What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

3D Print a Stick Grip?

Mark Dickens

Well Known Member
Patron
A question for the experts in 3D printing...would it be possible to design and print a custom control stick grip in two halves that would include an offset such that instead of bending the stick, the grip would have the offset built into it? I don't know about the strengths of the various plastics available for use and whether they would be strong enough to do the job. I've been looking for a practical reason to dip my toe into these waters, and if this is practical, I might just decide to try it out.
 
Shouldn't be an issue

I wouldn't call myself an 'expert in 3D printing' just someone who dabbles in 3D printing, but I see no reason this wouldn't work with something like ABS. Even PLA would probably hold up for many years. There are even Nylon filaments if you're feeling adventurous. A stick grip is going to be loaded primarily in compression and I'd like to see someone crush a properly done 3D printed part with their hand strength. Even with minimal infill. That carbon impregnated filament is pricey and I doubt necessary.

The hardest part would be modeling the stick grip.

If you want a 3D printer I'd say go for it. Too cheap not to these days.
 
I have designed and printed several 3D parts for my RV-12 using Nylon-X, which is a carbon fiber infused nylon material. Has great temperature characteristics for the temps you are likely to see in your cockpit and prints better than ABS. I usually use Fusion 360 to create the parts, I tried EAA Solidworks and found Fusion 360 was simpler for what I was doing. It usually takes me three iterations before I end up with the final design, so use lower cost PLA material until your are happy with the fit and finished design.

John Salak
RV-12 N896HS
 
Zach, I think he was talking about printing an offset tube attached to the bottom of the grip. Actual bending loads.
 
Zach, I think he was talking about printing an offset tube attached to the bottom of the grip. Actual bending loads.

Ah, I guess we should clarify that. If that's the case I'd be a pretty hard no on 3D printing it. It could be disastrous if that failed at the wrong time. I'd need to see or create data showing it good, and as far as I know there aren't reliable material properties for 3D printed parts readily available (real, statistically proven material allowables). Especially for home 3D printers where the process is not controlled.

For anything related to safety of flight I would say that home 3D printing is not the process to use.
 
Thanks guys...I wasn't talking about printing on a tube per se. I was talking incorporating the offset into the plastic part. But, I may have figured out how to accomplish what I want to do without going that direction any way. More later on that. But I still want to get into this, and I have 3D modelers who actually work for me in my business, so I'm just looking for a good excuse! :D
 
production bent stick

What we really need is a production-made steel curved stick that has the 2" or so set back built into it.
 
Mark,

The issue in the mod you're describing is that you're no longer squeezing the grip around the tube; you're now depending on the grip itself to handle the bending loads at the top of the stick.
 
Mark,

I would love to help with this or any of your other ideas to incorporate 3D printing. If you have the resources to create the CAD design within your business, we could help with the printing of the prototypes and final part. Shoot, even if you don't, we can help with the design here. We have the new HP Multi Jet Fusion 3D printer and we are able to print parts in production nylon pa12. This material and process will without a doubt be strong enough to handle the job. Also with this material, unlike other 3D print materials, will withstand time in the sun without any deterioration in properties. This is a durable and high temperature resistant nylon, just as when used in injection molding. I will post a link more info on the machine and process. Give me a call to discuss when you get the chance. 614-834-8659

http://aerosportmodeling.com/hp-jet-fusion-3d-printing/
 
What we really need is a production-made steel curved stick that has the 2" or so set back built into it.

Had the same issue on my rocket. Cut apart the front stick weldment, moved it back 2-1/2", TIG welded it back together. Done. No bent stick necessary.
 
This is experimental aviation, right? Well, here's an experiment:

IMG_1231.JPG


Yes, those are copper 45 degree elbows acquired in the plumbing aisle. Since those elbows are 1-1/8" ID and our sticks are 1" OD, I have used sections of scrap 6061 aluminum tube as bushings. It's actually from my first attempt at making the long elevator pushrod. That tube is conveniently 1" ID and 1-1/8" OD. Perfect for what I wanted. All riveted together with LP4 pop rivets (as also used on the elevator push rod).

Needless to say, it's pretty "industrial" looking and I will dress it up and re-attach my Infinity grip. I'm sure it's not what you'd want in an Extra 300, but I think it will be more than adequate for what we do in an RV.

OK, you may go ahead and start laughing! :D
 
How are you going to test that thing?

What limit loads and what load cases will you use to test it - and what test factors of safety?

Dave
 
I have no plan at this time to conduct scientific load testing nor do I think it's necessary for the plane I fly or the way I fly.
 
Brave man. Very brave.

If you mount the stick on its side so it's horizontal and put your full weight on the new end, that would be a reasonable test. Then rotate 90 degrees and repeat.

Dave
 
Brave man. Very brave.

If you mount the stick on its side so it's horizontal and put your full weight on the new end, that would be a reasonable test. Then rotate 90 degrees and repeat.

Dave

I'm no engineer and can't get into a debate about things I really don't understand, but I'd ask that if a control stick has to be able to handle close to 200 lbs of pressure on the long end of the fulcrum, would that not translate into a significant amount more on the short end? This stick measures about 20 inches long. I don't have it handy to measure, but I'd guess 2/3 is on the long end of the fulcrum, roughly speaking. That means that the long end is about 13.5" and the short end is 6.5". 185 lbs (which is unfortunately what I weigh) would translate into a force of close to 385 lbs, right? Again, I'm not educated in this stuff and it's been a long time since high school physics. So, what I hear you saying is that unless you can apply 385 lbs of force to the aluminum elevator bell crank structure and the elevators themselves, that stick isn't strong enough? My humble opinion is that if I need to apply that amount of force to the controls, I'm already dead and in a smoking hole.
 
I suspect that you have the force levels/locations reversed. The farther out on the lever, the lower the force, and longer the throw required.
 
As a guide, let's look at 14 CFR ?23.397, "Limit Control Forces and Torques". It says the maximum loads on the flight control surfaces must never exceed what would resullt from the given pilot forces. It gives the maximum (limit load) pilot forces for a stick as 167 pounds for elevator input, and 67 pounds for aileron input.

Also, 14 CFR ?23.395, "Control System Loads", states that " ... Pilot forces used for design need not exceed the maximum force prescribed in ?23.397(b)." And that "Pilot forces used for design are assumed to act at the appropriate control grips or pads as they would in flight ..."

The control stick should be designed accordingly.

--> So David Paule's suggestion that the stick should support one's weight is not a bad approximation (as long as you are about 250 pounds)!:eek:
(The 250 pounds is the Ultimate Load which is equal to the Limit Load of 167 pounds times the 1.5 Factor of Safety usually applied.)

(Yes, I know we are Experimental and the FAA design CFRs don't apply, but ignore them at your own risk!)
I hear all of that, but under what reasonable scenario in the planes we fly will 185 or 250 lbs be required? I fly my plane with my fingers. If I'm applying 10 lbs to the stick, I'd be surprised, much less 185 lbs. You are right, this is experimental aviation, just as I said in my first post today, sentence #1. Many planes owned by builders on this site have been built with parts obtained from the famous "aviation aisle" at Lowes and Home Depot. Not exactly approved by the FAA there...let's not talk about experimental engines, props and all manner of other stuff that doesn't comply with the CFRs...that's why we're EAB, and I gladly accept any risks that arise from my many experimental modifications on this plane. It's what I love about doing this. I've owned 5 certified planes and they all were boring, boring, boring compared to this and part of it is that I have the ability to make this plane mine in my own way.

In re the stick, I will be cautious and in the very unlikely case that my crappy shade tree engineering fails, I'll slide my hand down 6 inches to what's left of the official, highly engineered and tested piece of 4130 steel tubing provided by Vans, and then land the plane!
 
Mark, even according to that particular F.A.R., you can use a smaller limit load. Read the entire rule and you'll see. The minimum load allowed is more reasonable for an RV.

I expect that the higher load is designed to allow the airplane's primary flight control system to withstand a pilot who has a lot of adrenaline, but I don't know for sure.

A stout robust control system is an excellent thing to have in an airplane. And since a test can be done so easily, it's worth doing. Yes, it's called "experimental," but that means that we establish some goals and test for them. The testing is the key. While flight testing might be appropriate in many instances, this is one that can most suitably done on the part itself.

Dave
 
Lest anyone here think I'm some some sort of crazy wild-eyed maniac, I have no problem with a reasonable test. I never said I wouldn't test. I did say I didn't plan to conduct scientific testing. I don't have the equipment nor the knowledge for that, and I have to wonder if Vans even does that on the older models. Perhaps Scott will chime in on that...

I think I can rig up a reasonable test that doesn't involve me sitting on the stick (ouch). I am heading to the hangar this afternoon and I'll see what I can report back.
 
Back
Top