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Retracts and gear doors?

Old 09-13-2002, 06:50 PM
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Default Retracts and gear doors?

Building a plane with nose gear that has 2 door sequencing, front part swings down and should close after gear is down. Rear door attaches to leg and is not a problem. Question is if I use spring/air vs. air/air retracts, does the spring action opening downward create a problem for gear doors. I haven't figured out what design to use for the door. Having never used a spring air system, I don't know how quickly the gear comes down, that is, so rapidly that it would break a door with a simple mechanical linkage. Any thoughts?
Old 09-14-2002, 10:54 AM
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Default Retracts and gear doors

The problem can be salved with air line restrictors that Dubro sells. These little jobs will control the rate of opening and closeing of the spring air and also the air to air retracts. They only cost under $6.00 or so. And will save you your gear doors for sure. :idea:
Old 09-14-2002, 02:08 PM
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Default Retracts and gear doors?

While on the subject of retracts and gear doors, does anyone know of a how-to book (or magazine article, etc.) dealing with how to make gear doors that retract? I've been modeling for 50 years but have never tried retracts. Something with pictures would be nice! I purchased a set of Spring Air retracts a year ago for a future project (Hot Line Models Mooney Chaparral) and want to have operating gear doors. They don't need to close while the gear is down, only while the wheels are retracted. I contacted Spring Air re: instructions for operating gear doors and they couldn't provide any help. It seems like with all the retracts (both mechanical and air) in use out there, someone must have published a guide on how to do it.
Old 09-14-2002, 09:02 PM
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Default Retracts and gear doors?

You will have a very hard time getting the operation you are looking for with the use of air line restrictors. I think you need a presicion variable control valve, like one made by Ultra Precision. They come in various models do do varios things, and the rate of retract and extension is infinatly adjustable. Ultra Precision is in the modeling books.

Vince
Old 09-14-2002, 11:58 PM
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Default ultra precision valves

Found a place on the web-Art's Hobbies- that has the UP valves, and one specifically for spring/air, 3 to 10 sec delay. They have some other neat stuff too! The subject of gear doors has evaded me too, to some degree I guess you have to have detailed info on the particular gear but there are a few references in various articles on doors. I found a book, on the web, named Aircraft Landing Gear Design: Principles and Practice, by Norman S. Curry $67.95-purports to be the only book on commercial and military LG design- this might be a source for info.
Old 09-15-2002, 05:52 AM
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Default linclogs....You beat me to it.....

I was thinking about posting, and asking the same question.
Hopefully someone can put us on to a book that shows all the options. I'm flying an F-20, and an F-16 prop jets....and now that I have the retract thing pretty well down pat....I want to start covering those "holes" with some nice bay doors.

Maybe we should go ask the "jet-Guys"?
Old 09-15-2002, 03:31 PM
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Default Gear doors

There may be too many full scale variations of gear and doors to make general designs; however, it seems the two major types are straight forward open/ close, single/double(bomb bay type) and sequencing. What few articles/drawings I've seen suggest a simple "U" shaped wire spring attached to horns on the door(s) is a simplistic mechanical approach. I can't think of any way to do a sequential door except with air cylinders and appropriate valves. I've got a U2 I've been building on for several years and tried to copy the mechanical bomb bay type door operation and am close but very flimsy. Also scratching a Grumman Duck which I've tried building retracts, again from photos. I've got probably several hundred books, magazines and have yet to see this subject as construction articles.
Old 09-15-2002, 04:36 PM
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Default Retracts and gear doors?

It seems like it would be a good subject for a magazine article. Do the hobby mag folks read these message boards?

What I'm looking for is the simplest of gear doors. Ones that just "cover the holes". I'd even accept ones that still leave the bottom half of the wheels exposed when retracted (the mains). It seems like those doors could be mounted on the struts but I've heard you really have to be careful that a hard landing doesn't mis-align the strut which could cause the door to jam against the wheelwell frame when retracted. I still haven't envisioned a set-up for the nosewheel. Seems that would be a little trickier as the door would have to be on the front of the strut rather than on the side as with the mains. I like the idea of having a single door mounted to one side of the nose wheelwell. I've heard you do it with little springs and strings but I've never actually seen a set-up.
Old 09-15-2002, 11:35 PM
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Default I was afraid of that.....

I've got piles of magazines going back to the early 70's, and don't ever recall any articles about retract bay door operation, or design.

Old 09-16-2002, 12:24 AM
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Default Retracts and gear doors?

I don't know of any references for doing the inner gear doors that you guys are talking about but I have done a ton of them. Every jet I own has gear doors, some sequencing (close gear down) and others not. There are a number of different ways to accomplish this but the most reliable way is to use pneumatic retracts like Robart, or BVM makes a really nice set for the Balsa Bandit that can be adapted to many airplanes. Air up and air down operation and use small air cylinders to activate the doors. If you want to just close the doors in the gear up position then you can use a small button switch (air switch) and mount it where one of the gear struts wil activate it, or you can alternatively use the same valve but activate it with the same servo that operates your retract valve. When you do this it is helpfull to have a radio that has servo slow on it. You can also get gear door cyclers from Mini Hobby ATL, and EMS Jomar, I have used both and both work extremely well. RCJI (RC Jet International) magazine had a couple of articles about 2 years ago about inner gear doors, and a variety of different ways to do them. Probably the best description or how to manual would be in one of BVM's kit instructions. It might be worth giving them a call and ordering a manual for the Phantom, or Bandit, or F-100 just to see a good description of how to do it. Tell them you are interested in adding gear doors to a sport plane.


David Reid
Old 09-17-2002, 09:23 PM
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Default Retracts and gear doors?

With the top end transmitters you can use a separate door servo on its own channel, allied to servo slowing control and either use multi-point curves or software switches slaved off the retract to initiate door sequencing. You can do the full thing, door open, gear down, door closed again.

Harry
Old 09-18-2002, 10:56 PM
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Default Retracts and gear doors?

linclogs & Flyboy Dave,

Here's the web sites that you are looking for...

Sequential Landing Gear Doors:
http://www.fly-imaa.org/imaa/hfartic...o/v8-4-16.html

Sequential Tail Wheel Doors:
http://www.fly-imaa.org/imaa/hfartic...to/v9-1-5.html

These are the simplest and least expensive ways I could find on the internet to cover up those "holes". I also have a few more saved links with construction photos. But these two articles are fairly well written, with pictures too.

Juice
Old 09-22-2002, 06:40 AM
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Default Thanks Fellas....

....and thanks Juice, for the links ( printed 'em out ).

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