Other Effects On Turning

[phil c]

the "Flap Effects on Turn Radius" thread got a bit long.  One big effect I've seen on how pretty a turn looks is getting the plane to start and stop turning at the right time.  There was some discussion of flaps lowering the apparent or fuselage angle of attack in turns making the corner look better, but I've noticed something different that drastically affects how the plane looks, especially the bottom corners.

That is that the position of the plane in the maneuver, the neutral position of the handle, the neutral of your hand, the neutral position of your forearm, and the neutral position of the elevator all have to synchronize.  If they don't all hit neutral exactly where the plane is supposed to be going straight it won't look right.  And a significant added factor is the amount of "overhang" the handle has- the distance from where the lines flex and the place where your fingers rest.  Minimal or no overhang makes it very difficult to feel where neutral is.  Too much makes the controls stiff.  The pull on the lines, the speed of the plane, and the control forces all affect how much overhang is needed.  A light, slow, twitchy plane needs a lot more than the other extreme.

Getting all the factors trimmed is another excercise entirely from getting the plane trimmed.

[Dennis Toth]

Phil brings up some good points. Stunt is more than the "technical" correct aerodynamics. It is a subjective event and the illusion of how a maneuver looks is what is scored. Smooth, usually scores higher then hard cause it doesn't appear to "flow" through the maneuver. Wild Bill did a lot of work to try to hit the "5 ft" radius corner, it always seemed that non flapped ships would turn tighter and harder than flap ships. The difference was the smoothness of a moderate corner from the flapped ship vs. the hard bang of non flapped.

The one area I've notice that a flapped ship sometimes don't look as good is during outside maneuvers in high winds. Some ships develop a tendency to "kite" or float as they come over the top part of an outside maneuver. Even though the ship is traveling along the desired path the fuse looks like it is just a little behind the maneuver. I usually try to trim this out by adjusting the flap to elevator ratio to give the elevator a little more authority. This gives up a little lift but usually gets the fuse inline with the turn although I think with today's higher tail volume designs this may not be as be of a problem as with the Classic ships. Should be a way of calculating how much tail volume one needs for a particular weight, speed and wind speed one expects to see.

Best,   DennisT

[Brett Buck]

Phil brings up some good points. Stunt is more than the "technical" correct aerodynamics. It is a subjective event and the illusion of how a maneuver looks is what is scored. Smooth, usually scores higher then hard cause it doesn't appear to "flow" through the maneuver. Wild Bill did a lot of work to try to hit the "5 ft" radius corner, it always seemed that non flapped ships would turn tighter and harder than flap ships. The difference was the smoothness of a moderate corner from the flapped ship vs. the hard bang of non flapped.

    Almost any current competitive airplane (flaps or not) has the capability to turn MUCH tighter that anyone can actually handle. I could probably cut what I normally do in half or so. But, everything else will likely fall apart from inability to control something that takes so little time reliably or drag the speed down so much that the shape is difficult to maintain.

     We crossed the "turns are better than you need them to be" point about the time someone stuck a 40VF into an Impact. The obsession with turn radius and arguments over aerodynamics of minimum turn radius, wing loading, maximizing Cl, are just functions of the pre-tuned-pipe world that ended almost 30 years ago.

    It's not that anyone it trying to fudge it to get it to look better or "pretty", either. If you look at what wins most big contests, you will find that the top few generally get the shapes and bottoms right, and the contest is decided by turn radius that they can maintain consistently for the entire flight.

   Brett

[Ted Fancher]

"snip"

The one area I've notice that a flapped ship sometimes don't look as good is during outside maneuvers in high winds. Some ships develop a tendency to "kite" or float as they come over the top part of an outside maneuver. Even though the ship is traveling along the desired path the fuse looks like it is just a little behind the maneuver. I usually try to trim this out by adjusting the flap to elevator ratio to give the elevator a little more authority. This gives up a little lift but usually gets the fuse inline with the turn although I think with today's higher tail volume designs this may not be as be of a problem as with the Classic ships. Should be a way of calculating how much tail volume one needs for a particular weight, speed and wind speed one expects to see.

Best,   DennisT

Dennis,

I think you make some good points as well.  In particular with respect to tiny tailed classic airplanes which historically had way more flap than necessary.  And, yes, restricting the flap deflection is generally a good part of any fix with an inside/outside turn issue.

In my experience, however, when I've had a ship properly trimmed there won't generally be a difference between the fuse angle and the "track" of the airplane.  In fact, pretty much all of my airplanes are solider in outsides than insides (I've bloviated about P-factor, etc. excessively over the years so won't waste too many bits and bytes about it...nobody thinks P-factor is an issue other than me anyway [I know, "whine, whine, whine!"])

In my experience over the years any tendency for outsides to be less solid than insides is often best resolved by some bias of flap versus elevator...essentially always a bit of down elevator at neutral flaps (or, per David Fitz' "De-tails" column years ago in SN, build in a tiny bit of positive incidence in the stab.)  Brett has expounded on this a number of times addressing the vertical axis components of precession and P-factor due to the constant outward vector of thrust versus the circular track of the airplane.

One thing we've (or at least I've) learned since power ceased to be a significant issue for stunt ships is that maximizing lift is not always necessary and can be a negative factor if the combination of wing loading, angle of attack and high lift device deflection results in a lot more lift than is necessary to maintain the desired maneuver track.

Dinner calls.

Ted

[Howard Rush]

One thing we've (or at least I've) learned since power ceased to be a significant issue for stunt ships is that maximizing lift is not always necessary and can be a negative factor if the combination of wing loading, angle of attack and high lift device deflection results in a lot more lift than is necessary to maintain the desired maneuver track.

There, you've said it again.  I don't think that's what you mean, but I haven't been able to figure out what you do mean.  Lift determines maneuver track.  By "lift" do you mean "lift capability"?  Do you mean the propensity for the turn to tighten up or to go tighter than you intend it to, rather than following the intended track? 

[Ted Fancher]

There, you've said it again.  I don't think that's what you mean, but I haven't been able to figure out what you do mean.  Lift determines maneuver track.  By "lift" do you mean "lift capability"?  Do you mean the propensity for the turn to tighten up or to go tighter than you intend it to, rather than following the intended track? 

Add an inch of chord to your Impact's flaps; change nothing else.  Then go fly it and tell us honestly what differences in handling you experience.  I frankly don't care what you want to call it.  Then increase your flap deflection to half again more than the original elevator deflection and report back on the flight characteristics.  If I'm right the rate of turn will decrease significantly for a given amount of control input after each alteration.  If you're right it'll turn so quick you won't be able to win the W.Cs with it! 

Here's another way to experiment.  Build an Imitation like the plans show it with skinny, narrow chord flaps (constant 15% of the chord) divided into three sections per wing so you can go from full span (less tips on the original but make them full span if you prefer) trim it out to your preference with full span, then fly again with first one and then both  of the outer span segments fixed ; again, change nothing else and report back on the response rate with each set-up.  Here's what I think you'll experience.  With each reduction in flap span the response rate will increase; to the point that with everything else the same the corner will be too quick to fly consistently competitively without moving the CG forward.  Gotta admit.  I didn't make up this experiment from scratch.  Bob Gialdini wrote about the results of doing so back in the Olympic article when I was just a kid.  The comparison between a Nobler and a T-Bird corner was also instructive in that regard.

Or try this like I did.  Take a very nice flying unflapped Dick Mathis Coyote and add full span flaps to make it into a "real" stunt ship so you can fly in contests after a few years lay off; change nothing else and report back on the improvement in performance due to the addition of "high lift" devices.  Doing so destroyed the response rate...although moving the CG back would have regained the lost corner had I not pulled the fairlead out of the side of the fuselage trying to fly a triangle on the second or third flight when the music wire (before the invention of carbon fiber) pushrod buckled from the extra effort the pilot put into the corner.

Or do like we did with Paul Ferrell's "almost couldn't make it turn" profile ARF Cardinal.  Cut 3/4" off the trailing edge of each flap; change nothing else and go win Senior at the Nats (granted, the Nats winner was built from a kit to qualify but, rest assured, it didn't have stock barn door flaps).

Again, I don't know what an aero engineer would call it but the above experiments are verifiable by anyone that wants to try them out regardless of their field of study.  You can do it backward...just tape that extra inch of flap on your Impact and jump right into a five foot pull out on the wingover.  Even easier would be to leave the flaps stock, disconnect the elevator, fix it in neutral and just do the tricks using only the flaps.

[Howard Rush]

Captain, I wasn't arguing about what would happen with those experiments.  I just couldn't figure out what the phenomenon was that you were describing.  Now that you've told me what happens, I can benefit from your experience.  I wish what people were telling me had sunk in when I had my hexagon airplane.  It's flaps were too big and too stiff for the tail, with the result you describe above.  I had to operate it with a way-back CG. 

I think you mean by "excess lift" that a given airplane has either too much hinge moment to rotate the airplane adequately or too little net pitching moment to rotate the airplane adequately, or some combination of those.  In the case of the Impact, it was probably too little net pitching moment.  Both too much hinge moment and too little net pitching moment can come from flaps that are too big or, especially, have too much chord for a given airplane configuration.  Flaps do help with lift, but it's the flaps' other, nasty effects that too much flap gives too much of. 

There is another phenomenon that I thought you might have been describing: where at high lift coefficient, the restoring pitching moment peters out, making it hard to hold the target loop radius, hence my question about the propensity for the turn to tighten up.  Igor discussed this, I think, in his Stunt News article.  Looks like that's not what you mean. 

Assuming no side force component, lift is just the component of the aerodynamic force on the airplane in the direction perpendicular to the direction the airplane is going; drag is the component opposite to the direction the airplane is going.  I think one should use technical terms as they are defined, rather than to mean something else.   

[Ted Fancher]

Howard,

Thanks for the clarifying post.  I think we're getting somewhat closer to communicating.  We've got a houseful of people showing up for a big spaghetti feed in just a bit so I can't take time to respond right now.  I'll try to get to it tomorrow.

Ted

[Dennis Toth]

Phil,
One other component that has an impact on neutral control is mechanical drag throughout the control system. Some of the biggies are drag at the leadout guide, out of alignment hinges and dirt or stickiness of the lines. The leadouts with solid leads are critical to be very clean and also correct rake angle to minimize bending which causes them to drag. Hinges also need to be in alignment and not offset to the center of the hinge line. Last, clean lines so they slide smooth as you get a few turns in them.

Best,       DennisT