Selecting the proper prop?

[FearTheH]

Did a search on this to no avail, and having started my private pilot training I'm sure this will not be covered between now and commercial rating. My friends father attempted to talk me out of building since I work full time, have a wife and two kids, and am going through flight training, however, I still want to build in any spare time. Everything is fairly straightforward as I'm very used to prints, however I was wondering what factors determine which prop to use? What width? What pitch? And so on... Thanks!

[mikey]

if you are building from plans or a kit, prop size , for a given type engine, will typically be called out on the plans or manual. most of the prop manufacturers have lists of various airframe/engine combinations and if they don't have one listed, a simple phone call to tell them what you are building will get you a quick answer. if you want to build in your spare time, you should do so. very rewarding if you like to make stuff. any particular design in mind?

[FearTheH]

Awesome thanks. I was looking at the ground adjustable props to fine tune performance, but it doesn't really seem absolutely necessary.

I have been looking at the Mini-Max V Max and Eros for some time now, but at the same time I'd also love to do RV 10 or a Cozy Mk IV. With so many options it's hard to decide, but I really like the given stability of a canard plane but being a pusher configuration, the prop specs change

[DaleB]

A ground adjustable prop is nice, at least in theory. I have one on my RV-12. You could (in theory) switch from climb to cruise pitch depending on what you want to do. In practice, you set the pitch and leave it. I have adjusted mine once, because when I bought the plane the prop was set up with a little too much pitch. I may make one more tiny tweak during the condition inspection.

A prop manufacturer can give you a fixed-pitch prop in the diameter and pitch you need, and if you need it re-pitched for some reason they can usually do that too.

[FearTheH]

Would an in flight adjustable prop be worth the money then? Pitch it out for climb out on the ground then adjust it to cruise for efficiency?

[Frank Giger]

Depends on the plane.

A Cub has a fixed prop because it's not going to go much faster either way, and the durations of flights are pretty short. Long distance planes that are fast, like a Baron, would benefit, as it would impact fuel efficiency.

On prop length, that's determined by RPM's. The blade tips shouldn't exceed the speed of sound or they feather the ends (best case) or actually break.

[Bob H]

These days you have several material choices for props; wood, composite or metal. However, the engine requirements may dictate and exclude some materials.
Every engine has a polar moment of inertia limit for the prop. You need to assure that whatever prop is selected, falls within those limits. Putting too high a moment prop will overload the engine or gearbox bearings.
generally, wood props are the lightest, composites next and metal last. You don't want to put a metal prop on a Rotax 912; too heavy and too high a polar moment.
I like ground adjustable props because I fly from a high altitude airport and need to decrease prop pitch for best engine climb performance. Most fixed pitch props are designed for near sea level operations and will lug an engine at higher elevation static operations like takeoff.
Wood props are asthetically pretty but are subject to moisture effects and can change shape slightly from humidity. GSC in Canada makes wood props at reasonable prices; $500-700 for gnd adj. If you suffer a prop strike with a wood prop, it acts as an energy fuse by breaking and keeping strike energy from damaging engine.
Metal props are normal on certified engines and cost ~$4000-5000 but they generally last years. Composite props are light and strong and have become expensive. A 3-blade Warp Drive runs around $1700. I fly a Pulsar XP at 140 mph with a Rotax 912S and a 3-blade Warp Drive and get good climb and cruise at 7000' airport.
It's premature to be concerned about props before selecting a plane and engine. The prop choice can come later.