I can think of one particular type even without especially low fuel that you definitely didnt want to slosh the fuel to one side of the tank!
What is that type?
I recall a twin turbo prop crash on the runway in a crosswind landing following an engine failure and subsequent assymetric approach. As I recall one wing contacted the runway on touchdown resulting in a ground loop and substantial fire with multiple casualties. I think it was sometime around the early nineties but unfortunately I can’t find the details.
I recall my CFI at the time being of the opinion that an unbalanced wing down crosswind approach coupled with asymmetric thrust led to the crew getting into a buggers muddle at the point of touchdown resulting in the accident. (He was strongly agin wing down approaches)
What is the general view regarding the best approach technique with assymetric thrust?
You have been taught slipping as part of your PPL, yes? In UK money, that would have been Exercise 8.
It was a long time ago, but I was never taught slipping and indeed was told that doing it in a Cessna was “extremely dangerous.”
Interesting to hear it is now on the syllabus.
I can think of one particular type even without especially low fuel that you definitely didnt want to slosh the fuel to one side of the tank!
What is that type?
There are several types that will unport one wing tank in a slip, with the effect depending on fuel level and of course to which side you slip. Luscombes equipped with wing tanks are one type that you don’t want to slip for an extended period while drawing fuel from the down side wing, if fuel level in that side tank is low.
flybymike wrote:
It was a long time ago, but I was never taught slipping and indeed was told that doing it in a Cessna was “extremely dangerous"
Cessna 170s and 172s have an aerodynamic issue with slipping, with flaps fully extended although not otherwise. Slipping is the primary way of controlling descent rate in many other aircraft.
flybymike wrote:
It was a long time ago, but I was never taught slipping and indeed was told that doing it in a Cessna was “extremely dangerous.”
I actually have a T-shirt “Slips with flaps” (in the same vein as “Runs with scissors”).
This was a perennial topic on the old rec.aviation.* newsgroups (people generally declaring “Slips with flaps are prohibited, are you out of your mind!?”, hence the T-shirt). In reality there is a range of C172 models where the POH says “Slips with flaps should be avoided” and mentions a possible pitch oscillation when a slip is performed with full flaps, and that the oscillation will stop if you take the slip out.
Many aircraft slip with flaps just fine of course. My current aircraft does a good impression of a safe with the door open when you slip with flaps (in other words, matches the glide angle of a Piper Arrow with the engine at idle). The Piper Pawnee was another aircraft that would oscillate in pitch if you slipped with flaps – the manual didn’t mention it, nor did anyone else at the soaring club, so I discovered that one myself :-)
Silvaire wrote:
Cessna 170s and 172s have an aerodynamic issue with slipping, with flaps fully extended although not otherwise.
Only early versions with 40 Deg flap.
flybymike wrote:
It was a long time ago, but I was never taught slipping and indeed was told that doing it in a Cessna was “extremely dangerous.”
Your instructor was being disingenuous.
flybymike wrote:
What is the general view regarding the best approach technique with assymetric thrust?
Faster. You’re only asymmetric until you cut the power on the good engine. In very simple terms, an asymmetric approach is best flown in a relatively clean configuration with about 50% power on the good engine (I’m talking MEP) so the ‘assymetry’ isn’t particularly bad. I fly the approach fast and clean because that gives me more options if I have to go around. I would probably crab in this scenario because I’m already playing around with an imbalanced rudder authority.
Alexis wrote:
Only this much: Of course an airplane in a forced sideslip can EASILY be stalled in a strong gust. And strong crosswinds often come with strong gusts.
All I wrote is easily accessible basic aeronautical knowledge that cannot be dismissed by saying “it’s not true” or “why should it stall”.
It’s not (necessarily) true. Fancy a flight with an instructor/examiner?
Alexis wrote:
IF you stall the airplane cross controlled and close to the ground, for example in a strong gust, it will many times result in a deadly spin.
Slips in many aircraft are spin-resistant – and particularly in aircraft which were designed with slipping in mind (light tailwheel) are quite difficult to stall when in a slip. Of course your mileage may vary, specific aircraft etc. etc.
However, I did once try to aggravate my Cessna 140 in a slip to see what it’d do. The Cessna 140 is a type that can be spun in the conventional manner, and spun fairly easily.
In a maximum effort slip (rudder pedal to the floor, whatever aileron required to keep the aircraft from turning) and power to idle, with the yoke all the way back to the stop, what happened was the aircraft shuddered a lot – there was no way you could miss this – and there would be an oscillation in pitch. There was no tendency to do anything remotely like a spin, and in fact the typical break and nose drop experienced with a stall did not occur either. If there was an increase in stall speed, it was trivial.
Because you can spin from a skid, it doesn’t follow that all cross controlled flight will result in a spin. You need some yaw, and generally yaw is not a feature of a slip.
Fancy a flight with an instructor/examiner?
From what I read I think you are a more experienced FI, but I am one myself (CRI), so I have one on board on every flight :-)
What does it mean when you write it’s not “necessarily” true? I know that airplanes are different, but in general it’s simply, well … true!
at alioth:
Because you can spin from a skid, it doesn’t follow that all cross controlled flight will result in a spin. You need some yaw, and generally yaw is not a feature of a slip.
Yes, that is true. In my previous answer I mixed up skid and slip. While there should be a little yaw in every sideslip, it is very little.
You are right.
Stephan_Schwab wrote:
Maybe it helps to differentiate in the conversation betweena) flying a pattern and turning final at 500 AGL
b) flying a long 8 NM final with a DA below 500 AGLI’ve had the impression you’all were talking about slightly different things.
As far as I am concerned, my crosswind landing technique is exactly the same in cases a) and b).
Alexis wrote:
I don’t really care how others fly,…
I do. Firstly because my job involves monitoring the flying skills of students and colleagues and secondly because even at my age one is never too old to learn. Sometimes (more often then not) watching others do something differently from the way oneself has been doing it “forever” can improve one’s own performance…
Fuji_Abound wrote:
I can think of one particular type even without especially low fuel that you definitely didnt want to slosh the fuel to one side of the tank!
That reminds me of one of the more stupid flights I was letting myself get talked into in my earlier flying career. I was supposed to fly three people somewhere in a Seneca and back in the evening. Of course in the morning not three but five persons turned up for the flight. Young(er) and stupid as I was then (I still am but have perfectioned the art to say “No!” in the meantime) I still accepted to do the flight with minimum fuel so as not to be too much over the maximum takeoff mass and not too close to empty tanks at destination.
As it turned out, when we arrived there the tanks were even emptier than I had anticipated, so I happily accepted a direct approach to a runway which was more or less in our flying direction. As I had, based on the wind, planned my descent for a landing on the opposite runway, we came out very high on final initially. So I sideslipped that Seneca down for almost 3000 ft (female passengers shrieking in the back for a whole minute in stereo…) at minimum speed because the runway was not really very long for that kind of plane. We landed safely and had sufficient fuel to taxi to the ramp…
But after landing, I remembered an accident report I had read shortly before that flight of a twin crashing because the tank outlet ports became uncovered in a sideslip due to low fuel content resulting in one engine stopping. I don’t know how close I was to the same thing happening to me that day, but it can’t have been for more than a couple of millimeters of fuel. As my controls were already at their stops in the sideslip I would have had nothing left to counteract the asymmetry resulting from an engine quitting (or even coughing) and at low altitude this would have been a 100% certain unrecoverable crash claiming six lives, mine included.
That was the last time ever I sidelsipped a twin (piston, turboprop or jet, no exception) and I will never do it again, no matter how much fuel there is in the tanks.
A quick google search found these four accidents caused by fuel starvation due to sideslippig on the first page of results. And there are hundreds more:
http://www.bst-tsb.gc.ca/eng/rapports-reports/aviation/1994/a94q0164/a94q0164.pdf
https://www.aopa.org/asf/ntsb/narrative.cfm?ackey=1&evid=20121112X13818
https://www.aopa.org/asf/ntsb/narrative.cfm?ackey=1&evid=20130903X23635
https://www.aopa.org/asf/ntsb/narrative.cfm?ackey=1&evid=20141005X41513
