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Flying in the rain!

Yesterday I was fling IMC in some variable rain, some quite heavy, (Cessna 172) and was aware that the noise from the airframe changed. There was a noticeable howl or whistle effect that cleared as soon as the airframe dried between showers. Any one suggest what may have caused this? There was no noticeble change to the flying characteristics and I had no worries about anything.
Thanks

UK, United Kingdom

I already heard abiut a whistling there



It is a long video but in the middle, he enters IMC and say his aircraft always whistle in IMC, at a frequency changing with airspeed.

Our Jodel clamshell doors allow a draft in from the top. New seals were fitted to reduce this. Approaching Stornoway, I offered to orbit as an airliner, departing, was unsure of my position. This brought me into light rain, for the first time with the new seals.
I thought a bearing had gone when the whine started. Engine speed did not change it, but airspeed did, so, I relaxed.
Water in a door-seal leak, narrowing the gap to whistle, and possibly vibrating for the whine???

Maoraigh
EGPE, United Kingdom

Can strong rain (no wind, no thunders, no ice, just rain) take down a plane (small or large)?

United Kingdom

@mancival, rain can significantly increase the stall speed of some low-speed airfoils. In particular, I have seen such a warning in the flight manual for SF-25 Falke motor glider (also known as Slingsby T61).

Last Edited by Ultranomad at 18 Jun 12:22
LKBU near Prague, Czech Republic

I think it was the same with the Grob 109A motor glider. Rumours say it was not possible to maintain altitude on full power when the wing was wet. The 109B had another airfoil.

ESG..., Sweden

Ultranomad wrote:

I have seen such a warning in the flight manual for SF-25 Falke motor glider

Yes, I had the impression it is because of rain on wood structure until I heard someone who could not climb after takeoff with some water on wings until he reached 80kts instead of 55kts, luckily for him Lasham have a very long runway…

The C172 air-frame should cope with heavy rain but water droplets will increase your stall speed but I guess less than in those slick new air-frames (e.g. Gliders, TB20, DA40)

Tough I would never land/launch when rain arrives, wind change/gusts are not worth taking the risk when cold rain reaches the hot ground, I will wait for 10min or get there 10min before

Forward visibility is not great even if nice “VMC is foretasted” but looking left/bottom down the wing strut or side-slipping will give a nice view (I make sure left ventilation before side slipping , PT heat ON, Carburetor Hot all time)

Last Edited by Ibra at 18 Jun 13:17
ESSEX, United Kingdom

There are many stories about the uncertified Lancair wings suffering badly in rain.

I have no idea if these are true or how true they are, but obviously if you are flying “with your back to the wall” then any loss of lift could push you over the edge. How exactly you could get pushed over the edge at the relatively low altitudes in which rain is likely to be encountered (other than freezing rain in which case the game is going to over very fast especially with these types) is hard to see; in normal cruise obviously not because you have a good speed, low AoA (around 2.5 degrees) and loads of spare power. But if your stall speed goes up with a wet wing then a pilot who doesn’t know this could crash it during departure or arrival.

Worse than rain is likely to be icing, which is also likely to happen at high altitudes when you potentially don’t have spare power. Of course, in Europe, virtually all of these types cannot fly in IMC legally…

You do need door and window seals to be perfect in flying in the rain, because 100+kt airflow will force water in everywhere it can. Some years ago I spent ages chasing a little crack at the top of the front window in the original PR1422 seal which turned out to be a bastard to fix. Sikaflex 295 did it…

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

There are many stories about the uncertified Lancair wings suffering badly in rain.

Yes, I think they mean slow speed performance such stall speed increase or low climb rates at slow speeds

Any claims on cruise speed decreasing in rain is pure IMC hallucinations or genuine erratic ASI reading, bad mixture/engine setting, DA increase from rain

At slow speeds water sticks to wings and push laminar air flow to separate earlier, so there is no way to get speed increase on take-off/climb without loosing climb rate but once water flow along the wing as does the air it should be no issue, I don’t think we notice much of that while cruising with cars

Solid water is a different story, but I guess some FIKI aircrafts have the same concept of “high penetration ice speed/power setting”, tough you can’t clean much of ice by going faster once it is formed so stall speed catches you quickly…

Last Edited by Ibra at 19 Jun 20:10
ESSEX, United Kingdom

Some of the second generation glass gliders e.g. LS3 are well known to be affected by rain at cruise or climb speed.

Last Edited by Xtophe at 19 Jun 20:55
Nympsfield, United Kingdom
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