Short answer:
Yes, I have flown through light rain fairly often in the Europa.
I flew with a client with a dusty dirty aircraft to do a "jiffy wash" throu
gh the local stable air rain showers to clean off the grime. Vis was a bit
below 3 miles so heavier than we should have flown through.
In slow flight, one can see quite clearly (because of the dirty water) the
laminar to turbulent transition and then as the stall is approached the sep
aration point during slow flight and the affect on stall speed is slight bu
t noticeable. The drag is clearly increased. Air was smooth.
The cruise speed difference is about the same as flight with grime on the w
ings. (The splash of water hitting the wing tends to add a surface roughne
ss affect and the waves of water disturbs the laminar flow leading to a sta
ndard roughness effect on the airfoil which normally increases cruise drag
and decreases the stalling angle slightly. See "The Theory of Wing Section
s" as an easy way to see the effect in a wind tunnel or the papers referenc
ed below.)
For a well polished wing the rain creates a splash which is similar to stan
dard roughness. That does increase the stall speed slightly in a high camb
er airfoil (Motor Glider) and is slight in a more symmetric airfoil (XS sho
rt wing). The stall warning characteristics clean or dirty in my brief enc
ounters did not seem to change significantly. However, in heavy rain, rese
arch indicates that the stall is affected by the sheets of water over any w
ing. Stall characteristics in heavy rain would be difficult to flight eval
uate in my opinion. Normal techniques for turbulence penetration should be
considered, that is slow down to Va. Commercial aircraft equipped with bo
undary layer control, slats, flaps and other high lift devices are affected
differently by rain than say a GA aircraft.
What is noticeable is the down draft under a rain cloud as the rain drags a
ir along with it downward creating a downdraft that in a rear tail (CG forw
ard of the Center of Pressure) aircraft creates turbulence and pitch change
s in some aircraft. The tail in a downdraft normally increases its downfor
ce compensating for the loss of wing angle of attack and the pilot just fee
ls the bumpy air. Canards are affected differently as the lifting canard l
oses lift along with the wing and a noticeable nose down pitch occurs.
Longer Answers:
There was much work done in the late 80's on downdrafts, microburst, and op
erations in rain by many different government and research agencies. Opera
tionally in an aft tail aft aircraft like the Europa, in rain squalls, I ad
d 5 knots (65 vs 60 or half the gust factor) for simple rain from cumulous
clouds which normally occurs with shifty winds of anywhere from 5-10 knots
anyway. Vis is not a major problem in the Europa with a polished windscree
n, it is the downdraft and turbulence issue I'm concerned about as a pilot.
I have always avoided heavy rain in approach and landings in GA aircraft
as they don=92t have the mass to penetrate and can=92t climb or accelerate
as well as higher performance aircraft. In flight, I have flown through he
avy rain once as a demonstration for my wife to satisfy her query of why we
don=92t fly through small cumulous buildups that look pretty. It was grea
t, clear smooth air approaching the vertical column and then, instant turbu
lence, blinding heavy rain, and poof clear air again. Her comment was =93W
e don=92t need to do that again=94. I do not land in heavy rain as it is n
ot worth the potential landing mishap in a GA aircraft due to squirrely win
ds, downdrafts and lateral gusts. I have plenty of divert strips in my are
a. Unfortunately, operationally in the military I had to land in heavy rai
n a couple of times. The F4 just plowed through it as it was not microburs
t rain. I lost a good friend who was caught approaching the final approach
fix at night in his F106 when he hit a microburst. The central air data c
omputer went out, and the rate of sink was greater than full afterburner.
He hit the trees on a hilltop just beyond the final approach fix in a full
nose up attitude.
Since I have a turbo, rain ingestion is not an issue for me. However, a 91
2ULS may see slight engine performance differences and the extra moisture i
n the area of carb icing conditions, should be considered. (Not to spark a
new thread, carb heat for the 912ULS in the stock Europa XS is not a bad i
dea and should be considered seriously.)
For those who care to research:
I suggest a simple google search on "Effects of rain on stall speeds of air
craft" and read many of the fine papers done on the subject. Aerodynamicis
t's Hansma and Craig did a lot of work in the late 80s. If you recall, ther
e were a number of accidents due to microburst rain downpours and interest
peaked in that time frame. Recently, I read a paper done in 2016 by a Chin
ese student (Wu?) on his Doctorate out of Beijing University of Aeronautics
. A very good research paper summarizing the issues and affects of rain on
an airfoil with many references. Also, the US Transportation Department i
n the 80s did a number of grants resulting in papers that are also quite go
od. See Airfoil Performance in Heavy Rain: Transportation Research Record
No. 1428 - Public-Sector Aviation Issues Graduate Research Award Papers 199
2-1993 (trb.org)<https://onlinepubs.trb.org/Onlinepubs/trr/1994/1428/1428-0
04.pdf> for one example. One thing I was surprised at was the low camber
laminar flow airfoil normally has a sharp stall break but in rain actually
smoothed the stall break allowing a smoother transition to the stall and in
to the deep stall. However, the high camber laminar flow airfoils were aff
ected more in drag and early transition of the laminar flow to turbulent fl
ow was significant. (Note that turbulent boundary layer is not a separated
or stalled flow.) Many of these papers show the results on the airfoil al
one and I was disappointed in that the plain or simple Fowler flap lift cur
ve changes were not discussed. I didn't see much in actual in-flight testi
ng of different aircraft. Just accident results.
Just my observations,
Bud Yerly
-----Original Message-----
From: owner-europa-list-server@matronics.com <owner-europa-list-server@matr
onics.com> On Behalf Of Area-51
Sent: Friday, October 22, 2021 4:42 AM
Subject: Europa-List: Flying In Rain
<mailto:goldsteinindustrial@gmail.com>>
Has anyone got an experience they=99d like to share regarding flying
the europa through either showers or very light rain and how these conditio
ns may affect the aircraft=99s performance? For example a Schrieb Mot
orfalk=99s stall speed is raised 5kt if water droplets collect across
the wing=99s surface during light rain...
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