Antenna, Avionics, ADAHRS Placements

01/21/24, 01/28/24 and 02/04/21, 12h

Based on a review of the manuals and a few blocks, the following is the configuration of the antennas we are thinking to implement. This configuration is not final as we still need to further read the documentation of each antenna:

Generic info on antennas: https://www.aopa.org/training-and-safety/students/presolo/special/antennas

Performance considerations:

The physical condition of the antenna plays an important role in its performance. If the antenna is cracked, water may enter and cause delamination (a separation of the composite layers), which may render the antenna useless. And if the antenna base is not structurally strong, the antenna will vibrate from the slipstream and cause the skin to fatigue, eventually causing cracks.
The antenna must be electrically bonded (grounded) to the airframe so a good electrical connection is maintained. If some corrosion gets underneath the antenna, this bond may be compromised and the antenna’s efficiency may degrade. Sealant around the base of the antenna helps to prevent this. Antennas should never be painted over their original coatings; any paint buildup reduces the efficiency of an antenna.

Real estate is very scarce on an aircraft, and sometimes there is very little left for antennas. Every antenna location is a compromise between a solid mounting, shadowing, other antenna interference, ground planes, and aerodynamics.

Mounting and bonding:

  • Many factors influence antenna performance. Of course the physical condition of the antenna plays an important role. If the antenna is cracked or the paint worn off, water may enter and cause delamination (a separation of the composite layers), which may render the antenna useless. Another problem deals with the underlying structure and electrical metal bonding. If the antenna base is not structurally strong, the antenna will vibrate from the slipstream and cause the skin to fatigue. Eventually this causes cracks and may rip the antenna off the fuselage, especially if there is ice buildup on the antenna. A riveted doubler plate under the antenna base prevents the vibration and work-hardening of the skin.
  • The antenna also must be electrically bonded (grounded) to the airframe so a good electrical connection is maintained. If some corrosion gets underneath the antenna, this bond may be compromised and the antenna’s efficiency may degrade to the point that a com may only transmit a couple of miles. Without a seal around the antenna, water creeps underneath and causes corrosion in a very short time. This bonding is practically nonexistent if a mechanic uses a sealant under the antenna, trying to curb corrosion. The proper bond is a bare metal skin to antenna mating surface with sealant around the base of the antenna.
  • In addition to a skin doubler and good electrical bonding, a transmitting antenna also needs an effective ground plane. To transmit correctly, a quarter wave antenna (the antenna is one-quarter the length of the electromagnetic wave) needs an electrically bonded structure around it with a radius equal to the antenna length. In other words, lay the antenna down and scribe a circle. This is the amount of metal (ground plane) that the antenna needs around it to work properly. Those of you with composite aircraft still need this ground plane, which often consists of a metal plate just inside the skin. For instance, if a com antenna is two feet long, it must have two feet of metal around it. Just a few of those transmitting antennas are the com, DME, transponder, ELT, radar altimeter, satellite telephone, and HF.
  • Another problem is paint. Antennas should never be painted over their original coatings. Any paint buildup reduces the efficiency of an antenna. Transmitting antennas are particularly sensitive to paint problems, especially when covered with metallic paint

ADHRS

EMS (Engine Monitoring Module)

  • Avoid flimsy aluminum mounts (limit vibration)
  • The Hot side of the firewall will limit the lifetime of the product. 
  • Keep the EMS unit close to the engine to avoid long wires
  • The second bay, as we have it in the mockup panel seems like a good location.

GPS receiver

  • Don’t place near any transmitting antenna (ELT doesn’t matter because if the ELT does goes off, you won’t need the GPS anyhow because you will likely be in a crash on the ground)
  • To test the system and make sure your GPS receiver is in a good place, you can bring the airplane outside away from hangars, and bring up the “GPS fix status” screen to see how many satellites you can see. 
  • Many people place the GPS receiver on the aircraft skin, this is fine, but install a doubler plate for a more rigid surface.
  • Putting the GPS inside like the RV12 under a fiberglass cowling isn’t good ONLY because there is likely metal that obstructs the unit from a full 360 degree view. 
  • NOTE: The vertical stabilizer isn’t large enough to degrade much for performance so putting on the top rear of the aircraft is a good spot
  • DO NOT place the receiver on the bottom of the airplane (bad quality)
  • Don’t paint the receiver OR put a fiberglass part over the top 
  • Dynons ground plane is built into the unit and you don’t need to add an additional one
  • Dynons receiver is the antenna as well. It’s an all in one unit(some others separate the unit)

Garmin antenna mounting requirements:

The GPS antenna is a key element in the overall system performance and integrity for a GPS/WAAS navigation system. The mounting location, geometry, and surroundings of the antenna can affect the system performance and/or availability. The following guidance provides information to aid the installer in ensuring that the most optimum location is selected for the installation of the GPS antenna. The installation guidelines presented here meet the intent of AC 20-138A section 16. The greater the variance from these guidelines, the greater the chance of decreased availability. Approach procedures with vertical guidance are the most sensitive to these effects. LNAV only approaches, terminal operations, and enroute operations may also be affected. Because meeting all of these installations guidelines may not be possible on all aircraft, these guidelines are listed in order of importance to achieve optimum performance. Items 3a, 3b, and 3c below are of equal importance and their significance may depend on the aircraft installation. The installer should use their best judgment to balance the installation guidelines. 

  • Mount the antenna as close to level as possible with respect to the normal cruise flight attitude of the aircraft. If the normal flight attitude is not known, substitute the waterline, which is typically referenced as level while performing a weight and balance check. 
  • The GPS antenna should be mounted in a location to minimize the effects of airframe shadowing during typical maneuvers. Typically mounting farther away from the tail section reduces signal blockage seen by the GPS antenna. 
  • The GPS antenna should be mounted no closer than two feet from any VHF COM antenna or any other antenna which may emit harmonic interference at the L1 frequency of 1575.42 MHz. An aircraft EMC check (reference VHF COM interference check in Post Installation Checkout procedures) can verify the degradation of GPS in the presence of interference signals. If an EMC check reveals unacceptable interference, insert a GPS notch filter in line with the offending VHF COM or the (re-radiating) ELT transmitter. Page 2-2 GA 35, GA 36, and GA 37 Antenna Installation Instructions Revision B 190-00848-00 Note: When mounting a combination antenna, the recommended distance of two feet or more is not applicable to the distance between the antenna elements in a combination antenna (ex. GPS and COM, GPS and XM) provided the combination antenna is TSO authorized and has been tested to meet Garmin’s minimum performance standards. 
  • To maintain a constant gain pattern and limit degradation by the windscreen, avoid mounting the antenna closer than 3 inches from the windscreen. 
  • For multiple GPS installations, the antennas should not be mounted in a straight line from the front to the rear of the fuselage. Also varying the mounting location will help minimize any aircraft shading by the wings or tail section (in a particular azimuth, when one antenna is blocked the other antenna may have a clear view).
  • The GPS antenna should be mounted no closer than two feet from any antennas emitting more than 25 watts of power. An aircraft EMC check can verify the degradation of GPS in the presence of interference signals. 
  • To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should be mounted no closer than 6 inches (edge to edge) from other antennas, including passive antennas such as another GPS antenna or XM antenna. 

Comm Antennas

  • Communications radios can cause a lot of interference with GPS, because of the proximity of the panel units or their antennas. Therefore, it is important that the com and GPS antennas be mounted as far apart as possible. Sometimes a com antenna must be relocated to the bottom of the aircraft.
  • Communication antennas are basic in operation and have relatively few problems, except for delamination (more on that later). Each com transmitter has its own antenna, mostly for redundancy and a couple of technical issues. The antennas can be mounted on either the top or bottom of the aircraft, but each installation is susceptible to shadowing from the fuselage.
  • Shadowing is caused by structure, such as fins or gear doors, in the transmitting path of the antenna. Know where your antennas are and how shadowing may affect their range and coverage. If you have com antennas on the top and bottom of the aircraft, it helps to determine which antenna feeds which radio. The radio that feeds the top antenna would be better for communications while the aircraft is still on the ground, and the antenna on the bottom would be better for communications while airborne, having a clear shot of the ground antenna site in each case. Some older Cessna twins have a com antenna buried in the vertical stabilizer, which limits their range and coverage.

ELT

They are almost always on the upper skin of the empennage and are made of a flexible material. There are a few exceptions, though; some may be buried in the vertical tail or look like small com antennas.

Transpander

  • RG400 coax cable – do not bend it at any time more than 10x the radius. This can open up the mesh around the cable and there will be a degradation of the unit. (This can’t be undone and will need to be replaced)
  • Mount transponder as close to the antenna as possible – better performance. 
  • This unit has a TNC connector not a BNC(bayonette vs a threaded): Buy a TNC to a BNC cable – they are common in the marketplace and not too expensive. 
  • The farther the transponder is away from high energy EMI the better (keep away from servos,motor, strobe lights
  • Keep away from other transmitting sources. This unit is a higher transmitter
  • Antenna needs a ground plane and likely doesn’t come with one
    • Adding a doubler should work as a ground plane for you when attaching to the metal skin of the aircraft
    • Square ground plane like shown below is just fine for mounting. Doesn’t have to be a circle
  • Can running GPS wires with transponder, ADSB
    • Shouldn’t be an issue. GPS is a low current device, shouldn’t have interference with the other items)
    • Don’t run servo wires(high power) in this bundle
  • UHF Antennas (Transponder)
    • UHF antennas are commonly used for transponders and DMEs and are always found on the bottom of the aircraft. They are about four inches long, and the same antenna is often used for both systems because the transponder frequency is in the middle of the DME frequency band. Two types are commonly used, spike (Figure 5) and blade (Figure 6) antennas. The spike should only be used for transponders, because the antenna length is tuned to one frequency, the transponder frequency. The blade antenna is also called a broadband antenna because it is tuned for a range of DME frequencies. A spike would not work very well for a DME; the blade antennas are preferred because the radiation pattern is better and ice formation is less likely to break them.
    • The spikes are prone to caking up with oil, reducing the transmitting range. Often, just cleaning a spike antenna doubles your transponder range and gets rid of those intermittent Mode C problems. The reason is that the ground secondary radars need only one sweep to determine your squawk code (Mode A), but they need two good sweeps to determine altitude information (Mode C). Hence, a dirty antenna may not conduct a good signal reliably. This goes for all antennas; a dirty antenna does not perform up to its potential.
    • Transponder and ADSB antennas need to be at least 2 ft apart, further if you can – saw this in a dynon forum – who can verify?

Canopy Fiberglass continue

December 3rd, 10th, 17th, January 6th, 28th, Feb 4th, 38h

After many rounds of filling and sanding the surface, the canopy fits great! As well, we sanded the edges and drilled all the holes.

Continued sanding to get the canopy smooth and prepped for painting lead to the appearance of very small hallow dots, which we filled with a thin layer of epoxy.

In parallel, we did some more sanding and leveling for the tail fairings, given the similarity between the tasks.

Next: sanding with higher grits, 400 and above, then countersinking, then priming then riveting.

Canopy Skirt fiberglass continue

November 12th, October 3rd, 16h

Canopy skirt fiberglass sanding round 4 and 5:

  • After sanding the outside. I started examining the inside and I realized that it is not even, especially there was a line inside that is hallow that is leading to a very thin layer. So, I went ahead sanding the inside. Then I did another round of filling, this time both inside and outside.
  • Following that there was a long session of sanding, both outside and inside. I fitter the skirt, the fit looks fine. I filled a few areas in the inside. Then I prime the outside, so that we can start the final rounds of sanding, using the priming to stop low and high spots.

Canopy Fiberglass Skirt, continue

October 22nd, 28th, November 5th, 20h

Canopy and elevator fairings skirt sanding and filling with microspheres:

  • The canopy was sanded at little too much in a few areas.
  • The filling with the microsphere did not work great as it was very brittle, like chock, so not good for filling the few areas where there was too much sanding.

Canopy and elevator fairings skirt sanding and filling with flox:

  • The sanding was light, to only even out a few areas.
  • The floxed epoxy mix was used to fill the thin spots. Given that it is structural, it should hold well.

Following are picture after the second round of filling and sanding:

Canopy sanding anf filling round three:

  • The filling with the floxed epoxy was good at filling and also took lot of time at sanding. After hours of sanding, I had to change jobs to give my hand a break.
  • I used the angle grinder to cut the excess, but I left some excess that will need to be sanded.
  • I filled with floxed epoxy the areas that needed a little more

It is starting to get there, but there are still a couple more rounds of sanding an filling needed.

Panel Layout

10/15/2023, 8h

We are moving forward with the panel layout with the following plan:

Based on Skyview System Installation guide, the transponder and ADSB antennas need to follow the following:

  • The transponder antenna should be well removed from any projections, the engine(s) and propeller(s). It should also be well removed from landing gear doors, access doors or others openings which will break the ground plane for the antenna.
  • The transponder antenna should be mounted on the bottom surface of the aircraft and in a vertical position when the aircraft is in level flight.
  • The transponder antenna should not be installed within 3 feet (0.91 meters) of the ADF sense antenna or any COM antenna.
  • The transponder antenna should not be installed within 6 feet (1.83 meters) of a DME antenna.
  • Where practical, plan the antenna location to keep the cable lengths as short as possible and avoid sharp bends in the cable to minimize the VSWR (Voltage Standing Wave Ratio).

More information on the grounding plate and cable lengths and selection is on page 11-12. Note that once the cable run length is known, a cable type with low enough loss per metre that meets the above requirements can be chosen

Next:

  • Continue the work on the non panel avionics
  • Install the brackets for com, gps navigator and the knobs
  • Finalize purchase of the switch panels

ADAHRS Wiring/Plumbing Plan

10/01/23, 6h

Today, I focus on planning the wiring of the ADAHRS. After reviewing many wiring schemes, I decided on the following:

  • The air temperature probe will be in the left wing, right by the maintenance plan. This will guarantee that it is away from the sun and exhaust, and it will keep wiring/plumbing simpler.
  • We will need to drill a second hole on the fuse right behind the main spar, for the wiring/plumbing. The current hole will be used for one of the plumbing line and the air temperature wire, and the second one will be used for the second plumbing line. “Entry Holes”
  • We will drill second holes in the ribs, in the lower portion and right in front of the seat belt holders. We will drill these holes for this plumbing/wiring, and for future needs, such as antenna cables. “Rib Holes”
  • We will pass the cables through the Entry Holes, then the Rib Holes, then the left conduits. We will cut a hole in the conduit right post the baggage compartment to exit the cables. At this stage, we will pass the cable on the circumference of the bulkhead to meet the ADHARS.

Following are some pictures that I took through the research. The last picture is not applicable for the ADAHRS wiring, but it will be pretty useful for the antenna’s wiring:

Avionics Test and ADAHRS Install

09/24/23, 6h

We connected a 12V supply and we were able to turn on the garmin com, IFR navigator and G5. All works for far as expected.

Location of ADAHRS:

Next, we are working on the instal of the ADAHRS, the first step is to find the location. The ADAHRS needs to be away from ferrous materials. A few RV7 building put it behind the baggage compartment, in a U shaped piece hanging between the center rib and left stringer. We are checking with AFS, before finalizing the location. We find the following bracket to install in this location:

https://store.vansaircraft.com/rv-7-7a-9-9a-adahrs-bracket-kit-7-9-adahrs-bracket-kit.html

Another location suggested by Dynon is the HDX tray behind the panel, which is a bad location because of interference, however, the try might be useful for the other components:

https://dynonavionics.com/hdx1100-universal-mounting-tray.php

ADAHRS inputs:

  • A possible location for the OAT is on the left side of the plane, under the horizontal stabilizer. This enables it to be away from the exhaust heat and not under the sun
    • We need to finale location and drill the hole.
  • Static tube – runs from the rear of the aircraft
  • Pitot + AOA tube – runs from the left wing into the wing fuselage access hole and to the ADAHRS unit. (Figure out routing)
    • We need to determine the torque spec
  • To connect the lines to the tube fittings, we need to make 0.5inch mark and push the tube, until the mark is no longer visible. This information is from the Dynon plumbing kit.

Routing:

The pitot and AOA tubes: will comes from the back of the spar from the wings. We already have a hole in the left side of the fuse, behind the main spar, to route them and connect the the conduit, which will enable them to run under the seat. They will exit behind the baggage, to connect with the ADAHRS.

  • Need to figure out tube management. Currently the conduit that exits at the center is the right not the left one, and we need to figure out where to drill holes in the ribs to route the cable to the conduit.

Static: It is already routed

AOT: We can run it through the conduit, and cut a slot in the conduit to exit the cable by the ADAHRS

SV net: We can use the right conduit.

  • We still need to figure out cable management post conduit.

Fiberglass Canopy Skirt Continue

09/10/23, 7h

Today, we continued on the canopy skirt fiberglass. First, we did a round of fill with Cotton flox mixed with epoxy, we mixed it until it was the consistency of peanut butter. We filled all the low areas, let it sit for about an hour. Then we applied the last 2 layers of fiberglass, then added peel ply on top.

We briefly looked into the avionics, to try to turn on the comm, IFR navigator and G5, but then we realized that our power supply no longer works!

Avionics First Test

09/03/2023, 8h

We did the first test of avionics by testing HDX with the backup battery, ACM and all the SV network component. The HDX turned on, we were able to set a temp N number and see all of the SV network devices. The screen shows red Xs as the ADAHR, GPS and EMS were not connected. Some notes throughout the process:

HDX

  • Page 2-2: both Skyview network cable and RS-232 cable are 9 pin connectors, but they are NOT compatible. Plugging to the wrong location can lead to damage of HDX and other components.

To Do list:

  • Find location of ADAHRS, Dynon GPS, antenna, Garmin GPS, Transponder antenna, ADSB antenna and comm antenna and ELT.
  • Install pitch servo
  • Terminate ADAHRS, Dynon GPS, control stick, pitch servo, and flaps. 
  • Terminate pitot static tube
  • Figure out light interface with avionics (ACM)
  • Buy button panels with harness
  • Connect fuel pump to panel
  • Wire key switch
  • Find location of headset jacket

Questions/purchases:

  • Antennas cables: Garmin GPS, Transponder antenna, ADSB antenna, comm antenna and ELT..
  • Garmin comm, does it go to “audio panel” or “Nav-com-1
  • Buy button panels with harness