The trapeze mechanism on the F-22 actually refers to the system by which the sidebays open and launch WVR missiles. As for the J-20's weapons bay, if you look at the sliding section, it's actually quite similar to the F-22's lower weapons bay wherein there's two rear slanted sections, probably to reduce RCS and to improve aerodynamics when the bay is open.
	
	
	
		
		
		
			
		
		
	
	
		 
	
	
	
	
		
		
		
		
	
	
		 
	
Compare to the F-35, where the slanted sections either don't exist or are more a function of the bay than the bay ending.
	
	
	
		
		
		
		
	
	
		 
	
			
			 
	 
	Compare to the F-35, where the slanted sections either don't exist or are more a function of the bay than the bay ending.
 
	 
				 
 
		 
 
		 
 
		 
 
		