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  #1  
Old 02-09-2007, 01:11 PM
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neverquit neverquit is offline
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Default Makin' the wings n canard bigger

Since we're talking about radical mods can someone explain why our planes need to take off and land at 70kts? Guide me to the proper thread if this topic has been exhausted.
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Old 02-09-2007, 02:47 PM
Wayne Hicks Wayne Hicks is offline
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You mean, other than that's about the speed you need before the canard generates enough lift to get the nose off the ground?
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  #3  
Old 02-09-2007, 04:59 PM
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I'll take a stab at it because I know that if I'm wrong, someone will jump in with a correction.

The high stall speed on the canard is deliberate. It is protection against a 'deep stall', which is when both the canard and main wing are stalled. In such a situation, there are limited inputs available to use to un-stall the aircraft, and most of the published accounts of deep-stalled canard aircraft ended with the plane destroyed.

To protect against this, the canard stalls at a higher speed than the main wing on purpose, to protect against stalling the wing.

As for why the wing stalls at a higher speed than, say, a Cessna 152, the fan that keeps the pilot cool is stuck on the wrong side of the plane. When the propeller is in front, it blows across the wing generating some immediate, self contained lift. Because the LongEZ, Cozy, etc are pushers, the main wing doesn't see that same benefit.
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Old 02-09-2007, 05:16 PM
swinn swinn is offline
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I think what neverquit might have been asking is, why is the wing loading on the cozy as high as it is? The LongEZ can rotate and land at 65 knots safely. Could the wings, and in proportion, the canard be enlarged to obtain a lower overall rotation and stall speed? Obviously the cruise speed would be a bit lower.
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  #5  
Old 02-09-2007, 05:33 PM
kjashton kjashton is offline
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Bigger wings = bigger drag = slower top speed. Take your choice. I guess most of us like the higher speed. Actually, the longer takerolls are mostly due to the characteristics of a canard configuration. The airplane might well fly at 60 kts but on takeoff, the canard can't generate enough lift at 60 kts to put the airplane in a 60 knot deck angle for flight. It has to accelerate to say, 70 knots to lift the nose. If you installed an all-movable canard, you could conceivably rotate sooner but you'd lose the anti-stall benefits of the fixed canard.
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  #6  
Old 02-09-2007, 05:34 PM
SteveWrightNZ SteveWrightNZ is offline
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its justa fast plane, thas all..
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Old 02-09-2007, 08:56 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Chairboy View Post
The high stall speed on the canard is deliberate. It is protection against a 'deep stall', which is when both the canard and main wing are stalled.
The fact that the canard stalls before the main wing is certainly deliberate, but the speed at which that occurs is governed by the wing loading, as Wayne et. al. have stated. If it were possible to have the aircraft (canard) stall at a slower speed, and still have the high cruise speeds that the COZY does have, it would have been designed to do so. As Kent says, make the wings and canard bigger and it'll stall slower. But it'll also cruise slower.

Quote:
Originally Posted by Chairboy View Post
As for why the wing stalls at a higher speed than, say, a Cessna 152, the fan that keeps the pilot cool is stuck on the wrong side of the plane. When the propeller is in front, it blows across the wing generating some immediate, self contained lift.
That's a minuscule part of the difference, if it's even measurable.

The COZY stalls at a higher speed than a Cessna 152 because it has no high-lift devices like flaps, and it has a much higher wing loading. The COZY has a wing loading of around 20 lb./ft^2, while the Cessna is closer to 10 lb./ft.^2. One other reason the COZY handles turbulence a lot better, too.
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Old 02-10-2007, 02:21 AM
Leon Leon is offline
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on the other hand, a c152 wil have a hard time going 150kts +
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  #9  
Old 02-10-2007, 02:28 AM
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Well, at least more than once.
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  #10  
Old 02-10-2007, 05:51 PM
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karoliina karoliina is offline
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Quote:
Originally Posted by swinn View Post
I think what neverquit might have been asking is, why is the wing loading on the cozy as high as it is? The LongEZ can rotate and land at 65 knots safely. Could the wings, and in proportion, the canard be enlarged to obtain a lower overall rotation and stall speed? Obviously the cruise speed would be a bit lower.
Marc already answered, but I'll add to this specific question my observations:
- Cozy and Long-Ez have the same wings and canard.
So what happened when Nat made the Cozy & shortened canard 6 inches later?
* Instead of one person, Cozy has two persons on front seat, in front of the CG. This causes the CG to be more forward than in Long-Ez if there are average sized adults on the front seat instead of two Thai women. More forward CG -> canard has to lift more to support the additional weight -> higher stall speed
* gross weight was grown without increasing wing area to keep the wing loading the same.
* the wing area on the canard is reduced because it was shortened -> increased wing loading.

Increased wing loading -> increased stall speed.

Another observation:
- Looking though accident reports, types of fatal accidents:
- Long-Ez: lots of controlled flight to terrain, loss of control in IMC, doing low flybys too low etc. usual stuff. Didn't find any reports (didn't look through all of them though) for hard landing resulting fatalities. Same thing with RV, Lancair etc.
- Cozy, several: hard landing resulting fatalities
- Cozy: many more: hard landing resulting substantial damages to the plane

I think that is pretty much summarizes the difference of stall speed between LEZ and Cozy. Also all the other aircraft I checked were having slower stall speeds than Cozy, including turboprop Lancair and even the Viperjet. Of course it should be noted that there are individual difference between planes and sometimes stall speeds told on marketing material may not be 100% accurate numbers.

The bright side:
- I calculated Cafe score (the old score, not PAV score) over 3 million for Cozy if Marc's figures are correct & accurate on cozybuilders.org. Rutan Catbird was once thought to be unbeatable with 1.3 million, but Cozy wins it hands down. Of course it should be noted that the figures on Marc's site don't qualify for official cafe score, but the score is supposed to be calculated on some specific flight rather than just picking up the ideal conditions and ideal performance data.
- Cozy is fast and has convenient side by side seating

The dark side:
- Errors on landing have potential to be more hazardous than on Long-Ez and may hurt physically in addition to hurting the ego.
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  #11  
Old 02-10-2007, 06:02 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by karoliina View Post
- I calculated Cafe score (the old score, not PAV score) over 3 million for Cozy if Marc's figures are correct & accurate on cozybuilders.org. Rutan Catbird was once thought to be unbeatable with 1.3 million, but Cozy wins it hands down.
What figures and formulas are you using? It's inconceivable (please, no quoting Inigo Montoya) that a COZY has a higher score than either the Catbird or Gary Hertzler's Vari-Eze......

Pointers, please?
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Old 02-10-2007, 06:23 PM
deuskid deuskid is offline
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Quote:
Originally Posted by Marc Zeitlin View Post
What figures and formulas are you using? It's inconceivable (please, no quoting Inigo Montoya) that a COZY has a higher score than either the Catbird or Gary Hertzler's Vari-Eze......

Pointers, please?
trying to resist... trying to resist... the pull is too strong... can not refrain.... aaaarrrggggghhhhhh....

<I my hokiest non-pc pseudo-hispanic voice>

I do not think you know what you are asking for me to not
not say...

'I do not think you know what that words [sic] means'...

sorry....

self constraint is at its low ebb especially since in another thread someone was just lamenting that the quick repartee' [lame might be more applicable in this instance] has been lost in this forum...

signed [with a flourish]

the swordsmith friend of Pirate Roberts
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  #13  
Old 02-10-2007, 06:29 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by karoliina View Post
- I calculated Cafe score (the old score, not PAV score) over 3 million for Cozy if Marc's figures are correct & accurate on cozybuilders.org. Rutan Catbird was once thought to be unbeatable with 1.3 million, but Cozy wins it hands down.
OK, so after a bit of research, the CAFE formula is:

CAFE = speed^1.3 * MPH * payload^.6

Gary Hertzler's VE came in at 170 mph, 48 mpg, and 400 lb, for a score of 1.38 million.

Let's assume a COZY will cruise at 200 mph at 20 mpg with a 1000 lb. payload - the score is then 1.23 million - closer to the VE than I would have expected, but hardly 3 million. The best I could finagle the #'s to be would be to use the MPG and speed #'s from CAFE's review of Mark Beduhn's COZY MKIV - 186 mph, 28 mpg, and the 1000 lb. payload. Then the CAFE score would be 1.58 million.

According to the EAA, the Catbird's CAFE score was about 1.31 million - not far from the COZY.

So I WILL use Inigo Montoya's quotation on myself :-).

I am curious, though, where you got the 3 million score from......
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Old 02-10-2007, 06:30 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by deuskid View Post
trying to resist... trying to resist... the pull is too strong... can not refrain....
If you're going to quote someone, do it correctly :-). The correct quote, which I now direct at myself, is:

"You keep using that word. I do not think it means what you think it means."
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  #15  
Old 02-10-2007, 08:58 PM
deuskid deuskid is offline
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Quote:
Originally Posted by Marc Zeitlin View Post
If you're going to quote someone, do it correctly :-). The correct quote, which I now direct at myself, is:

"You keep using that word. I do not think it means what you think it means."
just as a nod is as good as a wink to a blind horse

so a paraphrase is as good as an exact quotation in casual conversation ...

and so..

no...

I believe I'll respectfully not defer to your pedantic insistence upon exactness but rather...

employ the joys of good enough for gov'ment work [or the girls with whom we date [depending]]....

when not building nuclear power plants

ain't nobody gonna fall out of the sky and die because of a paraphrase .... there is a time for preciseness and a time for laxity. Some folks are lax too much... some too little...


Balance


is everything.

John
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