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12 Aug  09

Boy, have I ever been skewered on the Van's Air Force web site.  How dare I suggest doing anything other than what is considered acceptable to the site visitors.  After all, these experimental RVs are really not experimental - a builder should only follow the plans exactly.

I dared to install a fuel selector with a "both" setting.  Blasphemy.

Burn him at the stake!

The guys on Van's Air Force web site have their own ideas about things and no amount of discussion (logical or not) will sway them.  I must admit there were a couple of guys who didn't scorn me.  Their minds were open enough to different ideas that they are willing to at least consider the idea.

I am very disappointed in Doug Reeves' action regarding the VAF thread - he shut it down - no more discussion allowed.  He lays blame on one of the moderators.  I lay blame on him.  The thread made it through about 20 or so postings and VAF turned it off.  Interesting that they see fit to limit discussion on fuel selectors for RVs.  Disappointing.

What follows is my logic on using a fuel selector with a both setting.

1. Many high winged, and several low winged, aircraft have used fuel selectors with a both setting for years.  There are accident reports related to fuel mismanagement with those aircraft, but it is because the pilot selected the left or right setting instead of the both setting and failed to reselect "both."  Cessna checklists call for fuel selector to both numerous times but especially at takeoff and landing.

2. I believe a fuel selector with a both setting is safer - and it is certainly easier.

3. In a high wing aircraft with a both setting, there normally is not an electric fuel pump and the fuel gravity feeds to the engine.  If one tank gets lower than the other for some reason (leak, for example), the fullest tank will feed at a higher rate until the two are balanced.  Then they will feed until the tanks are empty.  It is possible a pilot would not notice a leaking tank and his first indication will be when he realizes he can't make the destination or when the engine quits.  If the engine quits, then both tanks are empty and there is no chance of restart.

4. In a low wing aircraft with a both setting, a fuel pump replaces the gravity feed.  With equal plumbing from each tank, the fuel will feed evenly from both tanks.  Should a leak occur in one tank, the fuel level in that tank will drop to the level of the leak and then begin feeding evenly again.  The lowest tank will feed out first causing the fuel pump to draw air.  The engine will falter.  So, if the pilot did not notice the leak, he gets a second chance.  He switches to the fullest tank and the engine runs again.

5. I suggest that a both selection on a low wing aircraft is safer than one on a high wing aircraft.

15 Aug 09        Today's Time - 0.5        Total Time - 5.8

Got in a short 0.5 flight today in the pattern.  I wanted to see if the air dam and other changes to the air flow made any difference on the #3 CHT.  It turns out they did - but in the wrong direction.  The cylinder is running hotter now than before.  I can't understand that one because I've closed up many leaks in the baffling.

The changes I made were:

1. Add air dam behind #3 cylinder to direct air through the cooling fins.

2. Use RTV to close up leaks in the baffling.

3. Add fairings to the exit air opening.

So now I need to rethink the changes and maybe undo something.

There were three sets of engine readings that were at stabilized power settings.

As I look back and compare these numbers to previous flights using nearly the same MP and RPM, they match very closely except that the #3 CHT is 9 degrees hotter than previous flights.  The oil temp went up 2 degrees, so the negative effect on oil cooler air flow was not too bad.

Another builder on line suggested the problem may be with the injector and not the cooling air flow.  So, I think it's time for me to leave the cooling air flow alone for awhile and start looking at the #3 injector.  He said opening the injector jet VERY slightly will bring the CHT down.  I'll talk to the GAMI guys in Oklahoma or Airflow guys in GA and find out the techniques for tuning the injectors.

22 Aug 09        Today - 1.0        Total - 6.8

I decided to do some more flight testing today.  I've been working on various things for the past few days and I needed to check out the engine again.  The other day when I started, the plane had been sitting for about 2 weeks and it ran rough on the right P Mag so I had to run it up to 2000 RPM for a minute to clear out the carbon.  Then it ran fine.  Today, it did fine on the engine runup on the first try, so the key is to not let it sit too long.  During taxi out today, below 1000 RPM, the engine RPM would drop about 150 RPM and then recover.  I had to constantly nurse it to keep it from dying.  Above 1000 RPM it ran smoothly with no RPM drop or surging.  I tried turning on the boost pump but it made no difference.  I cleaned the fuel filter yesterday and it was spotless other than one tiny bit of metal shaving.  I also changed the oil yesterday and refilled it with mineral oil.

So for today's flight the plan was to:

    - Stay in the pattern until the certain the engine would continue running

    - Get several steady state engine readings.

    - Climb on top of clouds and DAB airspace

    - Fly triangular pattern for IAS and GS recordings

    - Calibrate the AOA

    - Follow checklists to verify them

    - Single pattern with full flap landing with crosscheck of AOA

I took off using the right tank because I want to burn it down so I can check the operation of the "both" fuel selector setting.  Next flight I will add fuel to the left tank but not the right and run it in both until loss of power and switch to the left.

For today's takeoff I ran up to 2200 RPM statically and released brakes and on up to full throttle.  The forward surge actually jerked my head back - I was surprised.  I don't recall that ever happening in a fighter, but I guess that's because you're expecting it and ready for it.  A very quick acceleration to 50 KIAS - airborne - and held it one foot off the ground until 100 KIAS then steep climb to pattern altitude.  Leaving the pattern I climbed at 130 to 6500 MSL for the flight tests.

At 6500' the OAT was 68F and I flew headings of 360, 120, and 240.  I used about 24 square on the engine and got speeds of 155 KIAS/183 GS, 153 KIAS/180 GS, and 156 KIAS/160 GS.  So the TAS was 175 and the winds were 235/15.

The AOA calibration requires a zero G maneuver and slow flight at 1.15 Vs with both clean and flaps down configurations.  During the slow down for the flaps down calibration, the throttle jammed on something and I couldn't reduce power to idle.  Then whatever was blocking it came loose and I had full throttle movement.  So, that will require some investigation.  I believe it was caused by interference between the three levers - throttle, prop, and mixture.  The three levers are very close together and I think the cotter pin holding in the clevis pin may have caught.  So, some more detective work ahead.

Anyway, that was enough for me so I headed back to the pattern for a full stop landing.  The AOA appeared to function properly during the landing, but I'll have to practice with it more to trust it's accuracy.

I was able to get six steady state engine readings and they follow:

The higher altitude readings yielded the most data and the duration of the readings was almost 12 minutes.  To the right of the average reading in that block are the peak readings.  I still have the highest CHT on #3 and it not coming down.  The oil temperature is still excellent.

Next Update in Sep 09