Exhaust Flow and Aero

[SPARKY]

Is the "Propster" alive  and well  or is that a pusher Canard  plane

[donpearsall]

I am pretty sure that photo was of the rear end of a Vari-EZ. I built one a long time ago.
Don

[superford317]

Drag increases with the density of the air. Drag increases with area.
Surface area is not important when one is dealing with pressure drag, but it is important when dealing with viscous drag. Drag is influenced by other factors including shape and texture.
As drag increases, acceleration decreases. Eventually one can imagine a state when the
drag and weight forces are equal. It will not cease to move, but rather it will cease to accelerate. We
have reached terminal velocity. There can be no speed greater than or less than this one.
a streamlined shape has much less drag than a non-streamlined shape. Whatever drag exists for a streamlined shape is composed primarily of skin-friction drag with the pressure drag being very small. The increase in skin-friction drag occurs because the streamlined body has more area exposed to the airflow and thus has a greater area over which the boundary layer may act. A streamlined shape also experiences almost no boundary-layer separation.
as i stated before, where and how to introduce the hot exhaust depends to a great extent on the shape and aerodynamics of your vehicle and also the benefit you wish to receive from the use of the exhaust.
you can gain more downforce and traction or reduce the drag and gain more speed.

[superford317]

The key parameters affecting straight-line acceleration are engine torque, gear ratios, aerodynamic
drag and the traction limit of the rear wheels.
Acceleration can be either traction limited or power limited. The approach used to define the acceleration is first to consider the effect of the engine and gear ratios then to superimpose the effect of the traction limit and aerodynamic drag.
By using only the heat from the vehicle cooling systems and engine exhaust we can manipulate 3 of the 4 key parameters in acceleration to a lesser or greater extent, discarded heat can not do anything for gear ratios, but it can power turbochargers to increase engine torque dramaticly and increase acceleration.
Aerodynamic drag, lift and downforce, can be alterd and influenced with discarded heat to decrease overall drag and increase speed and acceleration. depending on the body shape and if the wheels are open or closed, the redirected heat can do anything from reducing tire drag and lift, to reducing body friction drag and reduce pressure drag.  
lastly the discarded heat can be used to create downforce and thereby create more traction with the tires and increase acceleration, if the vehicle is traction limited.
you could increase your downforce on the salt and at the same time reduce drag and run a turbocharger to boost engine performance. using an exhaust augmenter you can increase engine coolling and at the same time reduce drag.
engine exhaust is a very powerful thing, 1/3 of the fuel burnt in an internal combustion engine is actually used to power the crankshaft, 1/3 is waste heat that is radiated from the engine and pickd up by the cooling system and the last 1/3 is sent out the exhaust as a waste product.
66% of the power from the burnt fuel is left for us to do with as we see fit, building the propper header, using coatings and wraps we can recover a lot of the exhaust gasses and using exhaust augmenters and redirecting the heat from the cooling system we can recover a lot of the radiated heat and also the heat from the cooling system.

[gearheadeh]

I am pretty sure that photo was of the rear end of a Vari-EZ. I built one a long time ago.
Don

I agree, had a ride in one that was there at bendover for a fly in convention of EZ home built planes.

[superford317]

MLSE, sorry about my ramblings, but I thought I would add a little insight to what the exhaust and radiated heat could be capable of, without knowing more specific details about your vehicle and class rules, I can only assume that by you saying production class, you will be very restricted as to what you can do to your car shape and underpinnings.
So for starters you will have to worry a LOT more about pressure drag than you will skin friction drag. We can minimize that as well as a few other problems with the proper management of the radiated heat from around the engine compartment and the cooling radiators, as in water, transmission and oil coolers.
If you are not running engine oil and transmission coolers, it may be worthwhile to think about adding them so we can add the recovered heat into our system, if not the power you lost from the internal friction of the transmission and the friction and radiated heat from the engine being transferred to the oil, will be lost, so no matter how negligible, it is a source of power we can use to our advantage.
If we do not recover this source of energy and put it to use, your competitor will.
I’m sure records are set and broken by fractions of seconds and tenths of miles per hour, look at all the small details and in the end they will add up to be a contributing factor to the overall package.
I have lost races by .002 seconds before.
If rules permit we can build a type of duct system around the engine to recover the radiated heat and direct it to the underbody, increasing engine cooling and improve aero forces.
I will assume also that you will be very limited to what you can do to the actual vehicle underbody. We can’t install a full underbody tray, but can we use air flow directors and vortex generators. Are air dams, splitters, diffusers and spoilers permitted.
I wish I had a rule book to review, is there one on line I can look at.
Without knowing more about your particular class and the type of car you have I can only speculate.
Give me a LOT more details about what you have and what you wish to achieve.
 

[SPARKY]

Now what we need is a Submarineer,  did any of you guys serve on a bubbler??

[joea]

..how about if this "energy" is applied to a "lever" arm to multiply the mechanical
advantage...say to an impeller or "prop" .......to impart yet greater thrust by said "prop"...

[jimmy six]

"Drag improves as the temperature of the air increases" (Previous quote)

Is this why I always go faster in the afternoon qualifing than I do in the morning on the back up run..it's the excuse I use..................JD

[superford317]

this is an example of what heat on or around a surface can do for boundry layer and airflow.
using the same sphere all 3 tests, the only difference was the temperature of the sphere.

[Peter Jack]

What were the temperatures involved?

Pete

[WhizzbangK.C.]

Just curious, what were the real temperatures of the sphere in each of those tests? One might be able to use that effect by placing the water tanks as part of the outer body work of the vehicle, or using the skin a as flat surface radiator in the return flow to the tank, to allow it to get to maximum available temperature without overheating the rest of the water in the cooling system.

That is, as long as extreme temps aren't required to produce a significant effect.

[superford317]

Boundary layer heating becomes more efficient with lower Reynolds number.
The skin friction is reduced as a function of the ratio of the skin temperature to the ambient temperature. The result is an effective drag reduction.
The velocity profile can be modified by controlling the pressure gradient using surface heating.
Heating the surface under a turbulent boundary layer reduces skin friction.

[superford317]

the american F117 nighthawk low visability airplane used slits along the entire back width of the tail as an exhaust outlet, very wide and narrow.
i have seen motorcycle rear fenders turned into the exhaust pipe, a mirror image welded to the fender and the exhaust directed between the 2 parts and blowing out the trailing edge.
have double panels on the car and dump the exhaust into them.
the spectre car as an example, imagine if you will the entire rear half of the vehicle being double walled and the exhaust flowing thru it and out the very trailing edge, the super heated body will lower the skin friction drag and the exhaust dumping into the ideal location at the rear will lower the pressure drag at the same time.
most of the streemliners dump the exhaust at a less than desireable location.

[superford317]

There would be very little restriction to the exhaust as using the body for the exhaust would be a lot of area.
Even if you lost some power the gain in aerodynamics at high speed would more than offset this and still have a faster speed.
Remember each time you double your speed drag quadruples.