Incessant problems #2a - lazy hands and lazy controls

[Brett Buck]

Another case where you see slow or tentative control motions cause problems, probably even worse than the round loops, is the outside square. Just like the rounds, the transition from straight line to corner and back takes an even more aggressive motion to maintain any semblance of a shape. It's particularly bad on the entry to the outside square.



Everybody who has ever judged a stunt flight has seen that track time and time again. If you get a little slow on the draw, or get scared to do it, and become tentative, you end up doing an elliptical or parabolic "radius" and get the airplane too far out to the left and too low. Once you are vertical but too low, the maneuver is blown, because all you can do is make a token attempt at flattening it out, then get repeat the same thing as you get too close to the ground.

 To do it right, you have to be very aggressive entering and exiting the corner, and move the handle all the way as fast as you can to the correct angle:



   Note that if your control response is too slow, getting the right rate quickly is impossible. It's particularly bad if you have to use your elbow to move your entire arm, which is a very common thing to tell beginners. For all intents and purposes, you use your fingers and wrist to move the handle, not your arm, because that's just too much movement to accomplish. If your controls are too fast, then you will find it very difficult to hit the right angle, because a tiny error in the control input will make a big difference in the corner.

   If you use "exponential" controls (in the bellcrank, handle, or airplane response (i.e. nose heavy and fast controls to compensate, or flaps too large)) you can have the "too slow" and "too fast" problem at the same time! It takes a lot of hand motion to get it in the right range, but near the right angle, even a slight error moves the controls a lot. If anything, after having flown a lot of the very best airplanes, they tend to be "reverse exponential", fast around neutral and slower at larger deflections. I shoot for linear

     This illustrates the difference between trying to smooth out the flight for INT/ADV/low EXP pilots, and the Paul/David/Orestes group, where the biggest problem is getting the controls to move smartly enough to clearly mark the transition from straight to curved to straight. Just like all the crazy stuff we tell beginners (lock your wrist, turn the handle sideways when inverted, etc) it's something that helps today but hurts 5 years down the road.

   Brett

[Brett Buck]

   Another thing that tends to mess up your attempt to be distinct in delineating the corner entry/exits is any sort of compliance/"give" in the controls. This is why cable handles, and smaller lines, cause an issue sometimes. It's like adding a spring to the system. If you move your hand fast, the spring will stretch and slowly move the controls, then "catch up", move it too far, and then oscillate. So it causes the "lazy hands" issue, AND causes the final control deflection to move around for a while.

   You can overcome this with a lot of practice, basically, you move the handle *much further* than it really needs just to get it going, then very quickly move it back towards neutral to cancel out the overshoot that would otherwise happen. If you practice enough with  compliant controls, you can get this to work for a particular set of conditions, and you might not even be aware of it. Until you do fly a system with less compliance, you really have nothing to compare it to.

    I switched from a cable handle and .015 lines on my old airplane, to a Fancher handle and .018 on my new airplane, it was great, but I had really no idea how much I had been compensating for compliance on the old system until I flew it at some demonstration. I literally couldn't get the corners to stop hopping, and the first wingover pullout was a real <1' crowd pleaser.


    Brett

[Mike Callas]

Brett,
I never considered the lines as springs in tension. Did changing to .018" lines required more tip weight and power to overcome the increased drag?

Thanks
Mike

[Brett Buck]

I never considered the lines as springs in tension. Did changing to .018" lines required more tip weight and power to overcome the increased drag?

   It certainly does require trim changes!  Big changes, leadout and tip weight in particular.

   But the spring constant of the lines is significant and a lot different depending on the diameter and length. For example, the spring constant of each line is about 2.5 lb/inch for .015x64, and about 3.5 lb/in for .018x64. That has multiple interesting effects, not the least of which being that the .015" lines stretch about 2" in flight with a 4 lb airplane at normal stunt speeds. .018x64 are about 1.4".

   Even more interesting, for fans of second-order damped oscillators, is that the natural frequency of the airplane stretching the lines is about 1.2 hz, for a natural period of about .8 seconds. Might want to compare that to the amount of time it takes to do the straight sections of a square and triangular loops.

 There's A LOT more going on than *just* that, but it shows you that anything that upsets the airplane equilibrium that you can control (in this case, waving you arm around and changing the line tension), you probably should.

   Brett

[afml]

Thanks Brett for the 'tips' and especially the illustrations!
To avoid any additional 'Points' GIVE AWAY, please read the rule book as to when judging begins on this maneuver.
Some give the plane a little 'nose up' twitch to slow down the first corner before the decent.
More experienced fliers sometimes knock off the the first corner upon completing the maneuver.
They want to add emphasis to the completion of the maneuver,  only they do it a little too soon!
Many thanks again & "Tight Lines!"
Wes

[Walter Hicks]

Brett, Thanks for the excellent posts. After the Stunt Clinic Marshall Palmer and I checked the CG on my Spitfire. It was indeed tail heavy. On my
catastrophic  Square Eight they were overturned on the first leg. After .7 oz of nose weight ( New metal spinner ) the plane now balances
much better and the square corners are now (key word is beginning to) become vertical.This will require lots of work but is now much more possible with a balanced CG as opposed to the tail heavy condition.

[Steve Helmick]

Thanks Brett for the 'tips' and especially the illustrations!
To avoid any additional 'Points' GIVE AWAY, please read the rule book as to when judging begins on this maneuver.
Some give the plane a little 'nose up' twitch to slow down the first corner before the decent.
More experienced fliers sometimes knock off the the first corner upon completing the maneuver.
They want to add emphasis to the completion of the maneuver,  only they do it a little too soon!
Many thanks again & "Tight Lines!"
Wes

I quit doing that little "down joggle" at the end of the squares...after Pete Peterson gave me a severe verbal beating for doing it in the wrong place. It's not in the rulebook, so it's not required. Better not to do it, IMO. I just fly 1/4 lap at 45 degrees and then dive to level flight.  Steve

[Keith Renecle]

Hi Brett,

Thanks for these great articles on incessant problems. They are much appreciated! Just a question on the springy lines thing. I personally don't like the extra drag from 0.018" lines. I always see that bow in the lines if my models are not too heavy. My step son built a Cardinal that weighed around 67 oz. and that was fine on 18 thou. Going down to 62 oz. I find that the 15 thou. lines are too springy and 18 thou. is too draggy, so I used to use 14 thou. solids which felt good to me but then solids have other issues especially in wet weather. I then used the PAW Staystrate lines which are 14 thou. 3 strand soldered lines and they also feel good to me. They are "dirty" lines from the lead and quite expensive. I then went to the brass coated 15 thou. lines which I am told are Russian/Ukranian combat lines. Igor uses these lines and I managed to get some. I now fly with these and even on my last overweight 67 oz. monster, they feel really good. I'm not sure about the stretch and I can't test them accurately, but I don't notice any bad springy feeling in hard corners. What are feeling on the 14 thou. solids and these other alternatives? Thanks.

Keith R

[Brett Buck]

What are feeling on the 14 thou. solids and these other alternatives? Thanks.

    The .014 solids are more solid-feeling than .018 stranded., but have the "lockup" issue if they are even slightly wet, slightly dirty, or have more than about 50 flights on them (at least with the Jersey Strand and Cable polished SS lines that we all use). The wear mechanism is micro-spalling, where the polished surfaces stick/cold weld to each other in microscopic small spots, and pull the metal out of one line and it sticks to the other line. My dad finally figured that one out, he is a *stellar* engineer and that was right in his wheelhouse, being the worlds expert, literally, on forming wire, particularly polished tungsten wire into coils for incandescent light bulbs.

     I haven't tried the .014 StayStrates on my last two airplanes, bit Phil uses them. They are not legal for my airplane in AMA competition, since I am right at the .015/.018 break point (64 ounces). I seem to recall that Howard tested them and found them to be no stiffer in extension than .015 7-strand, but I could be wrong.

    Brett

[Keith Renecle]

Thanks Brett. It will be interesting to hear if Howard has tested them. I know that the 15 thou. 7 strand cable I use from MBS is springy on any of my .50 to .60 size models, and I can't feel that with Staystrate or the Russian lines. I also tried the 19 strand 15 thou. lines from Tom Morris and they were also springy. I used them for a while on my .40 size models and they are really nice and smooth. I did however experience a strange flutter from the lines when I increased the speed. It's hard to explain actually.

Keith R

[Howard Rush]

I don't have the data where I am now. I'll look for it when I get home.