Humidity

[swagaero]

Michael Baxter wrote:
> 
> 1st and intro: My name is Michael Baxter and I'm new to the list. I'm building
> an EFI AMC 401 and you guys/gals will be hearing from me in the future on this
> project :-). I'm headed out on a trip on Thur. so, I'll ask all my questions
> after I return next Wed.
> 
>  2nd, Humidity: I'm a pilot and during flying career I've been taught that
> humid air hampers performance compared to dry air under the otherwise same
> atmospheric conditions. I was taught this in ground school when I was flying
> piston engine airplanes all the way up to ground school for the B-727. The
> engine performance charts in the manuals for all airplanes have some
> correction factor for high humidity and it is always detrimental.
> 
>  What I've been taught goes like this: Air in our atmosphere is made-up of 78%
> nitrogen, 21% oxygen and 1% other gases. That mixture stays pretty much the
> same all the way to space. It's a common mis-conception that oxygen content
> decreases with an increase in elevation. It's not true. The oxygen molecules
> are just spread out more. As you go up, there is less and less of our
> atmosphere on top of you pushing down. Less weight and hence less pressure
> pushing the molecules together. The air is less dense and the molecules are
> more spread-out.
> 
>  You have two sealed boxes/parcels of air each a cubic foot. One is totally
> dry and one is just short of total saturation. Both are at the same temp. and
> pressure. In other words, the density of the molecules in each box is the
> same.
> 
>  All the molecules of water in the near saturated parcel are displacing
> molecules of air. If you remove all of the water molecules from the saturated
> box/parcel, you are left with less air molecules than you have in the
> box/parcel with dry air inside. The air molecules in the previously saturated
> box will spread-out and become less dense. Less dense air equals less engine
> performance whether it's a internal combustion engine or a turbine engine with
> 7 stages of compression.
> 
>  Of course, all my piston engine aircraft experience has been with air cooled
> engines. I always noticed that my engines ran cooler on humid days. Some of
> this may be attributable to decreased power output because of less dense air
> but, I believe the humid air cooled the engine better. If that is indeed the
> case, I'm sure I gained some lost power back due to a cooler more dense
> fuel/air mix. reaching the cylinders.
> 
>  -- Michael Baxter, 74172.1164 at Compuserve.com
>  http://ourworld.compuserve.com/homepages/MBaxter
>  From Reno, NV USA on 23-Sep-1997 at 23:51:17 PDT
> 
> !^NavFont01F0007MGHHN9A07DA


fly in some of our hot dry air and then in hot damp air and tell which
is going to work better for hp.

Steve
-- 

                   ----|------||------|----
                     --|------[]------|--
                            0/  \0



www.flash.net/~swagaero