Following on from an earlier thread re side slipping on approach, is the stall speed affected by such an approach? (assume nil wind)
And, in the instance of a stiff cross wind in which the aircraft is already cocked into wind on the approach, (before straightening out prior to touch down) is there a better direction to kick the aircraft to side slip in? ie is it better to accentuate the angle already cocked into wind, or to do it the opposite direction?
You always slip into the crosswind, as opposed to away from it. Were you to slip away from it, you would be blown off the runway centerline rather quickly, and have a heck of a time getting back. Also, gusts could increase your sideslip angle more than you intend, and make a lot of work for you recovering with less than ideal amounts of altitude available.
Sideslipping will not increase your stall speed, however it would be unwise to test the margin too closely. You will probably find rather large indicated airspeed errors begin to creep in with sideslips, as the static ports do not share the airflow equally. Most aircraft have two, but for aircraft like a 150, with only one static port, it can get bad. That said, if you have chosen to sideslip, it is because you would like to go down, so you have no need to be nibbling the buffet of the stall to do that, some extra speed is fine. If you feel what the plane is telling you, a sideslip will work out fine. Some 172s have minor annoyance with slips with flaps extended, owing to the relative position of the outboard end of an extended flap and the horizontal stabilizer, the wake from the flap happens to impinge on the tail, and can reduce its effectiveness and crisp control a little. It’s not life threatening though, as long as you are actually flying the plane! Most planes are very happy to side slip, right up to Twin Otter and DC-3 which I have sideslipped on a number of occasions. just always feel for control harmony, and the trend of the sideslip, to keep it where you want it to be…
Apparently for some aircraft, sideslipping can increase your stall speed because of the extra lift produced by the fuselage. Presumably then, you could find yourself in a situation where you are fine in the slip, but stall whilst trying to return to normal co-ordinated flight. For example, if you suddenly look at the ASI and think… “whoops – way slow” then it seems to me the correct course of action is probably to push the nose down rather than to panic and immediately centralise the controls.
As Pilot-DAR points out airspeed readings whilst slipping are not to be relied upon (or altitude, for that matter) and you can make the needles jump about in all kinds of interesting ways by varying the direction/extent of slip. Personally I really enjoy slipping and normally add about 10 knots over the clean stall speed for luck, and make sure the trim is set properly so you don’t find yourself losing speed inadvertently. I do worry that it feels like something that might stress the airframe significantly if you were to overspeed whilst slipping so I try not to go too fast either.
Still fairly inexperienced so more than happy for any feedback on this approach.
Apparently for some aircraft, sideslipping can increase your stall speed because of the extra lift produced by the fuselage. Presumably then, you could find yourself in a situation where you are fine in the slip, but stall whilst trying to return to normal co-ordinated flight.
Are you sure you have that the right way round?
Sorry, you’re quite right – I mean to say that the stall speed can be lowered in a slip.
I think if you are flying that close to a stall on final something is wrong. I can’t believe the lift effect if it exists is anything more than nominal.
Well, yes. It’s not something I was advocating. But people do from time to time get caught out hence all the incipient stall/spin training we get.
There are also sources out there that suggest that stall speed is increased during a slip – I don’t know by how much. Here’s one source that states that the lift produced by the fuselage is significant, but it doesn’t say by how much which will obviously depend on the aircraft:
http://www.ainonline.com/aviation-news/ainsafety/2013-12-09/aerodynamics-final-approach-slip-explained
It’s probably not an easy thing to measure because of the effects of position error on the ASI.
