They say that propeller can be damaged if it hits a lot of water on the ground. Really? How can you fly in the rain then? Should one avoid flying in the rain? Or turn the rpm down when flying in the rain? Lets say we are talking about a fixed pitch metal prop which can turn 2700 rpm. Or some other prop.
We have two planes with wooden propellers in my club, and there we try to avoid flying in the rain in order not to damage them. But I’ve never heard this about metal propellers.
What I’ve had is on one C172 with a metal fixed pitch prop, whenever you fly through even just drizzle, there is a humming or whining noise. Don’t know why that is.
I would really like some evidence for this. Some discard the problem as nonsense, while others point out that erosion is quite natural when repeatedly hitting solid water (i.e. drops) at Mach 0,6 to 0,7.
Our motorglider has a composite prop, and our SOP is to avoid rain in the first place, for several reasons, but if flying in rain, then limit RPM (preferably use the coarse cruise pitch propeller setting).
It is a little like discussing shock cooling – of course it could be a problem, but is it really?
Did you know that the opposite causes damage to propellers as well?
huv wrote:
I would really like some evidence for this– granted, just take my word for it, I had damaged composite propeller prototype tips years ago. The manufacturer didn´t think it was necessary to have leading edge protected by “tape” all the way till the tips. After flying through moderate rain for few minutes I have both tips near to delamination….I was lucky I didn´t know that….
They say that propeller can be damaged if it hits a lot of water on the ground
At max rpm the blade tips are not that far short of mach 1, and liquid water is then like concrete. It’s density is only half an order of magnitude less than steel, after all. That’s why the prop blades of e.g. WW2 planes which ditched under power are seriously bent.
Interesting stuff about rain damage though.
I used to live in Vancouver where it rains all the time and various pilots I know would respond to the rain commensurate with their respect for the prop.
A brand new aerobatic airplane with a composite prop… slow down immediately and try to get out of the rain!
A 50 year old Cherokee with an old metal prop… why bother slowing? Presuming you are in cruise and not at full rpm – there is no need to thrash it unnecessarily.
The prop on a floatplane I used to own had a rough life. The spray off the floats can hit the prop when taking off and landing and the tips get eroded and look pretty ugly. Hence the need to be dress the prop occasionally.
Can some mathematician here tell us who fast the tips of a typical McCauley prop are travelling at 2700rpm ?
Must have something to do with Pi, and I don’t have the length of the blades handy right now
EuroFlyer wrote:
Can some mathematician here tell us who fast the tips of a typical McCauley prop are travelling at 2700rpm ?
“l” being the length of the blades and “s” the time unit second, it is: l*90*π/s. E.g. if the blade is 80cm, then the answer is 226.2m/s:
.8m * 90 * 3.1416/s = 226.2 m/s
Euroflyer:
For a 76-inch prop, it would be 76 × 25.4/1000 × π × 2700 / 60 ≈ 273 m/s, or M0.80 at sea level in ISA.
