REFLECTOR: speed brake ramblings

[michalk]

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.
>>>>