dynamite dean
28th May 2002, 18:42
1. Any good reason why one wouldn't sideslip with Flaps (light aircraft) meet many people who say you shouldn't but then they never seem to know why you shouldn't and the probable causes if you did?
11. What would happen if you stall a rudder? I wont try untill somebody lets me know what happened to them?
cheers a cautious pilot
oxford blue
28th May 2002, 19:10
If you stall a rudder, it usually happens at low speed, and very often, you go into a spin.
The Canberra and Meteor were both classic examples. The engines were set mid-wing. Such a configuration was bound to give asymmetric problems - and it did!
This is usually the reason why, on any twin with the engines set mid-wing, you have a Vmca. As the speed lowers, there comes a point where, one one engine, no matter how strong your knees are, you can't hold the asymmetric load any longer, because the rudder is not giving you sufficient authority at that speed. At that point, the aircraft departs - usually into a spiral dive.
In general, try to choose an aircraft with the engines set close to the fuselage - such as the Phantom, Buccaneer, Vulcan, or VC10. That way, if one packs up, you don't have too much of an asymmetric problem.
Sweet Surrender
29th May 2002, 01:09
DD As you intimate from your second question you already know the answer to question 1.
If you have a model or draw a diagram of a plane looking from above, and look at the where the airflow travels in a sideslip you can see that the airflow over the rudder comes from the inboard section of the wing - the flap area.
Now what happens when the disturbed airflow hits the rudder/ tailplane section depends on too many factors for there to be a straight forward answer.
I have sideslipped a number of singles and light twins without problems and I can honestly say that I have never heard of an accident due to sideslipping other than the "phantom diver" Meteor problems.
When teaching sideslipping however I do always mention that sideslipping with flap can cause problems. (Bit like on a cigarette pack and for the same reasons)
john_tullamarine
29th May 2002, 02:10
Sideslipping
You might consider the influence of the fuselage on the lateral airflow ... quite apart from any upwash or downwash effects it might add to the airflow, if you get a sudden separation of the airflow around the fuselage, the downslip wing and, more particularly, the horizontal tail surface, are put into a region of significantly disturbed flow.
The main concerns, as far as I can see, are the possibility, at low speed, of a rapid roll/yaw leading to a spin, perhaps, and a loss of tail download, with a consequent uncommanded nosedown pitch at low level on approach ... which is just when a light aircraft is likely to be sideslipped aggressively with flap ..... and we have all done it, haven't we ?
While I can't recall having read anything of an authoritative nature, anecdotal tales suggest that some aircraft are more susceptible to the problem than others and highwing designs likewise. Fortunately the SuperCubs I used to fly were quite docile when slipped very, very aggressively down to and into the landing flare .... else I might not be telling this tale, I should imagine ... sometimes I shudder to think what we used to do in our youthful ignorance as young tug pilots ...
Certainly the problem is not an academic issue and I can recall a number of light aircraft which have lurched and wandered about during slipping manoeuvring .... might I suggest, in the absence of manufacturer's guidance in the POH or similar documents, that it is prudent to examine the particular aircraft's characteristics at a safe height, in a progressive manner, prior to trying to slip it on approach. If the manufacturer suggests that it is not a good idea, this indicates that test pilots far more skilled than you or I have done these exercises and frightened themselves .. in which case ... why risk your own neck ... ?
Rudder stall
The rudder is a wing of sorts, mounted vertically. It has a similar sort of CL curve and so forth and will stall if too much is asked of it by the pilot. Two likely situations where this can arise are in
(a) low speed asymmetric work on a multi (those who have flown F27s will be quite familiar with the effect if full rudder is applied)
(b) aggressive sideslip manoeuvres.
In both cases, the effect is a reduction in achieved yawing moment and an observed uncommanded yaw. Whether this will present a handling problem depends on what sort, and rate of motions the aircraft undergoes and whether the horizontal tail surfaces are involved to any great extent. Potentially, at low speed, it could result in an asymmetric wing stall and spin with the potential for a significant bunt manoeuvre thrown in for good measure.
I would take a very small issue with OB on Vmca... any non-centreline multi will have Vmca considerations. If, however, the Vmca is somewhat less than Vs, as it can quite well be, then it may not be a problem ... but the effect is there, nonetheless.... In the case of the Canberra, for instance, the problem was more one of the aircraft's having an extremely high Vmca in the missed approach situation with the attendent risk of a Vmca departure in the event of an OEI missed approach which, I believe, took quite a few pilots to that great aerodrome in the sky ...