Primarily for general aviation discussion, but other aviation topics are also welcome.
#1817585
Looks like a good decision to me..... too many "holes in the cheese" is a good analogy.

Does this type of aircraft typically have a laminar flow wing section ? Those ice "bubbles" would have a major effect on most modern sailplane wings.....
JAFO, Nick liked this
By PA28
#1817606
It does have a laminar flow wing, the reason why it cruises at 160 kts and max level 178kts. The downside is the landing when it floats in ground effect and then abruptly stops flying with little notice. There are stall breaker strips on the leading to create some natural buffet at the stall. Vortex generators fitted to the outer wing section greatly improve the slow speed handling.
The designer did a great job creating low drag engine nacelles on an already really efficient airframe. When fitted with the optional tip tanks gives it a 7 hrs endurance at 150kts.
This particular aeroplane is the PA39 which is the most sought after of the Twin Comanches. It has the counter rotating engines.
ls8pilot, A le Ron liked this
By PA28
#1817615
The roof trimmer is fitted to the PA22, PA24, early PA28s and the PA30 and PA39. Don't know about PA23. It must have been replaced in the 1970s. I sometimes fly a PA28-160 that has the roof trimmer but the later Warriors don't.
I always find myself winding them the wrong way at first.
Luckily mine also has the electric trim.
By TopCat
#1817640
Bit late to the thread, but I'd say it was clearly the right decision. The temperature was dropping rapidly enough for the runway to start icing up and droplets of water on the wing to freeze, and as has been said, with the temperature approaching the dewpoint, goodness only knows what the visibility might have been like an hour later. Icy aircraft and runway, potentially poor vis, dark soon... I'm really not fancying it.

On another note, a question.

If frozen drops of water are bad for lift, why are liquid drops not also bad for lift if they don't run off? Because they don't always, and often if they partially do, they leave trails of smaller droplets behind that stick even more to the wing.

I realise that for takeoff, it's premature departure of the airflow over the leading edge that is most critical, but I've always felt a little uneasy when the wing is wet. I've never read anything to suggest different takeoff performance with a wet wing, though, only an icy one.

What's the obvious thing I'm missing?
By PA28
#1817647
Wings covered in ice are really bad. As any glider pilot will tell you a wet wing reduces performance. Glider wings are a perfect smooth surface to get the least amount of drag. They mostly use laminar flow aerofoil sections which don't perform well when wet or covered in flies. Most GA aircraft are covered in rivets and aerials so not as critical. When you observed water flowing back and then stagnating this is due to flow separating at that point roughly 60% chord. Some aircraft have the leading edge skins flush riveted back to the spar and normal dome head rivets behind the spar where the flow has separated and the surface finish is less important.
#1817652
TopCat wrote:Bit late to the thread, but I'd say it was clearly the right decision. The temperature was dropping rapidly enough for the runway to start icing up and droplets of water on the wing to freeze, and as has been said, with the temperature approaching the dewpoint, goodness only knows what the visibility might have been like an hour later. Icy aircraft and runway, potentially poor vis, dark soon... I'm really not fancying it.

On another note, a question.

If frozen drops of water are bad for lift, why are liquid drops not also bad for lift if they don't run off? Because they don't always, and often if they partially do, they leave trails of smaller droplets behind that stick even more to the wing.

I realise that for takeoff, it's premature departure of the airflow over the leading edge that is most critical, but I've always felt a little uneasy when the wing is wet. I've never read anything to suggest different takeoff performance with a wet wing, though, only an icy one.

What's the obvious thing I'm missing?


Wet wings are bad - it's just that iced-up wings are even worse. It shows up most (as @PA28 says) on modern laminar flow glider wings. A wet wing increases stall speed and can dramatically increase drag - an iced up wing even more. To give an example I once got a glider iced up in a cloud climb, when I emerged at 4000ft AGL I could'nt even make it to a nearby gliding club 7 miles away whereas with dry wings in that glider I would expect to be able to glide 20 miles and still have a 1000ft left for a circuit.

Some older (Wortman) wing sections are particularly bad - more modern sections have a degree of tolerance. On the worst types (eg DG200 or PIK20) you may need to to add 20% to your approach speed with wet wings and your achieved glide angle will be around half what it should be (I used to own a DG200 and a light shower put me into a field on several occasions).

We normally would not even try and launch a modern glider with wet wings & definitely not with iced up ones. By contrast older (wooden winged) machines are pretty tolerant of wet wings - their wing sections are non-laminar or limited laminar.

So you need to understand the wing section of what you are flying, highly laminar flow section + contaminated surface can produce all sorts effects at low speed, whereas a non-laminar wing might be quite benign. So you are right to be cautious taking off or landing with wet wings
PA28, T6Harvard liked this
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By ls8pilot
#1817657
Following on from the above - I assume with a twin and wet wings the flow from the props as you accelerate will clear the water drops off the leading edges pretty well so making wet wings less of an issue ?