Jabiru Engine Installation


My aircraft is a Q2 rather than the Q200. That is, it uses the GU airfoil for the canard, and does not use the Continental O200 engine. However, my engine is not the original 65hp VW based Revmaster engine.  I'm installing a 120hp Jabiru 3300 engine. The Jabiru engine weighs the same as the VW engine, 175lbs (80 Kilograms). 

If the aircraft's weight & balance is to be maintained the Jabiru's Center of Gravity (c.g.) must be placed in the same position as the original VW's c.g. This would place the Jabiru's rubber shock mounts directly against the fire wall.

An advantage to keeping the Jabiru 3300 close to the fire wall is that it would fit nicely under the original VW cowl with only a very small (about an inch) extension.

The problem with placing the engine so close to the firewall is that carburetor and ignition system would be buried behind the firewall and inaccessible. If you wanted to work on, or adjust either, you would have to remove the engine. Also, there would have to be a very large hole cut out of the firewall. Not Good!

The pictures to the right are mock-ups of what the installation might look like; the ideas is that a 1/4" aluminum plate (plywood template in David's right hand) would bolt up against the firewall and the engine would bolt to the plate..

From the 'access' perspective, moving the engine 6 inches forward would help a lot. However, it would move the unloaded c.g. forward, and the aircraft would be out of c.g. when loaded with a light (150lb) pilot, a full header tank, and an empty main tank.

I should add that Paul Spackman's Q2, converted from a RevMaster to a Jabiru 3300, balanced out nicely with the engine mounted six inches forward of the firewall, and Alan Thayer, who is working on a Jabiru 3300 installation on his new Q200, has calculated that he must have the engine even further forward.  

This is a mockup of one idea of what it might look like..


This is my friend David Joly holding what the Stack Up might look like.


Eight years have passed and I have settled on using Paul Spackman's approach. The motor mount was designed by Paul.

The big question now is where to place the engine vertically. The crankshaft center line of the RevMaster (VW) engine was placed 7.9" down from the top of the firewall, and the O200 was 7.6" down for the top..












The initial choice was to locate the center line of the crankshaft at 7.9" down from the top of the firewall, same as the RevMaster, but a problem quickly emerged.














When you project the top surface of the forward fuselage 30 inches to the prop hub you discover that you can only accommodate an eight inch spinner. This is because the Jabiru prop hub is 7 inches further forward than the RevMaster engine and the slope of the top of the fuselage relative to the firewall is 1:7.5., 1 inch in 7.5 inches. I've lost 1 inch in radius so the 10 inch spinner for the RevMaster engine is not going to fit, and worse yet the 9 inch spinner and the nose bowl I bought for the Jabiru engine isn't going to work either. (see picture below.)









The answer is to lower the engine thrust line about an inch. That will increase the allowable spinner diameter to 9 inch and the Jabiru nose bowl will work as the basis of the new cowl and the Jabiru spinner will also fit. It does mean that it will be next to impossible to fit the Jabiru muffler, but that's ok as I was planning to do away with it any way.




The 'jig' bolted to the motor mounts holds them properly spaced for positioning on the firewall.


First Fitting of the engine.


Measuring the radius of the spinner.

The engine is an inch too high for the Jabiru Nose Bowl. Now What!