protrusions from the body.  BUB and I talked about it and he likes NACA ducts, but placing them on the flatter parts of the body causes them to be in lower pressure areas than the nose.  Placing them near the rear where the air is collaping back together does provide higher , but more inconsistent pressure.  The front is so obvious, so controllable, and so easy to predict.

As I asked, what problems did this create for the E-Z?

[blackslax]

Next Question.

How does SCTA feel about parascopes or cameras? 

I am designing a very flat seating position. A anopy protrusion does help move the CP rearward, but realistically, they introduce flow dynamics greater than their benefit.  i would like to use side windows with a front camera (redundent if needed) or a parascope.  Any thoughts.  (I know full well there will be several.)

[Rex Schimmer]

Blackslax,
bbarn is correct regarding air openings with long runs to the engine, if you have the opening at the front, like the EZ-Hook you will need to expand the air channel as it goes to the engine, this reduces the air velocity and therefore the potential for the boundry layer along the intake track from becoming to thick and turbulant both of which effectively reduce the air to the engine.

bbarns comment " in some engine applications, you will need to slow the air down before it hits the engine." is completely wrong. If you are looking to increase the inlet pressure to the engine using the ram effect of your velocity you MUST slow the air velocity down. A guy named Bernulli came up with a formula, V1 x P1= V2 xP2 which means that the pressure of the incoming air increases as its velocity is reduced and this is the pressure that your engine inlet sees. So a well designed inlet will have an air inlet that is sized for the engine air requirements at the target speed and then the inlet tract will expand from that inlet to the hopefully very large plenum at the engine inlets which will provide the engine with low velocity but high pressure air.

Rex

[blackslax]

Blackslax,
 A guy named Bernulli came up with a formula, V1 x P1= V2 xP2 which means that the pressure of the incoming air increases as its velocity is reduced and this is the pressure that your engine inlet sees. So a well designed inlet will have an air inlet that is sized for the engine air requirements at the target speed and then the inlet tract will expand from that inlet to the hopefully very large plenum at the engine inlets which will provide the engine with low velocity but high pressure air.

Rex

I heard of that guy, think we met at a picnic or peace rally or someting.  I plan to have an airbox/plenum for that reason.  Unfortunately I have had no time to design because I can't get the shower curtain unstuck from my leg.  Wish I knew why

thanks guys. I knew that I would need to increase sizing, but the "backpressure" from that long a flow may defeat the high pressure from the nose.

[dw230]

The use a periscope is addressed on page 42 under section 4.V. This sentence applies to open cars where the driver would sit well below and inside the body. In a streamliner a periscope is still allowed.

With that said I would be careful incorporating a periscope in your design. Builders that have used them in the past have disgarded the periscope. Vibrations and a loss of position on course being a couple of reasons.

The use of a forward pointing camera has been discusssed on this board at some length. The reaction time of the camera(delay) giving cause for concern. Maybe someone can find the thread.

Sometimes the old tried and true methods are best leaving time and resources available for other challenges. My father said it best, "only walk the direction your nose is pointing".

DW

[bbarn]

bbarns comment " in some engine applications, you will need to slow the air down before it hits the engine." is completely wrong.

Rex, Not to pick fly specks out of the pepper, but isn't slowing the air down the same as reducing its velocity? 

...and yes, I meant slowing it down by increasing the volume by an exponent of the size of the inlet area. (as opposed to putting up traffic cones and PA state re-bumping workers in the ducts!  )

Blackslax,

If you are using a a NACA airfoil for your body design, you may be able to use the ducts to feed your inlets (Depends on your design). Place them just prior to the recovery point of the foil, you will have higher pressure air available there than post recovery.

Here is a chart that can help you in your sizing of the inlets. This chart shows diameter of inlet vs. velocity of the oncoming airstream. This particular chart is based on two inlets (so a 1" diameter inlet on the left actually represents 2 x 1" inlet in the data field). The data in the field represents CFM of air fed through the inlets.
http://s889.photobucket.com/albums/ac92/bbarnhart_photos/Misc/?action=view&current=PSI_FromVelocity.jpg


The second chart displays the PSI of air at a given velocity. Neither of these charts are corrected for Bonneville elevation or temperature. They are just reference at sea level with standard temperature and pressure.
http://s889.photobucket.com/albums/ac92/bbarnhart_photos/Misc/?action=view&current=PSI_FromVelocity.jpg

Do you have any drawings you can post of your design yet? We would all love to see them!!!

[blackslax]

 bet you would

I will post some after my CAD computer is fixed and returned

[High Gear]

Respectfully DW,

The Arrow motorcycle streamliner periscope works just fine and does not vibrate.

www.arrowracing.org

Gary

[dw230]

I amend my comment to: some builders have disgarded the periscope concept.

DW

[John Burk]

There's a difference in scoops and nose stagnation point inlets . With scoops the inlet area needs  to be right for the flow so they only work in high gear and restrict the flow in lower gears . If they're not in undisturbed air scoops don't get full impact pressure . Nose stagnation point inlets get good air but 100% impact pressure is only at one point and a 3" inlet gets a lot less . If the nose shape puts the stagnation point along a line the inlet can be long and narrow and get closer to 100% impact pressure . That's how I did mine .
John Burk

[donpearsall]

Good topic Blackslax. Question for all: If the air inlet is right at the nose, doesn't that reduce drag? My thinking is that there is less mass of air to deflect as the air column that would have been deflected around the nose is now being pushed/pulled into the engine. And if the engine is drawing in air faster than the relative airspeed of the vehicle, wouldn't there be a "pulling" effect?
Thanks
Don

[John Burk]

This is my 1.5" x 9" nose air inlet:

http://www.motorsportsinnovations.com/Bvile-pics/bs%20nose%203-07%20(1).jpg

The duct to the engine is about 2 ft long and at 7500 rpm the air will go about 129 mph and hopefully won't be too turbulent .

[blackslax]

There's a difference in scoops and nose stagnation point inlets . With scoops the inlet area needs  to be right for the flow so they only work in high gear and restrict the flow in lower gears . If they're not in undisturbed air scoops don't get full impact pressure . Nose stagnation point inlets get good air but 100% impact pressure is only at one point and a 3" inlet gets a lot less . If the nose shape puts the stagnation point along a line the inlet can be long and narrow and get closer to 100% impact pressure . That's how I did mine .
John Burk

Great point.  NACA ducts get high velocity air because of bernulli but it is low pressure. I was thinking that by eliminating the stagnation point with an inlet it would reduce drag.