11/26/2015 at 6:00 pm #42401
Instead of creating an electric carbon copy of all AMA power events, each with its own rules, the intent is to seamlessly integrate electric into all existing power events using the same models.
AMA general rules:
One can fly an electric powered model in any AMA land-based gas model event provided:
1. In each event electric motors and engines will have the same power-run times.
2. For a RPM test, the electric powered model will used the same prop as a typical engine in that event. At the power run’s midpoint the RPM of the electric motor can’t exceed the RPM of a typical engine under full power by more than 5%. A RPM test is done with a fully change battery.
3. The electric model’s speed controller will be set at a fixed level during the power run.
4. Actual electric flying can be done with a different prop.
5. An electric flier can be challenged to an RPM test immediately after the motor run. Failing the test or violating (3) will automatically be considered as a flight with zero duration.
a. Electric propulsion eliminates the noise and the fuel characteristics of engines. It opens the AMA power events to a fresh group of fliers, comfortable with electric technology.
b. The RMP test only requires a tachometer, eliminating all electric paraphernalia. In other words, the electric component is irrelevant.
c. Over time we could use standard RPM tables in (2) for different power events.
d. Electric power and water-based flying are prone to serious shorts.
e. The premise is that electric fliers can be trusted; otherwise, this undertaking becomes too complex.
[The original idea came from Jim Bradley who suggested using a formula based on the motor characteristics. But this would eventually lead to issues of energy and all its derivatives. Instead, a RPM test is fair and implementable.]
Comments/Objections/Support?11/27/2015 at 10:59 am #55654AnonymousInactive
I do not get it. I interpret the rules such as:
a) you adjust the power setting (in speed controller) such that the electric motor swings a typical power prop at RPM similar (or smaller) than the IC engine. But then
b) you may swap the prop after test?
So what stops you from using much larger prop and drawing much more power from the electric motor? The fundamental difference between an IC engine and electric motor is that you cannot overprop an IC engine, but with electric you get more power the bigger the prop (until you burn something).
-Tapio-11/27/2015 at 3:34 pm #55655
Electric motors and engines use different props. In fact, the bench mark RPM test might require using a special hub for an electric motor.
Suppose that in a particular event fliers uses a 7X3″ prop that runs 16000 RPM under full power. If the power run is 10 seconds, the electric motor running a standard 7X3″ prop can’t exceed 16800 RPM 5 seconds into the power run. The mid-point is required since the battery looses power as it discharges. The 5% margin accounts for temperature sensitivity of electric batteries. Also, once the speed of the BEC is set, it can’t be modified.
Suppose the wattage drawn using a 7X3″ prop is 60 Watts. If the electric flier decides to fly with a 8X4″ prop, its RPM will be lower – say 13000 RPM, drawing a higher wattage, say 80 Watts. And if the electric flier uses a smaller prop, say 6X2.5″, it’s RPM will be higher, say 20000, drawing 45 Watts. I contend that a model using a 7X3″ prop will out climb the slower (faster) larger (smaller) alternative prop, even though these props use more (less) energy during the 10 second power run. The reason is that the 7X3″ has been selected after many prop trials. (Skipping a more formal proof with J factors.)
Also, engines in a particular event might use a number of different props, so an electric flier can select which one to bench mark against.11/28/2015 at 1:10 am #55656
.11/28/2015 at 7:51 am #55658AnonymousInactive
@Aram Schlosberg wrote:
I contend that a model using a 7X3″ prop will out climb the slower larger alternative prop, even though these props use more energy during the 10 second power run.
No it won’t. More power drawn to the motor translates to more output power translates to more altitude (provided that the model trim is OK). As simple as that.
For instance, in Sweden I flew my “Pimenoff” E-36 with 7*4 folder, climbed to 60 meters. Recently I switched to 7*4.5 APC and the climb increased to 80 meters. Had to adjust the left thrust to compensate changed output power.
Electric motors work different as IC engines, the more you prop an electric the more there is output power (until the magic smoke comes out). Overpropping will reduce the efficiency, but that is not relevant here. In IC, if you get past the optimum prop your power output will decline. Electric and IC do not compare in this sense.11/28/2015 at 1:55 pm #55657
In your example, if the model with the larger prop ran with the BEC set to match the RPM of the smaller prop, the model would not climb as high. But if you set both props at full power, then if the larger prop climbs higher it means that it’s more efficient.
(To side step this issue, see the next post.)11/28/2015 at 2:13 pm #55659
To avoid debates about the performance of different propellers, the RPM requirement can be restated as:
Not exceeding the RPM of a legal engine (in that event) under full power by more than 5% at the mid motor-run, while using a propeller with a diameter and pitch that are within 1/4″.
For example if a legal engine runs at 18000 RPM with a 7X4″ prop, the electric motor can run up to 18900 RPM with a 7.25X3.8″ prop. (I’ve just invented it.) The point is that identical props might not be available.
Note that a ‘legal engine’ offers an electric flier a selection of different benchmark RPMs and props.11/28/2015 at 4:25 pm #55660
How are you going to check the rpm in a contest environment? Is the person timing the flight going to have to check the rpm just before you launch the model? There will be some who will push the rules to their advantage.11/28/2015 at 5:20 pm #55661
I’m presuming that an electric flier is likely to has fine tuned his BEC (controller) to satisfy the RPM test during a trimming session. (Of course there is the possibility that a model under full electric power will satisfy the RPM test.) One could do this calibration at the beginning of a contest but it might be a nuisance.
An electric flier can be challenged by a timer, the CD himself, or the CD following a protest after the motor run. Once the model is returned, the timer or CD could perform a (1) RPM test with a freshly charged battery or (2) check the motor run if that is an issue (without replacing the battery). So RPM/motor run challenges can be done as needed.
In other words – the person who pushes the rules has a good chance of being caught. Other free flight events have spot checks. One can weigh motors of rubber models, measure the length of gliders’ tow lines in tow lines or the energy of an EL in Q models.11/28/2015 at 7:11 pm #55662
Aram, You say you can check the motor rpm “after” the flight. What prevents anyone from changing the settings on his motor before bringing it back after the chase. I am not saying that someone would do this, but how can you ensure it will not happen. This is more involved then simply weighing a rubber motor after a flight or measuring a towline length. It puts a huge burden on the CD to enforce the rules. I think some more through needs to go into contest conditions which are quite different then bench testing a motor under ideal conditions or during test flying prior to a contest. Also with new and better motors and batteries coming out all the time, how do you adjust for new technology advances without making the existing motors and batteries obsolete, there bye driving up the cost to compete? I am not trying to be argumentative, but these are just some questions that come to mind.
Mike11/28/2015 at 8:50 pm #55663
In my many years of flying it is very rare that anyone cheats. I know of fliers that got disqualified due to sloppiness such as not weighing their motors carefully, tow lines longer by an inch or not checking the total area of a C model made by different producers.
In Q we occasionally we test the energy of models in the evening before a contest at the Nats. At the Eurofly fliers were suppose to check each other’s Q models but no one bothered. In fact the Italian fliers charged my batteries as I could only harge them off the car that was parked over half a mile away.
But a post flight option is important. An electric model should not consistently out-climb conventional power models! An if that happens, the CD can ask some one else to return the model, ask the flier for a fresh battery and perform the RPM test. This might happen occasionally but is far from being a ‘huge burden’ on a CD.
Agree that electric is evolving with new batteries and geared motors, but we are only testing the RPM, not the underlying electric and electronics. And all this is done to get more fliers to fly AMA power models.11/29/2015 at 12:38 am #55664
Aram Regarding the statement that allows any electric model to be flown in traditional AMA power events. Are the models to be used for electric flight different then existing glow powered designs? Are they similar to existing E-36 designs with extensive carbon fiber usage, or are they to be existing AMA glow powered designs with the glow engines replaced with electrics? There is a tremendous difference in weight alone between the two designs. Are you in fact trying to advocate for the eventual replacement of glow engines with electric?
Mike11/29/2015 at 5:18 am #55665
The proposal does not apply to any existing electric event (E36/A/B/Q). A and B electric are open to any electric innovation with locked and unlocked surfaces respectfully.
The proposal applies to all the AMA land based power events. AMA events are defined in terms of categories of engine volumes. These, in each category (1/2A, A, B, C payload etc.) produce certain ranges of power.
Electric/Internal power parity can be achieved in terms of output power (presuming the same motor runs) but it will require estimating the electric motor’s Wattage or it’s energy (with different motor runs). Besides being complicated as the Q demonstrates, it will invariably lead to DIFFRENT models. There will be endless arguments about parity.
Instead, the ‘simplistic’ approach is to match the prop characteristics and RPMs of a internal combustion engine. So all the electronic issues are brushed under the carpet. So, if an electric motor matches the characteristics on an internal combustion engine with the same power they would basically fly the SAME models, with or without carbon.
In fact, electric powered models are probably a bit heavier since they have a motor + BEC + battery + servo + e-timer versus IC models with an engine + fuel tank + mechanical timer. Well, as long as the weight difference is under say 5%, the effect is not discernable.11/29/2015 at 6:52 am #55666
Aram Using a typical 1/2A T.D. powered model which weighs in the 7 to 8 oz. range are your electric powered 1/2A models going to weigh the same? If a Class B model powered by a .29 engine weighs about 28 to 29 ozs. are your electric models going to weigh the same in that class also? This way everyone is on the same level playing field. What is the actual weight of a existing 1/2A electric model anyway? Charts and graphs showing rpm vs. prop sizes are fine, but is there a power advantage to flying a electric vs. a traditional gas model? Isn’t the real reason behind your idea to include electric in AMA gas events really all about adding more events for electric models to fly in? Why don’t you just try to add more electric events instead? I think you don’t want to go that route because you know how hard it is to add more events. I am sure aware of that problem.
Mike11/29/2015 at 3:52 pm #55667
Actually, the whole idea is NOT to add any new events! If someone wants to fly electric-AMA-B-gas then this is a straight forward path to that goal. Electrifying AMA gas models has the advantage of much less noise, no starter or gas and faster re-flying which is why it might appeal to a different group of potential fliers.
Because there are large variations among engines with a specific displacement, it might make sense to consider the average RPM for two or three standard props per event. Creating such tables would require input from those who fly the event.
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