Aileron Trim Part I

This blog covers the design and installation of the aileron trim. 

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.

FAA kit listing of the Tucano as 
complying with the 51% rule
Gold plated complience 

The real intent of the apparent discrepancy of work allocation between building a aileron trim and a wing including the aileron is for you to display your ability to fabricate and assemble a small piece of an airplane yourself then make possible to purchase a quick build wing while meeting 51% of the constructions tasks - make sense!

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.

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.

F_d = c_d 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

Infinity Grip Junction Box

This blog covers the trim junction  box

Overview
The trim control and sticks require a significant amount of mixing of the wires at some point and doing this behind the panel would have possibly created a lot of cross wiring in a small area. It was decided to create a junction box on the starboard side and the point chosen were the cables supplied with the Infinity grips meet.

The most practical way was to use a series of 9 pin connectors installed into a ABS junction box sourced from JayCar.  

Installation
Once the switch assignment was decided the grips were installed onto the factory sticks. Slots were then cut at the base of the factory sticks allowing the cables to exit and be terminated at the proposed junction box. 

The top side of the factory stick was covered with two [2] layers of gaffer tape that was folded over into the inside of the tube to provide anti-chafe protection for the wires as they entered the tube. The tape also provided additional diameter allowing the Infinity grip to clamp onto the stick tube as its diameter is about 0.4 mm undersize. 

Note: The Infinity grip was clamped using the screws supplied with the grip 

Cable to junction box from pilots stick

Use of 9 pin RS232 requires a number of holes to be created and a suitable punch was purchased to allow a professional job.

Four [4] dual relays were next installed onto the case front panel and secured with a suitable screws with two additional screws installed as a positive and negative tie points.

Wiring junction box
Note: RS232 had to be installed on the outside to operate correctly due to
the wall thickness of the case and the red crimps are the commons for the wire groups

All the plugs were wired using 22 gauge wire in every colour that was available in the ship. Each RS232 has a specific assignment allowing single looms to be created back to the flap junction box in the passenger compartment and to the indicators located in the panel

Once a loom was assembled it was then covered with self closing braided wire wrap from Jaycar with each end secured using suitable heat shrink creating a tidy loom while providing additional protection when run through the aircraft with little weight penalty.

Cutting braided - heated box cutter blade and cut while hot
this welded the woven mesh

A number of circuits from the sticks like mike, boost pump and flap had to be commoned and this was achieved by inserting the three [3] wires into a crimp lug and after crimping cutting off the lug with the exposed end coated in silicone to prevent possible electrical issues in service.

Trail mounting of junction box
Note: Plugs mounted on outside of the box

Two 0.020'' 2024-T3 aluminium lugs were manufactured then drilled to take four [4]  5/32'' pop rivets each. Once completed it was pop riveted to the longeron using 5/32 x 7 mm pop rivets. Studs were used to mount the box as it was found that fitting screws was difficult without the seat in position so removal at a later date would be challenging. 

Comments
The 22 gauge was stiff when loomed and I would use 24 gauge wire with the biggest problem just converting the schematic into actual wiring  with the schematic beign updated to as built.

A wiring diagram is normally done before commencing this type of work in industry but I started by connecting the pins as numbered on the original schematic and this resulted in a illogical layout requiring a rework as shown in the current schematic with the cost in time.

This is so 1980's you can just hear ABBA in the background

As this blog is not intended to give a day by day blow so  I have started adding updates on my personal Facebook under Gary Spencer Salt this may morph into a specific page and a notification will be placed on this blog is this occurs.

Trim Tab - Part 5

The tab clevis attachment requires a stiffener - a three [3] sided tray was folded with two sides trimmed to match the rib profile, The front edge was match drilled using the front edge of the tab. Two [2] angles were folded to tie the side webs to the front of the tab skin. All rivets used on the lower skin were 1/8'' counter sunk to allow the faring not to foul in operation on a dome rivet.

  

Tab clevis reinforcing plate

Stiffener was cut from the scrap material from the trim tab folding. 

The cover plate was slotted to allow the full operation of the MAC trim motor. It had to be wide enough to allow the clevis to clear the cover.

Trim motor cover

The final assembly with the faring cover for the tab and motor fitted. The cover for the motor was the prototype for the rear light of the rudder. This was machined from a 3D model in China but was not suitable for the task but has found a new home.

The inboard rib had a 1/2'' hole drilled on the same center as one of the lighting holes in the attachment plate for the shaft that connects both elevators. The loom for the trim motor exits through this opening to connect with a six [6] pin plug located under the rudder fin. Access  will be gained by removing the fuselage fairing. The hinge pivot was secured using a scrap piece of hinge pop riveted to the rib.

The threaded rod has a crank to allow connection to the tab clevis attachment to allow full stroke of the motor without fouling the tab spar.

Inboard rib details

Final task is to attached the tab clevis and test the assembly and at this time no problems are foreseen - famous last words ! 

Trim Tab - Part 4

The next task is to fabricate the braces for the stiffener installed in Part 5. A MAC trim is capable of a 40 lbs of thrust and the thrust is transferred to the rear spar via the ribs as per the factory installation.

A motor mount Z profile was folded from 0.025'' 2024-T3 aluminum - 60 mm wide with 10 mm flanges. Two lighting holes were created because a suitable flaring tool was on hand.

Z frame trim mount

Two angle mounts were fabricated and fitted at each end after a series of trial fittings ensuring that the second rib was maintained in its correct location relative to the mounting holes in the skin. Brackets were fixed with 3 x 1/8'' pop rivets to the face of the Z as shown above.

#3 Rib mount 

The cover plate was now slotted to accept the trim motor link.

Trail fit of MAC drive

The motor center line was located on the face of the Z and the first two mounting holes were marked with a felt pen - both holes were drilled and the motor mounted with cleco's then refitted, position checked and the rear holes marked.

On this install the rear two holes were moved up to provide improved access from the available opening.


All holes were fitted with 3 mm riv-nut's at the motors mounting points then refitted to determine the best angle to suit the available opening. 

The #3 rib the center hole was drilled, clecoed and repeated at the other side using one of the mounting holes for the new rib foot. Once the most suitable angle was determined using the trim motor the other holes were drilled and pop riveted.

Mounting Z Bracket at #3 rib

The motor was re-installed using four [4] M3 x 12 pan head screws then the stainless steel clevis attachment was fitted to the tab with 1/8'' pop rivets.

Trim Tab - Hitting a Wall

OH NO.!

At this point the builder stood back to admire his work and OMG the trailing edge of the tab was clearly not in line with the elevator skin. 

A loud crash of a builder hitting the wall was to be heard. After contacting the factory a series of photos's were received for guidance. 

I had swapped the inboard and the adjacent rib with the other frame's due to a mix up in the skin labeling as both had been cut and it was felt that this would allow me to proceed with both elevators. In trying to fix the problem by swapping the affected ribs it may have had unintended  consequences during the process of assembly .

Note: The frames are symmetrical so there is NO port or starboard until the tab is cut and positioned, its the relationship between the skin and frame that counts at assembly.

What to do

When you create a problem like this, how do you fix it is the $64 question. 

After a examination of the frame it was decided to remove the #2 rib, behold most of the misalignment was released. The next decision was to re-manufacture the trim tab spar as it was only fixed with clecos and it would allow me to start with a clean slate.

A fixed reference was created using a 1.5 meter length of 25 x 25 x 1.5 aluminium angle clamped to the elevator for all of the assembly tasks. One of the big differences between the factory and my procedure is the availability of jigs. The frame is a moving feast for most of the assembly period and this may have amplified any errors made.

A aluminium packer was installed at the underside of the outboard rib [#1] to improved fit to the new spar [see photo insert above]. The new spars were folded from 0.030'' aluminium [what was available] with the overall width matching the first full rib #3 and a second spar was folded with the overall width reduce 3 mm to clear the inside face of the first. 

First spar begin inserted - final assembly see insert

The procedure followed the previous blog on the original installation except that I started with the top spar to make alignment a little easier.

The front spar was cleoed at two places to allow a re-position if required. Next the lower spar was fitted to the underside of the first spar and cleoced at two places.

The spars were refitted and adjusted until the angle between the spar faces and the skins were are in alignment. The final tasks was to fix the two using 5/32 rivets pitched at 30 mm using the jig supplied to mark the spar.

Second Spar added with the first fixing

Riveting Tab Spar

The second rib had its mounting removed and was installed as a floating rib attached to the skin only. 

As this had created most of the previous error it was felt that it should not  exert force during re-assembly.

Tab Assembly

The original tab assembly was refitted and aligned using the angle as a guide and once satisfied the a cleco was installed at the inside rib. As the hinge was already drilled, alignment of the next hole required the used of a tab clecoed to the rear spar that allowed the hinge to be opened up, positioned and a hole match drilled. The tab was refitted and the whole alignment checked again - once satisfied two 5/32 rivets were installed.

Checking alignment of tab

The whole assembly was carefully checked and once satisfied the top spar's were match drilled from the skin's and clecoed to ensure that no unwanted movement occurred and then the trim tab hinge was matched drilled and pop riveted.

Once fully satisfied the top skin was pop riveted to the tab spar and the ribs except at the last rib and main spar to allow the D nose to be fitted later. The reason was two fold, one to make the final work to install the tab motor easier and secondly to CLAMP the frame up with the rivets

This time I was glad to see the finished product.

Trim - Factory

After completing my installation the factory forwarded the following images of the current method of mounting. The details will be covered in additional drawings to be added to the upgraded assembly package.

Cutout for trim tab

Trim motor mount
Note #3 rib from LHS rotated 180 degrees from plans

Rear spar

Rear spar fitted

Drilling skins

Trial Assembly

Trim Tab - Part 3

Cover

A cover was manufactured from 2024-T3 0.020'' aluminium to fit the available area on the underside of the elevator and mounting holes marked then drilled 3/32". 

A duplicate panel was manufactured from the same material with additional width to provide 15 mm flanges on both sides and matched drilled from the front cover.

Match drilling

Using the cover as a drilling template, it's positioned on the skin and holes transferred then drilled 3/32''. Once the holes are drilled a center-line's was marked through the hole's centers and a offset marked in 10 mm to become the opening. 

At each corner of the opening a 3/32'' hole was drilled and the edges cut with the Ofla knife, a hole was drilled at the center then aviation snips used to cut from the center to the corner holes. 

Once complete the 4 [four] waste pieces are removed and the edges dressed.

The holes were enlarged to suit the selected riv-nuts.

Elevator opening

The reinforcing panel had it edges folded at 90 degrees and the hole's were enlarged to suit the riv-nuts. These were used to locate the panel over the opening which was transferred to the reinforcing panel with a felt tip pen and removed.

A 3/4'' diameter hole was drilled on the center-line of the opening then 3/32'' holes drilled at each corner. The Ofla knife was use to mark the perimeter and the aviation snips used to cut to the corners and the 4 [four] waste pieces removed and the opening was dressed smooth. 

Once the the component are finished and primed the reinforcing panel was re-installed and M3 riv-nuts used to fix the two components. The front cover had all the holes enlarged to 3.5 mm and panel fixed with dome head screws supplied with the kit.

Finished doubler

To be covered in the next blog

Trial lower faring - Cover installed ready to be modified to take drive
Note the pop rivet shown fouled on cover

Trim Tab - Part 2

Trim Tab Drive Overview
The first decision is what kind of opening do I install for the trim tab. Reviewing the work of the RV clan shown opposite requires a lot of flush riveting and rivet nuts and I did not wish to invest the time required.

The decision was to manufacture externally mounted plate secured by M3 pan head screws fitted to rivnuts similar to the inspection hatch at the rear of the aircraft.






Trim Tab
A reinforcing plate was fabricated from 2024-T3 aluminium to mount under the clevis attachment supplied by the factory. The flanges were folded 15 mm and trimmed to fit inside the tab.

The shaft center was marked and the plate was attached using 0.005" double sided film adhesive to the inside face of the trim tab. The plate is located on its own center and about the shaft center line

The tape will hold the plate in position for riveting. OK - I was out of rivets and wanted to close the tab to allow the installation of the drive.

The location of the plate was marked onto the lower skin and 3 [three] 3/32'' pop rivets installed at each pitched 5 mm from the edge and at 30 mm centers. The clevis attachment will be fitted once the MAC trim drive is installed in the elevator.

The drive installation will be covered in the next blog post.

Trim Tab - Part 1

Trim Tab

Modification - refer disclaimer

The off cut was already modified when the decision to look at an alternative layout however the factory supplied blank skin was now employed.

The lower skin was folded to create a included angle off 80 degrees to create the lower flange. 

A matching end cap was folded from 2024-T3 over size to be trimmed later.

First fitting Tab

The trim tab skin upper edge was marked with mounting hole center line using the mid point of the hinge width as a starting point. 

Next the hinge and upper skin were match drilled at both ends and cleoced. The edge of the tab was positioned by aligning with the point of contact on the loops on the hinge.

The hinge was reassembled onto the elevator using the hinge wire. 

Match drill front cap

The front cap was positioned on the rear of the hinge after removing the skin and 2 [two] mounting holes duplicated. 

Rotated the assembly to check for correct operation and once satisfied marked holes onto the top side of the skin with a factory jig and felt tip pen - drilled 3/32''. 

Reassembled the skin, hinge and front cap - checked operation and then match drilled all holes 3/32''.

Checked operation.

Alignment Jig

Marking front cap

To assist in locating the lower flange of the trim tab a scrap angle was clecoed across the top of the elevator. These were cut and clamped to hold the trim edge in its correct location.

With the upper skin aligned against that angle and the lower skin positioned by hand a point was marked onto the face of the front cap. 

This was repeated at the opposite end and the assembly removed, line drawn and once satisfied the cap was cut to its correct depth and profile.

Trim was reassembled with the base two holes match drilled from the front cap into the folded flange of the skin and pop riveted.

The tab was remounted onto the elevator and the overall visual alignment checked, at this point all holes were matched drilled

Removed and reassembled - again.....!

Ribs
The outer rib was fabricated from one of the ribs supplied by the factory. 

Outer Rib

The next rib to be fabricated is the inner rib as the factory one did not fit correctly on this project - I suspect a error with the angle folded into the tab. This style of rib was taken from the RV series of aircraft. Both were cut from two of the factory supplied ribs. Note the inner rib is recessed to match the depth of the outer rib. The lower rib is pop riveted first then the outer.  

All temporary pop rivets were removed in preparation for priming and final assembly

Inner Rib

The trim tab components were primed for assembly ready to allow installation of the trim drive clevis reinforcement.

This is to be covered in the next blog post.