Electric Retractable Step Conversion

[takair]

Thought I would start a new thread on an old subject, the Retractable Step on our vintage Mooney’s.  We all know that they are worth a couple of knots when retracted and make boarding a little easier.  However, there are reports that they have been getting more difficult to maintain, between difficulty getting the pneumatic bellows or cables binding or breaking for the crank style.  Because of some peer pressure, I tackled an electric conversion.  My goals were to make it weigh no more than the original installation, be easy to install and maintain and to be reasonably priced.  As mentioned in another thread, I feel like I am close to meeting these goals.  My 1964 E model had the original crank style.  The actuator I used has 200mm travel and about 18 lbs of force.  To get the required travel of just over 15”, requires use of a pulley mechanism, similar to the way the pneumatic step works.  In the end, the actuator is modified with a relay circuit for automatic reversal and some hardware to mount the pulley and to mount the actuator to the aft bulkhead.  The actuator has built in limit switches.  I still have a little work to do on the up-limit, as there is a little dithering which eventually self clears.  The load near the top of retraction is quite significant due to the pulley loads and the down-assist spring load.  I am considering a stronger actuator, but it is much slower.  I suppose the only time the speed would be important is in an emergency, and in those cases, the step is a minor convenience only.  

I reuse most of the existing hardware, with the exception of the actuator, one fabricated cable and the addition of a single down-assist spring.  Repeat installations (not including build up of the actuator) would be about three hours if you have electrical power available aft (I have aft mounted battery)

I installed this as a minor alteration. I made the assessment based on my previous work with my ACO on Auto-Lean and Auto-Heat.  Mileage may vary with your own IA or FSDO.  If there is enough interest, I would be willing to pursue a PMA kit with my ACO, eliminating any legality questions.  Would want to do a local pneumatic step aircraft as well.  For DIY folks, I am also happy to talk you through your own buildup, just contact me via Email. 

Video can be seen here:  https://youtu.be/5vfc8iPqxwM

Actuator with step down

Actuator with step up, cable is new, trunbuckle is re-used.

 

[aviatoreb]

I love that - I wish I could install that in my Mooney.

[David_H]

Nice.

[yvesg]

How would this behave if the step would have some ice mid point that would jam it in the middle. Is there any current limit protection? Having a fuse would protect however would need to be replaced quite often. This event is fairly common at our latitudes. The vacuum system does not suffer when it happens.

Yves

[aviatoreb]

Just now, yvesg said:

How would this behave if the step would have some ice mid point that would jam it in the middle. Is there any current limit protection? Having a fuse would protect however would need to be replaced wuite often. This event is fairly common at our latitudes. The vacuum system does not suffer when it happens.

Yves

Good point.

Sometimes I get tempted to have my step removed.  Haven’t done it yet though.  Simpler than a retraction system but I love that device.

 

[David_H]

2 minutes ago, yvesg said:

How would this behave if the step would have some ice mid point that would jam it in the middle. Is there any current limit protection? Having a fuse would protect however would need to be replaced wuite often. This event is fairly common at our latitudes. The vacuum system does not suffer when it happens.

Yves

I wonder if using some sort of pinion and slip-clutch arrangement would work? Of course that increases costs and reduces reliability.

[yvesg]

The system I would want is something that would try the retraction a couple of times... and if too much current is senced, would just stop moving anything until the next flight, or some action from the pilot that would request trying again.

Yves

[takair]

3 hours ago, yvesg said:

How would this behave if the step would have some ice mid point that would jam it in the middle. Is there any current limit protection? Having a fuse would protect however would need to be replaced quite often. This event is fairly common at our latitudes. The vacuum system does not suffer when it happens.

Yves

I’ve not run into that before, but it would not like it.  Is it possible the oil or grease is just so congealed that the vacuum can’t muscle through?  Mine had many years of gunk and does make it more difficult to move.  In my experience, if the the step is that iced up, then the plane was too iced up to fly as well.  Depending on the actuator I end up with and the amount of ice, it would either muscle through, blow a fuse or pop a breaker (if you opt for that) or break the actuator.  As someone suggested, adding smarts or clutch would work but adds cost.  I suppose I could also add a self resetting thermal fuse, which may not cost that much, will consider that.  

[takair]

4 hours ago, aviatoreb said:

I love that - I wish I could install that in my Mooney.

Seems to me that it could be retrofitted using salvage parts.  With this set up, it would be even easier than before.  

 I always wondered why Mooney moved away from it.  There is a notable speed difference...even trim difference.  Granted, the retractable tubes are big and unaerodynamic.  Has anybody ever measured a speed difference by removing the fixed step?

[David_H]

6 minutes ago, takair said:

I’ve not run into that before, but it would not like it.  Is it possible the oil or grease is just so congealed that the vacuum can’t muscle through?  Mine had many years of gunk and does make it more difficult to move.  In my experience, if the the step is that iced up, then the plane was too iced up to fly as well.  Depending on the actuator I end up with and the amount of ice, it would either muscle through, blow a fuse or pop a breaker (if you opt for that) or break the actuator.  As someone suggested, adding smarts or clutch would work but adds cost.  I suppose I could also add a self resetting thermal fuse, which may not cost that much, will consider that.  

Using a safety fuse would likely be the least expensive and most durable solution. Having an in-line fuse would help with approval... and makes a lot of sense.  

[takair]

11 minutes ago, David_H said:

Using a safety fuse would likely be the least expensive and most durable solution. Having an in-line fuse would help with approval... and makes a lot of sense.  

I currently have an in-line fuse just not resettable.  You can hear the step moving up, so it might be apparent if it didn’t make it all the way up. Will look at a safety fuse.  Still need to get some of these loose ends tightened up, all of this input is helpful.

[N601RX]

If your having trouble getting a actuator that will fit and still have the necessary stroke look at using a small fractional HP dc motor with a small worm drive gearbox.  The worm drive will not move or backdrive when power is removed. Put a toothed belt pulley on the output shaft and use a length of belt to pull the step up and down and remove the spring also. 

[David_H]

18 minutes ago, takair said:

I currently have an in-line fuse just not resettable.  You can hear the step moving up, so it might be apparent if it didn’t make it all the way up. Will look at a safety fuse.  Still need to get some of these loose ends tightened up, all of this input is helpful.

Sensata makes self-resetting fuses for hermetic compressors. I'm unsure how far they go down in size but I expect the costs are relatively low since they're mass-produced for a commodity-based market. They're also tested very rigorously for performance.  

The Klixon line comes to mind... but I don't know how far down the currents go in that line. They probably have another product line that would work better.

...Just something to think about.

 

[takair]

10 minutes ago, N601RX said:

If your having trouble getting a actuator that will fit and still have the necessary stroke look at using a small fractional HP dc motor with a small worm drive gearbox.  The worm drive will not move or backdrive when power is removed. Put a toothed belt pulley on the output shaft and use a length of belt to pull the step up and down and remove the spring also. 

Thanks.  The one I am using uses a very small motor driving a jack screw,  under 1amp draw and less than 0.5lb.  I think I’m close, just trying to decide between the slower, but high torque unit or the one I have, which is adequate, but needs to be perfectly rigged.   The belt would certainly be another good  alternative.

[yvesg]

1 hour ago, takair said:

  In my experience, if the the step is that iced up, then the plane was too iced up to fly as well.  Depending on the actuator I end up with and the amount of ice, it would either muscle through, blow a fuse or pop a breaker (if you opt for that) or break the actuator.  As someone suggested, adding smarts or clutch would work but adds cost.  I suppose I could also add a self resetting thermal fuse, which may not cost that much, will consider that.  

There are at least 2 flights every winter for me where the step is iced up but the rest of the airplane is OK to fly. I have wing , tail covers, and canopy covers that protect from elements and when removed, there is rarely any need to thaw any part. When the step is iced up I am  usually telling myself... it will not go all the way up... and go do my flight. If it would be electric I would want something very safe like what I get with vacuum.

Yves

[aviatoreb]

Ideal would be a hand power retractable step with a lever accessible at the pilots seat. Rube Goldberg fans go to work!

Edited December 31, 2017 by aviatoreb

[Heloman]

Nice for the ever increasing number of people who want to remove their vacuum system.


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[takair]

3 hours ago, aviatoreb said:

Ideal would be a hand power retractable step with a lever accessible at the pilots seat. Rube Goldberg fans go to work!

Not sure which emoji to use, but you are describing what I just disabled.  

[takair]

15 hours ago, yvesg said:

There are at least 2 flights every winter for me where the step is iced up but the rest of the airplane is OK to fly. I have wing , tail covers, and canopy covers that protect from elements and when removed, there is rarely any need to thaw any part. When the step is iced up I am  usually telling myself... it will not go all the way up... and go do my flight. If it would be electric I would want something very safe like what I get with vacuum.

Yves

Working on a solution for this. You have a good point.  Feels like fuse or breaker alone are not optimal.  

[N601RX]

A dc drive with encoder feedback would normally be used to detect a stalled condition, but it would add complexity and cost. A time delay relay would likely provide enough protection  for a stalled condition. Just figure out how long a normal stroke takes and add a few seconds to that. The switch on the panel would trigger the relay and it would stay on for X seconds. 

[N201MKTurbo]

There are industrial automation electric linear actuators available that have all the smarts already installed. They are more expensive, but probably a cleaner setup in the long run. The only downside is they are almost always 24 VDC so 12 V planes would have a problem.

[carusoam]

experience from the GM world...

 motor with a worm drive actuated a nylon gear on the headlight door...

Plan A: the motor current is sensed. At the physical limit, the current spikes as the gears bind. The controller senses the amp spike and turns off the current...

Plan B: when Something fails to spike the current... the current gets shut off either way after about 15 seconds...

If there is a controller where you can add a timer to cut the power...

PP thoughts and borrowed automotive ideas only...

Best regards,

-a-

 

[takair]

36 minutes ago, N201MKTurbo said:

There are industrial automation electric linear actuators available that have all the smarts already installed. They are more expensive, but probably a cleaner setup in the long run. The only downside is they are almost always 24 VDC so 12 V planes would have a problem.

There are, but the ones I have found are very heavy and/or expensive.  

[N201MKTurbo]

Some questions:

What happens if it stops in the middle of the travel and someone steps on the step? Will the cables support the person? Will it drive the stage down till it hits the mechanical stops? What happens if the step is down and someone pushes it up? Will all the cables come off their pullies and get jammed up?

We build these kind of things at work and do FMEAs and have to ask all these questions.

[aviatoreb]

Seems cheaper and simpler just to cut the darned step off.