Sorry Glum, but if your supposition was true then logically, knife-edge flight by the aerobatic chaps wouldn't be possible, and it clearly is.
Absolutely, different designs will produce differing amounts of lift in a side slip, but it is difficult to imagine a design which would produce more total lift in a side slip. Don't forget that lift is the upward force supporting the aeroplane and if you are canted over in a bank, only the vertical component of your wings' lift counts. Factoring in the amount of wing blanked by the fuselage as well and its not looking great for a higher overall vertical lift component in a slip. Imagine a 30 foot wing at a 30 degree bank angle. Its only producing 86% of it's normal lift before fuselage blanking is considered. If you add 2ft of blanked wing at the root then you've got a total of 5.5 feet of wing producing no lift at all. There probably are not many GA aircraft designs that can produce more lift with a slipping fuselage than it can with five feet of wing.
Sure, your fuselage will be producing some lift but at the price of very high form drag (from being side -on to the airstream) and induced drag (from the large hole left in the air behind it that is a region of lower pressure 'sucking' the aeroplane backwards). Its this drag that we really want as we are side slipping in order to dump height without gaining too much speed.
All this drag however, does not act against the lift force because they act in different planes (axes). Drag is the horizontally retarding force that restricts our forward progress, whilst lift is the upward force that keeps us aloft, hopefully counteracting our weight.
As for knife-edge flight, you simply need enough power and at least some side-area to your fuselage. The more power you have, the less side are you need to produce a vertical lift component.
Simples.
In terms of real life though, I try my slips at altitude in a new type first. When coming out of the slip, I aim to come out in a nose down attitude which I then bring up once the controls are uncrossed and everything is stable.
Last edited by FleetFlyer; 16th Apr 2014 at 13:12.