I was wondering if one of you smart guys (or gals) could explain why a lot of jet and turbo-prop aircraft do not have anti-ice protection on the vertical stabilizer, particularly those aircraft with T-tails? Is it because these aircraft are not prone to collecting ice on the vertical stab? Or do they still collect ice, but "not that much"? Does a T-Tail configuration somehow make the aircraft less prone to icing on the vertical stabilizer? And if so, WHY? Is there some aerodynamic reason for this?
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I was wondering if one of you smart guys (or gals) could explain why a lot of jet and turbo-prop aircraft do not have anti-ice protection on the vertical stabilizer, particularly those aircraft with T-tails? Is it because these aircraft are not prone to collecting ice on the vertical stab? Or do they still collect ice, but "not that much"? Does a T-Tail configuration somehow make the aircraft less prone to icing on the vertical stabilizer? And if so, WHY? Is there some aerodynamic reason for this?
First off.....the Vert Stab is not a lifting surface. So picking up ice on the Vert Stab is only cause a weight gain. My guess is that on many airframes.....the bleed air lines to the Horizontal Stab runs up the leading edge of the Vert Stab and provides quite a bit of ambient heat. As to the T-Tail vs Mid Tail or other......I can't imagine that there would be a difference in ice accumulation....AFAIK
I'm going way back in the memory banks here so forgive me if I'm wrong.
I flew the 1900 for a few years, and if memory serves, it had some sort of a stick-on layer glued to the vertical that was supposed to be ice-resistant. The ice just didn't adhere to it well. How well it worked, I couldn't tell ya. I do know I flew that plane with a helluva lot of ice on it, and it performed well. I did declare an emergency for severe ice once, and it had nothing to do with rudder effectiveness, so my guess is that anti or de ice is just not that necessary on the vertical. If that gets to be a problem, you've got much bigger fish to fry.
The Lear 35 can develop tail-ice. The problem (other than an unknown aft-CG): Not enough down-force may be available to counter the nose-down moment of full-flaps.
So, if tail-ice is suspected, the Lear is landed with partial flaps. I can't rmember all the specifics; it's been 4 years since I flew it.
I've wondered that too. The older hawkers had it, but newer versions of the same series (700s for example) didnt. Guess they figured out wasnt much threat.
Questions like these are hard to know the answers to because the way a manufacturer would know if their airplane is susceptible to vertical tail icing is through wind tunnel and flight testing of their airplane, and the results are not the kind of thing most companies would want floating around in the public domain. The particulars for ice accretion and anti-ice and de-icing remedies vary among designs. I am not trying to dodge the question since it is a good one, but trying to point out why there is not much public data on it. Another factor in this may be the fact that icing is treated late in the typical certification cycle. It is not uncommon for a new airplane to be certified without FIKI and then add FIKI later, although this is less common in transports. If there is a non-proprietary source to be found on this I would look to NASA short papers and FAA Advisory Circulars on Part 25 certification. I do not really have time to do it but those sources are free to the public.
As for as my speculation on why some transport aircraft would seem to be immune to icing, it is because the vertical tail is not as critical to flight safety as the other lifting surfaces and when its effectiveness goes down, the main effect is on VMC. Transports tend to land in a crab and tail effectivenes is not all that critical for landing and iced tails do not occur prior to takeoff which is when VMC is most critical. The rest of it just cost and of course, weight of the added equipment.
The KC-135 doesn't even hae leading edge aiti-ice (although the bleed manifold runs through the LE). I believe that the thought process in the 1950s was that jets would spend 90% of their time above the wx and would be able to quickly climb or descend through icing conditions. For the most part this has proved correct although there have been a few occasions that I wished for something more than engine AI and pitot heat! Fact is turboprops spend much more time at potential icing levels and require more elaborate solutions than jets.
Back in the dark ages when they showed 8mm films in training I remember one that dealt with tail icing. It showed Boeing testing the 707 with what looked like 2x4s bolted to the horizontal stabilizers to simulate icing and prove that anti-ice or de-ice was not needed to safely fly the plane. Other planes I flew, the DC-9 and L-188 had tail de-ice & anti-ice. It was always explained by the instructors that certification testing determined whether or not tail anti-ice or de-ice was needed. The L-188 spent most of it's time around 18,000 to 25,000 feet and we used all of it's anti-ice capability. The DC-9 was short haul and was up & down all day and needed tail de-ice often. In 21 years on the 747 I only used wing de-ice once. It all hinges on the mission and certification. I seem to recall that the L-188 was the only transport category aircraft certified for all known icing.
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