February 23, 2015
This adventure is LONG, and maybe boring, but full of information!
Many might be bored and should stop now, but anyone interested in experimental aviation construction and test-flight should read on!
OK so the call finally came in from RDD that my r-Evo (N844X) was ready!
This is a project that has run through FOUR years, about twice the planned budget (due to my own custom avionics mods, NOT Lancair!), multiple design changes (all improvements!) made by Lancair during the construction (as problems with the Evo fleet have surfaced and then been addressed by Lancair), a number of sub-contracting companies shutting down operations with the requisite run-arounds, countless hours of learning, and now: The requirement to be ready for flight.
So I will start at the beginning:
Four years ago, my experience being only in flying certified airplanes, I assumed that every button, knob, and switch in an airplane did what is was supposed to, and that an airplane would always act in a user-friendly fashion where at most maybe ONE system might fail during a flight, and that failure would be resolved by telling a mechanic about it after the flight. When I took a test-flight in an Evolution, with a sleek, carbon-fiber airframe and 750 horsepower turbine, I assumed that if I purchased a kit, the resulting Experimental airplane would be just like the certified plane when done, only faster. I also assumed that the build and flight process would be predictable, scheduled, and the airplane would operate much like a car in the end: Just the way you expected, every time. I also assumed that I would be unable to MODIFY anything in the design, and that my airplane would just be like everyone else’s. (This was based, of course, on my experience with certified planes).
As you may guess, I could not have been more wrong, and I have now learned how much an airplane can demand, and how much it can give back if given the proper input.
So, four years ago, I started the 844X construction.
The first year was smooth sailing:
Cut strips of carbon fiber.
Work resin into them and let them cure.
Trim them into the desired shapes.
Prep surfaces for bonding with sandpaper and acetone.
Bond surfaces with hysol or resin.
Fill the (VERY VERY SLIGHT!) low spots and then sand them down.
Cut and bend aluminum tubing for fuel lines.
Sand the edges of windows until round, and bond them in.
Lay out wiring harnesses.
Mount various computer and sensor boxes in the fuselage.
Stuff like that: Construction.
Then, at some point, I realized that I did not HAVE to follow the plans.
My first target: The Moritz display. This is a touch-screen display in all Lancair Evolutions that is used to control the pressurization, heat, air conditioning, and electronic circuit breakers that operate all of the lights and climate control. Why not replace this unit with a much more capable touch-screen that controls the aircraft systems in a more user-friendly fashion, and offer backup attitude and synthetic vision as well, and even an AI to guide the plane to safety after an engine failure?
Thus, the Vertical Power VP-400 was born. Contracted and funded by me, this project ultimately ran years behind schedule and way over budget, never reaching a successful completion. Ultimately, Vertical Power sold the project to Astronics, gave up, and shut down operations. Astronics then proceeded to cancel the project. I had a malfunctioning, incomplete piece of avionics whose safest use could only be to occupy a garbage can. So there it went.
Then, BACK IN went the Moritz display once the VP-400 was pulled out.. after the Moritz spent SEVEN OF THE LAST TWELVE MONTHS IN THE SHOP, waiting for repairs! (This, after Moritz sold the project to Radiant, when Moritz decided that the project was not right for them! Argh!)
The Kollsman pressurization outflow valve (the most complicated part of the pressurization system, since its’ failure could, umm, blow up the airplane) changed hands through TWO different companies during construction… and that was the SECOND pressurization valve we used! The first pressurization outflow valve, made by a company called Dukes, had to be discarded when Dukes refused to share the format with us to DRIVE the valve so that we could pressurize the plane!
So look at the CORPORATE failures here, all happening during the construction of ONE AIRPLANE:
-Vertical Power STOPPED WORKING on a project they were contractually obligated to finish, sold off the project, and shut down operations, forcing the avionics made in that project to be discarded.
-Moritz sold their touch-screen system controller to Radiant, who took SEVEN MONTHS to do a repair.
-Dukes sold us a pressurization outflow valve, and then REFUSED TO GIVE THE MESSAGE PROTOCOLS TO DRIVE IT.
-Kollsman made a pressurization outflow valve, sold it to a different company, and then THAT company ALSO REFUSED TO GIVE ME THE MESSAGE PROTOCOLS TO DRIVE IT. (We are still able to use that valve since MORITZ knows the messaging protocols, and the MORITZ unit is the one talking to that valve! GAH!).
So what seem to me to be corporate greed and paranoia set the N844X project back by YEARS. But, those were only delays… I would not let them STOP the project!
So, with the old Moritz in the cockpit to control the enviro and lights by touch-screen, and an iPhone with Xavion on it to act as my back-up everything, off I went to Redmond on a one-way (whoo-hoo!) airline ticket to pick up N844X.
Did I just say that an IPHONE is a back-up EVERYTHING?
That sounds rather crazy, doesn’t it?
WEELLLLLL, Xavion, running on an iPhone, uses the iPhone’s internal magnetometer, gyros, accelerometers, and GPS to draw a full synthetic vision system! That includes attitude indicator, airspeed, altitude, heading, and full image of all terrain near you! So, Xavion backs up your standard six instruments, and even your WINDSHIELD, in a way, with the computer generated image of what you should see out the window! As well, with it’s GPS and terrain and nav database, it draws a moving map, thus backing up your navigation system. As well, since it devours weather by internet over WIFI, cell-towers, and ADS-B receiver (IF you, optionally, have one) Xavion gives you NEXRAD weather, winds aloft, and METARS for all reporting airports, thus backing up your on-board weather system. Also, since you can download charts and approach plates in Xavion, Xavion also backs up whatever you normally use for approach plates. And Xavion will guide you to the best runway to glide down to after an engine failure, thus coming kind of close to backing up the engine in many cases. Also, Xavion can use the pressure sensor in an iPhone6 or new iPad to warn of cabin de-pressurization, and (in the current version we are getting close to releasing now) actually take control of a TruTrak autopilot with ZERO pilot intervention to descend down to a safe altitude, thus coming kind of close to backing up the pressurization system. And, since (in the version of Xavion we are testing in-house now, to be released soon) Xavion will bring an airplane down to just above the runway automatically if connected to a TruTrak autopilot, any passenger can push the panic button and pull the throttle in the event of pilot incapacitation, so Xavion sort of backs up the pilot, in a way. And finally, a weak-spot of the Evolution is that it has only one electrical bus, and Xavion, acting as backup avionics, runs on the iPhone’s own internal power of course, thus acting as a backup electrical bus for the backup avionics, since almost all avionics are backed up on the iPhone!
So, when I say “an iPhone with Xavion on it to act as my back-up everything,” THAT is what I am talking about: With a simple iPhone with Xavion on it, I have backup altimeter, airspeed, heading, windshield, map, navigation system, weather display, maps, approach plates, electrical system, engine, pressurization system, and pilot. Holy cow!
Now, in the one-way airline on the way to Redmond, a certain thought kept running though my head: “There is no such thing as an airplane.”
This might seem like an odd thing for a pilot to say, but my foray into experimental aviation has proven it.
Having seen almost every system I can imagine be unfinished, mis-configured, not installed, or otherwise malfunctioning during the development process, I have seen that there is NOT actually any such thing as an airplane!
There are WINGS! They LIFT! But those are just some carbon-fiber foils that lift weight into the air… certainly wings alone are not an airplane.
There are ENGINES! They pull things along if there is air to be had… but engines are found on air-boats, blimps, and the like… they do not constitute an airplane!
There are flight controls, and they increase and decrease lift on the various foils sticking out of the body, but they will move in the OPPOSITE direction intended if various cables and push-rods are not organized a certain way inside the body.
There are TRIMS, but they could as easily as not move the wrong way (and, for me, they have, in two different cases so far) if simply hooked up to a wire or button backwards.
There are avionics, but who on Earth is to say that they will always work, and communicate with each other? Certainly, they have not always for me.
There are tubes pushing hydraulic fluid all about, hopefully in the right direction to push wheels up or down so the carbon-fiber shape can either roll or fly depending on the drivers’ intent, but a simple circuit breaker pulled out by a shop worker for maintenance will render the whole system inert, as I found out earlier today. A hydraulic valve left open will do the same thing, as I have also found out from experience.
There are resistors, capacitors, and inductors. Pushrods and cables. Reservoirs, pumps, tubes, and tanks. Springs and linkages. Wires and WIFI hot-spots. Transmitters and receivers.
All of these are parts, and each one of them could fail, or be installed backwards. Every one of them works in a way that would seem to accomplish nothing when you look right at it.
But, if they are ALL installed and working JUST RIGHT, then whatever somebody sitting in the left seat WANTS: HAPPENS.
THAT is what we CALL an airplane.
Just sitting in the cockpit on the ground, going through every system, we wind up with “squawk-lists” like this one… this is the sqawk-list on DAY 1 of the test and acceptance process:
(This list may be boring, but it is real!)
o2 block to run 1 cable to o2 system.. take the time to do it right
measure now to mnfctr for me to install at home, or install on next trip out here
The iLevil is going out today, BUT… remember I told you we were working on a dual band receiver?
I sent one of the prototypes iLevil2. It has the second frequency active (although software is not yet finished).
I currently don’t have user guides and labels for the iLevil 2, so I sent everything for the current iLevil. The only thing that changes is the DB9 connector to a DB15. So I wrote the Pins you needed to connect on a paper.
I tried to include all the connectors you might need in case the hangar doesn’t have them. I did not include 1/8 NPT connectors for the pitot lines because I don’t know the size of hose you use.
I wanted you to test the new hardware because it outputs a lot more data (due to the 1090 MHz receiver)
My cell below… call me for any questions regarding the iLevil2
config MFD for proper descent options (ete, vvi reqd!)
learn how this g1000 version works for approach and wxr and stuff
some switches are not lit
G900 failed data path
missing syn vis and tons of alerts
copilot seat hard to slide back.. hanging up on something? can we lubricate or something?
can i see the latest w/b?
engine limits sheet from dave, incl oil pressure
to do when i have my own moritz replacement:
go to dual bus for goodness sake!
can the o-2 bottle and ecb panel come DOWN at all?
this gives more waist room, which is tight right now
ipad mani where the moritz is now, of course… it fits perfectly
to do on panel face replacement, whenever that is:
move the landing gear circ breakers to the circ breaker panel
lots of unused switches… dump them, though a dual-bus system with cross-tie would sure be nice!
oh what the heck.. for the airplane image with the landing gear, make it an evo.. i can deliver the PNG fil
this part should be ready to go when i return
email mark to confirm a few weeks before i come back
o2 block to run 1 cable to o2 system.. take the time to do it right
measure now to mnfctr for me to instlal at home, or install on next trip out here
rgt flap needs to rig up!
it is sitting below the aileron kind of a lot!
These lists come up FAST, and evolve throughout the project. You keep testing every system in the plane, and in a rather complex turbine airplane with pressurization (+heat/air conditioning), retractable gear, and a lot of computers, there are a lot of systems that all have to work right for you to say you have an airplane. (See what I did there? I call it a bucket-o-bolts until it is DONE and working… THEN I call it an airplane.) Now, as you go through these to-do list items, you develop a flight-test protocol as well, planning everything you will test in flight to see if stuff is working as it should. For me, that results in lists like this:
(Another boring list, but it is real!)
Test the gear warn circuit (touch retracted switch to make us think we dont have 3 green) to see if the gear warnings squawk out (AOA aural).
umm.. how does the autopilot work?
check g-900 warnings and xm weather
check the gen and alt amps and bus 1 and 2 volts in flite.. mfd
check cabin alt and dp at alt
at 17500 should 6.5 psi
6.8 is max
Stall warning works OK from the AOA system?
It is audible?
what are the 2 yellow lites on the airplane image for the gear?
one yellow is hyd pump running
the other is up and locked, or ‘gear unsafe’… find out specifics from dave
Gear warning works OK from the AOA system?
It is audible?
Climb through 1250 AGL with the gear down: Do we get Xavion red-screen message and AOA aural message?
Descend through 750 AGL with the gear up: Do we get Xavion red-screen message and AOA aural message?
XAVION USE WITH ILEVIL:
get xavion guiding us perfectly
> I’ve noticed that after I’ve updated the new version I see the gps altitude drops to 0 for a split of a second every few seconds, and then comes back to my altitude, that drives the application crazy, the ui is going up and down render it almost unusable.
> The app parred with the ILevil SW ads-b.
get an sw.. mine is not:
ILevil SW ads-b keps dropping to 0 alt now and then popping back
-power-off panic button.. does that work in xavion?
-go to 15k, put on mask, and de-press.. do we get cabin alt warning on xavion?
So, what you have is an ongoing procedure of ground-test, complete or fix, and flight-test to confirm completion.
What I find so fascinating about this (besides the fact that we are programming computers that drive carbon-fiber airframes hooked up to turbines, of course!), is that I have to KNOW WHAT I NEED. GONE are the days of showing up to a certified airplane factory and saying: “What are you giving me?” The question is now inverted. We show up and ask: “What do we NEED to make this pile of parts into an airplane? How will we achieve it? How will we test it in flight safely?” We don’t ask what we GET. We ask what we WANT! And then decide how to GET it. This is a whole different suite of questions than I am used to asking. And it is really quite amazing to manage this sort of project, since the power available through computers (which can do anything we can imagine) carbon fiber (which can be shaped in any way we can imagine) and turbines (which put out huge power… from a package the size of a few mini-fridges), but the fear is always lurking as well, since you have to keep everything right-side up while everything from the environment to the airplane change rapidly while you test it all together. As I told a team-member earlier today: “I am rather at the ragged edge of my risk-assessment abilities here.”
So what is it like to fly?
OK, typical flight: We have a flight-test card of things to check on this flight, I am left-seat, the RDD build-shop manager or a flight instructor is right seat, and we have gone over the flight-test card inside, covering everything we want to do on this flight. Out we go to the airplane. It is still quite a thing to approach anything this big and sleek and fast. N844X is awkward to get in since it sits WAAAY up high to clear that big prop, so you have to climb WAY up onto the wing, and twist yourself around to squeeze into the cockpit, sitting snugly in the tight seat, a suite of computer displays in front of you, flight controls at left, and emergency oxygen system and circuit breakers at right. We check pressure on the emergency oxygen system to be sure we have enough, can check pressure in the emergency fire extinguisher, and mount the iPhone with Xavion to act as emergency backup avionics. The close-fitting hardware may well be wrapped in Plush Corinthian Leather, but is still highly purposeful. Flight controls are free and correct, and we close the door and belt up. We do flight control freedom and correctness BEFORE belting in. Why?
Well, once the BATTERIES are on, electrons are slipping away that we will soon need to start the engine, so once the batteries are on, we want to start the engine right away.
And, once the ENGINE is on, we are going through 30 gallons per hour at IDLE, so once we start the engine we want to get FLYING right away.
So, ANYTHING that can be done BEFORE engine start, is. Thus the flight-control check here. We make sure that the emergency door-seal dump (to deflate the door-seal and open the door in a hurry) is closed so the seal can retain pressure to seal the door. We make sure the emergency hydraulic bypass is closed. Hydraulic pressure raises and lowers the gear, but in the event of hydraulic pump failure, we need to be able to open a bypass to DUMP ALL HYDRAULIC PRESSURE, so the gear will simply FALL down! But if we ever want to RAISE the gear after take-off, we need to make sure that this emergency valve is CLOSED, so the hydraulic pump can pressurize the lines and push the gear UP to retract! We check to make sure the fuel selector is set to the fullest tank, and not the other, or the emergency shut-off position.
We then check the emergency oxygen masks. We are pressurized, but if cabin pressure is lost…. I designed and built the system to have oxygen masks at the ready, right under my right hand, hooked to an emergency pure-oxygen tank.
So, it is quite a suite of emergency hardware ready to go:
Emergency door-seal de-pressurization (to let air out of the cockpit and open the door if needed).
Emergency hydraulic valve to let the landing gear FALL down if the hydraulic pump fails.
Emergency fuel shut-off in case we habve an engine fire and need to stop fuel to the engine bay.
Emergency oxygen to breathe if we loose pressurization.
Emergency fire extinguisher in case there is a fire.
Emergency backup avionics on a different electrical system (Xavion on an iPhone!)
We then engage the batteries, and the fans in the cockpit spin up. About now, it sounds like the bridge of the Enterprise: A steady whirr of the cooling fans, with various beeping and c-tones as systems boot up and self-test. Next, we engage the electronic circuit breakers of the the various lights. With those electronic circuit breakers “energized”, the various light switches should work when called upon to do so shortly. We get ATIS now. Next we engage the door-seals to lock us into pressurized environment. Now the igniters come on. A tic-tic-tic sound emanates from the engine bay as sparks fly into the combustion chambers of the Pratt and Whitney PT6A-42, looking for fuel to ignite. Fuel pump comes on to give us a steady flow for engine start. Now we hit the starter (a bright red starter button from a Honda-S-2000 that says “It’s go-time”) and the most incredible climbing whine you can image starts right in front of you.
I don’t know if I am the first person to use the starter button from a Honda S-2000 to start a Pratt and Whitney PT6, but I like the result!
[clr]If a million dollars had a sound, THIS would be the sound. The whine of the jet inside the nose raises up and up, a subtle vibration from the compressors pulses through the whole plane. At 13% of the 39,000 RPM turbine redline (Not a typo. 39,000 RPM) you engage the fuel and the beast awakens. The turbine inlet temperature rises rapidly to OVER TWO THOUSAND DEGREES FAHRENHEIT, and only THEN does the prop begin to turn. As the airflow picks up through the engine, the ITT FALLS, and you have a running engine. Generator ON to re-charge the batteries, and fuel pump and igniters OFF since they are no longer needed. (The engine-driven fuel pump will carry the load from here, and the fire will burn without the igniters now). Advance the prop control out of feather to redline, and you can HEAR the prop flatten and race up in RPM as the whine of the turbine is supplemented by the roar of the prop. You are now going through 30 gallons per hour just to sit there, so it is now, officially, ON. The noise from the outside of the plane is now the most high-tech noise you could imagine: A mixture of the high, smooth scream of the turbine, and the windy, throbbing pulse of the prop, sounding radically different depending on the propeller forward/reverse mode and winds across the prop. The axial compressors of the engine are now providing more compressed air than the centrifugal compressor attached to them can handle, and bypass doors in the engine have opened, dumping out the excess air to keep the centrifugal compressor from stalling. Those with a skilled ear can HEAR the air coming out of the bypass valve amongst the other noise.
So this engine IDLES fast enough to get the airplane away from you, so you have to pull the prop into beta (a reverse-pitch of the prop to get reverse thrust) just to keep the speed under control in taxi without frying your brakes. The plane taxies very smoothly, with the door seals and tight airframe eliminating absolutely all outside noise, leaving you to hear only the sounds of the turbine and prop entering the cockpit, since they are transmitted though the airframe. Arriving at the run-up area, we set flaps and trim and perhaps give it just enough throttle to spin the prop up to 1,500 rpm and cycle the prop to test blade pitch control. Igniters and fuel pump go on as emergency backups, and onto the runway where we advance to one quarter power to look at how the engine settles: You feel the turbine scream up higher, the prop spin up, and then you get pushed back in the seat as the prop pitch opens up to avoid an over-speed. You see the prop RPM come up, the turbine inlet temperature come up as the fuel comes in, and fall as the cooling airflow through the engine catches up to it a moment later, and the turbine speed winding up to lead the whole process along. Satisfied, you advance to HALF power. That is take-off power. Half power. Any more would roll the airplane to the left due to the engine torque! With half power, you are pushed firmly back in the seat. The bypass valve that dumps out excess air from the axial compressors remains open. Air is still pouring out of the sides of the cowl from those valves. One of these days, I will learn how to hold the airplane right on the runway centerline during this process, but that day certainly was not today. Approaching 70 knots we raise the nose and the earth quickly falls behind. Raise the gear and flaps and let the plane build some speed. Now, with plenty of speed for flight control, we can afford to absorb all the engine torque. FULL POWER. The bypass valves close, and ALL of the air from the three axial compressors screams into the centrifugal compressor. The engine has entered the zone, the Genie is free from the bottle, and he is PISSED. You have to raise the nose to absorb the acceleration, and the climb rate transitions to 5,000 feet per minute. In 12 seconds, the traffic pattern is gone. In 48 more seconds, the cruise altitude for small planes is passed. In less than one more minute, the maximum altitude at which a normally aspirated engine can even make cruise power is passed. In two more minutes, the controlled Class-Alpha airspace designed for high-altitude airspace is entered. At full power and climb speed, there is a BUZZ as the prop-wash swirls around a tiny oil vent in the nose. The airplane is as big as car, but the only airflow you can FEEL is the buzz of air around a tiny overflow vent, just a few inches in size.
In theory, you have been keeping up with the constant changes in pitch, roll, and yaw required to stabilize the airplane in the constantly changing flap, gear, trim, engine-torque, prop-wash, and p-factor changes that have enveloped the airplane since power-application.
Backup fuel pump and igniters off.
Switch fuel tanks: You just used a good dose of fuel on one tank or another.
Check pressurization: Is it working? Bleed air has to come from the engine and be cooled before entering the cabin (Trust me: You want it to be cooled) and the computer-controlled outflow valve has to let the right amount of air OUT (you remember the part about the airplane blowing up if the outflow valve does not let any air out?) so the pressurization is worth watching.
Leveling off, the TruTrak autopilot announces in the sexy-lady-space-ship-voice “altitude hold acquired”, and you ease back the throttle and prop levers to keep things from getting out of hand. 375 miles per hour can soon be reached at 28,000 feet!
BUT, for now, we are doing flight-test to test out the airplane, so we don’t have time to wander about the Greater Oregon Area. We test the various avionics and other systems, mark what is passed or failed for the shop techs to jump on, and head back to the field.
Power-off, the Evolution glides like a glider, or a rock, depending on configuration.
If you push the prop to redline with power-off, the prop acts as a huge air-brake, and you come down at what feels like a 30-degree angle. But, if you pull the prop back to feather to eliminate all that drag, the turbine just hums along at idle while the feathered prop spins lazily, and the now drag-free airplane glides like a glider. So, you can come in shallow with little power and fuel consumption, but then firewall the PROP control to go to redline RPM when you are ready to get pushed forward in your seatbelt from the deceleration. Interestingly, this means that you can approach the runway at most any speed and altitude you like, and still do a normal landing: It all depends on when you firewall the prop. Lowering the gear adds far, far more drag than the entire airplane, so the plane basically gets stuck in pudding when you lower the gear. Bring in the flaps and the next thing you know you are having to CARRY power, the Pratt and Whitney screaming, just to HOLD a measly 90 knots! Over the fence, scrub off power and the plane decelerates nicely and touches down as smoothly and precisely as you please on the trailing-link gear.
Now, you pull back the throttle to idle, then pull a trigger and lift the throttle UP AND AFT and you go into reverse thrust. This, perhaps coupled with very modest braking, gets you down to taxi speed in no time.
Turn off the taxiway and taxi back, dropping into reverse from time to time to keep the speed from building out of control.
Get to your parking space, shut everything electrical down (except the electric fuel pump, which is left on during shut-down to lubricate the engine during spin-down!) and then yank the fuel lever. The turbine spins down to a lower-pitched whine, and then a grumble that you can FEEL in the cockpit. Exit the airplane, kiss the ground, and wait for the shakes to go away.
Next day, with a new flight-test card, repeat.
So, let’s go to day 2:
We continue to test fly, doing instrument approaches, touch-n-gos, and checking each item on the squawk list to see if it is addressed as the work on the plane continues between flights. So one thing that we notice is that our ears pop every time we taxi in.. It clearly has something to do with the pressurization outflow valve, but what? Why would it pop our ears like that? The outflow valve is SUPPOSED to bring us smoothly to the field elevation, but is instead doing SOMETHING different, which is popping our ears… why?
The stall warning works… when clean! When the flaps are down, though, we get no stall warning at all.
As well, we have no landing-gear warning at all! If we slow down, pull power, and lower the flaps, there is not a peep of a gear-up warning, which is a little scary. The angle-of attack indicator is flashing its’ lights crazily a lot… it DOES trigger the stall warning….
There’s an App for that.
I added a little code to Xavion that uses its’ GPS to record altitude, and its’ pressure sensor to record cabin altitude, every 10 seconds.
We then went flying with my iPhone running Xavion, and ran some flight-tests that involved flying at a number of different altitudes, so we could see what was going on with the pressurization when we landed.
So, upon return, I grabbed the files off of my iPhone and dumped them into Excel.
This is what I saw: (The blue area is the aircraft altitude in feet, the red area is the cabin altitude in feet, as controlled by the Kollsman outflow valve)
[clr]Isn’t that interesting?
Flying out of Redmond, OR, we are operating out of an airport that is at 3,000 feet above sea level.
As you can see, the aircraft altitude (blue) and cabin altitude (red) started off at about 3,000 feet. But, by the time we landed, the Kollsman outflow valve had our cabin altitude at about FOUR HUNDRED FEET! This, while landing at an airport that is at THREE THOUSAND feet! (And, yes, we DID have the destination airport dialed into the Garmins, which is what is supposed to feed the Kollsman outflow valve the info it needs to pressurize the cabin properly.)
So, we land in with a cabin altitude of 400 feet, even though the airport is at 3,000 feet! Soon, during taxi, the pressurization system realizes its’ mistakes and dumps all cabin altitude, and everyones’ ears pop sharply and suddenly. It is clear that something is wrong.
Now, the MORITZ display shows the cabin altitude and differential pressure registered by the Kollsman valve, but THAT IS IT! The Moritz does NOT show WHY the Kollsman valve is doing what it is doing! So, we have a valve that is pressurizing us far too much, but no way to tell WHY it is doing it, or what to do to FIX the problem!
For me, the major problem in finishing this airplane has been that computers talk to each other in secret languages that the manufacturer is for some strange reason afraid to reveal, so that the systems do NOT always operate properly with each other, and when they fail, their diagnostics are so minimal that we can never tell WHY!
I always release all X-Plane formats that people need to interact with X-Plane, and that has helped cause X-Plane to be the dominant flight sim on the market! The X-Plane log.txt file, text-file-readable by ANYONE, tells EVERYONE EVERYTHING it can about anything that might have gone wrong with X-Plane, thus allowing any problems that come up to be SOLVED! I always share my file formats and message protocols so people can interact with X-Plane as they like! Garmin, Dukes, and Kollsman have all refused to share this type of info with me, though, and now we have a Kollsman pressurization valve, being fed data by a Garmin computer, doing something STUPID AND WRONG in the airplane… and we can’t tell WHY.
After flying to collect the rather befuddling pressurization results shown above, we burned up almost all of the fuel on board, and returned the plane to the hangar at RDD with very low fuel. From there it was easy for RDD to drain the remaining fuel to do a careful weight and balance.
Let’s compare my current plane, a Columbia-400, to N844X:
|power||310||850 (brief surge to over 1,000 is allowed)|
|cruise speed||195 kt||325 kt|
|weight||2593 lb||2611 lb|
LOOK at that!
The r-Evolution, with three times the power, almost twice the speed, far more complex systems, and looking about 50% BIGGER… weighs… EIGHTEEN POUNDS more!
How do they DO that?!?!?!
(Answer: The body is round, so it pressurizes easily with almost no structure, since the pressure load just keeps the body round, 100% carbon-fiber construction, turbine engine which is very light for it’s output, composite propeller not metal, and very high quality molds so there is almost NO body-work filler anywhere on the plane).
No flying today, so analyzing some more data.
So the low weight of the airplane is nice, but I have been REALLY worried about the fuel flow of the big engine.
Most Evos have a 750-horse PT6-135, but 844X has an 850-horse PT6-42. The extra 100 hp is not really a big deal, but the PT6-42, with it’s extra compressor section, HOLDS that power to a high altitude!
So, though the engine is only 100 hp stronger, it DELIVERS all of that power up to a high altitude, so it can climb like crazy to any altitude up to it’s 28,000-ft RVSM-restricted ceiling (the ceiling is determined by the autopilot and altimeters and pressurization system, not the available engine power or aerodynamics, which could actually take the plane to about 50,000 feet) My huge concern about this engine, though, has been that it might waste fuel, which I HATE (for me, the biggest drawback to light-plane aviation is the large carbon-footprint). Now, I can see what the fuel flow is SHOWN as being in flight, but I am not sure if that fuel-flow number is CORRECT, since the fuel pressure of any given fuel pump might not be accurately turned into fuel flow unless the Garmin 1000 has been properly calibrated to turn that pressure into fuel flow, which mine might not yet have been.
SO, I grabbed the Pilots Operating Handbooks for some CERTIFIED airplanes that have the PT6-135 and PT6-42 engines, so I could see what the power and fuel flows REALLY are at various altitudes and power settings.
A nice thing about turboprop engines is that they always show torque and RPM, and since power is simply torque times RPM (times a conversion constant, of course, if not in metric units), we can easily calculate the exact power output of any turboprop engine from the RPM and torque settings listed in the Pilots Operating Handbook. And, since fuel flow is always also listed, and specific fuel consumption (the number of pounds of fuel than an engine will burn for each horse-power it puts out for an hour) is simply the fuel flow divided by the horsepower, we can EASILY determine the specific fuel consumption (or efficiency) of any turboprop engine from the data in the POH. Just take fuel flow in pounds per hour divided by horsepower, where horsepower is torque times RPM times a constant.
So, with some trepidation, fearing for the answer that I would find, I downloaded the Pilots Operating Handbooks for some various CERTIFIED airplanes with PT6-135 and PT6-42 engines, and threw in some power and fuel flows from my trusty Columbia-400 for good measure, which has a RECIPROCATING (twin-turbo) Continental engine. We all know that turbines are less efficient than reciprocating engines, right?
Well, look at the results: (We show torque as trq, fuel flow in pounds per hour as pph, horsepower as hp, gallons per hour as gph, and specific fuel consumption as sfc)
1900 rpm for the Pratts, 2400 rpm for the Cola LOP (best efficiency), 2600 for the Cola ROP (best power)
fl-200: (20,000 ft)
1417 trq =512.62 hp
299 pph =44.0 gph sfc=0.58 black-hawk XP135A king-air published perf
1814 trq =656.25 hp
358 pph =52.7 gph sfc=0.55 super king-Air (-42) POH
fl-240: (24,000 ft)
1245 trq =450.4 hp
268 pph =39.4 gph sfc=0.60 black-hawk XP135A king-air published perf
1200 trq =434.12 hp
260 pph =38.2 gph sfc=0.60 piper meridian, POH
1561 trq =564.72 hp
310 pph= 45.6 gph sfc=0.55 super king-Air (-42) POH
217 hp, 16 gph, 94 gph sfc=0.43 LOP (best eco) cruise, experience
263 hp, 25 gph, 147 gph sfc=0.56 ROP (best power) cruise, POH
310 hp, 40 gph, 235 ph sfc=0.76 climb, POH
fl-280: (28,000 ft)
1066 trq =385.64 hp
230 ph =33.8 gph sfc=0.60 black-hawk XP135A king-air published perf
1100 trq =397.94 hp
235 pph =34.5 gph sfc=0.59 piper meridian, POH
1382 trq =499.96 hp
266 pph =39.1 gph sfc=0.53 super king-Air (-42) POH
So the conclusions here are very interesting:
For sfc, PT6-42 is the same when matching PT6-135 power, and 10% better when running fast!
For sfc, PT6-42 is 5% worse than columbia-400 max-power cruise when matching PT6-135 power, and 5% better when running fast.
For sfc, PT6-42 is 27% better than columbia-400 at full power, 28% worse than columbia-400 at lean of peak.
So what does that mean?
Well, the PT6-42, when running at lower power, is basically identical to the PT6-135: Same power. Same fuel flow. Same thing.
(The engine just weighs about a seventy pounds more, weight that is offset by a lighter prop and batteries and, in 844X, with a lighter PAINT-job by being painted in only THIN layers of OFF-white, which can go on thinner).
BUT, if desired, I can push the black knob forwards for more power.
The fuel flow will increase as the power does, of course, but something interesting happens: The engine gets MORE efficient as it speeds up!
Turbines are designed to run fast, so when the PT6-42 is advanced to a higher power setting, its’ fuel efficiency actually INCREASES TO 10% BEYOND THE PT6-135!
So, the -42 puts out more power, AND does so with 10% GREATER efficiency!
BUUUUUT, there is a drawback: When going fast, the AIRFRAME piles on a LOT more drag is it runs into a brick wall of parasite drag.
When this happens, the gas-mileage FOR THE AIRPLANE PLUMMETS, thanks to all that parasite drag from going so fast.
Only a smaller frontal area (no room in the cockpit!), smaller wings (too high a stall speed!), or higher altitude (cannot do for RVSM!) would solve THAT problem.
So, going fast gives a slightly more efficient ENGINE, but the airframe drag more than makes up for this, so efficiency plummets. 🙁
As well, the PT6-42 burns more fuel at idle (it is dumping some of its’ air overboard, for goodness sake!) so the overall fuel burn for the flight will probably, in all likeliehood, be a little higher in a -42 Evo than a -135 Evo, but not by much at all if you have the discipline to not push the throttle too far forwards. But, if you are not going to push the throttle forwards, then you might as well just have the -135!
Another fascinating thing is that the -42 gets better SFC up high than down low. Since it has an extra compressor section to compress thin air, this is no surprise.
But the most fascinating thing of all is to compare the PT6-42 to the CONTINENTAL FLAT-6 TWIN TURBO RECIPROCATING ENGINE!
In flight, if run rich of peak at best power, the Continental has an SFC of 0.56. If you go back to lean of peak for most efficiency, the SFC goes down to 0.43. (Lower SFC is good! Less fuel burned!)
The PT6-42? SFC is about 0.55! That’s right! The SFC is the PT6 is the SAME as the SFC of a reciprocating engine being run at best-power mixture! The proof is here!
NOW, the PT6 will still burn WAY more fuel, since it IDLES at about 30 gallons per hour, and people simply ASK for more power from the engine simply because it is THERE, and of course if you double the power, you double the fuel flow. But the EFFICIENCIES are about the same! (NOTE: The Columbia-400 has the secret weapon of being able to run lean of peak, which improves its’ SFC by about 25%, thoroughly beating all competitors).
So, anyhoo, that’s where we are today… hope to have everything wrapped up by Monday afternoon.
…AND we got it wrapped up Tuesday morning instead… not too bad.
The pressurization system still does NOT work properly (it always pressurizes us down to sea level, no matter the elevation of the destination airport, which is wrong), but that is a detail that we can work out later… I am well past ready to take this plane HOME!
SOOOO, with the plane mostly dialed in but for a few minor tweaks yet to do, I took 844X from it’s construction site in Redmond, OR, clear across the Country to Columbia, SC, just the other day. The flight went fine with plenty of flying at around 300 knots at 27,000… ending with an ILS in actual IFR conditions into Columbia, SC… not bad for a first flight from the nest!