I asked Rex Johnston to send us some more info on his Davis with electronic fuel injection. He mailed back the following letter of technical notes and the photos. As you may be able to tell from the spelling in my previous post, my editor in chief, Grace, is out of town for a few days. This is my first try at posting pictures from files on the Web, we will see how it goes. Worst case, Grace will be back in a few days.
Again, hats off to Rex, as I am pretty sure he is the first guy ever to fly an EFI Corvair engine. A lot of people think about doing stuff like this, but a very special group of builders meet the challenges of doing something very different, and see the project all the way through flying. This is not for everyone, but the beauty of the Corvair is that you have the choice to build it the way that meets your personal needs. The Buy-it-in-a-box alternative engines only come one way, the configuration that makes the manufacturer the most money. With your Corvair, you are the manufacturer, and you can make the engine in the best configuration for your plane and personal flight goals.
Every Corvair builder, even the ones using simple carbs, can read this post and understand that Rex is to be congratulated not just for the EFI, but for finishing an outstanding aircraft, a plane he dreamed of, and then persistently worked on until it became a reality. You don’t need to ask if he felt like a king the day it flew. I am sure he will vividly remember the day for the rest of his life. Every Corvair builder reading this deserves to have his own personal version of that day. Don’t let anyone tell you that you can’t or that it will not be worth the effort. Reject these negative messages and go to work for yourself. Be persistent so that I can post pictures of your completed aircraft and you can enjoy the praise of fellow builders who truly understand your achievement.
Here are the pictures you asked for. Highly modified Davis DA-2A with RV-4 spar, Riblett airfoil, left side door, rounded fuselage and wing mounted fuel tanks.
3100 Corvair, machine work done by Ray Sedman. Standard VW cylinder and piston 3,100 conversion. 100LL only due to compression ratio. Roller rockers due to an off center valve guide on number 5 which caused the stock rocker arm to not stay centered on the valve. At least that’s what I think was causing it. Conversion parts are all yours from a few years ago. No 5th bearing but nitrided crank. May install a fifth bearing at some point but this is a 120 mph point a to point b aircraft and I’m not particularly worried about the crank.
Holley projection system modified for use in an aircraft. Manual mixture adjustment set by a wide band fuel air ratio meter. The system only picks up rpm and throttle position. Dual fuel pumps with a manual bypass valve to a nozzle in the intake to be used if the injection system fails. The engine runs surprisingly well at 2,500 rpm with just this nozzle. I run dual batteries in the aircraft with a generator failure warning system. I also have a knock sensor installed that is connected to a warning light. Neat system but I have no way to calibrate it so don’t know how useful it is. So far it hasn’t gone off but I haven’t done anything to the engine that I think would cause it to detonate.
Have about eleven hours on it now. Starts and runs very well. Hard to keep the mixture set during warm up in very cold weather but otherwise the mixture is very stable. I can take it anywhere from 11 to 1 to over 14 to 1. Engine runs smoothest in flight in the 14 to 1 range. I use 12 to 1 during high power settings.
Top view of the 3,100cc engine. It has a Front Starter and a rear alternator.
Above, a rear quarter look at the back of the engine. Note the cover that keeps the alternator belt from attacking the ignition wires if the belt is thrown. This is a crucial safety device.
Above, a bottom view of the engine. Note that it still has carb heat. Fuel pumps are on the firewall on the right in the photo.
Above, the modified airframe. A Davis is a classic design from the 1960s. Rex’s has extensive modifications.
Above, a view from the bottom of the left side of the engine. Large black strut is the nose gear.
Above, the same view from the other side.