Hi I was wondering what bad effects could heavy rain have on a jet aircraft. Does heavy rain increase drag? Thank You

I don't know about real airplanes but I can tell you my golf ball does not travel quite as far in a heavy rain, not that I would ever play golf in the rain. :)Rain (and snow) looks cool out the window on approach but in FS there is no performance change modeled at all.Mike

I don't know about performance but heavy rain means risk of aquaplaning after touchdown. If there is standing water on the runway pilots are encouraged to make 'positive' touchdowns to make sure the wheels get through the water.

November678x,Heavy rain (R+) is mostly a concern for take-off and landing performance (slippery wet runway) rather than flight. As a pilot, what concerns me more than the heavy rain per se is the phenomenon that usually causes it, ie thunderstorms, and all the hazards associated with that (wind shear, downdrafts, turbulence etc). From an operator perspective, the only precaution I may take for flying through heavy rain is to turn the ignitors on continuous, and if the TAT is <10, the engine/nacelle anti-ice.If my memory serves me correctly, many years ago, there was a DC-9 in the US that suffered a double-engine flame-out while flying through very heavy rain, but such cases would be exceedingly rare. If you avoid flying through or under thunderstorms, I doubt rain itself would ever cause you problems.As to the drag question, I don't know. If it does, it is not noticable. I don't ever remember having to increase power to maintain speed just because I entered a rain shower.Kevin in CYOW

November678x,As Kevin has already stated the only performance factor that is significantly effected by rain is the take-off and landing. Rain and moisture also causes an off glide path illusion. Light rays will refract while passing through the layer of moisture.In fact I encountered moderate rain while flying this morning, the only phase of flight that was slightly effected was the take-off and landing. Associated with rain is of course thunderstorms which produces hazardous downdrafts.Best Regards,

Hi AllWell, another fun trick heavy precip will do is attenuate the radar return, meaning you can't see thru the rain event to see what is on the other side-picking your way thru/aound cells can be more of an art than science...sucker holes and death valley effect is not a good feeling.That DC-9 was a Southern Airways flight that got hammered by not only rian but hail as well (that'll ruin your day). They got in the wrong place at the wrong time.Now the FAA/NASA/CAA are working on uplinked weather (think email type) of weather radar which is just coming on-line. The original FAA ATC radar were not the best at spotting cells but now the next gen of computer generated atc will have good weather overlays. Kinda nice to have everyone looking at the same picture....Besides the hydoplanning issue there is the spray generated as we lumber down the runway-most modern, well maintained runways are great at drainage and grooved but there are some that will have the odd puddle. The nose wheel tires will have "chines" or a ridge on the sidewall to kick the water away somehow (B+ in Physics so don't ask-works great, cost lottsa money-that's all you need to know).As mentioned earlier their is the "outflow" of air-think of a shaft of cooler, "heavier-more dense" air sinking rapidily to the earth. That'll get your attention on final.....Then there is clear-ice formed when super-cooled big-drops of moisture impacts the wings etc, freezing instantly (B+ in physics so don't ask).....Then there is that look the FO gives when I say...."why don't you do the walk around...."Tim_757

"Besides the hydoplanning issue there is the spray generated as we lumber down the runway-most modern, well maintained runways are great at drainage and grooved but there are some that will have the odd puddle."Just wondering if the "water injection" effect (into the engine inlets) offsets the drag of rain on the fuselage/or on the wheels from water-laden runways. Original 747 engines were somewhat underpowered, especially in hot weather, until water injection was added ;-)Not sure if it's true, but I heard somewhere that when it's raining, the air is less dense than when it's very humid??? (As strange as it sounds). Can anyone confirm this?Thanks.Cheers.Ian.

Hi IanWell, I have never seen a density altitude figure that took humidity into account-it is more of a by-product of the air temp. We look more at the dew-point temp spread for visibility reason vs performance.However, warm moist are is generally "less dense" than cold air. That is why more moisture can be held in warmer air.Rain has a tendancy to cool the air since it brings/drag cooler air down and evaperation cools the surfaces as well bringing down the temperature of the air around the event. So I guess in that sense it would be more dense-better performance. But again I have never seen a figure for "rain" being factored in for density altitude.As far as water injecion....just a tad before my time, but was that for cooling the turbine temps or fot steam power? I think in early jets temps were the big problem in power development....Anyway-it gets confusing from here on out.....Tim_757

Thanks, Tim.... Sometimes things get a little muddled in the old brain. I may have been dreaming."As far as water injecion....just a tad before my time, but was that for cooling the turbine temps or for steam power? "LOL. Also before my time. I just assumed it helped cool/condense the air, therefore allowing more air in at the front. I don't know if cooling the turbine increases engine efficiency.... you'd have to ask an engine expert ;-) I assume you mean the hot end of the turbine? The front (fan) would probably already be pretty cool.Cheers.Ian.

Hi allI cant help you with the drag bit but i can tell you a little about water injection, it was used on older jets ie BAC 1-11 , B707 etc and basically did one of 2 things depending where it was injected ( some turboprops also had water methanol injection to boost takeoff power ), if its injected at the front of the compressor it increases mass flow and power directly, if its injected at the rear of the compressor it cools the turbines which then allows you to increase fuel flow and power without exceeding you EGT limits ( done automatically ).

Last week I was in STR (EDDS) and we were scheduled to take off on rwy 25, however a light shower at that end of the rwy prevented us from taking off (Delta B763ER) due to an obstacle, aircraft weight, and performance on a wet runway. Thus we had to taxi to rwy 7 and await a clearing in the traffic due to taking off against all other traffic. In other words just a little rain can have a big impact. Heavy rain can and often has a major impact on all aviation.The above was not simulated by the way.Regards,Jay

Hi all. There is one slight effect rain will have on drag. Alot of aircraft owners will wash and wax their aircraft to make the airflow around it as smooth as possible. This will decrease drag with an increase of fuel savings. Drag will increase with dirt, oils, loose fastners, loose rivets and grime. As for heavey rain it will slightly increase drag as it strikes the wings and fuesalage. Imagine smooth air flowing over the wing. As rain drops strike the wing it penetrates the airflow. As this happens the air has to push and maneuver around the strike points. This increases the drag but not enough to be accounted for. There is also some info about this in the fe prep or the atp prep. Its been a while so i cant remember which one.

JayWere you limited becuse of the shower or contaminated runway environment?From the sounds of it you had a obstacle clearence limit since rwy 7 is the recip of rwy 25. Just have never seen a limit on 757/767 due to an active rain shower before, but have experienced tons of it due to standing water/density altitude as a result of it. Nice thing about the 757 is it has that extra power!Tim757