godbless
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More Drag When Planes Go Through Clouds?

Sat Dec 21, 2002 11:46 pm

When an airplane goes through clouds does that have any influence on drag and lift?
Isn't it that in clouds the humidity is much higher and thus the plane rides through water where the lift is higher but also the drag increases?
Or does flying in the clouds have no affect on the aerodynamic characteristics of an airplane?

Thank you in advance,
Max
 
cdfmxtech
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 12:57 am

I can't get too detailed into aerodynamic characteristics and such...but one thing u said IS wrong. Airplanes and engines in particular don't like humidity. Humid air contains alot of water, and in turn less air.
 
fspilot747
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 3:28 am

What causes all the turbulence in clouds? I've always noticed that whenever we descend through clouds, or ascend for that matter, almost immediately we hit a bit of turbulence...

FSP
 
FredT
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 7:06 am

Cdfm,
and water injection increases performance since... ?  Big grin

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Ikarus
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 8:58 am

FredT: Because it increases the mass flow through the engine, and hence the thrust (as it does not affect the exhaust velocity as much as the mass flow, if at all). If a lot of air in a cloud is replaced by water droplets, the effect would most likely be quite similar - i.e. a minimal increase in thrust. Though I am only guessing here, need a real engineer with experience to clear the issue up!

GodBless: Good question, I've never thought about that very much. Now my best guess is that the effects are minimal or even non-existant, as the properties (in terms of pressure, density, etc.) of the cloud are not too different from those of the "normal" surrounding air. (But if a meteorologist or an experienced aeronautical engineer could contribute, that would be great, as I am right now not actually talking about anything I've been taught, but merely guesstimating around...)

About the turbulence: I think clouds are more active patches of air in terms of their internal activity and gusts etc., so they do cause a slightly rougher ride than still air. I doubt the humidity has much to do with it, or a foggy landing would automatically be more turbulent than one on a clear day, which is something I have not noticed so far...

Regards

Ikarus
 
cdfmxtech
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 9:56 am

and water injection increases performance since... ?

Because it allows the engine to run slightly cooler. But water injection and flying through a cloudcan be 2 very different things. With water injection, you still have alot of "regular" air flowing through the engine and is augmented by the water injected into the compressor.
With a cloud, you've got this mass of moisture where the ratio of air to water is low.
 
SkyGuy11
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 10:10 am

Well if the moisture in the cloud condenses on the airframe than that water on the airframe could increase drag minimally. Otherwise a cloud is just like air except the moisture is visible... remember all air has moisture in it, a cloud is just visible moisture.
.
 
saxman66
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 2:25 pm

A plane flying through the coulds will have the same performance as with not flying in the clouds. The moisture content is about the same. Its just that inside the cloud, you can see it, because that is where the temperature and dew point meet.

With regards to turbulence in clouds, this will usually be found in cumuliform clouds. There is alot more vertical development with the unstable air, therefore cause some turbulence. You won't find this when going into stratiform clouds.
Ride Amtrak!
 
vc10
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 9:27 pm

Regarding engine performsnce with high moisture content I do believe that an engine will loose power as power comes from burning air [oxygen] with the fuel. If water replaces the oxygen then the fuel mixture becomes rich and power drops off.
In the old piston engines which used water injection, then these engines were modified for that purpose, so that when water injection was selected, then the the mixture of that engine was leaned off, back to " Best power " mixture so giving more power. This leaner mixture could be used as the water was providing the cylinder cooling, rather than than the excess fuel at the normal very rich mixture used at high powers. This cooling was required to prevent Detonation. In high humidity and normal rich mixtures piston engines will loose power, because the mixture becomes over rich.
I always thought that water injection on Jets was used to keep turbine temps lower so more power could be used without exceeding turbine max temps, but perhaps I am wrong on this idea.
regards little vc10
 
buckfifty
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 22, 2002 10:10 pm

This may sound like a broken record, but I'll throw in my two cents anyway.

Water injection for turbine applications, like many people said, is used to cool the air going into the compressor for increased performance, especially for hot and high conditions. How it does that is by the evaporation of the water (usually a water-alcohol mix), which takes away the heat energy from the surrounding atmosphere.

When you fly into cloud, on the other hand, the air isn't actually cooler than the surrounding atmosphere, because the evaporation rate is the same.

And clouds don't form necessarily because the humidity content there is higher. It could just mean that there are more condensation nuclei present than the surrounding air for the water content to attach itself to.

If anything, if the air is more humid, it would mean less drag, less lift, and weaker engine performance, simply because the air would be less dense.
 
saxman66
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RE: More Drag When Planes Go Through Clouds?

Mon Dec 23, 2002 1:36 am

Clouds don't form because there is more condensation nuclei present in one place than another. Its generally about the same everywhere. If you look at clouds, especially cumulus, you will find that they are flat on the bottom. That is the height where the temperature lapse rate meets the dew point lapse rate. It has nothing to do with condensation nuclei in the air.

Chris
Ride Amtrak!
 
buckfifty
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RE: More Drag When Planes Go Through Clouds?

Mon Dec 23, 2002 5:46 am

I beg to differ, and the case in point would be situations where you see scattered or few clouds in the sky. If what you said was correct, then it would always be overcast.
 
Transactoid
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RE: More Drag When Planes Go Through Clouds?

Mon Dec 23, 2002 12:55 pm

You've both missed an important point in cloud formation: Updrafts!

You see patchy spots of cumulus clouds due to localized cells of rising air. You're never going to get an entire "plane" of stable rising warm air...

(Well, in warm fronts, there is a close approximation to this wherein warm air is lifted en mass into the colder atmosphere)
 
buckfifty
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RE: More Drag When Planes Go Through Clouds?

Mon Dec 23, 2002 2:47 pm

Hey, good one.

I'm sure by the time we're finished, we probably would have written a text on this matter...
 
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Francoflier
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RE: More Drag When Planes Go Through Clouds?

Thu Dec 26, 2002 1:51 pm

Hi, I wanted to come back on this water-injected turbines matter a bit...

I have flown turbine aircrafts (turboprops actually) with water injected engines, and others that were injected with a mixture of wather and methanol (RR Dart for instance). For having used both, I can say that injecting water will lower the engine temp. The flight manual says it is designed to keep the temp within limits when the air is warm (above 23 degres C one the one I know of) on take off when you need an extra kick in the .... to lift off a dirty strip. I know it will also give you a little extra torque. (that, I can't explain)

Now, when injecting a water-methanol mixture (around 55/45%), the engine temperature will actually rise. The flight manual then gives you another higher temp limit for this instance and restricts its use in time. The higher temperature will give you more power.

I don't know much about the science of what goes on inside a gas turbine, apart from the basic thermodynamic cycle, but those are the facts I noticed.

About turbulence in clouds, I really think it is due to the convecting action that takes place in a cumulus type cloud, but when the air mass is stable you can fly into some stratus type clouds and have a really smooth ride...

Merry christmas and happy new year all!

Francoflier.
I'll do my own airline. With Blackjack. And hookers. In fact, forget the airline.
 
Klaus
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Francoflier

Thu Dec 26, 2002 7:44 pm

Francoflier: I know it will also give you a little extra torque. (that, I can't explain)

my guess:
The water will be evaporated (that´s how it cools the engine most efficiently). And the steam conversion should also contribute to the total engine power at that time (basically like in a steam engine).
 
airplay
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RE: More Drag When Planes Go Through Clouds?

Thu Dec 26, 2002 11:39 pm

Water injection increases the density of the air entering the combustion chamber, without increasing the pressure. Denser air means more horsepower.

This simple explaination applies to water injection systems used in piston AND jet engines. Pistion engines use water injections to increase the density and cool the air coming from the turbocharger, in order to avoid detonation (pre-ignition).

Sucking up clouds in your engine does not induce the same effect because the change in air density doesn't occur in a controlled chamber, therefore the physics are completely different.

If anything, engine performance will decrease and aerodynamic efficiency will increase in stable humid air since humid air is lighter (and/or less dense) than dry air. Of course there is always the turbulence associated with the activity in some clouds that affect the comfort level of the passengers.

 
airplay
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RE: More Drag When Planes Go Through Clouds?

Fri Dec 27, 2002 12:18 am

Water injection increases the density of the air entering the combustion chamber, without increasing the pressure.

Sorry....meant to say temperature instead of pressure!!!
 
vc10
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RE: More Drag When Planes Go Through Clouds?

Fri Dec 27, 2002 3:12 am

Airplay,
After reading the Wright notes on large piston engines, it states that water injection is used to cool the charge so as to prevent detonation, and so allow the mixture ratio to be reduced to chemically correct ratio,and it is this new ratio that gives the extra power not the water.If water is injected into any piston engines with no change in the mixture ratio, then that engine will suffer a "reduction" in power.
regards little vc10
 
 
vc10
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RE: More Drag When Planes Go Through Clouds?

Sat Dec 28, 2002 3:22 am

Airplay,
Thanks for the reference, but I noticed that it refers to Rally cars. Now an engine is an engine I would of thought but who knows these days.
I would post my reference, which is an old Lockheed/Wright Constellation manual, but my scanner seems to have Christmas Blues so I will type just a bit of it :-

" A water injection or wet engine uses water rather than fuel as a anti -detonant. When water is injected into engine a de-richment valve shuts some of fuel flow off resulting in a near best power fuel air ratio.
The anti-detonation qualities of water as a coolant are good and additional MAP is usually permitted.
Under conditions of high humidity, neither the wet nor the dry engine will produce as much power as it does in dry air. However the dry engine looses more power than the wet engine due to the over-enrichment effect "

Now I am talking about a 60 year old supercharged engine with mechanically controlled fuel injectors, where as your reference is talking about modern electronically controlled engines, so perhaps both are correct. If you would like to send me your e-mail address I just might be able to send you a copy of the Manual's page
Regards little vc10
 
delta-flyer
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RE: More Drag When Planes Go Through Clouds?

Sun Dec 29, 2002 3:22 am

Well, since this thread has migrated to water injection, maybe I can toss in my 2 cents worth.

The argument appears to be whether water injection cools the engine or increases power by reducing pre-detonation. The answer is both. By reducing pre-detonation, more fuel can be burned in the cylinder at each stroke, increasing power. However, that would overheat the cylinder. But it also happens that when the injected water vaporizes, it sucks up a tremendous amount of heat from its surroundings -- due to the high latent heat of evaporation -- making the added power practical without burning up the engine.

Without water injection, the same amount of power would only be possible using a larger engine.

For a turbine, the same principle applies -- the evaprating injected water reduces the turbine inlet air temperature, increasing its density, thus allowing for more fuel to be burned, increasing thrust.

Now, just a word of warning, I am not a propulsion guru, my opinions are based solely on basic engineering principles.

Pete

"In God we trust, everyone else bring data"

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