This will be my only post because I don't want to get into a argument.
It was explained to me that the Netzeband wall was the plane not having enough weight to fly smoothly through maneuvers due to loss of line tension.
So my question is (and my fix) Is it possible to hurtle this impossible wall with motor offset and line rake , rudder offset and tip weight. Of course making sure everything weight wise is in alignment. The next thing involved is super free (low friction) controls.
Engineer types answer here .
The "Netzeband Wall" is as Howard describes - when the line tension is insufficient to move the control enough, or as much as you want. Its about running out of control torque. It takes substantial torque to deflect the controls into the airstream, and the control system has to supply it. The torque is applied by differential line tension.
If you move the controls, the line you are pulling towards you has more tension than the line you are allowing to be pulled away from you. The maximum amount of difference you can get is the full line tension all on one line (one line taking all the load, or "hung on one line"). That amount of force times whatever bellcrank lever arm you might have, is the maximum amount of torque you can apply to the bellcrank. This torque, divided by the lever arm from the bellcrank pivot to the pushrod is the maximum amount of force you can apply to the pushrod. This force, times the lever arm of the control horn, is the maximum amount of torque that can be applied to the flap horn.
In any case, the controls will deflect until the differential line tension x all the mechanical advantage equals the torque required to deflect the controls. Since the line tension is limited, the controls can only move so far. If that is less than you need them to move, you hit the Netzeband wall.
With a conventional straight bellcrank and a normal control setup, the torque available to move the controls goes down as you deflect it. A neutral, on a 4" bellcrank, with 10 lbs of tension, you can get 20 inch-lbs of torque at the bellcrank (2" x 10 lbs). With a 3" bellcrank it's 15 in-lb - that's why you want a big bellcrank.
As you deflect it the lever arm at the bellcrank is reduced. If a 4" bellcrank is deflected 45 degrees, the lever arm goes from 2" at neutral, to 1.41", so you now only have 14 in-lb available. You can see it by figuring what might happen if you let the bellcrank go to 90 degrees - in that case, the leadout and the pivot are in line, so you get *no* torque at all.
While you are moving the bellcrank and reducing the torque available, the flap and elevator deflect, too, increasing the torque required. At neutral it takes nearly nothing to move the controls. As you go further, the required torque goes up very quickly. This torque is called the "hinge moment". So as you move the controls as a system the torque available goes down as the controls require more torque, and it will stop and deflect no further at some point.
Note that you might be tempted to slow down the control ratio from the bellcrank to the flap to make better use of the available bellcrank torque. That works to a limited extent (as Paul Walker has done it) but at some point, you have to move the bellcrank through such a large angle that you start losing torque because of the bellcrank angle.
Note also that making the handle larger doesn't make effect the available bellcrank torque at all. It's not like using a "cheater bar" on a wrench as some have suggested. You still only have so much line tension, once you hang it on one line, you are done, and with the other line hanging slack, it doesn't matter how far that side of the handle moves.
You can only do one of two things to improve this - either get more bellcrank torque, or reduce the control torque required for a given deflection. To get more bellcrank torque, you can make the bellcrank larger, making the lever arm larger, or get more line tension. The bellcrank can only be so big and still fit in the airplane, to you are necessarily limited there. Getting more line tension is certainly possible, and your first thought might be to speed the airplane up so you get more tension. Unfortunately, speed it up also increases the hinge moment, since it is a function of aerodynamics, it goes up quickly as the speed increase. As it turns out, many times speeding it up doesn't help at all, its faster but you haven't been able to increase the control deflection.
If you try to fly it slower, it reduces the hinge moment, but also reduces the line tension and thus the bellcrank torque.
You can try to get more line tension by other trim adjustments, without increasing the speed. This usually involves putting in extra tip weight, extra rudder offset, etc to "manufacture" line tension. The Nobler was set up like this, with an idea to fly it very slowly (compared to others at the time) by putting in large amounts of rudder offset and a far aft leadouts to yaw the airplane outboard. You can still do it that way, but it definitely compromises the trim in other ways.
You can reduce the hinge moment by changing the aerodynamics of the airplane. For example, reduce the flap or elevator chord, and make the span larger to compensate, or use aerodynamic counterbalances, or a servo tab like Howard did, or a number of things like that. That doesn't help the available torque, but it does reduce the torque required.
The other half of Paul Walkers "Impact" approach is to reduce the control deflection required by running the CG aft. If the CG is further aft, it takes less deflection, so less hinge moment for a given amount of turn, so you have more margin over running out of torque, or get more corner for a given hinge momement.
Finally, you can just make the airplane heavier. The weight is more-or-less a linear relationship to the line tension. Add 20% to the mass, and you get 20% more line tension, all other things being equal. That way, you can definitely deflect the controls further at a given speed. Or, you can get the same deflection at a lower speed.
Ted's Tucker Special experiment was the latter. The airplane was already built, so most of the other options didn't exist. The aerodynamics were set by the design, and since it was a classic airplane, couldn't be changed. The controls were installed and couldn't be adjusted in any useful way. It was pretty light to start with, with light line tension, and otherwise trimmed conventionally without compromises to increase the line tension (and create other problems). Plenty of power. It didn't turn very well, and was very floaty. The first thing he tried was to fly it faster. Eventually it was down to maybe 4.6 seconds a lap, but it wasn't any better because although it had more line tension, it also required more hinge moment, so it was no better off. We then added weight in 2 ounce increments, right on the CG. The first 2 ounces greatly improved the turn, and permitted significantly slower lap times. We then went to 4, then 6, then 8 ounces. Each time, the turn got better, the airplane could fly more slowly, and generally looked far more solid overall.
It was not a subtle effect, or a figment of imagination, it was a very large and blatantly obvious improvement.
In traditional lore, the turn should have degenerated because the wing loading went up dramatically, and the vertical performance would have suffered because dragging 46 ounces to the top of the circle is a lot harder than 38. In fact, the turn got *much* better, because the lift was not a limiting factor in the first place, and the controls could be deflected much further than before, he could get more lift (more flap deflection) and a higher pitch rate (more elevator deflection). By the same token, the vertical performance was hardly affected at all since it had much more power than the original.
Point being, of course, that if the weight is not the limiting factor in the first place, adding weight doesn't hurt, and may help. Of course, eventually, adding more and more weight, it would become a limiting factor and starts hurting. Even on a vintage design like the Tucker, with modern power, this is much higher than most people seem to think.
My other example was actually a real one - two 585 square inch airplanes, both with PA65s, one at 54 ounces, the other at 66. The 66 ounce airplane flies *much* better because it can be trimmed conventionally and still have enough margin over the Netzeband wall, and the light one has severe issues with trim and turns poorly because it runs out of control effort (among other issues).
So, the Netzeband wall is where the control torque required equals the control torque available. There are number of ways to improve the situation, but simply adding weight (either otherwise useless dead weight like this, or in beneficial added structure like the Infinity) can improve it, up to the point weight does start hurting in other ways.
Brett