This blog is for entertainment purposes only, and is not meant to teach you how to build anything. The author is not responsible for any accident, injury, or loss that occurs as a result of reading this blog. Read this blog at your own risk.

Friday, May 18, 2018

Ch 22 - Electrical/Avionics - Part 15

George is flying!

I finally got a chance to go out and test fly the servo installation by shooting an actual autopilot coupled RNAV approach, and the results were just amazing.

Check it out…

Letting "George" do some work at last!

I am tempted to say my work here is done, but I know better than that. 

I am however looking forward to more flying and less modifying from now on, and perhaps even getting back to my long term Long EZ project… remember that?! 😉

Sunday, May 06, 2018

Ch 22 - Electrical/Avionics - Part 14

Pitch servo flight test

The one year long upgrade process had come to the end, and it is time to see if this conversion has been a good idea, or a waste of time and money. 

As you might imagine, I couldn’t wait to go flying to check out the fully functional autopilot.

Would it work well?

Would it work at all?

The wait was killing me! Meanwhile 7JT sat quietly in the hangar, perhaps still a little sore from the latest cyborg implant.

Luckily, I wouldn’t have to wait long for a couple of sunny days on which to fly. 

I actually conducted four flights over two days, and aside from a couple of control reversal issues (fun fun) due to software settings I was positive I had changed, the installation only required a little more torque output from the servo (another software setting) before 7JT started to perform the way I knew she was capable of.


Unfortunately, due to reasons unrelated to the servo installation, and that were since resolved, I had to fly these flights in heading mode, and I didn’t get to shoot any approaches. I’ll try doing that over the next few flights, however I wanted to show you a few pictures of the pitch servo in action during a couple of descents, one in IAS (Indicated Airspeed) mode, the other in VS (Vertical Speed) mode.

First though, let me show you the only climb shot I’ve got in which the sun didn’t fade the whole scene out… 

Constant 120kts airspeed climb to 6500'

After climbing to 6500’, I made a few turns. Here’s one to the left…

Level turn to a southerly heading

After flying a 15 minutes closed loop in heading mode, I found myself on the way back home, needing to descend. I broke up the descent in multiple sections in order to get a little more practice, and highlight any possible issues.

For the first descent, I selected 5500’ and chose a constant speed of 160kts. The Flight Director immediately commanded a dive, but the autopilot was very smooth in lowering the nose to follow it.

Process of beginning a descent in constant speed mode

As the airspeed reached the selected 160kts, the Flight Director rose to maintain the speed, and the autopilot smoothly followed its command.

Constant speed descent established

Roughly 100’ prior to reaching the selected 5500’, the vertical autopilot went into “Altitude Capture” mode, during which the nose is raised to level the plane off. At this point I added enough power to maintain my normal cruising speed.

Starting the leveling maneuver

The autopilot then went into “Altitude Hold” mode. The airspeed decayed to whatever the power setting I used would support, and the autopilot pitched to maintain altitude.

New altitude reached and level off completed

The next descent to 3500’ was started in IAS mode at 180kts, but then I switched to VS mode at -500 fpm (feet per minute) due to turbulence, and also to check that mode.

New descent to 3500' selected, with constant airspeed of 180kts.

Too bumpy for 180kts, I switched to a constant Vertical Speed descent at -500fpm

Vertical Speed descent fully established

Once again the autopilot went into “Altitude Capture” first, then the “Altitude Hold”.

Should start to look familiar by now

"That's right... you've got this now!"

What else can I say… I am beyond ecstatic. 

As awesome as 7JT has always been, she has now become the airplane of my dreams. Long trips will now be less stressful, and more fun, and I’ll be able to spend more time looking outside, both for traffic and to enjoy the view. 

Should the occasional cloud get in the way, 7JT is now capable of just about any approach one can think of, precision and non, and do it all by itself, including Missed Approaches and Holdings. 

All it’s required of me now is to stay awake, and enjoy the ride.

I can hardly imagine money and time better spent.

Wednesday, May 02, 2018

Ch 22 - Electrical/Avionics - Part 13

Pitch servo installation

With spring warmth at hand, I decided to get cracking on the pitch servo installation. 

I had a pretty good idea of where the servo should go. I wanted the heavy steel mass as far forward as possible to help with the center of gravity (CG), but I knew this location would require dismantling some of my previous work, and perhaps relocating and rewiring the entire ground bus.

Aside from getting installed in a forward location, the pitch servo would also need to connect to the elevator pushrod. The place I had in mind was right in front of the engine instruments, on the right fuselage sidewall, where a bracket already existed from the vacuum filter days, though it was currently being used by the ARINC module. 

Bracket supporting the vacuum filter (before "steam gages" replacement)

Vacuum bracket liberated during EFIS installation

ARINC module looking for a home

Vacuum bracket repurposed as ARINC support

The area behind the engine instruments is pretty spacious, but more importantly it is right over the top of the elevator control tube.

Looks like the ARINC module might need to find itself a new home

I spent quite some time figuring out how to make this location actually work, but eventually I ran into an unforeseen problem. 

While busy congratulating myself on how smart I had been reusing the existing bracket once again, I noticed that my compass was indicating 60º off its normal reading. Initially confused by it, I tried moving the servo slightly, and the compass just went nuts! 

That’s when it donned on me that the big hunk of steel was rendering the compass useless. I really should have known.

Double “DOH!”

Oh... it looks so obvious now!

So, I tried moving the servo all over the cockpit while observing the compass. Sadly, any place within two feet of the compass adversely affected the compass readings. There was a slight possibility of installing it way up front in the nose, forward of the canard, but the connection to the elevator rod would have been at a terrible angle, and I would have had to really tear this plane apart to do it. Some things are just better done while building the plane rather than afterward.

Never fear though, I had a plan B up my sleeve, although it wasn’t as good as plan A for moving the CG forward...

Because the LongEZ has a rear control stick, I might still be able to connect to the elevator control tube there, perhaps without inconveniencing the passenger too much. The plan was still to place the servo as far forward as possible, which now meant against the front seat, then connect it somehow to the tube in question.

Often a one-man building team, I leveraged velcro power to help me find a new place for the servo, and hold things together while I pondered on the new setup.

Investigating an alternative pitch servo location

After talking it over with my friend Wade, plan B started making a lot of sense, and as a bonus I wouldn’t even need to machine a new connector if I attached the servo rod directly to the rear stick. All I needed was a longer bolt and a few washers.

That just looks made for it

Please forgive the huffing and puffing on the next video, as I was laying with my chest on the left longeron, feet on a step stool, trying to get a good shot for you. 

Checking the feasibility of this location

Having decided on the location of the servo, the multi-day installation process began.

Day one was clickbonds install day…

Location of servo bracket identified

Sidewall sanded

Clickbonds (with flox) bolted to the bracket

Epoxy painted on sidewall

Bracket in place secured with tape

Heat lamps helping the flox cure overnight

Day two was spent fiberglassing over the clickbonds…

Flox cured

Flox sanded smooth, and electric tape ready to protect the threads from the epoxy.

A few plies that will go over the clickbonds

Sidewall prepped

Pre-preg ready

Pre-preg going over the clickbonds

BID pre-preg installed

Peel-ply over fiberglass

Bracket lightly attached to the clickbonds

Day three was sanding, and servo mounting day…

Peel-ply removed, all edges sanded smooth.

Pitch servo solidly attached to the plane

Servo arm attached to the rear control stick

A view of the servo control arm

Day four was spent wiring the servo all the way to the instrument panel backplate (aka junction box)

Using a 90º dsub female to male connector to manage the wiring

Another look at the finished installation

That's it! The autopilot installation is completed. All that's left to do now is go fly, and make sure the autopilot behaves predictably.

I shall let you know how it all went, soon.

Friday, April 20, 2018

Ch 23 - Oil cooler fan - part #4

Fan flight testing

I highly encourage you to take a second look at last week’s post, as most of what I will touch upon here is predicated on the ground testing experiment conducted in the shop.

In order to gather the missing data, we will be going flying today. Later we shall analyze the results, and come up with conclusions as to the suitability of this installation to long term flight safety. Then and only then will I feel comfortable leaving the fan permanently attached to the plane as I await the arrival of the first hot summer days. 

Should today's test prove successful, when the warm season eventually arrives, we shall conduct the final functional testing of the fan’s actual effectiveness in reducing oil temperatures on the ground.

But, before we actually get airborne, we need to ready the airplane by temporarily wiring it up, so that our “testing equipment” in the cockpit (basic voltmeter) can connect to the fan in the engine compartment. 

As you might remember, the reason for using a voltmeter in flight is the correlation between volts as read on the meter, with fan rpm, and fan amperage output. We mapped this mostly-linear relationship in the last post, and we are now ready to use it.

10.8v corresponding to safe fan-rpm (see previous post)

Because this is a one time occurrence, there is no need to rip half of the airplane apart just to run a couple of wires, and since the fan is right below the oil filler door on the top cowling, I plan on running a few feet of wire outside the plane from the this door to the aft portion of the canopy, and then inside the plane all the way to the front seat.

Running wires from the oil filler door to the rear cockpit

In the airline industry, maintenance occasionally uses what they call “speed-tape” on the outside the airplane as a temporary fix, you may think of it as airline priced duct tape. In the past I have conducted my own tests on duct tape outside the LongEZ, it is crazy strong (you figure that out at removal time), so I have no doubt our arrangement will work just fine for one flight.

"Speed-tape" over the wiring

I chose to use insulated alligator connectors inside the cockpit to allow for a quick disconnect of at least one of the leads, should it become necessary to isolate the fan electrically, and placed them in a position where I cannot accidentally bump into them, but where I can still reach them with my left hand. Keeping the wires ends somewhat staggered prevents the fan from shorting itself should both alligator clamps become disconnected in flight.


So, what’s the plan?

I envision the flight testing program as a mostly scientific pursuit, with a bit of art and intuition thrown in, needing to foresee hardware malfunctions, as well as obscure remote failure scenarios, and unpredictable odds. 

Flight testing not only has to establish ways for the plane to collect the sought after data, but it also requires anticipating everything that could possibly go wrong, and design strategies that address those eventualities. From the look of things, we are well on the way to doing just that with our initial voltmeter and wires placement plan. 

Needless to say, the big bugaboo of the flight testing phase is going to be the remote possibility of a self destructing runaway fan on takeoff, or anytime thereafter. Not only would the data collection phase of the flight be compromised, but the safety of flight might be impacted as well.

Aviation safety has come a long way by basically adopting Murphy’s Law that “anything that can go wrong will go wrong” as its mantra, and relies heavily on strategies tailored to minimize and mitigate such eventualities. The point here is that risk cannot be completely avoided but it can and should be managed appropriately.

During our testing I will be using an “action camera” mounted on a chest strap to videotape the flight (airspeed and volts mainly), this way I won’t need a third hand and a spare brain to try to capture the details I need. I did not consider a data-capturing passenger to be an ethical (or legal) option, so this will be a one man flight testing adventure. 

From this point on, all airspeeds will be in knots IAS (indicated airspeed), and any voltmeter values outside of the normal range established during ground testing (0v to -10.8v) will be cause for an expedite return to base, and ending the experiment.

For our purposes, I am going to subdivide testing into three separate phases of flight, each with its own challenges and emergency actions. They will be the takeoff ground roll, the initial climb, and maneuvering flight. No need for additional phases, because if the fan makes it all the way to maneuvering, it will be just fine for approach and landing as well.

The takeoff roll phase will begin at power up, and end at rotation. Because this is the safest time to end testing, and involves the easiest emergency procedure by just closing the throttle and applying the brakes, I decided to extend the ground run to a slightly higher airspeed than normal, up to 80kts before taking “my problems” airborne.

Ready to go fly

Ready for takeoff at the end of runway 5, voltmeter reading 0v as it should, I made one last mental review of what to expect. From this point on I’ll be looking closely at my voltmeter for the first indication of voltage, and by correlation fan spin-up.

80 knots, 0 volts

With rotation speed easily made with no incidents, I entered right into phase two of flight testing, the climb. 

The expectations for the climb, as for the rest of the flight, are the same as for the ground roll, less than 10.8v (absolute value) reading on the meter. 

The emergency action are quite different however, should that not prove to be the case, and they include wrapping the pattern immediately to the left for a close downwind, slowing down to the lowest voltmeter reading, and landing immediately. I could be back on the ground in about one minute at this point, so the possible danger from the over-speeding fan would be kept to the very minimum.

Of course, by now I have already figured out that 80kts is a safe speed for the fan, and because it is also a flyable speed, my stress level just took a major dump. I now know that at this airspeed, there is not enough airflow through the oil cooler to spin the fan, and should anything bad happen, I can always slow down to 80kts to stop the fan. 

Granted, it is possible it might take more energy to start the fan than to keep it running, and perhaps slowing to 80kts might not stop the fan, however we just proved we aren’t remotely close to fan overspeed territory here, and that’s what matters.

After a few seconds climbing at 80kts with 0.000v showing on the meter, I decided to lower the nose, letting the airspeed build up and seeing at what point I’d get initial fan rotation. 

100 knots, 0 volts

I am sure by now you are probably wondering whether the voltmeter is even working, or perhaps it might have gotten disconnected. I had the same exact thought, and at around 500’ above the ground took a quick peak at the leads…

Nope! Still attached.

Well, that is just weird! Where’s the heck is the oil cooler airflow? 

Obviously the fan is not spinning, since even turning it with one finger produces enough tension to be read on the instrumentation, but does that necessarily imply that there is no airflow?

Let’s open a quick parentheses here… 

I later tested the fan holding it out of the window of my truck with another aircraft builder driving it (thanks Eddie), and quickly discovered it takes around 40kts (wind adjusted with opposite direction runs) to turn the blades over. 

The obvious implication is that just because the fan is not spinning, it doesn’t mean there is no airflow through the fan (read oil cooler). There could actually be up to 40kts of airflow through the fan before I can be alerted to it by the voltmeter. 

Close parentheses.

110 knots, -1.3 volts

At 110kts, I knew we had this b#*ch nailed!

Finally some voltage started reading on my meter, confirming not only that the fan had started windmilling, but that the fan-rpm were well within safe parameters at this airspeed.

Much relieved by how things had gone in this one minute flight so far, it was time to enter phase three… maneuvering flight.

The only emergency action at this stage would be to slow the airplane down to a previously identified safe airspeed where the fan would be controllable once again, then test some more, or call it done and go home.

Personally, I needed to see that I had full control of fan-rpm via changes in airspeed. I spent a some time going back and forth from 110kts to160kts with complete predictability, though the voltages were slightly different at individual airspeeds depending on whether I was accelerating or decelerating toward them, but all in the safe sub 10.8v (absolute value) range.

120 knots, -1.7 volts

130 knots, -1.8 volts

140 knots, -2.7 volts

150 knots, -3.2 volts

160 knots, -3.6 volts

What a great day of testing! 

So far I had managed to safely takeoff, climb, and maneuver to a pretty high cruising airspeed without any incidents or issues.

Because I rarely fly faster that 160kts IAS, I could have just packed it in for the day, and be satisfied with the results. But with an airplane capable of so much more, it wouldn’t have been a complete vetting of the installation had I not pushed it all the way to redline.

170 knots, -4.3 volts

180 knots, -4.9 volts

190 knots, -5.5 volts

195 knots, -5.8 volts

Ok, so technically I was a couple of knots short there, nevertheless I think we succeeded in proving a major point today…

The oil cooler fan installation is safe!

Whether it works as expected on the ground in reducing summer's high engine oil temperatures remains to be proven, but we can now take flight safety concerns off the “most wanted” list.

Unfortunately the camera was bumped into at some point before takeoff, and not all footage is usable as the speed-tape got cut out of the shot quite a few the times, plenty of it remained however to validate our results.

For those interested in the data, I compiled a graph based on some of the speeds and voltages taken from the inflight chest-cam video footage.  

Voltage output from the fan at various airspeeds

From the experimental knowledge we gained during ground testing, it is now possible to correlate actual indicated airspeed to fan-rpm.

Correlated fan-rpm at various airspeeds

As you can see, the highest fan-rpm reached at the fastest airspeed this LongEZ is capable of, is merely 2200 rpm, roughly half of what it normally spins when powered by the battery (4300 rpm), and from the table at the beginning of this post, we know that the maximum induced current would only be -15.5a, which is easily stopped by an appropriately sized diode.

I feel comfortable closing the inflight portion of the oil cooler fan testing now, and while the summer round of ground tests might still disprove our main assumption, we will still have had fun, safely learning and growing in the process. 

Isn’t that exactly what the FAA had in mind when they created the amateur-built certification category after all?