[NSRCA-discussion] YS Engine Mounting in Composite plane - reducing variables

[Woodward, Jim]

Hi Guys,

 

You know that mounting a motor setup is a difficult task at best to get perfectly done.  The main problem is that there are so many variables to be addressed all at once like: 

1.	Spinner position 
2.	Nose-ring position 
3.	Firewall position 
4.	Resultant thrust angles 
5.	Angle or motor tilt within the space 
6.	Matching flat surfaces together in a ½ blind situation (backplate of mount to firewall).  
7.	Small angle sag of mount with engine installed (happens to any mount that is intended to be used with a nose-ring). 

 

The typical mounting procedure I've been aware of and using is something like this:

1.	Mount the engine to the mount 
2.	Place this assembly into the plane 
3.	Mount the spinner backplate to the motor with a thin spacer (I use 1/8" spacer) 
4.	Jostle this into position then rough-out a firewall. 
5.	When you think you got the firewall sized right, tape the spinner to the plane, turn plane vertical, glue firewall in place - cross fingers 
6.	Return after glue dries, create a nosering then prey more.  Admire the work with a tinge of disappointment then..... 
7.	.... Create a small shim to get the correct thrust angles after you realize you are off a hair.... (I'm sure no one else has had to this right??) 

 

This time around while working on a YS installation in an Abbra I decided to reverse this scenario entirely and make attempts to reduce the number of variables and tolerance build up.  The easiest thing to get right and fixed is the center of the nose and spinner location.  So, step #1 was to:

1.	Install nose ring phenolic disk that I predrilled for a Central Hobbies nose-ring. 
2.	Once this was installed I can position the motor and mount assembly through the nose-ring with the nose-ring actually mounted to the plane.  This allows for some "movement" of the back of the motor to fine-adjust the resulting thrust angles. 
3.	*New step - maybe you guys were already doing this - Make a temporary spacer to lift and position the motor mount in the free space of the engine compartment.  This spacer places the motor & mount assembly into a fixed position to you can see the resultlant thrust angles. 

	a.	Once done, the motor is resting just where it needs to be without any pressure, forces, or chance while you can now trial fit the firewall. 

 

Firewall:

1.	However you got this, now you can trial fit it to the exact repeatable location every time because the motor and mount are installed in the plane (... with nose-ring already fixed - exactly where you want it to be for flight) (positioned by nose-ring and temporary spacer). 
2.	Once you get the fit you want, tack glue the mount to the firewall and unscrew the NOSE-RING from the front on the plane.  
3.	At this point the entire assembly lifts out of the plane 
4.	Remove engine from mount 
5.	Mark exact location of drill points for motor mount 
6.	Drill, fix, with blind nuts. 
7.	Reassemble mount, motor, and install into plane with NOSE-RING screws to disk. 
8.	Re-check for firewall fit and glue. 

 

At this point I have everything done up till the tack-glue point of the firewall to the mount.  I should get through it tonight and tomorrow.  Maybe you guys were already doing it this way, but this is the fist for me and using this approach has take some chance and tolerance build up out of the equation.

 

Thanks,

Jim W
 
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