Greg Arehart
Well Known Member
[note to DR - I am happy to give this to you, or anyone else, as a PDF file if you would like to put it into the archives that way - it's too big as a Word file}
Being a geologist, I?m always looking at the landscape and have taken a lot of photos out airplane windows over the years. In my work, I also have utilized standard aerial photographs taken by the BLM or other government agencies, but these are taken at odd times and from a standard platform. I was interested in being able to do my own photography so that I could get a broad or close view, or even oblique views, and also so I could do low-sun-angle photography which highlights some geologic features. Normal aerial photos that are commercially available do none of this. So when I started building my 9A, one of the personal modifications I figured I had to have was an in-wing camera. Ideally, this camera would be operable from within the cockpit, and ideally it would be tiltable to get an oblique view if necessary (yes, one can tilt the airplane, but doing so usually results in a turn rather than straight flight).
The solution ended up being fairly simple and this document is for anyone wishing to duplicate my effort, or as a starting point for your own modification.
The first question was where to put the camera, and I decided that the wing bay just outboard of the bellcrank was probably the best place. It is out of the way of any interference with the control rods etc. and is still somewhat near the middle of the wing which was designed to minimize any potential vibration. I calculated the window size necessary to allow the camera to tilt by about 30 degrees forward-aft or left-right, and ended up with a square 8 inches on a side. Since the wing skin is a structural member, I wanted to make certain that I did not compromise wing strength, so I added two ribs parallel to the spar and spaced about 9 inches apart. These were fabricated from 0.032 Al, and lightening holes drilled. Attachments to the original wing ribs were simply 0.032 Al that was riveted to the wing ribs and nutplates added for attachment of the cross-ribs. Thus the cross-ribs are removable if necessary to access other parts of the wing structure. Note in Figure 1 that the cross-ribs are not as thick (top to bottom of the wing) as the original ribs, thus eliminating any potential chafing on the wing skin.
Figure 1. Photograph of the extra wing cross-ribs in the bay outboard of the bellcrank.
I fabricated a backing plate for the camera window from 3/16-inch Al plate (fortunately I have access to the appropriate metalworking tools). In Figure 2, the ultimate resting place for the window is on the step in the center of the plate. The interior dimensions of the opening are 8 x 8 inches, and the step that holds the window is about 3/8? wide. The depth of cut is slightly more than the thickness of the window material (in my case, this is 3/32? plexiglass but one could use whatever dimension is appropriate for the window thickness desired).
Figure 2. Metal backing plate for the plexiglass window fabricated from ?-inch plate stock.
The next step was cutting the wing skin. In Figure 3, you can see the wing skin after cutting to fit the dimensions of the backing plate. In my case, the hole is 8.75? square. I drilled and dimpled holes for 4-40 screws on about 1.25? centers (probably overkill). Figure 3 shows the drilled holes before dimpling. I countersunk the skins and added four rivets (see the odd holes in Figure 4 closeup) to hold the backing plate in place on the skin, but most of the holding power will come from the screws. Screw holes were tapped for 4-40 screws into the Al backing plate.
Figure 3. Backing plate fitted to the wing skin. (apologies for the quality of the photo)
Figure 4. Closeup of the backing plate showing countersinks for the wing skin and one of four rivet holes (the odd-spaced rivet hole, not countersunk as much) that holds the backing plate to the skin.
This finished the skin part of the installation. The camera mount itself is a pair of fabricated boxes (Figure 5). The outside box has a bellcrank bearing (about $25 from ACS) on either side of the long axis of the box, and these are simply bolted onto the cross-ribs, allowing the box to rotate on the roll axis of the airplane. Within this box is a slightly smaller box that is similarly attached to the large box with bellcrank bearings, allowing for rotation in the pitch axis. Although I have not finished the controls for these rotating boxes, they will be driven by radio-controlled car servo motors (available from most RC hobby stores for about $25) that are wired to a pair of rheostats in the cockpit. Figure 5 shows a test installation ? the final installation (Figure 6) used an aluminum tube spacer rather than the wood one.
Figure 5. Nested camera boxes. It is important to get the holes in the two ribs in the right places so that the outer box can rotate freely.
The camera (I use a Canon Powershot G9,12 megapixel camera, but any good quality camera would do) is just mounted within the smaller box using a standard threaded tripod mount bolt with a knurled knob. I actually ended up fabricating a couple of Z-brackets to make sure that the camera would stay in place (Figure 6). The camera is padded all around the Z-brackets and the back using that rubberized, webby shelf padding available at Lowes or other home stores. This helps minimize vibrations and rubbing.
Being a geologist, I?m always looking at the landscape and have taken a lot of photos out airplane windows over the years. In my work, I also have utilized standard aerial photographs taken by the BLM or other government agencies, but these are taken at odd times and from a standard platform. I was interested in being able to do my own photography so that I could get a broad or close view, or even oblique views, and also so I could do low-sun-angle photography which highlights some geologic features. Normal aerial photos that are commercially available do none of this. So when I started building my 9A, one of the personal modifications I figured I had to have was an in-wing camera. Ideally, this camera would be operable from within the cockpit, and ideally it would be tiltable to get an oblique view if necessary (yes, one can tilt the airplane, but doing so usually results in a turn rather than straight flight).
The solution ended up being fairly simple and this document is for anyone wishing to duplicate my effort, or as a starting point for your own modification.
The first question was where to put the camera, and I decided that the wing bay just outboard of the bellcrank was probably the best place. It is out of the way of any interference with the control rods etc. and is still somewhat near the middle of the wing which was designed to minimize any potential vibration. I calculated the window size necessary to allow the camera to tilt by about 30 degrees forward-aft or left-right, and ended up with a square 8 inches on a side. Since the wing skin is a structural member, I wanted to make certain that I did not compromise wing strength, so I added two ribs parallel to the spar and spaced about 9 inches apart. These were fabricated from 0.032 Al, and lightening holes drilled. Attachments to the original wing ribs were simply 0.032 Al that was riveted to the wing ribs and nutplates added for attachment of the cross-ribs. Thus the cross-ribs are removable if necessary to access other parts of the wing structure. Note in Figure 1 that the cross-ribs are not as thick (top to bottom of the wing) as the original ribs, thus eliminating any potential chafing on the wing skin.
Figure 1. Photograph of the extra wing cross-ribs in the bay outboard of the bellcrank.
I fabricated a backing plate for the camera window from 3/16-inch Al plate (fortunately I have access to the appropriate metalworking tools). In Figure 2, the ultimate resting place for the window is on the step in the center of the plate. The interior dimensions of the opening are 8 x 8 inches, and the step that holds the window is about 3/8? wide. The depth of cut is slightly more than the thickness of the window material (in my case, this is 3/32? plexiglass but one could use whatever dimension is appropriate for the window thickness desired).
Figure 2. Metal backing plate for the plexiglass window fabricated from ?-inch plate stock.
The next step was cutting the wing skin. In Figure 3, you can see the wing skin after cutting to fit the dimensions of the backing plate. In my case, the hole is 8.75? square. I drilled and dimpled holes for 4-40 screws on about 1.25? centers (probably overkill). Figure 3 shows the drilled holes before dimpling. I countersunk the skins and added four rivets (see the odd holes in Figure 4 closeup) to hold the backing plate in place on the skin, but most of the holding power will come from the screws. Screw holes were tapped for 4-40 screws into the Al backing plate.
Figure 3. Backing plate fitted to the wing skin. (apologies for the quality of the photo)
Figure 4. Closeup of the backing plate showing countersinks for the wing skin and one of four rivet holes (the odd-spaced rivet hole, not countersunk as much) that holds the backing plate to the skin.
This finished the skin part of the installation. The camera mount itself is a pair of fabricated boxes (Figure 5). The outside box has a bellcrank bearing (about $25 from ACS) on either side of the long axis of the box, and these are simply bolted onto the cross-ribs, allowing the box to rotate on the roll axis of the airplane. Within this box is a slightly smaller box that is similarly attached to the large box with bellcrank bearings, allowing for rotation in the pitch axis. Although I have not finished the controls for these rotating boxes, they will be driven by radio-controlled car servo motors (available from most RC hobby stores for about $25) that are wired to a pair of rheostats in the cockpit. Figure 5 shows a test installation ? the final installation (Figure 6) used an aluminum tube spacer rather than the wood one.
Figure 5. Nested camera boxes. It is important to get the holes in the two ribs in the right places so that the outer box can rotate freely.
The camera (I use a Canon Powershot G9,12 megapixel camera, but any good quality camera would do) is just mounted within the smaller box using a standard threaded tripod mount bolt with a knurled knob. I actually ended up fabricating a couple of Z-brackets to make sure that the camera would stay in place (Figure 6). The camera is padded all around the Z-brackets and the back using that rubberized, webby shelf padding available at Lowes or other home stores. This helps minimize vibrations and rubbing.
