Rain Mooney

[201er]

I have heard that rain dramatically reduces performance on laminar airfoils and far more so than on conventional ones. Someone else (who doesn't fly Mooney) told me that's BS. I have never flown Mooney in rain and would like to know what to expect. How much does rain affect performance and what do you do about it?

[GeorgePerry]

There is a slight reduction in indicated airspeed.  Depending on the intensity of the rain and the type of mooney you might see a few knots slower than what you're used to until the wings dry off.

[Hank]

It can get loud inside when the rain is heavy, too. Either way, if it's more than a mist, your plane will emerge cleaner than before. I've never paid attention to the AI, focusing on course, altitude and attitude. If there is no convective activity nearby, the worries are fewer, but this time of year the problem changes to icing. Stay on course, pointy end forward, greasy side down. As my instructors have all told me, the plane doesn't know it's raining.

On Sunday, I caught a Bonanza on pattern entry and made a quick circle for spacing, 20-25º bank [he dropped his gear early as a speed brake, I made a power-on descent and couldn't see his gear go down when he was below me, but he quickly got big in the windshield]; I was visual out the side window and my wife commented that we had rain on the windshield. Just a few scattered drops, neither the plane nor I noticed.

[jetdriven]

I reqd somewhere that laminar flow airfoils do in fact lose speed in rain. It can't be laminar flow if water is running over it.  My wife thinks that is bunk.  The figure I heard was 3 KIAS on a Mooney. I know a guy with a 200+ KT Long EZ and he swears its more like 7 KIAS on his.

[201er]

Ok, cause I heard for gliders it makes a tremendous difference and is very noticeable between regular and laminar airfoils. That a 40:1 glider can turn into 20:1 in rain while an already 20:1 regular stays around the same with little loss. So from what I'm reading here, maybe there is or isn't a tiny barely noticeable loss. Good to know it's nothing like icing. While we're at it, what kind of performance loss you notice with varying levels of icing?

[bnicolette]

Quote: 201er

While we're at it, what kind of performance loss you notice with varying levels of icing?

[KSMooniac]

Mooneys do slow down in the rain, up to a few knots depending on the intensity.  If you're doing a max-performance XC flight it might be something to consider if flying in widespread rain, but most times it is nothing to worry about.

[201er]

What about damage to paint, glass, etc? Rain horizontal speed: 0, Mooney horizontal speed: 180+mph...

[carusoam]

201er,

Rain impact probably isn't good for paint.

Ice definitely is not.

Best regards,

-a-

[KSMooniac]

Rain will definitely erode paint if there is an exposed edge, and especially if there is poor prep on the paint.  If you get a chip on a leading edge. it is a good idea to sand it smooth and touch it up, because if you can feel any thickness at the chip you can bet rain will make it start to peel.  

I had some issues like that after my repaint, but got it fixed under warranty.  The second time it failed, they ran a bead of fuel sealant around the exposed edge of my windscreen and I believe that is a permanent solution that looks fine.  

[eldeano]

Living in the Pacific Northwest, I've found that the rain slows down all airplanes, not just laminer flow wings.  As for the paint, no one here uses wax, because the rain just strips it off.  At Kenmore Air our planes are subjected to rain, spray and saltwater. We use rejex, a polymer based coating that has drastically reduced our corrosion issues.

But back to the original post, our caravans, beavers and otters all slow down a few knots in the rain as does my Mooney.

[Vref]

On my previous aircraft a 17meter  Hi performance motorglider with flaperons you loose 20 Kts when at 7000 Ft flying WOT flying through a rain shower. I had the experience over the mountains...brbrrrrr.....Doing 105 Kts and went all back to 75 Kts to maintain altitude when the wings are wet. In gliding competitions this is a very well known phenomea. Rain destroys your laminar flow....I suspect the effect on a mooney is less then 10 Kts...Could influence the stall speed in clean config, I figure....? In a glider the angle of attack plays a huge diffrence on how fast the rain repells back on the wing, specially when you have flaps negative for speed......

[Becca]

Quote: jetdriven

I reqd somewhere that laminar flow airfoils do in fact lose speed in rain. It can't be laminar flow if water is running over it.  My wife thinks that is bunk.  The figure I heard was 3 KIAS on a Mooney. I know a guy with a 200+ KT Long EZ and he swears its more like 7 KIAS on his.

[mikefox]

Rain will definitely have an effect.  It can even be calculated.  The aircraft, when flying through rain, accelerates the rain up to the speed of the aircraft (or less, depending) for the rain which strikes the aircraft surfaces or is affected by them through viscous effects.  The details get complicated, as the angle the rain strikes the surface, and whether it "wets" to the surface or "bounces" off is important.

But the principle is one of momentum flux.  The momentum added to the water per unit time is equal to the force on the aircraft (drag) by Newton's laws.  So it matters how hard it is raining.  It also matters what the droplet size distribution is, since this affects how the water impacts the aircraft and the subsequent change in momentum of the water droplets.

[jetdriven]

I was thinking that the laminar flow gets interrrupted by the rain at the leading edge instead of at 30% of MAC. This effectively robs the laminar flow airfoil of the laminar flow.

 

here is some reading from those crazy folks at NASA   cafefoundation.org/v2/pdf.../AGP.NASA.NLF.Holmes.Varieze.pdf

 

[N513ZM]

Quote: 201er

While we're at it, what kind of performance loss you notice with varying levels of icing?

[Vref]

A modern glider with wet wings becomes a flying brick, so I gues it must have an influence on the mooney also as it is a laminar flow airfoil. With laminar flow wings it's the point where the laminar air starts to loosen which is changed significatly thus having an significant effect on the L/D curve (On a Cessna wing it's less of a problem as the wing is dirty from itself...)...One of the reasons I always clean my aircraft in summer...the bugs screws up your laminar flow also...but maybe I am biased having flwon too much gliders with a 1/40+ L/D curve.....In modern gliding competetions you can do In Flight Bug cleaning mayeb we should install something like that on mooney..

http://www.dg-flugzeugbau.de/mueckenputzer-e.html

[carusoam]

Luc,

That is spectacular!  A system designed to allow flight into known Bugs!

FIKB

Best regards,

-a-

[231flyer]

I haven't noticed much of a diference with rain.  Its a spam-can so it can get loud but I agree with earlier posts of ~5Knots max effect.  I flew gliders as a kid and we were specifically prohibited from flying in the rain (old metal Schweitzers not the sleek modern stuff).  

Unfortunately I have a lot of expereince with icing in a non-FIKI 231 and can attest to the absolute aweful flying qualities.  At 1/4" on the wings the elevator will show almost 1" build up, the Mooney will shed 15 knots easy.  At 1" on the wings the elevator control authority is greatly compromised and maintaining 120 knots is a challenge.  I have had to declare an emergency over Springfield CO and land on the snow covered runway.  Ice was not forecast at the altitude but things started going bad as I left BJC.  I managed to accumulate more than 11/2" on the wings and nothing I did (climb/decend etc) would get me out and ATC was equally clueless.  The airplane lteterally started to sing and I could barely muster 90 knots when I declared.  Springfield was 5 miles futher than Trinidad (CO) but in the plains and both were MVFR so I elected the former.  The runway was covered but GPS and my charts confirmed it was parallel to the road so I lined up and spotted the hangars at 100 ft.  I kept full power to touchdown and it wasn't pretty.  The elevators were so loaded that large chunks broke off from the jarred landing. MOONEYs dont like ICE.  I fly my Malibu Mirage if ice is even a possibility.

[jetdriven]

If the temperature aloft is forecast to be between 5C and -40C in visible moisture, thats icing conditions.  I don't get it why someone would fly a non-deiced airplane in that.

[231flyer]

Occasionally forecast conditions don't match actual.  When that happens (a down-slope in my case above) evasive action is indicated.  Else we would be waiting for perfect blue sky days (fortunately 300+/yr in Colorado).  I defintely had the get-there-itis; it was my daughter's first xmas eve and I was desperately trying to get home from a skiing trip with my college buddies.

In any case it is best to evade icing conditions even in a FIKI equipped a/c like my Malibu Mirage.  

[jetdriven]

Still if you are flying in clouds between 0 and -40C, you are techincally "in" known icing conditions.

from: http://www.ifr-magazine.com/defining_known_ice_certification_faa_ifr.html

(What do you think)

In explaining their definition of known ice, Loretta E. Alkalay, FAA Regional Counsel, referenced Administrator v. Curtis, NTSB Order No. EA-5154 (April 29, 2005). Here, the court ruled that conditions conducive to icing exists whenever near- or below-freezing temperatures and moisture exist together in a given area. It didn't matter that there were no reports or forecasts of icing conditions at any altitude anywhere near the route of flight.

The Regional Counsel's office also referenced Administrator v. Groszer, NTSB Order No. EA-3770 (January 5, 1993), which ruled that the threat of ice need not cover the entire area at all altitudes for the threat to be known or dangerous.

In short, the FAA defines known ice as any visible moisture (cloud or limiting visibility due to moisture) with temperatures at or near freezing. If you go there in a non-known-ice-certified aircraft, you are in violation. Period.

...................

The Regional Counsel's letter to me clarified the definition of known ice. You cannot legally fly a non-known-ice-certified airplane into any cloud near or below zero degrees C or you are in violation. If the FAA learns, either by direct observation or via a filed complaint, that a non-known-ice-certified aircraft entered a freezing cloud, it will initiate the EDT process and an enforcement may, or may not, result.

[231flyer]

"MOONEYs dont like ICE.  I fly my Malibu Mirage if ice is even a possibility."

[bnicolette]

For example, if a safety-conscious pilot, who actively participates in the WINGS program, elects to slither down through a narrow sub-freezing cloud with good VFR below, without adverse consequences, likely no enforcement action will result, even if a complaint is filed. (This, by the way, is one very good reason to have documented participation in the WINGS program.)

 

Phew!!!     I just can't imagine parking my airplane from November thru March!

[jetdriven]

That is assuming that you could maintain VMC conditions on top for the whole flight, there is no icing in the clouds on the way down, and that suitable minimums exist to land below.  Thats is a lot of "if's".