---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 11/18/13: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 0. 12:27 AM - Fund Raiser Behind By 25% - Please Contribute Today! (Matt Dralle) 1. 11:59 AM - Questions about Z-08 (Thomas Blejwas) 2. 12:52 PM - Re: Trim motor speed control (Eric M. Jones) 3. 01:54 PM - Re: Re: Trim motor speed control (Robert L. Nuckolls, III) 4. 04:09 PM - Re: Questions about Z-08 (Robert L. Nuckolls, III) ________________________________ Message 0 _____________________________________ Time: 12:27:37 AM PST US From: Matt Dralle Subject: AeroElectric-List: Fund Raiser Behind By 25% - Please Contribute Today! Dear Listers, The percentage of members making a Contribution to support the Lists this year is currently behind last year by at this time by roughly 25%. 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Matt Dralle Email List and Forums Administrator ________________________________ Message 1 _____________________________________ Time: 11:59:05 AM PST US From: Thomas Blejwas Subject: AeroElectric-List: Questions about Z-08 Bob,=0A-=0AIn the postings on running an alternator without a battery, yo u suggested I consider your new draft Z-08, which is buried in the long str eam on "EXP 2 Bus workaround."- The more I look at Z-08, the more I like the simplicity.- It seems to meet most of my design goals, but answers to a few questions would be helpful.=0A-=0A1.- What were your criteria in deciding to connect "Engine A" with a switch (1-3) and "Engine B" through a relay?- By the way, what does the "K2" inside a green hexagon indicate on the relays?=0A-=0A2.- You show both A and B connected to the "Motive Power Distribution Bus"-through a single stud and bolt connector.- I'v e read that lock washers do little to prevent a bolt from loosening.- Wha t do you do to give this type of connection the reliability one needs for c ritical components?- Or can we?- Wouldn't a different connection for A and B-be prudent?-=0A-=0A3.- With respect to screw type connectors, what about the ground connection to the-engine block?- The high vibrat ion of a running engine would seem to make these especially susceptible to loosening.- What about two block connections going to two brass bolts thr ough the firewall ground bus, or would this set up an electrically noisy gr ound loop?=0A-=0A4.- I found your discussions about single versus dual batteries and properly maintaining batteries to be interesting.- Since, a s I mentioned in an earlier post, I've experienced a car battery shorting w hile I was driving.- I accurately interpreted the limited info and stoppe d the car in a convenient place.- Yes, the battery did not get the kind o f attention you have suggested.- But will the next owner of my plane be a s conscientious as me?- So, what is the downside of changing the DC Power Master from OFF/BAT/BAT+ALT to OFF/ALT/ALT+BAT, assuming that ALT FIELD ca n be disconnected if the alternator needs to be disconnected?- If I did s o, I would use an MGL Battery Monitor to see both voltage and current acros s the battery.=0A-=0AI appreciate your approach to challenging people lik e me to think through our decisions.- Great forum?- Thanks.=0A=0ATom=0A =0AThomas E. Blejwas=0A12 Via Entrada=0ASandia Park, NM 87047=0A505-286-929 4=0Atomblejwas@yahoo.com ________________________________ Message 2 _____________________________________ Time: 12:52:57 PM PST US Subject: AeroElectric-List: Re: Trim motor speed control From: "Eric M. Jones" EMJ said: An important point of trim motor speed controlling is that the torque should not be reduced when the speed is reduced (in fact, it could go up...but not down). This makes regular voltage controllers undesirable except where torque isn't an issue. BN said: Not true. Speed and torque are not directly related in terms of motor performance. Speed of a motor is a function of terminal voltage AND load on the motor. EMJ said: Thats absurd and examples are so trivial I wont even bother to note one. Besides, I didnt say they were related. The point is that motor speed for trimming and flaps should be reduced at high airspeed to prevent overstressing the pilot and the aircraft. This is common practice. I didnt invent this idea. Furthermore reducing the voltage is a poor mans way to reduce the speed of any actuator. I didn't invent that idea either. BN said: Torque requirement for moving a flight control surface is a function of aero-dynamic loads. For example, the average torque needed to extend a flap from 0-10 degrees is often a small fraction of that required to push it all the way out to 30 degrees. Folks that would like to explore all the details of my assertion are invited to download the data package at http://aeroelectric.com/articles/Motors .... Virtually ALL voltage control methodologies popular with the OBAM aviation community are simply modifications to applied voltage. EMJ said: And they are all wrong. Start with yours. The modern methods for changing motor speed without reducing torque as I saidshould be used. BN said: Assertions for expecting loads on a motor to go UP as shaft speed goes down are incorrect EMJ said: And WHO said that Bob? I said the torque should not be reduced as the motor speed decreasesas is the case if the voltage is merely reduced. EMJ said: The second point is that trim speed should usually be reduced as a function of airspeed. Often this is critical and can give the pilot sudden difficulties. Tee-ing off the pitot line and using the pressure signal is easy to do. BN said: I've designed a number of pitch trim controllers. The first two went on the Lear 55 and the second was a fleet retrofit to the 30 series. I proposed a continuously variable pitch trim rate based on IAS but it proved unnecessary. Trim rates optimized for cruising flight fell into one fairly narrow range, speeds for approach to landing in another narrow range. Turns out that approach: cruise trims in the Lear systems were 4:1 ratio. Use a flaps-not-stowed switch to select high speed and we were done. EMJ said: Whatever... but Im not sure Learjet experience (where the amount of trim motion needed at 500 knots is tiny and the motor are big) is relevant for the stock RVs that have speed/trim problems using reduced voltage at high airspeeds. Thanks...the loyal (occasional) opposition. -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones(at)charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=413380#413380 ________________________________ Message 3 _____________________________________ Time: 01:54:18 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Trim motor speed control At 02:52 PM 11/18/2013, you wrote: > >EMJ said: An important point of trim motor speed >controlling is that the torque should not be >reduced when the speed is reduced (in fact, it >could go up...but not down). This makes regular >voltage controllers undesirable except where torque isn't an issue. Help me out. Are you talking about available torque or demanded torque? In the examples I cited and data plots published, torque demanded is a function of the mechanism being powered. I'm aware of no piece of machinery that demands more torque as the speed is reduced. A speed/torque 'curve' is not really curved but a straight line that depicts motor speed/torque performance based on terminal voltage applied. The 'curve' has downward slope and is set by the motor's internal resistance. Internal resistance limits AVAILABLE torque at that voltage. My assertion is that for any applied voltage you choose, performance of the motor is predictable and easily illustrated by plotting the appropriate 'curve'. >EMJ said: And they are all wrong. Start with >yours. The modern methods for changing motor >speed without reducing torque as I saidshould be used. Okay, suppose the target speed is satisfied by reducing applied voltage to say, 5 volts. Describe the mechanism by which a motor's performance is improved by using one form of voltage 'adjustment' over some other form. I.e., what is the "modern method" to which you refer? >EMJ said: And WHO said that Bob? I said the >torque should not be reduced as the motor speed >decreasesas is the case if the voltage is merely reduced. Okay, you've answered the question. My apologies. Yes, AVAILABLE torque can be degraded to the point where a motor is at risk for stalling at the lower extreme of RPM vs. available torque for the voltage applied. My assertion is that 5 volts average applied voltage produces the same performance irrespective of the mechanism by which that voltage is produced. >EMJ said: Whatever... but Im not sure Learjet >experience (where the amount of trim motion >needed at 500 knots is tiny and the motor are >big) is relevant for the stock RVs that have >speed/trim problems using reduced voltage at high airspeeds. No argument that adjustable trim rates for aircraft with broader operating speeds is a good thing and may apply to airplanes of any size . . . Pilots would like to ask for and get very tiny movements in the trim system at cruise. If the motor speed is optimized for that condition, then it's painfully slow for setting the airplane up to land. The idea that there was value in crafting a continuously adjustable trim rate was rejected as unnecessarily complex. Lear's pilots were quite happy with the 4:1 ratio. Trim motor motion on a Beechjet at Mach cruise needed to be so small that servoing to a speed was impossible. The smallest trim adjustment offered by the autopilot is a mere 133 milliseconds long. The Lear systems were SERVOed speed controllers where motor characteristics did not impact available torque from the motors. Voltage was adjusted to hold target speed irrespective of voltage or load. The controller that finally went onto the airplanes held +/- 1% of target speed over the full range of load, voltage and temperature. In the Lear system, tachometers on the motor shafts provided speed feedback data. The motors used in OBAM aircraft are seldom fitted with such devices. The PM motor CAN be used as it's own tach generator. If you PWM the applied voltage 0ne can sample the Cemf of the motor and use that value to report motor speed to the servo-loop. With a servoed speed control loop, the motor's speed/torque curve no longer defines performance limits at slow speed. The controller drives voltage to maintain target speed even at the maximum expected load. Bob . . . ________________________________ Message 4 _____________________________________ Time: 04:09:36 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Questions about Z-08 At 01:57 PM 11/18/2013, you wrote: >Bob, > >In the postings on running an alternator without a battery, you >suggested I consider your new draft Z-08, which is buried in the >long stream on "EXP 2 Bus workaround." The more I look at Z-08, the >more I like the simplicity. It seems to meet most of my design >goals, but answers to a few questions would be helpful. > >1. What were your criteria in deciding to connect "Engine A" with a >switch (1-3) and "Engine B" through a relay? the wires associated with "A" go mostly cold with opening the battery contactor. The relay is a 'mini contactor' located adjacent to the battery hence the contactor control switch "B" on the panel > By the way, what does the "K2" inside a green hexagon indicate on > the relays? Artifact reference designators not yet germane to the drawing. > >2. You show both A and B connected to the "Motive Power >Distribution Bus" through a single stud and bolt connector. I've >read that lock washers do little to prevent a bolt from >loosening. What do you do to give this type of connection the >reliability one needs for critical components? Or can we? Wouldn't >a different connection for A and B be prudent? The fuseblock connection is a stud that can be secured with a locking nut . . . unlike headed screws that engage threaded holes on popular terminal strips. > >3. With respect to screw type connectors, what about the ground >connection to the engine block? The high vibration of a running >engine would seem to make these especially susceptible to >loosening. What about two block connections going to two brass >bolts through the firewall ground bus, or would this set up an >electrically noisy ground loop? You could use two straps to the engine if you wish . . . but some thread-locker on the single bolt would secure it. Vibration is not an automatic loosening force on a threaded fastener . . . it's mass who's cg is not centered on the bolt that provides loosening torque due to vibration. In this case, a terminal on a soft piece of wire or braid doesn't offer a significant mass. > >4. I found your discussions about single versus dual batteries and >properly maintaining batteries to be interesting. Since, as I >mentioned in an earlier post, I've experienced a car battery >shorting while I was driving. I accurately interpreted the limited >info and stopped the car in a convenient place. Yes, the battery >did not get the kind of attention you have suggested. But will the >next owner of my plane be as conscientious as me? It should be noted in your POH/Maintenance documents. There are numerous critical structures that receive annual and/or pre-flight inspection. Adding the battery(ies) to such a list isn't a far-fetched idea. > So, what is the downside of changing the DC Power Master from > OFF/BAT/BAT+ALT to OFF/ALT/ALT+BAT, assuming that ALT FIELD can be > disconnected if the alternator needs to be disconnected? If I did > so, I would use an MGL Battery Monitor to see both voltage and > current across the battery. With the crowbar ov protection, you could do the DC power switching as a simple two-pole, on-off device. You can pull the breaker to kill the altenrator field circuit. > >I appreciate your approach to challenging people like me to think >through our decisions. Great forum? Thanks. > I'm pleased that you find value in the exercise. I believe that the attentive builder is a much lower-risk pilot because he is privy to things our flight instructors never told us . . . or were included in the cookie-cutter POH. 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