Before pressing B and pulling out blocks on the screen, you need to ask yourself.

"what am i going for?"

now theres alot things you could pick:

• Pioneer look
  
• WW1 look
  
• WW2 look
  
• Cold war look
  
• Modern look
  
• Sci-fi look
  
• Steampunk look
  
• Animal/Animal inspired
  
• Pure functionality
  
• Unconventional
  
• Replica
  
• Fictional
  
• ...you get the point

if you cant decide, lets break down your idea to a core word, or sentence.
what about... a huge Bi-Plane? or... a compact Jet? or maybe, you found some mechanism that appears in real planes, and you want to recreate the functionality of it in Trailmakers?

got it?
lets move on.

make a prototype!
you have to make it functional first, before adding looks onto it!
and if the looks add weight, or change something, fix the problem.

this might seem stupid, but this is pretty much how i do it, constant trial and error, i build the basic shape or the full appearance and make it functional, then i test it and see how it does in the air. If it tends to nose down in the air i can fix it by adding weight to the back, or subtracting weight from the front, or adding a wing/fin or two to the front, or by making the plane faster to generate more lift, etc.
This also works for the reverse if it tends to pitch up constantly when flying, and other problems that may appear when building.

it takes time, patience, knowledge, and experience to do this well, but if you have like 200+ hours in this game and you've made alot of planes, you can do this.

as I'm writing this i realize this guide didn't really help much with functionality, but i trust that you know how to make a plane.

here's just a simple list of all the little details that make a build feel more connected to it's backstory/plot, whether its a replica or something or just something you made up, this helps.

Pioneer period:
Sails (if you have High Seas), White/Brown color scheme, Biplane Triplane Quadplane or more, Propeller powered, Slow, unconventional design

usually a replica of a real plane like the Wright Flyer or 14-bis, or an ambiguous plane with these features

WW1 period:
Slow, Biplane or Monoplane with large/long wings, not very aerodynamic, propeller powered, sometimes unconventional depending on what you're going for, white/brown color scheme with minimal coloring on the tail, fuselage, or wings, sometimes colourful

usually a replica or an ambiguous plane that has these traits/features.


WW2 period:
a. Early War
Biplanes, and Early Monoplanes, relatively slow, propeller powered
b. Mid War
Monoplane designs that are fast/maneuverable/both/neither, Big bombers, propeller powered
c. Late War
Faster Monoplane designs, Faster and bigger bombers, propeller powered but stronger (use hidden mini thrusters to make the plane faster), also you can make it look like some of the very very early jets like the Me 262

Usually a replica, or an ambiguous plane that has these traits/features.


Cold war period:
Big air intake in the nose, and a jet in the back/Two jets on the wings (or something more unconventional), Swept wings [you can make the wings swept by using wedge pieces or by putting the wing on a steering hinge and using an altitude sensor set to be always on triggering it]


Modern period:
Swept wings, or Delta wing configuration, or even wings with adjustable sweep, "im fast as f**k", complex mechanisms and clever solutions.

tip for the modern period, if you cant add ailerons to the wings, make the back pitch fins also roll, you can do this via logic.

i wont explain it here but you could ask me in the comments section.

Other:
do whatever you want.
yeah literally just do whatever you want, its fictional anyways so... yeah just wing it

haha get it, "wing"

this is a pretty bad guide i know, but i hope these little tid bits can help in your plane designs.

cheers!