Wisdom of side-slipping a large jet?
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The fins of large aircraft are not designed to withstand the stresses induced from side loads (at and below Va = design manoeuvring speed) other than during normal flight ops, turbulence and single engine operation. The A300 accident in New York was simply due to mishandling rather than aircraft design flaw. Structural failure is likely to occur in any medium/large jet if handled in the same manner. To quote the flight manual 'Sudden commanded full, or nearly full, opposite rudder movement against a sideslip can generate loads that exceed the limit loads and can result in stuctural failure....CERTIFICATION REGULATIONS DO NOT CONSIDER THE LOADS IMPOSED ON THE STRUCTURE WHEN THERE IS SUDDEN FULL, OR NEARLY FULL, RUDDER MOVEMENT THAT IS OPPOSITE THE SIDESLIP'. (FCOM Bulletin No.827/1)
That said, I'm not sure if the original post was confusing wing down vs crab technique, with sideslip technique.
That said, I'm not sure if the original post was confusing wing down vs crab technique, with sideslip technique.
Last edited by GROUNDSTAR; 27th May 2007 at 19:08.
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This isn't dangerous just because of airframe stress. Think about the aerodynamic implications of side-slipping a SWEPTWING aircraft. The downwind wing's "sweep angle" is rapidly increased causing airflow over the wing to slow thus decreasing lift substantially. The oposite is happening on the upwind wing. (Think of it as a sort of Dutch-Roll.) Not only can the downwind wing ubruptly stall but the upwind wing can quickly rise due to the increase in life on that side. This is how a spin happens. All of this is exagerated by flap deployment.
The above senario could be terrible not to mention the effects of the sideslip on the engines (possible airflow reductions, over-temps, compressor stalls).
Bottom-line, sidesliping a large, swept-wing, turbine powered airplane close to the ground could go bad very fast.
The above senario could be terrible not to mention the effects of the sideslip on the engines (possible airflow reductions, over-temps, compressor stalls).
Bottom-line, sidesliping a large, swept-wing, turbine powered airplane close to the ground could go bad very fast.
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I did it once on a BCAL DC10. I was on a line check and I was a bit to fast to lower the gear. As I was about to intercept the glide I gave it a tad of rudder, lost a few knots and set of down the glide. I expect the trainer noticed but nothing said and I passed the check.
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Happy days
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ERJFO,
That's quite right, also relative airflow over the upwind wing will act at a more normal angle to the angle of sweep (also reduced spanwise flow) thereby producing more lift hence the tendancy for that wing to try to pick it self up (inherant stability of swept wing) thus in theory it's quite difficult to sideslip a swept wing aircraft in the first place.
That's quite right, also relative airflow over the upwind wing will act at a more normal angle to the angle of sweep (also reduced spanwise flow) thereby producing more lift hence the tendancy for that wing to try to pick it self up (inherant stability of swept wing) thus in theory it's quite difficult to sideslip a swept wing aircraft in the first place.
Psychophysiological entity
I'm not sure that your analysis of what's going on is correct. I don't know, but I'm not sure...if you know what I mean.
When the aircraft is in a stable side-slip, one would assume that it is descending. The wing loading will be reduced and the stall put back to comfortable distance from the airspeed over any part of either wing. Furthermore, a proportion of the aircraft's weight will be cushioned on the lower fuselage side, further reducing the chance of a stalled wing.
My reservations however, are in two parts. One, it would be difficult to assess the load on the tail without very skilled calculations. Two, the engine temps may not be showing some hidden parameters that they were never intended to display. But, I have seen huge loads on our brick built BAC1-11's tail, due to the strangest of occurrences. And I have seen the engine parameters showing extraordinary fluctuations due to other circumstances. During prolonged and repeated side-slips, I never saw the slightest variation in temps, just a little change in EPR
When the aircraft is in a stable side-slip, one would assume that it is descending. The wing loading will be reduced and the stall put back to comfortable distance from the airspeed over any part of either wing. Furthermore, a proportion of the aircraft's weight will be cushioned on the lower fuselage side, further reducing the chance of a stalled wing.
My reservations however, are in two parts. One, it would be difficult to assess the load on the tail without very skilled calculations. Two, the engine temps may not be showing some hidden parameters that they were never intended to display. But, I have seen huge loads on our brick built BAC1-11's tail, due to the strangest of occurrences. And I have seen the engine parameters showing extraordinary fluctuations due to other circumstances. During prolonged and repeated side-slips, I never saw the slightest variation in temps, just a little change in EPR
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When an Air Canada 767 ran out of fuel near winnepeg in the early eighties it became the worlds largest glider...... everyone survived though.
How do you think they lost the height to bring her down to a disused air force base? They side-slipped her several times
How do you think they lost the height to bring her down to a disused air force base? They side-slipped her several times
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landing technique
I agree with 'TROLLE' in his previous posting. There is a distinction between a steady state sideslip (as in a cross wind) and a forward slip, which is the technique used on light aircraft to lose excess height during approach.
I believe that the original posting on this thread was assess the relative safety of getting a swept wing transport into a forward slip in order to get height off.
The B777 flying manual specifically recommends setting up a steady state side slip in crosswind conditions and a max bank angle of 5 degrees is quoted. In limiting conditions ( 30-35kts crosswind) around 10 degrees of drift needs to be ruddered off and a control wheel deflection of 30-40 degrees results in order to keep the bank angle to approx 5 degrees. Therefore a sideslip manoeuvre IS permitted on swept wing aircraft, under specific conditions.
However,as in any sideslip, there is increased drag from greater control surface deflection and spoiler deployment on the raised wing, plus a loss of vertical lift component due to the bank angle. All of this results in an increased rate of descent on the B777 (or any jet) which has to be counteracted by a small increase in pitch attitude. If not, the aircraft will go low on the approach path. Within these parameters a small degree of sideslip MIGHT be used in non-crosswind conditions to lose height at constant speed.
If a similar technique were to be used in a forward slip in order to deliberately lose a substantial amount of height, it would be very easy to reach a point where where the rudder input would require full (limited) control wheel deflection in roll, to oppose the rudder . I would guess that this would occur at an offset heading of around 15-20 degrees, which is not a lot, visually. Would you really want to be at a control limit position at a high rate of descent close to the ground? Given the powerful roll/yaw couple of a jet transport, your sudden relaxation of the roll input when it is realised that roll control is being limited or lost could rapidly lead to to an uncontrollable roll-off at low altitude.
I believe that the original posting on this thread was assess the relative safety of getting a swept wing transport into a forward slip in order to get height off.
The B777 flying manual specifically recommends setting up a steady state side slip in crosswind conditions and a max bank angle of 5 degrees is quoted. In limiting conditions ( 30-35kts crosswind) around 10 degrees of drift needs to be ruddered off and a control wheel deflection of 30-40 degrees results in order to keep the bank angle to approx 5 degrees. Therefore a sideslip manoeuvre IS permitted on swept wing aircraft, under specific conditions.
However,as in any sideslip, there is increased drag from greater control surface deflection and spoiler deployment on the raised wing, plus a loss of vertical lift component due to the bank angle. All of this results in an increased rate of descent on the B777 (or any jet) which has to be counteracted by a small increase in pitch attitude. If not, the aircraft will go low on the approach path. Within these parameters a small degree of sideslip MIGHT be used in non-crosswind conditions to lose height at constant speed.
If a similar technique were to be used in a forward slip in order to deliberately lose a substantial amount of height, it would be very easy to reach a point where where the rudder input would require full (limited) control wheel deflection in roll, to oppose the rudder . I would guess that this would occur at an offset heading of around 15-20 degrees, which is not a lot, visually. Would you really want to be at a control limit position at a high rate of descent close to the ground? Given the powerful roll/yaw couple of a jet transport, your sudden relaxation of the roll input when it is realised that roll control is being limited or lost could rapidly lead to to an uncontrollable roll-off at low altitude.
revious posting, please read as 'spoiler deployment on lower wing' NOT the raised one!
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