Retractable Landing Gear ideas

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Flying Boat

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Hello Everyone.

I have been messing around with a number of retractable gear designs and I am not that confident with my ideas, so I was hoping for a fresh approach.

First off, it does need to be retractable because it is an amphibious aircraft. Second I have been told to stick to tri-gear because the landings are simillar to seaplanes and I am not sure I am up to mastering a tail dragger.

The plan is a flying boat (hence the moniker) with the main gear in sponsons attached to the sides of the hull and the nose gear retracting up into the bow.

If anyone has any thoughts or sources it would sure help me out.

Thanx:)
 

Holden

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Flying Boat,

The landing gear is the hardest part of a seaplane design if you want to make it fail safe. For me, the landing gear makes or breaks (pun intended) the design.

In my opinion, a seaplane is for the outback, just like a Cub. Being a bushplane it must be able to do all that a Cub can do, and not flip the airplane over in the event the pilot puts the gear down during a water landing. The amphib-gear-down-thing wrecks a lot of airplanes and drives a lot of the insurance costs and safety issues.

Over the years, I have developed some distinct ideas about landing gears. I don't use a tri gear or a tail dragger. But before I say anymore, could you tell me what you want to achieve with the gear?

In my case I had to "reinvent the wheel" to get where I wanted to be. I wanted all that a Sherpa can offer, but with lower drag and weight per unit energy absorption than the typical fixed gear. The typical Oleo strut cannot do my mission profile due several issues so I am designing a new one. Actually, Oleo struts have not changed much for over 50 years.

NACA has a lot of articles dated circa 1955. Report 1154 is good for modeling the gear if you are a interested.

http://naca.larc.nasa.gov/reports/1953/naca-report-1154/
http://naca.larc.nasa.gov/reports/1955/naca-tn-3426/naca-tn-3426.pdf

Let's talk about it...

Holden
 

Flying Boat

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Holden,

Thanks for your response and sorry for not getting back sooner. I have been out of town.

Yes, I do want the aircraft to be "like a Cub". Larger than normal tires. Trailing Design to bounce away from bumps. 3,600 # plane. Beyond that I am trying not to put too many design constraints until I find something I can work with.

I have one design that the main gear fold down from the bottom of the sponson to about an 8' track requiring a great deal of surface smoothness to allow the sponsons to work, another that rotates the gear down on the end of the sponson w/ the wheels exposed at the leading edge of the wing shaped sponson.

I have too many sketches of the nose gear to list.

Simplicity and toughness are my main criteria

I would like to hear about your design - not tri or dragger- the only choices left that I know of are bicycle and unicycle.

Thanks for the two articles. They gave me more accuate numbers to use and when I finally pick one design they will help.
 

Holden

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Flying Boat,

Any discussion on landing gear is more about design goals than anything. I need to know your goals.

The gear is a major key to great performance. In fact, you might say that it all comes down to the gear. (pun intended)



Holden
 
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Flying Boat

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Holden,

You have obviously spend a great deal of time considering landing gear and I thank you for your interest. My design goals are:
-Low landing speed, for rough water purposes more than land.
-High cruise speed is less important than low landing speed.
-Simplicity, in fabrication, maintenance and field servicability.
-Rugged (civil std 10 ft/sec rather than military std 12ft/sec)
-Half of the landings would be on paved runways and the other half on water with sporatic use on unmaitained turf. There is enough water around here that most forced landings could be made there.
- Easy to use -landing, taxying w/ forgiving characteristics.
-the aircraft is a 4 place single engine pusher similar to a Lake Renegade w/ a higher wing and side mounted sponsons for use around seaplane facilities.
-Track width of no more than 8' to use seaplane ramps.
- 8.00-6 main tires
-I am hoping for a 45 mph landing speed.


I considered bicycle gear but didn't like the idea of cutting into the main hull at or near the step because my impression of rough landing/wide CG range aircraft need to keep the center of rotation close to the step. The step and the hull a few feet forward, being the hardest working part of a flying boat.

Bicycle gear is lighter and less drag but usually more critical of landing attitude and air speed unless you reinvent the shocks. I have no experience w/ that kind of engineering... I am not the one to reinvent the wheel(pun intended)

What do you think of compressed rubber/neoprene rings stacked high enough to give sufficient damping? My understanding is that the shock absorbing efficiency is between cantilever spring and oleo-pneumatic. The simplicity of this system is very tempting.

The sponson idea gave me a place to hide the main gear, a walkway to seaplane docks, a way to suppress spray plus the airfoil shape gives some lift. I can attach the gear to the nose or the tail without perferating the hull.

I want an amphibious airplane, so insurance will be a factor I cannot control.

I felt that the old adage "there are two kinds of amphibious pilots those who have made a gear up landing and those who will" was probably accurate(that can't help the insurance rates). I had hoped to minimize that situation through Check Lists and a good indicator of where your gear is prior to landing for gear up on land or gear down on water. Your ramp idea for the main gear might be just the thing needed to add survivability to the design(at least on water). Not too many ways to design around the pyrotechnic display of a wheels up landing on pavement.

So what do I need? Good design ideas for retractable gear that either fold down from a wing like structure or can rotate downward from the leading ledge of the sponson.

I also like hearing about other peoples aircraft designs and thoughts. Even though they may distract me from my own project, I enjoy the logic and the problem solving. You seem very passionate about designing and I thank you for your help.
 
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uglycop

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ne wisconsin
neoprene cushions for landing gear

Norm:
Instead of using neoprene cushions take a look at urethane biscuits. There are a lot of styles and sizes that are used as return springs in dies for punch presses and such. Nice things about urethane are 1) **** near imprevious to oils and lubricants 2) Much greater consistency in hardness and deflection curves 3) come in greater variety of shore hardness grades than neoprene 4) greater wear resistance than neoprene 5) can be machined for special applications (altthough you need a really sharp tool and fine feed rates)

The neoprene springs or cushions need to be separated by metal washers, aluminum ones will work fine but steel washers can be thinner than aluminum if you can stand the extra weight or if you need to minimize the stack height.

You should expect stack heights that make the gear leg longer than the gear leg would be with oleo struts.

uglycop
 

Flying Boat

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Uglycop,

Interesting alias:)

Thank you for your opinion, I think your absolutely about using urethane biscuits. I don't suppose you know of any sources or information?
The height issue shouldn't be a problem because I seem to have a fair bit of room in the sponsons.

Thanx
 

uglycop

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Messages
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Location
ne wisconsin
urethane biscuits

The best/ most consistent urethane biscuits that I have found so far come from a company called FIBRO. check on internet at www.fibro.com

I have no idea who handles their product in Canada.

As for my own project, urethane cushions are planned for the mains
(conventional gear) and mains retract inward into the leading edge underside (similar to a t-6, but without a fairing - wheel goes all the way in)
 

Flying Boat

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Uglycop,

Sorry it took me so long to get back to thank you. I have been looking at the site you gave me and I am confident this will work great.

thanx again
 

PTAirco

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Corona CA
Landing gear on amphibians

A pesky problem. I am sure that's why Messrs Short didn't put one on their Sunderland.
I am designing (doodling) a twin engined amphibian along the lines of Grumman Goose and I do not intend to duplicate the diabolical ingenuity of their landing gear. Retracting them into sponsons on the side of the hull seem an eminently sensible approach. It ought to work for either taildraggers or tricycles. A simple approach would be to have a tubular beam running across the hull through watertight bearings with simple "L" legs at the end carrying the heels and rotating either forward or backwards to retract. Locking the tubular beam locks the gear up or down .
All solution are somewhat complicated, I am convinced there is nothing really simple that can be employed here. My design incorporates both rotary and lateral motion to swing the wheels sideways and up and pull them into the hull to nest in a box under the pliots' seats. Requires Machiavellien ingenuity to make it work and am not sure I have it.

Go to museums esopecially those with jet fighters, their methods always give me new ideas.
 

Flying Boat

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PTAirco:

Thank you for your response. I must be on the right track... I have ruled out all but a couple of designs and the "L" Bracket Idea is still my favorite. I also have a design w/ the wheel exposed on the leading edge/outboard and rotating out of the sponson float (still w/ the L bracket).

I also looked at Grumman's amphibians for ideas but didn't want to give up the cabin space (the complexity scared me , of course). I was trying to avoid drag of the exposed wing floats or further complexity of the fold down tip float. I wanted the sponson to add lift, supress spray and keep floats close to the hull in case the float caught a wave.

I have been looking in museums, books, old NACA documents (great source). Flying boats (and the people who believe in them) are a rare anachronism. Most of the enthusiasts seem to be model aircraft builders (another great source for drawnings and history). Most information available is on the larger flying boats and not much can be compared to a 4000 lb. single engine pusher.

If you subscibe (or know someone who does) to Experimenter magazine by EAA there is an article in Aug 2003 pg. 10 on Amphibians w/ a rather crude drawing of a Grumman Design of main gear. I wonder if patent drawings might show the geometry more accurately if you wanted to use the original design.

Multi engine sea rating would make you quite a rare pilot.

If you have any more thoughts on sea planes, flying boats, or amphibians I would love to hear from a kindred spirit.

Norm
 

Planeshane

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Oct 3, 2003
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Arizona, 350 days of severe clear!
Donuts

As I recall there are landing gear configurations that utilize the neoprene donuts in early Mooney aircraft. I have flown a 201 and an Executive that had them.. they are VERY simple in design and provide shock absorption adequate for the 10ft/sec target. I have to admit that on paved runways the touchdowns are very 'solid', for lack of a kinder word.. ;-)

Good luck, sounds like a cool project!!

Shane
 

Flying Boat

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Surrey B.C. Canada
Shane:

I appretiate your help. I had seen planes with a similar gear leg to what I wanted but couldn't figure out what type of plane it was from my side of the chain-link fence. Now that I know what planes to look for, maybe I can find something in the "bone yard" that can be adapted. I've used a fair amount of presious forest product trying to design something workable with a minimum of machine shop time.

If I recall correctly the gear folded down from inside the wing so if I can't get it to fold down rearward the I may have to find a way to build a cover that can handle water loads. I may be able to build enough flex into the aforementioned "L" Leg to absorb some of the "solid" feel (I probably shouldn't call it an "L" design since it really amounts to an 8' wide upside-down "U" where the bearing surfaces could be mounted anywhere from the fuselage at 4' wide on out, depending on how much flex and strength is needed). I hope the larger than normal tires will suck-up a bit of roughness as well.

Thanks Again
 

Planeshane

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Heya Norm,
If you have no Mooneys readily available for reference I can take a few pics at the local airport of the landing gear config and Email them to you within a couple of days at the most... I am sure you could make the config work with a few minor adjustments. The donuts and a fixed front fairing, maybe with a mechanism that rolls the assy rearward and up for aerodynamics... who knows. ;) Still sounds like a fun project.

Shane
 

Flying Boat

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Surrey B.C. Canada
Shane:

Sorry it took me so long to respond to your generous offer. Absolutly no disrespect intended. The truth is I have been without the computer for a week after trying to load a new CAD program and that set off a cascading series of hardware failures that ended with a new motherboard and operating system.

While waiting for the computer to come back from the shop I did get out to the airport and had a pilot friend let me onto the tarmac where I was able to make some sketches, notes and measurments.

The system is simple, appears strong and should be perfect for what I need.

I really appreciate your interest, thanks
 
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