GPS Replacement

This entry is part 61 of 66 in the series 13 - Electrical / Instruments

Long ago when I began this project, I decided on a glass panel. At the time, there were a number of vendors offering EFIS (Electronic Flight Information System) solutions. I decided on the Grand Rapids Technology product.  At the time, they had the HX EFIS products and an Engine Analyzer.

So I was going to have a single screen on each side of the instrument panel with the “radio stack” in the middle. This stack would have the communications/navigation radios, audio panel and GPS.

Once I started building, they released the HXr EFIS displays.  These displays support “remote” devices.  Which means the radios and audio panel are controlled through the EFIS and do not have to be located on the instrument panel. There was no IFR GPS option though so I was going to go with a Garmin 400W WAAS GPS mounted on the instrument panel.

Then a couple years ago I heard that GRT had an IFR GPS in the works. I asked them about it and was told that it was “in development” but would be ready in a year. Since I was still a couple years from needing it, I decided to go that route.

When I was time to order all the avionics equipment I placed the order.  But the GPS still wasn’t ready. So I started installing the avionics and left a spot available for the GPS.  In October of last year, I finally received the GPS!  Hooked everything up and I was good to go.

Except that I realized that I had never loaded the GPS database.  When I asked for instructions about doing that I learned that the software for the EFIS wasn’t finished. I was told November or December.

But I didn’t want to run version 1.0 software while shooting an instrument approach to minimums.

So I returned the GPS and began looking for a used Garmin 400w.

One of the glitches with this particular operation is that when I was laying everything out, I didn’t allow for a 12″ deep, panel mount GPS.  That means I have to do some rearranging.

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This is the avionics shelf behind the instrument panel. The multi-color rectangle is where I figure the panel mount GPS will be.

Obviously the audio panel is going to have to be moved. I think the cables from the hub (white cables to the left of the audio panel) will be able to be pushed down.  The pitot lines (red tubing) will have to be relocated as well.

My first plan was to remove the top shelf which currently holds the GPS, remove the trim controller and mount the audio panel just above With the audio panel out of the way, then I would just have to re-route the pitot tubes.

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So here I’ve removed the old GPS, trim controller and power stabilizer (more on that later) and relocated the audio panel above the VPX.

But there’s a problem… The audio panel cables aren’t long enough to reach to the new location.  Since I was going to need cables for the new GPS, I got in touch with Tim Hass at Approach Stack to ask if I could get an extension cable for the audio panel.  Normally, I would just replace it with a new, longer cable but the existing cable has wires running to all the headset jacks, control stick, right switch panel, etc. and I didn’t want to have to pull and reconnect all those connections.

While I was talking to Tim, I told him that I was looking for a used 400w but not having much luck and that if he knew of one to let me know. He said that he had a brand new Garmin GTN625 that he could sell me. This is basically the new, improved replacement for the discontinued 400w.  And the price was just a little more than I was finding for the old units. So I told him “sold”!

A while later, a box showed up with the new GPS, mounting hardware, cables and my new audio panel extension cables.

Uh-Oh…

The audio panel cables are huge.  They are thick and they don’t bend very much. Add in the connectors and I was having trouble routing the cables so that they didn’t interfere with important stuff. So I set that problem aside and started working on getting the GPS mounted.

I decided to mount the GPS in the center of the panel directly between the two EFIS screens. But the compass was in the way.  Since I had to eliminate the power stabilizer, I needed to create a backup power source for the primary EFIS/AHRS/Magnetometer. That means I do not need a traditional whisky compass. But I do need to fill in the hole where the compass used to be. Once that was done, I had to determine how I would support the back to the GPS.

I decided to support it from above rather than build supports from the avionics shelf. So I located the center of the inside of the fuselage just aft of the canard opening. Then I used spring clamps to hold the GPS tray in place while a used structural adhesive and rivets to attach a pair of aluminum angle brackets using the tray as a guide.

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Once that cured, I made some short aluminum supports to allow the tray to sit farther forward so that it could reach the panel.

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Then I leveled the tray up and marked the panel where I would have to cut an opening for the GPS.

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After I cut the opening (which took a while because I cut it small and gradually increased the size), I had to support the tray where is met the panel. I chose to bond a couple of aluminum angle brackets to the back of the panel.

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And then just to look at it with the GPS inserted.

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Then I removed the tray, mounted it to the rear support, put the instrument panel in and attached the tray to the panel brackets.

That’s when I discovered something; There’s enough room under the tray to fit the audio panel.  By placing it there, it would be almost in the same location as before so I wouldn’t need the extension cables (and the associated routing problems).

So I pulled the GPS tray out and built a drop-down support from the GPS tray.

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Then everything goes back in.

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I rotated the wiring hub so the cables weren’t pointing straight up.

The last task is rerouting the pitot-static lines. I used the heat gun to heat up the tubes and bend them.  I’ll redo this to make it prettier later.

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Now it’s time to put everything back together and power it up.

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Secondary EFIS Power

This entry is part 62 of 66 in the series 13 - Electrical / Instruments

Because I have an “all electric” instrument panel, there are some challenges. One of those is powering the basic instrumentation during engine start. When you hit the starter button, the battery gets loaded down and the output voltage can (and usually does) drop enough that the EFIS reboots. It takes the HXr about a minute to boot up. So for that first 60 seconds after starting the engine, all I’ve got for engine health is the “Low Oil Pressure” warning.

To resolve this, I installed the TCW Technologies Intelligent Power Stabilizer (IPS).  This small, lightweight box gets power from the battery and provided a constant 24 volts even when the input voltage drops to as low as 9 volts. It can only output 24 volts for a couple of seconds when the input power drops but that is sufficient to keep the EFIS up and running during engine start.  The HXr has three separate power inputs.  The primary power input is connected to the battery.  The secondary power input is connected to the IPS.

With the GPS swap requiring me to move things around, I had to eliminate the IPS. To keep the HXr powered up during engine start I will have to go with a backup battery.  I would have done this originally except that the optional backup battery is only available for 12v HXr’s. I looked for a 24v backup battery, but they were either too big or too expensive. This is what happens when you go with a 24v electrical system.

So I decided to think outside the box.

I call these “Barbie Batteries”.

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I found a store that sells “Scooter Batteries” for things like mobility scooter, small electric cars… You know, those little cars that parents get their little kids?

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I found that while the 24v batteries were big and pricey, I could get a pair of small 12v batteries that were very affordable. The batteries I got were 5ah SLA (Sealed Lead Acid). By connecting them in series, I would get 24v, 5ah.  Not only would this power the primary EFIS, AHRS and magnetometer during engine start, it would also keep the devices powered for at least an hour if the main electrical system failed.  An added bonus is that since the Magnetometer and EFIS will have an independent power source, I can eliminate the compass in the panel.

The down side is that they weigh 3.5 pounds each. Once I’ve verified this works, I may look for some new, fancy, hi-tech, low-weight batteries.

As for where to put these, I decided to put them in the nose. I noticed when flying alone that I required quite a bit of nose-down trim for level flight. Seven pounds in the nose should help that.

The first step is to make a tray for the batteries. So I wrapped the batteries with duct tape, took a piece of spare fiberglass, cut it to size and then applied some fiberglass strips to create the sides. Once it had cured, I removed the batteries and trimmed to size.

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Mounting in the nose was a bit of a challenge.  First I had to find a spot that was as far forward as possible but not interfere with the nose gear or anything else. Then I had to fabricate the supports and hold it in position while in glassed everything in place… And it had to be level.

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Once that was bonded in place, I had to fabricate the hold downs.

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Then I just had to wire everything up.

Battery

The primary power comes on whenever the master switch is on.  I’ll have a second switch on the panel to apply the backup battery power to the secondary input of the EFIS. So I’ll throw the backup battery switch while I’m doing the pre-flight check, Then when I’m ready to start the engine, the EFIS will be up and running.

Engine Dehydrator

This entry is part 45 of 48 in the series 12 - Engine / Propeller

One of the things that is bad for engines is moisture (that’s why all the aircraft boneyards are in the desert). A fellow member of the CPS (Cessna Pilots Society) has built an engine dehydrator. That I’ve been using for a while now.

You connect the tubes to the oil filler port and exhaust pipes. Then when you switch on the box, a small air pump recirculates air into the engine after passing it through a bottle of desiccant. The pump runs until the humidity gets to 5%.  Once the humidity rises to 10%, the pump turns on again so that in air inside the engine is always between 5-10% humidity.

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I’ve seen some of these homebuilt systems that run either continuously or on a preset timer. I like this one because it actively monitors the moisture level.

Not sure if it’ll make any difference but it’s a lot more humid here in FL than it was in IL.

If you’re interested, contact Jerry Olson at jolsonpt38@sbcglobal.net. He will need to know what type of engine and if you made any modifications that he needs to accommodate (like my breather tube into the exhaust).

Fouled injectors

This entry is part 46 of 48 in the series 12 - Engine / Propeller

After the first few flights, I had Malcolm open up the fuel filter and clean it out. I cleaned out the tanks as best I could before and after they were sealed, but you can never get all the debris out. So cleaning out the fuel filter after a few hours is called for.

Malcolm reported the usual amount of crud that he sees in the filter at this stage.

At about the 15 hour mark on my Phase I flight testing, I had a cylinder come up cold during the runup. Now I’ve seen this more times than I count.  It’s always a fouled plug that is usually from idling full rich for too long.  The standard approach is to run up the engine and aggressively lean engine.  And has so many times in the past, it cleared the fouled plug.

But then about two flights later, I had two cylinders come up cold on the run up pad. Now that’s one I haven’t had before. I leaned out the engine at run up power to no avail. After a few more attempts the cylinders were all firing properly again. I made a mental note to make sure and lean the engine for ground operations like I have been with the Cessna.

Two flights later, it happened again. But this time I was only able to clear one of the cylinders. So I checked the mags and discovered that the cylinder was dead for both mags.  When it’s a fouled plug, it’s usually the bottom plug so I should have seen power on the top plug. Which meant that it must be a fouled (clogged) injector. Oh well.  Back to the hanger.

I pulled the cowling and removed the injector for the offending cylinder and sure enough, it was clogged. I could not see light when looking through it. I got a paper towel and blew through the injector but it wouldn’t clear. I tried a few more times and still couldn’t clear it. While I was walking over the service center, I tried a couple times and it finally cleared. But since I didn’t have the paper towel over the end, I wasn’t able to identify what the material was.

I reinstalled the injector and cranked up the engine and all six cylinders were firing away so I made another flight.

The next morning when I started up, I had two more cylinders that were not firing. A mag check showed that it wasn’t the plugs which meant that I had two more fouled injectors.  So I called Malcolm to come out and give me a hand. While I was pulling the five remaining injectors he was removing the fuel filter.

I cleared out the injectors and then I heard Malcolm say “Check this out”. I looked at the fuel filter in his hand and it was about half full of crud. He cleaned it and this is what came out of the filter.

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He said that was two to three times what he found the first time he cleaned the filter. Our guess is that there was a pocket of fiberglass dust that was stuck behind one of the baffles and that after about 10 hours of flying it got flushed out.

When the filter was reinstalled, we disconnected the fuel line at the servo and directed it into a container. Then I ran the fuel pump for a few seconds. We got a small amount of crud. Emptied the container and did it again. Clear fuel this time.

Hooked the fuel line back up and the engine ran fine.

So I’m going to be checking the fuel filter about every 5 hours for the immediate future until it shows clear.

 

The end of a long journey…

This entry is part 5 of 7 in the series 16 - Flight Testing

Yesterday, I arrived at my home field with the Velocity.  Seven and a half years after making the first fiberglass layup.

Weather was tricky as there were showers and clouds between Sebastian and Orlando that I had stay clear of (there is currently no weatherstripping and the plane is not certified for IFR).  But once past Orlando is was a clear shot to Panama City.

Two highlights were having Tampa approach pointing me out to a passing Delta flight (“Delta 123, you have a Velocity off your right at 6,500″). I couldn’t figure out why a 767 would be so low or why they never called my to tell me about the Delta flight. Then I noticed they were at about 18,000′.  That was cool.

Then I passed a Skylane like it was standing still. That was fun.

Arriving at my home field it was empty.  I figured Ann would be waiting for me so I gave her a little show.  I did a low approach and overflew the runway.  I had to pull the power way back because it was really bumpy.

I had been wondering how visibly the flashing landing lights would show up. She said that she could see me coming for a long way off.

Video of the low approach and landing (apologies for the portrait mode… what are you gonna do?).

I’ve got some other posts that precede this one but I wanted to get this up ASAP.

Nose gear spring replacement

This entry is part 37 of 38 in the series 07 - Landing Gear

Bouncing along on a amusement park ride.

That’s what one of my landings felt like. But it wasn’t my fault!  Runway 05/23 at Sebastian is not a very smooth runway.  Lots of dips.  On the above referenced landing, I hit one of these dips and got catapulted into the ceiling.  Now even with my seat and rail system modified, I don’t have much headroom… so at least I didn’t develop much momentum.

I think it was the day after that landing I was rolling up to the builders service center and Scott was watching me taxi up.  He had a very concerned look on his face.  Which was causing me to get a very concerned look on mine.

I shut down and got out and said “What?!?!”. He said “Something’s not right with your nose gear strut.”  Then he walked over and with one hand pushed down on the nose. When he did, the nose when down and the nose wheel sprung forward.  Then he said “This spring is too weak.  I shouldn’t be able to compress the spring at all.”

Normally, it would take a putting the weight of your whole body on the nose to begin to compress the spring.

At some point in the past, Velocity had some weak-ass springs. Scott asked what color my nose gear spring was. I told I wasn’t sure but I would check tonight. He said it felt like one of the white ones.  So I put the airplane away for the night and once back at the hotel, I looked through my pictures.

From January 25, 2008…

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Uh-oh.

The next morning, I taxied over to the Builders Service Center.  Scott was waiting.  “Well?” he asked.  I just shook my head.  He was visibly unhappy. “I thought that we found everybody that had a white spring and replaced them.”

He said the biggest danger is that when the spring compresses enough, the top of the gear is not supported against side loads.

Here’s a diagram that shows the nose gear assembly from the left side.

Nose Gear

This is showing the “Down and Locked” position. At the bottom of the nose gear is the wheel (out of the diagram, bottom left). At the top is the spring (in red). The blue “captivator” is a U-shaped steel bracket which prevents the top of the assembly from moving left to right. When weight is put on the nose of the plane, the spring compresses, the wheel moves up (and forward) and the top of the assembly moves back. If it’s just a little, it’s not a problem. If the top moves back enough, the top is no longer in the captivator.

The big problem with my weak-ass spring is that with just my weight in the pilot seat, the spring was already compressed some. Any bump (or another person in the front seat) and the spring is compressed enough so the top of the gear assembly is now out of the captivator. Which means a nose gear collapse is just a matter of time.

Scott then asked about my takeoffs. I told him the plane stays firmly on the ground until I pull up. He nodded and said “Yep. That’s what I figured.”  With the pitch trim set for takeoff but the spring compressed, the canard was not at the normal angle of attack. So it’s not creating any lift.  But once I pulled back on the stick just enough, the spring would uncompress, and the canard would then generate lift and the plane leaps off the ground.

So now what?

Scott said it’s not too bad of a job to pull the shock out.  So I started by removing the canard. Then it’s just the two bolts at either end of the shock.  It took me about an hour.

Then we rode over to the machine shop where Scott had already pulled a new (red) spring. With a special fixture for the press, the old spring was removed and the new one installed in about 3 minutes. Without a press, that would have taken me a whole day to figure out how to do that.

Another hour to put everything back together and Charlie Mike was ready to go. Total time, about 2.5 hours. That right there made the numerous trips back and forth between Panama City and Sebastian worth it.  If I hadn’t been there, Scott wouldn’t have noticed it. And I wouldn’t have since I didn’t have enough Velocity time to know that is was too soft.

The next takeoff was so much nicer. The plane literally flew off the runway. And the landing was so much better as well.

Static Port Conundrum

This entry is part 60 of 66 in the series 13 - Electrical / Instruments

The static port serves two primary functions: 1) It provides the ambient air pressure which the altimeter uses to determine the altitude. 2) It provides a reference pressure for the pitot tube to determine the airspeed.

The static port called out in the manual is built entirely by the builder.  I elected to purchase a pair of static ports from Aircraft Spruce similar to the static ports on my Cessna 182-RG.  The reason for having two is to correct the static pressure when the airplane is in a slip or skid. If the airplane is in a slip or skid and you have only one static port, then it could be in either a high pressure area or a low pressure area.

When I flew my plane (solo) for the first time, I was elated at the indicated and true airspeed. Indicated (IAS) is what the airspeed indicator shows and true airspeed (TAS) is your actual speed through the air.  To determine true airspeed, you take the indicated airspeed and compensate for temperature and altitude. The bottom line is that I was hauling ass!

But then I noticed my groundspeed. Normally when you’re flying, there’s either a headwind or a tailwind. If your true airspeed is 190 knots and there’s a 10 knot headwind, then you’ll only be traveling 180 knots over the ground.  But when I looked at my groundspeed while traveling south, it was showing about 20 knots slower than my TAS. Okay, I’ve seen 20 knot headwinds more times than I can count. After I turned around, my groundspeed was still about 20 knots slower than my TAS.

Now that’s peculiar.

The next couple of flights, I did a tests of the airspeed. This is accomplished by flying at least three different headings (usually greater than 90 degrees), noting the groundspeed on each heading and by using a formula you can determine your actual TAS along with the current wind speed and direction. What I discovered is that at cruise speed, the airspeed was reading about 25 knots faster than I was actually traveling.

But the slower I got, the closer the TAS got to the actual airspeed.

Now if it were reading slower than actual, that would point to a leak in the pitot system. But faster?!?!

After a lot of thought, I came to the conclusion that the static port must be drawing a vacuum. Since airspeed indication is a result of the pressure of the air being forced into the pitot tube compared against the static air pressure, it seemed likely that if the static pressure were less, the airspeed would read high.

I talked this over with Scott and Rick at the builders center. Scott said that he’s had to put “trip strips” in front of the static port to disrupt the air because it was pressurizing the port but he’s never had a static port effectively de-pressurizing before. He suggested putting a small piece of stir stick behind the port. This should stop the vacuum by pressurizing the port. Once it’s determined that was the problem, then the thickness could be adjusted.

So I taped over one of the ports (easier to test with one port), hot-glued a short length of stir-stick behind the static port and went for a flight.

Now the airspeed is reading about 15 knots low at cruise. This would seem to prove the concept.

But… if the static port were drawing a vacuum, then altitude would be showing higher than actual altitude (less pressure the higher you fly). And if the static port were being pressurized, then the altimeter would be indicating lower than actual.

This caused the hair to stand up on the back of my neck.  Because if I’m flying along at what I think is 6,500′ (westbound VFR altitude) and the static port is being pressurized, then I could actually be flying at 7,000′ (eastbound IFR altitude). But air traffic control would keep me from bumping into someone else, right?  Nope.  ATC thinks I’m at the altitude that my transponder is sending… which is what my static port pressure says it is… which is wrong.

So I got back on the ground to figure this out.

After talking with Rick and Dale (sounds like a 60’s surfer rock duo, doesn’t it?), I decided to build a manometer. AKA, pressure sensitive water level. So I removed the stir stick and hooked up my home made manometer.

Here you go. Tell me that doesn’t scream “Experimental”.

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One end is connected to the static port (right tube), the other is open (if you already see the problem, you’re way ahead of me. But I figured it out at Sandy’s Grill over a cider that night).

Sitting on the ground, I made marks to show level and a few other reference marks. When air moves over the static port, if the water level in the left tube goes down, then the port is in a vacuum. If the level goes up, it’s being pressurized.

So here I am at 196 knots and 160 knots over the ground.

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Vacuum!!!

So I decided to change the shape of the static port from a flat disc to a dome (I’m obviously getting tired at this point) and went up again.

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Even more of a vacuum!?!?

That’s when I decided to call it quits.

Because it was Thursday night, I went to Sandy’s Grill (Thursday is steak night there). While I was there thinking about things over a steak ka-bob and an apple cider, I had a couple epiphanies. The problem with the manometer is that it was measuring the static pressure relative to the pressure in the cabin. Which is typically lower than the outside ambient pressure to begin with and at this point is a completely unknown variable. Which means that was a pretty useless experiment to begin with.  The only way a manometer reading could be valid is if I could locate a true undisturbed ambient pressure location for the other end of  the tube.

Second was the modification to the static port. But making it domed shape, I effectively created an airfoil. Like the top of the wing. Which is a low pressure area. Which means it would be creating a vacuum. That is why it showed an even greater vacuum.

So I decided to approach it as simply as possible. There are two primary sensing instruments based on the pitot/static system: altitude and airspeed. If there are no leaks and the instruments are calibrated, then the only variables are the static port location and the pitot tube location. I was careful to locate the pitot tube where the manual specifies which obviously leaves the static port position as the problem.

So all I need to do is get one of those two instruments reading correctly and the other will have to be correct. Because I can’t determine my altitude with any accuracy (without something like a radar altimeter), then I’ll just have to tweak the static port until the airspeed reads correctly. Once the airspeed is showing the correct speed, the altimeter would have to be accurate as well.

Now this makes some pretty big assumptions. I didn’t skimp when I purchased the pitot tube (it cost me about $500) so I’m comfortable it should be creating the correct ram air pressure. I checked the system for leaks so I know that’s good. The last variable is whether the GRT Air Data Computer/Attitude/Heading Reference System (AHRS) is correctly computing the airspeed. The AHRS is a rather complicated piece of electronics and at this point I have to trust it’s doing it’s job.

And finally, since the changes I’ve made to the static port created variations that are expected predictable, then I’m confident that’s where the adjustments need to be made.

So I removed the static port, got a file and started filing down the leading part of the port. I only took able 1/16″ of an inch off (right is facing the front of the airplane).

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Then I hooked it up and went flying.

When I crunched the numbers, the indicated airspeed was about 15 knots high.  I made a couple more passes with the file and did another flight. Now it was reading about 10 knots high.

So next I’ll make a couple more passes with the file and try again… and again… and again.  Basically sneaking up on it because I don’t want to go to far. When I get it to where the TAS equals the groundspeed (compensated for winds aloft), then the altimeter should be reading correctly as well. The only way that I can think of to test that is to make a high-speed low pass at the airport. If I do that at a visual height of 50 – 100 feet, then the altimeter should show that I’m flying at the field elevation plus 50-100 feet.

But for now, that will be one of the first things I do when I get back to Panama City.

 

First Flight! (for me)

This entry is part 6 of 7 in the series 16 - Flight Testing

Lots of things going on.  Because we sold our Chicago area house and bought a house in Panama City (literally on the same day), and said Panama City house needed a LOT of work before the planned move in date of 9/5, I haven’t had much time for airplane related activities. I did run down and get the roll trim installed but that’s about it.

Because I’ve only got 25 hours to fly off, I was planning on doing that in one trip.  And to handle the transportation, my good friend Rody (who was in the plane when I had the nose gear collapse on the 182-RG in Greensboro, NC) suggested that I just rent a car and drive down then drop it off there if I can fly off the hours in one trip. Thanks Rody!

So I got a car from Enterprise (only nationwide car rental company with an office in Sebastian) and drove down on Sunday, September 13th.  Then I got John Abraham to go up with me for a couple of quick take off and landings. Remember, I only have 5 hours in Velocities and that was the small trainer that’s fixed gear.

So we hopped in the plane and took off.

Holy crap, this this is FAST!  Rocketed down the runway, lifted off and before I knew it the we were at 130kts and climbing… rapidly. Then the “Low Oil Pressure” light started flashing.  A quick check of the gauges showed the oil pressure was reading right where it should. So we stayed in a tight pattern just in case.  After a minute, the light went out. It turned out that I had inadvertently set the alarm (which drives the “Low Oil Pressure” light) to indicate for low oil pressure and if a cylinder head temperature exceeded 400 degrees. Oops.

The two landings were far from impressive.  Long with lots of over-corrections.

Then I was up on my own.  I decided to fly south to Stuart (the south end of my test area) and then back north to Sebastian. This takeoff was even more… exhilarating.  With just me in the plane it accelerated like a sports car. In no time I was at 1,500 feet and climbing in excess of 1,500 feet per minute.

Lots of challenges here.  First is staying in front of the plane. I ran into this challenge when I moved from flying fixed gear Cessna 172’s to my 182-RG.  Lots more power and lots more speed. Eventually you start thinking far enough ahead that you’re playing “catch up” all the time.

The other challenge is migrating from “steam gauges” to a glass panel.

Here’s the panel I’ve been flying behind for the past 16 years.

6408S Panel 2 (low-res)

If you’re not a pilot, it may seem daunting, for me it’s been home for the last 16 years. Airspeed? Top left.  I haven’t really looked at anything other than the needle position for a long time. When I’m on base leg, the needle is about 3 o’clock. Over the runway for landing, 2 o’clock.  Vertical speed? directly over the yoke. Hard to miss being level or in a 500fpm climb. Altitude? Directly above the VSI.  It’s second nature.

Now…

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So now when I need to know how fast, there’s no needle. Just to the left of center is a vertical tape with (in this case) 165 in the middle. That how fast I’m going (indicated, not actual). Altitude? To the right of center. I’m at 6,510 feet.  Vertical speed?  On the left side of the altitude tape are some hash marks that angle up and down. If I was climbing at 1,000fpm, the area from the middle to the “1” would be shaded.  For a non-pilot that hasn’t been looking at the old six-pack or steam gauges, this probably makes perfect sense.  But I’ve been flying behind those old gauges for so long that this will take some getting used to.

Gear doors, rudders and roll trim

This entry is part 4 of 7 in the series 16 - Flight Testing

After the first flight, the first order of business was to get the flutter which was suspected of coming from the gear doors. Since I was having to head up to Illinois and pack up the remaining furniture, I had Malcolm handle those tasks.

When the plane was jacked up and the gear retracted, the nose gear doors weren’t fully closed so Malcolm adjusted those.  The left main gear door was hanging down about a 1/4″ so that was adjusted as well. He checked the incidence of the wings to try and determine if that was the cause of the left roll tendency. Both wings were perfectly set. Although the right wing did have some wash-out.  But if that was a factor, it would have had the opposite effect.  So the roll issue was deferred (for now).

John went up for the second flight on 7/14.  The flutter from the gear doors was gone.  But now there’s a flutter from the right rudder.  The plan was to shim out the rudders and see what that did.  The roll tendency toward the left is still there.  John and Scott Swing both feel that shimming a wing was overkill and that if I had roll trim it could easily be dialed out.

So before going any further, let’s discuss my decision to skip the roll trim mechanism. First, I wasn’t keen on the factory supplied mechanism.  Basically, it was a DC motor with a string wrapped around it a few times. One end of the string attached to a spring and then to the aileron bellcrank while the other end went around an idler pulley and attached to a spring and then to the other side of the aileron bellcrank. Here’s a picture where the string/spring attaches to the bellcrank.  Since the motor has continuous rotation, if it turns too far, the string will begin to slip.  That slippage also allows the pilot to overcome the position should the motor or motor control fail.

Click here for a picture of a dash-5 roll trim on Jorge A. Bujanda’s build site.

Well this string idea didn’t sit well for me. Geoff Gerhardt came up with a great idea of using a cog belt. So I ordered a drive pulley for the existing motor, an idler pulley and a length of cog belt. Started making the parts and pretty soon I had a good working roll trim mechanism. As I was about to get everything wired up, I started thinking…

I’ve never flown (nor heard of) a single engine piston airplane that had roll trim. I asked around and every A&P and IA that I spoke with said the same thing. Which was, if you’re using roll trim in a light single, you’re fixing a symptom while you should be fixing the problem of why it’s not flying straight.  This is what’s known as “rigging” an airplane. I had this done on the Cessna years ago. It involves adjusting the control linkages, setting the incidence of the wings and then flying it. If it doesn’t fly straight, you adjust linkages and wing incidence to get it flying straight.  So I decided that this roll trim thing is just a shortcut to properly rigging the plane in the first place.

And with that, I took all the roll trim parts off and put them in a box. No plane that I built was going to have roll trim so that I don’t have to get it properly rigged!

Then I got taken to school by Ken Baker.  I hadn’t considered dihedral.  All those other single engine airplanes have dihedral built into the wings. Dihedral is where the wings are angled up when looking at the plane from the front (or back).  With dihedral, when the plane is level, both wings a producing the same amount of lift. But if the plane rolls to one side, then the lower wing generates more lift and the higher wing generates less which causes the plane to level out… all by itself.  So if one side of the plane is just a little heavier (maybe because there’s more weight on side), this dihedral will help the plane fly level.

image3no

Guess what Velocity aircraft don’t have?

Velocity-side-Gear-Up DJ

That’s right, dihedral.

Which means that when they roll just a little, instead to dihedral basically self-correcting the unwanted roll, they actually roll even more. Which is why even minute weigh imbalance or a small difference in the wing shape can create a roll to the left or right.

So the roll trim box is going to have to get opened back up. But that will have to wait until I get back down to Sebastian.

Scott did the third flight. Malcolm shimmed both rudders. At around 165, the flutter developed in the right rudder and caused the entire winglet to begin oscillating.  Very disturbing.  When they looked at the rudders, instead of the outside surface being slightly concave (or scalloped) or even flat, they were convex (rounded out). This was causing the rudders to “hunt” for a neutral. Which means flutter. That movement transmits to the winglet causing it to start moving as well. If left unchecked it could cause the winglet to depart.

Here’s a main wing oscillation on a Hawker. (Warning: NSFW for language)

 

So it looks like my rudders were not properly constructed.

Malcolm removed them and began making them right.

Here’s the outside surface of the right rudder. You’ll notice that it’s not concave or even flat. In fact, there’s a pretty good outward curve on that surface.

2015-07-15 Left rudder

After removing all the filler, it’s still not right.

2015-07-15 Right 1

Here’s the rudder that was causing the flutter.

2015-07-15 Right rudder

Eventually, Malcolm ended up sanding deep into the foam before the he could get the correct shape.

2015-07-16 Both

Covered with uni.

2015-07-17 003

With filler. We now have a low spot on the outside surface.

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Painted and installed.

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I didn’t want to try and install the roll trim because I wasn’t sure when Scott was going to be able to make another test flight.

On the Friday the 31st, Scott made test flight #4. The plane accelerated through 165kts with no flutter.  He said that he got it up into the “170’s”, but the data log showed a max speed of 180kts. There was some scary weather approaching so the flight was cut short.

The next day, I installed the roll trim.

Here’s my roll trim mechanism.

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Since I had originally intended to install roll trim, I had pulled all the wires, I just had to terminate them.  Now for the pitch trim, I went with the TCW Technologies Safety Trim controller. I did this for a couple of reasons.  The primary reason was that the Vertical Power VP-X trim driver is designed for low power RC Allen trim motors and is limited to 1amp. They don’t recommend using it to drive Velocity trim motors. The other reason I used the Safety Trim controller is that it has some really nice features:

Dual speed; it will drive the motor faster at lower airspeeds when large changes in trim are needed quickly while at high airspeeds, it drives the motor slower to prevent trim overshoot.

Runaway prevention; If the pitch trim switch should fail in the closed position, the trim motor will not continue to run.  The controller will only allow the motor to run for about 3 seconds at a time.  If you need more trim, you release the switch and then press it again.

Reversible; If the switch gets stuck, you can disable and reverse the motor with a switch on the panel.

So when I realized that I had to install the roll trim, I was thinking that I was going to have to buy and install another trim controller. But fellow builder Bob Holtaway did some testing and determined that the pitch trim pulled significantly less current that expected.  And since the roll trim has much less load than the pitch trim, I decided to go that route instead.

Everytime I work with the VP-X, I’m amazed. Just about every aspect of it is well thought out and easy to use. Once I connected the wires, it took about 10 seconds to configure the VP-X to drive the roll trim motor.  I had the trim motor wires reversed so it ran backwards. It took about 2 seconds to correct that in the VP-X configuration.

So at this point, the gear door flutter, rudder/winglet flutter and left roll have been resolved.  I’m hoping that I don’t discover another surprise that rears it’s head at 190kts.

 

 

 

 

16 First Flight

This entry is part 3 of 7 in the series 16 - Flight Testing

First flight was scheduled for July 7th. We drove down on the July 4th.  Ann came down on this trip (for some reason) :-). The last time she was in Sebastian was when we came down to talk to Velocity and take the demo flight in June of 2007.

I spent the 5th and 6th preparing for the flight by finishing up the various odds and ends that needed to be done. On the 6th, the plane moved for the first time under it’s own power.

I was very pleased with the handling compared to the trainer that I flew a couple weeks earlier. After taxiing around for a while, I picked up Ann and we did a relatively high-speed taxi (~ 50kts). Once again, the airplane tracked very nicely.  Then we went over to the compass rose to align the AHRS and magnetometers. Then we put it away for the night.

John Abraham came over around 11am on the 7th and began his preflight.  While he was doing that I explained the systems that I thought were unique to my plane.  The only thing he found was the main gear cables were a little tight. He wanted a bit more slack in them. So we loosened them.  He checked a couple other things and then said “Looks like it should fly… Let’s go see.” :-)

So we pushed it outside.

 

John started the engine and we talked for a minute while the engine warmed up. Then he taxied off to runway 06.

 

Ann had a GoPro running and her iPhone at the same time (not sure how she did that).  The GoPro video is going to require some post-production work as the plane is so small that you can even see it. But until then, here’s the iPhone video.

John was up about 20 minutes.  During that time he check the control response, slow speed handling, monitored the engine and attempted to check the high-speed handling.

After landing, returning to the hanger and shutting down he explained that a flutter developed at about 160kts which limited the speed on this flight. He said that it seemed to be coming from one of the landing gear doors. The only other issue was a slight left roll tendency.

And with that, the first flight was over.

Now, in addition to being an “airplane” on FAA paper, it is also one in reality.

This calls for a celebration!

I’ve been holding my last bottle of Glenmorangie in reserve.  I had to do this because the sixteen men of Tain decided to sell their distillery to the French (YGBSM!) a few years ago. The current product, by the way, is barely acceptable for cleaning toilets. But we’ll leave that discussion for another time.

So I brought along my last bottle on this trip. I pulled out a couple of mixing cups because it seems appropriate that the cups which were used to mix the epoxy for this airplane be the preferred container for the celebratory drink.

2015-07-07

Now that’s how you finish an airplane.