(snip) Here's another question regarding flap chord. By reducing the flap chord toward the tips, doesn't that effectively produce some washout at the tips when the flaps are deflected? (Less angle of attack the tips) (snip)
Jim,
The above copied from one of your earlier posts!
I believe I've always advocated consistent percentage of flap chord for the flapped portion of the wing. I have, by the way, built planes my preferred way with "fixed trailing edges" for the span encompassed by the wing tips. This generally amounted to three inches or so because my ships have pretty much all had "swept" wingtips with curvature "raked" from leading edge to trailing edge.
I did, however modify my last Trivial Pursuit to increase the flaps to full span when I repainted it from the original red,white,blue of it's "Great Expection" years (which included a win at the 1986 Nats to the Pond Scum Purple refinish (per Bubba Hunt) when it won its last Nats in 2000. I did so solely because so many of my flying buddies... Dave Fitz, in particular, on very "similar" ships...utilized full span ones and were kicking my butt with unpleasant regularity.
For what it's worth I didn't like the altered version all that much...although it didn't stink. I felt the same corners required more effort on the part of the pilot which, as a finger and wrist pilot, I didn't appreciate. I postulated that the longer "flapped" segment increased the negative pitching moment of the now full span flapped wing, thus requiring the greater pilot effort. Although I'm less confident, I also postulated that the wing tip vortices, all emanating from the deflected flap itself may have also played a part in the increased "load" I was experiencing.
I don't feel that "lift" is the secret to sharper corners. If you ain't stalling in a corner you've got the lift necessary to accomplish it. If you don't...you won't! In addition, if you're developing more lift than necessary to support the weight of the aircraft the "angle" of the fuselage path around the loops, etc. will be modestly different from "straight" ahead per the radius you're attempting to track. You only "need" enough lift to support the "G" induced load required to maintain the desired radius of a "turn". If you "get" the required lift prior to the body reaching "parallel" with the arc of the desired path your flight path's intersection (of a horizontal eight for illustration) will occur prior to the fuselage reaching "vertical" and vice versa. As a result, disputes could be made as to whether you did or did not perform and accurate intersection!
Finally the wisdom of the search for the zero ounce stunter! First of all see the preceding paragraph and contemplate flying a figure eight with a 700 square inch full span flapped wing. I think the problem would be obvious.
Second of all, a real world example of the near opposite state of affairs; starring, yet again, the Trivial Pursuit...a "pig" of a plane at 73 oz, 650 sq. inches of flapped wing area...albeit with flaps ending three inches prior to the full span of the wing with tips. Also a "pig" of a plane that won one US Team Trials, four second place Nats finishes plus four other top fives. Not bad for a "Porker"!
Here’s the rest of the story, however. The part that more or less is the proof of the zero ounce pudding!
At one of the later Nats at which I flew the T.P. it was unusually hot and humid and during a practice flight prior to the start of the comp something happened. For the first time ever the T.P. stalled—dramatically, saved only at the last possible second--in the last corner of a triangle! Ooopsy!
Long story short, Brett and I diddled around with the ship and ultimately added a primitive form of vortex generator to the top of the wing…we taped a couple of feet of control line to the top of both wings an inch or so forward of the high point of the airfoil. Result, no more stalls and the T.P. continued to a top five finish!
Ultimately, to get rid of the ugly taped on wire I simply raised the elevator pushrod a couple of turns so as to get just a wiggle of additional flap deflection for a given elevator deflection and forgot about the issue from then to the time I stuck my finger in the prop setting the needle valve, snapped a blade off the three blade Eather prop and the poor T.P. shook its front end to death as P.W. tried to shut it off by pointing the nose down…but the froth in the tank just increased the RPM and…Good Bye T.P.
The reverse of all the above was well illustrated with the “career” of my ultra light (32 oz) Tucker Special which was built thus almost solely to experiment with the “zero ounce stunter” concept. The tale has been told several times here on S. H. but, long story short, the airplane was very difficult to fly well at that weight with corners seeming to take place at random places and radii. Making simple loops the same size--and round! --was very difficult. IOW, it pretty much sucked!
Brett and I took the ship to the field one day with the tool box refilled with stick-on lead weights cut in ¼ oz segments. In a series of flights we added these weights a total of one ounce per flight by sticking them, four at a time, to the wing near the fuselage, one each on the top and bottom of each wing at the CG, thus increasing the gross weight without moving the CG or unbalancing the wing inboard to outboard.
We eventually added eight total ounces to the ship flying it after every added one ounce of lead (four 1/4oz chunks). With each addition the consistency of all the above problem was mitigated and after a total of eight ounces was added the airplane was “dramatically” better and easy to fly competitively. No question, heavier was better!
The point of telling these stories is to illustrate how the tub of lard T.P. had always flown close to the edge of its lift margin yet had consistently placed near the top of some of the most competitive comps on the planet. Almost as illuminating was that it did so with powerplants ranging from, at first, a little piped VF .46 to, ultimately, a Ro Jett .61. The lesson, more or less, was that—when coupled to the earlier experiences with flap spans, Tucker Special tests, etc. was that building a stunt ship too heavy was almost as hard as building one too light but way less damaging to the score sheets.
What we need is access to “enough” lift but lift much beyond “enough” is likely to be harder on the score sheet. I’m simply not a big fan of maximizing lift for lift’s sake Given “enough” lift, centered in the right place with respect to the CG ; with the CG properly located fore and aft (near the center of lift) and a tailplane of the appropriate size and configuration and with the hinge lines sealed to insure uniform distribution of the lift they produce…plus several dozen test flights to optimize flight trim…is the appropriate path to success at the field.
Sure, it’s fun to diddle with the minutiae of the multiple facets of the “aerodynamicness” of the whole thing but, for the most part, I believe the minutiae in an aircraft as fundamentally simple as a CL stunt ship pretty much remains just that: minutiae.
Sorry. Got carried away. Between the smoke filled skies of the San Francisco Bay Area and the lock down of the COVID “Pandemic” one has to fill the forced indoor hours with something!