Linear Actuator

[skippydiesel]

Happy New Year to the Forum Brains Trust

 

I have had bad luck in the use of linear actuators, to operate my cowl flap. The first one lasted about 30 hrs before failing to retract, the second an hour.

 

I have been using the following (12V variant) supplied by CarryMart.

 

https://www.carymart.com/21mm-dc-6v-12v-24v-micro-electric-linear-actuator-max-thrust-42-lbs-188n-19kgs-p-2484.html

 

I was attracted to CarryMart because they have comprehensive specifications for their products (unlike identical looking ones on eBay). The specifications of the above unit fit my application.

 

FYI: By the time a received the actuator, it cost about AU$100,  x4-5 the price of an eBay similar product and it took 30 days from order to dispatch and another 10 days to arrive. Comprehensive specifications & cost, are not a reliable indicator of a quality product/service.

 

I am hoping some of you may have been down this track and can recomend a supplier of reliable actuators.

 

😈

Edited Wednesday at 02:54 AM by skippydiesel

[RFguy]

How much thrust is required when airborne at Vfe ? - you need to know this. Sonex aircraft will know.

how much room do you have ?

did you get a ball screw, rack or lead screw type ?

[facthunter]

There's not a great deal of force required.. Why have an actuator? Cable or rod with fail safe to OPEN. Spring + air load.  Nev

[skippydiesel]

59 minutes ago, RFguy said:

How much thrust is required when airborne at Vfe ? - you need to know this. Sonex aircraft will know.

how much room do you have ?

did you get a ball screw, rack or lead screw type ?

Hi RF,

I thought that supplying the web page would have given you all the info. you need.

 

I am not well versed in all of the options you have listed - short answer - don't know   suspect "ball screw"

 

The units(s) I selected appear to have all the characteristics I need to do the job - they just don't last. Both failed in the open position, which may be a good thing.

 

On dismantling the first failure, it seems that the electronic limit switch failed - which in my understanding meant that the electrical polarity could not be reversed ie no retract action. The electric motor ran perfectly when connected to 12V. The screw mechanism extended retracted when a screwdriver used to provide rotational force. Circuitry so small -  beyond my capacity to repair.

 

They claim a near 20kg extending force, which should be more than enough for a small cowl flap.

 

Sonex don't fit cowl flaps as part of their plans/kit offering - previous non conforming enquiries have not gone well.😈

[facthunter]

Some DC3s had the cowl flaps removed but you then can't look after the engines temps as well . OR reduce drag when the motor is feathered. Why design with electro/mechanicals that can fail Failing closed and continued flight may be compromised

[RFguy]

Sean, as you are aware, anything you buy on ebay from China- you got to plan for a failure in flight, but you know that.

Check if they live up to their specs etc. if it says 20kg, try 20kg, then try 30kg. and try pulling as well as pushing...they will be different.... and see how much there is in hand, and be sure to do it at 12V, not 13.8V etc on the bench , as  wire volt drops are not insignificant near stall. 

You want about 2:1 at least on whatever it needs. Can you monitor the DC current  during deployment at Vfe with the wing loaded ???

 

In the datasheet

- notice the "Duty Cycle: 10%" - you should treat that as a red flag- that tells me the motor is very underdone for the job- avoid or substantially lower the load. 

-" Full load current: 0.2~0.3A at 12V" . you need to measure this at Vfe in flight (with the wing loaded) and see what current you are pulling. SUggest at Vfe,  no more than 50% of full load current for whatever size you choose. 

- Note  the very important spec "and the pulling force is less than pushing force." - the spec is pushing force (19kg). the pulling force might be 1/2 or 1/4 etc ......

 

 

Edited Wednesday at 06:07 AM by RFguy

[facthunter]

Every light twin I've flown is direct cowl flap action. You just select Close and its closed. No waiting and no need to check if it feels normal.. Larger stuff is hydraulic actuated. with a closed Open and Trail position and inching up  or down in between. In heavy rain you are very busy when there's 4 of them to look after and carb heat as well. Every time you reposition the cowl flap the carbheat has to be readjusted as well.. In addition there's {Prop antiicing. Glycol and alcohol down the Carb airscoops as well and Rubber boots that cycle near the leading edges. IF you aren't really careful with them they Just raise the ice a bit and do little else. Read "Fate is the Hunter" . Nev 

[Red]

Vibration? 

[skippydiesel]

13 hours ago, Red said:

Vibration? 

???????

Please explain 😈

[Red]

14 minutes ago, skippydiesel said:

???????

Please explain 😈

You mentioned that the failure involved the electronics or a limit switch, both possibly susceptible to vibration damage

 

[RFguy]

those cheap chinese actuators are for things like kitchen robots, not airplanes....

[Marty_d]

There was an interesting cowl flap shown somewhere here, French bloke had it on top of his cowl to release heat while on the ground.

From memory it was hinged forward of the midpoint of the flap and lightly sprung, so at low speeds it would open but any wind pressure would close it.

[RFguy]

can we get back to the topic  ?

[Marty_d]

The topic is linear actuator for a cowl flap.

Suggesting that there are other ways to actuate a cowl flap is not really off topic.

[RFguy]

Oh , not the flap ? 

Doh I thought it was the FLAP actuator.

OK. 

"disregard last and all previous " 

It seems I cannot read.

Edited Wednesday at 11:16 PM by RFguy

[facthunter]

Surely NOT needing one should be part of the discussion.  Why do we always want to complicate things? Attend to the Nut holding the joystick    Do you WANT to fly or just play with gadgets and scare yourself.?   There's a safety aspect to this failing. ( including distraction).  Nev

[planedriver]

Simplicity is the essence of reliability, generally.

[skippydiesel]

Why did I decide on a linear actuator to operate my Cowl Flap??

 

Perhaps at odds with the concept of mechanical/traditional operation of a small aircraft cowl the linear actuator present's as an easier/simpler way of the pilot opening/closing the flap.

I can just hear you now - Naa! pull/push cable (traditional) must be the simplest.

 

The traditional system would require;

• Another hole in my firewall
• For intuitive action (In for Close/Out for Open) a direction reversing cam would have to be made/purchased/mounted - not simple!
• A suitable location, on panel, for the Cowl Flap button would have t o be found (Sonex panel real estate in short supply).

 

Reliability - Almost failure proof.

 

Linear Actuator;

• Electrical wires to control/energise Actuator pass through existing firewall hole - no modifications.
• Two way toggle switch on instrument panel, Up for Close / Down for Open - small LED to one side of switch red for down/green for up.
• No issues with working out cam rotation/arc ratio to flap movement. Actuator extension movement must be matched to Flap movement  - not hard.
• Linear Actuator - looks like a small hydraulic ram - is mounted in the exit air hole at one end  & on cowl flap at other. System works very well, that is until Actuator stops working.

 

Reliability -

If I can find a suitable Actuator (hoping you can help) the system should be reasonably safe.

Fail open  - There is a small amount of extra drag/reduced/ engine systems may stay cooler than optimum performance - barely noticeable.

Fail closed - There is the potential for increased engine system temperatures during Climb. The pilot may notice LED stayed green - abort TO. If in Climb should be able to manage this by reducing engine power, leaving prop pitch in Fine and returning for a landing.

 

In the absence of a suitable Linear Actuator, I think I will move to a very simple system - Summer: Exit Ait Open / Winter: Exit Ait Choked (partially closed)

 

[skippydiesel]

18 hours ago, RFguy said:

Sean, as you are aware, anything you buy on ebay from China- you got to plan for a failure in flight, but you know that.

Check if they live up to their specs etc. if it says 20kg, try 20kg, then try 30kg. and try pulling as well as pushing...they will be different.... and see how much there is in hand, and be sure to do it at 12V, not 13.8V etc on the bench , as  wire volt drops are not insignificant near stall. 

You want about 2:1 at least on whatever it needs. Can you monitor the DC current  during deployment at Vfe with the wing loaded ???

 

In the datasheet

- notice the "Duty Cycle: 10%" - you should treat that as a red flag- that tells me the motor is very underdone for the job- avoid or substantially lower the load. 

-" Full load current: 0.2~0.3A at 12V" . you need to measure this at Vfe in flight (with the wing loaded) and see what current you are pulling. SUggest at Vfe,  no more than 50% of full load current for whatever size you choose. 

- Note  the very important spec "and the pulling force is less than pushing force." - the spec is pushing force (19kg). the pulling force might be 1/2 or 1/4 etc ......

 

 

Thanks for all that RF

 

Duty Cycle: Not sure how this translates in this context. The flap goes from fully closed/open in about 1-2 seconds. Current only flows between fully closed/open when limit switch activates.

 

I thought a claimed 19 kg extension (pushing) force would be many times the effort required to open the flap ie a conservative capacity. Closing the flap (pulling force)will be assisted by air pressure, so much reduced effort required.

 

Linear Actuator RS! so not able to perform any tests at the moment - do you know of a quality Linear Actuator supplier?😈

 

[facthunter]

How do you know where the flap actually IS (position wise).? You are also relying on limit switches.  WHY have a system where you NEED electric power?  Nev

[onetrack]

Direction reversing cam?? A complex device? Surely you're joking? It's normally referred to as a "direction reversing linkage" and I could knock up a simple one for you, in probably less an hour.

 

Basics of Linkages - fundamentals of linkages.

WWW.FIRGELLIAUTO.COM

---

When two or more levers are interconnected, they form what is called a linkage. A linkage is a mechanism that transmits motion and force between the levers. By joining levers together, we can create a variety...

 

(Incidentally, the above site contains a link to a sales page for electrically-operated linear actuators, that appear to meet your build quality requirements)......

 

Bullet Series 23 Cal. Linear Actuators

WWW.FIRGELLIAUTO.COM

---

The Bullet Series 23 Cal. linear actuators are made from SUS304 stainless steel. Available in 12V or 24V & in various stroke lengths.

 

Edited Thursday at 01:02 AM by onetrack

[facthunter]

The common windscreen wiper is a reversing cycle with a fixed rotation motor. but all these things can fail. Would you accept your mixture control being operated this way, or any other for that matter.. Nev

[skippydiesel]

21 minutes ago, onetrack said:

Direction reversing cam?? A complex device? Surely you're joking? It's normally referred to as a "direction reversing linkage" and I could knock up a simple one for you, in probably less an hour.

 

 

Thanks for the correction in terminology.

 

".......I could knock up a simple one for you in probably less than an hour."

 

As for simple - perhaps I am overcomplicating, the system, in my mind;

 

Ratios to be considered - Input length of actuating button movement : reversing arm linkage length & location of input/output cables : flap movement

• Acquisition of suitable button & double acting cable system
• Will button fit in switch location on panel
• Measure button movement 
• Dont have a reversing linkage, but like you could probably make one. Unlike you would take several hour/days (after acquiring materials) & include method & location of mounting.
• Mounting location may take several days to sort out, IF practical at all.
• I guess the position of the firewall hole, for the cable to Flap,  would arrive as part of installation process - not happy with the idea of additional holes in firewall.
• I do have a flap that is capable of moving through 90 degrees (I will limit to Max 45 degrees) - a suitable mounting for the actuating mechanism to attach, would have to be fabricated

Simpler (to me) to mount a two position reversing polarity switch (JayCar)

Run a suitable 12V wire to  power source (via fuse JayCar) and to Linear Actuator (have wire on hand)

Mount Actuator (seeking advice on supplier of reliable unit) such that it will open & fully close Cowl Flap

What's not to like???

 

Thanks for the "The Bullet Series 23 Cal. " suggestion from  Firgelli - I had looked at these, unfortunately the closed length is around double what I require (see opening specifications). IF the Bullet is the only viable option, may have to reconsider existing mounting system. Firgelli used to do a much shorter/smaller range of Actuators (have one on my desk but seem to have dropped them). Firgelli (Canadian) likly have their actuators made in China & charge  about x 10 the price of the very similar looking eBay offerings (see my opening comments).

 

😈

[BrendAn]

i think nev has hit the nail on the head. simple is best. a cable or rod is nearly foolproof and you don't have to wonder if your chinese electrics are going to fail.

 

[facthunter]

Why deny an incremental adjustment possibility as well.  Just a few notches on a rod. Electric wires need grommets in firewalls and the insulation can burn.. How's your throttle linkage done? Do it the same way.  Nev