Lycoming cruise power schedule

Lycoming recommends that for maximum engine service life, to use a cruise power of no more than 65% BHP and lean the mixture for best power (100 deg. F rich of peak EGT). This is recommended even though the maximum cruise power setting is 75% BHP (also this is the maximum percent power for leaning). The exception to this being, during new engine break-in. For the first 50 hours of operation or until oil consumption stabilizes, you should run the engine at high power setting (65 - 75% BHP) in order to properly seat the piston rings. 

But how do we know what combination of engine settings gives a certain %BHP? This information is especially vague for engines having a fixed pitch propeller. You can't simply use RPM to determine what %BHP the engine is producing - it depends on other factors; namely, pressure altitude and temperature. Running the engine at maximum RPM does not damage it provided that the corresponding %BHP is not above limits. A cruise power chart/table is needed to determine this...

Referring to the Lycoming Operator's Manual, O-360 and Associated Models, for the IO-360-M1B (180 hp), there are two engine performance charts found in this book. In Section 3, there is Figure 3-6 and Figure 3-26. 

Starting with Figure 3-26, titled "Sea Level and Altitude Performance - IO-360...-M1B", a complex looking chart used to find actual horsepower from altitude, RPM, manifold pressure, and air inlet temperature. However, it seems that this chart is primarily used when performing run-up of the engine to determine if it meets the promised performance. It is not in an easy to use format to be used in the cockpit or during preflight planning to determine cruise power settings.

In Figure 3-6 titled "Part Throttle Fuel Consumption - IO-360...-M1B", this chart simply plots fuel consumption in pounds/hour versus actual brake horsepower. Lines on the chart show 2200-2700 RPM for both best power fuel mixture and best economy. While I have never used a cruise power chart in this format before, this is the best one that Lycoming provides for our engine. For the cockpit checklists, one of the items on there will be this cruise power table, consisting of data taken from Figure 3-6...

RPM                        75% BHP (GPH)              65% BHP (GPH)               55% BHP (GPH)

2700                        11.6                                    10.5                                    9.3

2600                        11.5                                    10.1                                    9.2

2500                        11.3                                    10.0                                    9.0

2400                        11.0                                    9.6                                      8.8

2300                        10.8                                    9.5                                      8.6

After climbing to cruise altitude (which is not a factor in this table) and setting cruise power with throttle at, say 2500 RPM, the mixture would be leaned until the engine monitor shows the EGT 100 deg. F rich of peak. If the fuel flow gauge shows about 10 GPH, I'd know right away that the engine is producing about 65% BHP. The highest altitude at which 65% of power can be produced, will be when the RPM is 2700 and the leaned fuel flow is about 10.5 GPH. 

Corrosion protection for quickbuild wings

South Texas has a breeze out of the S-SE most of the year. This brings in moisture from the Gulf of Mexico where it will inevitably try and cause airframe corrosion. The humidity is so bad here that during the summer months it feels hot all the time, even in the early morning. A low layer of broken-overcast clouds frequently greets us in the morning that will often continue to persist hours past forecast times.

In choosing the quickbuild wing option, we noticed bare aluminum on the inside of the completed wings. Although a corrosion protection compound is applied to the quickbuild wings during assembly at the factory, it probably isn't as robust as an epoxy primer, especially in our climate!

Since priming was no longer an option however, we sprayed a layer of Zip-Chem CorBan 23 inside the wings for additional protection. This is an aerosol corrosion inhibiting compound that sprays on tacky but then dries to a long lasting protective film. It comes with a long application wand that sprays in a fan pattern that reaches deep inside the wing through the rib lightening holes and access panels.

 

The airframe is not the only corrosion-prone system on our -7A  in our coastal location.  Our avionics systems provides primary flight instruments, communication, navigation and engine monitoring, so we have decided to protect our avionics system connectors and terminals, using Zip-Chem's D5015NS Avionics Corrosion Preventive Compound.  We used the sprayable version (Class 2) which is QPL listed meeting the requirements for MIL-C-81309G, Type III (solid film, avionics grade).  Shake will and spray connectors and terminals before installation and we can have confidence in our electrical and avionics system. 

Funny

It's not all serious work after all. Here's some of the funnier pictures from the past years...

The AN960-10 is the most commonly used washer on RVs. They're about 5 cents apiece. But if you don't change the quantity in your order, the folks at Aircraft Spruce will send you one, just like you ordered!

The guy that needs a lot of help bending his sliding canopy frame.

It's really not this difficult to bend the canopy frame!

Experiencing the new Lycoming engine smell

Perfect timing...or not

A little bit of everything on this workbench

Our cat from under the glass table

Dynon EMS issue

The red X "EMS FAIL" was an unexpected problem we had to work out (red X for transponder is ok as it was not configured yet). This has since been fixed, but not in the way we planned...This is the only disappointment with Dynon and Vertical Power since installation. Nowhere in either company's product documentation do they state that the SkyView EMS must be installed when using the VP-X. The assumption held by Dynon is simply that builders installing a SkyView with VP-X will also be installing the Dynon EMS, despite the EMS being listed as optional equipment in a SkyView network. In lieu of the SkyView EMS, we chose a different engine monitoring configuration to save money, get a more reliable system, and to un-clutter the screens. In a non-VP-X installation, this would not generate a problem, since the EMS is optional equipment. The design is such that this is not true if you are using the VP-X. The problem was identified when the VP-X page was not found within the ENGINE page on SkyView. Dynon later confirmed via email that this page will not appear unless the EMS module is installed and configured. The module was offered to us at a $250 discount for our troubles, which is ok since it does work just as promised now. We simply do not have any probes connected to it.

What not to rivet together

For some part assemblies, you can't install rivets in every hole at the same time. Some have to be left open to be installed with a different part later on. That was the case during this stage of the fuselage build. To prevent installing rivets in certain holes, we took a handful of clecos and wrapped some black tape around them. Then simply use these special clecos in place of the non-marked clecos and you'll stop having to drill out perfectly good rivets!

Instrument panel and electrical

Perhaps one of the most significant accomplishments of the build is the instrument panel. The choice of avionics and configuration took several months, mostly because we were thinking about the panel layout long before we were ready to cut holes in the panel. As I started seeing the instrument panels in other airplanes during flight training for my instrument rating and commercial pilot training, I soon identified the good and bad designs. I took up the responsibility for drafting possible panel layouts on the computer using Solid Edge. My first draft was quite different than what our actual panel looks like. Certain avionics of choice were no longer available when the time came to purchase them, however, new and improved versions took their place. For example, the old Vertical Power VP-200 with its own screen was replaced by the VP-X, which integrates with the Dynon SkyView EFISs. Here's a complete listing of what's installed:

• Dynon SkyView 10" as the PFD. Includes Dynon Mode S transponder (mounted behind the 10" EFIS on the sub-panel) and backup battery
• Dynon SkyView 7" as the MFD. Has its own backup battery
• Vertical Power VP-X Sport electronic circuit breaker system (mounted underneath the panel)
• Garmin GNC255A NAV/COM (10W transmitter). Interfaces with the SkyView digital HSI via RS-232 connection. This interface also allows the frequencies selected on the radio to be displayed on the EFISs at the top.
• MGL Stratomaster Velocity EMS (monitors CHT and EGT probes).
• Flight Data Systems FC-10 fuel flow indicator. Fuel flow sender located in fuel line after electric fuel pump.
• Precision Aviation lighted vertical card magnetic compass
• Lighted analog engine instruments from Van's. Includes tachometer, oil pressure, oil temperature, fuel pressure, L/R fuel gauges, and manifold pressure. Instrument lights are spliced into the position light power pin on VP-X and dimmed via a rheostat on the panel.
• Switches to control power to devices (via programmed VP-X) with independent lighting circuits. Switches light up to indicate when device is on.
• Ameri-King 121.5 MHz ELT. Includes panel mounted control panel (this is not yet installed)
• Odyssey PC680 12V battery
• Plane Power 60A alternator
• Ray Allen flap position indicator and position sensor.
• Hobbs meter and oil pressure sensor with low oil pressure light on panel
• Cessna style battery master and alternator master switch
• Panel labels made using a Dymo label maker

Ultimately the best way to decide how to arrange the panel was to do a little artwork with permanent markers. Then we moved it inside the cockpit to see how it looked before cutting out anything.

A sharp fly cutter on an overhead milling machine makes quick work of the round instrument holes

Ouch! Where did all that come from!?

No worries, it looks worse than it really is. This picture was taken just before the panel was lifted inside the plane. All the longer wire bundles were first stacked on top of the radio tray. After moving the panel inside the plane, we pulled the wire bundles off the radio tray to let them hang underneath before screwing the panel in.

Now what do we do!?

The next step wasn't very enjoyable...We took turns organizing and sending the wires where they needed to go. Having labeled wires is what will really help you here. We have a combination of Dymo labels and masking tape labels. The Dymo labels however tend to fall off, leaving you with an unlabeled wire. Plastic tie wraps help to secure wires underneath the sub-panel (these are not permanent). Once everything was tied up, it was much easier to switch from tie wraps to wire lacing. Sore necks and backs are a necessary side effect of this job, but it does pay off.

A little while later and it looks much better!

Before flipping the switch for the first time, you must test the individual devices. This is done by connecting a 12V battery (a lawn & garden battery works fine) to each device and verifying that it turns on. A fuse appropriate for the device's power wire size (i.e. for an 18 gauge wire, use a 10A fuse) is placed inline with the test lead. With the battery grounded to the airframe ground, pushing the test lead into J10-1 for example should cause the device on J10-1 to come on. Do this for all the devices to verify that they don't blow the fuse and that the correct devices are in the correct pins on the connectors.

Using car jumper cables to connect the battery to airframe ground. Alligator clips connect the positive side of the battery to the fuse and test lead inside the cockpit

Alligator clips first connect to an appropriately sized fuse, then to the test lead (bottom)

Inserting the test lead into a power pin

The screen comes on for the first time when testing the PFD pin on the Vertical Power connector

The test lead inside the J12 connector

The heart of the electrical system is the Vertical Power VP-X Sport. It is this device which convinced us that DIY'ing a complex panel like this would be possible. By the time panel design was coming into play we realized we can work with sheet metal pretty well. The same could not be said for electrical work. Knowing the alternative was going to be a painstaking wire-by-wire installation process, taking advantage of the simplified electrical system installation using VP-X was the only way to go. In our installation, the engine ignition does not rely on the VP-X. The engine still uses dual magnetos for safety. Using the Vertical Power panel planner website, it allowed us to assign devices to power pins and print out the configuration sheet. Once finalized, you can create a configuration file on the panel planner website. The configuration file is loaded onto the flash drive that is included with VP-X.With the help of the Windows XP compatible VP-X Configurator application, you can program the VP-X with the configuration file at the click of a button. A standard ethernet cable links your PC to the VP-X.

Here you can see the schematic of the VP-X system with an old version (right) and finalized version (left). Scribbles on the old layout came about after realizing that certain power pins on J10 and J12 connectors have maximum current values. This meaning, you can't have an 18 gauge wire (which can support a maximum of 10A) pinned to J10-2 which can supply a maximum of 5A unless you know the device cannot draw more than 5A. Most of the time if the device draws a maximum of 5A then a 20 gauge wire will be specified, allowing you to use the J10-2 power pin. However, for some devices, the current draw is not specified; only the gauge of wire you are required to use. That means even if the device will draw less than 5A, if it is using 18 gauge wire and the actual current draw isn't specified, it should be on a 10A or greater power pin. Luckily there were just enough pins on the VP-X Sport to get all the devices assigned properly. This pin reassigning is what happened between old and new configuration pages.

All the avionics powered on for the first time after programming VP-X

Special crimp tool and power pins needed for J10 and J12 connectors

The VP-X with power pin connectors and main power wire (right) and d-sub connectors (left)

String ties were used to create all harness, they are gentle on wires, are more compact and  have a longer life than tie wraps and won't cut your hands when working behind the panel.  The transponder (gold box)  and backup battery for the Dynon display (black box ) are shown here.  Spiral wrap is used to prevent chaffing of wires. 

SkyView main wiring harness

Even with the VP-X, there still will be some tedious work within the SkyView connectors. That's because only a few of the wires go to VP-X. The rest have to do with the SkyView network...with connections going to other displays, the nav/com radio, and GPS receiving devices (on this installation, the FC-10 fuel flow unit). All the switches however (with the exception of the battery master) are quite easy to wire. They are simply used to signal VP-X when to send power to certain devices. A connection to ground is completed when turning the switches "on", and the VP-X interprets this and internally switches power to the designated device power pin(s). The same method applies for the flap and trim switches. VP-X even provides automatic runaway trim protection.

Switches on the panel are used to signal VP-X what device to turn on or off. It receives switch inputs through the J2 d-sub connector

Torque seal

What's that strange orange stuff on all your bolts you may ask...Torque Seal is an anti-sabotage lacquer used to mark a line (the torque stripe) across the heads of bolts and other threaded assemblies. If the assembly loosens, it will be easy to tell because the once straight line of Torque Seal across the fastener will be displaced. It has an additional and, during the build process, a more important role. It is a great way of indicating when a fastener or part has been final torqued. This way, if you tend to rough assemble a lot of parts on your airplane, you will be much less likely to fly your airplane without something final torqued if you torque stripe the final installed parts. When it comes time for a DAR to inspect your airplane, he'll be glad to see torque striping on at least the critical fasteners. The Standard Aircraft Handbook recommends that torque striping be done on the head of bolts, if possible. Sometimes this part is not accessible or visible, and so in that case, a stripe across the nut is acceptable.

Torque Seal used on the aileron bellcrank assembly

Tubes of Torque Seal (available from Aircraft Spruce)

Fixed pitch vs. constant speed propeller on RVs

Some pilots may think the performance of airplanes equipped with a fixed pitch propeller is never good in comparison to those with a constant speed propeller. That tends to be true because the airplanes that have the fixed pitch propellers are trainers with not so great power-to-weight ratios. Performance is just not something the designers had in mind. However, if pilots believe performance airplanes must always be equipped with constant speed propellers, these people have obviously not flown an RV...

It turns out I got used to how a well powered airplane performs after flying 8.5 hours in RV-6A N666RV (with a fixed pitch propeller) for transition training. When I went back to flying a Mooney M20J (with constant speed propeller) the following week, on takeoff I doubted whether the engine was developing full power. The engine was fine, it was just surprising how sluggish the acceleration of the Mooney is in comparison to the RV. This is true despite the Mooney having the "performance airplane" equipment (c/s prop) and the RV having the "trainer airplane" propeller.

Ultimately it comes down to power to weight ratio; in my example the Mooney just can't compete. 666RV weighs just 990 pounds empty and has 160 hp (even less horsepower will be produced on takeoff due to fixed pitch prop); while the Mooney has an additional 40 hp but it weighs almost twice as much. That's a lot more weight to accelerate down the runway, and it turns out the full 200 hp and 2700 rpm doesn't hide the weight very well. The Mooney gets the speed that it is famous for in cruise flight by having retractable gear, movable empennage, and other drag reduction techniques such that the lower power-to-weight ratio doesn't matter. RVs simply do it with horsepower.

The bottom line is: RVs have a greater power to weight ratio at less than 100% BHP than even certified airplanes with constant speed propellers. That provides plenty of excess horsepower to use for climb performance. It isn't compromised very much when it's turning a cruise propeller. Once your quick climb to altitude is finished, your propeller will already be set for efficient cruise operation. The fixed pitch option will save more than a few thousand dollars...it is the lighter weight option, and it's easier to operate and maintain.

"The List"

Since the beginning of this year we have been checking off items on "the list" as we call it; the things that still need to be completed before the airplane is moved to the airport for final assembly. The airport is not very far away from home, about a half hour drive, but one must consider that once the big move is made from garage workshop to hangar, it has now become substantially more difficult to complete construction. That is why the goal is to complete as much work as possible in our shop so that the bare minimum is being done at the airport. This would include not much more than final assembly of wings to the fuselage, rigging of ailerons and flaps, weight and balance, engine run-ups, airworthiness inspection, and preparation for the test flight period. When we initially think we are ready for work to start at the airport, there will probably be a bit more work that can be done at the shop, and so we'll delay the move just a little longer. Once the big pieces are at the airport, you will have to arrange all the tools you will need in advance to make sure you don't forget anything. This is yet another reason to not leave too much left to do in your hangar. With that said, here is what we have left on "the list":

Install and rig empennage
Install flap position sensor
Make & install ELT coax cable
Paint wing tips and spinner blue
Wheel and landing gear fairings
Install fiberglass baffle flares inside cowling
Cut out and install interior carpeting
Nav antenna installation on vertical stabilizer
Install tail strobe/nav light
Install seat belts
Install propeller, spinner, and alternator belt
Oil dip stick door hinge
Make permanent (steel) cowl pins
Non-stick material for steps & wing roots
Finish spiral wrapping and wire lacing under instrument panel
Purge fuel and oil lines
Final clamp heater scat tubes
Fuel tank screws - final torque
Install fuel tank drains
Finish ADAHRS plumbing
Change CHT probes from the under the spark plug type to the bayonet type
Make covers for headset and mic jack wires
Route OAT probe wires
Change VP-X configuration for fuel flow gauge (move from avionics switch to main circuit)
Install adelle clamps on rudder cables
Make ELT bracket for under instrument panel

What's Coming

Welcome to our RV-7A blog! There are many discussions to come, they just need to be compiled from several years of construction. What follows is a listing of some of the topics I plan to discuss here. They are in no particular order, just the order in which I came up with them. There will be many more that have yet to be listed!

Torque striping
Brake line relief bends
Brake master cylinder springs
AN flare fitting torque
Lycoming "driving torque"
Tapered NPT thread torque and sealant
Oil cooler hose fittings
Fuel tank sealant - other uses
CHT probes
Instrument panel design
Vertical Power VP-X
Fixed pitch vs. Constant speed propeller on RVs
Engine control lever brackets
Landing gear nut cotter pins
So many nutplates
Blast tubes
Baffle seals
Use of AKZO Nobel primer
Do it yourself paint job
Heat shrink tubing
Soldering vs. crimp on splices
D-sub pin crimping
Firesleeve material uses
Magneto ignition lead routing
Wire lacing
Firewall cable sealant
EGT probe location
Precision machining of parts
Crankcase breather tube
Adelle clamps
Electrical terminal boots
Engine ground wire
Lycoming engine configuration change (C/S to fixed pitch)
Lighting (position, strobe, landing lights)
Oil sump quick drain
Finished subassemblies
Corrosion protection for quickbuild wings (CorBan 23)
An attempt at paint finishing
Climate control in your shop
Zinc chromate primer
UHMW tape
Magnetic compass
Dynon ADAHRS
Lycoming fuel delivery manifold ports
Fuel flow sender
Engine temperature limits
Cruise power chart for fixed pitch propeller installation
Transition training
Flap setting choices
Panel switch labeling
Aero Graphics striping and N number
Equipping for IFR flight