# 125 cc engine, 64" propeller 3 blade, 180 kg gross weight, will it climb?

I'm a government teacher in school, currently I made an RC aircraft and flew it, now I'm working on a single engine light weight aircraft, I want to use a Honda CG 125 (single piston) engine, with 64" propeller 3 blade, engine RPMs are 3000, wings length is 29' feet and width is 4'6" approximately, and the length of aircraft is 20', empty weight of aircraft is 130 Kg, gross weight will be 250 Kg.

I want ask you: will this climb?

• In order to give a better answer, please provide geometrical data, airfoil, landing gear - all what is needed to determine lift and drag. Commented Mar 30, 2018 at 14:13
• Don't know if it can climb but will you ride it? Or will it be a rc plane? Are you sure this engine can provide enough power at a specific rpm range for a long time? Commented Mar 30, 2018 at 17:14
• Title says 180 kg gross weight, text says 250 kg gross weight. That's a pretty hefty difference.
– user
Commented Mar 30, 2018 at 20:10

I found a google site that showed: Honda GC 125 - 124cc, 10.8 bhp, @ 9000 RPM.

Seems to me it would be much less at 3000 RPM. Can you use pulley/belt system to achieve high engine RPM (smaller pulley) and lower prop RPM (larger pulley)?

The frontal area you provide:

wings length is 29' feet and width is 4'6" (54") approximately,

sounds similar to a Cessna 150, which has a narrower cabin (just about two adult shoulder width, 38 inches), and that needed 100 HP to fly, coming from a 200 cubic inch engine. It's overall weight was higher tho, 1600 lbs gross (in my 1971 model) vs the 250kG/552lb you provided. If the extra 16" of width is all in the cabin, that will be a lot of extra drag to overcome with that low horsepower engine.

As stated in this answer, the Wright Flyer could take off with 12 hp at 274 kg, so you do seem to be in the ballpark. But note that the Wrights had a long wing span, two wings, and two large & slow turning propellers.

For successful take-off Lift = Weight and of course Thrust = Drag. The L/D ratio of the whole aeroplane thus becomes equivalent to the W/T ratio, increase L/D to reduce T at a given W. So increase L/D as much as possible, by:

• Reducing induced drag => increasing wing area and/or aspect ratio. This one is dominant at lower speed.
• Reducing parasitic drag, only dominant at higher speed.

The engine should be run at its highest HP setting during take-off, and geared appropriately to generate a propeller tip speed of 0.8M. The larger the prop, the better it can convert power into thrust.

It should climb, you don't say what rate of climb you're expecting but with a 125cc engine and 250 kg gross weight you should at least get airborne.