Why are modern jet tails not de-iced(in flight)?
 

Er.....that's my question.

Because the aircraft is demonstrated to meet the stability and control requirements with ice accretion to the required levels during testing.

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.

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

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.

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...

I'll have a pint of what he's drinking......:ok:

That was either very tongue in cheek (given the Chemtrails/Proon history) or err a pint for me too :p

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.

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?

Must admit, I've wondered about this too.

Also, I know many big jets rarely turn on the airframe a/ice, whereas on the regional jets wot I've flown we're always turning it on.

Let's hear it!:ok:

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

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.

FWIW The 747 is fitted with wing leading edge de-ice - Now ask everyone how many times they've ever used it. :)
I did about 5,000 hours in the 747, never needed it nor do I know of anyone that's ever used it.

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. :ooh:

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!

Mansfield

Thank you for a very informative post. Pls check your PM.

GF

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.

Not sure abt that. It seems that the design of the wing prevents the formation of ice. Interesting thing is that on a A330 that has just landed after a long flight, ice up to a quarter of an inch thick could be found on the underside of the wing close to the fuselage.

The proper term is anti-ice. De-ice is used to describe devices that destroy ice formed on the wing surface like pneumatic boots. :)

Well, the manuals for the Boeings I flew (IIRC) said the systems could be used for anti-ice or de-ice.

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

I have seen the visual ice detector catch an inch of crystal clear ice in seconds.

If the LEs dis catch it like that...

During the past few weeks we had to use wing anti-ice almost daily, flying around in that ridiculous winter here in western Europe. Wing anti-ice normally is not required at higher altitudes and at high speed, but during vectoring at reduced speed (around 220 KIAS) and at lower altitudes with temperatures around -5°C to -10°C ice can build up quite quickly.

I would strongly recommend to use wing anti-ice as recommended by the manufacturer (in my case Boeing) and to get rid of that fine white line on the LED whenever it forms, since even a small amount of ice there can have a significant effect on the airflow around the leading edge, especially at high AOA during final approach.

A good indicator for the need to use wing anti-ice can be ice accretion on the windshield wipers or in the corners of the cockpit front windows.

I still don't feel comfortable with the tail not being equipped with ice protection. The horizontal tailplane has a sharper leading edge than the wing and should thus be more susceptible for ice accretion, shouldn't it?
So if the wing picks up ice, chances are that the tail has picked up even more. With a forward C.G. and ice on the horizontal tail, why should that tail not stall during flap extension under extreme conditions? Has there actually ever been an accident caused by a tailplane stall on a jet?

Depends how you define "jet". There was a Viscount (turboprop, of course) that crashed in 1977 after a tailplane stall on finals to Stockholm: see

ASN Aircraft accident Vickers 838 Viscount SE-FOZ Stockholm-Bromma Airport (BMA)

The type had bleed air deice/antiice on the tail, but it had been ineffective because of low engine power during descent and approach.

Please excuse my ignorance, I am not a pilot but have done a fair bit of flying in light aircraft ( as technical photographer or just plain ' sitting there ' in transit ) but have often wondered about iceing.

The only time I have come across it was in a PA-44 Seminole at around 10,000' over a summertime Wiltshire, and frankly I was amazed how quickly the ice accumulated on the windshield and leading edges.

Rather happily this aircraft had been fitted with extra anti & de-ice kit as a demo' subject, which I'd photographed air-air through the removed W.C. window of the company Dove for their stand at the Farnborough show - didn't even get a sticker / zap, ta very much, so only poetic justice if the kit saved my life !

When the ice seemingly came out of nowhere and accreted VERY rapidly - I'm talking of less than 20 seconds or so by memory before it was easily 1" thick & building - the Test Pilot selected ' de-ice ' and was already diving as he called ATC for permission to do so.

Do I take it ' Ram Rise ' is a function of energy, so smaller slower aircraft are more susceptible ?

Still a good question re. tail surfaces...

TAIL ICE -
OK.....you got me back yet into another 'problem' area of aviation.....TAIL ICE.

Believe me if there's ice on the wing, there's ice on the tail. I don't care what kind of airplane it is. It's sad that cost considerations seem to come into play where de-icing the tail is concerned. The 737 has a real nice "heater" back there that could very easily be put to use to de-ice the tail, but Boeing was able to convince the FAA that it wasn't needed. HOGWASH. I don't have a copy of the report that I submitted (41 years ago now) to everyone I could think of about an incident I experienced with tail ice on the 737(200). Stall speed was a full 20 knots HIGHER in the landing (40 Flap) configuration. We had well over an inch of ice on the wings. I won't go into all the details here as it would take up too much space. I can tell you it was during flight training and I was flying (right seat). It took almost TWO THOUSAND feet to recover from a full stall because the Flight "Instructor" made me "take it to the stick shaker" when we were doing approaches to stalls.
- - - - -
Mansfield -
Read my above regarding Boeing being able to certify without tail de-icing.

Again, read the above.
- - - - -
NGjockey -
Can't say as I blame you. Carry some extra speed when in icing conditions.
- - - - -
kenparry -
I couldn't find who you quoted, but even though I was somewhat involved in the United Midway adccident, the NTSB rulled out tail ice as a possible cause. Why? Because Charlie Fox Dog (the Chicago Fire Department) said there was no ice on the airplane when they arrived at the scene. Well.....DUH.....the airplane was on fire !! How long did they think the ice was gonna hang around. Those of us "in the know" still maintain the aircraft stalled on approach.

All I can say is.....y'all be careful out there. Aviation is NOT an exact science. Never has been and never will be !!

Most uk service stations wil do you one of those scraper thingys for a quid if you fill up, just use that, works a treat!

Although for severe ice you can't beat a kettle of luke-warm water..!!

This thread has drifted away from the original subject of tail de-ice. To Mansfield's excellent discussion of size. Then to people who state that they have thousands of hours on specific types and have never used the wing de-ice. I guess it depends on your routes, obviously some here have never flown in the Canadian winter. Before widespread radar coverage and R-Nav approaches you could acquire quite a load of the white (or clear) stuff during a full procedure turn and subsequent circle-to-land operation. I have seen more than an inch of it on the radome many times.

So, in some environments, wing anti-ice is very necessary.

Now back to the subject of tail de-ice, I think Mansfield again hit on the answer, namely the design of the horizontal tailplane and elevators. There used to be a story in the folklore that when Boeing certified the B-727 they somehow attached 2X4's to the horizontal stabilizer leading edge to demonstrate that it was capable of controlled flight with a large quantity of ice there. Whether that was true or not I don't know but I do know that the reason you gave the DC-9 tail a shot of heat on approach was to ensure a clean edge when you extended landing flap. Ice would act as a spoiler blanking the flow to the elevator. Not sure if it was in the manual but it was well known in the DC-9 community that if you ran out of elevator after selecting flap to 50° the solution was to retract the flap one step back (to where you had had control).

If you think about it, the wing generates the lift that keeps you flying so ice could be critical there - ergo, get rid of it. But the tail only creates "lift" (down or up depending on CofG) for longitudinal balance purposes. Its other purpose is to provide a home for the elevator. So if you make the elevator big enough that it is still effective even with a badly contaminated stabilizer, you don't need to remove the contamination. That must be what Boeing (and others?) have done.

Does that make sense?

Edited for grammar, colonials are slow but we do know!

I've understood that on laminar flow surfaces the "moisture" component of the airflow doesn't come into contact with the cold metal, therefore no ice can develop.
Most manufacturers fit wing de/anti-ice systems because the CAA/FAA are not entirely convinced .................but they let the tail surfaces remain unprotected to prove the point !

I've have over 10,000 hours on various 747s and although I did use the wing anti-ice systems a handful of times, it was mainly to keep the other two guys happy and not because of any evidence of wing icing. (Of course, on a Boeing747, wing anti-ice doesn't work when the leading edges are extended - which is probably the most vulnerable time to collect ice)

Ditto with my command experience in the L1011 type (16,000 hours and counting)...wing anti-ice selected on just to keep the other two junior crew members satisfied.
Anyone with a lot of flying experience in large swept wing turbofan powered aircraft will tell you about the same...wing/tail surface icing is simply...not a particular problem.
Turbopropellor types?
Another story, altogether.
Can NOT link the two types.
Anyone who thinks otherwise is full of baloney....lots of it.
And yes, the problems with Viscount were most serious.
Hello?
A turbopropellor type...not a swept wing jet.:rolleyes:

With about 18,000 hours on various Boeing aircraft, I have only needed to use wing anti-ice about three times. I guess you could say from my experience and others that have posted here, it is not used all that often!

You know.....I go along with most of your posts on here, but that one surprises me. That simply is NOT true. Ice can and does form on swept wing turbofan powered aircraft if conditions are right. I've seen it more than once. Maybe a 737-200 doesn't fit your description ??


And to the rest of you with your tens of thousands of hours: ICE can and WILL form on the tail of your swept wing turbofan powered aircraft if conditions are right. So add a few extra knots on your approach or pay the price like they did in Midway.

Correct, not a large heavy jet.

Recent Southwest, perhaps?
If so, airframe icing was not their problem, poor procedures and an inability to actually appreciate the runway conditions...was.

Possibly correct about the Southwest one. Didn't really follow that one. I was talking about the one I mentioned in my prior post: the UAL 737. Another reason I liked the DC-8.....a hot tail ! (if needed)

To NG Jockey's query regarding tailplane stall events in jet aircraft: there have been no accidents that I am aware of. However, as I indicated previously, the DC9/MD80 design, which includes the 717, is susceptible to the ice contaminated tailplane stall problem. For reference, go to the NASA ASRS website and look up this report: 392928. This is the only published report of such an incident, but I am aware of two others anecdotally.

You are correct in the statement that the stabilizer is generally a thinner airfoil and thus more efficient at ice accretion. The idea that Boeing and Airbus have applied is to design the stabilizer so that its normal operating envelope is well below Cl max. Therefore it can tolerate a significant degree of degradation in Cl max, due to ice accretion, before any problems arise. This appears to have been rather successful since no events have been reported. The certification is typically done with a three inch ice shape modeled on either analytical or wind tunnel data.

With regard to the question of whether large aircraft need the use of airfoil anti-ice/de-ice, I would recommend a very conservative approach. As I stated in an earlier post, scale plays a significant role in the relative degradations experienced in icing. That said, airfoil ice will most definitely shallow the aerodynamic margins. As the pilot, you have absolutely no tools with which to measure or assess that degradation. One of the more insidious characteristics of icing degradations is that, for many airfoils, the Cl curve with ice lies extremely close to that without...until Cl max is attained, at which point the wing's behavior can become "non-linear", which is another way to say you go off a cliff.

During the years that I have worked with this topic, I have become concerned that the large jet icing accident, were it to occur, would take place during a maneuver that required a significant bit of the margins built into the normal operating envelope. The one that always comes to my mind is the go-around from a low altitude. In fact, in 1989, a Canadian DC-8 experienced a pod strike and landed off the side of the runway at Edmonton following a low visibility ILS approach in freezing drizzle. Despite noting ice accretion, the captain had declined operation of the airfoil ice protection system. The investigation was unable to determine whether a stall had taken place, but noted that the approximately one inch of rough ice on the wing may well have precluded a successful go-around once the approach stability was lost at around 100 feet.

In March of 1996, a Canadian Airlines 767 experienced a tail strike at Halifax. There were a number of reasons for this, but one aspect was a performance degradation noted in the DFDR data beginning at around 400 feet. The investigation was unable to explain this, but considered that ice accretion may have been the cause of the degradation. Again, the crew had not operated the airfoil ice protection, again in a freezing drizzle condition. In this case, they did not see any ice on the wipers, etc.

In 1997, an A300 experienced a roll upset while entering holding near Miami. Ice accretion was considered to be one possible explanation, as the upset could not be duplicated in a simulator.

The use of of the wiper nut and such other indicators is a bit problematic. Several years ago, departing Milan in a 767-300, we heard an ATR issue a PIREP of severe icing (this was well after the ATR debacle). I became very attentive, as I wanted to see just how this would manifest itself. We saw nothing on the wipers or windshield area. However, the relief pilot stepped back and examined the wing leading edge. He reported about three quarters of an inch of very rough ice on the protected surfaces of the wing. Several minutes later, and after we had actuated the wing anti-ice, we finally noted a very small and clear ice accretion on the wiper. At night I don't think we ever would have seen it.

The simple fact is that, unless you're in a 727 trying to get above FL310, there is little reason NOT to use the wing ice protection.

DC-ATE, I'm not sure I see the connection between your 737 event of forty some years ago and ice contaminated tailplane stall. It sounds to me more like a regular old contaminated wing stall, although I'd sure be interested in more details. Along those lines, there have been a couple of good ASRS reports involving 737s. Look up these NASA ASRS report numbers: 426216 and 815450. In the first case, I know the captain who wrote it and I have seen his pictures. He wasn't exaggerating.

Virgo, there is no evidence that laminar flow airfoils will naturally avoid ice accretion. Laminar flow is a pretty fickle thing to maintain in the real world, what with dents, dings, bugs and such, but there have been a bunch of wind tunnel studies done with some laminar airfoils, particularly the NLF414. This airfoil may have a better behavior with ice than some of the classics, but not nearly enough is known to make concrete statements. In any event, it accretes the ice just fine.

I'm trying to dig out the photos but not having much luck right now.

During the certifying test flight of the Ejets. They had false leading edges fitted to the stab. Rather than 2x4 as someone said earlier. These were replicas of the shape and size of ice build up as created in wind tunnel tests. The only difference between the fake ice leading edges and real ice build up is that the fake couldn't be shed whereas in reality such large build ups would partially or fully shed with changing airflows.

Before seeing the picture I would never have believed the stab could operate with what amounted to a 2 to 3 inch extension of oddly shaped "ice". But in fact the aircraft flew to all corners of the envelope.

Of course we do have the Stall protection Ice speed system which increases Vsr by about 5% after flight in icing conditions but I'm told this is as much to do with wing and fuselage ice as it is the stab.

If you have access to the Embraer cold weather ops video you can see the fake ice stab leading edges on the test aircraft. Also note how much Ice they get to build up on the inboard slat which isn't anti-iced.

I read both reports. Similar in a way to my experience, except mine was a training flight. I've stalled a few airplanes in my day [NEVER a jet transport.....until this incident], and never had one behave like this one did. The elevator became useless in my hands well before stick-shaker ever activated. To me that was an indication of an approaching stall, which is what we were training for and I commenced the recovery
procedure. But the "Instructor" said "No, no...take it to the Stick Shaker." So we did the maneuver again. This time I got the same indication, only a few knots sooner [a good 20 knots above what it should have been]. I pointed this out to the "Instructor", and he said to take it to the stick shaker. I would not have continued had we not enough altitude. We were 10T above ground. So, I "took it to the Stick Shaker" and the aircraft really started to stall well before it got there, but I hung on until we were in a full stall and the stick shaker came on! So, I looked over at him and said, "NOW do you believe me?!" He just sat there. I shoved the throttles full forward [mistake Number One], shoved [or tried to] the nose down, and called for Flaps 15. Naturally, the aircraft kept going DOWN with its nose in the air. I knew what I was going to do, but looked over at my "Instructor" and asked him. He just sat there with his eyes twice thier normal size not having a clue what to do. I merely reduced power by about 50%. The nose came down, airspeed increased, and we flew out of it. But...it took 2000 feet to recover!

About the only thing this "Instructor" did right was to have the engine anit-ice ON. We were doing all this at night in the overcast in the COS 'training' area. My 'stick partner' was in the middle seat and wondered if we had any ice. We flipped on the wing lights and sure enough.....about 2 inches or more.

Maybe our "Instructor" went to the same school as 411A and others on here who seem to think airfoil ice on jet transports isn't anything to really worry about. Anyway, there wasn't any ASRS back then as I recall, but I submitted 'my' report to our ALPA Safety Rep, and my Flight Manager. I was told a copy was sent to Boeing but never heard anything about it.

That was the first of two incidents I experienced with TAIL ICE on the 737-200. Another time was after landing in CMH. We had been in the overcast for some time and had engine and wing heat ON. We wished we had tail heat. We carried an extra 20 knots on final. When we got to the gate, I ran out and looked at the tail. At least FOUR inches of ice was till there AFTER we had been clear of clouds for the past ten minutes !

Both of these incedents were before the MDW one. When that happened, we were unsuccessful in presenting 'my' reports to the NTSB. They simply were not considered.

Ice on jet transports of ANY size is something you should be concerned with no matter how many thousands of hours you have.

Over a period of twenty years on DC8's, 737's, 757's and 767's I never had to use airframe de-icing. However, the Britanna was another story!

DC-ATE

Not having tail anti-ice doesn't mean it won't accrete, it just means the accretion won't affect control and stability as prescribed in FAR 25. The 4 inches was there, it just didn't have a control effect.

I think there is something to the "bow wave" effect forcing some of the water droplets to not impact and accrete on the airframe. The bow wave of a C-5 approaching a tanker is amazing and quite noticeable 50 feet back. I can see were the bow wave of a jet at 200 knots would have a centrifugal separator effect. Like I said, we didn't have any wing anti-ice on either the A-10 or the C-5 and they have flown around in lots of ice in NA and Europe without problems. I've flown in icing, for 4 hours around the traffic pattern, with ice detectors indicating icing with zero wing accumulations. Surface temps were about 0 C. I have seen ice build on the pylons and bombs on the A-10 but little to none on the wing.

GF

galaxy flyer -

Well, I don't doubt what YOU have experienced any more than I doubt what _I_ experienced. It was definately effecting the performance of the aircraft in the first incident I described. Oh I know about Boeing and their ice shapes in the certification process, but after I saw first hand that ice can form and effect the performance, I acted accordingly for the rest of my career. I just think it's stupid to have that nice heater in the tail of the 737 and not put it to use when needed.

From my observations it seems that in general terms, pilots are loath to use anti-ice. It almost seems that one's not a real man (no offence intended to women pilots) if one uses anti-ice. :sad:

The number of times I've heard, "this isn't thick (cloud) I won't use the anti-ice", doesn't bear thinking. Also amusing to me are the folk toodling along in and out of cloud who turn the engine anti-ice on and off and on and off and ...

Each to their own with the second scenario but if one is in and out and in and out, why not just leave the engine anti-ice on until it's no longer needed?