NOTE:  I have yet to figure out how to do tables. THey look write during the edit, then don't align when posted. hopefully you can follow until I get it sorted. Thanks  

How about a 
Plane-perk number: because planes are faster, tougher, more heavily armed than one another, this number would characterizes those attributes with higher being better. 
And...
a 
Bomb-perk number which is scaled with Bomb load. 
See the following tables…….
Plane perk number
Plane           Plane-perk   
A-20       0   
B-17      1   
B-24      2   
Lancaster   2   
Ki-67      0   
B-29      4
Bomb Perk number    
Bomb Load   Bomb-perk   
0      0   
1000      0   
2000      0   
4000      1   
6000      1   
8000      1   
10000      2   
12000      2   
14000      2   
16000      4   
18000      4   
20000      4      
The Perks required for each incremental bomb load are the product of the two numbers……
   Bomb perks per incremental Bomb Load                           
Plane    0   1000   2000   4000   6000   8000   10000   12000   14000   16000   18000   20000
A-20   0   0   0   0   0   0   0   0   0   0   0   0
B-17   0   0   0   1   1   1   2   2   2   4   4   4
B-24   0   0   0   2   2   2   4   4   4   8   8   8
Lanc   0   0   0   2   2   2   4   4   4   8   8   8
Ki-67   0   0   0   0   0   0   0   0   0   0   0   0
B-29   0   0   0   4   4   4   8   8   8   16   16   16
The total perks per Bomb load by plane are the sum of the values across the rows as the load increases and are shown in the next table…..
   Total Perk Points per Bomb Load by Plane                                    
Plane    0   1000   2000   4000   6000   8000   10000   12000   14000   16000   18000   20000   
A-20   0   0   0   0                           
B-17   0   0   0   1   2                        
B-24   0   0   0   2   4   6                     
Lanc   0   0   0   2   4   6   10   14   18         
Ki-67   0   0   0                              
B-29   0   0   0   4   8   12   20   28   36   52   68   84
I picked values for bomb-perk and plane-perks to illustrate the point of how required perks could vary with both plane type and bomb load. I'm not recommending these exact values, this is just a starting point to discuss the method. 
If you land the plane successfully you get all of your perks back. If you don't you lose them, just like today.