32 Replies Latest reply on Mar 5, 2018 9:03 AM by Evan Dlugopolski

# Actuation Forces

Hi,

I am modelling a set of landing gear for a university dissertation. It has a couple actuators on it and I am baffled in trying to figure out the forces that each actuator needs to pull the assembly. Is there a way of either using a pen/paper or solidworks itself to find out what these forces are. Just to give you an idea of one of the actuators, the picture attached is of a stripped down version of my landing gear showing a very basic version of the model i need to make calculations on.

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Can you describe in better detail what this actuator is used?  Where are the forces? etc...

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Yes, sorry. The actuator is used to retract the landing gear into its wheel bay. The picture shows the maximum retraction of the strut. For basic calculations, just the force due to gravity acting at the center of gravity of the strut which for this specific strut is 11440 N. A force of air drag can also be used which can be approximated to be concentrated at the center of gravity. The value for this is 24000 N. I need to calculate what the force can be applied to the actuator so that it can pull the strut roughly 90 degrees. The second picture shows the direction of the force.

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Just so I have this clear...are your landing gears this style?  With the wing actuators folding in and the front folding back?  Which landing gear is your example for?  Nose or wing?

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My landing gear system is the main gear of a 777. The full model is below. And although the actuator is moving the entire landing gear, I can model it as a static force at different points of its retraction and use that to interpolate the data if needed to find the maximum force required. I am just confused how the free body diagram would look like with forces such as the force of gravity acting beside point A in your free body diagram. Hopefully this picture helps give you a frame of reference.

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Ahh! Now I understand!  Thanks..

There probably a few ways to skin this cat... but here is one way..

Since the max force required to lift the landing gear would be needed when the armature/linkage (or whatever) is horizontal, we can solve our static equation at that point.

A couple assumptions or things to keep in mind here...

ABD is ridged...in other words ridged bodies ABD and BC are linked and will pivot at B.

We can transfer the force at the center of gravity (from the weight, air resistance etc) along its axis to the horizontal intersection of point B to create the horizontal AB section.  I think there is a theorem/rule for this but I cant remember what its called... Once you are to this point it should be pretty straight forward!  I am out of practice with these problems so hopefully I am in the ball park!

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Thanks for this! Ill definitely give it a try by resolving all the forces.

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Is it me or does this actuator look terribly undersized? I would do as the others have suggested, and try the motion analysis, I have used it before and you can see results over the range of motion required. Then you can get your results, and incorporate a Factor Of Safety. Since this is used for hauling people I would assume the FOS is quite high. After you get your result, you can shop for the actuators available that meet your needs, and then you can compare (by inspection) if your results "feel" correct. Example: If you have say results of 1.5 ton and you find an actuator in that range, and the actuator is in fact much larger than your actual landing gear, then I would go back and re-calculate your forces. I would also check you FEA results to see if you set it up as accurately as possible.

A lot of good tutorials on YouTube

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The goal of my project isn't to perfectly size each component, rather get a good approximation and find ball park figures for forces that might be applied to the actuator. So the size of the actuator is rather unimportant. I am also not looking to buy/build this but run various optimizations on it in the near future.

I have been running tests to guesstimate my forces but that is unfortunately not enough for my report.

I'll be taking a look at the tutorials as well.

Thanks!!

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"rather get a good approximation and find ball park figures for forces that might be applied to the actuator. So the size of the actuator is rather unimportant." Pretty sure its important. Why find the forces? to get a working actuator? Isn't that the whole point?

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Like he said, he’s only solving for forces right now...pretty hard to size a component when you don’t know how much forces are on it   your Talking about step 2 but his question is about step 1.

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Without knowing more, maybe this will help?

Always start with a free body diagram that includes all forces.  I am assuming the linkages are under compression in my FBD...

There is probably some external forces on you actuator?  Add them to the FBD, then solve each joint using your static equations...if you need to actually MOVE something with this actuator, that changes things a little but this would be my starting point.

As far as SolidWorks goes, I am not an FEA expert, but i dont know how much it will help you with explaining the amount of force it would take for a body to move something.  FEA is good for stresses, strains, etc. on bodies given external forces and pressures but that's about it.  Again, I could be wrong here. Maybe SolidWorks does have something for this type of analysis. I am assuming you are on a student licence which should come with FEA.  Do some digging and playing around.

I only have simulator xpress which is pretty limited.  But you can do things like this...

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Side note...I cover topics like these on my YouTube Channel.

Here is my latest video...

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Evan Dlugopolski wrote:

Side note...I cover topics like these on my YouTube Channel.

Here is my latest video...

Does this qualify as "trolling"?

Dictionary.com

16. A lure used in trolling for fish?

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I am sharing links to related topics.  Trying to add value versus putting posters down... so yeah big difference IMO.

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My first thought when I read the OP's problem description, "Where is your instructor?"  Not a put-down of the OP, but a direct concern for value of tuition paid.

My first thought when I browsed your links, "Missed the boat"  (pun intended).

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Agreed! So then why would someone come in with condescending comments to the OP? Rather than trying to help them? And why am I the bad guy here when I seem to be the only one trying to help him?

Your feedback is appreciated!  I'd love for you to inbox me some constructive feedback!

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But, yes you're right, I am trolling for viewers...at least there is value to be shared here though!

Much better than trolling for opportunities to put posters down like some others do..

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Do you have SolidWorks Motion?

Perhaps you could graph the forces?

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That's what I was thinking of! I am only familiar with FEA portion of SolidWorks Simulations..

I don't know if this comes with student versions of SolidWorks though!

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Evan Dlugopolski wrote:

...I don't know if this comes with student versions of SolidWorks though!

Student Engineering Kit (SolidWorks SEK) has motion analysis.

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Nice...OP should definitely be able to use it for this application then!

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Hi,

Yes I do have solidworks motion which is what im using to try and narrow down the forces that might be required but i need some sort of mathematical proof behind it. As far as I know, I need to input some force into solidworks for it to result in some graphs which would show me the changes.

Thanks

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Why don't you help him solve it then instead of trolling!

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Because if he's too inexperienced to solve the problem then there is a high likelihood that he is not presenting the problem well enough to solve it or even know if it is properly solved. There's a huge difference between getting software to work and actually solving an engineering problem.

This problem can be answered with an Excel spreadsheet for the full range of motion.

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Whoa!

It would appear by forum post evidence that over time

Perhaps you should think a little more before calling people out!

Dave.

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You are correct sir! However lately I am not seeing it..like in this post. Where

is the value? Where are the good opinions?

I know Mr. Schwartz is a very intelligent and experienced professional.  I just like to give him a hard time when he starts acting like the grumpy old guy in the office

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Thanks for that reply. And a dissertation implies a report for an academic degree. I am a third year aero student if that helps you out. But anyways thanks for that passive aggressive comment.

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He's always trolling around on here...I keep telling him that's what Facebook is for but he doesn't get it!

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You're quite welcome. No passive-aggression intended. Contrary to an opinion popular among people who are not, I don't like to arbitrarily hurt people for fun. Sorry about your feels. I don't care about them either way. However, if it stings, it may mean you best pay attention.

There are plenty of competent people going after your CAD solution. What caught my attention was the who, what, and why of the question. When smart people ask dumb questions, there's usually a bigger problem to solve.

This is a problem I understand well. I once had an entire section of a lab set up to test nearly identical mechanisms. It distills down to a few simple variables once all the forces and constraints are worked out. If you had taken the time to do that on paper, the CAD solution would likely have dropped into your lap.

I've also seen equally simple problems get totally blown up in CAD. The result is a CAD solution that solves elegantly but is still simply wrong. People much more experienced than you have made this mistake. There's a lot of good-looking bad CAD out there.

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Thanks. I have tried multiple different methods to calculate the forces using the most fundamental principles with a pen and paper that would be acting on it but after hitting a brick wall at each stage, i decided to post my questions on a couple different forums. And don't worry, you're gonna have to work a lot harder to hurt my feels.