Is a sideslip a "Manoeuvre"?

[Pilot DAR]

It has recently been proposed to me that, for the purposes of certification, and possible limitations, a sideslip is a "manoeuvre", and could be subject to limitation. I think not, because I think a sideslip is incidental to "normal" flying, and could not be subject to limitation, as it is very difficult to quantify.

It was suggested to me that a flight manual statement should be included in the limitation section, to tell the pilot that sideslips should be done with caution. Isn't flying with the ball in the middle simply a part of basic pilot training, just like flaring for the touchdown at landing? Flight manuals don't seem to tell the pilot that an unsafe condition could be created if the pilot fails to flare for the landing, why need the flight manual tell a pilot that an unsafe condition could come to exist (in this case, brief power loss due to fuel tank unporting with low quantity) as a result of sideslipping. Don't pilots know this already? Where is the line between the basic pilot knowledge base, and information we need to remind a pilot, which would be common to most aircraft types anyway?

Your thoughts will help me do my job better... Thanks,

Pilot DAR

[Lightning6]

Sideslipping is a "manoeuvre", Much the same as turning left or right is...Check your POH, some aircraft manufacturers disapprove of sideslipping mainly due to flap extension, but I've sideslipped 150/152/172's no problem, I prefer the crab method though, takes a bit of practice when to kick the rudder...I assume you are talking about crosswind landings.

[ClippedCub]

There's an/are airplane/s out there that experience rudder lock in side slip. Maneuver. The 172 limitation started back in the days of 40 degree flaps.

[Lightning6]

There's an/are airplane/s out there that experience rudder lock in side slip. Maneuver. The 172 limitation started back in the days of 40 degree flaps.

Interesting...I've never come across the rudder lock problem before with sideslipping, out of interest, what aircraft are you referring to?

My POH for the 172 states that sideslipping should not be used with flap extension greater than 30 degrees due to a nose drop problem, but it does recommend sideslipping as against crabbing with as minimal flap setting as necessary according to runway length and wind strength.

Again, check your POH.

[Fitter2]

Interesting...I've never come across the rudder lock problem before with sideslipping, out of interest, what aircraft are you referring to?


The Weihe vintage glider for one - conversion briefing includes this effect, and instruction to try the effect at altitude if intending to sideslip for approach control. The force required to 'unlock' the rudder is surprising on first encounter.

[flybymike]

What aerodynamic or other reason would there be for such a "rudder lock?"

[ClippedCub]

There's also a four engine transport with rudder lock due to sideslip.

[englishal]

why need the flight manual tell a pilot that an unsafe condition could come to exist (in this case, brief power loss due to fuel tank unporting with low quantity) as a result of sideslipping.
Because one can be reasonably sure, due to their training, that should one not flare during landing one will crunch the aeroplane. Like wise if one gets too slow in an aeroplane, it will stall. This happens in all aeroplanes.

I can sideslip my aeroplane however I want - to get down from a high approach with full flap etc.... Now to try that in other models of aeroplane in certain configurations and it may lead to unexpected results (rudder lock for one), nose drop and if it happens close to the ground could result in sudden death.

So yes, the POH should state any unusual characteristics.

[Pilot DAR]

Perhaps I should clarify:

reading the POH in this case won't help, because the excersise is to write it - it is not finalized yet.

Rudder lock is not the issue, unporting the fuel tank is. I have sideslipped this aircraft many times, and aerodynamically, it's just fine. Rudder lock is not an issue for the certified GA aircraft we fly, as there is a design requirement that such a characteristic may not be present at all. The C 172 situation is simply due to mushiness in pitch through certain speeds, and is really more an annoyance, than a safety issue, if the aircraft is being flown with care, and a margin for safety.

The question remains, do pilots know as a result of their basic flying training, that the ball should be kept in the middle, and if slipped with low fuel, brief engine stopping could result?

Pilot DAR

[englishal]

Yes, but my basic training taught me how to slip on approach to get down if I was too high. In this case the ball is most certainly not centered.

I'd say "brief engine stopping" should certainly be noted in the POH because every aeroplane I have ever flown would not suffer form "brief engine stopping" if slipped. (I don't fly with such low fuel quantities that low fuel would be an issue).

[bjornhall]

The question remains, do pilots know as a result of their basic flying training, that the ball should be kept in the middle, and if slipped with low fuel, brief engine stopping could result?

I should hope so! :eek:

But perhaps more to the point, sadly: Could someone sue the manufacturer if they sideslipped the aircraft, had problems, and there was nothing in the POH about such problems? If the answer is yes to both questions, then the pilot does not need it to be in the book, but the manufacturer might...

Maybe this could be put in the limitations section to cover all such issues:
"Minimum required crew: 1 pilot. A moron is not an alternate means of compliance." :E

Seriously though, was the suggestion really that "sideslips should be done with caution"? In the limitations section? How does one comply with that? If the limitation is that sideslips of more than a certain duration are prohibited with less than a certain amount of fuel, then I can sort of see the point.

[BackPacker]

Pilot DAR, I think the main question is: do you want the pilot to know about this specific issue or not? You are writing the POH for the benefit of the future pilots, so if you think they need to know this, put it in. Me personally, as a pilot, I would want to know this.

To answer the other questions: I agree that in general pilots should approach side slips with caution because its effect depends to a large extent on the side surface area. Some aircraft can be slipped without any height loss, others will sink like a stone. Just like the first take-off, turn and landing should be approached with caution. That's not something that needs to be in the POH.

But the fact that the engine is starved of fuel during certain flight maneuvers is something that I would not expect intuitively and as far as I'm concerned should be in the POH. But there should not be a general sentence "with caution". As bjornhall wrote, there should be a specific amount of fuel listed, below which side slips with the ball more than x out of the center may lead to fuel starvation.

And if this is a problem in sideslips, could this not be a problem in steep climbs or steep descends as well?

And maybe another avenue of thought: there are different categories for aircraft maneuvers: "normal", "utility" and so forth. I would expect that an aircraft certified in category x would not suffer from fuel starvation during any maneuvers that fall within the limits that category. Those category descriptions, do they mention something about sideslips by any chance?

And just to add another precedent: I fly a R2160 which is certified for the Aerobatics category. The POH details entry speeds, approved maneuvers and so forth but since the aircraft is not equipped with an inverted fuel/oil system there are specific warnings too that any negative g will cause power loss and flying (floating) inverted is limited to 20 seconds. It's sort of the same problem you're having.

[Pilot DAR]

I appreciate your respective contributions. A caution note is planned for the flight manual. Being a light twin, sideslipping would not be a "normal" thing to be doing for the purpose of glidepath control. I have flown the aircraft extensively with each of the engines shut down, and in all of the attitudes to be expected for this type of aircraft, with no power interruption at all. The sideslip which resulted in a power loss was reported as being "severe".

Your comments have been a small part of the drafting of a flight manual, for an aircraft which you might find yourself flying in the near future. Always have a mind for the flight manual, and the team of people who have to decide what to include, and what is too much. The "man on the street" comments are helpful for me, to remind myself what the average person is expecting to be reminded.

Thanks, Pilot DAR

[Tester07]

You need to consider stress.

Whether or not you decide to define sideslip as a manoeuver, this will result in stress on the airframe, and you may not be able to apply full rudder throughout the performance envelope. Hence defining a Va, and also how much rudder can be applied above Va.

So Va is telling you that you cannot conduct full rudder sideslips above this speed.

This speed is normally high enough not to affect the ability to sideslip on the approach, but as previously mentioned rudder overbalance can be a factor, notably on the 4-engined transport also previously mentioned!

[TheGorrilla]

of course sideslipping is a manoeuver. So is shifting your weight from one buttock to another...

[Lightning6]

:) My point made in post #2, Pilot DAR stated off on the wrong foot I think, but explained himself a bit better later in the thread.

[Lightning6]

Pilot DAR...Correct me if I'm wrong, but is this a new aircraft type? If so, should these doubts be verified by a qualified test pilot?

[Pilot DAR]

The subject aircraft type is not a new design, though it is being re-engined, and STC approved for the new engines. The aerodynamics, handling and stress characteristics of the aircraft are not in question here, they are already validated. It is only the issue to do with possible interruption of fuel flow during extreme sideslips, and resulting power interruption, which has prompted some discussion. This is an element of the STC approval process for fuel flow. Design compliance has been shown for all other aspects.

All pilots flying the test aircraft (including myself) have done so in accordance with Transport Canada approved test plans. There was a "grey zone" of agreement between myself, and the opinion held by some Transport Canada staff (who will issue STC approval), as a result of the observations of another qualified pilot. Neither opinion wrong, but each seeing the baseline pilot skill set a little differently, as it applied to this characteristic.

It appears from various opinions I have received (including here), that I had set the bar higher than perhaps most appropriate for the "average" pilot (whatever that is?).

The issue has been resolved, and agreed by all, and the flight manual will contain a caution note.

Thanks for your thoughts....

Pilot DAR

[Lightning6]

Understood, best to keep the bar high, the low fuel possibility is not one I considered I must admit, I've never been in that situation, definitely worth noting in the manual, and possibly other POH's. A good point has been made from this thread, which I have not seen in the POH's of any of the aircraft I have flown regarding fuel flow.