Control Column Force

[Lissart]

Gentlemen,

Doubtless this might be considered a daft question but being in ATC I just don't know....!

Following the recent poor weather in the UK and Europe, have been discussing de-icing etc. I understand that certain fluids require a greater than normal control column pull force on rotation. This led me to speculate: How hard do you actually have to pull on the column for normal and de-iced ops? Having never flown an airliner I just don't know what it feels like! I suppose one should measure this force in Newtons, no??

Just humour me and don't knock ATCOs with an interest in wider aviation....

Regards,

LISSART

[BOAC]

No difference that I have ever seen. Who told you that?

[Lord Spandex Masher]

I wonder if you may be refering to rehydrated deicing fluid refreezing in control surface hinges and the like. This can, potentially, restrict the movement of the control surfaces but with powered flying controls it would likely be unnoticeable in the flight deck.

Control column force will vary by type and airspeed, dynamic pressure feedback, but there is a maximum force allowable by certification.

At a rough guess I would say most types I have flown would be somewhere up to 75 pounds of force required to achieve full back stick. But I reiterate that that is a guess.

[safetypee]

IIRC some types of thickened anti-icing fluids (type 4) have caused problems on a few aircraft. This involved types with manual controls, but not necessarily servo-tabbed controls, which independently, suffered problems from re-hydrated fluid residues. Also, the airfoil / control surface sections were of a modern design – reflex surfaces.
ATR and Saab experienced problems with heavy control forces during rotation. Again from memory there was one incident involving an ATR where the crew ‘failed’ to rotate due to heavy controls – either too heavy, or the crew failed to pull hard enough (non normal control feel).
Several manufacturers have conducted tests to check for problems, including loss of lift performance after take off.
Where conditions result in unacceptably high control forces, (adverse cg, wt, configuration) manufacturers should have published appropriate procedures. Again IIRC, these include restrictions on configuration / cg, type of fluid, repositioned takeoff trim setting (to reduce forces – but a/c must still be in trim after takeoff), and / or changes in takeoff speed schedules.

CS 25.143 – maximum control force (short term):-
Control wheel – one hand 220N, 50 lb.
Control wheel – two hands 334N, 75 lb.

[Lissart]

SafetyPee

Yes, I had heard it was ATR/type 4 but didn't know the details - thanks. What does 75lbs equate to then? I mean @ 35 bags of sugar is quite heavy. Obviously this is going to be type specific but some power assisted cars feel "heavier" than others.

Thanks for the answers,

L

[Mad (Flt) Scientist]

Not just ATR and SAAB or just Type IV. Rehydration events have occurred on a number of aircraft now, and with Type II as well as Type IV. Type III isn't widely used, but there's no real reason it shouldn't do it too - all the anti-icing fluids have thickening agents and those are what cause the problems.

Events have occurred on aircraft with manual controls, but also on some powered control aircraft as well. EASA issued some kind of safety alert about it earlier this year, if I recall correctly, and it's been an active topic of discussion within the SAE fluids world too.

[safetypee]

MFS, I think that there are two separate issues here.
Rehydration is a significant issue affecting many aircraft types, which has been discussed widely. Many rehydration instances involve control jams or restrictions, which can result in heavy control forces, particularly with servo-tab controls, but assuming correct before-takeoff control checks, problems are not encountered during the takeoff rotation. This issue invariably involves freezing of the water-laden residues during flight.

The problems relating to the thread question (heavy forces during rotation) appear to result from the fluid dynamics, reportedly as the interaction of the deicing-fluid / air flowing over the aerodynamic surfaces (reflex sections) and / or through the tail–elevator hinge gap, thus changing the hinge moment and thence the control force.
AFAIK the problem was predominantly associated with the thicker fluids (type4 or equivalent) which have properties of high dynamic viscosity, i.e. viscosity changes with change of speed of the adjacent airflow.

Lissart, the control forces quoted were maxima.
Manufacturers would normally design a system well below these limits, harmonizing the pitch control system with the roll forces, and allowing a significant margin for a range of wt / cg, and configurations.
IMHO, pilots would be very surprised if faced with the limiting case – cf ATR incident (there was a safety report). This lack of familiarity can cause further problems with requiring the correct use (understanding) of control breakout systems in the event of a ‘mechanical’ jam during rotation. Also, this may lead to an unnecessary rejected take off above V1; again cf ATR incident.

[Checkboard]

The aircraft trim produces more variation than de-icing fluid application. Lissart, the stick force for rotation is low enough to comfortably pull the stick back with one hand. If the trim has been miss-set, you might have to make a conscious effort to pull the stick back, but still using one hand.

[First.officer]

Lissart,

On the Cessna CJ's you certainly notice a difference when rotating with a coating of De-ice/Anti-ice fluid covering the surfaces - this was admirably demonstrated on a recent LPC by myself, will admit i'd noticed it (the relatively speaking extra force required on rotation) and hadn't made the mental link and it wasn't until the CRE/CRI i was with asked if i'd noticed anything 'on rotation' that the penny dropped ! In answer, certainly on the CJ's this is due to the relatively low rotation speed being around the speed at which the fluid would normally start to shear and the bulk leave the airframe.

Hope my basic understanding of this is of help, all previous comments also seem to apply but thought i'd add my specific case.

F/O