Haven't really read much on electrics but was wondering if the electronics provide any motor speed control during manovers or does it just work to keep the prop at a constant RPM?

Yes, basically not, but some guys can do it:

  (sorry for posting again ... 187993 time)

 

here you can see it in reality:

http://stunthanger.com/smf/index.php?topic=12673.0

Wet setup has almost unlimited power, so it is easy to waste it on places where you do not need it (level) and have it when you need it (uphill). You need only flat prop and something limiting RPM (pipe, valves). But electric has limited power (or electric has far less energy in tank) so clever control cas save it to some extent, or it can act like a stronger setup with the same battery.

Look to my indoor model, constant RPM will not bring it overhead at such a slow speed and low mass inertia. So active controll is necessary. Larger model fly well at constant RPM, but anyway, only to the point when you try something better :-)

I haven't measured a 4 stroke engine, but I am convinced that no glow engine will keep rpm constant in a climb--they will all lose rpm. If Bob would like to record his flight (from center of the circle of course) I am willing to run it through my analyzer. I'd like to do the same with a piped setup.

That of course doesn't mean they don't work! But what it does mean is that simply keeping rpm constant is already better than what we already have with glow engines.

How much better is certainly an open question .At this point I believe it depends on the prop selection (thrust vs airspeed curve at constant rpm) and how the airplane itself behaves in sharp corners (i.e. how much airspeed it loses). I can easily believe you can lose the constant rpm advantage by poor choices and poor flying. By this I mean I also include my own choices and flying too!

Bob,
If you look at my first post ( http://stunthanger.com/smf/index.php?topic=14196.0 ) about the analysis in the Engineering section, I tell how I did it.

For a basic rpm analysis, I need a sound recording taken by some method from near the center of the flying circle--otherwise the Doppler effect completely dominates the rpm plot. I have used a laptop to capture the sound through its built-in microphone, and also a Canon camera operating in video capture mode (with sound).

The best setup would be two devices, one to capture the sound for the rpm analysis, the other a video camera placed on the upwind side of the circle (where the judges would stand) that would be able to video the actual maneuvers. That allows you to correlate the rpm plot with what the plane is actually doing. I start both setups, then start the engine. The engine starting noise on both setups allows me to synchronize the video camera with the audio capture.

Of course both devices could be video cameras.

Another option would be to put a person with the video camera in the center and have them follow the action (of course without talking and disturbing the pilot or the audio recording!). That would eliminate the need for another setup on the outside of the circle. I did this once, but it is a little difficult since you need to keep low on the ground to keep out of the control lines and yet follow the plane through the maneuvers.

I have been able to use a Youtube video, so that might be one way to get me the data. Or if the data could be temporarily posted on a web site, I could download it from there. It isn't a negligible amount of data--it would certainly clog most e-mail accounts. For example the Audio Wav file is ~62Mb (it could be mp3'd and I believe I could convert it into the wav format I need) and the video downloaded from the camera ~800Mb. The youtube video was ~40Mb, a reasonable contraction. The sound was still ok for the analysis, although since it was taken outside the circle, the Doppler effect washes everything out . The apparent rpm changes are large compared to actual rpm changes, and trying to correct would be a nightmare--because you would need to know the plane's flight path at every instant!

I haven't measured a 4 stroke engine, but I am convinced that no glow engine will keep rpm constant in a climb--they will all lose rpm.

I've watched Bob's 4-strokes power thru the pattern without missing a beat like a tractor plowing soft soil. I'm sure there is a little rpm loss, but hardly perceptable. His Saitos produce Torque, and tons of it at a decent rpm.

Bob, if we could rig up a funnel or something conical around a mic and have someone in the circle behind you pointing it at the model, we could get a more clean recording (directonal). A modern cell phone w/ vid might work?

MPI does make a variable pitch prop, but it's for Sailplanes, I think.

http://www.maxxprod.com/mpi/mpi-29a.html

I've watched Bob's 4-strokes power thru the pattern without missing a beat like a tractor plowing soft soil. I'm sure there is a little rpm loss, but hardly perceptable. His Saitos produce Torque, and tons of it at a decent rpm.

....<snip>

Doug,
Of course it remains to be seen what is actually going on, but I am coming to the conclusion (yes maybe a bit premature!) that by the nature of the beast, all IC engines have to lose rpm--at least in the beginning of a vertical maneuver. Here's my thought--


When the plane is in normal level flight, the engine is producing enough torque to turn the prop to offset the drag the plane is seeing. So at the in-flight rpm, the combustion process is "tapped out". Just enough air is being pulled in with fuel to provide the energy that turns the prop. The level thrust provided by the prop is actually quite modest, most of the heavy lifting is in the wing--that is what is fighting gravity.

When you pull up--and lets assume for the sake of ease of argument, that the plane doesn't lose any airspeed (it does of course),  the nose is now pointed vertically. At this stage, there are only 3 forces--thrust, drag, and gravity, with only thrust pointing up! Since the speed is assumed the same, thrust just equals drag (actually may be a bit higher since the induced drag due to the wing lift is gone if the plane is really moving and pointing vertically). But anyway we have added a huge slug of gravity and nothing really to counteract it.

So the airplane does the only thing it can so---it begins to slow down. As it slows down, the propeller begins to see a larger angle of attack (a larger load). However as mentioned before, the engine itself is tapped out. It had just enough air/fuel to fight the level flight drag and no more. So the prop does what it has to do--it begins to lose rpm. But now as the rpm's drop, the engine has a longer time to pull in air, since the valve (for a 4 stroke) is open for a longer time. Here I am assuming that the 4 stroke has been limited in its breathing capability in level flight--something that Bob has shown to all of us. Since the engine can pull in more air --and I might point out since the air is moving a bit slower across the venturi, the fuel draw will slightly get worse, or the mixture will be a bit leaner (% wise). So when the engine fires, there will be a larger, slightly leaner charge inside the cylinder, so actually it will produce more energy for that particular stroke. This helps the engine fight the lowering rpm--but I think the rpm will still drop.

Now we are climbing with the airspeed dropping, the rpm dropping, the prop load increasing, but the engine beginning to develop more power. At some point the airspeed will stop decreasing, mainly because the prop is making more thrust (maybe at a slightly lower rpm), the engine is producing more power, drag has dropped due to the lower airspeed, and not the least I think, the airplane is not moving directly against gravity anymore -- at 45 degrees elevation, gravity is also at 45 degrees to the plane's motion as it arcs over the circle. Anyway the airspeed comes up again.

Now what is interesting is seeing how all types of our propulsion systems handle this simple load change. All airplanes will lose airspeed, unless you have some way of "goosing" the power enough to counteract gravity. From some simple calculations I made a couple of years ago, (for a 10.5x6" Aeronaut prop http://stunthanger.com/smf/index.php?topic=7574.0 ), the extra thrust of a 1000 rpm boost only provided about 30% of the force needed to counteract the initial "1g" force of gravity. So to completely keep airspeed constant you will need one honking goosing!

Of course, we are all flying the pattern right now with what we have, so none of these things overwhelm our planes. I am just interested in understanding what actually is going on.

....<snip>
If I remember right, an Electric DC motor has a linear torque curve - pretty flat (correct me if I'm wrong on that) add to that a governed ESC and you have a pretty sweet powerplant for Stunt!

Doug,
Yes the torque curve is basically linear in the range we use the motor. I am not sure what you mean by flat (straight?), but the torque goes to zero at the no-load rpm (kV*battery voltage). It rises as as rpm drops (with a straight line). If the stator wouldn't saturate, the maximum torque would be at 0 rpm.

In addition I note that a sensorless brushless motor torque isn't max at 0 rpm because the ESC doesn't know which way to turn the motor, but that is a detail.

Typically our rpm band ranges from ~60% to ~90% of the no-load rpm. 60% is pretty inefficient due to resistive heating (maybe stator is also beginning to saturate at that current). 90% is getting inefficient because you are losing power to magnetic losses (eddy, hysteresis...) which begin to get comparable to the power out level when the motor is so lightly loaded (---reason to not "super" size your motor!).

Yes you "got it". 

The other thing to know is that the prop load, in our rpm range, decreases as airspeed goes up. So running your setup on the bench for any significant time might overheat the motor and ESC.

That's why if I want to test rpm settings in governor mode, I'll put on a smaller prop--or no prop if I am using my data recorder with rpm sensor. Also for bench motor testing, I found that an APC TE 11-5.5 nominally loads the system like my APC 12-6 TE prop does in level flight.

Doug,
It also explains why a lot of pipe setups are not what I would call optimal.
The steeper the slope of the falling torque with rising RPM, the better.
The E-governor makes that line almost vertical!
Dean P.

Alan, Do you mean the 11-5.5 in a static run loads the motor like a 12-6 in flight? That's a good thing to know. 

John

Yes that is what I meant to say. I am not even sure why I mention it. I only used it when I was looking at motor efficiency (varying cell count, ESC PWM rates etc) for my Scorpion 3020-xx motors and trying to simulate roughly what the motor was doing in level flight.