propeller efficiency

Dave, I've always been interested in the subject, but unfortunately lack the patience to follow through.  I go to the field with a notebook planning to test props and have so much fun flying I just quit caring and never take a note. I do know APCs of comparable length and pitch will let Cox engines turn faster than any other plastic props I've tried, even though they are heavier than the others. But whether that translates to faster forward speed remains unknown to me. I think that lighter props take less fuel flow to turn the same RPMs as heavy ones. I believe that because I've switched between Wooden TFs and plastic props of the same specs, but not of the same brand or shape, so there's no science there either. I stick with the ones that are a combination of tough but easy to balance, and trust my engine to have the power to turn it. I would never use an e-prop on an IC engine. They aren't designed to take the hammering of combustion pulses at the hub. Sounds dangerous. And a flexible prop will probably accelerate and climb better without loading the engine, as they have reduced pitch when flexed out. Sort of like down-shifting when climbing a hill.

I wish I had a more helpful answer, but that's about what I know. Maybe someone else can help. I know we have at least a couple of members who have kept notes on propeller performance.

Rusty:

You are not alone on the matter!

IIRC the subject of propeller efficiency was orginally titled "propellor dynamics" though I'd have to consult the "search file" to be sure. I'm off on another project to fix our motor home generator at this time.

I think the voltage regulator is fried but I'm too cheap to spend $400 for a replacement unless I know for sure. (The genie puts out 160 volts rather than 120!)

SD

Seems quite hard to say about efficiency of props, but just want to know what prop you guys like to used. Like Rusty said, soft nylon will be more climb power than others.

Too bad that I'm in Asia country, or Dave can ship your malfunctioned regulator PCB to me, I can repair various type of industrial boards.

Ew

For sport flying, I like Windsor Propeller Company's Master Airscrew GF series propellers. For 1/2A engines I buy the 6x3 and cut it down to whatever size I need. They are tough, though not flexible, and easy to balance with a magnetic balancer and sandpaper glued to a glass pane. I also like APC in some situations, and they come in a wide variety of sizes.

I find the Master Airscrew 6x3 pulls my planes with much more authority than the 6x3 Cox rubber ducky.

I find the Cox rubber ducky survives bad landings and many crashes while the Master Airscrew shatters in tall grass.

I use the Cox Rubber Ducky because I fly over tall grass and have horrible landings.

Efficiency can change depending on how you are measuring it.

Phil

Thanks for sharing your experience. I'm using Master Airscrew 6 X 3 too, so far it survived some twitchy landing on grass field. Graupner 6 X 3 looks heavier and I never use it. my Cox 6X3 rubber ducky can't really balance well. thinking of buying some other props to try out, APC are really sharp on its tip.  wood prop? some say not efficient, I don't know, no experience with any wood props yet. I have one used top flite 6 X 3 which came with an old cox engine, since its hard to come by, I'm not plan to fly with it yet, just bench test with high RPM than others.

pkrankow wrote:I find the Master Airscrew 6x3 pulls my planes with much more authority than the 6x3 Cox rubber ducky.

I find the Cox rubber ducky survives bad landings and many crashes while the Master Airscrew shatters in tall grass.

I use the Cox Rubber Ducky because I fly over tall grass and have horrible landings.

Efficiency can change depending on how you are measuring it.

Phil

A few months ago I ordered a pile of different props from Bernie, Matt, eBay, and Hobby King.  I wanted to bench test and see what the RPM and static thrust was on the lot.  I probably have 10+ different plastic props (no wood, not interested) to try in 5x3, 5x4, 6x3, and 6x4.

I haven't done this because the test rig I built won't stay on my work table with a running engine attached to it! I was trying to avoid making proper pivots by using round headed carriage bolts.  The thrust would be measured directly with a digital scale using equal lever arms.  The lever arm idea is pretty standard, however a proper pivot with resistance to all other directions of movement is required. (I wanted to pull torque out directly too, but have realized it is not as important)

RPM would be measured with an optical tachometer, specifically the hobby king unit.

This project is on my maybe list now.  Maybe I'll get back to it.  Maybe I'll just fly with the different props and write down if the performance is favorable.

Phil

Every time I use a wood prop, I come home without a prop. Honestly I'm kind of scared of them exploding in my face. Of the ones I have tried, I find no obvious flyability advantages. My MA props stand up to punishment pretty well, but that may be because they're all cut shorter than 6". For 1/2A control line engines, 6" is too much to swing anyway, unless you just want to fly circles. They bog the engines in hard loops, even on a Big Mig .061.

I think I have 1 MA prop left. I'll try cutting it down and put it on something with landing gear...possibly my baby ringmaster after I get the wing reattached, the blue broke. My baby stunt bee is going on when I finish, so it should have plenty of power.

Phil

pkrankow wrote:A few months ago I ordered a pile of different props from Bernie, Matt, eBay, and Hobby King.  I wanted to bench test and see what the RPM and static thrust was on the lot.  I probably have 10+ different plastic props (no wood, not interested) to try in 5x3, 5x4, 6x3, and 6x4.

I haven't done this because the test rig I built won't stay on my work table with a running engine attached to it! I was trying to avoid making proper pivots by using round headed carriage bolts.  The thrust would be measured directly with a digital scale using equal lever arms.  The lever arm idea is pretty standard, however a proper pivot with resistance to all other directions of movement is required.  (I wanted to pull torque out directly too, but have realized it is not as important)

RPM would be measured with an optical tachometer, specifically the hobby king unit.

This project is on my maybe list now.  Maybe I'll get back to it.  Maybe I'll just fly with the different props and write down if the performance is favorable.

Phil

Guys,

propeller efficiency is only one factor affecting the actual performance you get from the engine. You get the highest engine performance if you use a propeller dia/pitch combination that will allow the engine to reach the rpm where it provides the highest shaft performance. You may want to check this out:

http://www.mh-aerotools.de/airfoils/cox_frameset.htm

Click on the "Performance" tab on the left side of the page and you will find a collection of COX engine performace curves. For instance a COX Tee Dee 049 will provide the highest shaft power (80 Watts) at around 22k rpm so you must make sure you use the propeller that will allow the engine to peak out at 22k rpm or so. (My best fit is with Bernie's 5x4 black propeller where I tach 21k on my TE DEE 049 and it pulls my Toucan RC the fastest.) The same engine with a 6x3 propeller will only run around 18k where the shaft power is more than 10% less (70 watts) than the peak, and the speed of the plane as well as its maneuverability drop sensibly.

Try these:

http://www.drivecalc.de/
http://www.drivecalc.de/PropCalc/

I haven't tried this one yet:

http://www.ecalc.ch/motorcalc.htm

eCalc is pretty good. On my electric RC drivetrain the calculated results matched the static test almost exactly through a meter.

Phil