Why are modern jet tails not de-iced(in flight)?
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Not just for 'modern' jets, either.
The L1011, for example, has no tail anti-icing.
Altho the B707 was so equipped, it was allowed to be disconnected on later models, as additional flight testing showed that tail anti-icing was not required.
The L1011, for example, has no tail anti-icing.
Altho the B707 was so equipped, it was allowed to be disconnected on later models, as additional flight testing showed that tail anti-icing was not required.
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Ram Rise
It's been awhile, so I stand to be corrected.
Ram Rise - will raise the static air temperature by about 10C when over 250kias. Since most icing happens between 0C to -20C this will raise the temp out of the icing range for a SAT down to -10.
Here's an old thread that covered the topic of ice collection efficiency:
http://www.pprune.org/archive/index.php/t-175794.html
Cheers,
FTP
Ram Rise - will raise the static air temperature by about 10C when over 250kias. Since most icing happens between 0C to -20C this will raise the temp out of the icing range for a SAT down to -10.
Here's an old thread that covered the topic of ice collection efficiency:
http://www.pprune.org/archive/index.php/t-175794.html
Cheers,
FTP
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Boeing is very adept at designing in huge stall margins on the stabilizer. Sadly, Douglas thought they could with the DC9 but discovered late in the program that their tail was a bit small. Hence the add-on, "either or" deicing system. Most subsequent manufacturers have followed Boeing's design philosophy.
No evidence whatsover of tail stall issues with any large jet...except the DC9/MD80. Turboprops are another story, except those designed after the new cert requirements for the pushover maneuver (like the Q400). Pretty much everyone else has had an issue at one time or another, including Saab and ATR. Of course, then there is the Viscount, YS-11, Jetstream, and, believe it or not, even the Piper Cherokee. It isn't icing certificated, of course, but it has demonstrated a propensity to bury the nose on landing with a bit of ice on the tail.
No evidence whatsover of tail stall issues with any large jet...except the DC9/MD80. Turboprops are another story, except those designed after the new cert requirements for the pushover maneuver (like the Q400). Pretty much everyone else has had an issue at one time or another, including Saab and ATR. Of course, then there is the Viscount, YS-11, Jetstream, and, believe it or not, even the Piper Cherokee. It isn't icing certificated, of course, but it has demonstrated a propensity to bury the nose on landing with a bit of ice on the tail.
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De-icing in flight?
But they are, they are!
What do you suppose all those long white streaks of, well, stuff, are that follow aircraft across the sky?
We all know the Governments tell as that it's water vapour when everyone knows the atmosphere is totally dry up there.
It's the chemicals they use to stop us thinking; the con that aircraft tails are not deiced is all part of the Great Plan that They've been running for years to bamboozle us into chemically fuddled submission.
Read the Truth on the Chemtrails website, and be amazed!
After all that, mere de-icing seems a bit pointless...
But they are, they are!
What do you suppose all those long white streaks of, well, stuff, are that follow aircraft across the sky?
We all know the Governments tell as that it's water vapour when everyone knows the atmosphere is totally dry up there.
It's the chemicals they use to stop us thinking; the con that aircraft tails are not deiced is all part of the Great Plan that They've been running for years to bamboozle us into chemically fuddled submission.
Read the Truth on the Chemtrails website, and be amazed!
After all that, mere de-icing seems a bit pointless...
Last edited by Agaricus bisporus; 26th Feb 2010 at 18:50.
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Some a/cs have very little anti or de-icing in the wing itself to begin with. The A380 only has one slat on each side of the wing with ice protection. Other than that, there is no ice protection along the entire LE of the wing. The A330 only has anti-ice for four slats on the outboard side only.
The C-5 has no LE anti-ice on the wings or tail, only engine anti-ice. I've flown many times in what should have been icing conditions and made only slightest amount of ice. I flew the Citation in the NE US for 4 years and 2800 hours and rarely used the boots.
Jets seem to have less problems with airframe ice than turboprops/piston aircraft. I think ram rise helps, abundance of power helps--fast climbs and descents thru likeliest icing conditions. Flew Aztecs and Barons in the same areas and nearly got "shotdown" in ice several times--I respect it from experience.
On the ground, different story--clean wing or off to hotel.
GF
Jets seem to have less problems with airframe ice than turboprops/piston aircraft. I think ram rise helps, abundance of power helps--fast climbs and descents thru likeliest icing conditions. Flew Aztecs and Barons in the same areas and nearly got "shotdown" in ice several times--I respect it from experience.
On the ground, different story--clean wing or off to hotel.
GF
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The most significant factor in this issue is scale. The simple term that is used in the engineering work is called k/C, or a non-dimensional roughness parameter. "K" is the measured height, perpendicular to the airfoil surface, of the ice shape. "C" is the chord length. This term is has a major role in the aerodynamics of the contaminated wing.
Any given icing environment will yield a range of ice shape dimensions and features. However, it is more or less intuitive that a C-5 passing through Cloud X will encounter the same droplet size, liquid water content and droplet distribution that a Citation will encounter in Cloud X. The C-5 will accrete quite a bit more mass, due to the area swept by the wing, but the nature of the ice shape is unlikely to be greater in measured height than the shape found on the Citation.
Therefore, the "k" term will be somewhat comparable, for the sake of the argument at least. There are other factors at play, but they can be set aside for the moment. If the "k" term is the same, but the "C' term is so radically different...well, you get the idea. The k/C ration for the Citation is much, much larger than the k/C for the C-5.
The C-5 will also push a lot more droplets just plain out of the way, due to the wing size and the pressure wave ahead of it. Smaller airfoils arrive at the cloud with less "warning" to the droplets, and more are accreted. This is why the tail often ices when the wing doesn't.
Thus, no C-5's or 747's dropping out of the sky. Those of us in this part of the business have contemplated for years the possibility of an engineering standard reflecting scale, but we just don't know enough to really define one. Instead, the manufacturer works this out on a case-by-case basis. Airbus knew they wouldn't need much protection, so they designed accordingly and were easily able to certificate that design.
Unfortunately, many, many pilots live under the impression that their airplane can "handle" a lot of ice. As I have said in other threads, this is truly a myth. Trunov and others showed as far back as the seventies that only a few thousandths of an inch of roughness was required for substantial degradations. Douglas pointed this out in their many ground deicing cases as well...look up the work done by Ralph Brumby. In the icing accident database that I maintain for the FAA, the average ice accretion either found afterward or reported by the pilot is between one quarter and one half inch. Often, one eighth is sufficient...particularly for the Citation, by the way.
The problem is, you can't identify the critical parameters, such as horn angle, horn height, roughness, etc. from the cockpit. And you have no idea how close to the modified Cl max you are at any point. The only real solution is to get rid of the ice...which is where good, hot, thermal systems work best.
Any given icing environment will yield a range of ice shape dimensions and features. However, it is more or less intuitive that a C-5 passing through Cloud X will encounter the same droplet size, liquid water content and droplet distribution that a Citation will encounter in Cloud X. The C-5 will accrete quite a bit more mass, due to the area swept by the wing, but the nature of the ice shape is unlikely to be greater in measured height than the shape found on the Citation.
Therefore, the "k" term will be somewhat comparable, for the sake of the argument at least. There are other factors at play, but they can be set aside for the moment. If the "k" term is the same, but the "C' term is so radically different...well, you get the idea. The k/C ration for the Citation is much, much larger than the k/C for the C-5.
The C-5 will also push a lot more droplets just plain out of the way, due to the wing size and the pressure wave ahead of it. Smaller airfoils arrive at the cloud with less "warning" to the droplets, and more are accreted. This is why the tail often ices when the wing doesn't.
Thus, no C-5's or 747's dropping out of the sky. Those of us in this part of the business have contemplated for years the possibility of an engineering standard reflecting scale, but we just don't know enough to really define one. Instead, the manufacturer works this out on a case-by-case basis. Airbus knew they wouldn't need much protection, so they designed accordingly and were easily able to certificate that design.
Unfortunately, many, many pilots live under the impression that their airplane can "handle" a lot of ice. As I have said in other threads, this is truly a myth. Trunov and others showed as far back as the seventies that only a few thousandths of an inch of roughness was required for substantial degradations. Douglas pointed this out in their many ground deicing cases as well...look up the work done by Ralph Brumby. In the icing accident database that I maintain for the FAA, the average ice accretion either found afterward or reported by the pilot is between one quarter and one half inch. Often, one eighth is sufficient...particularly for the Citation, by the way.
The problem is, you can't identify the critical parameters, such as horn angle, horn height, roughness, etc. from the cockpit. And you have no idea how close to the modified Cl max you are at any point. The only real solution is to get rid of the ice...which is where good, hot, thermal systems work best.
Thus, no C-5's or 747's dropping out of the sky.
I did about 5,000 hours in the 747, never needed it nor do I know of anyone that's ever used it.
Bottums Up
I thought the Douglas/Boeing 717 was a modern jet. It has engine, airframe (main wing leading edge) and tail (stab leading edge) anti-ice, all bleed air fed.
T'other night, cruising about 2000' below the maximum permissible level with all the anti-ice on, at turbulence penetration speed of M0.75, we picked up a load of ice that had us sitting 20 kias below the set speed, with engines at max cruise. This lasted for a minute or so.
T'is a good ice accretor the 717.
T'other night, cruising about 2000' below the maximum permissible level with all the anti-ice on, at turbulence penetration speed of M0.75, we picked up a load of ice that had us sitting 20 kias below the set speed, with engines at max cruise. This lasted for a minute or so.
T'is a good ice accretor the 717.
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Mansfield.
I landed in Zurich about a year ago in my RJ-100 (Bae 146).
Damn it there were giant jaggy shapes jutting out from where the pylons met the wing.
I'm talking about 40-60 lbs of jaggy ice lumps sticking forward from the pylon/ wing junctions.
If one had sproinked off and landed on a pax it would have killed him dead.
Only a fuggin idiot would have taken off like that, but we landed like that!
I landed in Zurich about a year ago in my RJ-100 (Bae 146).
Damn it there were giant jaggy shapes jutting out from where the pylons met the wing.
I'm talking about 40-60 lbs of jaggy ice lumps sticking forward from the pylon/ wing junctions.
If one had sproinked off and landed on a pax it would have killed him dead.
Only a fuggin idiot would have taken off like that, but we landed like that!
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The Boeing 707 originally had de-icing on the vertical and horizontal stabilisers. It was a rubber boot with electric heating wires embedded in it, with an external protective covering of stainless steel.
It had a problem that a lightning strike on the leading edge would burn a hole through the stainless steel covering into the wires in the rubber boot and sever the heating wires. This then required that the whole leading edge had to be replaced.
Boeing did tests with 'mock up' ice forms on the tail leading edges and this proved that the requirement for tail de-icing was not needed.
It had a problem that a lightning strike on the leading edge would burn a hole through the stainless steel covering into the wires in the rubber boot and sever the heating wires. This then required that the whole leading edge had to be replaced.
Boeing did tests with 'mock up' ice forms on the tail leading edges and this proved that the requirement for tail de-icing was not needed.
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Interesting. So are those A380 and A330 wings just able to cope with ice accretion or do they have some other way of stopping the ice from building up too much?
The 747 is fitted with wing leading edge de-ice
The proper term is anti-ice. De-ice is used to describe devices that destroy ice formed on the wing surface like pneumatic boots
As said above, rarely needed: in 13 years on the 737-200 I recall only one occasion whe we got ice on the wings. Climbing out of Malaga over the Sierra Nevada (the original one, for you chaps West of 60W) we went through some lenticular cloud at about FL200 and the climb rate dropped to zero. The wing was visible from the flight deck, and a quick burst of wing anti-ice did de-ice it PDQ and the climb resumed. Later, on B757/767, I don't recall ever using the wing anti-ice.
FWIW