Assembling a Harrier with a .91 thunder tiger. (broken in already) The enging mfg. recommends prop 8 prop sizes from 11-11 to 14-6.
Where do I start?
Is there a criteria to use?
I hate to buy 3 or 4 and not use most of them.
I'll be sport flying the machine next summer.......

Are you talking about the .91 four stroke ?

FBD.

If it's the four stroke, and the Seagull Harrier 3D, I suggest the 14x6 or even a 15x4. The "3D" planes are usually not intended to be fast so that typically points you to large diameter and low pitch.

Prop selection seems to be voodoo sometimes. And it can be personal preference. I liked the way a certain prop worked on my trainer. Another pilot tried one on his plane and hated it. Similar plane and engine, just different likes/dislikes.

If it's a different engine or plane, ?????????????

Sorry guys, yes it's the TT 4 stroke .91. and the Seagull Harrier 3-D. I must have been in a hurry when I wrote it!!

Do I understand correctly a longer prop with less pitch will give me more torque?

What's a shorter one with more pitch do?

I would guess I have enough ground clearance to install a 16" if I had to.

More pitch typically equals more speed.

The engine has a certain amount of power so you have to use different combinations of diameter and pitch to keep the engine in the right RPM range.

These are made up numbers but hopefully illustrate what's going on

Prop Max RPM Thrust Speed
12x10 10,000 4 pounds 100 mph
13x8 10,000 5 pounds 80 mph
14x6 10,000 8 pounds 60 mph
15x4 10,000 10 pounds 40 mph
REPEAT, THESE ARE MADE UP NUMBERS.

carrellh,

WOW! Thank you--that's the explanation that makes me understand what's happening up there when I open the throttle. I won't take your numbers literally, but it's a good comparison.

I realize the Harrier 3-D is not made for eye watering speed so I'm going to start off big prop/low pitch.

Since all planes handle differently I'm going to ask around and see who's been flying Harriers and what they use.

Thanks again, EXPO

I put the disclaimer in so there wouldn't be a hundered replies saying "no way it is that fast / that slow / that much thrust / that little thrust"
There is a pilot in our club with a Funtana 90 running a YS-110 engine. He's very skilled at hovering, blenders, waterfalls, and other 3D stunts. He uses the wide blade APC props with 4 pitch. I forgot what diameter he uses but it's big.

I'd guess the APC 15x4W or 16x4W would be right for the 91 four stroke. They cost 13 bucks each so experimentation is a bit costly.