SparrowHawk Suspension

[Greg Lockhart]

OK, I'm retired now and starting to spend more time building my SparrowHawk. I'm working on the gear now.
I've always wondered how well the SH suspension works. I don't have any personal experience (yet) with this suspension so I may be totally wrong, but it doesn't look like there would be much compressing of the rubber "donuts" and therefore not much travel & cushioning. I could be wrong.. it may work well. But, when I start flying this SH I'm sure I'll go through a learning period where I'll probably make many poor landings and a good suspension would probably help. So, if I could replace this setup with a more conventional shock absorber I would be interested in doing so.. maybe something like I've seen on some RAF's. Does anyone know of a system that would work well on the SH?
Thanks,
Greg Lockhart

[MichaelBurton]

In Some of the kits the rubber is harder than in others. With any of the rubber "shocks" I would be surprised if you get more than an inch of compression. This is an area that I would like to investigate as well. The shock would need to be a structural component if it just replaces the current setup.

[Dennis D]

Hi Greg.
I’ve had good results from the air bags I built.
Been using them for almost two years now.
I primarily fly off of a grass strip and they smooth
out the bumps really well.
Also, they are easy to adjust.

Dennis

[Greg Lockhart]

Dennis, your air bag looks like it was made to replace the stack of rubber donuts on the SparrowHawk. Is there a rod or shaft that goes through your air bag to keep the upper and lower plates connected and in line? Like Michael said, we need a structural component to replace the original design.
Thanks,
Greg Lockhart

[Dennis D]

Yep.
As the pictures show,the top tube slips into the bottom tube and keeps everything aligned, the bolt acts as the stop.
At the ends of the tubes are aluminum plugs with “O” ring grooves to seal in the air.

[mgoroff]

There's very little clearance on the tailwheel in the SH. I suspect that much more suspension travel on the mains would cause the tailwheel to hit and rather abruptly cause the nose to pitch down.

If you are flying from a paved runway, there really isn't any need for more suspension travel IMHO. Those big sport copter blades cushion all but the highest flare landings just fine. If you flare way to high, add some power to cushion the landing and all is forgiven. If you are flying from rough strips, the SH is not a good choice. Even with more suspension travel, there isn't much ground clearance under the dropped keel.

Marc

[Greg Lockhart]

Marc,
That's a good point... I hadn't thought about the tail wheel clearance... definitely something to keep in mind.

Thanks,
Greg Lockhart

[Dennis D]

Hi Marc
The only other reference I have is my old SnoBird. It used a design similar to the SH with rubber doughnuts and you feel every little bump. With the airbags adjusted correctly its a much softer ride and its definitely easier on the airframe during take off.
I agree, the SH probably isn’t the best choice for a rough field machine but IMHO they would be an improvement over the existing design.

[MichaelBurton]

Dennis,

Can you give me a list of parts and vendors. What parts did you machine and would you be willing to machine similar parts for the SH?

[Dennis D]

Hi Mike.
I’ll look up the information and get it to you by tomorrow.
Also happy to make parts.

[MichaelBurton]

You are the best.

[Greg Lockhart]

Dennis, I would be interested in the parts information also... thanks.

Michael, I believe your SH is one of the early kits like mine. Are you going to increase the size of the upper strut on the landing gear? I don't know if you were aware of it, but about 3 years ago GBA sent out larger diameter tubes for the lower part of the upper gear strut. The original was a 1 inch tube and they went to a 1 1/8 inch like they put on the SHII and SHIII (I understand that one or two of the original 1" tubes had bent). But the larger tube also had a much thicker wall (same ID as the 1" tubes) to accommodate the original threaded inserts. I wasn't too interested with the larger tube they sent out because they were very heavy. I'm going to try to come up with a way to use thinner walled (.065) 1 1/8 inch tubes (same as the lower gear tubes) on mine as I look at doing something different with the suspension.

Greg Lockhart

[Dennis D]

Mike and Greg.
Here is a list of the main components for the struts.
If we were to build a set for you we should make a few changes.
I tried to upload a CAD drawing and a scan from the Firestone engineering manual but the file size was to big to upload.

Air Bags, Firestone Airmount # 160
Upper tube, 1”x.065 4130 steel.
Lower tube, 1.25x.065 4130 steel.
Bag mounting flange, .099 4130 steel.
Slide bearings, MD nylon.

Dennis

[Mike Stone]

Dennis...
I find this thread of interest to myself also. I have been working to modify my RAF project to incorporate the AAI Stability Augmentation Kit that I purchased years ago. I will be operating the craft from a grass strip and have always thought there had to be a better way to soak up the field roughness than with what has been supplied thru the doughnuts.

[Dennis D]

Hi Mike.
Originally I wanted to use a conventional air cylinder but found the operational pressure to be to high to be convenient.
The bags I’m using run at about 60 PSI which is half of their rated working pressure.
The Viewmaster weighs in at 561 LBS. and I weigh close to 250.
At 60 PSI the struts are closer to the top of the stroke so I feel them hitting the upper stops just before it lifts off.
The nose wheel bag runs about the same pressure.
While doing my original taxi testing I filled the bags with enough pressure to keep them hard against the upper stops because I didn’t have any experience with suspension.
With the ridged mast I could feel every little bump on the asphalt taxi way through the cyclic stick.
Eventually I lowered the pressure and it made a huge difference in feedback.
It does rock from side to side a little bit but that doesn’t seem to hurt anything and after awhile you get use to it.
The only drawback I have found is one bag has a very slow leak "in the bag itself” and after sitting about a week I have to put in a little air.
If I build another set I’ll test the bags before using them.

[Mike Stone]

Dennis...
Thanks for the reply. I too am around 250#...not sure of the final weight of my modified RAF but will probably be a little higher than yours. I will watch for your posts on any testing you may be doing. Keep up the good work with the R&D.

[MichaelBurton]

Dennis, I would be interested in the parts information also... thanks.

Michael, I believe your SH is one of the early kits like mine. Are you going to increase the size of the upper strut on the landing gear? I don't know if you were aware of it, but about 3 years ago GBA sent out larger diameter tubes for the lower part of the upper gear strut. The original was a 1 inch tube and they went to a 1 1/8 inch like they put on the SHII and SHIII (I understand that one or two of the original 1" tubes had bent). But the larger tube also had a much thicker wall (same ID as the 1" tubes) to accommodate the original threaded inserts. I wasn't too interested with the larger tube they sent out because they were very heavy. I'm going to try to come up with a way to use thinner walled (.065) 1 1/8 inch tubes (same as the lower gear tubes) on mine as I look at doing something different with the suspension.

Greg Lockhart

Greg,

This is the forth SH I have been involved in building. I have seen more than one suspension failure. The tube that fails in every case that I have seen is the lower main tube below the rubber donuts. I noticed that the lower tube used by Dennis is 1 1/4. In my opinion this is sufficient to prevent failure in all but extreme cases.

Did you get the larger tubes from GBA? If you did I may be interested in them.

[MichaelBurton]

Dennis, What happens if one of the bags deflates? Can this cause the gyro to tip over? Perhaps we should have the two bags connected so that they would both deflate.

The empty weight of most SHs is around #900 and the SH maxes out at #1500. do you think these bags are large enough?

[Greg Lockhart]

Michael, do you know what size tube (below the donuts) GBA used on the II and III? Is it 1 1/8" with .065 wall thickness... same as the two lower gear tubes? If so, has there been any failures of those to your knowledge? That is what I thought about using to upgrade my upper tube instead of the tubes sent out by GBA.
The tubes that GBA sent me for the upgrade are 1 1/8" with .120 walls. They are heavy... about 2 1/2 lbs each (compared to about 1 1/2 lbs. for the .065 wall ). I thought the thickness (and weight) was overkill. I think they used that wall thickness to get an inside diameter that would fit the other original parts (like the threaded inserts).
I guess my question is this: Is a 1 1/8" (.065 wall) tube considerably stronger than a 1" tube of the same thickness ... and is it adequate for this application? I'm trying to keep from adding unnecessary weight if possible.

Also, I like to keep things as simple as I can (and less expensive if possible). What about just replacing the stack of rubber donuts with a spring of the right stiffness to allow a little bit of compression? I don't know how well that might work... or if it would be possible to find a spring of the right diameter, length and stiffness.
Thanks,
Greg

[Dennis D]

I figured we would need to make changes. I have to leave now but will be back later on today.
Dennis

[Dennis D]

Mike B.
I asked those same questions,what if one bag deflates? and, should I connect them?
I decided that since they were running at half of the rated working pressure, chances were in my favor that they wouldn’t blow out catastrophically, but were more likely to develop a leak and deflate sitting on the trailer.
As for tying them together, I think separately they work better in keeping the gyro upright.
I’ll email the scan of the performance chart to you so you can make a decision wether or not there is enough of a safety factor.
If “this" bag isn’t enough they make bags that will support up to 98,180 LBS. at 100 PSI.
If anybody else would like to see the chart P/M me with your email and I’l send it to you.
Dennis

[MichaelBurton]

Link to PDF (http://docs.google.com/fileview?id=0B0v8ppE_BifQYjI0NjZiNzEtOTU4NC00NjYzL WIzYTgtMzA3NTcyMzFkNThk&hl=en&authkey=CM-DiZ8H)for the actuator.

[MichaelBurton]

Dennis,

The reason I was thinking about tying them together was to prevent tip over if one bag were to leak out causing the gyro to tip. If the bags were linked then both would deflate and there would not be a tipping problem. Another option would be to limit suspension travel preventing a tip over with a deflated bag. I am not sure how far the gyro can be tipped without causing a problem so this may not be a real problem.

Thanks for the info on the bag. I posted the link in case there were others interested.

[MichaelBurton]

Michael, do you know what size tube (below the donuts) GBA used on the II and III? Is it 1 1/8" with .065 wall thickness... same as the two lower gear tubes? If so, has there been any failures of those to your knowledge? That is what I thought about using to upgrade my upper tube instead of the tubes sent out by GBA.
The tubes that GBA sent me for the upgrade are 1 1/8" with .120 walls. They are heavy... about 2 1/2 lbs each (compared to about 1 1/2 lbs. for the .065 wall ). I thought the thickness (and weight) was overkill. I think they used that wall thickness to get an inside diameter that would fit the other original parts (like the threaded inserts).
I guess my question is this: Is a 1 1/8" (.065 wall) tube considerably stronger than a 1" tube of the same thickness ... and is it adequate for this application? I'm trying to keep from adding unnecessary weight if possible.

Also, I like to keep things as simple as I can (and less expensive if possible). What about just replacing the stack of rubber donuts with a spring of the right stiffness to allow a little bit of compression? I don't know how well that might work... or if it would be possible to find a spring of the right diameter, length and stiffness.
Thanks,
Greg

Using a thicker wall tube for greater strength is rarely worthwhile. A better solution is to go up in tube size while retaining the original wall thickness.

Data for a 1 Inch OD tube with a .065 wall thickness
Cross Section: 0.191 Sq. In.
Weight per Foot: 10.4 ozs.
Moment of Inertia: 0.021

Data for a 1.25 inch OD tube with a .065 wall thickness
Cross Section: 0.242 Sq. In.
Weight per Foot: 13.184 ozs.
Moment of Inertia: 0.043

In this example you can see better than twice the bending strength with a weight increase of less than 3 oz per foot.

Data for a 1 inch OD tube with a .13 wall thickness
Cross Section: 0.355 Sq. In.
Weight per Foot: 19.328 ozs.
Moment of Inertia: 0.034

With this tube we have a weight increase of about 9 ozs per foot and strength that is only 3/4 of the larger diameter tube.

[MichaelBurton]

I don't know of any SHs with the larger main tubes that have had gear collapse.

Data for a 1.125 inch OD tube with a .065 wall thickness
Cross Section: 0.216 Sq. In.
Weight per Foot: 11.76 ozs.
Moment of Inertia: 0.031

Data for a 1.125 inch OD tube with a .12 wall thickness
Cross Section: 0.379 Sq. In.
Weight per Foot: 20.64 ozs.
Moment of Inertia: 0.049

I think I would put a sleeve on the insert if I wanted to retain the original parts for the rubber bumper. Then go up to the 1.25 inch tube and have a lighter gyro with similar strength. I believe that the one inch tube will fit inside the 1.25 .065 tube. In that case it would be easy so use some of that tube where the lower tube attaches.

[Dennis D]

Mike,
My concern with linking the bags together was that when you make a turn the weight shift is to the outside airbag which compresses the existing air.
By allowing the higher pressure to transfer or equalize into the inside bag, you would loose the pressure differential that tries to keep the gyro upright.
I do agree that one bag deflating instantly could be fatal under the right conditions.
Do you think the safety margin I figured in is inadequate for safe operation?
It would certainly be possible to build a valve body that would sense a given pressure differential if one bag did burst and release all pressure. But then again there is the rubber doughnut idea....

[PW_Plack]

The reason I was thinking about tying them together was to prevent tip over if one bag were to leak out...

Mike, a couple of people have had the same thought about the air shocks on Dominators (or just wanted the convenience of a single fill point) and put a tee, without a check valve, to feed both shocks off the same filler valve.

As Dennis notes, as soon as the gyro leans at all, air from the side with more airbag compression (and pressure) rushes through the interconnect to the other side, so you have no roll resistance left in the suspension (except for damping of the roll rate based on the size of the connecting tube.) The thing wants to tip over almost immediately. You also have more points for potential leaks.

At least the Dominator also has gas shocks inside the air bags, which slow the roll down.

I'm not sure there's any more chance of a single-point failure of the airbags than there is of an ordinary spring and its retention hardware. Trucks use airbags for springs routinely, and if they failed much at all, trucks would start bending stuff. It would be easy enough to practice...try taxiing with one bag low.

I would, however, want to be comfortable with the resistance of the airbags to UV radiation.

[MichaelBurton]

Mike,
My concern with linking the bags together was that when you make a turn the weight shift is to the outside airbag which compresses the existing air.
By allowing the higher pressure to transfer or equalize into the inside bag, you would loose the pressure differential that tries to keep the gyro upright.
I do agree that one bag deflating instantly could be fatal under the right conditions.
Do you think the safety margin I figured in is inadequate for safe operation?
It would certainly be possible to build a valve body that would sense a given pressure differential if one bag did burst and release all pressure. But then again there is the rubber doughnut idea....

Dennis,

It did not look like there would be a problem with the size of the bag. I think I am fine with the configuration of the system. I just needed to think through the problem. How long do you think it would take to make a set for me?

[Dennis D]

Not long at all once we have a sound design.
I would like to make a few changes to simplify the way everything is sealed.
Do you have a CAD program? I could make a few changes to some existing drawings and
we could collaborate on the final design.
I can export in .dxf /.dwg /.prt

[Dennis D]

I’ll make a call and verify that the bag we are looking at is still available.

[MichaelBurton]

Dennis,

dwg or dxf should work for me.

[oldsparky]

71229
Photo of my suspension.

It is thin wall alu tube, 50 mm dia. with a plastic piston and 2 hydraulic seals.
A little oil covering the piston helps the seal and lubricates the bore.
I use one of those cheap 200psi 12v compressors to put about 150 psi in.
Its set up so its normally fully out and only works when subject to extra load.
My MTOW is about 730 lbs.
This system is light and dependable, its 10 years old now, and may need a air maybe once a year.
Air is a brilliant lightweight system with excellent progression.
I learned to fly from the ground up in this gyro which subjected it to some serious punishment but the suspension soaked it all up.
I do not have a prerotator so have to do a fair bit of taxiing over rough ground at times to get rotor speed up and this system keeps a lot stress out of the airframe and control system.
If I did it again I would use a larger dia. to reduce the air pressure.
Anyone with a lathe could build these easily.
cheers Bruce

[Dennis D]

Hi Bruce.
When I was building my gyro I wanted to use air cylinders.
With the way my suspension is set up there is a leverage disadvantage working against the cylinder or air bag.
I don’t remember what the ratio is, but it’s around 2.5 to 1.
I spent a lot of time modifying the cylinders in the pictures but finally decided the air pressure would need to be to high and went with the air bags.
I tested several different bags before choosing the Firestone #160

[oldsparky]

G'day Dennis,
I also looked at commercialy available cylinders but had the time and use of a lathe so did the sums and built my own and have been very happy with the result.
One heavy landing resulting in a collapsed suspension is a very expensive event and justifies a good suspension.
I was at a fly in once and most were complaining because we had to taxi over some curbing between our marshalling area and the runway, and it was knocking their planes about and the violent movement of the airframe was causing violent movement in the control system.
If you can keep these stress's out of the airframe and control system, all the better.
anyway, I'm sure youre happy with your system, you should be,,, well done!
cheers, Bruce

[lanichol]

Interesting ideas. So why not use a commercial hydraulic cylinder filled partly with oil and partly with air. The air will compress, so you could control the volume and travel by air pressure and the amount of oil.

[oldsparky]

Hi Larry,
Why not use a hydraulic cylinder? Weight!!! I begrudged every gram on my gyro. The suspension I made is light. I would make these for the local gyro boys but now I am retired I don't have the time.
cheers Bruce

[Dennis D]

G’day Bruce.
You’ve got me thinkin again about using a cylinder.
Maybe someone out there knows where to find a cheap high pressure air compressor in the 700 to 1000 PSI range.

Hi Larry,
I tried to find surplus aircraft hydraulic cylinders that were designed to be light but couldn’t locate anything that was the right size that was inexpensive.

Thanks for the input.

[Brent_Brown]

I use a set of RANs S-12 gear and they work great. The S12 is a 2 place that can see 1200 pounds so it is over kill for mt 750 pounds gross gyro. If I use them agine I would put more cin them so they are flat with me in the seat.

[bmoore2156]

Dennis,
Depending on the cost, I would also be interested in the airbag setup.
Thanks
Brad

[Mike Stone]

Dennis...
From an earlier posting on this thread, I would be interested in also purchasing a set.

...Mike

:sorry:
Not to highjack the thread, but to Mike B...Can I assume the ship you may be putting this on is your trainer? I need to send you a P.M. about getting an add-on to my ASEL ticket later this fall.

:yo:

[Dennis D]

Hi All.
I have an appointment tomorrow with the Firestone Rep. I want to make sure there isn’t anything new that might be better for our project.
As soon as we finalize the design I can come up with a price, I was quoted $97.20 per bag for the #160 and they said they had 200 in stock.

Dennis

[Dennis D]

Think I’ve found a better bag but won’t know about availability until Monday.

[MichaelBurton]

I will be out of town for a week starting Monday so I won't be much help. I just wanted you to know so that you would not think I had lost interest.

[Steve McGowan]

Fellows,,

Yall need to LEARN how to land the Fat A$$ Sparrow Hawk and not mess with the suspension. Mr YOPP built it to carry 1500+ pounds.

It's by No Means a ButterFly, or a Monarch which was built for a drop in landing.. It's a CADILLAC,, Not A Porch or Corvette..

Ya Gonna BUST It Up...

But Hey,, Thats Just My ASSUMPTION and we know what that means..

Have at It!!

[Dennis D]

Well, I finally heard back from Firestone and the new style of airbag that I would like to use is not available for about three months.
They have moved their production out of the US and hope to be up to speed soon, but are not there yet.
When I get a chance I can check around and see if Goodyear or someone else makes a similar style.

Mike,
I asked if there was a chance they could come up with just two so we could make and be testing a prototype pair but they said “none" were available.
How far away are you from needing your suspension?

[MichaelBurton]

Dennis,

I have been out of town for the week. I need the main gear legs now. I can not remount the pod or the engine until the gyro can support itself.

[MichaelBurton]

Fellows,,

Yall need to LEARN how to land the Fat A$$ Sparrow Hawk and not mess with the suspension. Mr YOPP built it to carry 1500+ pounds.

It's by No Means a ButterFly, or a Monarch which was built for a drop in landing.. It's a CADILLAC,, Not A Porch or Corvette..

Ya Gonna BUST It Up...

But Hey,, Thats Just My ASSUMPTION and we know what that means..

Have at It!!

Hi Steve,

I have the old landing gear from the SH1. It is inadequate for the weight of the gyro. I have always felt that the SH could use a bit of cushion. I am not looking to make it a drop in lander I just like my fillings to stay in place as I roll around the airport.

[Riff Raf]

Mike
Wouldn’t the different attachment points make a difference in the leverage ratio put on the airbag maybe calling for a different airbag for the application.
such as lowering point (A) downward (like on a SH) would in increase the leverage through point (B) to (C) (which would go higher i.e. a SH) and you would have to have more air in the bag to compensate, will this bag go that far? oh and the difference in weight between the two gyro's?
Isn't there some kind of algebraic (sorry physics equation) / triangulation for this?
where's CB when you need him

[PW_Plack]

Roger, lowering the attachment point at (A) would decrease the leverage on the bag, not increase it. Minimum leverage would occur if the tubes along A-B were at 90º to the vertical tube between B & C.

I believe the bags Dennis has used have a tremendous amount of excess capacity if further inflated.

[Steve McGowan]

Hi Steve,

I have the old landing gear from the SH1. It is inadequate for the weight of the gyro. I have always felt that the SH could use a bit of cushion. I am not looking to make it a drop in lander I just like my fillings to stay in place as I roll around the airport.

You are so RIGHT Michael..

[Greg Lockhart]

Everyone, thanks for all the comments, suggestions and help.

Brent Brown, what does the Rans S-12 suspension look like.. is it something that would work on a SH type setup..can you post a picture?

Master Roda, is the suspension on the Sportcopter II a proprietary design or off the shelf components? From the pictures I've seen it looks compact and simple (just what I'm looking for). I imagine it would work well on the SH since they are of similar size and weight.

Thanks,
Greg Lockhart

[Dennis D]

Hi Mike.
Would it be possible for you to use the old struts while completing your build?
The reasons I would like to wait for the new bags are,
1 The bag itself would require no modication to replace when needed.
2 The factory seal is used instead of a “Gasket”.
3 Easier to build which translates into cheaper.
My original idea when you became interested was to build a set for you and let you do some testing, then give your opinion on their operation.
The set I build for you, should be very close to ones I build for others "if anybody else is interested”.

HB.
Firestone uses a three fold safety factor, normal maximum operational pressure 1/3 bursting pressure.
At close to the center position in the stroke, 100 PSI. generates close to 2200 LBS. of force in the #160.
With my all up weight being close to 850 LBS. + -, I use 62 PSI.in the Viewmaster mains and 60 PSI. in the nose wheel.

Goodyear doesn’t have anything in the style we are looking at.

Dennis

[Brent_Brown]

Rans S12 would be a good plane to convert to a gyro. I look for damaged S12s maybe find a deal and convert one.
The S12 is lighter than a SH so it might not be a good replacement

[Brent_Brown]

Her is one with just a mini body

[MichaelBurton]

Hi Mike.
Would it be possible for you to use the old struts while completing your build?
The reasons I would like to wait for the new bags are,
1 The bag itself would require no modication to replace when needed.
2 The factory seal is used instead of a “Gasket”.
3 Easier to build which translates into cheaper.
My original idea when you became interested was to build a set for you and let you do some testing, then give your opinion on their operation.
The set I build for you, should be very close to ones I build for others "if anybody else is interested”.

HB.
Firestone uses a three fold safety factor, normal maximum operational pressure 1/3 bursting pressure.
At close to the center position in the stroke, 100 PSI. generates close to 2200 LBS. of force in the #160.
With my all up weight being close to 850 LBS. + -, I use 62 PSI.in the Viewmaster mains and 60 PSI. in the nose wheel.

Goodyear doesn’t have anything in the style we are looking at.

Dennis

Dennis,

I can put the old gear legs on until I am ready to fly. I just don't like them at all. I could even get the gyro inspected with the old gear legs. I just don't want to fly with it in this configuration. So I guess we have some time.

[lanichol]

Dennis,

I can put the old gear legs on until I am ready to fly. I just don't like them at all. I could even get the gyro inspected with the old gear legs. I just don't want to fly with it in this configuration. So I guess we have some time.

Mike,

I agree for two reasons: The suspension as you have discussed, and second the attachment points. I like the lower attachment position of the Super Sportcopter. Had the drop keel been block out larger and towards the front it would be possible.

[Dennis D]

Hi Mike.
I have tried every avenue to get a couple of #160’s.
The #160 is a single convolution, 4 1/2” stroke and weighs 3 lbs and close to $120.00
The next choice in the correct style #255-1.5 has two convolutions, 4" stroke and weighs 4 lbs and probably more money.
I’ll check availability today.

[Dennis D]

Mike.
The 255-1.5 is available, $140.59 ea.
Think it over and let me know what you would like to do.

Dennis

[Greg Lockhart]

Still looking for an alternative for the SparrowHawk suspension.
Dennis, I appreciate you checking on the airbags... at this point I think I would prefer to go with a more conventional shock.

Does anyone know what kind of spring / shock this is on an RAF?

Thanks,
Greg Lockhart

[lanichol]

It looks like the Don Parham mod. "rfi"

[Dennis D]

Your welcome Greg.
Mike and I are proceeding with the air bag design and should be posting the results of his testing.
Dennis

[Riff Raf]

Couldn't you just use a tire with more air volume? it's an air bag!
boing,boing,boing. :confused:

[vickijohnk]

That shock in post 60 looks to be "coil bound" and would not have any travel at all. John K.

[tomhall]

The shock on the RAF is indeed a Parham system. The shock is from Azusa; they sell a lot of go-cart and mini-bike things. It is designed to be fully compressed on the ground and loosens up on take off. It is then able to absorb any landing shock. Fully compressed on the ground lessens any ground handling problems. Tom T. Hall in MN

[cgmg]

Here's a source for the shocks Don Parham used:

http://www.gokartgalaxy.com/shock_absorbers.htm

It's the red one. I've saved this bookmark for when my shocks wear out.

[lanichol]

The problem is you have to make one end of the shock connector solid, in Don's mod, I believe he used flarred exhaust tail pipe.

[Greg Lockhart]

Thanks Mark,
From the pictures on that link it looks like the black shock in the middle of the page would fit down in a tube better than the red one since the bottom part of the shock is longer and looks smaller in diameter. Do you know what the diameter of the lower part of these shocks is? I guess I'm looking for something small enough to fit inside a 1 1/8 or 1 1/4" tube. Do you have any pictures of your setup that you could post?
Thanks,
Greg Lockhart