Prop for .91 4-stroke?
 

I need some help picking a prop for tomarrow morning. I Just hooked a Thunder Tiger .91 4-stroke on my Big Stick .60 (for a test bed). I bench ran the engine on my test stand with a 15x6(what the manual called for) and it seemed to run great. Problem is that prop pretty much scrapes the ground when mounted on the big stick. I have a couple other props to pick from,but not a 14x7 that I'd like to have. A 14" prop will give me about a tad over an inch ground clearance which I think should be enough for now. I'm definely flying this thing tomarrow morning so I wont be able to make it to any hobby shops. I have a 14x8 and a 14x6. I also have a 13x6 and a 12x8,but they just dont seem big enough.

The stick had a .90 super tigre swinging the 12x8 and flew awesome. So,I want to go with the 14" props,but I'm just not sure If I should go with the bigger one or the smaller one. This is my first .91 sized for stroke,and I'm just not sure which sizes it will like.

Which one!?

RE: Prop for .91 4-stroke?
 

I'd try the 14x8 first.

RE: Prop for .91 4-stroke?
 

A second on what ChuckW said. Try 14x8

Ken

RE: Prop for .91 4-stroke?
 

I have a 14X6 on my minnow. Its a OS91 surpass. It only runs about 50-60mph. I have some 13in props to throw on at a later date. Hope to get around 100mph. Of course Im not good enough yet to fly it so its gonna wait. The 14X6 flys good though. im no expert but the 14X6 or 8 should be fine.

RE: Prop for .91 4-stroke?
 

Thanks guys. I ended up throwing on the 14x8 because it was already out of the package and the 14x6 was still new in wrapper and is actually to give to a guy at the field to replace the one he gave me last week. Sounds like both will work anyway,I just hate making the call on dumb stuff like this. Now if I crash I can blame it on Chuck and Ken,lol.

RE: Prop for .91 4-stroke?
 

That's not how you do it. Always blame a radio glitch, sudden wind shift, and stuff like that that nobody can actually verify. That way they will never know you dumb thumbed it.

RE: Prop for .91 4-stroke?
 

I think you'll find the 14X8 to be a tad too much prop for that engine. That is the perfect prop for a 1.00 class engine. All of my .91 FS's run either 14X6 or 13X8. I've tried 14X8 on them before (because I also own a saito 100, so I have some 14X8's laying around). The .91's struggled a bit to achieve a good top end, and also ran very hot. But you can see if you get any different results..

RE: Prop for .91 4-stroke?
 

Well,it seemed the 14x8 was a bit much. I did have trouble getting it to reach a consistant top end. After playing with it on the ground,we stuck on a 14x6 and it was noticably better. I still actually though that even this prop was a bit much for my Big Stick as it wouldnt stay put at idle. The plane just wanted to roll away. The field instructor had his skybolt there with an OS .91 swinging a 14x4 sport prop and as always.....it flew fantastic.

I did get to test the Thunder Tiger .91 4 stroke(this was the whole purpose) and it ran ok,although it is fussy to tune. I think if I do fly this plane/engine combo again before taking the motor off for my new Hog Bipe.....I'd try the 14x4,just to try to get the plane to sit still while idling.

RE: Prop for .91 4-stroke?
 

I'm running A 16X4 W on my Kaos with the OS .91 but I was trying to slow the plane down for smoother stunt work. It worked out fine for me. I have about an inch of ground clearence on this prop and plane but I also made up longer gear for it years ago for some of the fields I was flying from.

RE: Prop for .91 4-stroke?
 

14x6 or 13x8 for more speed.

RE: Prop for .91 4-stroke?
 

The rule of thumb for props is: longer prop, less pitch = more torque less speed. Shorter prop, more pitch = more speed. That's why you need so many props in your flight box. You want to find the prop that works best for the pilot. It's also fun to see how they effect the planes flight. ;)

RE: Prop for .91 4-stroke?
 

Depending on ur flying abilities and prefferences,for most all 91 class FOUR STROKES accept the YS brand,you'll find they run the best with any prop between 12/11 to 14/6 size and pitch. On my OS,Magnums,Thunder Tigers,Satio's,Enya's and even my ASP 80,the best all round props i've found are the Master Airscrew 13/6,13/8,or 14/6 props. As to the YS 91,nothing smaller than a 14/8 Gruptner prop. If you really need ground clearance,you can always use a 3 bladed prop on your 91 in the 12/8,13/6,and 14/4 configurations.

RE: Prop for .91 4-stroke?
 

On my 91 four stroke, I use a 13x8 and it pulls my ultrastick through the air with authority.