Brand new at this please help !

[Freud]

I think I just heard the bell for recess.

FREUD

[Dr Goggles]

I think I just heard the bell for recess.
FREUD

.....did someone say RUMBLE! 

[tortoise]

Kid posing as adult on internet - kind of funny.
Adult posing as kid on internet - very bad.

[McRat]

Beer-Thirty x Newbie = Pointless Rambling!  

Exhaust micro-ports is the next step in wheel driven records.

Unless the rules are changed, exhaust thrust from piston engines is valid, and will exceed the wheel driven thrust at some speed.

The correct placement of many small exh ports pointed aft that help reduce aero problems are the next step.  With a big enough engine, the total net aero drag will be negative, yet still have wheel driven acceleration.

Think about this.  Our piston engines work entirely by the expanding volume of gases.  Much of the aero drag is created because gases are forced to swirl backwards when they have nowhere else to go.

If you can get the volume of the exhaust gases to exceed the frontal area that is displaced at a given speed, you can end up with zero net drag.  A big enough engine will do it.

Personally, I don't agree, but the rules are the rules.  I didn't work out the boost and CI required, but there is a point when it becomes critical.

Bikes are limited by an arbitrary CI limit, so it will certainly be a car.  

A bike is still the most efficient design, but the rulebook will keep cars ahead of the game.

[McRat]

Ignore everything I posted.

I had a dog medicine tablet in my right hand, and a pretzel in my left.

Things got skewed.

I've brushed my teeth 3 times, and I still taste rotten dried liver in my mouth.

You ever wonder why dogs lick their butts?  To get the taste of medicine out of their mouths.

[hotrod]

I've brushed my teeth 3 times, and I still taste rotten dried liver in my mouth.

You ever wonder why dogs lick their butts?  To get the taste of medicine out of their mouths.

Does that mean you need to go lick your dog's butt?

Larry

[Dr Goggles]

I started on a response, it quickly boggled my mind and went wanting for sense. Just calculating the volume of gas produced by gasoline combustion relied upon neurons that were packed up and recommissioned a very long time ago. When you say big, you're right...but , anway.

What I do know is that when we were still in the design stage of the Spirit of Sunshine we happened across an engineer who worked for the navy in , IIRC, underwater stuff.

He liked the idea of what we were trying to do. He was kind of bemused that we thought he could help us and I think he was loathe to talk about anything other than what he was utterly sure would be of benefit. He said from what he could see we should point our exhaust out the very tip of the car as he saw three positives.

1./ directing the exhaust in any direction other than that of travel would be counter-productive to our efforts of trying to keep the boundary layer attached to the car.

2./ We would receive the benefit of " a couple of pounds of thrust", he laughed but said " mightn't be much , but it's free"

3./ "Rapidly cooling gas is collapsing in volume at a rapid rate, that is a very good way to de-energise the wake. By feeding exhaust into the turbulence behind the car you will make a huge reduction in total drag."


Oh and if that earlier comment was directed at me , mwah.

[taper41]

Beer-Thirty x Newbie = Pointless Rambling!  

Exhaust micro-ports is the next step in wheel driven records.

Unless the rules are changed, exhaust thrust from piston engines is valid, and will exceed the wheel driven thrust at some speed.

The correct placement of many small exh ports pointed aft that help reduce aero problems are the next step.  With a big enough engine, the total net aero drag will be negative, yet still have wheel driven acceleration.

Think about this.  Our piston engines work entirely by the expanding volume of gases.  Much of the aero drag is created because gases are forced to swirl backwards when they have nowhere else to go.

If you can get the volume of the exhaust gases to exceed the frontal area that is displaced at a given speed, you can end up with zero net drag.  A big enough engine will do it.

Personally, I don't agree, but the rules are the rules.  I didn't work out the boost and CI required, but there is a point when it becomes critical.

Bikes are limited by an arbitrary CI limit, so it will certainly be a car.  

A bike is still the most efficient design, but the rulebook will keep cars ahead of the game.

Not that you car, but how can you say that a motorcycle is the most efficient design?  Just from what we have discussed on here,Traction, power, stability all come into play to get the most out of the vehicle at top speed and all seem to be advantages of a car rather than a bike.

[fastman614]

My ultimate goal was to find out if there is one factor that is more effective than the other for top speed. Or if they would produce the same result

What I'm getting out of this Larry, is that using percentages to find this is not the correct way to go about it, and fractions are ?

The whole point is to make EQUAL changes and find the result.

are percentages the wrong way to go about this because your decreasing one and adding on the other ?

The question I have just suddenly seen here is .... To what end?... Is it the ultimate top speed increase that is the hoped for end result?.... Or is better fuel economy the hoped for end result?

I know I just threw in a "twist" here.... but ultimately, the reduction of drag will have a greater positive result on fuel economy than the increasing of horsepower (at least the way most of us Land Speed Racers do it - which is at about 20% to 23% efficiency) .... Increasing your horsepower will cost you A LOT MORE at the ERC Truck than decreasing the aero drag... decreasing aero drag will come at (probably) 100% efficiency....

Just saying.....

[fastman614]

I had made a reference to a quote from another poster.... This is it! Specifically, see the bold and underlined area....


Posted by hotrod

     Re: Terminology
« Reply #10 on: June 04, 2012, 04:38:03 PM » Quote 

--------------------------------------------------------------------------------

Quote
(his computer constantly comes up with "we can't go as fast as we just did" type of results.... but then, maybe the salt flats tilt - but only for us!)

When models disagree with reality, reality is always right! 

Since you are not designing an airplane all you need is an ability to repeat measurements to determine if a change helped or hurt. As long as your satisfied no really silly mistake is being made, tweak the frontal area and CD until the computer model results match the real world and use those numbers in the future.


Even the big boys use low tech analysis to solve problems.

http://www.degreeinfo.com/off-topic-discussions/8194-burt-rutan-rolls-out-his-new-spaceship.html




Quote
Stability problems with the spacecraft tail were detected in unpowered drop tests over the Mojave desert, making some redesign work necessary. (That's why they have test pilots.) So the schedule slipped.

Rutan doesn't use wind tunnels. He uses a sophisticated computational fluid dynamics computer model to virtually design aircraft. But the tail problem necessitated some empirical experiments. Here's their "wind tunnel" to test new tail ideas: A Ford pickup truck with model tails mounted on it:

http://www.scaled.com/projects/tierone/New_Index/photos/images/800/wind_tunnel_800.jpg  <--- link is broken may be on the web site but probably re-named

Another location has the image ---- http://stargazer2006.online.fr/others/trucktunnel.htm

Not exactly high technology! (But it worked.) Can you imagine NASA doing that?? A pickup truck and a few weeks? NASA is so afraid of the political repurcussions of failure that they would have spent 24 billion dollars and 14 years studying the problem.

The tail is all fixed now.

Here is a test rig used by NASA to test chute deployment:

http://www.dfrc.nasa.gov/gallery/photo/X-38/HTML/EC96-43844-4.html

You don't have to be fancy to get basic aero info.

Larry

[Tman]

Somebody owes Jon for a heck of a lot o' bandwidth!

[fastman614]

Somebody owes Jon for a heck of a lot o' bandwidth!

Tman, I'm "afraid" you're correct!....Better get out the credit card and click the icon....on the home page

[taper41]

OK  i have another question now, and you can choose to answer it or not but i was just curious I know how important power to weight ratio is when it comes to accelerating , but what about top speed.

I know there was a bike that hit 312 mph ( bill warner) tradition motorcycle, had a bike that weighed 586 lbs with 1000 bhp.
if it was an inclosed bike like the rest of the streamliners

Would it beat a car that had a weaker power to weight ratio but more power, lets say weighed 2000 lbs with 3000 bhp? for a max speed

[Peter Jack]

It's time to go build something taper41 and figure these things out for yourself.

Pete

[taper41]

Why, because i ask questions, its just a point of discussion that I like to talk about.  I don't understand the big deal.