27-41 Rudder Assembly (LD)

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27-41 Rudder Assembly (LD)

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Builders Database Link to27-41 Rudder Assembly (LD)

 PD Rudder Assembly Manual

 Rudder Assembly 3-D E drawing

 PDF 27-41-00-01 Rudder Spar Locations

 PDF 27-41-00-05 Rudder Assembly (LD) Overview

 PDF 27-41-00-09 Rudder Assembly (LD) Rivet Layout

 PDF 27-41-00-11 Rivet Layout rib number 1 & 2


List of Revisions

Revision 1 (Leading edge Modification) 

The original design consisted of a sheet-metal leading-edge. By modifying the leading edge to a smaller wrapped “D” tube construction we were able to reduce the cost of manufacturing of this part. The aesthetic contribution was significantly improved by increasing the radius of the leading edge. And the overall weight of this part was reduced by half. But more importantly it reduced the cost of shipping the entire rudder kit substantially by reducing the shipping box by half of its size.This modification was done without any changes to the original parts configuration and is readily adaptable from one designed to the other.

Video Links

Time Lapse Covering the Rudder Assembly

Rudder Assembly Video

Building the Rudder Spar Video

Rudder assembly Procedures

27-41-00 Rudder Assembly

27-41-00 Rudder Assembly Parts List

P/N Nomenclature Quantity
27-41-10 Rudder Spar LD 1
27-41-12 Rudder Mid Support 1
27-41-13 Rudder Spar Lower Support 1
27-41-14 Rudder Spar Upper Support 1
27-41-50 Rib 1 1
27-41-51 Rib 1 Support 1
27-41-53 Rib 2 Left 1
27-41-54 Rib 2 Right 1
27-41-55 Rib 2 Support 1
27-41-56 Rib 3 Left 1
27-41-57 Rib 3 Right 1
27-41-58 Rib 4 Left 1
27-41-59 Rib 4 Right 1
27-41-60 Rib 5 Left 1
27-41-61 Rib 5 Right 1
27-41-65 Trailing Edge 1
27-41-72 Rib 6 1
27-41-73 Rib 7 1
27-41-78 Leading Edge 1
27-40-20-L Rudder Control Horn Left 1
27-40-20-R Rudder Control Horn Right 1

Rudder Hardware Kit

P/N                  Nomenclature                    Quantity

MS21078-4     Nylock Nutplate                                3
BSPQ 4-4         .125 x.5 pop rivet aluminum            8*
BSPQ 4-2          .125 x.25 pop rivet aluminum         200*
CCP 4-4         .125 x .5 pop rivet Stainless Steel      40*
CCP 4-2         .125 x .25 pop rivet Stainless Steel    35*
AN43B-20A     Eye Bolt (Rudder Hinge)                3
AN 960-416     Washer                                             3
AN3-21A        Bolt                                                   4
AN960-10         Washer                                            4
AN365-3         Nut                                                    4

* Extra Rivets Included In rudder kit

list of Drawings

27-41-00-01 Rudder Spar Support Locations
27-41-00-05 Rudder Assembly LD Overview
27-41-00-09 Rudder Assembly LD Rivet Layout
27-41-10-02 Rudder Spar LD Manufacturing layout
27-41-10-10 Rudder Spar Sub Assembly
27-41-10-01 Rudder Spar LD Cut Dimentions
27-41-12 Rudder Mid Support
27-41-13 Rudder Spar Lower Support
27-41-14 Rudder Spar Upper Support
27-41-00-11  Rivet Layout Rib 1 & 2
27-41-65-02 Trailing Edge position

List of Tools

Standard Hand Tools
Drill Bits, 1/4, 3/16, #30
Pop Rivet Gun
1/8 Copper Cleco’s (50)
3/16 Brass Cleco’s (6)
Cleco Pliers
Digital Calipers

Assembling Rudder Spar Sub-assembly

Before beginning assembly print or review all the drawings in the builder database for the rudder assembly. Having these drawings readily available during the construction process will make it much easier.

Spar Insert Supports

The spar inserts are designed to strengthen the spar in the area where we drill the 1/4″ holes for the eye-bolts that will act as the hinges for the rudder assembly.

Drill and Prep Rudder Spar

Begin by locating the 3 holes in the main spar that will be used for the eye bolt hinges.

We will be working on the aft side of the rudder spar. and we will start with the upper support 1st then move on to the mid support  and lastly  the lower support.

These holes will be located between the 2 holes that are used to attach the Nylock nut plates to the spar.

We will enlarge these holes on the rear side of the spar to 1/4 inch diameter hole. A unibit works well to insure a smooth transition from the 1/8” hole to a 1.4” dia hole. If you do use a unibit insure that you DO NOT enlarge the hole bigger than 1/4”

We will be drilling out the aft side of the spar where the nut plate attaches only.
Drill all 3 eye-bolt locations as shown on  drawing 27-41-10-10

Reference Drawing 27-41-10-10

Rudder Spar Upper Support

There is one hole drilled  in rudder spar upper support tube..
Using a sharpie or magic marker  draw a line  parallel with the tube through the center of the existing  hole  that is drilled for the  rudder hinge eye-bolts.

Insert the rudder spar upper support  inside of the rudder spar  and using the  line as an alignment guide,  call line  the upper support  with the lower support  bolt hole.

Push the support using a stick or a another smaller tube up to the upper hole until  the line on the tube can be seen through the spar eye-bolt hole.

If necessary rotate the tube  using a pick or a knife  until the  alignment line  is in the center  of the bolt hole.

Next, simply  push the  insert in until the bolt holes are closely aligned.

Next  an alignment punch can be inserted  to further align the bolt holes.

Now remove the punch and using the internal  support as a guide drill completely through the rudder spar. this will ensure that the  rudder spar  and the internal  support  bolt holes  are perfectly aligned.

With an alignment  pin or  the eye-bolt  holding the alignment of the internal support  tube drill the nut plate holes  using the  pre-drilled spar  as a guide.

Once the nut plate mounting holes have been drilled  you can install a cleco  to hold the  internal  support tube  in place while you remove the alignment pin.


And you are now ready to install the  nut plates.

Nut Plate Installation

The nut plates that were going to install, the MS21078-4 Nylock Nut-plate has holes pre-drilled into the mounting legs  that are drilled with a number 40 drill bit.

We will need to drill out each of the legs to accept a 1/8 inch  rivet using a number 30 drill bit.   
You will need to place the nut plate in a vice with smooth jaws to hold  it during the drilling process.

Temporarily insert AN 4 bolt or the eye-bolt  for the hinge through the rudder spar  with the  eye and of the bolt facing forward and the threaded portion of the bolt facing aft.

Next  spin a nut plate on to the eye bolt. In this case there is no need to insert the threaded portion of the bolt into the Nylock region of the nut plate, simply  thread the bolt in  far enough until it bottoms out on the nylon portion  of the  nut plate.

Now cleco one leg of the nut plate to the spar.

Using a BSPQ 4-4 .125 x.5  aluminum pop rivet  secure the nut plate to the spar.

 Remove the cleco and install the other rivet  in the other leg of the  nut plate.

27-41-12 Rudder Spar Mid Support

 Duplicate all of the procedures that were used in the installation of the upper support.
The rudder spar mid support needs to be installed before  the rudder spar lower support can be installed.

27-41-13 Rudder Spar Lower Support

 Duplicate all of the procedures that we just used in installation of the upper  and mid supports for the lower support as well.


 Drilling Rib Attachment Holes

Now that each one of the spar support inserts have been installed into the rudder spar  we need to  drill the remaining holes on each side of the spar using the predrilled holes  in the rudder spar  as guides.
Use a number 30 drill bit to drill each of the remaining holes.
There will be 3 holes on either side of the upper support.
There will be 4 holes in either side of the mid support.
And there will be  3 holes total  on the lower support on either side

 De-burring  Spar Sub-assembly

 Any of the holes  in the  completed  spar sub-assembly  should be de-burred at this time.
You may use a  slow spinning  cordless drill for de-burring with a  countersink attachment.

Be careful not to countersink any of the holes.

The de-burring process should be used for only removing any burrs that may interfere with  the installation  of any of the other sheet-metal parts that will  be attached to the  rudder spar. Holes that do not have any burrs on them do not need to be de-burred. When you are  finished with the de-burring process running your hand slowly over the  finished holes  will easily identify any holes that still need to be de-burred.

 Caution: Aluminum can have a very sharp edges that can cut your hands..

Trimming Upper Spar

The upper spar will interfere with rib number 6  if it is not trimmed.

Cut, sand,  or file a chamfer or radius on to the  top of the rudder spar to provide clearance for rib # 6.


 A minimum edge distance from the top rivet hole to the edge of the chamfer  should be retained with a .25”  dimensions  from the center of the rivet hole to the edge of the chamfer.

Rudder Assembly

Rib Identification

Rib #1

Rib #2

Rib #3

Rib #4

Rib #5

Rib #6

Rib #7

Rib Coding

Rib Numbering System

There are several methods by which we identify each of the ribs.

The 1st of which is the rib numbering system each rib  can buy identified by the number of holes drilled in the forward  section  of the rib

 This rib here is rib number 5  and you can see at the forward  edge 5 holes  drilled  horizontally  and parallel with the axis of the rib.

In addition  you can see that the left side ribs  are longer than the right side ribs. The purpose for this is to offset the rivets in the trailing edge so that they do not interfere with each other during the installation process.

The right side ribs  also have the rib numbering system with holes drilled to identify  which rib  is indicated.  However on the right side ribs in addition to being shorter than the left side  of the rib identification holes are drilled at an angle.


Rib #5

Rib #5 is the 1st set of ribs to be installed  on to the  spar sub-assembly. Cleco both the left and right tip ribs in place  these are p/n 27-41-60 rib number 5 left  and p/n 27-41-61 rib # 5 right.  The ribs are two-piece ribs  that overlap each other. As can be seen in this  diagram  the left rib overlaps the right rib.  All of the ribs during the initial installation will be cleco’d in place and no rivets will be installed until the majority of the structure has been assembled.


Rib #6

Rib number 6  is the top leading edge rib  and intersects with both  rib number 5  and  the rudder spar subassembly. Cleco in place as shown.


Rib #4

Cleco both left and right rib halves together 27-41-58 rib 4 left and  27-41-59  rib  5 to the main spar  with the flanges facing upward. Note the  rib overlap orientation.



Rib #3

Cleco both left and right rib halves together 27-41-56 rib 3 left and  27-41-57  rib  3 right to the main spar  with the flanges facing upward. Note the  rib overlap orientation.


Rib #2


Rib #1

Rib number 1 is a single  piece rib that is pre-bent into the shape  required for final installation.
During the manufacturing process there are 2 tabs on either end of the rib there used for proper alignment  in the CNC press brake.


The aft tab can remain in place which will assist in holding the fabric in that location. However the forward tab  will interfere with the rudder spar and as such needs to be trimmed  from the leading edge bottom V. After cutting  the alignment tab  you will need to  file and deburr the trimmed area.  Cleco rib number 1 in place as shown in the diagram.

Rib #1 Support  27-41-51

Rib number 1 support ties the 2 legs of rib number 1 together.
Cleco the rib support  in place  as shown in the diagram.

Rib #2 Support  27-41-55

Rib number 2 support ties the 2 legs of rib number 1 together.  Cleco the rib support  in place  as shown in the diagram.


27-40-20 Rudder Control Horn Installation

The rudder control horn attaches to the rib number 2.

Enlarge the number 30 holes to a 3/16 inch  hole using  a 3/16 inch drill bit. Start by drilling one of the 2 holes located in the spar sub-assembly.  note that this picture was taken before the redesign of rib #2  was modified to include the extra tabs that make it easier to install. The new tabs allow for permanent affixing of the rib to the spar while allowing the control horn to be removed. once rib #2 has been installed drill and affix the additional tabs with a number 30 drill bit and a copper Cleco after drilling.

Place the rudder control horn on to the spar  using a 3/16 inch brass cleco. Then using the control horn as a drill  guide  drill the remaining holes in both the spar and rib number 2 and rib number 2 support. Cleco  the rudder control horn  in place using 3/16 inch brass cleco’s. Duplicate the process for the opposite side.


Trailing Edge 27-41-65

Before we insert the trailing edge  into each of the rib locations we need to place the trailing edge material  in position on top of the ribs and mark them so that the lower end of the trailing edge is parallel with the lower edge of the number 1 rib.

Next insert the trailing edge material in between  each of the rib  tabs. Position the trailing edge centered and parallel with the  trailing edge tabs located on each rib.

 Using a pair of calipers  or ruler  measure the distance from the trailing edge to the  edge of each rib.

For proper positioning refer to  drawing number 27-41-65-02 Trailing Edge Positioning. During the installation of the trailing edge  you should be able to  site down from both ends  while  you are drilling  to ensure that the trailing edge positioning  is centered on  the profile of the rudder.

Drill only 1 hole  in each side of  rib #1 and rib #5 and verify that the trailing edge  is perfectly centered  then proceed to  drill the remaining holes alternating from side to side and from rib to rib  once again ensuring  that the trailing edge remain centered and straight  during the drilling and cleco in process.

 27-41-65-02 Trailing Edge Positioning

Trim Trailing Edge at Rib #5

Once the trailing edge  has been properly positioned  and all of the holes  drilled you will need to mark the trailing edge at the  rib #5 position  and cut it  to match the profile  of #5  rib.

Rib Number 7

Insert rib number 7 into the lower  dge of the leading edge sheet-metal skin. Cleco in place every 3 to 4 rivet holes.

Leading Edge Installation

Revision 1 to the rudder assembly changes the leading edge to the new style wrap around “D” tube construction leading-edge.

The leading-edge will be squeezed together and then riveted along the overlapping flanges that form the false spar. These can be riveted together with 1/8″ aluminum pop rivets.

Next step is to Cleco the leading edge to rib #7 on the bottom and rib #6 on the top as well as the overlapping section on to the top of the main spar.l the leading edge


Refer to drawing 27-41-00-09 for rivet placement.

Leading-Edge Riveting

 We can begin by riveting the leading-edge to rib #7, and #6.

Trailing Edge Riveting

BSPS-4-2 aluminum pop rivets in the trailing edge. Removed 2 cleco’s from each rib and insert rivets, then go back and remove the  remaining cleco’s and install rivets in  those holes.

Join Ribs

CCP-4-2  stainless steel pop rivets  for joining the rib halves.

Attaching Ribs to Spar

CCP-4 – 4  stainless steel pop rivets are used for  attaching all of the ribs to the rudder spar.

Rivet Layout Rib 1 and 2 

All of the holes that are on the side of  rib  3, 4, 5 are holes that are used to attach the fabric to the rudder structure  and do not require any rivets until  at the time of  fabric installation.

In ribs 1 and 2  there are  rib support  ribs  that need to be secured with stainless steel pop rivets.
We will be using CCP-4–2 stainless steel pop rivets  in the specified locations.
Refer to drawing 27-41-00-11 rivet layout rib 1 & 2. for the proper location  of the stainless steel pop rivets.

Additional References




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