There are several ways to build an engine mount, but this is a couple ways I use. For a one off engine mount, I do it this way.
First,I get someone to help me do a W&B with me in the seat so I can work out the length of the engine mount to put the CG where I want it with no fuel. Working that out is another topic. Once I know the length I need for the mount, I start by leveling the airframe and use wood 2x4's and plywood and screws and make a table to set the engine on that is the correct height so the engine will be on the thrust line by the plans.
Then I drop a plumb bob down from the center of the fuselage tail , then from the center of the firewall and mark the floor for all of these positions. Then strike a line over these marks, extend the line forward of the front of the engine. Position the engine so a plumb bob will center on the line on the floor when placed on the center of the prop hub and the center of the rear of the engine, (if the plans calls for no offset). Make sure the engine is level or positioned for the down thrust, if called for on the plans and the correct distance from the firewall by the W&B results. I bolted the engine mount spools on the firewall, and engine before starting. Now I cut and fit the tubing to the spools on the engine and firewall per the plans. I just put a couple good tacks on the end of each tube. After all the tubes are tacked then I carefully remove the engine mount and finish welding. When welding the engine mount at the required angles, they WILL draw out of line a small amount, so you will need do a little heating with a torch to put them in perfect position.
The other way is what I use when I want to make several engine mounts where they are all the same. 4 Bearhawk fuselages and engine mounts were built from these jigs. I use scrap steel angle and make a square where I can drill holes to match engine mount holes in the firewall. Same for the a square that matches the engine . Then I position correctly and weld angles from one to the other for the correct length of the engine mount and the correct height. I do all the welding of the engine mount while in the steel jig. After welding I use a torch and stress relieve each weld to keep from the engine mount legs springing out of position when removed from the jig.
The Red Bearhawk engine mount jig bolts to the fuselage jig and you build the engine mount to the spools bolted to the fuselage that is in the fuselage jig. This mount is for a straight mount (narrow deck) Lyc-360 engine.
Maybe the pictures will give you a better idea.
First,I get someone to help me do a W&B with me in the seat so I can work out the length of the engine mount to put the CG where I want it with no fuel. Working that out is another topic. Once I know the length I need for the mount, I start by leveling the airframe and use wood 2x4's and plywood and screws and make a table to set the engine on that is the correct height so the engine will be on the thrust line by the plans.
Then I drop a plumb bob down from the center of the fuselage tail , then from the center of the firewall and mark the floor for all of these positions. Then strike a line over these marks, extend the line forward of the front of the engine. Position the engine so a plumb bob will center on the line on the floor when placed on the center of the prop hub and the center of the rear of the engine, (if the plans calls for no offset). Make sure the engine is level or positioned for the down thrust, if called for on the plans and the correct distance from the firewall by the W&B results. I bolted the engine mount spools on the firewall, and engine before starting. Now I cut and fit the tubing to the spools on the engine and firewall per the plans. I just put a couple good tacks on the end of each tube. After all the tubes are tacked then I carefully remove the engine mount and finish welding. When welding the engine mount at the required angles, they WILL draw out of line a small amount, so you will need do a little heating with a torch to put them in perfect position.
The other way is what I use when I want to make several engine mounts where they are all the same. 4 Bearhawk fuselages and engine mounts were built from these jigs. I use scrap steel angle and make a square where I can drill holes to match engine mount holes in the firewall. Same for the a square that matches the engine . Then I position correctly and weld angles from one to the other for the correct length of the engine mount and the correct height. I do all the welding of the engine mount while in the steel jig. After welding I use a torch and stress relieve each weld to keep from the engine mount legs springing out of position when removed from the jig.
The Red Bearhawk engine mount jig bolts to the fuselage jig and you build the engine mount to the spools bolted to the fuselage that is in the fuselage jig. This mount is for a straight mount (narrow deck) Lyc-360 engine.
Maybe the pictures will give you a better idea.
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