AH! CARB ICING! (at least for me...)

 

Yeah, but what if the plane was on a conveyor belt?

Or had square tires and was in outer space even?

 

Yeah, the relative humidity, the term most used in common interactions, the weather, etc, has an effect on the human body, the environment, metal, wood, etc.
But, it's the ABSOLUTE humidity that the engine cares about when making power (the higher the absolute humidity the less oxygen available for making power)
People get mixed up: a misty cold morning does have high relative humidity and equates to denser air and more power. But, that's because it's colder and the absolute humidity in that situation is actually less than on a hot dryish day (low relative humidity).
Also, humidity by definitiion is vapourized water. When water is already vapourized it has no cooling effect in the intake tract or whatever. The reason water injection works is because it still needs to be vapourized and then in takes heat out of the system to do it. The horsepower potential comes from the fact that there's more air molecules gained by the decrease in temperature vs what's being lost by the increase in absolute humidity (from the vapourized water).

 

that's why I like dewpoint temp as a reference...
RH without the temp is useless...

good example: cold misty/foggy morning...
temp is say 35 deg, and the fog indicates it's close to dewpoint, or 35 deg, which is low moisture content... gr H2O per lb of air
where as fog at 75 F indicates high content
although both have high RH and are close to saturation...

good graph
http://en.wikipedia.org/wiki/File:Relative_Humidity.png

 

Performance sucks! Density altitude goes up and performance plummets. On a day like we've been having recently a C152 at max take off weight (1670lbs) would be lucky to get a 300fpm climb. Thank god I'm done with the 152!!

 

A C152 isn't much on a hot day especially if the pilot and passenger weigh over 150 lbs. I have not not been able to fly one since high school.

What did you move up to? C172, C182 or C210

The C182 was a personal favorite when I lived in Sacramento with its hot summers and nearby mountains. Not as pricey to fly as the C210 and not as sluggish as the C172.

 

My father used to have a 182RG turbo....the turbo set up is amazingly basic!

We did fly a 172 out of Sant Fe once - 7000' altitude....that thing did not want to fly, the 182 turbo was much nicer!

 

Here's a good comparison. On a warmer evening this past week (80-something degrees, forgot humidity), I took my car out for a fun drive. Aside from not having AC and feeling a bit hot in the driver's seat, it was fun. On a hard 1-2 shift, the car just seemed to grab and go. No fuss. It was quick, but not overly thrilling.

Just last night, I went out and it was about 62 out, Again not sure about humidity. I decided to punch it through 1st and caught second pretty good, like the other evening, but this time the rear-end greated me with a tail wag and a, *ERK* from the tires. Also, the car seemed to pull quite a bit stronger. Quite a bit. I've also noticed a seeming loss of power when it's hotter out. Like mid 90's. Just seems to fall on it's face.

The things I want to look at after I get some gauges are boost pressure (how well it holds) and I'd love to get a g-meter to document the car's performance in different conditions.

 

A turbo Skylane is wonderful plane. However, I am not a big fan of retractable gear. Back in the 80s when I learned to fly, a 172RG from my flying school had a gear failure and the pilot was seriously injured in the crash. The "RG" helps with the aerodynamics but adds weight reducing payload. When I fly I am in no hurry to get anywhere. I would gladly sacrafice the a little speed for safety and carrying capacity. RGs are also more expensive to buy, rent and maintain.

Back to the question in discussion about a 944 and the weather. In a small plane you use carb heat during descents to protect against icing. Once you pull the **** engine power drops immediately and significantly. Although the 944 will not respond as dramatically because the temperature range is smaller and spread out over time, the impact should be the same. Warmer air reduces density and power.