Re: Wing Icing?


On Feb 16, 1:51 am, Peter Skelton <skelt...@xxxxxxxxx> wrote:
On Sat, 14 Feb 2009 23:56:28 -0800 (PST), Eunometic



<eunome...@xxxxxxxxxxxx> wrote:
SNIP
Sounds like a repeat of the American Eagle Accident ATR-72
http://en.wikipedia.org/wiki/American_Eagle_Flight_4184

and another good reason not to go on a scheduled turboprop flight
in colder climates. Shitty little things really, In Australia Qantas
has gotten rid of them for fear of damaging their reputation for safety.

As far as your idea that the engine exahust could be used to supply
molten wax. I recall a Do 228 testbed several years ago that had
laminar flow wings that had a continuously secreting substance
designed to keep with wing clear of bugs and ice in order to maintain
laminarity.

I think its baloney that the excuse that turbo props don't have enough
power to keep their wings properly de-iced. What they are saying is that
they
want to maintain their 20-30% fuel advantage over jets by skimping on
de-icing.

<s>

A little research will cure your ignorance.

I've often noticed that what knowledge you do have is undone by over
confidence and resulting ignorance. Too bad for you.



More generally folks, the idea that turbo-prop or even piston
aircraft are more vulnerable to icing than jets doesn't hold
water (or ice). The vulnerability goes more with size, then with
wing design. Arrow was a DC-8 IIRC.

Well, there you go helping to contradict yourself by saying large
aircraft aren't as vulnerable by quoting a DC8 incident since the DC-8
is a rather large aircraft.

Here is a couple of pointers on icing for you that have nothing to do
with size of the aircraft.

Jets often do not bother with tailplane de-icing. The all moving
stabiliser is just to powerful to require it and the speed and
altitude of a jet means that it probably isn't exposed as often.

De-icing equipment was in fact often disconnected from the B-707
tailplane as superfluous.

All moving tailplanes are quite hard to achieve in prop aircraft as
the prop slipstream tends to cause fatigue or flutter in the tail and
putting it into a T removes some of the STOL advantages due to
difficulty in rotating.

The all jet Bombadier CRJ 700 and CRJ900 have hot bleed air de-icing
of the leading edges and engine inlets but apparently nothing for the
tailplane. Bombadier Dash 8-Q400 which carries the same number of
passengers and is about the same size and weight as the above jets has
inflatable boots all around including the tailplane.

The PW150A turboprop engine of the Dash 8-Q400 has a mass flow rate of
14.5kg/sec.
The CJ34-8 of the similarly sized CRJ700 & 900 series has a mass flow
rate of 200kg/sec, with a BPR of 5:1 to 6:1 that means 40kg/sec
through the core.

In other words the core engine of a similarly sized jet has two to
three times the mass flow rate and around twice the thermal power as
the equivalent turboprop. That means plenty of reserve power for de-
icing.
ftp://ftp.rta.nato.int/PubFullText/RTO/MP/RTO-MP-008/$MP-008-04.pdf


The Jet has to have almost twice as much engine core power than a
turboprop in order to travel 1.5 times as fast but it doesn't consume
twice as much fuel because its higher speeds mean less fuel burn.
The upside of the extra power is plenty of bleed air for de-icing.

Since the CRJ-700/900 are the same size as the DASH 8-Q400 yet the
latter must use extensive mechanical dicing boots over wings and
tailplane whereas the former doesn't even seem to bother with
stabilator de-icing suggests that turboprops are more prone than jets,
irrespective of size.

C-130 use hot air de-icing, turning the de-icing system on bleeds of a
very noticeable amount of power and that in a handsomely powered
aircraft.

A lot of facts are screaming that turboprops are not only more
vulnerable to icing due to their lower speed and operating altitude
and some other design features but also that due to lower thermal and
mass flow power levels are less capable of implementing powerful de-
icing techniques.

If there are ‘size issues’ they are not dominant and predominantly
hypothetical. Maybe your up to arguing your point, maybe not. A
large wing might be effected more by equivalent surface roughness from
icing since boundary layer turbulence and separation will be over a
proportionately more chord.

So rather than develop and deploy alternative de-icing systems that
work in more extreme conditions the industry makes do with de-icing
boots that in their extended form (as increased on the ATR-72 after
its accident) can clear at most 12.5% of chord back from the leading
edge even after it has been shown by tests conducted as a result of
the American Eagle ATR-72 crash (flying a ATR-72 in formation behind a
'spray tanker') that disruptive formations of ice form at 23% of
chord where the boots can't reach.

What we are left with is recommendations for pilots to avoid certain
conditions rather than an implementation of new but simple de-icing
technology that would actually work in wider extremes that have now
killed several passenger loads of aircraft and will continue to so
when an aircraft stumbles into those systems. Systems such as ice
warning sensors, electrical resistive heating or mechanical vibrators
that tap the upper surface of the wing to dislodge ice or secretion of
polyethylene glycol (a conditioner and shampoo additive) we see no
action. Part of that motivation to inaction is to keep the running
and purchase cost gap between Jets and Turboprops as wide as possible
and to do that they skimp on de-icing while telling us how safe the
airline industry supposedly.

The industry sucks like any other because it deals with the same
sleazy human psychology. McDonnel Douglass produced a shit aircraft
with faulty outward loading cargo doors that could open in mid flight
and no electrical or mechanical backup for the tailplane hydraulics
nor armouring for the hydraulics. Other companies did provide all of
those things. Some companies seem to think deicing boots are adequate
as well.


.

Relevant Pages

  • Re: Cant De-Icing Fluid be Used?
    ... > retention of the de-icing fluid? ... > The de-icing only needs to remain effective for a couple of minutes after ... > blast off, no more time and probably less than terrestrial aircraft, so ... > chemical de-icing as an effective solution to the icing problem? ...
    (sci.space.shuttle)
  • Cant De-Icing Fluid be Used?
    ... retention of the de-icing fluid? ... The de-icing only needs to remain effective for a couple of minutes after ... blast off, no more time and probably less than terrestrial aircraft, so ... chemical de-icing as an effective solution to the icing problem? ...
    (sci.space.shuttle)
  • Re: Wing De-Icing Question
    ... I guess de-icing is going to be a popular subject. ... is there any in-flight deicing system for the wing and tail ... How in general is wing de-icing accomplished on these new, modern jets ...
    (rec.aviation.piloting)