Motor Box
Construction Sequence and Images for Building the Motor Box
Started 1/4/2015 ... Updated 2/1/2015


The Motor Box is complete through the Cleco stage with some riveting.  It has taken nearly one month.  That month of work also includes "overhead" work such as reorganizing the work area, improving the fuselage stand, finding misplaced parts and tools and reviewing images of other projects on the internet.  Work remaining: final trimming of parts, reaming holes to #30, cutting and flanging holes in Bulkhead "A" (or nosebowl).  Internal baffle hasn't been made yet.




                          
 

Early stage for my motor box:  

Factory Image for the Motor Box Parts:         
     My annotations ...                           


A few more Motor Box parts ...
Cowl Skin brace: either 1/8-inch or .040 aluminum

Upper Cowl Piece



Bulkhead "A: or nosebowl with Upper Cowl Piece

Engine Support Angles ... note: there is a temporary brace at the front to hold the angles 11-inches apart

Wood spacer or pivot point will be replaced ... see below







A few of the best images from the web:
Upside-down ... Charles Snyder
The Bottom Cowl Baffle was very baffling to me.  Finally, I determined that the Mylars from the factory were different from the factory drawings.  FURTHER, nearly everyone seems to have gone their own path. 

Very nice execution by Charles Snyder.  His blog shows 230 hours for the engine compartment.
www.cwsnyder2001.blogspot.com/search/label/engine%20compartment


Charles Snyder
Here, the baffle appears to be flush ... but the angle is deceiving

Dennis Brooks
Beautiful job on the motor box:

... anyone for tennis?
Bill DeFreze

Bill DeFreze


Major Goofs:
Before you get too far into building your motor box ... you should avoid making the mistakes that I made.
- Not so bad:  I established the center of the Upper Cowl Piece off-center!  After back-drilling about a dozen holes starting at the top and working
down both sides, I discovered the problem.  Fortunately, I merely rotated the piece to be centered and the holes were mostly in-line due to
precision drilling.  Three holes were perfect.  Three holes were so off center enough that I had to ream them with a #30 drill bit.  The rest were very
slightly off and reamed with a #40 drill (I drill all holes initially with a #41 drill bit).

Something I did different:
The plans indicate making the small, curved triangular Motorbox Front Piece by forming over wooden form.  I merely used fluting pliers to make the curved bend,
then used a bending brake to make the second bend.  Easy!

The sequence for building the Motor Box:
- Accurately install the Firewall Support Angles  ... 3/4 x3/4-inch angles ... level, parallel, perpendicular to the vert stab, and 6-inches apart, bottom to bottom
- Install the Engine Support Angles (1x1-inch ) to the lower Firewall Support Angle ... centered and 11-inches apart on the inside, 13-inches outside
- Install a temporary cross brace near the front of the Engine Support Angles to maintaim the 11-inch separation
(use an angle made from .016 aluminum with ends that lie flush on top (drill holes in the engine support angles about 1.5 inches from the front)
(use an temporary rivet to hold the angle in place ... a Cleco will get in the way later)
- Install the Motor Vertical Component to the Engine Support Angle ... make certain it contacts the Lower Bulkhead "B" Doubler and is plumb and level.
- Install the two Lower Cowl Braces while making certain the Motor Support Angles are perpendicular to the Firewall and parallel
(I've decided that it make no difference if the Brace is installed now or later.)
- Attach the Motor Horizontal Component flush with the Bulkhead "B" Doubler and the front outside edge of the flange is flush with the outside edge of the Engine Support Angle.
- Clamp the engine support angles with a temporary spacer angle.
- Remove temporary loose rivets from the temporary cross brace and drill hole into the Motorbox Horizontal Component.  Do for both sides.  Insert Clecos.
... more to come
At this point you should have a very rigid lower Motor Box that is plumb and square to the aircraft.

Step 1: Accurately install the Firewall Support Angles (3/4 x3/4-inch angles).  Ensure that the angles are level, parallel, perpendicular to the vert stab, and 6-inches apart, bottom to bottom (angle opening faces upward).

I cut the two Firewall Support Angles from "scrap" angle.  This angle was originally to be a wing spar cap ... but I drilled a mirror image (GOOF).  Thus, the angle was already drilled at the 1-inch spacing as called out on the drawings for the Firewall Support Angles.

Material:  3/4 x 3/4 x 1/16th 2024T3 ... 17.75 inches long and 17.625 inches long.

GOOF! ... You will note that the A-B skin was trimmed flush with the A bulkhead at the lowest portion to allow the fuselage to pivot on the fuselage stand.  Plans call for a 5/8-inch extension of the A-B skin past the bulk head.  The doubler will fill this spot.

As I added parts to the Motor Box, the nose started getting heavy from all the Clecos.  That resulted in flexing of the Bulkhead "B".  A new pivot stand attachment was fabricated. 

This version used 1/8x1/8x1-inch angle and scrap 3/8-inch plate from the center wing carry-thru.

The Firewall Support Angles now carry the weight of the nose without any flexing.  Also, the support plate is further from the firewall allowing more of a pivot before contacting the Bottom Cowl Braces (which I have left off to allow more pivot).

This image is out of chronological order.
Cross support angle in addition to being riveted with Type 1 rivets is bolted to the side rail angle using two AN3-5A bolts.

Side rail awaits final trim flush with cross support angle.

Side rail will be trimmed flush with cross support angle.


Install the engine support 1x1-inch angles to the lower cross brace angle ... centered and 11-inches apart on the inside, 13-inches outside.d

In this image, I show a 1/8-inch bar stock holding alignment near the front of the engine support angles.
See Next:

The bar stock brace thickness interferes with installing the Horizontal Component; thus ...

- Use an angle made from .016 aluminum with ends that lie flush on top (drill holes in the engine support angles about 1.5 inches from the front)

- Use an temporary rivet to hold the angle in place ... a Cleco will get in the way.


Install the Motor Vertical Component to the Engine Support Angle ... make certain it contacts the Lower Bulkhead Doubler and is plumb

A spacer is temporary installed to represent the space that will be taken by the Motorbox Horizontal Component.


Drilling corner hole through Vert Comp and Engine Support Angle.
Attach the Motor Horizontal Component flush with the Bulkhead Doubler and the front outside edge of the flange is flush with the outside edge of the Engine Support Angle.

Motorbox Horizontal Component held in place with cleco.  Square up the Motorbox and drill holes into Bulkhead A Doubler and into the Engine Support Angle about 1.5 inches from the end (or what ever you like).

The circular Sharpie lines on the Vertical Component were the lightening holes for the wing spar.  The wing sparweb developed a kink due to an accident ... but most of the sparweb was usable.  I could get out the alcohol and remove the Sharpie lines :-)

Cut and bend two lower cowl braces (.040 aluminum)

GOTCHA:  Note that the mylar drawing shows the part to be 1/4-inch wider ... I added another 1/8-inch ... and wish I had added 1/4-inch for a total of one-half inch! (GOOF)

(The orange line is the size on the plans, Page 2, location E4)

Bend the 90-degree flange before drilling any holes!

To effectively use the shoe-shine method of bending the heavy .040 aluminum, I cut a rectangle of aluminum big enough to build two Lower Cowl Braces; plus, and extra two inches.  This length is required since the shoe-shine method will not work with a narrow piece of metal.  A block of wood clamped to one end helped bending at the edge.

Bending the 90-degree flange was straight forward using only Avery fluting pliers (see quid.us/hummel/tools).  Gradually crimp and bend while pushing down against the table.





Install the two lower Cowl Braces while making certain the motor support angles are perpendicular to the firewall and parallel

You can see why I would have added another 1/8th inch.  Alternatively, better positioning would have solved the problem ... BUT, I back-drilled the two bulkhead holes before making the 90-degree bend.  That left narrow margins for the first hole between the brace on the flange on the Vertical Component.  GOOF!    

Test fitting mylar.

I marked on the mylar along edges that should be extended one-quarter to on-half inch to be later cut down for an exact fit.


Test fitting rough-cut right Bottom Cowl Skin. Inside and outside views; plus side view before trimming to size

Front Nose Piece: Instead of building a form block over which to form the Nose Piece ... I merely used fluting pliers to form the curved flange ... crimping while bending ... pressing hard against the workbench.


Then I used a brake to form the other flange.  The narrow tip gets slight deformed during the bend, but nose pliers easily straighten the flange.



Trial fit of the Motor Box nose piece.

Note: the piece is not pushed flush with the Bottom Cowl Skin.

Installing Bulkhead "A".  Checking for square to the Motor Support.
Used vice to hold bucking bar:

Nose Bowl and Lower Cowl Skin Doubler:
(I choose 2-inch wide .040 in place of 1/8-inch bar stock)



Motorbox Bottom Cowl Baffle:

Small bent tab on exit borrowed from Charles Snyder:

Motorbox Bottom Cowl Baffle:

Motorbox Bottom Cowl Baffle - inside view:







[Return to Homepage]

Address of this Webpage:   http://quid.us/hummel/motorbox
Copyright 2008, by S. Steve Adkins, all rights reserved. 

Disclaimer: Website Editorial Policy & Copyright Notice
These pages are presented here are for the use, education and enjoyment of those interested in the world aircraft homebuilding.   No claim is made for the accuracy of materials presented. Content and/or policy opinions expressed within these pages are solely those of the author. They DO NOT necessarily reflect the position of any other person nor organization. Responsibility for accuracy in referred and hyperlinked materials rests entirely with the applicable author and no remuneration is made.