highhorse

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Try not to flame me toooooooo harshly if this seems like a REALLY stupid Q, as opposed to the garden-variety stupid Q's I see posted now and then:

With all of the effort that goes into redundancy and safety, it sure seems like spring-down gear are a no-brainer so that an air leak can't cause a gear-up landing.

And as a bonus, the plumbing is simpler with as many as 8 fewer (potentially leaky) junctions if down lines are removed from the equation, so a leak is less likely in the first place, right?

So what advantage is there to a non-spring system that makes them so prevalent? What am I missing here? I hope I don't feel like a complete moron when something obvious is pointed out.[&:]



Thanks, Don.

DelGatoGrande

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http://dreamworksrc.com/catalog/prod...roducts_id=804

mr_matt

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Well they do work but it is a compromise.

Whatever spring you use for the down side has to be compressed when you bring the gear up, so you do not get your full air pressure lifting the gear on the up side.

This is not as serious as the down side challenges. The spings are usually no where near as powerful as a normal air down system, for the reason stated above. This usually works fine, but I found they tend to not be as reliable going down as the slightest distortion of the frame, or dirt etc in the mechanism would cause them not to lock down.

But they can work, I used them for years on sport planes.

erbroens

Dont´t think it is stupid question, but if it was I wouldn´t say it to you.


As Matt said the spring down system isn´t as powerful as the two way air system. For example in a fast plane like a Hotspot it is usual to the front wheel not lock if the gear is deployed before slowing down the airplane.

However I used them without problems for years in almost every jet.. I like the fact that they have almost 50% less chance of developing a air leak compared to a two way system.

highhorse

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George, thanks for the link. I was already aware that extra equipment can be bought to extend gear in the ecent a minimum pressure is reached.

In other words, I can spend $110 on still one-more-piece-of-gear and then try to make room for it, all in an effort to make air-down gear mimmick spring-down gear.

Matt, thanks for that observation. Something to consider for sure.

You too, Ebroens. Thanks for sharing you experience there.

mongo

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only time i have ever had to land a plane with the gear up, was on a spring air equipped curare back in the 80s.

most anything not right, will override the spring force and keep the gear up.

grbaker

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I have used Spring Airs on lots of DFs and a few Warbirds and I still have a set of them on my Facet 2300. The only major problem I have ever had with any of them was on a 1/5th scale P-39 nose gear. The strut was very long and it failed to lock down a couple of times till I added a second spring to the air cylinder.

As Matt pointed out they can be weak on the up side if you have heavy tires or struts. They have to override the spring and lift all of the weight. If you use full gear doors, then the spring down feature won't help you with a low air pressure scenario. The spring won't normally be powerful enough to push the gear doors open.

Transportation can be a problem with Spring Airs also. If you disconnect air lines to disassemble your plane, then the gear are going to stay down during transport. (I like to transport my planes with the gear up). Doesn't sound like much of a problem, but you would be amazed at how much the gear can get in the way when loading a lot of stuff in a small space.

I would not hesitate to use Spring Air in a sport model without gear doors, but not on the scale stuff.

highhorse

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Oops. THERE's the obvious thing I knew I must be overlooking ! I knew there was a forehead-slapping moment headed my way when I started this thread..........Geez.

Thanks for pointing that out Gary, and thanks for doing it so gently. I only feel about half as dumb as I should [8D] LOL.

grbaker

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I must be mellowing in my old age.

Spring down are great for some applications, just not in most of our jets.

rhklenke

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Except that Clippard (and others) make single-action spring return cylinders that can be used as gear door operators on spring-down gear installations...

bcovish

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Hang it there highhorse, someone will make you feel completely dumb in a little while

highhorse

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That someone is usually ME