Engineering reason for complicated, expensive landing gear?

[RobertE]

It's hard not to marvel at the cleverness and complexity of our nose and main landing gear. Just fabricating them with all those tubes and designing a mechanism to extend/retract them is brain bending. My question is, why must this be so complicated? I was checking out the landing gear of a Lancair (I think that was it) the other day and nothing could be simpler. Nice, beefy aluminum castings with an oleo strut than has a simple, straightforward hinge. This would seem significantly cheaper and more reliable than what we've got. What's the engineering reason that simpler and cheaper wouldn't work?

[carusoam]

Why is simpler cheaper?

The Lancair I looked at costs over $1MM.

http://www.controller.com/list/list.aspx?manu=LANCAIR&mdltxt=EVOLUTION

Redesigning and certifying an old system is not low cost.

This is why we like to buy last year's technology, previously loved...

As for mind bending 60's technology... This is why Mechanical Engineers got paid the big bucks back then. It's not so brain taxing when you have the degree.

The marketing guys sure made it sound like magic...

Best regards,

-a-

[KSMooniac]

I suspect it was easier to weld steel tubes into landing gear in the 50s and 60s versus designing castings and oleo struts. Once that choice was made, that led to the smaller volume required for the donut style gear and we got what we got. There isn't room to put oleos in the same space, so that is one reason why it hasn't changed IMO.

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[M016576]

I suspect it was easier to weld steel tubes into landing gear in the 50s and 60s versus designing castings and oleo struts. Once that choice was made, that led to the smaller volume required for the donut style gear and we got what we got. There isn't room to put oleos in the same space, so that is one reason why it hasn't changed IMO.

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Probably some materials overlap as well- certainly cheaper to fabricate the main gear w/ same steel tube as the frame rather than have to buy or fabricate Oleos for installation.

[BorealOne]

Oleos ain't all that. Lose an o-ring and you've got a big problem. The Mooney design is pretty much bombproof.

 

[triple8s]

And...............if a Mooney nose gear isn't rusted/corroded on the inside, or maladjusted there just isn't much they won't take. Yes the discs can burst but I'd say they are probably lots tougher than the lancair nose gear. I have seen a certain Mooney pilot take his Mooney into places that I doubt any lancair a has gone.

[Hank]

Our gear moves all three wheels with a single motor. Bo's have three motors, thus three gear up / gear down lights. I prefer our one.

The "complicated" design is a simple four bar linkage, studied extensively in engineering school. Google it, they are simple to design and build and easy to operate, although they can look quite complex.

[RobertGary1]

Not too many gear systems as simple as a Mooney's.

[KSMooniac]

Lancair nose gear is very weak.

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[ryoder]

The motor that moves my Mooney gear is 18.7 inches in circumference and gets a thorough cycling a couple times a week in my home gym.

[DrBill]

I suspect weight is the biggest difference.  MY Beech Sundowner had a cast magnesium gear with donuts. It was pretty simple but it was not light.  I think the Mooney design is much lighter.

[ryoder]

A friend of mine designs and builds light sport airplane's, trikes, and gyrocopters for a living and he was amazed at how complex my Mooney is. I like it but it would take so many hours to fabricate something like my Mooney today.

[cujet]

As a fabricator, engineer and mechanic, the most difficult task is to make a system simple.

A hs125 Hawker 700 landing gear is a most absurdly complex system. A Pilatus PC12 has a remarkably simple gear retraction system.

Both accomplish exactly the same task.

If I had a preference, it's a hydraulic gear with a direct acting actuator per leg, including integrated locking mechanisms.

[cliffy]

Think back to where Al Mooney built airplanes in the 50s- the hill country of Texas, not exactly the airplane manpower mecca of post war LA or Seattle. Welding steel tube was easy compared to getting castings and forgings done in the back country of Texas then.  Also it's fairly light weight compared. 

Think about push pull rods and one big arm to put it up and down compared to Beech's electric system even back then. 

[Andy95W]

If I had a preference, it's a hydraulic gear with a direct acting actuator per leg, including integrated locking mechanisms.

If I had a preference, it would be for a simple, reliable system that incorporated a positive locking over-center mechanism that was so reliable and fool-proof that it was the only retractable gear ever certified in the modern era without an emergency extension system.

Oh, wait, that's what I already own...

[jetdriven]

My boss's Piper Arrow has hydraulic landing gear. That system has some 15 hydraulic hoses, a 1500$ power pack, dozens of feet of hydraulic tubing, 3 hydraulic dual action cylinders, seals, and nitrogen charged struts. It also has 3 gear up switches and 3 gear down switches. It also used to have the auto-extend feature with its own pitot tube, a bellows and a couple extra valves, but that's been removed.  

 

It looks simpler than the Mooney landing gear system but once you look at the whole thing, its just as complicated and, IMO, more points of failure as well. For example, any part of the system leaks, the pump runs continuously until the fluid runs overboard, then the gear extends automatically due to the springs overcoming the cylinder pressure. It has a Eaton pressure switch on the power pack as well. It shuts the pump off at 1500 PSI when the gear is up or down. If the switch fails to close (and it has, which is why I know about it), the pump runs up to 3200 PSI. It sits there, running against a full load with the motor pulled down and straining, until the motor thermal switch opens. It cools a couple minutes, then starts up again to run against a full load until it thermals again. It repeats this until the motor burns out. All of this is unknown by the pilot and even on jacks, it difficult to detect.  The switch is 1000$. The power pack another 2 grand laid in.

[1964-M20E]

I like the simplicity of the Mooney all manual gear.  The simplest is fixed gear with no struts to maintain. 

 

Like any engineering problem there are trade offs for function and reliability.

[N201MKTurbo]

I have never replaced any parts of the landing gear except some parts in the actuator. I don't know how you can say it is complex. It is the simplest landing gear system of any retractable I've ever worked on. It is easy to take apart (if you have the special tools) and easy to adjust. The only maintenance it takes (except for the actuator) is lubrication.

[kevinw]

Lancair nose gear is very weak.

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with a history of collapsing on hard landings.

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[KSMooniac]

with a history of collapsing on hard landings.

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I wish I had video of the early tests for the Columbia nose gear drop tests. They launched the nose wheel more than 100 feet across the ramp.

[kerry]

The weight difference between Mooney D fixed gear and a Mooney C retract is 70 lbs.  The weight difference between a Lancair Legacy fixed gear and a Legacy retract is 100 lbs.  Seems like the Mooney wins in weight savings.  I'm sure the later model Mooney's added weight with gear motor and secondary mean of lowering the gear, but the original design is well proven.

[RobertE]

Well, if it's genuinely simple, OK. It sure looks like it's got some complicated geometry.

[Hank]

Well, if it's genuinely simple, OK. It sure looks like it's got some complicated geometry.

The design looks a lot simpler if you envision each gear leg as a single straight piece. The various bends and extra parts are required to carry the load, taxi and land well are extraneous to the retraction design. Three straight legs and the connections under the belly skin are pretty simple, then add some bearings, supports, grease fittings, suspension parts, wheel attachment brackets, etc., it starts getting cluttered and complex looking.

Talk to someone about the retraction mechanism in a Cessna or Comanche. Transmissions, hydraulics, hoses, pumps, etc. We have one electric motor and a slew of grease fittings, and we can never hang one wheel.

[mooniac15u]

we can never hang one wheel.

 

Never?

[Hank]

Never?

Not unless something is badly broken. Unlike Bo's, where each wheel moves with its own motor, actuator, etc.