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AIR SUSPENSION LANDING GEAR ,..OPINIONS OF ALL FLAVORS WELCOME

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Chase Balcom
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#1 Posted: 1/1/2010 21:34:28


I am considering using a design like this on my  project for the landing gear ,..aside from a weight factor ..any ideas?? pro's or con welcome

 

 

AIR SUSPENSION LANDING GEAR.jpg 

 

Chase



Joanne Palmer
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#2 Posted: 1/1/2010 22:20:27

There are two issues.  Fist the kinematics (that's the moving of the linkages.  Will require some analysis.  This layout may have some higher forces than meets the eye at first glance.  It also looks to be more complicated than required, but the analysis will tell the story.  The size of the airbag looks small for the energy absorption, but it could be replaced by a rubber donut stack.  Rubber devices are inhernetly non-linar in their response to compression unlke metals. 

I've designed landing gear for airplanes professionally and I'm not sure I'd follow this path.  But some analysis may prove me wrong.   When you analyze it you first set a stroke on the wheel (start with the diameter of the wheel) , and with that you use the energy of he landing aircraft to start the process. 

 See Landing Gear Design for Light Aircraft by Ladislao Pazmany http://www.amazon.com/Landing-Gear-Design-Light-Aircraft/dp/0961677708/ref=sr_1_1?ie=UTF8&s=books&qid=1262405894&sr=1-1

 for details on how to design and size landing gear.

Chase Balcom
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#3 Posted: 1/1/2010 22:45:27

  Thanks Joanne,.. for your input,..

after analysis I think you'd find the linkages provide less  shock force then dead weight on the air bag .

   I used this same air bag on a retractable landing gear system that I built for a set of floats,.it has 6 inches of travel and can support  a direct  3,000 lbs of impact load,.( a rather redneck approach of a test ,..dropped 3,000 lbs from 5 feet onto a platform that had a single airbag supporting it,..crude but effective).that's without any linkages breaking down the force. 

   the float gear used 2 bags with no linkages.

  As for travel,..this design,.. potentially going on a tail dragger ..a limiter of some sort  to limit travel of the gear would have to be installed to avoid  prop strikes for other then 3 point landings.



Chase Balcom
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#4 Posted: 1/1/2010 23:04:10 Modified: 1/2/2010 00:17:08


 

as for recoil of the airbag ,..something like this could be used to dampen it

to put this in motion ,..when you land the  dampener ram would move to the right allowing air to enter the cylinder thru the diaphram,..once the gear maxxed out  to the right and tried to return to the unloaded position..the diaphram closes forcing the air to escape thru the adjustable bleeder valve at any rate that the  operator sets it at,..actually if the designer of this was thinking
confused ..he could also use the dampener as a limiter for gear travel and in the cylinder between the ram head and the bottom of the travel ,..on the right of the inside of the cylinder ..a cushion block  could be installed  ,..

 

I keep this up I'll talk myself into using this system  :)

 

someone try to talk me out of it :)

 

Chase

 

landing gear buffer.jpg

 

 

 

 

 



Chase Balcom
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#5 Posted: 1/1/2010 23:13:36

  I can't remember the name of the company that builds stol aircraft out of lebanon NH,.. but they use a  oil shock absorbing system that when the plane is set down hard ..the shock system deadens the rebound 80% plus so the plane stays on the ground with hardly any bounce on hard landings,..

   with a dampener like the above drawing,.. it should do the same effect but at less then 80% rate only due air compresses more then oil

 

Chase



Joanne Palmer
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#6 Posted: 1/2/2010 10:16:55

Rather than having an air bag AND a damper, if you compbine the two you then have an oleopneumatic shock absorbe (oleo for short).  This is hoe just about all landing gear ae designed.  In these you can design in a specific compression damping profile by using a metering rod.  you can also define low extension damping so long as you have snubbing as the shock gets to be close to full extension.  All this is covered in the book identified above.

Most high wheel travel landing gear designs use a trailing link style.  This has the slightly higher weight than a staight leg style but they have a smaller space requirement for a given wheel travel.  This is why they get used more on bizjets. 



Chase Balcom
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#7 Posted: 1/2/2010 12:42:48

   Thanks Joanne ,..again,..

when I was racing I used differential shocks with 80/20 dampening or 60/40 etc

but also had to use a spring,..

an oleopneumatic shock would serve for both  a shock and a spring ,.. if I could find one that  could fit into my application and support 700 lbs x 3 ..(not that I plan on doing any 3 G landings ..ouch ) ,..but the plane should weigh in at 700 lbs when completed with a 700 lb  payload,..equals 1400,..leaving a window for at least a 2 G landing ..which could happen in rough country.  my back is hoping that I don't



John McGinnis
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#8 Posted: 1/2/2010 19:38:32 Modified: 1/2/2010 19:42:01

Chase,

My concern echoes Joanne's in that your diagram conveys a non-movable linkage design if the pivots are understood to be fixed, rotating points and there are no provisions for translational movements or (very) significant flexure. The bottom three pivot points on each side comprise a triangle. If they are to allow rotational movement about the outer pivot locations, either the lower light blue horizontal legs must get shorter with actuation or the lower portion of the gray linkage must get longer with actuation. If there is a provision for this it is not evident. If a slot in the blue legs is created for this purpose, a potentially troublesome liability is created. For linkage systems of this sort, try to work with four pivots, not three.

 



Chase Balcom
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#9 Posted: 1/2/2010 21:44:54

 

your both right John and Joanne ,..it should look like this ,..I wasn't too thorough with my drawing,..in my mind I knew what I wanted ..just didnt reflect it on  paper,..the lower horizontal tubes would travel at most 4 inches down in the center to keep a safety margin from a prop strike if landing on mains instead of 3 point

 

SUSPENSION LANDING GEAR.jpg



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AIR SUSPENSION LANDING GEAR.jpg (51190 bytes)
Chase Balcom
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#10 Posted: 1/2/2010 22:11:52

   the center vertical short grey linkages would travel no more then 4 to 5 inches down,..the linkages can not get flexed to the poit that the short vertical grey linkages alligned with the longer horizontal linkage of the bottom of the "triangle" thios would cause either for the linkage to lock or  go the wrong way on recoil.

  this design  would support the aircraft at gross in the posisition depicted in the drawing ..it would not be flexed,..the reasoning for this suspension is for rough field landings ,..which would have to incorperate the afore mentioned above sketch of the dampening cylinders ,..basically the landing gear lower legs are of a bungee set up similar to the Kitfox or Avid which also supports the aircraft at gross and only flex's on rough field landings ..but it has no recoil restriction which inherently creates a good bounce,..on a short rough field landing this is not good

   I was just thinking of a possible solution to incorperate into an existing suspension system that would replace the bungee set up with a system that would dampen the recoil to keep the plane on the ground once touch down was aquired,..even at a more then 1 G landing situation,..

thank you both for your input .. ..keep it coming ,..now that I clarified the system ...maybe you know of a better adaptable approach?

Chase



John McGinnis
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#11 Posted: 1/5/2010 00:52:49

Chase,

Much better, but I'm not buying your assertion of no linkage-reversal lockout. You're too close and that means Murphy will get you. One way he bites in this case is that as the links move from perpendicular to increasingly obtuse angles, they become asymmetrical in their response to tension/compression force reversals. All is well under tension, then a sudden shock the other way causes a poorly tolerated compressive load on linkage that can bind a pivot and bend a link. Use the rusty bicycle chain visualization in thinking about how what works in tension can snap unexpectedly in compression despite adequate statics.

All in all, your design has potential but my view is that a more direct solution will work just as well with fewer parts and modes of failure. Let me know if you'd like it modeled using real parts in SolidWorks.



Joanne Palmer
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#12 Posted: 1/5/2010 11:05:04

Looking at this one more time, i see that if these small links move 4 or 5 inches down, then the wheel travel is about 4 or 5 inches.  The plane may feel "stiff legged" when landing with this little wheel travel.  You'll need more travel as well as large wheels for rough fields. I would say that a minimum travel of the wheel would be 8 to 10 inches.  There is some shock absorption in compressing the tire, but for rough fileds you have the air pressures set low enough that little energy is absorbed. So all the energy has to go into the landing gear damper.  I don't see any damping other than pivot friction.

Whther this linkage can be designed to not go over center or not has to be determined otherwise stops will have to be provided in the structure.  And speaking of structure, the analysis for all of these has to consider the deflections in the structure.  As it presently exists the structure will have singificant bending moments applied and it cannot be considered infinitely stiff.



Chase Balcom
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#13 Posted: 1/9/2010 13:00:56

  thank you both again for replies ,..

  one thing to concider ,.I think I mentioned in a previous post the bag is  6 inches  fully extended ,..if I did not mention that ,..my bust,.. this would allow the top arm to move 3 inches per side toward the bag in a flat landing scenario,..or 4 and 2 etc.the forces on the linkages don't change,.they just increase in one dirrection due to the force of the landing,..and recoil is buffered by the "recoil buffer's" shown in a seperate drawing above,..as for the wheel travel ..if the linkage moves3 inches at the bag,..the linkage should allow total travel of  6 inches plus ,..at then end of the arm where the gear is ,..it will or should travel near 10 inches,..the gear leg's are longer then the linkage's almost 7 times longer if the gear leg is around  30 inches and since the pivot of the leg and the pivot of the arm/linkage is not in the same place it reduces the full travel of the wheel,..if the pivots where closer ,..between the linkage and the landing gear pivot,.it would move the wheel further ,..it increases the load on the bag on intial impact of landing ,..but because the arms are short ..the inherent load on the airframe is not a hi impact load ,..or should not be ,.because of the linkage.

I did not draw all of the airframe components around the gear so visual of the linkage would not be obsstructed,..

 

thanks again for your input

I guess a working model is the next step,..I'll get on it

 

Chase

  



Jay Fortner
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#14 Posted: 1/9/2010 17:11:51

Hey Chase, I'm no "engineer" but have you thuoght of what might happen to that air bag at high altitude? I for one would be more in favor of a coilover shock arrangement with a 80-20 ratio. And I think bump stops are gonna be a given. They've got some pretty strong but lightweight shocks nowadays. Just food for thought.       J.



Thomas Muller
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#15 Posted: 1/10/2010 18:54:22

I've used airbags on cars and motorhomes for many years and don't think they have the reliability needed for aircraft use.  They are prone to leakage and a deep pothole (or a hard landing) can blow one out.  I have just about given up using them on my Winnebago and am looking for helper springs for added load.   What happens if the bag goes out during the takeoff roll or a PIO-type bounce and you have nothing left for the actual landing?  Consider a solid rubber device such as a Mor-ride spring.



Chase Balcom
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#16 Posted: 1/12/2010 22:19:15

   Thanks Thomas for your input ,..

I too have used airbags ,,on tractor trailers ..mobile home toters ( built 3 toters with air suspension) ,..campers ..and airplanes I have a retractable gear that I designed (airbag suspension) ..12 years ago? that's used on floats ,..works great,..

as for blowing a bag ..it's only a 6 inch bag ..so 3 inches of travel per side going towards each other,.. also ..if my plane weighs anywhere near what a winnebago weighs I'm in trouble ,..might as well put curtains on the windows and call it a wontflyabago ha ha  sorry couldn't help myself

solid rubber just doesn't turn my prop it's just too..... solid .. I've seen too many mooney's bounce down the runway and also have prop strikes due to the bounce .. ( sit at biore field on a warm training day)

  this airbag system would be going on a 700 lb static ,. 1400 lb gross tail dragger,..  a very light aircraft,..

thanks again for your input ..I'll admitt ,..if I hadn't had 20 years on and off of building trucks as a part of my background ,.. you would have almost convinced me

 

  keep it coming

 

Chase



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#17 Posted: 1/26/2010 09:45:46

Hi Chase,

kudos for investigating airbags for landing gear.  This is how we learn better ways.  Keep in mind that an air bag is essentialy a spring. 

Consider  using two air bags, one on each gear.  What happens while taxiing at one G where there is some gear extension?  Does the aircraft rock to one side?

Just  food for thought.

 

M. Crown

 

 

 

 

 

 

 

 

 

 

 

 



Rick Nordgarden
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#18 Posted: 1/26/2010 11:53:41

 

Chase, it seems that the geometry you've drawn is essentially the same as that used on the rear suspension of Formula Vees (cars, not airplanes!): when weight is on the wheels and the vehicle is subjected to roll forces the spring assembly is not compressed or extended but just displaced laterally, leaving it unable to resist roll. This is known as a "zero-roll-stiffness" system (often abbreviated as "zero-roll suspension", which of course it isn't -- it allows plenty of roll). This is just the ticket for alleviating some of the adverse effects on handling of the antiquated swing-axle rear suspension used on Vees, but on the main landing gear of an airplane it would leave the vehicle unable to resist roll except by aerodynamic means; as the plane came to a stop it would roll over onto one bump-stop or the other. To give your plane roll stiffness you would either have to split your single springing medium into two springs bearing against a fixed central spring-perch (so that one spring or the other would always resist roll) or else attach an anti-roll bar (often miscalled a "sway bar") as used on almost all cars and trucks -- and on the front end of every Formula Vee.