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  #1  
Old 09-18-2005, 01:42 PM
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karoliina karoliina is offline
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Default Cozy specs potential incompatibilities with Finnish CAA

Hello,

I noticed the following requitements for experimentals in Finland (from another forum, from CAA representative):

- must be able to withstand at least +3.8/-1.5 G at VA, otherwise not approved. Nat Puffer states that MKIV is +3.8/-1 g which is below the required number.
- VD must be 1.35*VH. Cozy stated VNe is
220 mph. VNe = 0.9*VD -> VD = 245 mph
1.35*VH = 245
245/1.35 = VH = 180 mph,
meaning that the maximal horizontal speed needs to be limited to
180 mph if that number stays. However, if we accept that the plane goes 200 mph,
then VH must be at least 270 mph which yields VNe = 0.9*270 = 243 mph.

In other words, it looks like to get MKIV design approved as it is here, this is required:
- Prove that the structure can withstand +3.8/-1.5 g at least instead of the +3.8/-1 g.
- Test fly flutter tests up to 270 mph (instead of 220 mph).
If the above is not possible, the plane needs to be strengthened I guess.

Any comments?

Best Regards,
Karoliina Salminen
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  #2  
Old 09-18-2005, 06:18 PM
Nathan Gifford Nathan Gifford is offline
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I think you will need to investigate what proof the Finnish government will require.

Maybe Marc will chime in here, but I think you could load the wings to those levels with no problem at all. If you remember some years ago, there were questions about how much loading a VariEZE could take. I think they loaded the canard and wings to over 12g before they failed.

If lowering the Vne to 180 will keep the government happy, that seems OK. I think someone has pushed a LongEZE to 270 during flutter tests, but a Long is not a Cozy.
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  #3  
Old 09-18-2005, 10:39 PM
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i see NO problem with flutter test/ test flying to 270 mph. others on this forum have tested to faster speeds
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  #4  
Old 09-19-2005, 03:20 AM
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Why not take the easy route: Ask the builder of that Finnish Cozy that I saw at Jämi, how he dealed with it
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Old 09-19-2005, 12:58 PM
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Quote:
Originally Posted by Dust
i see NO problem with flutter test/ test flying to 270 mph. others on this forum have tested to faster speeds
ok, i had a complaint so i will elaborate.

Normal Vne testing is to 110% of listed Vne. so for a 230 Vne that would be a test to 253, all in MPH. lets round that off to 255 mph, or 15 mph slower than the 270 i quoted. we have at least one member here that has done this.

one than i know of on the forum has flight tested to 280 KNOTS, but it was on a LONG. Now the canard is longer on a long than on the cozy and being longer it would flex more, not be as stiff. Sooooooooo, it would be more prone to flutter than a cozy canard, both being constructed identically.

This is the whole story, my 2+2 was that the extra 15 mph would not be a big deal and i plan on flight testing to well over 300.

I know, I know, why when top cruise is 200 or so, i plan on cruising at 25000 at 200 mph ias. the decent will be for 50 minutes at 500 fpm. so, i have 200 IAS, 300 TAS and the need to lose 25000 feet and not go over my Vne. the thought of losing 25000 and 100 mph doesn't give, so i will stand my cozy on its nose and test away, 5 mph at a time

and yes - it is all just BS until i fly it, but a goal is a goal and this one i will not give up.
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  #6  
Old 09-20-2005, 07:07 AM
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Hello,

About the g-loading - it is already solved:
I got a reply from Nat and the correct g-limits are +3.8/-1.5 not the +3.8/-1g that the Cafe report states and in truth it is really stronger than that. It is just categorized to normal category. Thus it will fit into Finnish minimums, no problem in this regard.

Best Wishes,
Karoliina
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  #7  
Old 09-20-2005, 12:02 PM
Glos Glos is offline
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Dust

The Vne book value for my Long is 196 kts. This is from the Rutan POH.
I think I remember something a long time ago that the design structure with the thickness of the wing, the way it attaches and the number and orientation of the lay ups etc. precluded a much faster Vne. This was in response to an inquiry by someone that wanted to put a jet engine on and go "real" fast.

Since the same basic structure and lay-up scheme is present on the Cozy, it may be interesting to verify this. Naturally, there are examples that have gone much faster and routinely at that, but are these examples are flying with basically the "stock" design wings or something more robust. I don't remember where or when I saw this but I do remember something about it.

Stiffness and twisting loads come to mind also. The winglets were also a consideration. They have a lifting moment toward the center of the plane that increases with speed. Is the the stock structure strong enough for this.

280 Kts on a Long EZ, wow. That is really up there and I wonder if this is within the realm of design limits. Safely that is.

Is the "rated" Vne from the Cozy POH really up to 230 Kts. If it is then, there must be a difference between the Long wing and the Cozy wing.

Just food for thought.

Rick

Maybe someone like Mark can comment on this.
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  #8  
Old 09-20-2005, 12:12 PM
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Quote:
Originally Posted by Glos
Is the "rated" Vne from the Cozy POH really up to 230 Kts.
i believe it is MPH and the post that started this conversation was in MPH
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  #9  
Old 09-21-2005, 09:13 AM
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Correction noted. Mph it is.
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  #10  
Old 09-21-2005, 11:04 AM
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Yes, a cozy canard entered flutter, the pilot pulled power and aft stick and the canard stopped its 12 or so inch blurrrrr flutter.

the plane was being flown by the third and finishing builder. the elevators had not been properly balanced during construction. the elevators were properly balanced, a really, really really simple task, and the plane is back to flying. i think nat inspected the canard for damage and found NONE. It was inspected and NO damage was found, not sure it was Nat.
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dust

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  #11  
Old 09-21-2005, 01:04 PM
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Real simple on the canard - that stupid lead weight we are talkin about on the other thread - it is in front of the canard and another one is inside the fuse, if i remember right. after the canard is finished - hang it by hinge, level, let go, it must drop down promptly nose forward.

dat be it, simple as pie.

After fill and paint - must be checked again, hopefully without dropping it on the floor
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dust

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  #12  
Old 09-21-2005, 01:26 PM
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Dear Karoliina,
With regards to wing flex and flutter; I believe the German FAA made Uli Wolters add a bolt to the leading edge where the leading edge of the wing meets the leading edge of the strakes. It satisfied them although from what I have heard this is a bad thing because the wings are supposed to flex so this now becomes a stress point?
...Chrissi
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  #13  
Old 09-21-2005, 02:03 PM
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Default Extra wing attach bolt

Quote:
Originally Posted by Cozy Girrrl
Dear Karoliina,
With regards to wing flex and flutter; I believe the German FAA made Uli Wolters add a bolt to the leading edge where the leading edge of the wing meets the leading edge of the strakes.
snipped
...Chrissi
Exactly,
you can actually see this extra bolt with the carbon-fiber "bell" to be attached to the strake in the first of the photos I posted about my project in my second post in the "Cozy III project pictures" thread.
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