Linear Actuator

[onetrack]

Skippy, did you do any failure analysis on your two failed actuators to determine the exact cause of failure? You seem to blame it on cheap Chinese construction, but it may have been caused by excessive loading, or a design fault in the actuation movement, that can only be discovered by careful examination, and a reconstruction of the failure sequence. Failure analysis is an entire field in itself.

[onetrack]

deleted - double post

Edited January 8 by onetrack

[Geoff_H]

One way to check is if you have an actuator that is able to be used is to put a multimeter ( or resistive load with voltmeter) i series with the actuator and get a passenger to record the current, or use a recording multimeter.  Use this amperage to check against the manufacturer details.  Next thing to do is look at the voltage drop owing to current drawn in cabling.  Low voltage can burn out a motor.   What size cable are you using?

 

[Geoff_H]

I just looked at the specs of the actuator that you quoted early in the chat.  In my 'guess from experience " the 10% duty cycle indicates a current restriction.   The force available seems low,  particularly in flight.  The dynamics of how the actuator forces the flap could produce a larger force than the quoted figure, try the current test on the ground,  then loan flap with hand and see what happens.  I am like a pig in mud, I did this style of investigation before I retired,  loved the work, these days I just wish that I was not retired.

[facthunter]

The answer/solution  is worse than the original problem.  Manual actuation gives you "Feel" so the linkage doesn't get destroyed by something getting misaligned etc.  The controls on a DC-9 are manual by servo tabs. Ona DC 4  they are just manual Max wt 72,000 Lbs.  You are talking about a single cowl flap on a very LIGHT plane.   Introducing risks where none needs to be. Weight Costs Complexity and unreliability. BAD design and design philosophy.   Nev

[Blueadventures]

22 minutes ago, facthunter said:

The answer/solution  is worse than the original problem.  Manual actuation gives you "Feel" so the linkage doesn't get destroyed by something getting misaligned etc.  The controls on a DC-9 are manual by servo tabs. Ona DC 4  they are just manual Max wt 72,000 Lbs.  You are talking about a single cowl flap on a very LIGHT plane.   Introducing risks where none needs to be. Weight Costs Complexity and unreliability. BAD design and design philosophy.   Nev

When I did my rudder trim bungee I settled for the KISS manual principle with a sort of jack screw setup.  Teleflex cable and a threaded wheel that moves the inner cable in or out with the distance from one turn being the thread pitch.  Works a treat for the required movement.  Could have fitted a trim servo and switch but settled for the simple and practical manual turn method.  The cables come in 1, 2 or 3 inch movement.

 

Edited January 8 by Blueadventures

[Geoff_H]

If you want simple automatic and probably the lightest solution use an expanding wax (as per water thermostat technology).  It is used in the cooling flap of a rear engined air cooled motor vehicle, a Fiat if my memory serves me right.  Just an actuator "piston" rod with the appropriate wax inside. Simple.

[Geoff_H]

Skip, the maximum operating temperature of your actuator is 85deg C.  Maybe that's your problem. 

[skippydiesel]

1 minute ago, Geoff_H said:

Skip, the maximum operating temperature of your actuator is 85deg C.  Maybe that's your problem. 

I doubt if it ever got above 60C . This is the max under cowl temp recorded after flight/hot day.

[Geoff_H]

But the air that goes out the flap maybe aitr that has just passed over the cylinders and heads rather than the cowl still air

[skippydiesel]

7 minutes ago, Geoff_H said:

If you want simple automatic and probably the lightest solution use an expanding wax (as per water thermostat technology).  It is used in the cooling flap of a rear engined air cooled motor vehicle, a Fiat if my memory serves me right.  Just an actuator "piston" rod with the appropriate wax inside. Simple.

With aircraft, marginal cooling, you really need to be ahead of engine temperature rises - Cowl open for Taxi/TO/Climb-Out. Open again down wind, so engine cooling before even touching down and in case of full power go-round.😈

[facthunter]

Now we are going Automatic.? .Totally unnecessary. A wax stat has very little actuating power  and moves about 5/16 th of an inch.  That Fiat is also fan cooled and operates under widely varying loads in a totally different environment to an aero engine, on the ground, where IF it fails you just stop and fix it.   Nev

[facthunter]

Cowl control is before the event as well as reactive to a condition. ie shock cooling on a Power off descent of significant duration Like  after para drop or when an engine has been feathered.  Gills to "Trail" in the circuit where you are busy and open on the ground after landing.  Nev

[Geoff_H]

I now regret even suggesting it.  Novel ideas  ot accepted willingly here.  At Umi easily I was taught be excessively creative, find the problems with discussion in a group and then either develop or scrap. Mmmmm.

[skippydiesel]

14 minutes ago, Geoff_H said:

I now regret even suggesting it.  Novel ideas  ot accepted willingly here.  At Umi easily I was taught be excessively creative, find the problems with discussion in a group and then either develop or scrap. Mmmmm.

I am with you all the way - intrigued by Blueadventures pull/push cable - have started looking into it.😈

Edited January 8 by skippydiesel

[facthunter]

Rubbish Geoff. My view is fully backed up by my explanations based on a lot of experience. Discipline is a vital part of  aircraft design more than most other and I put safety at the top of the list and will continue to do so. I'm, NOT against cowl flaps and have pushed them for YEARS. Simplicity IS safety. I'm very open to GOOD practical ideas. Overcomplicating this actuation is certainly NOT one of them.  ALSO you are not the only person with University engineering and materials and structural  technology  training.  F me this shouldn't need to be said. "Fiddling" with things aeronautical is risky. Nev

[skippydiesel]

This has caught my eye;

 

Ultraflex B14 Engine Control 

Can see this being linked to a direction reverse lever/pivot, that moves a rod tp push/pull Cowl Flap up/down. Will contact suppliers for full dimensions.😈

[facthunter]

Have either of you two ever operated planes with cowl gills? Nev

[Geoff_H]

"Rubbish Geoff"  Why are you so sure that you are right.  I have used the Brain Storming" technique all through my career with great success.  Without it we may still be flying in Wright Flyers.  I will now bough out of this .

[Thruster88]

9 minutes ago, skippydiesel said:

This has caught my eye;

 

Ultraflex B14 Engine Control 

Can see this being linked to a direction reverse lever/pivot, that moves a rod tp push/pull Cowl Flap up/down. Will contact suppliers for full dimensions.😈

I would mount the cable directly and not be concerned if the knob is in or out when the cowl flap is closed as long as it is labelled. Can also anchor the inner and have the outer doing the movement if there is room for the cable to move without fowling on anything, if that makes sense, this would reverse the movement. 

[facthunter]

You haven't listened to a word I've said. "Bow" anyhow. Nev

[facthunter]

Thruster 88 I suggested something like that what now seems ages ago. A design has to be practical or it's a gadget or contraption. Form follows Function.  Nev