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Aerodynamics in a side slip

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Aerodynamics in a side slip

Old 27th Feb 2018, 11:50
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Aerodynamics in a side slip

Hi All,

I am asking this question for interest of understanding what is happening in this manoeuvre. In a sideslip approach, with no wind, how does the fuselage blocking the trailing wing effect the lift that this wing can generate at its angle of attack? Assuming the wings are level and therefore the AoA also, does this not affect the wing behind the fuselage because a large component of the relative air flow is coming from the "glide angle" towards the aircraft, and there fore the side on fuselage is disrupting a relatively small amount of the airflow? Or is it that the trailing wing's lack of airflow is compensated by the fact that the right aileron is down, and therefore the wings angle of attack is slightly higher and it is generating more lift? For sake of simplicity can we ignore the lift generated by the fuselage.

In simple terms, how does having less of the trailing wing facing the relative airflow effect its lift capabilities, and why does this not translate to a lower stall speed (I understand stalling is related to AoA, but in this case one wing is generating less lift for the same AoA due to it not being able to make use of its whole surface area?)

Appreciate any comments, or help with understanding what is happening. I apologise in advance if my question is not that clear.

PelicanSquawk is offline  
Old 27th Feb 2018, 12:03
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A bit difficult to read. Perhaps where you write "effect" you mean "affect"?

Also I fail to imagine how the wings can be level in a side-slip, as you assume.

Still trying to reply: I always learned that side-slipping does increase the stall speed, however it so much increases the rate-of-descent that one still gets to the ground sooner - which is the primary goal of the manoevre (apart from the sheer excitement, of course )

Last edited by Jan Olieslagers; 27th Feb 2018 at 12:19.
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Old 27th Feb 2018, 12:17
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Thanks for the reply. Yes I meant "affect". And I realise I have indeed got a bit confused about the wings being level!

I guess if you keep the site picture the same, the increase in descent actually means the airspeed is staying the same, but you're trading distance horizontal through the air, for elevation?

OK I've just realised that you lower the nose, to maintain the same airspeed in the slip, and that is why your rate of descent increases. Sorry I think I understand it a bit better now, keeping the same site picture relevant to the horizon would slow the aircraft down, which you wouldn't want if you're already at the correct approach speed, so you would lower the nose to keep the desired speed?
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Old 27th Feb 2018, 15:44
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I wouldn't rely on the ASI in a sideslip.

Also check your POH wrt sideslip and flap settings. Some POH don't recommend sideslipping with flap, certainly the older 172's with 40 flap selectable don't, as I recall something to do with blanking off the elevator and causing oscillations in pitch.
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Old 27th Feb 2018, 18:32
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Much will depend on the type and wing configuration of the a/c; high/low. Are you side slipping to increase ROD, = high side slip angle, or side slipping for x-wind landing reasons = less angle and power on?
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Old 27th Feb 2018, 20:16
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Some aircraft sideslip better than others, Cessnas are not too good as you can only drop the wing by about 30 degrees. Other more aerobatic aircraft, and some of the older wooden gliders, with comparatively large rudder areas, allow a bank angle of 60-70 degrees, and the really aerobatic models can allow knife-edge flight with vertical wings (with maybe lots of power added.)
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