Dominator landing gear in action-video [Archive]

scottessex

07-31-2008, 05:46 PM

Mark, yes they are a coil over shock, they are Chirco VW dune buggy shocks, (about $60pr) the springs are off a motorcycle of undetermined origin. I had them on the shelf, I don't know where they came from. The dune buggy springs were way too soft.
Trez (Cracker) here on the forum is doing a similar mod and was able to get about 3 different pair of Harley springs off Ebay, I hope he chimes in.

mark treidel

07-31-2008, 05:50 PM

Thanks Scott, I've been waiting for this type of information for a long time now. Seems like its finally coming together. Are the shocks the 16" travel like Ernie uses on the air shocks? Bolt directly on? Any modifications you had to do?

scottessex

07-31-2008, 05:52 PM

Yes Mark they are the same length. I had to make a few mods but nothing major.

gyromike

07-31-2008, 05:56 PM

Scott,

How does it feel when you're taxiing around?
Any roly-poly feel when turning?

Racer

07-31-2008, 06:06 PM

Great Idea Scott, Love that camera angle.

scottessex

07-31-2008, 06:13 PM

Mike it feels great! very smooth and does not want to tip side to side, very stable, and no duck walk!
The takeoffs are super smooth.

Phil_Ruffin

07-31-2008, 06:25 PM

I have these on mine and are super smooth. The 1700-246 version.

http://www.azusaeng.com/shocks/shocks.html

I'm also very happy with them. The runway I use was a little rough but not anymore.

PPG Doug

08-01-2008, 07:18 AM

Would you post some details of your shock set up for us, non mechanically inclinded?

I have a Dom. and the "no duck walk" part really caught my attention. I'd love, as would everyone I'm sure, some good details and pics of the mod's necessary etc...

Can you lend us a hand?

Thanks and congrats on the upgrade!

Alan_Cheatham

08-01-2008, 02:36 PM

I have these on mine and are super smooth. The 1700-246 version.

http://www.azusaeng.com/shocks/shocks.html

I'm also very happy with them. The runway I use was a little rough but not anymore.

Three weeks ago I purchased a pair of Azusa 1700-246 shocks and when I got them I measured their specs to make sure the dealer shipped the correct ones. According to the Azusa catalog and other web sites the -246 should have 3" of stroke and 730 lbs total load compression. The other shock like this one, the 1700-128 is listed at 2.5" of stroke and 500 lbs of total load compression. The shocks I received measure 2.5" of stroke, (easy to check with a ruler) and only 477 lbs of compression measured with a hydraulic scale and at full spring compression. I called the dealer, he said they were the correct ones, -246, so I e-mailed Azusa and gave them the specs and they confirmed they are the -246. So if you order some for a gyro don't be surprised it they don't measure up to specs, but if they work good that's all that counts.

mark treidel

08-01-2008, 04:46 PM

scottessex

08-01-2008, 04:49 PM

the problem with shocks is figuring out all the engineering. just because they are rated at a certain LB compression does not mean anything other that the spring compression.
A lot has to do with the angle, the lever arm of the gear, the mechanical advantage the gear puts on the shock depending on location.
I just use the trial and error method. I know it is not scientific but I can usually make it work.
I am working up some info to help y'all out, but this is where the "experimental" in experimental aviation comes in.
I will post some info and pictures very soon for those who are interested.

I have some theories on the duck walk and air shocks too.

Ernie builds a very fine machine and every time I have second guessed Him and tried to change something, I have gone back to the way Ernie built it, He knows his stuff no doubt. He builds them like that for a reason. It works.
The air shocks are great from a manufacturing standpoint, they work for every engine combo and pilot weight. But on a light gyro I was never able to get a happy setting, either too soft or too hard.
If you do the coil over mod, you will be tuning your gyro for YOU, and your specific gyro,
so you may have some trial and error before you get it where you are happy with it.

So far I love it, Trez (Cracker) converted his, and the two aircommands I did the shock mod on still have happy pilots, (Phil R. and Greg S.)

MikeBoyette

08-01-2008, 06:54 PM

Hey guys,
There might be a factory mod coming for those who want it. Trez showed dad his at 4th of July and dad is very interested. His biggest concern is continued availability. The air shocks are great for this. If he can get the springs and they are constantly the same spring rate then he will start offering them.

Alan_Cheatham

08-01-2008, 06:57 PM

Al, are they 16" long at full extension? The add says 12". What type of gyro do you have them on? I'm looking for ones to put on my Dominator but they have to have a 16" throw, same at the original air shocks. Thanks,

Mark, they are right at 12" as per the specs. The nice thing about them is it's easy to sleeve a tube over them, and I'm sure an adapter could be made to extend the eye to eye length to 16". Take a look at Phil Ruffin's thread here for ideas: http://www.rotaryforum.com/forum/showthread.php?t=15004&highlight=shock&page=2

Trez

08-07-2008, 06:15 PM

There's a parallel thread on this subject at:
http://www.rotaryforum.com/forum/showthread.php?p=243452#post243452

scottessex

08-08-2008, 04:41 AM

I am still going to post info, just haven't gotten around to it yet, after this weekend I'll have more time and get something together, hang in there....Thanks Trez!

mark treidel

08-08-2008, 06:38 AM

Racer

08-08-2008, 07:00 AM

Scott, looking forward to you informative post. I guess I'm looking for numbers for the shocks & springs that no one has put up yet. What I really want is a spring over shock with 16" travel that will simply replace the air shocks I currently have on the Dominator. Seems to me that there has to be something that will just 'substitute out' without having to make any modifications. Just dont know the numbers... Anybody have any other info??

Here ya go Mark, http://www.afabcorp.com/AFCO_Dynatech_USbrake/merchant.mvc?Screen=CTGY&Store_Code=A&Category_Code=ct_r-alum-sm-th
A bolt on replacement shock and light weight as well.
Order any rate of springs you want http://www.afabcorp.com/AFCO_Dynatech_USbrake/merchant.mvc?Screen=CTGY&Store_Code=A&Category_Code=ct_small-coil-over
and ""shazam"" You have nice shocks that will outlast your gyro.

Here is a cheap spring that is rated @ 500#
http://www.afabcorp.com/AFCO_Dynatech_USbrake/merchant.mvc?Screen=PROD&Store_Code=A&Product_Code=29500-1&Category_Code=ct_coil-over-sb10
That should work good for you with your setup and it would be stiff enough to keep you from doing the "Duck Walk" If you need help on exact shock #'s I would be glad to help.

I know they are expensive but it is only money... right?

gyromike

08-08-2008, 08:30 AM

I have a pair of AFCO's sitting in the hangar with 500 lb. springs, but that's too stiff.
Heavy too.

mark treidel

08-08-2008, 09:53 AM

Todd, thanks for the info....I will call you on the land line for a follow-up. Would you please PM me your phone # again...

Mike, is that 500#'s per side or total? My all up weight is about 750 #'s. and the current air shocks I have on (Monroe) have a 16" full extension. Let's talk....Thanks,

C. Beaty

08-08-2008, 10:18 AM

You want a static deflection at the wheels of 3-4 inches. This will give a ride rate in about the same range as small pickup trucks.

Suspend the gyro from the teeter bolt, remove the existing spring/shock and measure the deflection between shock attachment points while moving the wheel a known distance.

If the movement between shock mounting points is 1” for a 2” wheel deflection and the normal weight on the wheel is 300 lb., you’ll need a spring rate of 200 lb/in to give a static wheel deflection of 3”.

A 3” static deflection will produce a ride rate of 108 cycles/minute

A 4” static deflection will produce a ride rate of 94 cycles/minute.

Harry’s 1979 Oldsmobile Toronado has a ride rate of ~60 cycles/minute, requiring nearly 10” of static wheel deflection.

Racer

08-08-2008, 11:12 AM

Thanks Chuck,
I was actually going to call AFCO technical support and give them all the dimensions and angles before I ordered anything. They are very helpful in figuring out exactly what you need.
Your advice is very helpful, I have several sets of springs on the shelf that I can test for this application, I do believe they will be too soft though, they are for the front of my race cars and do a great job at absorbing the large bumps but they do move a lot.

How stiff should the suspension be to prevent the famous "Duck Walk?"

P.S.
Mark,
I will help get you set up nicely, if we do not get the correct spring setup the first time I will eat the cost and order another set, my pocketbook.
That way you have nothing to loose, You will only pay for what you keep.

Racer

08-08-2008, 11:27 AM

One nice thing about the AFCO shocks is that black rubber ring on the shaft measures how much travel the shock is experiencing.

C. Beaty

08-08-2008, 11:52 AM

mark treidel

08-08-2008, 12:13 PM

Chuck, thanks for the info. Since Im not too swift with a slip stick...where would I fall with an AUW of 750#? Empty weight is about 430#. Would that mean I need a 375# spring on each side??
Todd, no you wont 'eat' any costs for me but I would be more than happy to use your help in the set up & absorb your costs up here. Send me your Ph. #. I cant find it anywhere....Thanks
Forgot to add that I would like to find a pair with the stiffness adjustment as in the other shock thread. Do the AFCO's have those Todd?

C. Beaty

08-08-2008, 12:35 PM

Mark, if I knew the ratio between wheel travel and spring compression, I could give you the proper rate spring but I don’t.

If you have 75 lb. on the nosewheel, the remaining 675 lb. should split evenly between main wheels, loading each to 338 lb. If the linkage ratio between wheel and spring was 1:1, you would need springs of ~100 lb./inch. But I doubt if the ratio is 1:1.

mark treidel

08-08-2008, 12:39 PM

Chuck....If memory serves me, I believe Ernie said the ratio was 2/1.
From what you are saying, I should be able to use 2/350# springs..corrrect?
I'm confused....

Racer

08-08-2008, 12:50 PM

Mark, The reason I am suggesting AFCO shocks for you is they would be a direct bolt on that are very close to 16" The body of the shock is threaded so you can pre load the spring and adjust the ride height a bit. When I get home I will weigh the complete setup so that we know exactly how heavy they are.

Chucks advice is very helpful, We will set you up nicely.

gyromike

08-08-2008, 01:44 PM

Mike, is that 500#'s per side or total? My all up weight is about 750 #'s. and the current air shocks I have on (Monroe) have a 16" full extension. Let's talk....Thanks,

Mark,

That would be 500 lbs. per spring.

Spring rates are measured per inch of compression. These are rated @ 500 lbs. of force to compress them one inch. They have about 5 inches of range before they bind, so it would take 2500 lbs. of force to fully compress them. 5000 lbs. for the pair.

They're pretty hefty. I weighed the whole setup once, but I don't remember the numbers. The aluminum dampers themselves are pretty light though, and they come with rod end bearings on the ends so a little misalignment is no problem.

mark treidel

08-08-2008, 01:52 PM

Mike, that is probably more spring than I require (although I'm not quite sure how to figure that). I'm thinking about 375 per side but waiting for Chuck B. to weigh in here again. Back with you after that. Thanks,

gyromike

08-08-2008, 02:04 PM

A 6” static deflection may get you into the duck walk range. That gives a ride rate of 76 cycles/minute, pretty much into the “cushy” range.

The duck walk is a function suspension geometry; tire scrub vs. suspension travel, producing a sideways pole vaulting effect.

If wheel travel was vertical, there would be no duck walk no matter how soft the springs. Stiffer springs limit normal wheel travel, which reduces scrub.

Chuck,

I have been pondering this for a while (ever since you showed me how to calculate ride rates).

I have been thinking of making new struts and control arms for my Dominator project that would have the attachment of the lower control arm moved up on the leg similar to yours to eliminate/reduce tire scrub.

But I am not sure how much larger I would have to make the strut to deal with the bending moment on the strut.

Aircraft Spruce suggests that 1.5"x.049" 4130 round tube to be the equivalent of the streamline tube you use but I think they're talking tensile strength.

C. Beaty

08-08-2008, 02:33 PM

Mike, a friend of mine made a Dominator with the lower A arms nearly level and got by with 1” x 0.125 wall round tube for the legs.
************
Mark, a nominal load carrying capacity doesn’t mean very much. For spring data to be useful, the rate must be known, i.e., how many pounds per inch of deflection. Like the data given here:

http://www.jegs.com/p/AFCO/759674/10002/-1/10077

These people list springs ranging from 80 lb/inch to 550 lb/inch. This is the first one that popped up on Google but I expect there are plenty of others, perhaps cheaper.

If in fact the linkage ratio between wheel travel and spring compression is 1:1, a 100 lb/inch spring would be in the right ball park. But I have no certain knowledge of what it is.

The only real criterion for the shock is that it fit the attachment points and not be too firm.

gyromike

08-08-2008, 02:40 PM

Mike, a friend of mine made a Dominator with the lower A arms nearly level and got by with 1” x 0.125 wall round tube for the legs.
************

The only real criterion for the shock is that it fit the attachment points and not be too firm.

Thanks Chuck.

I also need to email AFCO for an explanation for the numbering system they use for damping. I don't think the ones I have are user adjustable. I may have to send them back to be reset.

What would be the proper way to determine what's "too firm"?

C. Beaty

08-08-2008, 03:06 PM

For shock stiffness, stay near those designed for vehicles of similar weight per wheel. I’ve used VW Beetle and Corvair front shocks in the past with satisfactory results.

Racer

08-08-2008, 03:06 PM

I would think too mushy would be a bad thing especially when dealing with a crosswind condition while taxiing, I could see how the wind could blow your machine at a very uncomfortable angle if the suspension was too soft.

FYI I run 145lb springs on the front (Weighs 300 lbs) of my race car and the suspension is very mushy if you jump up and down on it, uses up two thirds of the shock travel.
I am guessing this spring weight wold be much to soft for a heavier Gyro.

I should shut up now and do the math to find out the real numbers, not just guesstimate things while I am driving around chasing cars.

Racer

08-09-2008, 06:53 PM

OK, I did go out to the shop today and grabbed a bunch of shocks and a scale and here are the results of what I found

The AFCO racing shock/spring setup came in at 4lbs 9.8oz
Some coil overs I got off the snowmobile that I used for my motor (aluminum with black coil spring) Weighed in at 3lbs 11.2oz

I had a pair of stock Dominator style shocks and they weighed in at 4lbs 2.2oz

Bottom line the sled shocks were the lightest but the coils were also the weakest as well, If anyone did want to use this style shock you would probably want to buy stronger coils, which would increase the weight a bit.

mark treidel

08-10-2008, 09:28 AM

Todd, I took measurements today...16" full extension hole to hole. I believe 17" would camber the tires outward at the top (a no no). I'm going with the AFCO blue with a black spring but they need to be adjustable...no option there. Are they available that way?

gyromike

08-15-2008, 07:07 PM

Question for Scott Essex:

Do you recall how long the spacer was that you machined for your shock mods?
Also how long were the original springs?

Alan_Cheatham

08-15-2008, 10:03 PM

Well, I ordered a set of springs form the web site Trez (cracker) got his from, http://www.dtproduct.com/motorcyclesaccerssories.html and they arrived yesterday so I did some measuring and testing on them, here are the specs.

8 inch shock
2.435" o.d.
1.700" i.d.
coil wire thickness .366"
3.25" compression travel
about 223 lbs per inch compression force
weight is 4 pounds 13.5 oz per pair

7 inch shock
2.435" o.d.
1.700" i.d.
coil wire thickness .366"
2.563" compression travel
about 235 lbs per inch compression force
weight is 4 pounds 9.0 oz per pair

If anyone is interested in these springs you should check out this parallel thread, especially the comments Trez and I made concerning our ordering experience.
http://www.rotaryforum.com/forum/showthread.php?t=17127

gyromike

08-16-2008, 04:27 AM

I emailed the seller at http://www.dtproduct.com/motorcyclesaccerssories.html, and he said that he has some 9.75" springs, but they aren't chromed.

I don't know how long the spacer is that Scott used, but maybe these will be long enough to eliminate it.

scottessex

08-16-2008, 05:05 AM

Mike I used a 3" spacer, it is a PVC pipe coupling with the PVC pipe inside of it, so it is double the wall thickness.

Sorry I have been extremely busy this past week with moving my son from NC to south Georgia.

gyromike

08-16-2008, 05:18 AM

No problem Scott.
We appreciate the work you did on this.

gyromike

08-20-2008, 01:26 PM

I ordered two sets of springs on Saturday from the link above. I specified that I wanted two pair of 9.75" springs.

I got them today...plus a set of 7" and a set of 8" springs at no extra cost!

Now I need to get the shocks.

Scott, are the springs hard to change? Any special tools required?

scottessex

08-20-2008, 01:56 PM

Mike I used a large manual arbor press, and a bearing plate to compress the spring, and slid out the top keeper, then installed the spacer, and the new spring. the spacer should be long enough that the spring has some tension on it when the shock is just setting there, other wise the keeper could fall out when you have no weight on the landing gear.