Shock absorbers / Dampers for light gyros

Brian Jackson

Platinum Member
Greetings All.

I've read through a few old threads about this topic and wanted to ask the knowledgeable folks here about a topic of which I've little practical knowledge beyond the general physics. I would like to incorporate a damper(s) with sufficient travel into the main gear vertical strut on a GyroBee, in lieu of the bungee setup. StarBee uses what I believe might be go-kart-like shocks (damper with spring coil) but their low-attached strut pivots in a way that appears to me to require, due to leverage, a stiffer shock than if the attachment point were higher up on the mast and the load more vertical.

I am in the process of selecting/purchasing an in-line damper and find myself with "consumer paralysis", which I often feel when browsing down the shampoo isle. I also see that Sport Copter use a small-ish damper with no visible coil on some of their ships, and Dominators that use coil shocks.

So my hope is for a bit of guidance from those whom have grappled with (and solved for) this problem. Many thanks in advance for replies.

Respectfully,
Brian Jackson
 

neutrax

rat now
No Title

Brian

On my much modified 1966 Bensen I used urethane donuts from sportcopter. They act as a spring and a damper on rebound. As they get compressed they grab the rod going through them.

They have worked well for me. The top attachment is threaded for a 1/2" rod that goes through the donuts and slides in and out of a bushing inside the down tube and has a locknut on the end with a nylon washer and steel washer.
 

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scottessex

Sling-Wing Pilot
Air command used a small rubber bumper, at the top of the gear, I will have to find a picture, sno-bird used a rubber bumper inline like sport copter but less travel, and of course the Dominator has full suspension. Are you looking for just a damper or suspension?
I like suspension for take off on rough fields, it shortens the takeoff roll.
also squishy tires make a big difference, but gyros do not need tundra tires. :)
 

Brian Jackson

Platinum Member
Thank you gentlemen. Full suspension is probably what I'm looking for provided the weight penalty is reasonable. Also of great interest will be the attachment couplings, etc., to design for the correct tube diameters. I also understand that there are shock systems that allow the user to adjust the stiffness by some method (pneumatic?). I might imagine this to be a great feature in order to tune the system to the forces applied and thus travel distances, becoming stiffest at a certain point before bottoming out.
 

Vance

Gyroplane CFI
No Title

There is a lot to suspension Brian and the best design depends on what you are trying to accomplish.

For paved runways just about anything will work and many systems rely on scrub for dampening.

In my opinion some sort of dampening has value in off field operations where there is no scrub dampening available.

If your suspension has an A to mount the wheels make certain you have a brace across the bottom of the A to manage the torque of braking. Spend some time thinking about how the brake torque is managed and what the load path is.
 

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Brian Jackson

Platinum Member
Vance;n1130315 said:
There is a lot to suspension Brian and the best design depends on what you are trying to accomplish.

For paved runways just about anything will work and many systems rely on scrub for dampening.

In my opinion some sort of dampening has value in off field operations where there is no scrub dampening available.

If your suspension has an A to mount the wheels make certain you have a brace across the bottom of the A to manage the torque of braking. Spend some time thinking about how the brake torque is managed and what the load path is.
Thank you Vance. Yes, there is much to learn, and I am considering all forces involved. I'm not putting brakes on the mains so some of the torque loads will not apply. I like the ones in your photo. What are they? Travel distance will also be a concern since the Bee airframe has much less ground clearance than other types. I imagine the shock travel needs to be in the 2~3 inch range based on some rough sketches.
 

Vance

Gyroplane CFI
No Title

Brian Jackson;n1130365 said:
Thank you Vance. Yes, there is much to learn, and I am considering all forces involved. I'm not putting brakes on the mains so some of the torque loads will not apply. I like the ones in your photo. What are they? Travel distance will also be a concern since the Bee airframe has much less ground clearance than other types. I imagine the shock travel needs to be in the 2~3 inch range based on some rough sketches.
That is the main gear on The Predator; a one of a kind gyroplane.

As far as I know the gear is not off anything.

The part with the spring is just a tube inside a tube with a slot and a pin to keep it from over extending. There is no dampening other than the internal friction.

It holds up well to hard landings so I can let my clients explore that part of learning to land.

I like having brakes on the mains when I am doing the magneto checks and The Predator steers with differential braking and toe brakes.
 

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Brian Jackson

Platinum Member
Re-visiting this topic due to build project being ready for shocks. Kind of thinking out loud here with the hope someone will correct me if in error.

I do not know the formula for progression rates or how to talk intelligently with someone on this subject. As I read more about the various types and loads it quickly becomes overwhelming... and I'm in the engineering field. So I'm working with the assumption of a 500lb AUW, divided by 2 main wheels gives 250 lbs per wheel. Due to the rather upright angle the strut/shock assembly will sit (approx. 30 degrees from vertical), I calculate that for 3" of upward wheel travel there will be roughly 2.5" of compression length. This creates a leverage multiplier of 1.2. So the 250 lb per wheel static load = 300 lbs on each strut (250 x 1.2).

On a hard landing I would expect 2G to be a reasonable design limit (someone please chime in if this is in error). I would surmise that 300lbs static X 2G gives us a 600lb max load on the shock before it bottoms out. But due to a shock's progressive resistance this is where my guesswork and limited knowledge fail.

What I think I'm looking for is:
Coil-over shock/damper
Gas-adjustable hydraulic for fine tuning sag of pilot weight and stiffness
Progressive rate spring

If anyone knows of a good source for high quality shocks like this (under $300) I would be grateful for pointing me in the right direction. Google has a plethora of all things shock-related but most of the sites seem to be geared for car model-specific replacement parts, not engineering of systems, and I'd really like to choose the right pair the first time rather than trial and error. Thanks for any help.
 

Vance

Gyroplane CFI
This is an area I have a lot of experience with as related to motorcycle suspension.

There are no answers here, only more questions.

The spring requirements go up by the square of the ratio.

For your example that would be 1.44 times 250 pounds or 360 pounds.

You are probably leaving out some ratio because the spring in inboard from the wheel. I like to actually measure the ratio.

Then it comes to dampening. With more compression dampening you can get away with less spring.

How much pre-load. Springs are rated in pounds per inch so 100 pounds of load (with the ratio) will compress a 100 pound one inch. If you have an inch of pre-load it will take 200 pounds to compress the shock one inch.

Is the suspension to manage hard landings or takeoffs on rough fields?

Hard landings probably would like compression dampening with she springs nearly bottomed at the bottom so you don’t have a problem with roll.

Rough field takeoff probably wants more rebound dampening and one third compression of the spring.

For me the best way was to go to the race track with as many springs and shocks as I could get ahold of and try them all taking lap times and making notes.

You won’t have the same parameters but the same advice holds true.

Copy someone who has a similar gyroplane and then try more and less spring and different dampening schemes.

In my experience trying to figure it out before hand and get it right the first time is just not reasonable.

Personally I like more travel, springs run near the bottom and fifty-fifty compression-rebound dampening for smooth fields and inelegant landings.

For rough fields I would run the springs compressed about a third and more rebound than compression dampening.

Be aware that many gyroplanes run no dampening and use tire scrub to dampen the rebound. This does not work well on wet grass.

I also like front suspension particularly for inelegant landings.

I am in the middle of working on The Predator so this was not edited.

Best of luck on your adventure.
 

Brian Jackson

Platinum Member
Thank you again, Vance, for your wonderful guidance. So it's not necessarily a brain failure of mine, but rather a maddening set of variables. I can see now why this might be as much an art as a science. I will spend some time digesting the info you have provided. I appreciate your taking the time out of your schedule to help. Have a great evening.
 
Just food for thought, and I haven't thought this through completely...

You can buy gas Springs/Shocks with 16" of stroke and up to 600lbs force for $75-150.
Weight is under 4 lbs.

The Additional force needed will be the tangent of the angle time the ratio of the axle arms.
If the shock tower is angled at 30°, Tan(30) = 0.58, 1.58*250= 394 x 1.2 = 473lbs

A 500-550lb gas shock on each side might be about right.

Look in the Zoro(Grainger) or McMaster catalogs.
 

Vance

Gyroplane CFI
Here is a small explanation on the way of suspension ratios.

Imagine a one to one ratio. With a hundred pound per inch spring with no preload it takes 100 pounds to move the spring or the wheel one inch.

Imagine a two to one ratio with a hundred pound spring. If we move the wheel one inch it only moves the spring a half inch so 50 pounds.

Because it is working back through a two to one ratio it only takes twenty five pounds at the wheel to move the axel one inch.

In other words to get the same response at the axel with a two to one ratio we need a 400 pound per inch spring. That is the square of the two to one ratio.


The dampener is even worse because it needs to manage the 400 pound spring with half the movement.
 
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