Refer disclaimer
Overview
Obtaining of the approval to use the original quick build kit from Flying Legend was a difficult one and took this builder about 3 months work to understand and then learn to apply the rules.
Put simply the chart of tasks contained in AC29.xx allows points to be granted to the builder or the manufacturer and the balance must be that the builder has 51% of the work as outline in the document.
Chose to fabricate a complete set of wings from scratch and assemble them you would be granted one [1] point for each or a total of two [2] points - simple eh..!
Now chose to fabricate a trim for the aileron on the wing that you just built you are granted one [1] point for each task or a total of two [2] points - confused, join the club.
At this point Martin Ongley of the SAAA came to my rescue to explain the underlying rules because at this point the 51% just kept creeping away. So if a builder does some fabrication and assembly on a factory quick build he can take a point also, its called tap - tap. This is not to have you fabricate or build a wing, the rule makers just need you to understand the process by your input.
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| FAA kit listing of the Tucano as complying with the 51% rule Gold plated complience |
Back to today, as this was the submission that opened my account and with the initial resistance to use of a quick build kit on display at my original approach to the governing body's in Australia, it would be best that this builder sticks to the guideline agreed on and checked by CASA.
Note: CASA AC29 is a direct copy of the FAA guidelines. The factory now has a 51% FAA listed kit so there are no issues to new builders - just follow the plans and factory notes and you are there.
Design
The first task was to layout a suitable mechanism and after many hours of drawing the design outline was fixed. It places the trim drive at or near the hinge line driving a 2 mm carbon fibre tab fixed to the trailing edge of the aileron with extruded piano hinge. The push rod is a length of 2024-T3 tube fitted with 4 mm od aluminium rod ends to accommodate the misalignment created by the geometry of the mechanism.
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| Final Layout |
The next task was to determine how much force could be developed by this arrangement.
To estimate of the force exerted by the tab and to keep it simple it will be treated a plate in a stream of air with the formula used shown below.
Fd = cd 1/2 ρ v2 A - all information extracted from the Engineering Toolbox
Where Cd = 1.98 v = 84 / 70 m/sec
A = 0.008 m/sq projected @ 30 degrees
84 m/ sec = 300 kph
70 m/sec = 250 kph
Using the numbers at max a force of 67 N [big arrow] creates a rod thrust of 27N [max] with the tab having a available force of 33 N and reduced by 83% at cruise
The actuator selected is a Actuonix L12 12V 210:1 Miniature Linear Actuator providing a peak trust of 80 N and operating peak of 62N @ 3 mm / sec with a mass of 40 grams with a total travel of 30 mm or 15 mm on each axis.
This package will fit in the D nose of the aerlion and should provide adequate thrust based on the calculated and manufacturer specification. The bell crank will be machined from a solid bar to avoid welding and will be pivoted in sintered bushes off 5 & 6 mm diameter mounted into a 2 mm aluminium bracket riveted to the face of the aileron spar which will also will reinforced the opening for the push rod.
A rough comparison using the same techniques shows the torque exerted by a aileron at 30 degrees deflection compared to the tab showed it to be about 3 - 5% of that of the aileron assuming tab was neutral, so it can be assumed this is a safe starting point. The tab could be widened if required once the the results in the real world testing are confirmed.
Comment
In detail if the numbers are right extreme care still has to be exercised as this is only a basic mechanical analysis using simple assumption but dose provides a guideline and is better than a wild guess.
Next task order part, manufacture and install - Part II
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