Max weight for a Ryobi?

Thoughts of a twin Ryobi have been bothering me for months. Don’t build worth a hoot so it will be necessary to find and modify an airframe already built. Knowing the all up weight of your single with a Ryobi would help to establish some design parameters.

What is the all up weight of your airplane with Ryobi?

Thanks.

Bill

Maybe a better question would have been:

Will a Ryobi pull a 20-pound airplane with 28oz/sq ft wing loading? I rechecked the weight and wing loading on another Ryobi project and have become concerned.

Bill

Hi Bill,
We don't know what type of airplane or airfoil you are using. If you are using a flat bottom wing with a strong Ryobi you should be fine. If you are using a weak Ryobi or symetrical airfoil you will be marginal at best. If the engine will spin an eighteen inch prop in the seven thousand rpm range I would consider it a strong engine. Spiiining a sixteen inch prop in the high six or low seven range might cause problems. If you put one strong Ryobi on each wing it would add six pounds and give a wing loading of about 35oz./sf. The power loading would be about 1/3hp per pound. This would be minimum aerobatics capable. If the 20 lb plane isn't a floater, you should look for a stronger motor like a Homey 33cc Bandit chain saw. Easy conversion and lots of power.

Dave

Thanks Dave,

The twin disease is bad and even an occasional fix doesn’t help.

I have a hand me down pattern airplane in reasonably good shape with sheeted foam wing (1580sq. in. or so). Original plan was to use a Ryobi and fly it as a single. I had already mounted the engine. While checking to see if it might be used as a twin the wing loading was checked. Surprise the airplane will weigh will be just short of 20#. Oops maybe a Ryobi won’t fly it at 20# and 28oz/sq ft. Engine far away from fuselage for prop/gear clearance, not much ground clearance along with 35oz/sq ft wing loading gives serious concern as a twin. It would probably work great with three 90 two strokes on glow.

So far my twins have been conservative and successful. With enough power 28 would be OK. But 35 in a twin is not conservative. Good news is the wing would be plenty strong.

The other airframe being considered is a 96” Stick with symmetrical wing and dihedral. It is 35# and flying with a 57cc gas engine. Rough calculations indicate that as a triple it will require 2# in the tail and as a twin 1 1/2# will be required in the nose. A triple would be in the 47# range. I didn’t build the overweight monster but have been flying it for years.

Thanks again.

Bill