REFLECTOR: speed brake ramblings

[Jim Sower]

I've already got a 3-pos UP-OFF-MomentaryDOWN switch for my belly 
board.  All I need to do is beef it up a bit and I'll be there.  NO 
extra wire, technology, transducers, failure modes.
I like it simple ... Jim S.

michalk wrote:

> Right.
> But in my last paragraph I addressed your point.  A DPDT switch would 
> be needed, increasing the complexity.  The speedbrake system might 
> behave something like this, using a DPDT switch, wired such that one 
> end reversed the polarity:
>
> case1: 0 to 75lbf: switch is engaged such that correct polarity is 
> applied.
>
> case2: 75 to 100lbf: switch disconnects power to speedbrake.  Of 
> course what happens if you want to retract?
>
> case3: over 100lbf, the switch reverses the polarity.  But what 
> happens if you are commanding a retraction?  It would go the wrong way.
>
> Like I said, the SPST is easiest, the DPDT auto-retract would take 
> more thought.
>
> Jim Sower wrote:
>
>> But it wouldn't prevent you from over speeding the speed brake if it 
>> were already deployed, or retract it automatically when limits were 
>> exceeded?
>>
>> michalk wrote:
>>
>>> The diode would allow you to retract the speedbreak if the cutout 
>>> switch were engaged.
>>>
>>> Jim Sower wrote:
>>>
>>>> <<flip the switch to extend the board, and let the cutout switch 
>>>> decide when to extend it some more What would happen if you were 
>>>> cruising at low IAS (say at 15k'), extended the board, dumped the 
>>>> nose and accelerated to some point beyond the limit?  Sounds like 
>>>> your scheme would prevent you from extending at excessive speed, 
>>>> but not be able to retract it if the speed became excessive after 
>>>> it was already extended.
>>>> Am I reading you right? ... Jim S.
>>>>
>>>> michalk wrote:
>>>>
>>>>> Incrementally extending...
>>>>>
>>>>> I was just thinking about this on your first post.
>>>>>
>>>>> It seems it would be quite simple to add a force actuated switch 
>>>>> that would not exceed some limit.
>>>>>
>>>>> I do not remember what the current actuators are rated for, but 
>>>>> let's assume they are 100lbs.
>>>>>
>>>>> Make a collar that fits around the keel end of the actuator, with 
>>>>> a spring with the appropriate K factor to move .25 inches when 
>>>>> 75lbs is applied.  Put a switch in series with the actuator, with 
>>>>> a diode so that the switch is bypassed if you want to retract 
>>>>> while the cutout switch is engaged.  Normal operation would bypass 
>>>>> the diode (no voltage drop), when the cutout switch is not engaged.
>>>>>
>>>>> Want to go down? just flip the switch to extend the board, and let 
>>>>> the cutout switch decide when to extend it some more.  Just don't 
>>>>> exceed the limits by increasing your airspeed.
>>>>>
>>>>> I suppose one could get fancier with a DPDT switch that would 
>>>>> retract it if the forces get too high, but I haven't put enough 
>>>>> brain cells into that problem.
>>>>>
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