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  #1  
Old 08-10-2006, 12:20 PM
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Default Landing Gear Geometry

Quote:
Originally Posted by Wayne Hicks
The Cozy III that I'm flying will not tip over backwards unattended. I highly suspect that the original builder set the main gear 2 inches aft of plans just so he could leave the plane unattended with nose gear deployed.

Just 2 inches is all it took.

Velocities don't tip over backward. I think I heard a rumor that their is set 3 inches aft of the natural balancing point.
This is the kind of info we NEED. If I would have heard this when I started, I probably would have done it. So a smaller hell hole? so what

No tippy problem and better prop clearance on take off and landing

Listen new builders and new designers. this is GREAT stuff
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  #2  
Old 08-10-2006, 12:34 PM
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that is one of the mods i was planning on making, moving the gear as far aft as possible - I was thinking of some kind of vertical shock absorber shrouded in such a way to also serve as a vertical stabilizer fin, and rear far enough to prevent any chance of a prop strike (sort of like the "training wheels" on the japanese shinden)
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Old 08-10-2006, 12:46 PM
Wayne Hicks Wayne Hicks is offline
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Wait, wait, wait!!!

While this sounds like an attractive option, there are serious performance consequences!!! The farther back the main axles, the harder the canard must work to provide enough lift to lift the front seat weight (because of the "extra" lever arm). The more lift needed, the faster the airspeed needed to obtain it. The faster the airspeed, the more runway takeoff distance needed. And it's heavier to lift during ground handling.

Personally, I'd rather leave the axles postioned per plans. Retracting the nose gear slightly accomplishes the same thing.

The size of the hell hole doesn't change. The location of the LG bulkheads, and the space between the bulkheads don't change. You simply jig the gear bow slightly different when you build the landing gear tabs. Only the leg angle with the fuselage is changed.
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Last edited by Wayne Hicks : 08-10-2006 at 02:29 PM.
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Old 08-10-2006, 12:46 PM
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My solution is to mount the engine 3" higher than plans and to make my mount as short as possible
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  #5  
Old 08-10-2006, 01:01 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Dust
This is the kind of info we NEED. If I would have heard this when I started, I probably would have done it. So a smaller hell hole? so what

No tippy problem and better prop clearance on take off and landing

Listen new builders and new designers. this is GREAT stuff
You assume that there was no reason to have the main gear where it is when you claim that this is "GREAT" stuff. Yes, it is the case that moving the main gear back a couple of inches will prevent the plane from tipping over backwards when sitting on all three gear - so will putting some ballast in the nose, or lowering the nose 1/4 - 1/3 of the way down with the electric nose gear.

The downside of moving the gear backwards is that you will have higher rotation speeds and lower front seat weight limits for rotation - you will need longer runways than you otherwise would.

Does this seem like a reasonable tradeoff? Not to me. I'll take lower rotation speed and higher weight carrying capacity any day over not having to lower the nose 1/3 down to prevent tipover. Wayne's aircraft would take off sooner with the gear in the correct location.

Jumping to conclusions based on snippets of information without understanding all the tradeoffs involved in design decisions does not lead to an optimal path.

So, listen, new builders and new designers. this is NOT great stuff - if true, this was a poor choice of landing gear placement by the original builder (and possibly explains the inconsistent W&B I saw on this plane while viewing it in PA once for Richard Hughes).
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Old 08-10-2006, 01:09 PM
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Well, front seat limit is set at 400, per Nat - he has loaded to 440 with no problems.

I have larger elevator than plans by quarter inch

Adjustable prop, shortens take off

I would also install nose gear strut 1 inch longer to help the canard angle

Lets look at the whole picture
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  #7  
Old 08-10-2006, 01:25 PM
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Most accept the cozy idiosyncrasies, i do not

"you gotta remember" is something i just don't want to have to do

I did think it through, that does not mean more thought could not be put forward
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dust

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  #8  
Old 08-10-2006, 01:28 PM
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Quote:
Originally Posted by Dust
Lets look at the whole picture
Dust, this is another case where I wish, for the benefit of the unsuspecting, that you would say 'Student Pilot since 19??' in your signature. People who know that you're one of the forum masters, far along Cozy building, and a Financial Advisor with international clients may assume your 'thinking out louds' are too golden. Money and lives are kinda on the line here. Just saying it straight.
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  #9  
Old 08-10-2006, 01:42 PM
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one thing to remember, the original designers,both rutan & puffer, have both said that compromises were made in the original designs

while there are those who think everything should be built strictly according to plans, i think there is always room for improvement based on your intended mission

and yes, any modifications should be made only after the appropriate engineering calculations have been done
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Old 08-10-2006, 01:57 PM
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Quote:
Originally Posted by tnt
and a Financial Advisor with international clients may assume your 'thinking out louds' are too golden. Money and lives are kinda on the line here. Just saying it straight.
Not a financial advisor, M&E tax, M&E appraiser, and a few other hats

Yes, have to get back to flyin

IF this was a place where I was an admin that did not allow others to disagree with me - i would agree with you.

That is not the case, i say the most and am disagreed with the most.

I am continually Bent, folded and mutilated

Now, back to business. Is anybody here gonna put 440 in the front seat? Or do you wish to ignore Nats statement that he went 440 with no problem.

Test Flights

They are very important

When i am done, off to willow run airport i will go and test my forward CG limits, nice long runway.

The way i look at it is - the comments against my statement were not fully thought out - just a knee jerk - you change you die

I see the changes, the multiple planes that are flyin both wider and longer

the gear position that some say are modified

nose gear attach breakin

the canopy leaks

the prop strikes

i see the pimple, love the bird, will fix what i can now and let others explore what is too late for me to fix, I'll just have to remember
ahhhhhhhhhhhhhhhh
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dust

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  #11  
Old 08-10-2006, 03:11 PM
Wayne Hicks Wayne Hicks is offline
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Why is "front seat weight limit" so hard a concept to grasp?

If you believe in the designer's CG range, then you can SAFELY load the plane in any manner you wish just as long as you don't exceed gross weight and the forward CG limit. Use the W&B calculator on Marc Z's website and you can convince yourself there are plenty of combinations of front seat weight that fit within these constraints!

Unfortunately, Nat really shot himself in the foot by proclaiming "400 pounds" as a limit. He should have called it an opinionated recommendation. It was his opinion that 400 pounds was about all you could put in the front seats before the plane started handling like a pig.

Now, everyone's quite jiggy with the aft CG limit. Everyone's jiggy because we've all heard and seen where violation prompts main wheel stall. That is a LIMITATION we can appreciate and accept.

Forward CG limit isn't as easily appreciated because we know it's arbitrary. We want to fly with our plus-sized friend and Nat's forward CG limit may not allow it. In my sarcastic explanation, the very extreme forward CG limit would be with full elevators down and barely able to hold attitude. ANY cg forward of that and the plane will descend. I believe that theoretical cg is forward of the limit Nat set.

But that's not very SAFE. You gotta have enough elevator authority to take off in a reasonable, safe distance. You need to be able to arrest a descent and level off the plane (like when landing). So, the forward CG is moved aft to maintain a level or performance.

How far forward of forward is an acceptable forward CG? I guess that depends on your perspective and your personal tastes. Nat likes alot of elevator authority so he never crashes. So he sets it at where it is now. It's at his minimally acceptable level of performance. It's his design, his opinion. And he tested it there.

You want to be brave and accept less control authority? Then go ahead and move it. Even test to that condition if you like. It's your plane.
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Last edited by Wayne Hicks : 08-10-2006 at 03:26 PM.
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  #12  
Old 08-10-2006, 03:26 PM
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ok, so we move the axles back 2 inches, either by moving bulkheads or by changing the gear angle.

How exactly is that affecting the forward CG, except to move it backward a hair as weight has shifted
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  #13  
Old 08-10-2006, 03:31 PM
Wayne Hicks Wayne Hicks is offline
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Axle position won't affect the PLANE'S cg. However, how ever you loaded the plane, the CG FOR THAT FLIGHT AT THAT MOMENT IN TIME is 2 inches more ahead of your main wheels as it would have been if you left the main axles at the plans location.

All that translates to more weight on the nose gear, more lift needed from canard, more time to reach rotation speed, more takeoff distance, blah, blah, blah, blah, blah.
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Old 08-10-2006, 04:08 PM
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I don't know what airfoil the Velocity uses, but if you've ever compared the Velocity canard to the cozy/long-ez canard, you'd see that the Velocity appears to be set at a higher Angle of Incidence, presumably to help w/rotation.

Dust -- I wouldn't put your engine 3" higher. That will only hurt takeoff performance, unless you change the thrust angle too.
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  #15  
Old 08-10-2006, 04:30 PM
SteveWrightNZ SteveWrightNZ is offline
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question: why not just raise the nose an inch on its gear to improve the takeoff stance? nb. noob alert - I dont know jack about this.

thinking out loud..

nosetip water tank and rear(somewhere) water tank with little electric (washer?) pump to move the CofG on pilot command. or drain it entirely.. a gallon of water in the nose makes how much difference ?

computer-controlled leading-edge slots on the main and the canard, extending automatically on inceasing AofA, and during takeoff, pilot-overrideable retract/defeat - (defeat it at your peril at high AoA.) and to the nay-sayers I say "BAH, are we men or are we mice!"


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