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  #1  
Old 01-24-2007, 08:31 PM
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Default Moving Mains back and other Surprises

heh heh heh

had a thought a while ago - that the stagger EZ was the same air frame as the cozy so today i called Steve Wright, designer and builder of the stagger EZ and asked him

His reply was YES, basic air frame changes made were moving gear back 6 inches AND raising engine UP 7 inches.

He feels his rotate distance is 50 to 100 feet longer than a standard cozy.

I told him of Marcs insistence that is would make a far longer take off distance and he requested that I post a request for him to Marc. At Oshkosh this summer, he would like to take off in formation and actually see the difference. He feels it may even be the same.

The engine raising of 7 inches blew my mind. The effect is a slight pitch change on a go around and he emphasized slight. He compared performance in pitch changes similar to what retracts do to a cozy, he compared notes with chris and his 540.

Geometry, especially when combined with the gear placed 6 inches back that makes a prop strike near impossible AND

and this is the very cool one, at altitude he loaded the plane very far aft CG and then deep stalled it almost. Then he applied full power AND - he powered out of a deep stall.

food for thought - all of it - I'd say lobster, filet and peaches flambe with cognac
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  #2  
Old 01-24-2007, 09:03 PM
chasingmars chasingmars is offline
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Quote:
Originally Posted by Dust View Post
...and this is the very cool one, at altitude he loaded the plane very far aft CG and then deep stalled it almost. Then he applied full power AND - he powered out of a deep stall...
I'd note that, my understanding of deep stall recovery in the cozy is that if you almost deep stall it, the immediate action is to apply full power to get out, so I'm not sure how this is different from the normal behaviour, though the higher thrust line will give some pitch down on full power, you can't have it both ways, it's either minor enough to not affect slow flight control authority (and therefore has minor effect on stall escape), or it's not - both circumstances are reacting to the same force vector.

Most of the annecdotal evidence I've read on the StaggerEZ is that, while it is a beautiful plane, take-off roll is quite extended, though, I haven't seen it myself - still, if it can be shown it's the same we have a starting point for analysis... the next question is what is the engine, prop and weight for the "same run" distance on both aircraft being compared.
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Old 01-24-2007, 09:34 PM
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Originally Posted by chasingmars View Post
the next question is what is the engine, prop and weight for the "same run" distance on both aircraft being compared.
It seems as though the engines are quite similar and the suggested loading was to have them the same.

lets hope that the actual comparison can be done at Oshkosh.

Steve is a pretty darn bright and knowledgeable guy, if he feels there is a big difference in the escape from a deep stall with his configuration, i tend to believe him.
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Old 01-24-2007, 10:04 PM
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Originally Posted by Dust View Post
It seems as though the engines are quite similar and the suggested loading was to have them the same.

lets hope that the actual comparison can be done at Oshkosh.

Steve is a pretty darn bright and knowledgeable guy, if he feels there is a big difference in the escape from a deep stall with his configuration, i tend to believe him.
I agree actual data would be useful. Bright is good, but I've generally found that pilots are surprisingly ignorant of how their aircraft really fly, and many explainations (including those presented in ground school theory classes) are equal parts myth and oversimplification - I don't know Steve or his knowledge base, but you can't cheat physics, if your thrust line offset is substantial enough to be able to do a power recovery from stall by providing that much pitching moment, it's also going to be almost as significant in effect on slow speed flight on a go-around...
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Old 01-24-2007, 10:31 PM
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Originally Posted by chasingmars View Post
if your thrust line offset is substantial enough to be able to do a power recovery from stall by providing that much pitching moment
It is all a matter of balance, the increase in thrust will not be enough to offset a 10 inch further aft CG, but may support a 1 or 2 inch further aft CG.

for myself, the interesting point is twofold, plane is not tipsy anymore AND the allowable angle for a prop strike is substantially increased.
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  #6  
Old 01-24-2007, 11:55 PM
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As Marc hasn't posted yet, I'm going to go out on a limb here and cite his source for concern on aft-shifted mains. I hope to get the details right on this, and I'm sure that Marc can certainly correct my statements here. If I have the opportunity, I'll get more details tomorrow.

Mike Melvill is the one who informed him of the problems of gear that is moved aft. In the Long-EZ, moving the gear just an inch rearward causes a major increase in take-off roll. Keep in mind that the runways at MHV are VERY long. If the change in take-off roll caused concern for Mike, then I think that we would all be wise to heed his warning. It stands to reason that the Cozy is similarly affected as it is just a wide Long-EZ.

The Stagger-EZ is different enough, that it may not be affected as much by the position of the mains. As noted, the driveline is in a different position. Quite possibly, the Stagger EZ's CG would be considered out of limits aft CG in a Cozy. This would lighten the load on the canard and would counteract the rearward shift of the mains. Maybe you have to "hold down" the nose on take-off in the Stagger-EZ until a sufficient speed is reached where deep stall no longer becomes a problem. It's a different plane, and so far as I know, only Steve Wright has flown it. If anyone else has had the opportunity to fly it, I have not seen an independent handling comparison that would be constructive in dissecting the changes to determine suitability for Cozy Mk IV's.

-- Len
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Old 01-25-2007, 12:05 AM
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I just had a "Duh!" moment after I hit the post button. Steve doesn't have the same front seat weight capacity that the Cozy Mk. IV has. Keep in mind that the canard has to lift the front seat weight to rotate the aircraft. Even with a second passenger, his CG position doesn't move that far forward, as the station of the second passenger is behind the pilot (as can be seen in the attached picture). Also, he may have pushed the canard forward to compensate for the rearward shift of the main gear.

-- Len
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Old 01-25-2007, 12:33 AM
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(hoping Dani doesn't look in this thread)
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Old 01-25-2007, 12:38 AM
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Originally Posted by levansic View Post
As Marc hasn't posted yet, I'm going to go out on a limb here and cite his source for concern on aft-shifted mains. I hope to get the details right on this, and I'm sure that Marc can certainly correct my statements here. If I have the opportunity, I'll get more details tomorrow.

Mike Melvill is the one who informed him of the problems of gear that is moved aft. In the Long-EZ, moving the gear just an inch rearward causes a major increase in take-off roll. Keep in mind that the runways at MHV are VERY long. If the change in take-off roll caused concern for Mike, then I think that we would all be wise to heed his warning. It stands to reason that the Cozy is similarly affected as it is just a wide Long-EZ.

The Stagger-EZ is different enough, that it may not be affected as much by the position of the mains. As noted, the driveline is in a different position. Quite possibly, the Stagger EZ's CG would be considered out of limits aft CG in a Cozy. This would lighten the load on the canard and would counteract the rearward shift of the mains. Maybe you have to "hold down" the nose on take-off in the Stagger-EZ until a sufficient speed is reached where deep stall no longer becomes a problem. It's a different plane, and so far as I know, only Steve Wright has flown it. If anyone else has had the opportunity to fly it, I have not seen an independent handling comparison that would be constructive in dissecting the changes to determine suitability for Cozy Mk IV's.

-- Len
i flu it, it was gr8 all 10 min of it.
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Old 01-25-2007, 10:43 AM
Wayne Hicks Wayne Hicks is offline
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I guess people will hear what they want to hear, believe what they want to believe, conclude what they want to conclude. (Selected reasoning.)

I, too, had a long talk with Wright about the Stagger-EZ. One of Wright's design goals was to be able to fly the plane with/without passengers without having to shift ballast. Wright fufilled this with the staggered seating. With just the pilot aboard, the plane is flying very near rear CG. The pilot's seat is just far enough forward to ensure the plane is never aft of the aft CG under all solo loading conditions.

Fly with a passenger in the staggered seat, and the plane is flying with a more forward CG. The staggered seat allows him to carry much more weight in it before violating the forward CG limit.

(The location of the third seat is very near the plane's empty CG, so it factors very little in moving the CG.)

Play around with Marc Zeitlin's W&B spreadsheet, and you can see how this staggered principle works. It's not magic, only physics. You'll find that under the same loading conditions, Wright would be able to take a 250 pound person with him, whereas the IV might only be able to take a 100-pound person.

Now, I'll match my lobster against yours that if you load the Stagger-EZ and the Cozy IV identically -- i.e., loaded CG in relation to the planes' empty CG, and to gross weights -- the IV will lift off sooner.

The Cozy III that I'm flying has its main wheels mounted 1.5 inches aft of where their supposed to be. (I finally confirned that two weeks ago.) I don't notice it much flying solo. I seem to use only slightly more runway than my EZ friends. I recently flew with a Piglet in the front seat. (Piglet is Tom Robson, F-18 Hornet pilot and Cozy IV builder.) We chewed up alot of runway and had to get to 90 knots before the nose would even budge.

All of you out there that want to focus on the one, skinny tree in the forest, you go right ahead and move the gear back 6 inches. I urge you to stand back 6 miles and take in the whole forest first.
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Old 01-25-2007, 10:46 AM
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Quote:
Originally Posted by levansic View Post
Also, he may have pushed the canard forward to compensate for the rearward shift of the main gear.

-- Len
(hoping Dani doesn't look in this thread)
Nope - he said it is in the same position, I checked with him on that. Steve has done quite a few things to his plane, some have worked and some have not, he is quite honest on what has and what has not worked. Also he built and flew a vari ez (i thinks it was a vari) before the stagger and flew it for 1,000 hours earlier in his aviation career.

Maybe we could ask for a fly off 2 ways, one loaded the same for pilot only with weights to equal CG and gross and one loaded for a 180 lb cozy front seat passenger.
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Old 01-25-2007, 10:55 AM
Wayne Hicks Wayne Hicks is offline
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Oh, the reason the Stagger EZ gear is six inches aft? Because Wright mounted the gear onto the main spar. Why? So that he could position the gear farther outboard, farther outside of the prop arc. It's not because he was concerned about being tipsy.

The Stagger-EZ does not have a main gear bow like the IV. There are two curved gear legs. The gear legs do not enter the fuselage, nor are they interfaced into landing gear bulkheads like the IV.
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Old 01-25-2007, 11:29 AM
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Oh, the reason the Stagger EZ gear is six inches aft? Because Wright mounted the gear onto the main spar. Why? So that he could position the gear farther outboard, farther outside of the prop arc. It's not because he was concerned about being tipsy.

The Stagger-EZ does not have a main gear bow like the IV. There are two curved gear legs. The gear legs do not enter the fuselage, nor are they interfaced into landing gear bulkheads like the IV.
My conversation with him yesterday contradicts that statement - he had a tipsy plane before, the vari, and his change was to make this plane stable in all loading conditions. Not tipsy!

This was definitely one of his design criteria

talk about only seeing one side
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Old 01-25-2007, 01:05 PM
Wayne Hicks Wayne Hicks is offline
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Okay....

I just got off the phone with Steve Wright:

(1) Per Steve Wright, his primary objective for moving the gear was so that he could operate off grass fields. He wanted the wheels outboard of the prop arc to keep from throwing debris through the prop.

(2) Per Steve Wright, his second primary objective was to widen the stance to counter the right-drift effects of his off-center nose gear strut. A10 warthogs have off center nose gear. They have a tendency to drift right during taxi. This was where he derived this motiviation.

(3) Per Steve Wright, making the plane tipsy free was not a design goal. It was a DERIVED BENEFIT. His exact words were, "After thinking about it for a while, I discovered there would be a fall-out benefit." (The use of his word choice "discovered" infers to me that he didn't intentionally try to design out tippiness.)

(4) Per Steve Wright, the Stagger-EZ is not tipsy free. With little fuel in the plane, it takes only 15-20 pounds to raise the nose and tip it. While he considers this to be tipsy resistant -- 15-20 pounds is intentional, not accidental -- it shows again that it's a derived benefit; not something he intentionally tried to design out of it. With alot of fuel, it takes about 30-40 pounds lifting the nose to tip the plane over.

(5) Per Steve Wright, his normal solo rotation speed is 80 knots. By comparison, I rotate at 65 knots solo in the Cozy III. What can make up the difference is his O-360 (180 HP?) accelerates his plane faster to rotation speed than does the O-320 (150 HP) in my Cozy III. Faster acceleration means less runway roll required to reach rotation speed. In his words, "That probably accounts for why I rotate at similar distances as other Cozies and Long-EZs."

(6) Steve Wright says to "be careful" (his words, not mine) when trying to compare the Stagger-EZ to the Long-EZs and Cozies. While there are many similarities in the airframes (like location of wings and things), there are also many differences. Until the types can be compared with head-to-head fly-offs, "you're just comparing apples to oranges." (again, his words. Not mine.)

Now, I was under-educated about his gear attachments. His gear is not mounted under the center section spar. The mounting interfaces are ahead of the spar and use the top and bottom strake skins and the forward face of the spar for the structural load paths. And the very inboard end of the gear legs do follow along the forward face of the spar into the fuselage by a few inches. I didn't do a good job with my earlier comment. I was hoping to imply that the Stagger-EZ's gear doesn't enter into the fuselage that way that the Cozy IV gear does. And that it doesn't rely on landing gear bulkheads inside the fuselage the way that the IV does. I apologize for that. I'll try to be more accurate next time...
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Last edited by Wayne Hicks : 01-26-2007 at 09:51 AM.
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  #15  
Old 01-25-2007, 02:23 PM
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Quote:
talk about only seeing one side
There's rarely one side or another, and reported second or third hand statements are always open to misinterpretation, intentional or otherwise.

I don't think we can safely extrapolate Steve Wright's results (which are not accurately known) to how a Cozy IV would perform with certain modifications.

Anyone wanting to push the gear back from stock, go ahead. Just test (all c of g and gross weight conditions) on a long runway where you have room to stop if lift-off does not occur when expected.
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