Guys,
The drag we're "discussing" here (flap size, deflection, etc.) is -- as Howard so nicely pointed out -- induced drag, or the drag that is the byproduct of producing the lift required to carry the weight (multiplied by the G load) necessary to perform the mission of the airplane.
The key word there is "necessary". With our control systems the amount of lift (and, thus) induced drag we produce is not necessarily equal to the lift (and, therefore, induced drag) necessary to do our tricks. The flaps are deflected solely based on the amount of elevator input that is demanded by the pilot. The resulting lift that deflection drives the wing to produce can be 1. too little, 2. just right 3. too much; all based on how much the flaps are deflected by the demands of the elevator input. All too often we produce more lift than required to perform a given trick and that complicates the trim process as a result.
For a given amount of lift produced the drag which results from a given wing will vary only modestly based on whether that lift is gained through cambering (deflecting flaps) or a higher angle of attack or a greater speed (the three variables we can work with). If the lift produced is regulated to closely match the lift required from a nominal five to one aspect ratio wing the drag produced will be fractionally close to one another (aspect ratio, on the other hand, can make a huge difference).
To do the "job" with shorter span flaps will require a bit more angle of attack and vice versa. The resulting drag will be in the same ballpark regardless.
Stick forces are affected by the amount of lift in excess of that required we develop by not having a proper trim relationship between the flaps (of whatever size or configuration) and the lift necessary. They are also affected by the location of the CG relative to the lift they produce. This is like a dog chasing its tail … the more forward the CG the more elevator required thus the more flap deflected and the more lift and drag produced. BAAAAADDDD!
Stick forces are also affected by the aspect ratios of the movable surfaces. This is not a huge issue with any “normal” distribution of flapped span for a given amount of flap area. If, however, you attempted to get half span flaps of the same area as large full span flaps the aspect ratio (and thus the torque required of the control system to deflect them is substantially greater. Just envision 150 square inches of flap on the inboard ¼ of each span. You’ll quickly get a mental picture of how much more difficult it will be to deflect such fat narrow surfaces.
Again, within reason, it’s not something that will be disabling but IT IS A FACT of physics.
Here’s an example. For years I sailed an Aqua Cat (sort of an old man’s Hobie Cat) catamaran out of my back yard. This had a retractable rudder of approximately a four to one aspect ratio that was retractable at the waterline thus reconfiguring itself to a one to four aspect ratio. It was possible to “steer” with the rudder in either configuration. The difference was that in the normal extended configuration it required very modest, nearly light tiller pressure to deflect clear up to its maximum. It was also very powerful in directing the yaw of the boat in that configuration.
In the “up”, low aspect ratio position, it was very difficult to deflect and very inefficient at steering the boat. At speed I wasn’t strong enough to steer to any degree at all.
This is clearly an extreme example but is, nonetheless, indicative of the physical realities involved in wide chord versus narrow chord flaps on a stunt ship. It IS a real phenomenon.
Good discussion.
Ted
Topic: Howard Rush's flaps (Read 10855 times)