How to locate an engine on firewall with built in offset angle?
06-04-2007, 10:34 PM
#1
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How to locate an engine on firewall with built in offset angle?
What is the proper way to locate the engine/mount on a plane that has a firewall or an engine box with built in right and down thrust angle? I am attaching some generic photos - I do not have this plane but I think the photos are good reference.
How do I use the marked x-hairs? Why are there two vertical lines? Should I locate the center of the thrust washer aligned with the center line or should I reference some other location on the engine?
Second, how important is it to locate the engine vertically? I got a 46 size edge 540 and I would like to mount OS61. The engine and engine mount are laid sideways with the upper mount butted against the top of the engine box. If I try to mount the larger engine I need to relocate the lower half of engine mount down to make room for larger case. That puts the CL of engine approximately 4mm lower. Other than mismatched cowl, what else may be affected?
How do I use the marked x-hairs? Why are there two vertical lines? Should I locate the center of the thrust washer aligned with the center line or should I reference some other location on the engine?
Second, how important is it to locate the engine vertically? I got a 46 size edge 540 and I would like to mount OS61. The engine and engine mount are laid sideways with the upper mount butted against the top of the engine box. If I try to mount the larger engine I need to relocate the lower half of engine mount down to make room for larger case. That puts the CL of engine approximately 4mm lower. Other than mismatched cowl, what else may be affected?
06-05-2007, 01:20 AM
#2
RE: How to locate an engine on firewall with built in offset angle?
The most important thing is that the angle is the correct one, which is a quite difficult parameter to find out prior the maiden flight.
The location of the engine centre line will just determine the position of the spinner tip protruding out of the cowl.
Some planes with a significant thrust angle look like funny to me, it seems that they got a punch on their nose.
I rather prefer to have little thrust angle and compansate the fly attitude with some clicks of the rudder trim, especially in the scale planes.
In some planes, like my Sukoy S31, you get no choice but to centre the engine thrust line as much as you can according to the cowl.
The location of the engine centre line will just determine the position of the spinner tip protruding out of the cowl.
Some planes with a significant thrust angle look like funny to me, it seems that they got a punch on their nose.
I rather prefer to have little thrust angle and compansate the fly attitude with some clicks of the rudder trim, especially in the scale planes.
In some planes, like my Sukoy S31, you get no choice but to centre the engine thrust line as much as you can according to the cowl.
06-05-2007, 10:42 AM
#4
RE: How to locate an engine on firewall with built in offset angle?
Lowering the engine 4mm won't hurt anything, but you still must get the cowling to
align with the spinner. Usually there is some wiggle room when mounting the cowling,
and it will still fit OK.
The whole deal with the offset marked on the firewall, is because there is an angle
(engine thrust off-set) built into the firewall. You must shift the engine to the side a
little bit so the engine propshaft sticks out close to the center of the front of the cowl.
If you didn't shift the engine over, the propshaft would be too far over to the right.
FBD.
align with the spinner. Usually there is some wiggle room when mounting the cowling,
and it will still fit OK.
The whole deal with the offset marked on the firewall, is because there is an angle
(engine thrust off-set) built into the firewall. You must shift the engine to the side a
little bit so the engine propshaft sticks out close to the center of the front of the cowl.
If you didn't shift the engine over, the propshaft would be too far over to the right.
FBD.
