January 2003 (Volume 2, Issue 1)
Making an Accurate Instrument Panel
By Dave Mullins
First, make a list of what equipment is required for VFR day/night or IFR whichever you intend to fly. Add the equipment that you want to the list. Do not forget switches, lights, and Headphone jacks. Second, make a template of the perimeter of your panel. Get the entire instruments and radio sizes. Most can be gotten out of your suppliers catalog or from the manufacturer’s website. Cut them out of stiff cardboard. Position them on the outline template, moving them around to get a design that makes you happy. Tape down the cutouts as a guide.
There was a Panel Planner CD circulating the net. I do not know its whereabouts right now. You could use this as a design tool, but, getting the instruments to line up correctly is a hit or miss task and you need the Pro version to output a CAD file.
I decided to use a real CAD program after fiddling with the panel planner software. I used TurboCAD for this task. You can download a free 2D version from http://www.turbocad.com. CompUSA carries version 8 standard for $100. I will also make my file available to those that need some where to start, at http://n323xl.iwarp.com/N323XLpanel.zip. Remember, if you use my file it is made to fit my bird and is 4” taller and wider than stock dimensions. Just pull the component cutouts to use.
After I had drawn my panel out, I triple checked all the dimensions to make sure everything was correct. I included both drilling guides and notations of hole diameters. I used a plotter to print out the finished drawing.
At this time you could use spray adhesive to mount the drawing to your panel material (aluminum, wood, fiberglass, etc). Center punch and drill all your holes next followed by cutting all the square holes for the radio stack and other panel equipment holes.
This would be fine for most people, but I wanted my panel to be more accurate than that. I located a machine shop with a waterjet cutter. A high-pressure stream of water mixed with a tiny abrasive cuts aluminum like butter.
Hollis Line Machine Company Inc 295 South Merrimack Road, Hollis New Hampshire, 03049 Tel: 603-465-2251
Their OMAX waterjet cutter can handle 60” x 120” sheets up to 2.5” thick. I took the CAD drawing over to Hollis and got a quote for the job. I asked them what type of file format they needed, the reply was AutoCAD - DWG or DXF would work and to remove all the notations and center marks. Just leave what you want cutout.
TurboCAD is compatible with these two formats and a host of others, no problem there. Depending on the complexity, your costs may vary.
The job was complete within a week. I wanted a couple of bends in the bottom of the panel to stiffen the bottom edge. I went by another builder’s hangar to borrow his eight-foot sheet metal brake. Well it tried to bend it but no go it was just too much. The panel was cut from .063” 2024-T3. This material needs a radius bend of 3 to 5 times the thickness. Now I needed a hydraulic press brake to bend it.
Networking with other builders, I found Greenfield Industries in Hollis. The owner was more than helpful in bending my panel. I have some sheer jobs for my fuel tanks I will take him next week.
I had the rivet holes for the radio stacks cut slightly small and drilled them to the correct sized drill bit. Even though the waterjet is accurate to about .003” of an inch, I did not want too much slop for the rivets.
When they were drilled to the right size, I used a microstop countersink drill for flush rivets.
I fitted each of the instruments and other items I had. The only things needing slight fitting were the indicator lights a circuit breaker switches.
I have two of my gyros already so the panel needs to be shock mounted. Now you could by the aircraft ones for $8-10 each or you can do what I did and get them from your neighborhood VW dealer for $2.50 each. Thanks Mark Langford!
After all the fitting of your instruments, clean the panel paint it with a coat of zinc chromate primer, followed by your finish color. Mine will be ultra flat black to cut down on any glare reflections.
There are many ways to light your panel. What I chose to do is use electro luminescent lights. There was a discussion on the Aeroelectric list a few weeks back about it. So searching the web I found the stuff for aircraft at $300, too rich for me. Continuing the search, I came across a kit for 5’ of 7/16” EL tape and a 12V inverter for $45. Now that is more like it.
This kit is made to modify your computer case and light up the inside after you cut a window in your PC. Check them out at http://www.highspeedpc.com. I will see if a dimmer can be attached to it. While my panel was being cut, I included my N-number in the cutouts.
I will take a small piece of the EL tape and put it behind the panel illuminating my N-number. That will be a nice addition to my panel. Some letters and numbers will not work this way but mine did.
Here’s a trial fit of the instruments I had at the time.
And the finished panel in the fuselage.
Keep tuned to my website for the latest updates
Website – http://www.n323xl.iwarp.com/
Email - mailto:N323XL@attbi.com
The following is a list of popular coaxial cables indicating their nominal impedance and their loss.
CABLE NOMINAL IMPEDANCE ATTENTUATION OUTSIDE
In ohms In decibels per 100 ft. DIAMETER
RG 8 52 2.8 0.405 in.
RG 8 FOAM 50 1.9 0.405
RG 8 A 52 2.8 0.405
RG 9 51 2.8 0.420
RG 9 A 51 2.8 0.420
RG 9 B 50 2.8 0.420
RG 17 52 1.2 0.870
RG 17 A 52 1.2 0.870
RG 55 53 ½ 5.5 0.216
RG 55 A 50 5.5 0.216
RG 55 B 53 ½ 5.5 0.216
RG 58 53 ½ 5.3 0.195
RG 58 FOAM 53 ½ 1.8 0.195
RG 58 A 53 ½ 6.0 0.195
RG 58 B 50 6.0 0.195
RG 58 C 50 5.3 0.195
RG 174 50 12.0 0.100
RG 174 A 50 12.0 0.100
RG 223 50 5.7 0.212
Belden 9913 50 1.4 0.405
Belden 9914 50 1.4 0.405
Decibels are a logarithmic function, so the loss in watts increases exponentially as the numbers go up. For example, if a cable has a 3 db. loss per hundred feet, the power output to the antenna is ½ that of the transmitter output. A 6 db loss would result in only ¼ of the signal at the antenna; a 9 db loss is 1/8 the output of the transmitter at the antenna; and a 12 db loss is 1/16 the output of the transmitter at the antenna. At 12 db with a 100 ft. long cable, the output of a five watt transmitter is only 0.31 watts.
The power loss in the coaxial cable is linear along its length. If your installation has 10 feet of cable between the transmitter and the antenna, your loss would be 1/10 of the figures in the table. If your length is 25 feet, the loss would be ¼ of the figures in the table.
The larger diameter cables have less loss, but are difficult to install because they require much larger bend radii. And, they weigh a lot more.
Notice that for a given diameter, FOAM dielectric coaxial cable is considerably more efficient than solid dielectric found in most cables. Foam coax can be purchased at radio or electronic outlets. Radio Shack coax is the very cheapest and you aren’t getting a bargain.
The impedance of coaxial cable is given as NOMINAL impedance, since variations in the manufacturing process and installation can cause it to vary. Therefore, 50 through 54 ohm cable will match and perform similarly.
The figures in the chart are for a perfectly matched antenna. If your antenna is not tuned properly, the coaxial cable then acts like a matching transformer, and length and orientation becomes quite important. The result is a much greater loss in the cable. For example, if you use a cable with a 6 db. Loss per 100 feet and your antenna is mistuned so you have a 4 to 1 standing wave ratio, the power output to your antenna will be less than 10% of the output of the transmitter. I have measured installed antennas that had standing wave ratios of 10 to 1 ! Even factory made airplanes are not always perfect.
What you do to improve your transmitted signal will similarly improve your received signal. Of course, ignition and other electrical noise can affect the received signal, too.
To summarize, the best coaxial cable for aircraft installations is RG 58 FOAM. It is also very important to have your antenna tuned properly, especially if you are going to cover it up so you can’t get to it later.
In the radio amateur crowd, there are many technicians who work hard to get their coaxial cables and antennas to perform perfectly. I’m sure they would be willing to check your antenna for you. They would enjoy the opportunity to work on something different. And their charge is much less than going to a radio shop.
I have a cheapy SWR meter that I bought from Radio Shack years ago, as well as my industrial strength Bird wattmeter than cost over $600. Since you are interested in relative measurements as you tune your antenna, the inexpensive unit would probably do the job. Radio Shack may still offer them. Interpreting what they tell you is an education in itself, so it would be an advantage to have a radio type help you.
You can contact me at Vance@ClaflinWildcats.com.
In 1971 I graduated from college and accepted a teaching position in Houston, Texas. After a couple of months I started thinking about what I wanted to do with the huge amount of money I was earning ($6,000 per year). Being single, and having no girlfriend, I decided to do something I had always wanted to do: learn to fly. Accordingly, I presented myself at Hobby Airport, checkbook in hand. A few months later I received my Private Pilot’s License. During the year that I lived in Houston I continued my reading of Flying, including Peter Garrison’s articles on his homebuilt airplane, Melmoth. I assumed that building one’s own airplane was not something normal people did.
A few years later I accepted a Call to teach at Trinity Lutheran School, Potter, Wisconsin. One of the first people I met there was the pastor, Rev. Ferdinand Timler. He mentioned that he was building his own airplane, something called a KR1. He told me about the EAA, and took me to my first EAA meeting in Manitowoc. We also spent several days at Oshkosh that summer, and I started thinking about building my own airplane.
I decided, after looking at all the various planes there at Oshkosh, that I wanted a two place plane that could use a VW engine. The next summer Rev. Timler and I again spent several days at Oshkosh, and on one of those days I purchased a set of plans for the KR2. The cost was reasonable, even by 1975 standards. Of course, all I got was a little yellow booklet with a few drawings.
Over the next 20 years I would take those plans out once in a while and think about building my own airplane. Each time, though I would put them away, as other responsibilities made their claims on my time and finances. I left Wisconsin in 1977. A wife was added in 1983, and children in 1985 and 1986, along with a move to Missouri. In 1989, however, things started looking up. We purchased a building that had originally been built to be a clinic in 1914. Sometime in the mid 1960’s it had been moved to its present location, and about the time I was purchasing my KR2 plans a 3-car garage was built. The back garage, approximately 12 feet x 24 feet, was just begging to become an airplane factory. In 1993, therefore, I insulated the garage, replaced the old door with an insulated one, and added lights, a workbench, and a kerosene heater. I ordered a 4 x 12 piece of ¾ inch particle board for my table, and on a vacation trip, visited Wick’s Organ for the purchase of enough spruce to build the boat. A neighbor took the original drawings and created a full-size side drawing, so that all I had to do was put my wood between the lines and glue it together.
Yeah, right! Building those two sides took me nearly two years, even with the full-size drawings. As those who have built a KR know, there are very few 90º angles in the sides. I didn’t count the gusset (corner) blocks, but there are many of them.
The summer of 1998 saw another move, this time 100 miles away from that house in Concordia to 10 acres in the Ozarks. No garage, no basement, no house, no buildings of any kind, in fact. How does one build an airplane in that situation?
My solution was to purchase an 8 x 12 storage building and to cut my particle board table (yes, I kept the particle board) to fit in the shed. I used the 2x6’s that had been the forms for the house’s slab to make the supports for the table. This table is actually studier than the one I had in Concordia, probably because it is supported on three sides by 2x6 supports nailed to the shed walls and by 2x6 legs on the front, which are attached to a 2x6 that runs along the front.
Unfortunately, one of the two sides I built in Concordia was damaged in the move, and I’ve been studying the possible solutions to the problem. I built my sides per the original plans, and I’m seriously thinking about just starting over and adding additional length forward of the front spar and aft of the rear spar, a la KR2S. The cheapskate part of me objects to the expense, though, and is arguing for simply gluing some additional ⅝ spruce on the top and inside around the break. Since the break is near the tail, the repair won’t be visible, and the plywood skin will be on the outside and bottom. I’ll probably end up just cutting out the broken piece and replacing it as a compromise.
I’d like to keep my KR pretty much stock, with one major exception: I’m definitely going to widen the cockpit! I got a chance to ride in Marty’s KR2 at Red Oak (thanks again, Marty) and we were definitely a tight fit. Although I’m not much taller than Ken Rand was, my wife, twin daughters, and the good cooks at church and school are all making sure that I never again will see Ken’s weight!
So where do I go from here? During the winter I’ll make up my mind about the damaged side, and in February or March I’ll start doing whatever I decide to do. I’d like to get the boat stage done before next winter. Of course, that means deciding whether to put the skins on before or after the fuselage is formed! Then there is the suggestion to make the sides vertical all the way, rather than to have them taper in at the cockpit area. Decisions, decisions.
Comments, suggestions, and visitors are welcome. Contact me at:
42 Rountree Rd
Urbana, MO 65767