Hi.
It's the 3rd flight on my GP Super Sportster 40 ARF with an OS 65LA.
I tried these props:
APC: 11x6,12x7,13x6,13x4
The 11x6 seemed to performed better.
But i want some speed more from it.
So,
what prop to use please?
Kostas

....use an 11-8 Zinger, or MAS.

FBD. [8D]

Got the same kit with a Supertigre 60 with Hatori turning a 11x9 APC... lots of speed... awesome!

Τhank you guys.
Kostas

Noooooooooooooooooooooooooo!

11x7 APC

My vote is for the "meat slicer"
APC 11 X 7 or 11 X 8

I don't mean to butt in on your thread, but I have a Evolution .61 that is running the factory 3-blade prop. I would like to change to a 2-bladed prop.
I thought about 11 x 7 or 11 x 8. The engine is on my Alpha 60 trainer. I not particularly looking for speed. I am learning so I would like power in
case I get in a tight spot. Would the 11 x 8 be better for power?

Thanks

by power I take it you mean better pull. you should try a 12-6 or 13-4, 13-6. To get more thrust you go down in pitch and increase the diameter of the prop

I browse tower and found the APC 11x11????????
[sm=confused.gif]

The LA is going to have a hard time turning the 11x11, its too much prop for that engine.

APC 10x8, 10X9 or 10x10 possibly?
Prop choice is not a very exact science because everyone has their own opinion of what is "good."
Unfortunately that seems to mean you have to stock up on a bunch of sizes and experiment until you find the one that is best for you and your plane.
Luckily the 10 to 13 inch props are not extremely expensive; but in total you will spend a lot to experiment.

Like Carrelh says..it's not a very exact science. It's a "try & see" sort of thing.

While the .65LA is a pretty good engine, it'll never darken the doorstep of the winners circle at the races. Whatever "speed" you manage to coax from it will surely come at the expense of some other aspect of performance.

I'd prop the plane (SS40) to fly well and leave it at that. If you want a pylon racer....they are available.

Safebet- 12x6 >>> Period

I had a Thunder Tiger 61 Pro on my trainer.
The “benchmark� prop for my engine is 11x7 according to a LHS owner who says he got to tour the factory and talk to some of the engineers.

My trainer would float forever with this prop. My engine had a good slow idle but my instructor usually had to kill the engine on final to get good landings.

I put on a 12x6 and it made a lot of difference. The extra diameter gave more thrust for shorter takeoffs and stronger vertical climb; and the decreased pitch allowed the plane to slow down just enough to land with the engine running.

I tried the APC 13x4W “3D Fun Fly� series on my trainer. I really liked the performance but not the expense for a beginning pilot. They cost about $8 each. I had 3 ‘nose down’ landings one day and broke $24 worth of props; so I went back to the $3 12x6s

I don't think so.

The 11x7 prop size WAS in the right range, when piped F3A engines of the 1970s and the beginning 1980s peaked on them, in the RPM range of 14,500-15,500. The prop sizes between 11x7 and 11x7.75 would put these .61 pattern engines in the 'meatiest' part of the power curve in flight, while performing their high-speed maneuvers (most pattern planes of that era would fall out of the sky at 50 mph... Not exactly 3-D types...).

Most muffler equipped .61 engines, the Thunder Tiger Pro included, now peak much lower in the RPM band, around 13,000 RPM, and without the tuned pipe; burdened instead by a 'noise regulations' restrictive muffler, produce significantly less torque around their peak.

As such, they typically need a significantly heavier prop to produce their best performance.
A vintage 11x7 would have the engine buzzing beyond its peak HP, for most of the flight, being on the rapidly descending, 'over-run' part of the power curve.

These engines will be close to their peak power in static condition, but with the smallish prop-disk of an 11" diameter prop, would not even make initial acceleration very dramatic...


The 12x6 size will load the engine down and is much closer to exploiting the meaty part of the power curve.
Perhaps a 12x7, or a 12.5x6 would be even better and this size range is the current benchmark for 'sport' .61 engines; not the bygone 11x7.


These 'factory engineers' are wrong, which may explain why TT is not winning too many events...

In the booklet (TT), or sheet of paper (ASP), that came with the engines I own; both TT and ASP list 11x7 as the recommended prop for break-in and general usage on their .61 two strokes.

Is the manufacturer wrong? Maybe yes, maybe no.

I know the 12x6 and 13x4W worked well on my trainer; and the 11x7 didn't work the way it needed to for that particular plane.

A fellow club member took one of my 13x4Ws and tried it on a 61FX and hated it.

Prop selection is one area of RC where there is no shortage of opinions. What one person thinks is good performance; the next person may think it sucks.

Carrell,


Like some other items (... Clint Eastwood - Dirty Harry)), everybody has an opinion...

But, read my explanation thoroughly.


I do agree that an 11x7 prop is great for break-in on this engine and on most other .61s.

For general use, however, it is the wrong prop for most sport .61 engines.


For the prop to be suitable it must fulfill two different tasks simultaneously.

1. To have the engine spinning under full load in the fattest part of its power curve.

2. To have this happen with the particular model at its designed typical flying speed, with the effective pitch.


Vintage pattern models would maneuver at high speeds and their engines would peak around 14,500-15,500 RPM.
That would make an 11x7-11x7.75 suitable, since the engine would spin at its most effective RPM range and the prop blades would pull well at high speeds.

Current sport engines peak at a significantly lower RPM...

So if you were to be flying a vintage pattern model (high speed) with a contemporary, muffler equipped sport engine, the right prop would possibly be an 11x8, 11x9, 11.5x8. This would have both tasks fulfilled on this particular model.

If it is a sport model that flies more slowly, the venerable 12x6, 12.5x6, 12x7 would do great and for a slow bi-plane, or a 3-D model, the 13x4W would do wonders.

But try the 11x9 for the 3-D model...


For general use, the 11x7 is the wrong prop.
It simply cannot load a contemporary, muffler equipped sport engine sufficiently and the engine would just over-run at high speed; like selecting your car's transmission's low ratio on the highway...

Dar, I could convert my LA .65 back to glow and run a Bolly 12.5x6 tomorrow and get some numbers using 5% nitro/20% castor.

Prop selection is voo-doo magic that's why I have more props in the shop then my LHS does
I know tach readings are fun and all but you really need to fly a prop to know if it's any good
I have had plenty that didn't seem to work good as fans but sure fly sweet once there unloaded
with so many different planes flying with different type wings there is no way to know what prop will fly well without a test flight or two
ay least that's what I have found trough trial and error

Dave,


Good luck on that. I believe you will be seeing very close to 11,000 RPM on that prop size.

It should load the engine about the same as an APC 12x7...

Cheers.

Interesting......