[dean2287]

I have a Evo .46NT in my Pitts, and have been running a 10x7 prop. It hasn't been performing that well lately, and I noticed that the benchmark prop for this engine is a 11x6. Would it make a big difference? And, does running a smaller prop hurt the engine?

[cassat]

Hmmmm....the smaller prop is better for the engine lifewise. 11 x 7 is probably too much load and may overheat your engine.
Please tell us what type of fuel you are running ? how old is it? where do you store it?
outside on the patio? etc
Also, what brand and number glow plug you are running?

[pipercub17]

Originally Posted by cassat

Hmmmm....the smaller prop is better for the engine lifewise. 11 x 7 is probably too much load and may overheat your engine.
Please tell us what type of fuel you are running ? how old is it? where do you store it?
outside on the patio? etc
Also, what brand and number glow plug you are running?

Hmmmm
this is not true one of the biggest problems in this hobby is guys trying to get max rmp
out of there engine
running small props = more rpm
more Rpm is not always a good thing
the standard was a 10/6 prop for this size engine but now days thay have more power
you have to mach the prop to the plane i would try a 11/6 or better yet a 12.25/3.75 apc if this one http://www.greathobbies.com/producti...d_id=APC123038
give the bigger one a try you wont be sorry
also this one would be worth trying http://www.greathobbies.com/producti...d_id=APC115040

[wymbly1971]

There's no such thing as a stupid prop question. Choosing the "right" one is an art....

The 11x6 will pull harder, but with a decrease in top speed.

You'll likely find a small drop in max RPM and maybe a rise in engine temp.

Matching the prop to the plane is an important factor. A prop that is over pitched may cause your aircraft to have landing speeds that are too fast, for example.

At least that's the theory......

[gkm41]

Great point, one that I always try to tell people but few listen... the prop not only has to be matched to the engine but to the plane as well... there are always suggested starting points, but if you have a large Yak type cowl, sometimes a larger prop is needed, and the type of plane always plays a huge factor, from a high drag trainer to a sleek pattern ship, it all makes a large difference... as does the type of prop.... you can ask all kinds of questions, but comes down to some experimenting with different types of props and different fuels until you get something that you are happy with,,, all hands on kinda stuff.

[michel gravelle]

Hi

It,s not about youre prop , but it is a question about youer engine . You mentioned that youre engine doesn,t run well .

Change the O-ring on the needle valve , for an OS , O-ring , BIG difference .

These are good engines .

BTW ,............... the only stupid question , is the one you DIDN,T ask , I think youre question is good

Michel

[sport_flying]

I fly with a fellow who was using an 11x7 on a GMS47. I gave him an 11x6master airscrew to try. It made a huge difference providing longer flight times and increased performance.
The engine will rev a little higher but will be well within the proper operating range.
The 11x7 propellor is more suited to a .60 size engine.

[twobladeprop]

Originally Posted by dean2287

I have a Evo .46NT in my Pitts, and have been running a 10x7 prop. It hasn't been performing that well lately, and I noticed that the benchmark prop for this engine is a 11x6. Would it make a big difference? And, does running a smaller prop hurt the engine?

A rule of thumb for glow engines is to run them on the rich side of lean for one, and second high rpms always kill engines. Over rev and expect disaster. I have learnt to always over prop and under pitch. With a 12X4 on that engine, expect awsome thrust and not that crazy of revs. Especially with a biplane.

[JimMcIntyre]

Originally Posted by twobladeprop

With a 12X4 on that engine, expect awsome thrust and not that crazy of revs. Especially with a biplane.

Great prop for a Funfly plane but, the issue may be speed.

I flew (or attempted to) my Kyosho Pitts with an MVVS 45 running a funfly prop (APC 12.25x3.75), the engine ran great but I couldn't reach sufficient speed to keep her much above a stall (when I could get her off the ground). I went to an 11x6 and she was an entirely new aircraft, quite capable of sustaining knife edge etc.

As already mentioned, matching engine to prop to aircraft is more art than science, keeping the engine from over-revving or overheating is the first concern, getting the aircraft in a decent flight envelope the second.

I'm not sure what Pitts you own but, for a Pitts, I doubt there will be any issue of any prop (for that engine/plane combination) resulting in too high a speed at idle (assuming the engine is tuned to achieve a decent idle) to land.

Also, as already said, I would like to emphasize running the engine a little rich, this will keep the engine cool as the extra fuel will absorb heat and remove it through the exhaust.

[dean2287]

Thanks for all the replys, great information...

Jim - Mine is also the Kyosho Pitts. The engine is the Evo .46NT or "Trainer Power System". It's a GREAT engine, very consistant and strong...I really shouldn't have said that the engine isn't running well lately, in retrospect the plane has always been lacking a bit of thrust, most noteably for loops. If I've got the needle set spot-on she pulls just enough, but other times not quite enough.

So the question then is - would a 11x6 give me more thrust than a 10x7 for this engine. My understanding is that the best thrust comes from a higher diameter prop with a lower pitch, provided the rpm's aren't reduced too much. If the overall load on the engine is apx. the diameter x the pitch, then an 11x6 would actually produce a bit less engine load than a 10x7. In fact, a 12x5 should produce even less load...