RE: RYOBI 31cc
No.
You need a mount and a prop hub to turn it into an airplane engine. Thats all.
Now if you want to get fancy, you can put an aluminum muffler on it. You can change out the magneto for an electronic ignition unit. You can even machine the fins off the flywheel if you so desire.
But the only thing you NEED is a mount and a prop hub.
You can get that stuff for about $15.
You can buy a brand new weed eater from Harbor Freight and have it shipped to your fornt door for less than $70.
Let's see:
$60 engine + $15 prop hub and mount = $75 engine that will outlast any glow engine on the planet and run on 1/10th the fuel.
The 700R engine is a short shaft--the one listed in the link sscherin provided
The 725R is a long shaft
Both work fine for airplane engines. They just require different prop hubs.