Real Fowler Flaps
On page 113 of the April Model Aviation, I was intrigued to read that Jim Hiller was going to fit "fowler flaps" to his model in an attempt to "...see if they are as effective on a model as they are on a full-scale aircraft."
I am intrigued to see how he handles the intricately machined dual tracks (at each end of the flap recess) necessary for Fowler flaps (note the upper-case F) to properly function. Why the tracks? They are necessary because Mr. Fowler's flaps are area-increasing flaps.
A "roller skate" cam follower at the end of each flap is engaged in the dual tracks at each end, so that the flaps are guided to travel aft a considerable distance and lower only about three degrees to the loiter position before commencing to steeply move down to the maximum lift-and-drag position. This was plainly visible on the P-38 as well as the Constellation airliner.
Any other type of flap on which the flap hinge is located well below the bottom wing surface is nothing more than a simple slotted flap, as seen on the humble Cherokee and some airliners. The Cessna Paraflift™ flap is only a variation of the Fowler, since it, too, follows a track.
In all fairness, I don't see how your columnist can inform his readers if his RC model flap is better than the full-size equivalent anyway, since he neither has "hands on the stick" nor the instrumentation to inform him if the design parameters are being met. He has only the humble Mk. I eyeball — and that is far from accurate.
In any case, will he be following the clearances (defined by NACA) between the flap and the airfoil trailing-edge lip? These are necessary for a slotted flap to produce the desired results with any airfoil section. Add to that the confusion caused by Mr. Reynolds and his Reynolds numbers at model scale.
Jim Newman Kent City, Michigan
Transcribed from original scans by AI. Minor OCR errors may remain.
