Pattern prop trials
 

I am brand new at pattern, currently learning to fly the Sportsman routine with my Extra 330S (67"/8.5lbs). I am using an OS 65 LA with a 13-6 APC prop. Measured RPM and thrust are 11,300 and 8 1/4 lbs respectively (this amount of thrust really surprised me!). Also, I am using a Bison Pitts style muffler. Needless to say, the power is more than enough for the Sportsman routine. But ...... , I just had to try a 12-10 APC pattern prop to see what this will do to the flying characteristics of the plane. Being fairly well versed in aerodynamics and such, I would think the plane will fly faster, but pull vertical less smartly. A new pattern friend of mine has a 12-10 on a Webra 60 in a Kaos with pipe. His plane does the Masters pattern beautifully. I don't understand (he doesn't either. He says it just works!). With this prop the RPM and thrust are 9,300 and 6 1/4 lbs. Also, things are a lot quieter (by my ear, not measured). I haven't flown this new prop yet due to high winds which should go away tomorrow. I thought it would be interesting to hear peoples opinions on what is going to happen when I fly the plane through the routine, and maybe an explanation as to why. In a car when I want to go up a hill I down shift ( less pitch, higher RPM). That I understand. One last thing, 9300 is right at peak torque for the 65 LA.

Pattern prop trials
 

In level flight, I think you will have very good speed (even with that big plane and small engine) but as soon as you will get the nose up, your RPMs will drop to that 9300 and the aircraft may slow drastically.

To me, it is not a goog thing since you will have to get speed far before any vertical maneuver and go vertically the ballistic way. That is not very good for that constant speed we all try to keep...

Stick to the APC 13-6, all you are missing is 1/4 lb of thrust to have about unlimited vertical and at 11 300 rpm you must have the speed and thrust needed for anything but vertical snaps.

What is your airplane ? Sounds like a very light Extra you have !

Prop choice
 

One of the major factors in choosing a prop is noise. This a very general statement......but...you are too loud I would almost bet it. Not saying you should change it but turning 11,000+ rpm on a 13" prop I would bet money you setup is too loud regardless of your muffler setup...In addition to your muffler setup I would think its too loud partly because of the muffler system being used.

Ok that all being said...If it works for you go for it.

The reason the pattern flier chooses a prop the way he does is based on acceleration and braking. For the most part the 10-12 pitch props seem to be the best at this. Yes the flatter pitch props will give more vertical.....and tend to have more brakes on the downline...However just like your car in sometimes in windy conditions you can't carry enough energy for the wind. The flatter pitch props also tend to jump to life when getting on the throttle....This makes it tough to fly a sequence with smooth throttle transitions (not the mixture transition) but the guy on the sticks transition. This jump to life and instant acceleration is what the guys doing 3D like because it can save their bacon....

That added pitch can give a little speed in some cases it also tends to run the motor at lower RPMS which can help reduce noise. Diameter also helps the noise control...A 16" prop will tend to be quieter on the noise meter than a 17" prop...even though the 16" prop can turn higher RPMS....so we pitch it up a little to carry the same RPMs....

Ok this all being said some motors don't lend themselves to being run at these lower RPMS.....the "long Stroke" motors of the past liked a lower RPM like below 10,000....where as your 65LA is ported and setup to run in the higher RPM range...this is where it makes it power. The Webra was designed to run in the lower RPM range being a long stroke motor( depending on which webra) I'm not a Webra expert from back in the 60 sized birds.

Next thing your flying the Sportsman pattern right? There are no vertical upline snaps in that sequence.....you don't need a 1:1 power ratio in that sequence. What you need is a smooth throttle response and a very consistent pull and good acceleration when you want it. Prop choices are like CG many people have their own opinions. My advice is worth what you paid for (zip) get a prop combo that your motor likes whether thats the 13-6 or the 12-10 and gives you the best performance in the air.

We all strive for a better prop setup. I usually find a prop I like and fly it for a while...Then I found another combo I like and fly it for a while...sometimes I go back to an older setup and sometimes I venture out to a never tried setup. The plane has more to do with prop selection than motor. You're flying an Extra...It most likely has a wider nose than your buddies Webra powered model. I have found that the larger diameter props work better on the wider nosed models.

Not to mention flying style plays a role also. One guy may like a 15-12 and the other guy may go for the 16-10 or 16-11 on the exact same model..same weight, same conditions......

The reason APC makes the selection they is to give options and people ask for them...Take the 15-12 we ran this on the YS 140 FZ's and L's for a long time. The selection is wide in this size prop......15-12, 15-12W, 15.5-12, 15.5-12W, 15.5-12.5, 15.5-12.5W...all these props will act a little different in the brakes and on the acceleration...not to mention the noise meter.....This then branches out to the 15.5-11W or up the 15-13N...There is a huge selection of props in this range of 15-10 to 15-14...some go Narrow and some wide.....then the same motor will turn the say 16-10 or 16-11 nearly the same......Its all preference. APC props are cheap and try lots of them....not because I have stock in APC but because the different props can make a little difference in the way the model flies. Back in the 60 sized props you don't have such a large selection.....but there are choices back in these smaller props too. Get a setup that works best for you.....

If I was running your setup I might try going to like a 13-8 and see how the motor likes it. If it gets hot and doesn't like the lower RPMS then run it back up in the RPM range it likes......

Another issue is that the larger the prop in both Diameter and Pitch...the longer it takes for the motor to spool it up and down....This is some of the reason guys use the Narrow bladed props...this narrow blade tends to cancel some of the braking effect of the larger diameter....but like in your case the fuse has a bit more drag and maybe will not care as much as a narrow more traditional pattern model of the 60 sized era.....


RPMs are not always equal....chances are that Webra even though it has less RPM with perhaps the same prop might be able to provide more grunt than your plain bearing non-piped 65.....how the motor responds under larger loads is another critical factor......RPMS on the ground are not nearly as important as how it handles the real test in the air. HOw does the model pull through a top corner of a maneuver..or how does it handle when the wind comes up and you need a little more speed....What happens when you change conditions....like Hot and humid air compared to cool thick air in the early mornings, What happens when you go to a contest and its 2500ft elevation and you're used to flying at 500ft above sea level.....

All the props will respond a little different...You want to pick one that gives a happy medium and performs well in most conditions...maybe change props a little when it gets really windy and choppy.

BOTTOM LINE: Try different props and find a setup that works in your application. I will say this the same prop that gives torque roll ability will most likely not be the right prop for flying a smooth and precise sequence. Since there is no upline snaps in any AMA pattern class (only the F3A sequence has them) prop the plane to do what you need and don't worry about upline snaps except in playing around. The F3A class of pattern is more akin to the top level Unlimited pilots or the TOC/Don Lowe Masters level of schedules. These schedules are not intended for the guys just learning to fly precision. Not trying to discourage you from trying the stuff in these schedules just trying to focus your attention on what you need for the AMA Pattern classes. Most pilots spend years moving up the ranks and gaining the skills needed to perform those sequences with precision.


As usual I have talked way too much I hope it helps you out a little. Again its worth the price you paid! So good luck with your experiments...Oh and WELCOME to the world of precision Aerobatics.

Pattern prop trials
 

3djoy and tnewman,
Thank you for taking the time to pass on your knowledge of this subject. It will be very helpful as a reference as I progress in my pattern adventure. The plane is a KMP 330S ARF. The 330S does in fact have a very wide nose, especially compared to the Kaos. I will try the 12-10 for no other reason than it will be interesting to evaluate the results.

The 12-10 setup flies
 

Good weather and good flying with the 12-10; I like it!
Just like it is supposed to, I have much less throttle management work in order to maintain the same speed throughout the Sportsman maneuvers. I would guess I am moving the throttle half as much. The up line is slower but adequate. The plane is not nearly as jumpy with throttle movement. Of course I have to anticipate power change requirements a little better because the acceleration isn't there. I let the upline determine my speed and throttle down for everything else. The plane just isn't as squirrelly. I will use this setup for awhile and then go back to the 13-6 and see if I still see the difference. I am a little concerned that the loss of 2 pounds of thrust is going to really show up when it is windy. We will see. Overall, my pattern learning is coming along well and I am very pleased with the choice of plane, engine and prop. It still surprises me how well the $105 65 LA pulls this 67" plane around. The guys at the field really question what is under the cowl. By the way, with the 12-10 the engine is a lot quieter and sounds a little like a FS.

Windy
 

In the wind would bet the 12-10 would still outperform the 13-6....

Usually windy conditions mean down in diameter and up in pitch to get some energy and speed.

Glad to see you felt the difference in the way the props can change things.....Those same changes...may not be so profound...but are available in changing minor values like I mentioned the 15-11.5W and the 15-12 and the 15.5-12W......Thats why APC makes all those different sizes.....

Cool Huh?

Thats one thing I have not figured out on the big gas motors and the IMAC guys....most of them haven't learned that props play such a huge role....Look at the selection of props for say a 100cc motor....There are 26-10's and 28-10's and a few others aside from the 3 blades and such..but really in comparison there is quite a limited selection....The biggest selection is different manufacturers rather than different sizes....This work similarly....but it just might be the price of props too...The 26-10's and so on are the $35-60 variety rather than $10-12 on the smaller APC props.....

Glad to you are happy with the prop and the noise issue too....Its kind of cool isn't it?


Troy Newman
Team JR

Pattern prop trials
 

I am sorry to have misguided you Rchardfast. Sounds like it also sums up to personal preferences. I understand the smaller diameter prop will require less rudder corrections due to torque but the sluggishness in vertical is just not acceptable for me.

I like IMAC and have found (at least in IMAC) that it is not a good thing to fly fast. The past season taught me to fly as slow as possible staying true and straight.

Anyway, this discussion has brought me to think a lot. Maybe I will try smalled diameter and higher pitches too...

Pattern prop trials
 

But as my username suggests, I love thrust too...