[NSPYR]

I was wondering if altitude affects the car ? I recently drove my car from Hainan island to Kunming and the altitude here is around 1800 meters above sea level.

I feel that the car seems to be less powerful...

Opions ???

 

[Skylinegtr06]

yup less oxygen=less power

 

[NSPYR]

yup less oxygen=less power

Will this also affect my intake pressure ? as my intake pressure gauge now is making totally different readings then before...

 

[dobiejoe]

It really does not have anything to do with less O2 even though you will have less O2. Its a lower pressure when you raise alt. The higher you go the less pressure. The lower press cant hold as much O2 and the atoms in the air are more spread apart so when your cylinder sucks in air and tries to squeeze it it has less to work with. Heat also lowers pressure to some degree but mostly just spreads the atoms in the air even farther apart.

So if its hot and hi alt, Now your ihave a double screw job.

 

[peter_x]

Cars have altitude compensators.

 

[dobiejoe]

Cars have altitude compensators.

The only way to compensate for alt and low pressure that a car can do is to reduce the air/fuel ratio. The only other way would be to compress the air back down to a sea level pressure, that would be like a small supercharger, and cars dont have anything like that unless it is supercharged.

 

[shipo]

Cars have altitude compensators.

:rotfl: ROTFLMAO. Please doctor, explain how these "altitude compensators" work.

 

[shipo]

So if its hot and hi alt, Now your ihave a double screw job.

Then there's the whole humidity card to play (water molecules weigh less than the surrounding "air" molecules and as such cause the air to be less dense). As any pilot can tell you, any combination of heat and/or humidity and/or altitude can make it difficult to get a fully loaded Cessna 172 off the ground.

To adjust your phrase a bit, "So if its hot, humid and hi alt, now you have a triple screw job." :thumb:

 

[Firestrife]

there was a case here where someone was in a high altitude area and had problems taking off from a stop and it does slow you down.

 

[dobiejoe]

Then there's the whole humidity card to play (water molecules weigh less than the surrounding "air" molecules and as such cause the air to be less dense). As any pilot can tell you, any combination of heat and/or humidity and/or altitude can make it difficult to get a fully loaded Cessna 172 off the ground.

To adjust your phrase a bit, "So if its hot, humid and hi alt, now you have a triple screw job." :thumb:

I think you got it backwards. Humidity (water) is more dense and would increase a air charge. As far as the pilot question. Yes I do fly DC-10 aircraft for a living and we do not take humidity in account when calculating aircraft performance, its only a plus. Thats why some older aircraft like the older KC-135A models and jets from the 50's-early 60's used water injection strait into the engine to increase the air charge.

 

[shipo]

I think you got it backwards. Humidity (water) is more dense and would increase a air charge. As far as the pilot question. Yes I do fly DC-10 aircraft for a living and we do not take humidity in account when calculating aircraft performance, its only a plus. Thats why some older aircraft like the older KC-135A models and jets from the 50's-early 60's used water injection strait into the engine to increase the air charge.

Ummm, no, I have it correct, water vapor is far less dense than the air it is mixed with.

http://en.wikipedia.org/wiki/Density_altitude

FWIW, I used to fly an old O-300 powered 172 out of an airport in New Jersey (altitude 182') and am very versed at calculating the Density Altitude. Going over my log I see that one flight in August a few years back had a Density Altitude of a whopping 3,816'. Why? Because of the humidity. That particular day the OAT was 97 and the dew point was 95, however, if the dew point had been at a more normal 70 or so, the Density altitude would have been only 3,414, a difference of over 400' in altitude.

FWIW #2, on a training flight from that same airport the OAT was -20 and the dew point was -50, equating to a density altitude of 5,019 feet below sea level. That day I got the plane off the ground in about 30' at a whopping 25 mph. I was practicing departure stalls over a reservoir up in the mountains and at one point flying into a fairly stiff headwind, I was actually watching the mountains passing me as I had a negative ground speed.

 

[dobiejoe]

Ummm, no, I have it correct, water vapor is far less dense than the air it is mixed with.

http://en.wikipedia.org/wiki/Density_altitude

FWIW, I used to fly an old O-300 powered 172 out of an airport in New Jersey (altitude 182') and am very versed at calculating the Density Altitude. Going over my log I see that one flight in August a few years back had a Density Altitude of a whopping 3,816'. Why? Because of the humidity. That particular day the OAT was 97 and the dew point was 95, however, if the dew point had been at a more normal 70 or so, the Density altitude would have been only 3,414, a difference of over 400' in altitude.

FWIW #2, on a training flight from that same airport the OAT was -20 and the dew point was -50, equating to a density altitude of 5,019 feet below sea level. That day I got the plane off the ground in about 30' at a whopping 25 mph. I was practicing departure stalls over a reservoir up in the mountains and at one point flying into a fairly stiff headwind, I was actually watching the mountains passing me as I had a negative ground speed.

I don’t want to turn this into a pissing match but I guess my 6000 hours in large multi jet aircraft of different types compared to your little 172 may be different. But NOT in a single aircraft performance chart of any jet I have flown or in any FAA approved training manual have I ever seen, was humidity calculated in any way for aircraft performance. Temp and PA are the only factors. I will give you PA may be based on humidity for calculating airfield pressure alt but not in any part of aircraft engine performance other then we use this airfield PA for a starting point. But airfield PA comes from you local FAA approved weather shop. Humidity plays such a small role it’s not even a factor. Temp increasing and calculated pressure alt is the big factor.

Let’s not HIJACK this thread that was started for CAR performance and talk about airplanes that bore most people.

PM me. I’m always willing to talk about aircraft and performance in a polite and professional level.

 

[shipo]

^ Okay, let's try it another way. Clearly you don't believe me that humidity affects air density and as such the amout of power an engine can produce, so go to any dyno correction calculator you choose and see what effect that adjusting the humidity has on engine output.

http://wahiduddin.net/calc/calc_hp.htm
http://www.anycalculator.com/enginehorsepower.htm

Like it or not, humidity reduces air density and as such reduces both engine output (especially normally aspirated intermittant combustion engines) and lift/effective altitude (see the calculator below), even you don't care.

http://wahiduddin.net/calc/calc_da.htm

 

[anavrin351]

A jet engine is not a K20Z3 either

Your car will lose power in high altitude. I was in a high altitude going 80+ and my car wouldnt pull in 6th gear, barely in 5th, and even 4th was week for being in v tec

 

[Si 07]

at first glance i thought the title said "attitude"

 

[BigT]

Cars have altitude compensators.

A car's engine computer does in fact compensate for altitude by adjusting the air/fuel mixture accordingly to keep the engine from running poorly at different altitudes.

However, this compensation will keep the car running smooth and reliably, but it will still lose power. If the computer didn't compensate the air/fuel mixture would go rich and the car would start running bad. The computer compensates for this by reducing the fuel to match the lower pressure/oxygen levels. But the engine output will indeed be lower with less air and fuel entering the cylinders.

 

[shipo]

Exactly. :yeahthat: