Ted’s pieces above have pearls of wisdom. As usual, somebody follows up like Mike did with “I bet all the guys reading this who like to understand why stuff works will be grateful for the benefit of your expertise.” I am one of those guys, and I am indeed grateful for the benefit of Ted’s expertise, but I seldom understand his explanations.
The primary role of flaps on a stunt ship are to provide the lift "necessary" to allow a competitive pattern to be flown with a small amount in excess for adverse conditions one might encounter. Such a wing could be smaller in overall area and, thus, less distressing in adverse air. Remember, it is entirely possible to fly competitive patterns with an unflapped stunt ship under "most" conditions.
Yep. If it's not the primary role of flaps, it's at least #3.
Note, however, that for a given amount of needed lift to be obtained the area required for doing so is greater on a wing with "no" high lift devices (flaps) attached. Generally speaking the necessary lift must be achieved with greater area...
Not quite. The relationship among wing area, airplane mass, and lift capability is clear when you look at what’s happening in a loop:
Lift = “centrifugal” force
Expanding,
˝ x air density x speed squared x wing area x lift coefficient= airplane mass x speed squared / loop radius
Solving for loop radius, not counting gravity or the cosine thing,
loop radius = airplane mass / (˝ x air density x wing area x lift coefficient)
So for a given airplane mass, air density and wing area, you can turn any size loop you want if you have enough lift coefficient. You control lift coefficient with your handle. You need about 0.1 in level flight. The most you can get without flaps is maybe 1.1, with flaps maybe 1.9. The extra you can get with flaps allows you to use more paint and have less turbulence response for the same minimum corner size or a tighter corner for the same paint and turbulence response.
...or higher airspeed...
Ted’s said this before. Yes, airplanes can get more lift by going faster, but for an airplane turning a loop of given size, the lift it gets by going faster is balanced by the lift it needs by going faster. To wit, not counting gravity,
Lift = “centrifugal” force
Expanding,
˝ x air density x speed squared x wing area x lift coefficient= airplane mass x speed squared /loop radius
Behold that speed squared appears on both sides of the equation, so it cancels. There are three caveats:
1. The speed on the left is airspeed, the speed on the right is inertial speed, so they don’t quite match, particularly in an overhead 8 on a windy day.
2. Gravity has more influence when you’re going slow than when you’re going fast. If my ciphering is correct, for 70-foot lines and a standard 45° stunt loop, acceleration is 5.1G at the top and 6.8G at the bottom at 50 mph. Acceleration is 14.0G at the top and 15.7G at the bottom at 80 mph, still 1.7G different, but smaller relatively.
3. In our Reynolds number range, maximum attainable lift coefficient goes up an RCH with speed.
Combat planes can generally turn tighter than stunt planes because they have lower wing loadings, not because they go fast.
However, a large tailplane on an unflapped ship, while technically "stable" with an aft CG (as appropriate for a big tailed flapped ship) would provide very little "feed back" (feel due to control loads) to the pilot during maneuvering. The feedback necessary for the pilot to "feel" and "perfect" his shapes becomes nebulous and flying decent patterns difficult for that reason...although the ship is "technically" stable. Flapless stunt ships instead regain the necessary "feel" by moving the "center" of gravity forward of where the the wing's lift is "centered". Thus the need to accelerate the forward CG in the pitch direction desired at the rate desired will require overcoming the natural tendency of the forward CG to pitch the airplane the opposite direct...thus providing "feel" to the pilot.
Here, Ted writes approvingly of feel due to control loads (hinge moment, we call it). I take it that some is good, but the amount you get with lots of flap chord is bad. The dynamic response is way different between flap and no-flap configurations, and I wonder if that is some of what he feels. The dynamic response (the transfer function between control input and airplane path) feels better with flaps because of direct lift control: you don’t have to rotate the airplane to increase lift. I reckon this is the second most important benefit of flaps, if not the first.
The big tailed flapped ship, on the on the hand, can, on a ship with an aft CG near where the lift is centered, produce the desired feedback/ feel to the pilot by virtue of the negative pitching moment produced by the flaps' deflection (opposite to the pitch desired for the maneuver) coupled with the air loads that must be overcome to deflect the flaps in addition to the elevators. This aftward CG location pays great dividends when flying in other than ideal conditions by all but eliminating the need for greater control inputs for a given rate of pitch change and, as a result, a much reduced tendency to speed up...and thus open up...maneuvers.. I.e. the inputs required to fly competitive sizes/corners will be very little greater than under good conditions.
Having the same control inputs for different conditions is good, but I don’t see how this paragraph explains how you get there.
The point with respect to this discussion, re refinement of the flap cross section etc., is that all these "configuration" subtleties under discussion here make almost no difference. The only flap design factor I consider truly important is that the chord of the flap (as a percentage of the wing chord) be no greater than "necessary" to support the maximum loads the ship is likely to encounter plus a tiny bit in case you get carried away with the clear kote!
Ted’s flap chord observation is one of his best wisdom pearls. I wish I’d learned it sooner. However, you can lead a horse to data, but you can’t buy him a drink. Is that how it goes? My interpretation of figure 19 of the TE bevel report (here’s a better copy:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092890.pdf) is that a 30° bevel on a 20%-chord flap on an NACA 0009 gives you the same hinge moment reduction as reducing the flap chord by 40%.
Tailoring hinge moments was a big deal in the days of aluminum airplanes and composite men, and there is a bunch of cool NACA reports available to everybody now, many of which I bet are pertinent to stunt. I thought the art died when hydraulic boost spoiled everything, but I had an interesting chat with Tim Just the other day about the stuff they do with full-scale aerobatic airplanes. I don’t know how it applies to toy airplane stunt, but it’s really cool.
I just don't think there is any "magic" in flap design configuration that will predictably produce better scores on an otherwise just OK machine. I love the interest in such things but feel it is important not to make modest factors "primary". I also, however, appreciate the inventive mind's desire to inquire and, if he/she so choose to say thanks but no thanks. I opine primarily because I spent a measurable part of my stunt "career" investigating/experimenting with such factors and found assigning greater importance to such things unconvincing. I could be wrong! but, so far don't think so in any significant way.
Herein is another Fancher pearl. Guys (me, for example) will sieze on one idea and figure it will make them winners while neglecting other, necessary things. I’ve seen this effect even more in the real airplane business than with modelers.
One more thing: what’s with the quotation marks? Is that a stunt thing? Bill Werwage used quotation marks like that in his Ares article. Walt Kelly did something like that in Pogo captions. Some words had bold lettering, some didn’t. He explained that he had two pencils, a sharp one and a blunt one. Sometimes he’d use one, sometimes the other.