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jdubner
Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR
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 Posted: Sun Mar 03, 2019 10:37 am Post subject: Landing gear electric actuator circuit |
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My Long-EZ nose gear uses an electric actuator. The actuator does not have internal limit switches but I have added them and use them to control a pair of relays (see schematic: http://forums.matronics.com/files/nose_gear_actuator_108.pdf). (The electrical load is up to 10A -- too much for my limit switches -- hence the relays.)
I would like to incorporate a backup electrical extension system that would eliminate any single point of failure (other than the actuator itself) and my attempt is shown in the schematic. It's close, but not exactly failure-proof because it adds the backup switch contacts as a single point of failure.
Can anyone suggest a better scheme?
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| Description: |
| Nose gear electric actuator circuit. |
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sun Mar 03, 2019 12:09 pm Post subject: Re: Landing gear electric actuator circuit |
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Those limit switches are suitable for 10 amps. No relays are necessary. A snap
action switch can easily carry the same DC current at 12 volts DC as it can at
125 volts AC, which is 15 amps in this case. This is true because the DC
voltage is only 1/10 of the AC voltage. If you do not believe it, ask Bob N. or
call Moujen USA and ask them what current the rating is at 12 VDC. Do not
tell them that you will put the switches in an airplane. If they ask, it is proprietary.
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Joe Gores |
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jdubner
Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR
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| Posted: Sun Mar 03, 2019 6:54 pm Post subject: Re: Landing gear electric actuator circuit |
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| user9253 wrote: | | ...call Moujen USA and ask them what current the rating is at 12 VDC. ... |
I looked at the Moujen spec for the MS2 series switch (available here: http://www.moujenswitch.com/products/mj2/mj2_characteristics.htm) and decided it wasn't suitable for 10A operation at 12VDC in a critical application.
If Bob or anyone has better data, I'd be glad to look at it.
But I don't think that substituting the switches for the relays would solve my problem: I need an alternate electrical method of gear extension if something in the circuit (but not the actuator) fails.
A separate switch wired to the battery in the correct polarity to only lower the gear seems reasonable. But the motor is kept shorted by the relay contacts in at least one failure mode of the circuit so the separate switch must interrupt the wiring to the motor which adds a whole new failure mode.
If MIL-HKBK-217 has taught us anything, it is that adding components decreases reliability 
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Mon Mar 04, 2019 10:22 am Post subject: Re: Landing gear electric actuator circuit |
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Would this propeller current limiter be suitable for shutting off the landing gear
motor when fully extended or retracted?
http://www.matronics.com/forums/viewtopic.php?t=101826
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Isn't a pilot more likely to fail than a switch or relay? There is a saying that
there pilots who have forgotten to put the gear down and pilots who will.
How about a circuit that will automatically extend the gear?
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gilles.thesee(at)free.fr
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| Posted: Mon Mar 04, 2019 5:20 pm Post subject: Landing gear electric actuator circuit |
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Le 04/03/2019 à 19:22, user9253 a écrit :
| Quote: | How about a circuit that will automatically extend the gear?
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Joe and all,
This has been done before.
Some years ago I flew a PA28 with a special probe to automatically
extend the gear below a certain airspeed. Due to nuisance gear
extensions, an AD (or was it just an SB ?) had been issued to disable
the device.
Some airplanes have a horn going off any time the throttle is pulled to
idle with the gear up, etc.
The horn could be a good idea - but of course it will sound anytime you
reduce power in flight...Unless you add an airspeed sensor (how do you
establish the speed threshold ?), ground height sensor...
I'd personnally beware of any device trying to do my job in my place :
what when flying an airplane with *no* gear auto-extender ?
--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr
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yellowduckduo(at)gmail.co
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| Posted: Mon Mar 04, 2019 6:26 pm Post subject: Landing gear electric actuator circuit |
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On 04/03/2019 8:08 PM, GTH wrote:
| Quote: |
Le 04/03/2019 à 19:22, user9253 a écrit :
> How about a circuit that will automatically extend the gear?
>
Joe and all,
This has been done before.
Some years ago I flew a PA28 with a special probe to automatically
extend the gear below a certain airspeed. Due to nuisance gear
extensions, an AD (or was it just an SB ?) had been issued to disable
the device.
Some airplanes have a horn going off any time the throttle is pulled
to idle with the gear up, etc.
The horn could be a good idea - but of course it will sound anytime
you reduce power in flight...Unless you add an airspeed sensor (how do
you establish the speed threshold ?), ground height sensor...
I'd personnally beware of any device trying to do my job in my place :
what when flying an airplane with *no* gear auto-extender ?
I don't like giving any control over to electronic devices but I
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consider warning devices to be extremely valuable. The challenge is that
they must not nuisance trip which trains us to ignore them. These days
it is relatively cheap to incorporate ground sensing devices or gps
altitudes (with a database) into the warning logic.
Ideally we'd never hear such warnings and would not count on them
whether the aircraft had such a device or not. Interesting that the
same concerns are very applicable to current automotive systems.
philosophy according to Ken...
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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
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| Posted: Mon Mar 04, 2019 6:42 pm Post subject: Landing gear electric actuator circuit |
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Given the aerodynamics today, why bother with folding gear? Good wheel
pants and gear fairings today have the speed penalty down to around 5
kts at typical general aviation speeds. I had a Mooney that would do
150-155kts on 10 gph. I now fly an RV-10 with fixed gear that does the
same speed on the same fuel flow (and faster if I want to burn more
fuel). It has bigger fuselage/cabin and same number of seats and useful
load as the Mooney, with bigger engine..so not truly apples to apples.
Just the speed gains may not be worth the cost/risk. JMHO after 18 yrs
of flying retractable, without a mishap...other than the gear mechanism
failing on different brand, but managed to still land it on the wheels.
On 3/4/2019 7:24 PM, C&K wrote:
| Quote: | > Le 04/03/2019 à 19:22, user9253 a écrit :
>> How about a circuit that will automatically extend the gear?
|
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Kelly McMullen
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argoldman(at)aol.com
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| Posted: Mon Mar 04, 2019 8:14 pm Post subject: Landing gear electric actuator circuit |
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The Bellanca super Viking also had a mechanism called auto-axion which would lower the gear when the airspeed dropped. Below 90 mph. It worked well and only became a problem when practicing stalls. We would, from my memory, jjust pull the breaker to defeat it. It was a simple pitot pressure activated switch. The arrow was more complex and had its own pitot tube mounted near the pilot’s window. As mentioned before it was less than successful. The bellanca system, on the other hand , was successful.
We of the canard persuasion do have an option of automatic nose gear extension based on pitot pressure. It contains some logic to enable defeat when desired.
The main problem I see with any auto system is that a pilot may become less than diligent and rely on the security of the automation
Rich
Sent from my iPhone
| Quote: | On Mar 4, 2019, at 7:08 PM, GTH <gilles.thesee(at)free.fr> wrote:
time
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Fri Mar 08, 2019 6:50 am Post subject: Re: Landing gear electric actuator circuit |
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Below is a circuit to lower or raise a landing gear or to control the direction of any small PM DC motor.
The toggle switch controls the motor direction of rotation.
The relay turns the motor on and off.
The limit switches open the relay circuit at end of travel, thus stopping the motor.
Diodes across limit switches allow the current to reverse direction when a limit switch is open.
On the right side, there is an optional emergency switch to lower the gear.
Back to back zener diodes across the relay coil limit inductive voltage spikes.
Disclaimer: The circuit has not yet been proven to work.
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