firegremlin
Active Member
Hi everybody!
First, a bit about my project: I'm building a lightweight, simple ultralight flying boat with two small pusher engines. It'll be completely enclosed and rather well-streamlined; the idea is to have a slow low-altitude cruiser than can fly around for hours on end at ~40mph. Nothing sporty
I want to have all parts priced out and have the final blueprint on paper before spring, and the plan is to finish it in three months, before June. I've got plenty of enthusiastic helping hands, as well as an aerospace engineer and a mechanical engineer as advisors (both recent graduates, though). We certainly lack experience but have the desire to learn, and most of us have non-aviation skills that would come in handy during construction. I'd like to stay within a small budget but I'm not afraid of throwing money at the project to finish it on time and within design limits.
Anyway...
I decided to go with small indurstrial motors for low fuel consumption and noise, slow running speed, low cost, and ease of tuning and maintenance (for me, at least). For my meager cruise speed requirements two 7hp EX21 would do the job; however, I'm having trouble finding propellers for those. Arrowprop does make low-hp propellers but they're a bit heavy and short. 1/4 scale 36" propellers are relatively plentiful but they are again rather short and are generally made for higher speeds and engines that spin over 6000rpm. Carbon-fiber propellers cost more than the engine, but that wouldn't be that big of an issue if again I wouldn't be afraid of them being designed for much bigger motors.
So, the question is: what propeller would you recommend for a motor that makes peak 7hp @ 4000rpm, has ideal fuel consumption at 5hp @ 3600rpm, has torque curve flatter than Kansas, and will be installed as a pusher in a plane that will cruise at 40mph and have a top speed of a bit below 50?... I can mount at most a 54-inch propeller; after that I'll be too close to the fuselage for my comfort.
First, a bit about my project: I'm building a lightweight, simple ultralight flying boat with two small pusher engines. It'll be completely enclosed and rather well-streamlined; the idea is to have a slow low-altitude cruiser than can fly around for hours on end at ~40mph. Nothing sporty
I want to have all parts priced out and have the final blueprint on paper before spring, and the plan is to finish it in three months, before June. I've got plenty of enthusiastic helping hands, as well as an aerospace engineer and a mechanical engineer as advisors (both recent graduates, though). We certainly lack experience but have the desire to learn, and most of us have non-aviation skills that would come in handy during construction. I'd like to stay within a small budget but I'm not afraid of throwing money at the project to finish it on time and within design limits.Anyway...
I decided to go with small indurstrial motors for low fuel consumption and noise, slow running speed, low cost, and ease of tuning and maintenance (for me, at least). For my meager cruise speed requirements two 7hp EX21 would do the job; however, I'm having trouble finding propellers for those. Arrowprop does make low-hp propellers but they're a bit heavy and short. 1/4 scale 36" propellers are relatively plentiful but they are again rather short and are generally made for higher speeds and engines that spin over 6000rpm. Carbon-fiber propellers cost more than the engine, but that wouldn't be that big of an issue if again I wouldn't be afraid of them being designed for much bigger motors.
So, the question is: what propeller would you recommend for a motor that makes peak 7hp @ 4000rpm, has ideal fuel consumption at 5hp @ 3600rpm, has torque curve flatter than Kansas, and will be installed as a pusher in a plane that will cruise at 40mph and have a top speed of a bit below 50?... I can mount at most a 54-inch propeller; after that I'll be too close to the fuselage for my comfort.
