Posts tagged ‘Airplanes’

Upgrading the tailwheel spring retaining clip with a D-shackle

The rudder of a tailwheel airplane typically connects to the tailwheel with a combination of chains and springs. At each end, there is a teardrop clip. These clips will fail sooner or later – and usually at a very inconvenient tile. As was the case for me. One clip failed during a recent landing. Thankfully the landing was back at my home field.

Since others had experience with this situation I investigated their solution. Was there a better option? Yes!

A 3/16″ stainless steel D shackle fits nicely. A little safety wire insures the pun (oops, that should probably be ‘pin’) can not rotate and fall out.

retaining clip vs D-shackle

retaining clip vs D-shackle

In the picture, the top shows a standard retaining clip and then the D shaped shackle.

Now it’s back to flying!

The importance of prototyping a design

I recently completed an industrial design project. Sadly, I ignored or dismissed a very important step in any design project – prototyping.

The project was a new instrument panel for a tandem seat aircraft. (Readers may recognize this as a redux of a similar project 2 years ago.)

rv8_panel_ifr_v3-mockup

The panel cutting was done by a third party so the process began with a sketch by me. I then generated a high fidelity mockup from the sketch. It took about a week of "an hour here and an hour there" until I had a a mockup which I really liked.

rv8_panel_ifr_v3-cad

The fabricator then worked with me on several iterations to create a CAD drawing of the new panel. Version #6 was the final drawing. I signed off on it and the panel was cut and shipped. During the iterations we addressed various physical requirements such as the width and height of the actual switches and breakers, the mounting bezels for the GPS and screens, etc.

Once the panel and all of the equipment was in my shop, I settled down to the task of wiring. This started by temporarily installing all of the equipment into the panel and then working from the back side to deal with all of the audio wiring, data & communications, and then all of the power connections.

IMG_6342

After the basic system tests were completed, I disassembled everything and took the panel to the pain shop for base coat, labeling, and then clear coat finish (with a flattening agent to reduce reflections). I was very happy with the results.

I reassembled everything and then installed the new panel along with some new components in various locations in the airframe in support of the new panel.

All of the basic tests passed. The new panel was ready for flight testing, calibration, and training.

IMG_6343

The first test flight exposed a fundamental user experience error. Do you see it in the last picture ?

Here is what happened …

  • My sketch was done on paper.
  • My high fidelity mockup was done on the computer screen.
  • The layout and labeling was done on the cut panel.
  • Initial testing was done on the bench

All of these were looking either on a flat representation or looking strait ahead at the panel.

When you sit in the airplane, the pilot’s eyes are approximately 20" from the panel and the pilot’s sight line is level 10" above the center of the panel. The pilot is looking down between 20 and 30 degrees at the panel. As you can see in the final picture, a portion of the labels are obscured because the center display’s bezel is 9/16" deep at the bottom.

A physical mockup would have detected the viewing angle and the label position could have been adjusted.

POH Kneeboard 2.0

New POH Kneeboard with write-on surface
New POH Kneeboard with write-on surface

A little less than two years ago, I wrote about creating a combination pilot operations handbook (POH) and kneeboard.

One aspect of the implementation bothered me from the very start – the metal front and back covers could be hazardous in an accident. The military use a polyethylene plastic material which is somewhat flexible and less likely to injure.

A separate problem surfaced when I used the kneeboard – my scratch paper would move around and curl. A fellow pilot had described using an arm band – like [US] football quarterbacks use – and a grease pencil.

I decided I’d address both issues with an update to the kneeboard.

The flexible translucent PE plastic is 1/16″ thick. It has a smooth side and a slightly textured side. Normally the smooth side would be considered back. Since I plan to write directly on the cover, I used the smooth side as the face. This makes it easy to wipe it clean.

Garmin understands amateur aircraft builders

For anyone who has worked with Garmin’s prior generation of aircraft avionics, they are all too aware of the challenges of wiring high density D-Sub pin connectors, threading back-shells, and conforming to old standards. So I keep being amazed by the small changes Garmin has made with their latest generation of avionics targeting the amateur home built aircraft community.

I’m very grateful for the switch to standard D-Sub pins and the open top connectors makes the assembly much easier. And here is another example of Garmin thinking like a builder rather than an engineer – mounts which can be switched from the ends to the sides of their new remote mounted radio.

When building a kit plane, everything is up to the builder and this means every airplane is a bit different with hundreds of decisions.

In my RV-8, finding a location for the remote radio was becoming a challenge of compromises. I finally located a suitable space but the radio mounting tabs were in the wrong place to make it work. I was about to concede and build new mounting tabs but when I removed the factory tabs I discovered Garmin had anticipated my need!

With the factory installed mounting tabs at each end of the radio, it can be mounted horizontally or vertically with ease. In my case, the problem was that I needed to mount it across between the RV-8’s forward baggage bulkhead and the Z-brace. Ideally, I wanted those tabs to be on the sides of the radio rather than the ends. Thankfully, Garmin attached the mounting tabs with screws. When I unscrewed the tabs I was delighted to see that Garmin had designed the tabs’ screw locations and the radio’s screw holes (two extra ones hidden under the tabs in their original locations) to rotate 90 degrees and re-attach! All I had to do was unscrew the tabs, turn them 90 degrees and there were nut plates already installed for the alternate orientation.

Garmin had designed the radio to give the builder multiple choices for how to install their radio.

This truly is an example of designing for their end user!

GTR-20 with adjustable mounting rails
GTR-20 with adjustable mounting rails

A 6PDT push button for COMM1/COMM2 radio switching

switch stereo audio, mic, and signals
switch stereo audio, mic, and signals

Traditional aircraft used an audio panel in the avionics stack to handle multiple radios, audio sources, and intercom between the occupant headsets. This was logical when there were so many audio sources which needed to be monitored for different segments of flight – two radios, identifying VORs and NDBs, listening for the outer marker signal, etc.

With the growing availability of GPS for all segments of flight including precision landing, some aircraft have done away with an ADF and even NAV radios. My plane is one of these. There are pros/cons to this configuration but for a lot of domestic flying, it’s safe and complete.

Many newer radios incorporate the intercom and even have alert and auxiliary audio inputs. With all of he capabilities of these modern radios, most of the audio panel capabilities are redundant. The exception is supporting two radios.

Two radios are handy since one radio should always be setup to talk to the airport or to air traffic control. The second radio can handle things like checking weather at the departure or arrival airport. It can also be helpful when you know you will be changing frequencies multiple times in a short period – eg: weather, clearance, ground, tower, then departure control.

Having two radios doesn’t dictate an audio panel. Switching frequencies has become much easier with database integrated radios and EFIS/GPS connected radios. With these systems, a frequency change is often a press of a button.

This leaves the listening to weather and the “convenience cases” when you want to load up clearance and ground to a second radio. The “listen” to the second radio can be handled through an auxiliary input on the primary radio. Now we have only one case to solve – temporarily switching to the second radio.

In a side-by-side airplane, both occupants have access to the panel but in a tandem (or solo) only the pilot can reach the panel. Only the pilot really needs access to both radios. My airplane is a tandem and I fly 99% solo.

A pilot headset has a MIC, a push-to-transmit, mono or L/R headphones, and the ground wire. That’s 5 connections. A switch can handle toggling all 5 wires at once between two radios.

The sixth switch lets us listen to the second radio while connected to the first.

Below a video of the switch. The switch has both solder lugs and PCB pins. The pins can be cut off when using the solder lugs. The push button switch “latches” when pressed and releases when pressed again. It has a mechanical colored indicator that is visible when pressed to the “latched” position.

6PDT Push Button Switch

Simple DIY “remove before flight” covers

1.5 inch red ribbon
1.5 inch red ribbon

For safety reasons it a very good idea to have covers the the various tubes sticking out of an aircraft. It helps keep bugs and debris from clogging vital systems like the pitot tube and the fuel tank vents.

You can buy very clear cover-flags for $10 to $20. Or, you can make about a dozen for less than $4.

You need a sewing machine (or the patience to do a bunch of hand stitching) and you need a roll of 1.5″ or 2″ ribbon.

I cut pieces about 12″ long. I used a lighter to singe the fray ends. Next I folded the long way and stitched about 4-6″. That’s it. They fit perfect over the 1/4″ tubing. For a full sized pitot tube you cut two pieces of ribbon – one at 12″ and one at 6″ and stitch then face-to-face.