I hear that of icing protection of a hot prop amounts to 70% of the total icing protection. In other words the remaining surfaces (wing, elevator, rudder) only contribute 30%. Is this true or just an anecdote?
Surely that depends if it is cruise or climb or descent protection? surely prop TKS fluid will spill all over the place on remaining surfaces while having heated surfaces does not make any difference to output power
Different question: if you suspect ice on a non-heated props will you go fine or coarse pitch? more tempted to say high RPM/fine pitch even in descent but one could also argue about coarse pitch/low RPM for balancing & vibration? obviously getting RPM to swing quickly between 2200RPM/2700PM then back to fine pitch may remove some ice and restore smooth running, the last wild card is to spill some hot oil from CSU/Spinner if you know how to do that 
It depends if your intention is to go on top a hot prop may help. Three weeks ago I used TKS for the first time in real conditions. A hot prop alone may have worked but I wouldn’t have taken the risk. I entered cloud at 8500 and popped out at almost 12000. MSA was 9000 for a while 15 minutes. Climb performance in a NA is not that great at that altitude. OAT was -4. I knew that I could remain in IMC for an hour or longer if needed before conditions improves.. With a hot prop alone this scenario may not work…..So percentages alone don’t give the full story…
I have no direct experience yet, but have read many bits of information repeatedly mentioning that if you have compromised thrust you’re in major trouble right away, but if you have a fairly powerful aircraft, a hot prop or TKS prop you still have some time/options.
If you gain too much ice on the prop despite loss of efficiency you may have to severely reduce power to prevent catastrophic issues due to imbalance.
So even if a deice prop is all you have and you need to find a safer bit of air, it may help you get there despite having no other deice. Obviously a turbo __may__help you avoid excess ice in the first place.
What should those 70% and 30% mean anyways?
That in 70% of icing conditions you get away with a hot prop only w/o wing deice? Definitely not!
That in light to medium icing you get 2,33 (70:30) times as far before you crash if your wing deice fails compared to if your prop deice fails? Might be – but what is it good for?
If prop icing or wing icing is a bigger problem depends very strongly on the conditions, type of ice, phase of flight, speed, altitude, etc. Flying into ice w/o either one is just not a good idea.
Lucius wrote:
I hear that of icing protection of a hot prop amounts to 70% of the total icing protection. In other words the remaining surfaces (wing, elevator, rudder) only contribute 30%. Is this true or just an anecdote?
I don’t know about the figures but I do know that tailplane icing has killed people due to loss of control in icing. I know from experience that even a small amount of ice on the wings can have a significant effect on cruise speed and climb rate.
I hear that of icing protection of a hot prop amounts to 70% of the total icing protection. In other words the remaining surfaces (wing, elevator, rudder) only contribute 30%. Is this true or just an anecdote?
I think it is meaningless, and probably dangerously wrong.
I have had a TKS prop for 16 years and full TKS for 2 years. Obviously TKS keeps the prop clean and ensures max available power, plus it keeps the front window clean in all icing conditions, even 3cm in 5 mins which is a “high moderate” rate of ice accretion.
But if you collected ice at that rate all over, as I did on that occassion, the plane would not fly after 5-10 mins. Maybe for 20 mins with a PT6 on the front You have to get out of it. With full TKS you can have 3cm all over the unprotected bits for as long as the fluid lasts, and I’ve had that too, with a minimal impact on performance.
A hot prop is usually found together with rubber boots everywhere, too. It’s not an option on a TB20. And if you are upgrading from a TB20, it makes absolutely no sense to go for anything less than fully ice protected, and I would argue only a TP will deliver a significant mission profile increment.
Peter wrote:
I think it is meaningless, and probably dangerously wrong
I would agree if one would simply stays in icing conditions. The intent, however, is to increase escape options. Why is increasing escape options dangerously wrong?
Lucius wrote:
The intent, however, is to increase escape options. Why is increasing escape options dangerously wrong?
The only way is not flying into icing conditions in the first place plus leaving the icing conditions on the fastest possible way in case of in adverted entry. Both is not changed by a hot prop.
The reason why this is “dangerously wrong” is that planes are flown by humans. And humans might be tempted to think “I have a hot prop so let’s pass this icing layer” or “I have a hot prop so I don’t have to turn around but can leave this icing area by flying through it”. Both would kill people.
Summarizing all of this: Everything short of full FIKI capabilities does not improve survivability in icing significantly but does increase the risk that pilots underestimate the dangers significantly.
Flying into potential icing conditions in an aircraft that is not fully deiced is akin to Russian roulette: you may get away with it several times before it kills you. Icing comes in many different ways, so it is not possible to state percentages of importance for various anti-ice devices…
Even in a FIKI certified aircraft, I view icing as a dangerous flight condition and will not accept it if there are no viable exit options. For example if the temperature on the ground is negative and I am unlikely to find safety below the cloud level, I consider the risk unacceptable.
In our small aircraft, safety is an attitude and I think that having the option of delaying or cancelling a flight is an essential, probably the single most important safety factor. In my flying budget, the cost of a wasted hotel booking and last minute airline flights is probably 10% of the total!
