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View Full Version : Need Advice on Rigid Gear Struts



Jim Miller
01-17-2011, 11:16 AM
I have heard some guys mention they are going to use rigid main gear like a PA15.
How well does this work? I will be operating off long smooth grass and paved runways
with a gross under 1320. If I use 6 by 6 tires with low pressure (What would be an acceptable tire pressure) will a rigid gear work satisfactory? I have plans and springs
and could replace rigid gear later if it didn't work out.

Thanks
JM

cubdriver2
01-17-2011, 11:48 AM
The Vagabond gear legs are at a steeper angle or closer to vertical then a Cub gear leg and have less of a mechanical advantage or leverage to stretch the bungees so the ride is the same with or without the bungees ( very hard ), I had a Pa15 for a while and it had been converted to the bungee gear and even with 2 people aboard you could stall it in from 5' :oops: and the bungees never moved, Jim Jenkins had both type Vags at one time and told me he liked the solid gear better because it was faster and that the 800 X 4 were the only cushion that a Vag had with or without bungees so if you were to run 600 tires with higher air pressure you would not have any suspension unless you went to bushwheels.

Glenn

Jim Miller
01-17-2011, 11:56 AM
Glen
I wonder how it would work with the 600 using the lowest pressure I could or going to a slightly larger tire
with low pressure. I would want to use enough pressure that the tires could never spend on the wheels
of course.

qsmx440
01-17-2011, 12:19 PM
What is the weight trade off bungees vs low pressure bush wheels on rigid gear? Maybe a better question would be (for experienced people) your given a choice medium/large wheels or small wheels with bungees but not both. Assumining (the above posts parameters) pavement or normal grass runways which would you take? Is the choice major? And Jim you could run both depending on the load. I see where your going with this (1320#) and I have been wondering about this too. Aoss and small wheels seems most likly to me but I know nothing about wheels so far except they are big bucks and you want to get it right the first time. My fuse is sitting on "EMT" rigid suspension with 5" donated (from local A&P trash bin) Cessna 150 nose wheels for now. They fit the old 1 1/4 Piper legs perfectly.

d.grimm
01-17-2011, 01:50 PM
TCDS for the PA15 Vagabond show a 5 lb. weight for the shock struts. As with most other weights of Pipers this vintage I believe that is probably closer to 5 lb. per gear leg.
Ski and Tundra Tire installations require the shock struts. I was advised against changing to rigid gear on mine for airframe life.
Dave

Jim Miller
01-17-2011, 05:04 PM
A rigid gear is probably not the best of idea's in my case. What is the name of the gear mod that has two springs and
some kind of hydrolic action? I remember seeing a picture of something like that.

Jim

Steve Pierce
01-18-2011, 08:00 AM
The Vagabond also had 800x4 tires which had a lot of side wall and shock absorption. A friend had a Clipped wing Cub with these tires and stiff gear and it worked fine but you knew if you dropped it in.

qsmx440
01-18-2011, 10:14 AM
I wouldn't even consider it if it wasn't for weight savings and this is probably one of those areas where I best at least start off with "correct" gear since i don't have my TW endorsment and then maybe consider something different. Someone ask about the "dual spring" setup: http://www.calumetcub.com/products.html

Jim Miller
01-18-2011, 10:51 AM
I wouldn't even consider it if it wasn't for weight savings and this is probably one of those areas where I best at least start off with "correct" gear since i don't have my TW endorsment and then maybe consider something different. Someone ask about the "dual spring" setup: http://www.calumetcub.com/products.html

Thanks, I will check it out. Also for general information about springs. The Danley co. website (Danley makes most of
the springs suitable for our aircraft) has a catalog feature where you can plug in info and get the spring part #.
The springs from Spruce are yellow (extra heavy duty) with a deflection of 1/10 inch for every 142lbs (My guess). The next weaker spring is Red and the same size 6" X 2" OD and has a deflection of 1/10 inch for every 88 lbs. The red are
considered Heavy Duty. These 6 inch springs can be depressed about 2 inches under full load. The load required to
depress the Yellow is 20 times 142 or 2840 lbs. The force required to depress same size (6 inch X 2" OD) Red spring
is 20 times 88 or 1760. In both cases the forces are to bottom out spring (depress 2 inches). Question is would the
Red spring possibly be heavy enough for a LSA type cub with a 1320# gross and about 1200# average operating weight?

qsmx440
01-18-2011, 11:38 AM
With a spring it's not just what it will support but also the "rate" at which it supports the weight. The motocross community went through all of this years ago and many different configurations were tried with the ultimate goal that the suspension "evenly" support the weight through about 12" of travel. Different shock rates were needed for compression and rebound. If you want maximum effectivness there are many parameters. It is almost like music and depending on gross weight, terrain, skill, strength, gear weight allowance, etc. many different "correct" ,solutions and way more wrong . Suspension of anything that moves is way more complicated than it first appears. Experience is the best indicator of being able to come up with a new solution and you would need a few years and probably a 200K budget while you were testing. My opinion is that the AOSS guy would be the best person to come up with a new better and even cheaper solution to his current apparent "state of the art" system. The only short circuit to that would be to find another application that mimmicks the cub parameters and has a worked out solution to that system. Or just plain brilliance or dumb luck!

qsmx440
01-18-2011, 11:51 AM
I think there are two similiar threads going ? I think I meant thmy post for the other one.. Oh Well

Jim Miller
01-18-2011, 11:57 AM
qsmx440
I am willing to settle for the limitations of a coil spring. I just want to get the best one "Not too stiff, Not to soft. I have
an inquiry in to Legend Cub for advice.

Jim

qsmx440
01-18-2011, 12:14 PM
qsmx440
I am willing to settle for the limitations of a coil spring. I just want to get the best one "Not too stiff, Not to soft.

Jim

That was my point in that long post. The first 1/10 inch maybe 142# but the next 1/10 inch will be more. The longer the spring (but heavier in weight) the less the difference inch to inch. Don't overlook making two rates by stacking two springs with a collar in between in series (Oh shoot, I forgot cub springs work backwards! grrrr (except for those Calumet things)). The first one for the little bumps (soft) and the second (hard) for those big ones.