Tail icing
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All I can say is that after my experience with ice, I added ten to fifteen knots to the approach speed anytime wing de/anti-ice was needed on the 737s.
I could NEVER understand the Boeing idea. There they had this nice big heater right there in the tail [the APU] that they could've easily adapted, but chose not to to save a few bucks. Oh well................
I could NEVER understand the Boeing idea. There they had this nice big heater right there in the tail [the APU] that they could've easily adapted, but chose not to to save a few bucks. Oh well................
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With all due respect Sir, that's BS that was fed to you by Boeing probably.
Lockheed actually glued five inch typically shapped ice formations on the horizontal stab...and found no problems, whatsoever.
As in none.
Info directly from the guys that did the flight testing, at Lockheed.
737?
Can't say, never flew that small jet.
Large heavy jets are simply in another category, altogether.
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Large heavy jets are simply in another category, altogether
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The only section of the A380 wing that has Wing Anti-Ice is Slat #4 on each wing. ie. the middle slat of the three slats between the engines. (No Anti-Ice on the tail)
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Well, I consider "my" DC-8 a large heavy jet, and it was a real airplane
The B707, which is just as large/heavy...had none.
Even with the tail anti-icing deactivated, which was the norm with many operators.
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The May-June 1962 issue of Boeing's Airliner magazine details the deactivation and removal of the 707 stabilizer ice protection system. It is quite a classic read from an icing standpoint, reflecting a number of misconceptions about icing that have since been severely challenged, such as cloud vertical extent and droplet distributions, as well as the frequency of severe encounters. However, the key statement is that during testing with a representative three inch ice shape, no changes in control forces or stability were noted. This is the most important aspect, although they then devote a lot of verbiage to things like fuel consumption and landing climb weight limits due to limited thrust in some airplanes.
The only real threat from ice on the tailplane, and it is a big one, is tailplane stall during slightly higher speed approaches with full flaps. The early stages of this threat are manifested by changes in the control balance of the elevators, resulting in stick force lightening or outright reversal. This has a devastating effect on longitudinal stability, and quickly leads to elevator snatch, driving the control column full forward with the resulting pitch down.
This problem is neatly solved with irreversible (powered) flight controls, which are quite capable of overpowering a change in elevator balance. Thus, nearly all large jets have none of this issue, ice protection notwithstanding, because the elevator can easily be re-cambered to avoid the stall. The L-1011, of course, is a different animal due to the full flying tail, but I suspect that the aerodynamic analysis required to support the operation of that design in various flap configurations probably included huge margins to deal with ice contamination.
The 707, however, does not have powered elevators, nor does the DC-8 or DC-9 and MD-80. I know little about the DC-8 beyond noting that Douglas, apparently, opted to keep their tail ice protected when Boeing dropped it. That ought to raise a red flag; the Douglas fellows probably knew something that did not encourage them to press for a similar de-activation. I do know that the DC-9/MD-80 fleet has a problem with tailplane stall, and there have been a number of incipient cases with full flaps selected. Boeing, on the other hand, had enough stall margin designed into the 707 stabilizer to preclude any issues with the tested ice shape, and there is no service history that I am aware of in the zillion or so hours it has flown. Boeing has continued to design in that stall margin on subsequent stabilizer designs, while arguing insufferably against any certification requirement to do so.
The only real threat from ice on the tailplane, and it is a big one, is tailplane stall during slightly higher speed approaches with full flaps. The early stages of this threat are manifested by changes in the control balance of the elevators, resulting in stick force lightening or outright reversal. This has a devastating effect on longitudinal stability, and quickly leads to elevator snatch, driving the control column full forward with the resulting pitch down.
This problem is neatly solved with irreversible (powered) flight controls, which are quite capable of overpowering a change in elevator balance. Thus, nearly all large jets have none of this issue, ice protection notwithstanding, because the elevator can easily be re-cambered to avoid the stall. The L-1011, of course, is a different animal due to the full flying tail, but I suspect that the aerodynamic analysis required to support the operation of that design in various flap configurations probably included huge margins to deal with ice contamination.
The 707, however, does not have powered elevators, nor does the DC-8 or DC-9 and MD-80. I know little about the DC-8 beyond noting that Douglas, apparently, opted to keep their tail ice protected when Boeing dropped it. That ought to raise a red flag; the Douglas fellows probably knew something that did not encourage them to press for a similar de-activation. I do know that the DC-9/MD-80 fleet has a problem with tailplane stall, and there have been a number of incipient cases with full flaps selected. Boeing, on the other hand, had enough stall margin designed into the 707 stabilizer to preclude any issues with the tested ice shape, and there is no service history that I am aware of in the zillion or so hours it has flown. Boeing has continued to design in that stall margin on subsequent stabilizer designs, while arguing insufferably against any certification requirement to do so.
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411A -
...any problems with tail icing?
...any problems with tail icing?
If "your" de-activated 707 didn't have problems, maybe you were just lucky. Seems like even though Boeing built/sold more a/c, the DC-8 outlasted the 707.
And, as "Mansfield" said: "...the Douglas fellows probably knew something that did not encourage them to press for a similar de-activation."
OK.....I'm outta this discussion. You guys go fly your unheated tails but don't tell me that airfoils can't ice up under the right conditions and lead to fatal accidents like the Midway one. Most of us in/near that one ALL agree that tail ice brought that a/c down. In my write-up here on this Forum I mentioned the portion of the Accident Report that said that there wasn't any ice on the a/c because Charlie Fox Dog [Chicago Fire Department] said that when they got to the scene there wasn't any ice on the a/c. Well...DUH...the aircraft was ON FIRE !!
Good night.
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There seems to be a horrible confusion in some people's minds between "no effect due to icing" and "no icing on the surface".
I don't believe anyone at an OEM in any way inviolved in the design for flight into icing would ever say "flying surface X doesn't catch ice". If they did, they need to find a new job, because every flying surface on every aircraft ever made collects ice. It's the basic physics.
But I do believe that they could easily say "there is no (perceptible/significant) effect of icing on surface X". By which they mean "a pilot can't (easily) tell if there's ice on that surface" so we can, in most cases, just ignore it. I know I can happily make exactly that statement for many of our aircraft, with respect to ice on the tail; unless you're really paying attention to the trim required, you'll never spot the effect of ice on the tail. Because by design the tail is nowhere near stalling anyway, so a slight shift in the efficiency of the tail is all you see, which just shows up as a shift in the stab trim you use.
And yes, if you really work at it, you can even defeat that assertion - go fly in SLD, for example, and all the OEM's work for icing certification is valueless, and your only defence is to get the Hell out of the SLD, because we have virtually no idea what will happen - but we're pretty sure it'll be nasty.
I don't believe anyone at an OEM in any way inviolved in the design for flight into icing would ever say "flying surface X doesn't catch ice". If they did, they need to find a new job, because every flying surface on every aircraft ever made collects ice. It's the basic physics.
But I do believe that they could easily say "there is no (perceptible/significant) effect of icing on surface X". By which they mean "a pilot can't (easily) tell if there's ice on that surface" so we can, in most cases, just ignore it. I know I can happily make exactly that statement for many of our aircraft, with respect to ice on the tail; unless you're really paying attention to the trim required, you'll never spot the effect of ice on the tail. Because by design the tail is nowhere near stalling anyway, so a slight shift in the efficiency of the tail is all you see, which just shows up as a shift in the stab trim you use.
And yes, if you really work at it, you can even defeat that assertion - go fly in SLD, for example, and all the OEM's work for icing certification is valueless, and your only defence is to get the Hell out of the SLD, because we have virtually no idea what will happen - but we're pretty sure it'll be nasty.
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I would agree. Clearly ice can accumulate anywhere, and if I think about how quickly ice can form on a flat, heated windscreen, then I dont want to think how fast it can collect on the tail of my 737. But surprisingly I've never seen large accumulations of ice on the tail after landing (after an approach in severe icing conditions), not much more than a light coat of rime ice on the leading edge without any noticable change in handling characteristics.
Something I recently read - Airbus chose to equip the mighty A380 with wing anti-ice, but actually the only part of the wing that is heated is the number four slat on each wing, nothing more. Is the airfoil designed in such a way that ice either has great difficulty in forming or that it can just take a lot of ice on the leading edge? Seems half-hearted to me, a bit like the 737-NG WAI where the outermost slat isn't anti-iced (just more extreme)....
Something I recently read - Airbus chose to equip the mighty A380 with wing anti-ice, but actually the only part of the wing that is heated is the number four slat on each wing, nothing more. Is the airfoil designed in such a way that ice either has great difficulty in forming or that it can just take a lot of ice on the leading edge? Seems half-hearted to me, a bit like the 737-NG WAI where the outermost slat isn't anti-iced (just more extreme)....
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You cant design an airfoil to not accumulate ice - if its stuck out in the breeze, it accumulates ice.
What that implies is that they have designed the wing so that ice on the rest of the slats/wing doesn't degrade the handling or performance enough that they need to antiice anything except the $4 slat. Usually there is a critical part of any wing - if you can protect the critical part, the rest can be left to fend for itself. The question is, how much do I have to preotect - it can be "all but a little bit", or it can be " just a little bit". Depends on the rest of the design.
What that implies is that they have designed the wing so that ice on the rest of the slats/wing doesn't degrade the handling or performance enough that they need to antiice anything except the $4 slat. Usually there is a critical part of any wing - if you can protect the critical part, the rest can be left to fend for itself. The question is, how much do I have to preotect - it can be "all but a little bit", or it can be " just a little bit". Depends on the rest of the design.
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STBYRUD -
Clearly ice can accumulate anywhere, and if I think about how quickly ice can form on a flat, heated windscreen, then I dont want to think how fast it can collect on the tail of my 737.
Clearly ice can accumulate anywhere, and if I think about how quickly ice can form on a flat, heated windscreen, then I dont want to think how fast it can collect on the tail of my 737.
Not nice to mess with Mother Nature !!
Not nice to mess with Mother Nature !!
B737NG?
Very interesting thread is this.
One comment puzzles me however.
My understanding is that even though Boeing consider it ok, the FAA (and every other NAA too) have insisted on the clean wing policy. I'm sure there's a directive somewhere.
Unless I'm just out of touch of course, again.
One comment puzzles me however.
BTW: My employer together with Virgin Atlantic (hearsay) is pushing Airbus to allow some upper wing frost (cold soaked fuel), similar to what 737NG is allowed to.
Unless I'm just out of touch of course, again.
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In a marked area on the upper wing is thin hoarfrost allowed, ice build up is very common there especially if the fuel is cold from the previous flight. We had serious problems in the beginning because the planes iced up in the canaries and it took up to 8 hours until the frost was completely gone, no deicing equipment there of course. Boeing OKed it and our local EU-authority is happy with that.
On the lower side of the wing icing up to 3mm is allowed as it was already on the classics.
On the lower side of the wing icing up to 3mm is allowed as it was already on the classics.
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Boeing OKed it and our local EU-authority is happy with that.
Nothing new, either.
Now, lets look at wing anti-icing on large (heavy) swept wing jet aircraft.
I flew the 707 in command for seven years, and did not once use wing anti-ice
No problems noted.
Now, after flying the L1011 for thirty years, used wing anti-ice perhaps half a dozen times...and only then because the airplane is equipped with an airframe ice detector, and the new First Officer bacame agitated and thought we would fall out of the sky, otherwise...gotta keep the co-pilot happy.
I don't think any of us are questioning the way ice is formed (due to cold soaked fuel).
I was just trying to determine whether or not FAR121.629, with regard specifically to the B737NG had been revoked.
For those not familiar here it be....
I was just trying to determine whether or not FAR121.629, with regard specifically to the B737NG had been revoked.
For those not familiar here it be....
(b) No person may take off an aircraft when frost, ice, or snow is adhering to the wings, control surfaces, propellers, engine inlets, or other critical surfaces of the aircraft or when the takeoff would not be in compliance with paragraph (c) of this section. Takeoffs with frost under the wing in the area of the fuel tanks may be authorized by the Administrator.
Only half a speed-brake
I had seen this argument before, sounds honestly valid. Still, my understanding is that some NG operators are cleared for UWF within certified limits.
PS: Dunno about NG, but Airbus SA suffers UWF due to structural cold-soak on reinforced undercarriage rib. Indeed, tankering fuel won't help.
PS: Dunno about NG, but Airbus SA suffers UWF due to structural cold-soak on reinforced undercarriage rib. Indeed, tankering fuel won't help.
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Turin,
I discussed this with the FAA yesterday...they do not allow any exception to 629. The 737 upper wing frost allowance was, apparently, based on an allowance by Transport Canada for West Jet (there may be other authorities involved, I'm not sure). The FAA was asked to look at it, but turned it down flatly because they cannot identify a reliable method for the evaluation of upper wing frost, i.e., 1/8 inch or 1/4, how can you tell by looking out the cabin window at night...
Frankly, I think they're spot on. A failure to detect upper wing ice during the preflight inspection is pretty common, particularly around the wing root area which is not visible from the cabin windows. I'm not sure how anyone can accurately assess a frost presence beyond determining that it is, or is not, present, and even that determination is not always reliable...
I discussed this with the FAA yesterday...they do not allow any exception to 629. The 737 upper wing frost allowance was, apparently, based on an allowance by Transport Canada for West Jet (there may be other authorities involved, I'm not sure). The FAA was asked to look at it, but turned it down flatly because they cannot identify a reliable method for the evaluation of upper wing frost, i.e., 1/8 inch or 1/4, how can you tell by looking out the cabin window at night...
Frankly, I think they're spot on. A failure to detect upper wing ice during the preflight inspection is pretty common, particularly around the wing root area which is not visible from the cabin windows. I'm not sure how anyone can accurately assess a frost presence beyond determining that it is, or is not, present, and even that determination is not always reliable...