I understand the concept that  motor running on the ground or a bench would not be the same as in actual flight. I was wondering how the motor might be test for in flight conditions if a fan and a grid to straighen the air movement out were placed in front of the motor being tested?

Jim,

One way to get close on the ground test is to put on a prop that is 1 inch smaller than your flight prop. This will get you in the range of the in flight amps. If you use an ESC with governor mode it will hold the rpm and you can test to make sure the governor is governing with the flight prop. I start by doing short runs without the governor engaged first on the small prop to see the max low load rpm, then with the flight prop to see the max loaded rpm. You can start the setup process for the governor with the small prop, set for the rpm you want in flight (i.e for a prop pitch of 5" a starting point for 63' line length would be around 8800 rpm). Once you get the throttle % set with the small prop you can check the flight prop, it should hold the same rpm. If the rpm is lower you are loading the motor to much and need to either use a smaller prop or add more battery volts. I like to have about 10% head room from the max full throttle rpm on the flight prop to the governed rpm so it has room to move voltage up as the battery is pulled down.

Best,        Dennis

The throttle response being at low made no difference in the bench run time.

Walt,
I have a set up I'm going to use for OTS in a Barnstormer.  It is a E-flite Park 480 1020kv 275w motor, E-flite 1800 mah 3s 20c battery, and an Align 25a esc in governor mode.  I set the timer for 4 minutes and at 3:45 it goes into lvc and pulses the motor till the "burp" then it spools down nicely to a stop.  The esc I have set for no brake, mid-timing, 3.1v lvc, governor mode, and fast throttle response.  On the bench I'm using 1520 mah from start to finish.  the esc isn't very warm, but the battery is quite warm.  I can grip it but it does fell hot to the touch.  i'm sure I'm nowhere near the 140f that the instructions say never to exceed.  My prop is an APC 12 x 6e and the rpm I'm showing on my tach is 7000 +/- 200 rpm.

Hi Crist
I ran some numbers you may want to consider. At 7000rpm and 6"pitch your pitch speed calculates to be approx.40 mph. This is not the exact flight speed but it is close. If you use Dean's formula for "Target" RPM: 1020kv*11volts*.70 battery you
get 7854 rpm. If you use that to get a pitch speed of 50mph you need a 6.7"pitch prop. You can heat and repitch your 12x6 but, you will draw more amps from your
battery unless you cut down on the diameter. You may want to try a higher rpm and
a smaller prop on the bench and make sure you are not going to draw too many amps from your battery and for your motor. You will need approx 100 watts per pound for
a decent flight pattern. That is within your motors limit of 275 watts so that should
not be a problem. However your battery may need more MAH . You should check this on the bench to avoid damage to your battery.

Walt     

Walt,
The 7000 rpm comes from where I have the timer set.  Max rpm at turn on is 7800 and then it quickley goes to @ 7200 rpm within the first 15 seconds then it stabilizes there for several minutes.  I just ran it again without the governer and the rpm started a little higher but continued to go down and I got the lvc at 3:30 instead of 3:45.  I'll play with the set up some more.  I can do it in my garage, even at 10:30 at night!

I plan to use about a 55 foot line length eye to eye on the Barnstormer to get the 5 sec laps I'm hoping for.

Alan,
I have a 12 x 6e cut down to 11 inches.  I'll try a run with one of those and let you know what happens.

Crist,
One comment is that a 12-6 E cut down to 11-6 is still a lot bigger prop (in blade area) than the 11-5.5E prop (not accounting for pitch of course).
My guess is that with that particular battery, you will need a still smaller prop. Again as an example, on my Super Clown,  I used  1700mAH from a 3s2100mAHr FMA pack. Now your Barnstormer may get better "mileage" than my SuperClown (better streamlining perhaps). As a factoid, my SuperClown weighs in at 28oz, including the battery pack, motor, ESC, and timer. I fly for a little over 5 minutes to complete the full PAMPA pattern. I'll attach a Eagletree plot of one of my SC flights, showing what the draw and wattage looked like. I note that the rpm is oscillating around ~8500 rpm with the APC 10-7 prop----I don't see that with my Nobler, I assume it is due to having to use "Low Governor"mode of the CC ESC--but I am not positive.

Alan,
I cut down the 12 x 6 to an 11 inch prop then I made the blades narrower.  I ran it on the bench at 7800 rpm ( just off full throttle) and it went the distance of 4 minutes and held the rpm throughout the run.  It drew 19a at first thenslowly worked its way up to 22a at the 4 minute mark.  It drew 1224mah.  The battery was warm, while the esc and motor was slightly warm.  My question is this thing about unloading in the air.  How much does it and is that why I shoud invest in a ammeter to measure what it actually does during a flight?

I'm impressed! It sounds like you made an 11-6 out of an 12-6. I'll stick with my ARF 11-5.5 prop.

By the way, the reason the amps increased at the end is that as the run progresses, the battery voltage drops. However if the rpm is constant, the power (watts) stays the same, so the amps have to increase---the ESC is increasing the throttle to keep the rpm constant.

What unloading means is that in the air, 7800 rpm will use less power---the voltage won't drop as fast since the amp draw will be less. You don't really need a data logger unless you are obsessive! If you can handle the rpm statically, then you should be fine in the air. The only issue is whether you will get the flight speed you want. That's always a guess at first.

Hi Crist
Your latest bench run sounds promising.7800rpm gives you a chance to have a nice flying ship. I agree with your 11" dia prop but your 5.5"pitch will not make your desired
flight speed. However you can repitch to 6" or 6.5" pitch and come close.Make sure you use APCe props. Their blade thickness,weight and proportions are best for the size you are using.Good luck with your maiden flight.

Walt
   

Well guys just got back from flying it.  With the 12x6e prop at  "full throttle" it ran the 4 minutes I set and the lap time was 5.5 secs on 52 foot lines eye-to-eye.  It only used 736mah.  Itried the cut down 12x6 to a 11x6 with thinned blades and it basically flew the same for 5 minutes and drew 1150mah.  The last flight I tried a buddy's 10x6 Graupner prop.  Same speed, 5 minutes and it drew 1012mah.  I tached the prop at 8600 rpm just after it spooled up to full throttle.  I'm thinking maybe the ESC isn't allowing full throttle even though I set the throttle high and low limits using the timer (my timer uses a small pot for speed setting).  I have to do some more testing.  The motor, esc, and battery after every flight wern't even warm.  Barely above ambient.  I'm thinking about going higher in pitch if all the electrics are performing like they should.

Alan,
The difference in lap times between upright and inverted is easy......the earth's rotation.  Remember that you're going the opposite direction when inverted.  We should get an electric clockwise flying airplane and time the laps both upright and inverted and see if my theory holds any water.  Or maybe we go below the equator and try it out.  Anybody from Australia fly electric?  Maybe we can recuit a willing participant in this noteworthy exercise.  BTW is the battery above or below the motor?  I had to ask.

Alan,
I think Dennis has a more plausible explanation.

Crist

Congratulations on your first flights. Yes, I think you need more pitch but I think 8" P
may be too much. If you stick with APCe props until you get the right combo It will
be easier. You can use Windy's method of very hot water or a Heat gun to repitch. I have used both but lately have been using a heat gun for 20 sec then twist and  measure until you get the pitch you want. You said you tached the prop at 8600rpm. My question is did you tach both props at 8600? If you did you Gov. is working . If the 10 x6 turned 8600rpm and the 11x6 was less then your Gov. is not holding the constant RPM you want. I think a 11 x 7 would put you close to your desired lap speed. Good Luck.

Walt       

Walt,
I picked up a couple of 11x7e props along with a 11x5.5e too.  I'm testing them on the bench to see what gives.  The 8600 rpm is just after turn on and the governor will not hold that rpm.  I'll see what I can determine on the bench tonight.  Especially at the highest rpm the gov will take effect.

Update.  I tried an 11x7e cut down to a 10x7e and again the gov. mode max rpm was 7200 rpm.  Looks like the ESC won't allow a higher rpm.  I'm going to try the "high time" mode.  right now I'm running "middle time".  This setting is for more than 2 pole motors.  The high time is supposed to give higher power at the expense of efficiency.  Maybe I need another kind of ESC.  I'll try flying it though with the 11x7 prop at 7200 7300 rpm first.

Hi Christ,
You have me confused so please let me lay out the ESC adjustments as I understand them.
The governor has a HI RPM range and a LOW RPM range. The ranges are there for the difference between many pole outrunners and low pole count inrunners. I think you are in LOW range, which is why you never see more than 7200 RPM.

The Timing adjustment is something else entirely. The timing on a Dc electric motor, both brushed and brushless, is naturally retatrded compared to the ideal, because the motor windings are inductive, and it takes time for the current to build to its peak value. The guys with brushed motors would actually rotate the end bell of the motor that carried the brushes in order to add timing advance, and center the actual current pulse in time to co-incide with the magnetic pole faces. With brushless motors, it's just software to achieve the same thing. Actually, efficiency, input power and output power will all peak at the ideal advance for a given load. You probably want to stick to medium or low advance with an outrunner. The Castles seem happy in medium, all the time.

More importantly, take the ESC out of governor mode and put it back into fixed-throttle mode. Then check that the motor and battery combo is capable of achieving the RPM you want. If it doesn't, then the motor/prop/battery combination is wrong. In this setup, the desired RPM should happen with maybe 3/4 to 7/8 throttle, or 1.7  to 1.85 milliseconds of control pulse width.  After verifying that the prop is an appropriate load put the ESC back in the high range governor mode and see if you can adjust to the desired RPM. At least you know the motor is capable of getting there.

Please remind me, what motor are you running, and what is its Kv?

Hope I helped,
Dean

Crist,
If you put a little bitty prop on--like a 7" or so, will the motor spin it past 7800?
If you look at my data chart above, you can see when my prop starts to spin, the voltage drops from my battery. The initial drop is just the internal resistance of the battery. So with your 3s battery fully charged but unloaded, you would see ~12.6V. As soon as the current flows, you will probably get a ~1V drop or so--it depends on how high the current flow is and particulars about the battery.

So for the sake of argument, if the voltage drops to 11.5V on first turning on, that would mean with your ~1000kV motor, it should turn ~11500 rpm with no load. Typically we try to setup to run at an rpm ~75 to 80% of this value, or no more than 9200 rpm. So I would say a small prop should at least get to this value or higher (in non-governor mode).

At this point it would be nice to have the Eagle Tree or a simpler Watt-meter inline between the ESC and battery to verify that your battery can actually handle to load, but soon you will be able to find out when the Eagle Tree arrives. Welcome to the electric money pit!

Hi Christ,
Hi Alan,
Of course a tiny prop will turn faster, a 1/2A prop should turn close to 11,000 RPM on this motor. The Park 480/1020 has about 60 milli-ohms of resistance, so the ground current should be limited to maybe 22A. Above this, or an inflight current of 16 or 17A, the efficiency will be awful, and motor heating will be an issue.

Then I read again ... a 12-6 prop! You ain't turning a 12-6 prop with that motor!
I'll be back in a minute, i'm going to go run some numbers through a motor calculator.
Fortunately, your 30-ounce ship will fly well on just under 200 Watts.

Dean

Dean,
OK, I'll try the smaller props and monitor the mah used.  The numbers you give me are when flying...right?  This is where the E-logger will pay off. 

With an APC TE 10-7 on my SuperClown Electric, I needed about 8500rpm to fly comfortably (4.9 s laps with 58 foot lines. This is the chart I posted above. Actually it was a little too fast, but with that motor (the Stock SC Motor from Brodak) and the CC ESC in low governor mode, I couldn't make finer adjustments. As you can see, my average power (watts) was in the 180 range, maxing out at 310 in the vertical maneuvers.

With shorter lines you will need less speed for tension of course, but I am not sure rpms less than 8000 are going to work well with a 10-6 prop. The real question is the overhead stuff of course. But you need to try!

As an aside, I'm replacing the 10 magnet Brodak motor with my own Scorpion 3014 motor with 14 magnets. The main advantage is I can use the high governor mode of the ESC and have a finer throttle adjustment (the timer bits will make a smaller rpm change in the ESC in high gov mode).

Should have it at Sig, both for the Profile Contest on Saturday, and if Crist is there to [also] take the heat, maybe I'll enter it in Old Time. Of course I should fly the Old Time pattern at least once ahead of time. I wonder if Marvin D. will be there to witness the end of OT.

Dean,
I checked when the governor kicks in and it is about 75% on my servo throw fixture.  I don't know what the ms reading would be.  Probably right in the ballpark of what you thought.  Next time out I'll try the smaller props and start with a 7 pitch then go from there.  I have a 10x7e that is a cut down 11x7e that I will use and go 4 minutes at first.  Thanks for all your help.

I'm curious what tune was it singing? Was it "I'm in the money"

Remember, it was the motor singing, and its got its 3 brushless leads right into your wallet and sucking the cash out like there is no tomorrow!

Alan,
The difference in lap times between upright and inverted is easy......the earth's rotation.  Remember that you're going the opposite direction when inverted.  We should get an electric clockwise flying airplane and time the laps both upright and inverted and see if my theory holds any water.  Or maybe we go below the equator and try it out.  Anybody from Australia fly electric?  Maybe we can recruit a willing participant in this noteworthy exercise.  BTW is the battery above or below the motor?  I had to ask.

I'm in the Netherlands (N-hemisphere) and I had 5.17 and 5.19 laps (71 ft lines). Just shimmed the battery.....