carbon fibre landing gear

[metalman]

Yeh, I'm a bit big to fit in one too!

 

 

[Yenn]

As an armchair expert giving my opinion, I was only stating what my impression was to someone who was thinking of doing a spring rebuild. I assumed that he was not an expert on composites and was trying to get him to do some more research on the subject.

 

I havn't found the Corby spring but I do remember it was basicly uni directional. As far as watching a wing flex at take off I remember watching a reinforced concrete chimney flex in high winds, I don't think it would be good material for a spring.

 

 

[facthunter]

Not terribly scientific Yenn. Brick chimneys are not built to flex.( Reinforced concrete will.) I mentioned the difficulty of carbon fibre in compression hence suggesting a laminate to combine the excellent strength to weight of carbon fibre, with other materials. The weight is a concern in metal spring undercarriages, and they crack, so it is a goood subject to investigate.. Nev

 

 

[metalman]

As an armchair expert giving my opinion, I was only stating what my impression was to someone who was thinking of doing a spring rebuild. I assumed that he was not an expert on composites and was trying to get him to do some more research on the subject.I havn't found the Corby spring but I do remember it was basicly uni directional. As far as watching a wing flex at take off I remember watching a reinforced concrete chimney flex in high winds, I don't think it would be good material for a spring.

Thanks for the input, I've done a fair bit of glass work with non structural stuff ,this is a first foray into something a bit more critical ,and disastrous if I get it wrong, so I'm open to everything going to get as much info as possible.

So far as I can see the fiberglass seems to be the way to go ,but I also like the look of the carbon fibre, it maybe a matter of doing a laminate between the two, I've seen it done with alternating layers of kevlar and glass ,seems to work well and is lighter than just glass fibre

 

Met

 

 

[djpacro]

I never cease to be amazed by the armchair experts so willing to jump in and offer totally uninformed opinions...

I do my best work from an armchair. And I form my own opinions.

 

The ... site was used purely as an example do some web surfing there are others and regardless of operational arena there are certain design rules to which all aircraft designers adhere undercarriage stress (impact, fatigue and otherwise) being one of them.

Matt may like to buy a landing gear off the shelf to suit but I doubt he will find one of carbon to suit. As for design rules, there is mainly the specified vertical velocity (equating to a drop height if you want to test it) and a range of structural load factors. Consider how far your landing gear will deflect in meeting those requirements vs other considerations of landing gear height such as ground attitude for a taildragger and prop clearance. Plus taxi loads, handling considerations etc.I don't recall any design rules for little aeroplanes relating to fatigue ........

Matt, at Avalon, I took a pic of a friend's composite tail wheel spring details for you. The aeroplane also has composite main landing gear legs.

 

 

[metalman]

Heading down there on Friday(Avalon ), so I'll be a happy snaps pest , hoping to see a highlander down there for a gander

 

 

[M61A1]

It shouldn't be too hard or expensive to make a couple of trial runs for something as small as a tailwheel spring. I do work with the stuff, although I am not a design engineer. I would suggest maybe try using the carbon on the tension side of the spring and glass on the compression side, both in a unidirectional fashion. Perhaps add a layer of bi-directional glass over both sides. Don't put aluminium in direct contact(on the aircraft) with the carbon. An aluminium former should work nicely to get your shape, use some release ply with some air weave over the top with a sandbag on top should be sufficient if done right. Choice of resin will be important...I can't help there, but "Scotchweld"or "Hysol" make some good stuff.

 

 

[Old Koreelah]

It shouldn't be too hard or expensive to make a couple of trial runs for something as small as a tailwheel spring. I do work with the stuff, although I am not a design engineer. I would suggest maybe try using the carbon on the tension side of the spring and glass on the compression side, both in a unidirectional fashion. Perhaps add a layer of bi-directional glass over both sides. Don't put aluminium in direct contact(on the aircraft) with the carbon. An aluminium former should work nicely to get your shape, use some release ply with some air weave over the top with a sandbag on top should be sufficient if done right. Choice of resin will be important...I can't help there, but "Scotchweld"or "Hysol" make some good stuff.

That's pretty much what I did. It works, but I didn't end up saving much weight.

 

 

[M61A1]

That's pretty much what I did. It works, but I didn't end up saving much weight.

I don't think there's much weight to be saved by using monolithic composite structure, the real weight savings come using sandwich type structure, which isn't really suitable for landing gear applications.

 

 

[djpacro]

Just found some time to do a bit of number crunching for constant thickness main landing gear leg, tapered in width.

 

f^2/E.w ends up being a figure of merit where f is the bending limit stress (or fatigue limiting stress); E is Young's Modulus and w is material density (units of lb and in). Fibreglass is way better than steel or aluminium. Haven't crunched the numbers for anything else yet.

 

 

[metalman]

Just found some time to do a bit of number crunching for constant thickness main landing gear leg, tapered in width.f^2/E.w ends up being a figure of merit where f is the bending limit stress (or fatigue limiting stress); E is Young's Modulus and w is material density (units of lb and in). Fibreglass is way better than steel or aluminium. Haven't crunched the numbers for anything else yet.

Geez Dave ,I wish I was smarter I would've understood much more of that :-)

Flew the fox again tonight, seems to be pretty good so far

 

 

[Chird65]

You would not be the first to make a composite gear. See the attached WEB page http://www.diehlaero.com/landing.htm

 

 

[George Sychrovsky]

I just signed up and I see a link to my page here, its outdated about 12 years

 

With lower cost and wide availability of carbon fiber now I use carbon in the springs and most everything else.

 

Btw, reading the armchair experts comments is quite amusing.

 

 

[bexrbetter]

Brick chimneys are not built to flex.

Well as one of the team who encased the Fairfield Hospital's old 250ft brick chimney in a steel exo-skeleton because it was flexing past the 3 meter limit on gusty days I might disagree!

 

 

[metalman]

I just signed up and I see a link to my page here, its outdated about 12 yearsWith lower cost and wide availability of carbon fiber now I use carbon in the springs and most everything else.

Btw, reading the armchair experts comments is quite amusing.

G'day George, thanks for the input, I guess your in business doing this but I'm open to advice with composites if your willing .

Cheers Matty

 

Very informative website by the way ,

 

 

[kaz3g]

Why wouldn't laminates of carbon fibre and other materials make a good undercarriage leg?As far as bouncing any UNDAMPED spring will store energy and give it back later. Those leaf spring undercarriage legs are heavy and quite a few have broken in service. Nev

I just put new bungees and new tyres on BYM....goodness, there is some stored energy there, Nev!

 

Kaz

 

 

[kaz3g]

Yeh, I'm a bit big to fit in one too!

Definitely no ballerina!

 

Kaz

 

 

[Guest Maj Millard]

MM, feel free to call me an armchair expert if you wish, however I do have an FAA Level 2 certificate in advanced composites . What a lot of folks don't realise is you have to 'engineer' with composites, the same as you would with any other material. Laying up with fabrics in various orientations (directions) achieves different structural qualities and strengths. Often a designer will use a combination of different materials to achieve a desired quality, combining say carbon fibre with Kevlar or any number of other 'exotic' fibres now available each with a different quality.

 

Normally a degree of structural testing is also carried out to 'test or prove' different combinations.

 

You are doing exactly what you should be doing in contacting someone who is working at the cutting edge and who hopefully will be up to date with all the latest cloths, resins and techniques......................Maj...