The Zero's Maneuverability (4 Viewers)

Holtzauge · 2024-09-05T03:10:25-0400

Some more info on the Zero's cable stretch solution for the elevator:

While the solution as such may sound simple, in the book Horikoshi mentions that it was not the first thing he thought of and that he actually had to fight for it because just as can be expected, the Japanese design practice at the time was to design the control circuit as stiff as possible using rod controls if possible. So he actually had an uphill struggle before he managed to convince the customer to even try it out. And connected to this is a funny story: Apparently Horikoshi was away on other business when they planned the first flight trials with the smaller cable diameters. But when the test pilots heard about the modification they were afraid it was too flimsy and would not fly it! So he had to go to the airfield and convince them personally before they would take off! However, the flight trials were a success and showed it worked just as he had hoped for, and the solution was accepted for inclusion in the Zero's series deliveries.

And I can really recommend the book: It's not only a good read because of Horikoshi's memoirs about his life and work at Mitsubishi, but there is also a lot of technical details, figures and photos, flight trial and accident investigation data etc.

Engineman · 2024-09-05T06:17:02-0400

Holtzauge said:
About the Zero's elevator responsiveness and the cable stretch solutions: I noticed that this was mentioned earlier on in this thread and that someone was looking for a reference. There may of course be Allied reports saying the same thing, but the information can also be had from the horse's mouth so to speak :

In his memoir book Eagles of Mitsubishi, the Zero's Chief Designer Jiro Horikoshi actually dedicates a number of pages (pages 72 to 83) on this subject, and begins by stating that it was though that the Zero was actually TOO responsive in pitch at high speeds. That the roll response at high speed was poor is acknowledged in other parts of the book, but apparently the elevator was considered to be too responsive even at higher speeds. So while he confirms that stick forces in roll were too high, apparently they were not it pitch.

And those pages in the book also cover the solution, which was reducing the diameter of the elevator control cables from 4 to 3.5 and 3 mm in diameter. This introduced more flex in the elevator control circuit at high dynamic pressures, and it seems to have worked, because when they did flight trials, they concluded that not only did this fix the excessive responsiveness at higher speeds, but at the same time it did not mess with the low speed handling which still remained crisp.

Picture below from Jiro Horikoshi's book Eagles of Mitsubishi

View attachment 795618

This is an unusual description of flying control cable stretch function. Twisted steel Wire control cables are usually pre-stretched and installed with a set preload. The cables do have a linear elastic stretch rate in service and that might be approx 0.1% of nominal length at a working load around half of the max working load. So, for a say 15 foot cable, that would be less than a fifth of an inch elastic stretch of an installed cable, not much.
The elastic stretch is at a fairly linear rate between zero and 60% of proof load, so the elastic elongation would not occur at a set load, it gradually stretches and the slight elongation would not be noticable. However, above about 60% proof load, the cable will stretch with permanent deformation and damage.
So, an interesting subject. The described "stretch" above a certain load would seem to more describe a spring-box with a pre-loaded spring motor.

Eng

The Zero's Maneuverability (4 Viewers)

More options

Holtzauge

Airman 1st Class

Engineman

Staff Sergeant

Users who are viewing this thread

Similar threads