Density Altitude / Speed

[mstephenson51]

The answer is still the same and I can?t figure out what all the different posts are about.  The original question was ?will a normally aspirated piston engines vehicle go faster at Bonneville or sea level?. If you look at performance charts of any normally aspirated piston engine aircraft that allows full power operation at sea level you will find the higher you go the slower you go using all available power.  These charts are for standardized temperature and pressure at the various altitudes. There is no "crossover point" that I have ever seen.  Jet aircraft are a whole different animal and have no relationship to normally aspirated piston engines

?will a normally aspirated piston engines vehicle go faster at Bonneville or sea level?.  With almost all cars, it WILL go slower.  But, There is a crossover point, and with the previous "most cars", its already been past, and you loose speed as you go up in altitude.  Jet engines act like blown piston engines in that the extra forced induction simply changes the slope of the decrease in power vs. altitude that I spoke about b4.  That change in slope moves the "crossover point" up.

strictly speaking about the Normally Asperated recip engine in the question, if it were on a dyno, it will lose power as it goes up in Density Altitude.

[tortoise]

?will a normally aspirated piston engines vehicle go faster at Bonneville or sea level?.  With almost all cars, it WILL go slower.  But, There is a crossover point, and with the previous "most cars", its already been past, and you loose speed as you go up in altitude.

Can you give us an example (actual or hypothetical) of a car that ain't like "most cars", and gains speed with increasing altitude?

[Speed Limit 1000]

As you go up there is less lift, but the plane goes faster and adjusts the angle of attack slightly up to compensate.

Does that hold for NA piston engines?
[/quote]

A NA piston driven aircraft can only go faster at alt. if you are trading alt. for airspeed, then only to the point of impact.

[Flyboy]

Does that mean that acceleration continues until the airplane impacts the ground-- like in Kamikazes?

[Stainless1]

Gravity power, applies to flying airplanes, but not to landspeed racing, we race on a flat surface.  I guess that is why the apples and oranges are  not the same.  We must be done with this thread, it has gone several directions but the answer is still in Ack's post. 

[mstephenson51]

?will a normally aspirated piston engines vehicle go faster at Bonneville or sea level?.  With almost all cars, it WILL go slower.  But, There is a crossover point, and with the previous "most cars", its already been past, and you loose speed as you go up in altitude.

Can you give us an example (actual or hypothetical) of a car that ain't like "most cars", and gains speed with increasing altitude?

The reason that planes go faster when you go up a bit in alt. (even na piston engines) is because the drag coefficient is down around .2-.3.  With a car that has good aerodynamics, you should see the speed increase a little going from 60 degrees and sea level up to a couple thousand feet and 80 degrees.  I have even seen the increase in Indycars.  we had a cold practice day, down around 50 degrees, and as it warmed to 75-80, the cars all got faster.  Since they ALL got faster by the same amount, it cant be any effect of the cars "coming into the setup"  Then as it heated up the next couple days above 85 degrees, they started slowing again.  Not quite as slow as the 50 degree day, but slower than the 75 degree day.

[JackD]

While DA might be almost perfected, it appears the LSR community is not waiting.

Yup, it is kinda like I said.

THE END

[dwarner]

I agree with JackD and Stainless, btt for the answer.

DW

[Dean Los Angeles]

I know, I know!

We need a two mile track that has the start line at 10,000 feet and the end at sea level!!!!! (No two way passes!)

[bak189]

All this stuff about Density/Altitude/Speed is to much for me to understand.....but if you want to know about loss of power on a N/A engine just race up the Pikes Peak International Hill Climb like we did for 5 years with a sidecar.....You start at 9000 feet and 12 miles and 125 turns later you are at 14000 feet......try jetting for that with carburation on a big bore KZ Kawa.  At 9000 feet
(if jetted close) you have a powerful sidecar........
at 14000 feet you have the power of a 49cc scooter......plus you have trouble breathing..........
Lot of fun!!!!!!!!!!!!!!!!

[JackD]

To maximise the fun the race should be run down hill.

THE BITTER END