Knee Windows on Cozy Mk IV?

[Arbiter]

Hey Fellas and Fellets ,

 

Ever seen this modification on a Cozy Mk IV? Does someone know who's aircraft this is? I would be very interested in incorporating this into my airframe from increased visibility and it looks pretty sweet! I'd like to open discussion on the implications of incorporating this into a design. Is there a kit for it somewhere I am un-aware of? What are the structural implications, and how big could they get? Any insight would be greatly appreciated!

 

-Chris

[ZUCZZ]

Can't help with the ID, but that is one sleek machine standing in the background there!

 

Regading the window ... in that area the skin has been thinned out anyways, might just as well use the same technique as the side windows in the canopy to fit such as shown.

[Steve Innova]

Well, for starters you're reducing the strength of the forward fuselage. To restore it, the longerons would have to be reinforced quite significantly.

In a turn or turbulance, the floor and the longerons are carrying all the twisting loads between the canard and the wings.

 

Is this a problem? Under regular flight loads, probably not. If the the twisting was excessive, you'd probably see the evidence in the "knee windows" popping out, or cracking.

 

In a crash though, the result could be that the nose folds back at the IP. Not a desireable outcome, since your legs and waist happen to be there. (but the nose before F-22 is also a weak link, and would probably crush first. Choose your poison.)

[Steve Innova]

For my modified fuselage, I shortened the fuselage depth from 23" to 18". To restore the rigidness of the fuselage, I added an extra layer of BID inside and out, and reinforced the longerons with two layers of 3" UNI spar cap tape. We'll see if that's enough.

[Hans S]

I know this doesn't help, but he has a website and has more pics and a write up of the windows. I've been to the website, but can't remember how I got there. It's been awhile.

[Hans S]

Found it

http://www.ez.org/feature/F0502-1/F0502-1.htm

[Cozy Girrrl]

Visibility is good without them and you would be weakening the crush zone as well. Same reason you want to glass in the armrests.

...Chrissi

[Hans S]

Ha! I think the visibilty of the Wonder Woman plane of the 70s TV series is the answer.

[Marc Zeitlin]

Well, for starters you're reducing the strength of the forward fuselage. To restore it, the longerons would have to be reinforced quite significantly...

While not usually an advocate of structural modifications, I had created a FEM of the Long-EZ fuselage structure (very rough - no details) to analyze the issue of removable fuselage tops and removable instrument panels. Both of these had a very strong effect on the structural rigidity of the fuselage in torsion.

 

I modified this model to address the concern here of the windows (and the armrest glassing, rather than being removable, which some have done [including myself, on my COZY MKIV]) and here's what I found:

 

1) The armrest removal made the Long-EZ fuselage about 5% - 15% less stiff in torsional twisting than the fixed armrests. There are a lot of assumptions built into those numbers, none of which are particularly accurate, but it does show that the armrests DO add some measurable amount of stiffness. Critical? Hard to say. There are numerous aircraft flying with removable armrests, and none fall out of the sky, but I'd be the first person to point out that that's hardly proof of a damn thing.

 

2) The window cutout made approximately a 1.5% difference in torsional stiffness, all else being equal - to me, this is in the noise - I wouldn't hesitate to put the windows in without structural concern if I wanted them.

[Cozy Girrrl]

Marc,

I can see where as part of the skin it is not going to change the torsional stiffness, what about in the case of impact?

...Chrissi

[Hans S]

Crissi,

 

Are you talking lawn dart or skidding? Either way, it just isn't a hole. There is a frame that is built into the skin to hold the window. Then there is the window material itself (glass, plexy, Lexan, whatever material) filling that hole pushing on its edges against the frame. Then there is the outer frame that actually holds the window, so it doesn't just fall out. Unless it is built with some rigidity, it's going to whistle. That area will probably be stronger with the mod, but heavier for it too.

[Marc Zeitlin]

... what about in the case of impact?

No clue. Sometimes adding/subtracting material helps, sometimes it hurts. Without a bunch of crash tests, like they do with cars, or some heavy duty non-linear FEA (which I neither have access to nor time for) I don't think there's any way to intuit what would happen in either case. Maybe you're taking away the piece of sidewall that will keep the IP from smacking you in the forehead, or maybe you're taking away the one piece of sidewall that will collapse inward and crush your leg. No idea.

[Edge 513]

If a builder wants the extended elbow strakes for front seat comfort, this window thing is outta real estate. Given a choice between the two; an extremely comfortable interior that doesnt widen the fuselage tub and installing these Varieze windows that dont add much, I think the elbow strakes win.

My .02

 

Now do as I am doing and form acrylic to the shape of the elbow strakes at your forearm location, and you might have something. [Well, at least I might have something-we'll see.]...much better location. Doesnt affect the forward stiffness, and is more usable visibly. Also doesnt look like youve got holes in your fuselage. IMHO.

[Cozy Girrrl]

And you can shine a flashlight out there for taxiing, landing and flash the tower for recognition

[Cozy Girrrl]

I'll conceed to Marc, no way of knowing so I will go by pure intuition.

...Chrissi

[Kraig]

Damn, Edge.

 

You got extra sunroof windows in the canopy, and now windows in the strake area's....................Sooooo cooool!!!!

 

Keep up the snarky mods,

 

Kraig

[Edge 513]

Thanks Kraig. I have surprised you once again, no? =]

Once I was told [before it was trite] ''He thinks outside the box"...[but it was a good thing, because it was a pretty dam big box everybody had been stuck in. The key was just thinking a bit bigger. I liked the varieze windows first time I saw them but didnt feel they were in the right place for a Cozy, so thats why I went into the strakes. I dunno if everybody shines to what I come up with, but its different. I'm good with that.

[ZUCZZ]

Just to re-iterate my earlier contribution ...

 

In that particular area, the foam has been reduced in thickness already, so the installation of a like size window could hardly be a major problem.

 

IMHO and your results may vary

[Arbiter]

Wow,

What a huge host of posts, all with good insight! Thanks for running the FEM on it Marc! Edge, neat idea of doing extended strakes with a window in them, that's something to consider! How are you working to accomplish the molding? Cozy Girrl has a good point about impact.... Does anybody have any data from any accidents that show how an impact can affect this region of the aircraft?

 

I thought these windows would be cool in flight and also serve a purpose of allowing visibility to the ground in higher angles of attack. Added visibility is always good! I'd be curious to know how this person mounted and reinforced his fuselage to accomodate the windows. Either way they look cool and I think it's something I will consider modding in after I have thought about the crash related stuff some more. Don't want to trade safety for looks!

Thanks for the posts, keep em' coming!

 

-Chris

[longezdave]

I gave Bill a heads up that his windows were being discussed in case he wanted to chime in. Here's his response -

 

Hi Dave-

 

The following is a brief description of the background on the window. You are welcome to post it if you can. Thanks for the heads up! -Bill

 

 

 

Side window, N95BJ

 

During building, structural effect of the window was analyzed with several experienced canard folks. Attributable to CSA.

 

 

 

The plans emphasize the importance of not encroaching the ten inch fuselage area around the canard bulkhead or main spar, which was not an issue. I would agree with Mark Z’s comments about the relatively small loss of strength.

 

 

 

However I (we) worked to retain at least normal strength. When building, the wooden longerons were doubled per LongEZ, and then overlayed with seven layers of glass. Around the window, a one inch perimeter of fuselage wall foam was replaced with a “U” frame of seven layers of UNI and BID. That became 14 layer, one inch diameter wall around the window. For a smooth exterior surface the plexiglass pane has a step to compensate for the exterior fuselage skin.

As for visibility, the pilot’s line of sight parallels the structure between the canopy and window. The one inch thickness of the structure is minimal and is pretty much ignored. A nice capability with the window is to check for opposing traffic in a turn. And when approaching a runway overhead its easier to check ground traffic and the windsock, things which would normally only be visible off to the side.

 

As was mentioned, the window approximates the thinner glass to glass fuselage area next to the LongEZ stick, providing knuckle room. The side consoles were narrowed about an inch each so the thigh and instrument panel legroom is per LongEZ dimensions. The extended fuel strakes include LongEZ elbow room in the front seat.

 

Additional local strength is gained by moving the canopy lip aft a couple of inches, with structural attachment of the top of the instrument panel to the top of the fuselage with corner tapes inside and out. This allows more strength around the bulkhead plus an instrument access panel. While there are a few mods on the plane that improve operational friendliness, the airframe is built per plans. After 12 years of flight on the plane I am a happy guy.

 

 

 

I appreciate the experience and knowledge that you guys and gals instill, cultivate and perpetuate. You are welcome to spend some time reading about 12 years of flying the VariEze on the sites below.

 

 

 

Bill James, Fort Worth VariEze

 

Featured Canards on ez.org

 

EZ Chronicles link on ez.org

 

http://www.ezchronicles.com/blogger.html

[Cozy Girrrl]

Its nice to see the extra work that went into Bill's plane in this area. Thats something to keep in mind when you see a mod and want to copy what you see, there may be a whole lot more to it than floxing in a piece of plex as in this case.

Thanks Bill!

 

Regards, Chrissi

[Bill James]

Chrissy nice to see y’all at Oshkosh.

[Cozy Girrrl]

Chrissy nice to see y’all at Oshkosh.

Bill, Thanks for dropping by the booth, I never did get out to the flight line.

Are you coming to RR?

...Chrissi

[Bill James]

Came home from Osh with a couple of things in mind to do on the plane. Am certainly aiming to have them done or stabilized in time for RR. Looking forward to seeing what everyone's been up to!

[Cozy Girrrl]

Oh good, then go over and turn up the heat on Vance so maybe he can get that paenl done and come too =)

...Chrissi