Today's Message Index:
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1. 06:03 AM - Re: Re: Replacement tail rod...? (John Hauck)
2. 07:30 AM - Re: Re: Replacement tail rod...? (Jack Hart)
3. 08:31 AM - Re: Re: Replacement tail rod...? (John Hauck)
4. 09:13 AM - Re: Re: Replacement tail rod...? (Bill Berle)
Message 1
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| Subject: | Re: Replacement tail rod...? |
To the best of my knowledge, the only aircraft Homer Kolb designed with
rigid gear was the Flyer and the Ultrastar.
The Firestar was the first to have flexible main gear legs. The gear legs
were designed to be flexible, to give the aircraft landing gear some spring
suspension to take landing and ground handling loads off the airframe.
All Kolb aircraft models from the Firestar on are designed with spring
landing gear legs, flexible, not rigid.
The rigid gear on my Ultrastar was not forgiving in the least. On my first
landing in my unimproved cow pasture airstrip, my roll out took me across a
cow path (rut) that took out the main gear, my prop, and the little turned
up nose skid of the airframe.
Del Cross, who flew a Kolb Flyer at Sun and Fun and Lakeland, upgraded his
rigid main gear to 7075 aluminum rod, making them longer to get the nose of
the Flyer out of its normal level attitude on the ground. Del was killed
when his Flyer crashed some years ago. RIP.
john h
mkIII
Titus, Alabama
From: owner-kolb-list-server@matronics.com
[mailto:owner-kolb-list-server@matronics.com] On Behalf Of Jack Hart
Sent: Sunday, February 25, 2018 11:11 PM
Subject: RE: Kolb-List: Re: Replacement tail rod...?
John,
I believe you have it right. The FireFly gear is rigid by design and the
aluminum leg bends so easily. If you apply a 330 pound load in any
direction at the axle, the leg will bend at just below the fuselage socket.
By adding the cable I have, indeed, reduced one degree of flexsure and
gained some freedom from plops.
As for the photo, it is difficult to tell if it was or was not a level plop.
At the time it felt like it was. Both legs had to be straightened. It
could be that the right tire broke loose from the asphalt first.
Jack B Hart FF004
Winchester, IN
_____
From: "John Hauck" <jhauck@elmore.rr.com>
Sent: Sunday, February 25, 2018 7:28 PM
Subject: RE: Kolb-List: Re: Replacement tail rod...?
Jack H/Kolbers:
By adding cables and restricting outward flex of the gear legs, your
modification effectively kills the spring in the direction it is needed
most, outward. To me, what you have done is change flexible gear to rigid
gear.
Spring gear is much easier on the aircraft than rigid.
>From the photo of your airplane, it is obvious you landed on the right gear,
putting all the load on one leg. I do that too, but on the left leg.
Message 2
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| Subject: | Re: Replacement tail rod...? |
John,
If the below is so, why is it that the FireFly legs bend in a 1.8 G plop?
Jack B. Hart FF004
Winchester, IN
----------------------------------------
From: "John Hauck" <jhauck@elmore.rr.com>
Sent: Monday, February 26, 2018 9:06 AM
Subject: RE: Kolb-List: Re: Replacement tail rod...?
All Kolb aircraft models from the Firestar on are designed with spring
landing gear legs, flexible, not rigid.
Message 3
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| Subject: | Re: Replacement tail rod...? |
Springs are flexible to a point. When overstressed they bend or break.
That's how my springs work. Isn't that how your springs work?
Didn't your gear legs flex to the point you over stressed and bent them?
I've flown with a G Meter since my Firestar days. If you sneeze while
taxiing, you'll get 2 or 3 Gs very easily.
Jack H is wearing me out. I quit. ;-)
john h
mkIII
Titus, Alabama
From: owner-kolb-list-server@matronics.com
[mailto:owner-kolb-list-server@matronics.com] On Behalf Of Jack Hart
Sent: Monday, February 26, 2018 9:30 AM
Subject: RE: Kolb-List: Re: Replacement tail rod...?
John,
If the below is so, why is it that the FireFly legs bend in a 1.8 G plop?
Jack B. Hart FF004
Winchester, IN
_____
From: "John Hauck" <jhauck@elmore.rr.com>
Sent: Monday, February 26, 2018 9:06 AM
Subject: RE: Kolb-List: Re: Replacement tail rod...?
All Kolb aircraft models from the Firestar on are designed with spring
landing gear legs, flexible, not rigid.
Message 4
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| Subject: | Re: Replacement tail rod...? |
After having made numerous landing gears out of fiberglass, carbon fiber, etc....
the world's largest manufacturer of landing gears for light aircraft (Grove)
uses 7075-T6 exclusively. Using a direct comparison between MATERIAL PROPERTIES,
the 7075 has better stress/strain/yield/weight and all that high brain function
engineering stuff I don't understand.
But when you put a FIXED CROSS SECTION into the mix, things change. For a given
size, thickness, or diameter, then steel starts to show its advantages.
A few years ago I took over the FAA "STC" approval for changing the tricycle gear
Cessna 172 back into a tailwheel configuration (like the Cessna 170). As part
of that process, I learned a whole lot about this stuff, thanks to an old gray
engineer who was kind enough to put up with my lack of a formal engineering
education.
We wanted to replace the steel Cessna main gear legs with aluminum, because the
exact steel alloy that Cessna used was a special order from a steel mill. So
my engineer did a bunch of calculations, and he figured out that to replace a
13/16" thick spring steel main gear, we needed a 1.25" thick piece of 7075-T6
aluminum... to get the same spring properties, energy absorbtion, and impact capability.
How is this relevant to a discussion about Kolb landing gears? Because on a Kolb
aircraft the size of the main gear is always limited to the size of the round
socket tube that Kolb builds in to the fuselages. With a given size fuselage
socket tube, if you want or need a "stronger" main gear than the original 7075
Kolb gear leg, you have no choice but to change materials and use steel. (even
carbon fiber wouldn't help you because you would need a 2 inch socket tube
to make the gear out of carbon.)
So John H made the only upgrade that was legitimately possible, by moving from
aluminum to steel. Kolb figured this out at some point when they wanted to build
heavier two seat airplanes,a nd they went to hardened steel as well.
For the people who are obsessed with weight, or who are on a quest to meet Part
103 weight, then aluminum or carbon is worth pursuing, but to really be able
to use those materials you would need to increase the diameter of the socket tube
in the fuselage. That would be quite a project !
Bill Berle
www.ezflaphandle.com - safety & performance upgrade for light aircraft
www.grantstar.net - winning proposals for non-profit and for-profit entities
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