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Zenith XL601. Main gear position.

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Don Hodges

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0235 with wood prop. Seems to be a common problem. At rotation speed it takes a lot of back pressure to raise the nose. On landing the nose wants to fall thru abruptly. Here is what think. Too much weight designed forward of the mains. I spoke to Zenith and was told the design included the 0235. I've considered moving the axles fwd a few inches, some calculations involved, letting the tail have a little more authority. Everyone's thoughts?
 

TFF

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Gear is usually placed in relation to the CG. An O-235 is normally at the forward end of the CG on one of those unless they tail is ballasted for a more center CG. The only time I have been around one was someone putting one in in place of a Rotax.
A friend in his AA1 flies with five gallons of water in the cargo, when he flies solo. Easy enough to dump the water if he brings someone back, the containers are cheap enough that if he had to leave them for room, no big deal.
Is it gear placement or is it CG? Safe CG is not necessarily a pleasant CG. Have you tried removal ballast?
 

Don Hodges

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Nice idea. Thank you. I'll work some numbers. I'll have to watch gross weight. I believe it is gear placement with this engine. The water ballast is a much easier change.
 

Don Hodges

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Thank you BJC. I remember the concept I just couldn't remember which models it was used on. What would be your suggestion to compute the length of the extender? I'm thinking near the CG for Max take off weight as a starting point. Your thoughts?
 

mcrae0104

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Don, how much weight is on the nose and the mains at TO weight & landing weight? IIRC 8% on the nose is the rule of thumb but I'll check Pazmany tonight.
 

Pops

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You can bolt some axle extenders on like was done of the Cessna 120, 140's . (STC) Made is a little harder to put the taildragger over on its nose with too much braking. On my daughter's C-140 , she took them off.
On the JMR, I drew a scale drawing and with the tail on the ground ( 18 degs ) (Tri-Gear), then located the main gear axle location by drawing a line straight down from the rear CG limit. Worked out at 49.6% of the cord. Worked out to be perfect. There is 207 lbs on the nose wheel with the fuselage level with empty CG. Of course, with me in the cockpit and full fuel the CG is were I wanted and a lot less weight on the nose gear.
 

Don Hodges

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I will have to get back to you on that, my log books are at my hangar, but I will. If my memory is correct I believe it's closer to 12 or 15%.
 

BJC

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Thurston’s general guideline places the main gear wheel ground contact point on a line that extends aft of the aircraft CG at an angle (aft of vertical) of 3 degrees more than the tail angle (down) for 0.90 Clmax in landing configuration.64437499-DF4A-4B71-A14A-6012F1159663.jpeg

BJC
 

mcrae0104

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I will have to get back to you on that, my log books are at my hangar, but I will. If my memory is correct I believe it's closer to 12 or 15%.
Pazmany: "The normal nose wheel load is in the order of 10%-20% of the aircraft weight... The best compromise is to have approx. 15% of the weight of the airplane on the nose wheel at the static level attitude... Also, it was found that when the nose wheel load is less than 10%, for example, 8%, a slow oscillation in pitch, called porpoising, may occur."

Raymer: "If the nose wheel is carrying over 20% of the aircraft's weight, the main gear is probably too far aft. On the other hand, if the nose wheel is carrying less than 5% of the aircraft's weight, there will not be enough nose-wheel traction to steer the aircraft. The optimum range for the percentage of the aircraft's weight that is carried by the nose wheel is about 8%-15% for the most aft and most-forward c.g. positions."
 

GeeZee

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Wow funny coincidence. I was just at my neighbors helping with instrument panel wiring on his Zenith 650 with Lyc o235. Just out of the blue he says “you know some people that are using the O235 flip the gear around and it puts the mains about 4” forward, it takes some weight off the nose wheel. What do you think”. Of course I said well I don’t know. 4” sounds like a lot.
From the above post it sounds like we need to weigh the plane.
 

BJC

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you know some people that are using the O235 flip the gear around and it puts the mains about 4” forward, it takes some weight off the nose wheel
That sounds like a better solution than extenders, a la Cessna.


BJC
 

Mitchell

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What direction is your gear mounted? I’m putting a light engine on mine and have the gear raked back. But in the drawings they show the gear raked forward. That’s a fairly simple fix and would move the wheels 3-4” foward
 

rdj

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Search the zenith.aero site. There's posts there about this issue. Those with heavier engines such as the O-235 mount the gear forward, and those with lighter engines such as the Jabiru mount it aft. With the gear forward, the posts note that a large pilot on the step, or two persons trying to board at once, tend to tip the plane down on its tail. Lean forward.
 

Don Hodges

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I Got by my hanger and had a look a the weight and balance sheets. It turns out my nose gear has 293 pounds which works out to be 35.5%. With my main gear slanted forward. It's gonna be a difficult fix.
 

TFF

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Depending on components, you might consider light weight starter, alternator, and battery if it’s up front. That’s assuming you don’t have those. Even though Sensenitch prop seem to be more efficient, they weigh about double what a McCalley does.
 
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