P-51 Voodoo Project - A Learning Experience

Update because too much stuff has taken me away from the Voodoo repair task I haven't had time to get to it.  I'm shooting to have it done before the end of May, after I deliver the Florence High School commencement address on May 27th.

I acquired this plane at the Feb 2011 Sky Corral Club auction from Mark Sieman for a reasonable price. It looked as if it was well used. It was built by Ron Stark in 2006 who flew it for a few years and then sold it to Mark. He, in turn flew it a lot too. There were signs of several repair jobs. It took me almost a year before I got around to turn it into flying shape.  I procrastinate a lot.

I ran into some unique (for me) challenges with the Voodoo. These were: 1) inverted engine, 2) almost fully cowled engine, 3) retractable landing gear, 4) flaps. And this was my first warbird.

I mounted my trusty Magnum 91 four-stroke to the firewall after considerable measuring to insure the spinner backplate aligned with the fiberglass cowl. I built in 2 deg. of right thrust that also had to match the cowl. The next problem was the fuel tank; with the tank neck protruding through the firewall and the tank was considerable higher than the Magnum’s fuel inlet on the carburetor. I knew this might cause in-flight running problems. I subsequently added a fuel pressure regulator as suggested by Model Airplane News’ engine expert Clarence Lee in a recent article to compensate for the changing fuel head pressure.

Radio installation was straight forward with a Futaba 7 channel 2.4Ghz radio receiver. The same for the servo installation except for the mechanical retract servo setup. I realize now (after dismantling the retract hardware) there is a specific range of pushrod travel to insure positive retract performance. Days later, on the maiden flight, this gave me problems.

After final assembly I began some simple engine fueling and running plus taxi trials. I soon realized that the Magnum 91 did not run well inverted at reduced throttle settings and died when I removed the glow igniter. Also this first test was made before the installation of the pressure regulator so the tank drained out rapidly through the carburetor.  In spite of all these problems I did get the engine running and I did some limited taxi test runs on my driveway.

I rigged up an internal glow plug driver using a micro switch and two AA 2600 mah NiMh batteries. This setup will light the glow plug when the throttle is operating at 1/3 throttle or less. After this, I finally received and installed the PCFS fuel regulator. After these were installed the next test run proved that the combination of the regulator plus onboard glow driver solved all the engine problems and the Magnum performed very well.

In early March I gave Voodoo its maiden flight. Mark Sullivan assisted me. As soon as it took off we know there where problems as one landing gear failed the gear down lock and almost collapsed the instant of takeoff. I raised the gear but it wouldn’t fully retract or fully deploy down and locked. I flew it around and Mark and I kept cycling the retracts but to no avail. Otherwise the plane flew well and the engine ran great at all throttle settings. Only two clicks on right aileron needed was needed to trim it out. Landing with a partially retracted was a bit tough on the gear and airframe. Mark and I screwed around with the retract mechanism until it finally appeared to function properly. 

The second flight on March 14th was longer and more pleasant without the retract distraction. I operated the flaps and there was no trim changes or ballooning tendencies with the flaps down. Rudder turns were not as effective as on my J-3 Cub or on my LT-40. The Voodoo weighs in at 8 pounds and has a much higher wing loading than these other two planes. Still it is a sweet plane to fly, has great wind penetration, and it will be a good sport flyer. The Magnum 91 was just the right power plant for it. On landing Mark and Cloyce both warned me to not let my airspeed drop too low; a problem with flying warbirds. I was probably bringing it in at too high a speed and smacked it down hard first on one the right gear and then the other. Both gear collapsed and tore the retracts out of their wing mounts. 

It wasn’t a pretty sight and I have some extensive repairs to do before my next Voodoo flight. As I started out saying, it is a learning project. I'm glad that I gained this experience with this plane since I have a couple of other warbirds in the shop waiting to be assembled and flown.