• Flight Club Aerospace

Landing Gear Design Part 1: Concepts and Decisions

Updated: May 20

The landing gear is a hugely important part of any aircraft. They allow you to taxi the plane, land smoothly, and much more. The first step of designing our landing gear was determining what kind of landing gear to use. The main types used in ultralight aircraft are tricycle, taildragger, monowheel, and tandem wheel. After some deliberation and analyzing pros and cons, we ended up choosing taildragger for the following reasons:

  • It is inexpensive

  • It is lightweight

  • It is structurally simple

  • And it is better adapted for undeveloped runways

The main con of taildragger landing gear is that they have the tendency to ground loop due to the center of gravity being located behind the main wheels. That issue can be mostly mitigated by being able to lock the tail wheel during takeoff and landing (our tail wheel will rotate with the rudder so we can steer better during taxiing).

The next step is figuring out where exactly our landing gear go. This can be done by following these steps, as shown in the hand drawing.




  1. Determine the highest vertical CG location at the forward and aft CG limits and plot on the diagram as shown. These two positions are critical to the proper positioning of the main landing gear (use side view).

  2. Raise the plane so the propellor is exactly 9 inches above the ground (required by 14 CFR 23.925(a))

  3. Draw a line at between 15 and 16 degrees (we used 15.5) through the forward CG limit (see drawing below)

  4. Draw a line at 25 degrees through the aft CG limit

  5. The bottom of the main tires will lie on the intersection point of these two lines

  6. Draw a line at 12-15, degrees (whichever is closest to the plane’s stall; for us it was 13 degrees) from this point going upwards toward the tail

  7. The bottom of the aft tire should be located on this line and placed on the tail such that it carries under 5% of the plane’s weight when the CG is at its forward limit and under 10% at its aft limit

  8. RT=WxMxM+xT, where RTis the tail wheel’s static reaction load, W is the weight of the plane (loaded or unloaded, depending on what you want to calculate), xMis the x-distance from CG to main tire, and xTis the x-distance from CG to tail wheel (we plan on weighing it manually during construction to ensure total accuracy).

  9. Tire placement width (the angle formed by the ground and the line between the middle of the propellor and the bottom of either main wheel) should be over 25 degrees

  10. The main wheels still need to be wide enough to keep the craft stable

  11. The tailwheel spindle axis should be roughly 5 degrees. Nose Wheel spindle axis should be 0.


*taken from GENERAL AVIATION AIRCRAFT DESIGN: APPLIED METHODS AND PROCEDURES


We did end up having some problems implementing these exact locations (see Landing Gear Blog 2), but everything should still work, in theory. The next step in designing our landing gear was choosing the right type of shock absorbers. The purpose of these is to lessen the impact of landing on both the pilot and the frame of the fuselage/landing gear. Although shock absorption is often unnecessary in ultralight aircraft due to their light weight and sometimes strict budget, we decided on adding some, as our final design added very little complexity. The main types of landing gear are leaf-springs, rubber doughnuts, rubber bungees, coiled steel springs, and oleo-pneumatics.

KS= efficiency of shock absorbers, 1 means it can deflect infinite force over 0 distance.

KSof steel spring = .5 and KS of a tire = 0.39 to 0.47.

KS is crucial in determining the shocks we want, as we want shocks that can actually work.


*taken from GENERAL AVIATION AIRCRAFT DESIGN: APPLIED METHODS AND PROCEDURES


Here is a diagram of landing gear types that I made, with their main pros and cons.

Based on the information we compiled, we decided that bungee landing gear would be the best for our purposes. We originally decided to pursue cub style landing gear, due to their relatively high efficiency and ease of implementation, but we decided against that (see Landing Gear Blog 2).

Finally, we had to decide which braking mechanism to use. The three options for us are no brakes, manual brakes, and hydraulic brakes. We opted for hydraulics, as having no brakes is very dangerous and manual brakes just don't produce as much friction and aren’t as efficient as hydraulics. For the type of brakes, disk brakes seemed the clear choice as they are easily the most efficient without a huge additional cost compared to other options.

*Editors' note: the thought processes and design choices presented in this article don't necessarily represent those implemented into the final design and are subject to change. Flight Club Aerospace is a group of amateur students with no formal education in any fields of engineering. We present this information for educational purposes only, with the understanding that it is not to be re-created without adequate professional oversight and mentorship. For our latest designs and updates, please see our most recent blog posts.