Can you please explain
 

Is there a significance in the way these 2 props are shaped? Both are 10x6, does it have to do with performance and if so which one will work better with an OS MAX 40 FP, and when should you use one over the other. Or is just different presentations among vendors.
Please elaborate.

Thanks

RE: Can you please explain
 

Well, one is an APC, and the other seems to be a Master Airscrew. You could have told us the brand names, the prop shape gives it away.

APC makes a very efficient prop that works great on almost any engine. The MA prop tends to flex a lot and wastes a lot of engine power. I've used APC props on all my small (under .90) engines for many, many years, and I'll never go back to anything else.

Dr.1

RE: Can you please explain
 

I tryed both. APC and Master Airscrew. Now i only use APC props. I noticed that the Master Airscrew props that i used had a weird noise. I had no problems with APC :)

RE: Can you please explain
 

I agree with scolpit, the black master airscrew while it does work ok, is a very noisy prop, the APC is my preferrence for slightly better performance , and less prop noise.

RE: Can you please explain
 

It's a subject of frequent debate whether APC or Master Airscrew is better. There's a common theory that the flexing of MA props makes them inefficient. It's also common for people to put comparable size MA and APC props on an engine, tach them, see that the RPMs are higher on the APC, and then conclude that it is more efficient. Are they really more efficient, or is it just manufacturer hype? In the end, it doesn't matter for this discussion, because efficiency, real or perceived, has little meaning on a trainer airplane.

On the other hand, it's widely felt that the sharp tips on the APC props make them more dangerous than MA props. I find the MA props to be more durable, and with the wider tips, a bit safer.

Personally, I use both.

RE: Can you please explain
 

Propping is 50% theory, 50% experience & 50% opinion. Which tells you that it is as much suck-it-and-see as it is theory.

I tell my students to use MAS prop because they are reasonably tough & performance doesn't matter much with a trainer.

When the going gets tough -- it's still cut-&-try. It is VERY dependent on airframe configuration, engine characteristics, altitude, temperature, & end-use. In orher words everything is important & everything affects the choice of a particular prop.

I generally prefer APC props for performance applications, but not always. It depends on --------

RE: Can you please explain
 

I'm kind of laughing as I type this but I had a very scientific reason for buying an APC over the MAS.
In Realflight G3 you can configure your engines & it tells you how much static thrust the plane has. When you put the APC on the nexstar it gave it about 20% more static thrust versus the MAS. :D There you have it, scientific fact! hehe.

RE: Can you please explain
 

Look at the shapes of real props and boat props. None are very straight edged.
Noise means wasted power. So does silence.
I judge by pulling power in my calibrated hand and the Fish Scale pull. Then I go for the stopwatch.
Pull and speed.-------Quiet or loud.[sm=thumbup.gif]

RE: Can you please explain
 

Neither boat or "real" props can be equally compared to our model props. Our model props are usually much smaller and turn much faster than either. They all operate in the same density air (and the same molecule size) so there's where the comparison gets tough.

Dr.1

RE: Can you please explain
 

I have used just about every brand of prop there is including the Topflite and Graupner props.
Master Airscrews are great for the early flights when I'm breaking an engine in.
After that, I bring a fist full of sizes and brands to the field with me. I try different diameters and pitches and brands. When you find the one that gives the best performance, you will know it. Frequently that brand has been APC. Sometimes it has been Graupner.

About your original question. The simatar shaped propellers became very popular again in the 1990's. Thats true of models and of real airplanes. I have personally witnessed a twin turbo prop Dornier exceed 400 knots across the ground. It uses a multi blade simitar configuration that claims greater effeciency and is quieter. ATR's also use a similar propeller.

The folks at APC took this data from full scale manufactures and decided to produce model props with the simitar shape. The results were good. There are actually mathematical equations which date back to the Wright brothers that prove that this shape is the best shape for a propeller. I don't know why there was such a long period when the simitar shape was ignored. Perhaps it was difficult to manufacture.

The only down side that I am aware about the APC props is their appearance. I build scale. There aren't many scale singles that use a simitar shaped prop. But they look about the same when the engine is running.

Although I like APC props, I don't always choose to use them. Your needs often dictate which brand to use. Do you need the best climb ? The best acceleration ? The best top speed ? The least thrust at idle ? Your propeller choice may vary depending upon which side of the envelope you are attempting to extend.

RE: Can you please explain
 

> The only down side that I am aware about the APC props is their appearance. <

If memory of my brief foray into APC props is correct, the hubs are thick and may not fit some spinner/crankshaft combinations. And the blades are very hard so that it is difficult to ream them to the necessary diameter.

RE: Can you please explain
 

"Propping is 50% theory, 50% experience & 50% opinion." - Hey, that's 150%... no fair.

From my experience, which is worth 50% and my opinion which is worth 50% (Does that mean I'm 100% right?), the APCs tend to develop better static thrust, which is generally what I am looking for. It's hard to explain, but the bite and response at mid and low throttle seems better than other props I've tried. It seems like up-line response when going from mid throttle to high bites better with the APCs I've tried vs MAS, Zinger, Bollys.

However, I've had a few planes where I actually liked the squared off ugly MAS prop better. On the one case I can fairly clearly remember, I was going for speed. I tried several prop sizes, pitches, makes, etc. The MAS I selected seemed to let the engine rev up and unload better at the high end with the net result being more RPM and speed in the air. BUT, I really don't know if the MAS vs APC had anything to do with it. It may have been that in the bucket of props I brought, the MAS just happened to give me the best result because of my limited prop selection that day.

Cheers.

RE: Can you please explain
 

Hey, don't blame me -- it was all started by Yogi Berra :D

RE: Can you please explain
 

The comments on fly and try are right on. I generally start out with an APC, but I may end up with something different. The last round of testing I did, I ended up with a best prop and three others, quite dissimilar, which were almost as good. None were APC. I've done the bit of taking engine, fuel, fuel tank, best prop, etc. and putting them in another similar airplane, and they don't work worth a darn. Go figure!

RE: Can you please explain
 

So, is it not the same to test the prop on the bench cheching for RPM or shall it be tested in flight?

RE: Can you please explain
 

The only thing that matters is how the model performs in the air. RPM or measured thrust while held stationary on the ground doesn't always equate to flight performance. One of my brother's planes flew the same with APC 11x4 or MAS 11x5. Does that mean MAS is less efficient or inferior in some way? Who knows / who cares? By using the size that worked in each brand they were equivalent.

RE: Can you please explain
 

I agree with what the others have said, try several props until you find the one that gives you the best performance and then use that. Even the same prop can give different performance on two different planes/engines, so you have to try until you find what you like. For me, I mostly fly APC props on my planes, with a few exceptions. One huge exception is my Hog Bipe. For some reason an APC prop just doesn't look right on that biplane!! :D So I use a Master Airscrew.

Hope this helps

Ken

RE: Can you please explain
 

Ditto with others. You can get some information from ground RPM tests and with a semi-educated guess you can estimate what will happen in the air. But some factors such as unloading and engine power curves are often difficult to "guess." In the example I mentioned in post #12, I'm 95% sure the "confusing" issue was engine power curve. I was using a piped YS45 on very high nitro. Without getting into all the ins and out, I just wasn't "on the pipe", i.e. the engine wasn't in a RPM range where the tuned pipe gave the boost I was looking for. All my on the ground testing was worthless, as I never hit enough RPM to get to the pipe. But in the air, as the prop unloaded and the RPM went up, the pipe started to kick in and then the RPM really jumped. If I had to estimate, I figure 3K more RPM in the air vs the ground. It took awhile to find a prop that would unload properly, yet had high enough pitch to get the speed I was looking for, and the only way to really test was in the air. Cheers.

RE: Can you please explain
 

Well written Piper Chuck... Bravo.

RE: Can you please explain
 

Most people seem to think that because they get more revs using an APC then they must be better. What it really means is that, for one reason or another, the APC isn't as good at converting HP into thrust. This could be because the actual pitch is different to what's marked or because the skinny tips on an APC don't do anything compared to the wide tips on a Master. Most of a props work is done by the outer roughly 30% of the blade and a prop is just a wing that goes round and round rather fast :) (especially at the tips). APC's though are known to be very accurately moulded so there's almost no variation between any two props of the same size picked out at random.

RE: Can you please explain
 

Must agree with downunder (no it's not an aussie conspiricy!) Example: had a big scale model with a 120 4 stroke & a big radial cowl using a Master 16x8 prop (those supposedly in the know in oz call them paint stirrers). Performance was a little lacking so a friend lent me a fancy german scimitar shaped 16 x 8 carbon fibre prop, yes you could see the weave of the carbon - beautiful thing, and the motor picked up about 15% more RPM. Great I thought, performance plus! In practice the performance was so poor I was lucky to make a circuit & land. For what it's worth I tried APC props on my 40 FP's in a 4 engined scale model & went back to the Masters, reason, I got sick of cutting myself on the sharp, pointed tips working around the model cleaning, fueling & preparing it. The thought of sticking a hand in a spinning prop is just scary. Do I work for Master or hate APC for some reason - no. For electrics I use APC's all the time because they make special electric props which are very efficient. For an FP 40 in a trainer I'd go for the Master, efiicient enough, stronger & safer. Whatever you use make sure you sand off the sharp edge where they came out of the mould & balance them. - John.

RE: Can you please explain
 

"Most people seem to think that because they get more revs using an APC then they must be better. What it really means is that, for one reason or another, the APC isn't as good at converting HP into thrust."

I don't believe we can draw that conclusion without more evidence. Why couldn't it be that brand X prop gets more RPM because it has less drag? That would actually make it more efficient in converting HP into thrust. You have a point that measured pitch and disk image can make comparing two identically marked props (i.e. two 10x6 props, etc.) difficult, but I don’t think you can conclude that the faster a prop spins, the lower the efficiency.

Cheers.

RE: Can you please explain
 

In my expereimce I have found that APC props are way better on smaller glow engines and also some bigger ones. While everyone can debate this until we are blue in the face [&:] I'll use real world examples and we will not quote RPM figures

Lets take my Showtime. It's powered by a YS110 and everyone agrees the APC 16X6 is the prop to go with on this engine. Now when I first flew this plane I had the APC 16X6 on it and vertical was great not unlimited but great. It was fairly quiet and spool up was pretty good but it built to much speed for the airframe.

Someone suggested I try a wood prop so I found a Pro-Zinger 17X4 and put it on. Now my vertical pull was fantastic but two things happened. I lost the amount of vertical and the engine could break the prop loose (you could here this happen) and the plane would literally quit pulling and it got quite a bit louder, but the time it took for the engine to get to max rpm was greatly improved which is what you want for 3D. So now I plant the plane into a hover at about 20 feet and firewall the throttle, the plane starts pulling hard and within a few seconds the prop breaks loose and the plane all but stops. YIKES, this is not good

So I land and replace the prop with an APC 17X4. Now it's back to being really quiet and spool up is still pretty quick so I hover it again. This time when I punch it it rockets out and just keeps gaining speed and altitude.

I did similiar tests on my Twist wth an OS46AX, An OS91 FS, A Saito 100, OS108 and a few others. In all of it APC always seemed to give better pull and was much quieter. It cost me a bunch of cash for testing but I always came to the same conclusion. I also tested MAS props in some cases and everytime I could break the prop loose and it had not near as much pull as the APC. Now APC pops are heavier so take that into account if you use them.

Now only if Bambula, NX, MSC, Bolly and Mezjlik and the other high dollar props came in smaller sizes. I use strictly NX and Mejzlik props on my gas engines and the NX are wood and nice and quiet but pull like there is no tomorrow and the Mezliks are CF, look cool, pull like you would not believe but are somewhat noisier.

It all boils down to what others have said, test several props and see what works best but stay within they manufacturers recommended sizes

RE: Can you please explain
 

Good discussion. Now my 2cents. I have had quite a bit of experience with Master Airscrew props on trainers that beginners have brought to the field(s). In almost all cases where the student is considering getting a bigger engine changing to an APC prop will make the plane perform as if it has the bigger engine installed. With APC you will need to increase the diameter or pitch to keep the engine from over-revving. If you change from a 10-6 MA go to an APC 11-6 as an example. Many Sig LT-40's with OS-LA-40's will fly just fine with this combination. They barely get into the air with the MA prop. The APC props simply produce more thrust from an efficient design. This allows more prop to be turned. Try running the engine up. Change to the APC and try again. The extra amount of power will be quite evident.

Safety is always a concern however any prop will cut you if you contact it. Learn (or teach) safe modeling. Stay out of the prop arc and behind the aircraft when tuning the engine. Be aware of other pilots near by in the pits (they have their attention on their own planes!). Painting the tips white will make the prop visible. You can paint one only if you need to balance a bit. Removing the mold flashing (on all pros) will make them less likely to cut when starting as the trailing edges are quite sharp. Always use a "chicken" stick or other devise to start the engine (not your hands).

Common sence should always be used. I'ts like the wood shop saying: "DO NOT USE REMAINING FINGERS AS PUSH STICKS!"

EXCAP232

RE: Can you please explain
 

There is lots of folklore re props, particularly APC & MAS props -- & lots of it is wild conjecture.

To begin with, APC props don't always give more RPM than MAS -- often enough a MAS prop will out-rev an APC. That is no indication of anything other than a particular prop on a particular engine will give a higher static RPM -- not more thrust. Nor is it an indication of in-flight performance, because different props have different flexural stability & can behave significantly differently when unloaded (in-flight). Additionally, engine power characteristics have a huge impact on prop performance, & vice-versa. An engine-prop combo that gives high static RPM may not work particularly well when unloaded in flight -- due to both engine & prop considerations. The converse is also true.

One thing is certain -- because of the construction material, APC props retain their design shape more accurately under load than MAS props do. That gives APC props a better chance of consistent performance.

WRT the blade shape -- high aspect ratio props, just like high-aspect wings, are more efficient than lower aspect ratio types -- they have lower drag vs the lift developed, meaning that less engine power is wasted in blade-drag. Similarly, narrow tips generate notably smaller tip vortices, & hence, less drag & lower lift-losses due to high-pressure air recirculation to the low-pressure side of the blade. Thin tips also have less frontal area, and again, have less drag & lower power losses. A long skinny tip can easily be doing as much effective work as a wide blunt shape.

For sure, trying to judge a prop's performance potential by looking at its shape is not a very profitable expenditure of time. The real criterion is how the engine-prop-airframe combo works IN FLIGHT. Sometimes an APC varient works better than a MAS, & sometimes it's the other way around.

Suck-it-and-see.