The molding flash is the sharpest and most dangerous part of the edges of the prop. It also is an unintended part of the airfoil. Shaving off the molding flash makes the prop a lot less likely to cut you, and it also makes it more efficient by restoring the designed airfoil configuration.

Jim

I did extensive prop testing about 15 years ago ( flying two cycle glo for 23 years )
The APC props out performed every other prop i used
My test for performance is the unlimited vertical ( straight up from level flight at full throttle ) and APC props would pull me higher and faster than any other

The 12/6 should be good on the 61 SF
Is what i use on my 61SF
It is a long stroke engine unlike many earlier 60 size engines and will not like the 11/7 ( that is a higher RPM prop)
The long stroke is a torquier engine and one of my favorite engines for power output in its size

Do realize you always prop the airframe for-- its best possible performance with a given engine

Always balance every prop you use

All prop are dangerous but APC is a meet slicer - so Beware !
Do not get distracted and focus when working around a running prop

Use a chicken stik or electric starter to prevent being cut

The largest prop you can use with the lowest pitch you can use --to run the engine at the Mfg recommended RPM ( on the ground ) will always give you the most control feel flying where you will need it the most
Best power output for manuvers and throttle control on final

Above applies mostly to two cycle glo as that is my thing
The engines from 46 to 1.08 glo would be best for APC but the engines larger than this - wood props are just easier to use and aquire
Expense in the larger size props is an issue to consider always

Enjoy

The Ultasport 60 is an exceptional flying airframe
One of the very best 60 size Flyers
The 61 SF is a very good engine and it is propped right for the airframe
It is a fast performance plane that is not recommended for a beginner
You may want to restart you RC experience with a trainner and work your way into the US

I run a 91 Fx in my own and had to lengthen the tricycle gear i designed into my plane for prop clearence
The 91fx is in a 60 size crankcase that is stroked --so it is 61 engine weight-- with 91 power output !

Enjoy

You can view my purple Ultrasport in my --Gallery -- to the left of this post

Happy Landings

Enjoy

But, Ultra Sport 40-60 has a brotherhood thread. I'm sure the spectrum of side comments are practically unlimited, like those 61SF and 91FX are long discontinued, parts unavailable, and the SF peeled nickel liners....US60 is a 3rd plane choice, maybe stick one in the closet before they're gone like the .40 size?

See you on the USB thread.

Gas/nitro:
You prop an engine to achieve a specific engine rpm at wide open throttle. Engines tend to have a peak power at a certain rpm, depending on unload, typically you shoot for a couple thousand under peak on the ground. Fortunately there are plenty of trade offs between pitch and diameter for sport planes, I like having enough pitch that I can fly a decent knife edge which limits the diameter. Then I shoot for the largest diameter for best acceleration and climb without loosing the speed for knife edge.

Once the best prop for the engine airframe combination is found, I then start to look at the engine thrust line, general balance and rough trimming. When it is correct, (does not climb or dive with power changes, and will pull easily into a straight up vertical with just a slight amount of right rudder). Then I start looking at inside and outside loops. With the wings level it should take about an even amount of right rudder to do an inside loop ast it takes left rudder to do an outside loop. The size of the he loops should also be the same size for this test. Once this is done, try a few props that are very close to see the effects and if you find one that performs better you will have to redo almost everything again, though by a very slight amount. After this fly about 20 flights to explore for slight trim problems that might indicate other problems.

Are they flying the planes we fly? Until they fly a second hand plane that was tuned already, they likely have no idea what they're missing. You can't expect the same level flight line with a trainer wing or shoulder wing plane especially if it's not fully symmetrical.
How about cutting a pipe? Isn't "peak for an OS" is like finding peak on a Prius or Nissan Cube?

Think back and remember, he's running on the rich side to be safe. He's learning how to adjust mixture between low speed and high speed needles. His ARF engine mount is assembled from the factory and that is going to be the thrust line for that plane until it crashes. He's not changing his thrust line for many planes to come. He needs a baseline setup, to pick a prop that didn't come with the ARF, so he saw two brands and wants to pick one.
He's working on his landing, touch and go's, maybe building confidence to fly on a windy day.
His training jargon doesn't include knife edges, coupling, 125% endpoints, or tossing OS for real engines like NovaRossi or Jett who haven't given up, yet. Hopefully everything won't be EP and lipo velcro'd into styrofoam and beer coolers.

So much so much of aviation relates to power to weight ratio, it is important to know how to prop glow engines. Generally much of what has been published by engine manufacturers is useless because they are looking at minimizing noise which mean lugging the engine down to much lower rpm's. Lower rpm also means lower power and worse yet a much more critical needle setting. A lightly loaded engine is very easy to needle with a broad range, while a heavily loaded engine has a narrow range that varies greatly with slight changs in temperature and humidity. For sport engines and sport airplane's including trainers, having a reliable engine run makes it much more likely to have a less stressful flight with an overall better outcome.

OS does publish the rpm where each engine makes it's peak power, and that includes the muffler it is sold with. Now an airplane running wide open on the ground is a loaded rpm, and as the airplane takes off, the engine/prop unloads. While it is possible with today's telemetry systems to take measurements, ground rpm and knowledge of unload gets you close enough. For 14,000 in air, you would shoot for about 12,000 on the ground. A muffler equipped sport engine is not very peaky, the power band is usually fairly broad, over a range of a thousand either way. So you are just about as good at 11,000 to 13,000 and this is best determined by flying. These numbers are generic 40-45 type numbers, so 60's might be slightly lower, etc.

It is unfortunate if people assume the thrust line on any model is a well defined position for a specific design. Manufacturing tolerance, weight, balance, engine and prop selection make a difference. Getting one setup correctly makes the flying characteristics of any airplane better. Even a change from a 2 cycle to 4 cycle engine will generally make a difference in the prop size which means that one setup does not work the same for either engine selected. Generally the larger diameter requires a change to the right thrust, and errors in down thrust causes greater difficulties in pitch control for landings. A handful of small washers is about all it takes to change the thrust line of 99% of models.

Not all the information directly applies to a very basic trainer, but I have noticed that some pilots are already looking at there second or third models, so they need to be aware of more advanced subjects long before they actually get there. Virtually all of the information I talk about here is nothing new, I read about it in the mid-60's in the pages of RCM, Flying Models, American Aircraft Modeler and other magazines of that era, which was two and three years before my first RC model. As a result I was able to build the airplane, break in the engine, and solo'ed on the third flight at the age of 16. I even landed the model on the first flight and did the take off on the second. And that was the extent of my formal training, the rest was just hard knocks. However this was after flying control line for 6 years.

A great example of calling out a prop for a plane that just doesn't work can be found on the new Ultra Sport .46 ARF ad. Prop spec'ed for glow is a 12 x 7 prop along with the OS .46 engine. I would consider using a 12 x 7 on a .75 not a .46 engine. A 11 x 6 would work much better.

They recommend that prop for the alternate 4 stroke .70 engine, not the .46 two stroke. None of this thread is about pitch for a particular size engine but what material or other differences between a MAS and APC exist. A 12X7 works on a .70 4 stroke and up from there. Check out the OS 72 specs.

Check out the OS .46, they call out a 12 x 7

From the OS 46 product page at Tower.

Recommended Propellers: 10.5x6, 11x6-8, 12x6-7, use 10x6 for break-in

Good thing you have 10.5x6, 11x6-8, for application. Use common sense.

On the prop selection topic, I'll respectfully say that I think some have overcomplicated the issue. You prop for one thing only- in flight performance. It doesn't matter what your RPM on the ground is or if you are using the biggest or highest pitch prop your engine can turn. It only really matters how your plane flies.

Case in point- I've been doing the trimming on my Intruder for senior pattern flying. Lots of guys run an 11x7 Scimitar prop with that plane on an OS .65 with a Jett muffler. Their planes come out around 7.5 pounds and fly nicely. I went with a heavier engine (Novorossi .60F) and wound up just a tad over 8 pounds. The engine could turn that 11x7 very well, and you could hear that it was in its happy place RPM wise. But the plane didn't fly right- hot straight line speed and not enough vertical. 11x6 was worse. So I tried a 12x6 APC and got what I was looking for. With each prop, I played around with engine tuning to be sure I was peaked at the in flight RPM. A 12x6 Scimitar gave me a little more straight line speed at the cost of vertical performance. On a different plane, that might be great. But for pattern, it wasn't.

So with the prop I've settled on, I'm turning about 2k less RPM on the ground than with the 11x6. The engine probably isn't making its peak horsepower. But the plane flies right. I could probably experiment a bit more and find that one brand of 12x5 was better, or maybe not. But the plane is performing well, and I'd rather spend my time fine tuning it and myself for competition.

Hello everybody! Compares APC and TGS screws. TGS screws more productive. TGS Sport propeller (electric). Step and the diameter of the screw are the same.