Today's Message Index:
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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
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| Subject: | 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%. We got off to a
slow start this year with the network DNS issues on the kickoff weekend, so please
take this opportunity to show your support for the Matronics Lists and Forums!
Please remember that it is *solely* your direct Contributions that keep these Lists
and Forums up and running and most importantly - AD FREE! If the members
don't want to support the Lists directly, then I might have to add advertisements
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that. I really like the non-commercial atmosphere here and I think that a lot
of the members appreciate that too.
Please take a moment to make a Contribution today in support of the continued ad-free
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Or, drop a personal check in the mail to:
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I want to send out a word of appreciation to all of the members that have already
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Matt Dralle
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Message 1
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| Subject: | 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
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| Subject: | Re: Trim motor speed control |
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
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| Subject: | 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
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| Subject: | Re: 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.
Bob . . .
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