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More Drag When Planes Go Through Clouds?  
User currently offlineGodbless From Sweden, joined Apr 2000, 2752 posts, RR: 16
Posted (11 years 7 months 1 week 10 hours ago) and read 3137 times:

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


21 replies: All unread, jump to last
 
User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 1, posted (11 years 7 months 1 week 9 hours ago) and read 3107 times:

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.

User currently offlineFSPilot747 From United States of America, joined Oct 1999, 3599 posts, RR: 12
Reply 2, posted (11 years 7 months 1 week 6 hours ago) and read 3084 times:

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


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 3, posted (11 years 7 months 1 week 2 hours ago) and read 3052 times:

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.
User currently offlineIkarus From United Kingdom, joined Jan 2001, 3524 posts, RR: 2
Reply 4, posted (11 years 7 months 1 week 1 hour ago) and read 3030 times:

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


User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 5, posted (11 years 7 months 1 week ago) and read 3022 times:

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.


User currently offlineSkyguy11 From , joined Dec 1969, posts, RR:
Reply 6, posted (11 years 7 months 6 days 23 hours ago) and read 3014 times:

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.

User currently offlineSaxman66 From United States of America, joined Sep 2000, 518 posts, RR: 0
Reply 7, posted (11 years 7 months 6 days 19 hours ago) and read 2975 times:

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!
User currently offlineVc10 From United Kingdom, joined Nov 2001, 1406 posts, RR: 16
Reply 8, posted (11 years 7 months 6 days 12 hours ago) and read 2951 times:

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


User currently offlineBuckfifty From Canada, joined Oct 2001, 1316 posts, RR: 20
Reply 9, posted (11 years 7 months 6 days 11 hours ago) and read 2936 times:

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.


User currently offlineSaxman66 From United States of America, joined Sep 2000, 518 posts, RR: 0
Reply 10, posted (11 years 7 months 6 days 8 hours ago) and read 2921 times:

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!
User currently offlineBuckfifty From Canada, joined Oct 2001, 1316 posts, RR: 20
Reply 11, posted (11 years 7 months 6 days 4 hours ago) and read 2894 times:

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.

User currently offlineTransactoid From Canada, joined Mar 2001, 788 posts, RR: 0
Reply 12, posted (11 years 7 months 5 days 21 hours ago) and read 2856 times:

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)


User currently offlineBuckfifty From Canada, joined Oct 2001, 1316 posts, RR: 20
Reply 13, posted (11 years 7 months 5 days 19 hours ago) and read 2843 times:

Hey, good one.

I'm sure by the time we're finished, we probably would have written a text on this matter...


User currently offlineFrancoflier From France, joined Oct 2001, 3735 posts, RR: 11
Reply 14, posted (11 years 7 months 2 days 20 hours ago) and read 2736 times:

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.



Looks like I picked the wrong week to quit posting...
User currently offlineKlaus From Germany, joined Jul 2001, 21406 posts, RR: 54
Reply 15, posted (11 years 7 months 2 days 14 hours ago) and read 2721 times:

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).


User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 16, posted (11 years 7 months 2 days 10 hours ago) and read 2713 times:

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.



User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 17, posted (11 years 7 months 2 days 9 hours ago) and read 2708 times:

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

Sorry....meant to say temperature instead of pressure!!!


User currently offlineVc10 From United Kingdom, joined Nov 2001, 1406 posts, RR: 16
Reply 18, posted (11 years 7 months 2 days 6 hours ago) and read 2697 times:

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


User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 19, posted (11 years 7 months 1 day 9 hours ago) and read 2660 times:

http://www.rallycars.com/Cars/WaterInjection.html

User currently offlineVc10 From United Kingdom, joined Nov 2001, 1406 posts, RR: 16
Reply 20, posted (11 years 7 months 1 day 6 hours ago) and read 2644 times:

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


User currently offlineDelta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 7
Reply 21, posted (11 years 7 months 6 hours ago) and read 2622 times:

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



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