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nuckolls.bob(at)aeroelect
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 Posted: Sat Jan 11, 2014 7:30 am Post subject: How to Toggle Speed Brakes with Momentary On Switch? |
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At 04:04 PM 1/10/2014, you wrote:
| Quote: | Thanks Bob McC. I'm checking with Precise Flight if maintained
input is okay. Seems like it would be.
I didn't know that latching relays would toggle the switch without
changing the polarity at the coil. What does the relay symbol look
like for that?
Does anyone know of a good source for a 24 VDC SPDT Bi-Stable/Latching Relay?
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Don't think you want a bi-stable device. These are MECHANICALLY
bi-stable with two coils and would still require some external
electronics to achieve the P-ON/P-OFF behavior.
I don't think you want a device that can remain in the ON state
after power down. My favorite approach to this design problem
is shown here . . .
http://tinyurl.com/jwzaocy
You need a DPDT relay rated at 1/2 your system voltage. If
you've got a 24v system, then a 12v relay. Select resistors
equal to the resistance of the relay. If power is shut off
the relay relaxes and stays in that state.
When power is applied, capacitor C charges to 1/2 system
voltage through the voltage divider of the two resistors.
Pushing the button discharges the capacitor into the relay
coil causing it to energize and latch through the lower
normally open contacts.
In this state, the capacitor finishes discharging to
zero volts through the paralleled resistor. Pushing
the button again causes the capacitor to act like a
momentary short across the relay coil causing it to
de-energize, opening the latching contacts.
If you HOLD the button closed for an OFF cycle the
relay MIGHT re-energize on the approximately 1/3
system voltage applied to the relay coil . . . which
. . . depending on the relay might cause it to re-close
after the capacitor charges up. If this happens, adjust
the resistor across the capacitor downward until this
phenomenon stops. This generally isn't an issue if you
keep the button pushes short.
You will want to fiddle with this a bit and adjust
R across the capacitor as needed. I've used this
circuit many times . . . most recently to convert
a momentary contact radio remote to Push-ON/Push-OFF
for the driveway light on my garage.
Suggest you purge the term "speed brake" from your
language used to talk about this system. It's
a spoiler system that kills lift . . . designed to
INCRASE rate of descent without materially
increasing forward velocity. A speed brake puts
out DRAG intended to slow the forward velocity.
A pilot flying a Lanceair IVP with Precise Flgiht found
himself on short final to the rocks out in California
a few years ago. Check out the narrative paragraph
3 here http://tinyurl.com/m3zxgpw
His deployment of "speed brakes" in fact increased
his downward velocity. The Precise Flight system
is not a speed brake.
Bob . . .
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Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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| Posted: Sat Jan 11, 2014 8:56 am Post subject: How to Toggle Speed Brakes with Momentary On Switch? |
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Bob;
Respectfully beg to differ on your comment below that bi-stable relays are
dual coil devices requiring some additional electronics to operate with a
single button. While this is correct for SOME bi-stable relays others are
single coil devices simply changing state on each subsequent operation,
while still others are single coil devices which change state when alternate
polarities are applied to the coil. The Omron G4Q-212S-xxVDC series for
example are ones which have a single coil which alternates the contacts each
time the coil is momentarily energized.
I don't disagree with the rest of your comment however, but the question
posed was "How do I do this?" and the single coil bi-stable relay is one
simple inexpensive solution. Granted it is one of many and the plusses and
minuses of whatever method is chosen must be assessed before a "best
solution" is decided upon.
Bob McC
| Quote: | -big snip-
Don't think you want a bi-stable device. These are MECHANICALLY
bi-stable with two coils and would still require some external
electronics to achieve the P-ON/P-OFF behavior.
I don't think you want a device that can remain in the ON state
after power down. My favorite approach to this design problem
is shown here . . .
-another big snip-
Bob . . .
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_________________
Bob McC
Falco #908
(just starting) |
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Valin
Joined: 13 Apr 2010
Posts: 31
Location: Colorado
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| Posted: Sat Jan 11, 2014 9:04 am Post subject: How to Toggle Speed Brakes with Momentary On Switch? |
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Thanks Bob and everyone for your most excellent help. I’m a novice at electrical circuit stuff as you can tell – but, eager to learn and willing to ask questions.
And yes, I agree, “spoilers” is a more accurate term for these lift disturbing devices – I’ll correct that.
Thanks again,
Valin
--
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mmayfield
Joined: 09 Oct 2009
Posts: 40
Location: NSW Central Coast, Australia
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| Posted: Sun Jan 12, 2014 7:14 am Post subject: Re: How to Toggle Speed Brakes with Momentary On Switch? |
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| nuckolls.bob(at)aeroelect wrote: |
Suggest you purge the term "speed brake" from your
language used to talk about this system. It's
a spoiler system that kills lift . . . designed to
INCRASE rate of descent without materially
increasing forward velocity. A speed brake puts
out DRAG intended to slow the forward velocity.
A pilot flying a Lanceair IVP with Precise Flgiht found
himself on short final to the rocks out in California
a few years ago. Check out the narrative paragraph
3 here http://tinyurl.com/m3zxgpw
His deployment of "speed brakes" in fact increased
his downward velocity. The Precise Flight system
is not a speed brake.
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Unfortunately I'm going to have to disagree with Bob here! I'd suggest the term "speed brake" is quite appropriate when looking at how the Precise Flight system is designed to work. so it's no surprise that the company have named them "speed brakes".
Spoilers are designed to reduce lift and moderately increase drag. They do so by creating a controlled stall over that section of the wing immediately behind them. Speedbrakes are primarily designed to increase drag with minimal effect on lift.
On the Boeings and Airbuses I've flown in my day job you'll see the lever which actuates the spoiler panels labelled "speed brake". On the ground, they function as lift dumpers. In the air they function as speed brakes. The function is defined by how many spoiler panels extend and to what degree. On fighter jets the "speed brake" is normally a pure speed brake - panels extending from the fuselage and having minimal to no effect on lift.
Going by the photos on their website, the Precise Flight system is narrow perforated flat plates extending perpendicularly from the wing. I'd suggest this is a classic speed brake design characteristic, not a spoiler design at all, even though it's on top of the wing.
In any case, the increased drag of speed brakes or reduced lift/increased drag of spoilers, can both be used to either increase descent rate or reduce forward speed. The dominant effect on flight path depends entirely on what the pilot does with the pitch attitude of the aircraft. It does not necessarily define whether they're primarily "spoilers" or "speed brakes".
Food for thought. 
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Mike |
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Mon Jan 13, 2014 4:48 pm Post subject: Re: How to Toggle Speed Brakes with Momentary On Switch? |
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Switch Design 101:
Each switch is to be labled describing its function. The condition of the switch must be apparent from its mechanical position, whether or not power is applied.
Airplanes have no momentary bi-stable switches.
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Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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