One of the most common questions we get is simply: “which size do I need?” It’s a fair question, because unlike a lot of RC parts, landing gear isn’t sold by a universal sizing standard — it’s matched to the airframe and, often, to the engine size the model was designed around.
The starting point is always your model’s manual or manufacturer spec sheet. Most kit and ARF manufacturers will state a recommended engine displacement (in cc for petrol/glow, or a motor/prop combo for electric), and gear is generally sized to match that bracket — for example 26cc-35cc, 50cc, 80cc, and so on up to 200cc+ for the larger scale aerobatic types.
If you no longer have the original documentation, the next best method is measuring your existing gear (or the mounting points on the fuselage if you’re starting from bare wood or foam) and comparing against the dimension charts on each product page — fuselage width, undercarriage widh and track are the three measurements that matter most. you will see on most of our undercarriages a diagram with A, B, C and D measurements. compare these with what you have, or had, and you can start working on a suitable replacement.
A word of caution: “close enough” isn’t good enough with landing gear. Too light a gauge for your model’s weight and you risk flex or fatigue cracking after repeated landings; too heavy and you’re carrying unnecessary weight for no benefit. If you’re between two sizes, it’s almost always worth sizing up rather than down, particularly if you fly from grass.
One thing to consider is putting in an undercarriage in two parts. by splitting it in half at the ‘A’ measurement, allows you to both widen or narrow an undercarriage that may be right in all other aspects but not fit across the fuselage. Good bolts and fixings help with split undercarriages and many large models come originally with split undercarriages.
If you’re ever unsure, get in touch with your model, engine size, and roughly all-up weight, and we’re happy to help you land on the right choice before you order.
Our Carbon Fibre Undercarriage for 100cc models – suits Yak and others. UK stock is a good illustration of the kind of fit and finish to look for.