Cozy MKIV: Rounded Fuselage Concept (caution: LONG!)

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cattflight

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Folks,Posting this here to test the waters before I ask the same of the Cozy Builders Group. Because this is conceptual in nature, I want to avoid the common "stick to the plans" response that often occurs on those forums...especially around the concept of widening the fuselage. I find this board to be a bit more agnostic, a bit more technical (which I lack in the aeonautic capacity), and a bit more...well...productive. I thank you all in advance for your comments and advice. Here's a (not so brief) summary of my challenge and concept with a visual aid attached. Forgive me if this is a reprise of a previously posted idea. I searched in every way I knew how and didn't find anything quite like it.

Cozy MKIV "Rounded Fuselage" Concept:After many years of investigation into the homebuilt world, I have settled on the plans built approach, recently jumping from a Vision build decision to a Cozy MIKIV. It simply fits our mission better. I won't belabor the justification here in the interest of brevity. The one challenge I have with the design is, ironically, the "cozyness" of it. I want to minimize the modifications to keep the project on track, and I want to keep the modifications to the more benign areas of the aircraft, keeping all flying surfaces as-they-are, where-they-are. What I need is 1) more space at the elbows 2) more space around the legs (and leg opening) and 3) a less-aggressive taper to the canopy at the instrument panel. #3 can likely be accomplished using Todd's Texas Canopy, but #1 & 2 require airframe mods.

Here's my idea:Rather than simply widening the fuselage by adding 4-6" down the center, I am proposing I only widen the plans bulkheads by 2" down the center, but curve the exterior walls to accommodate the elbow room. This will also allow the instrument panel to be wider at the top of the leg openings, allowing a wider leg opening and easier ingress/egress. The only bulkhead I intend to keep per plans is the firewall bulkhead (tapering the fueslage back to that dimension).

Additionally, I plan to curve the fuselage bottom for two reasons...one of which I can defend, the second of which I am hoping others can offer some commentary. 1) I would like to increase the depth of the leg openings under the IP, but retain some structure to that bulkhead. I have seen others remove the lower slot ahead of the seat but others have said this lends some structure to the fuselage and should be retained. 2) with the wider fuselage, I am concerned about creating too wide a flat surface on the underside of the aircraft. Folks have mentioned how the flat fuse bottom acts as a "lifting surface" and definitely influences the flight characteristics (deep stalls were mentioned! Yikes!). My intent here was to minimize the impact of drag and potentially increase airflow over the entire fuselage by maintaining some curvature.

I will let the sketch speak for itself as far as placement of the arm rests and side sticks, heat duct/keel and IP/leg opening alterations. The reason I am posting this here is to understand what you all believe the aerodynamic impacts of this concept will be and what construction challenges I might have with the foam core, layups and resultant structural loads. Plans call for 3/8" PVC for side walls. Wondering if I need to buy (or create) kerfed cores for the curves or if PVC will work with some heat carefuly applied. Maybe step up to 1/2" kerfed PVC? I am also considering building this as a single fuse over a full length form rather than 2 sides plus a bottom. Presumably my glass layup schedule could remain the same as the Cozy plans schedule with carefully-placed joints in the PVC near the tighter curves. The Vision fuse construction process drove this thought.

There ya go. Thoughts? Am I just chasing my tail? Should I just widen the whole plane down the center and be done with it? May just bow the sides and keep the bottom flat like the plans?
 

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Synergy

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Glad to hear you want to pursue this general idea. It can bring great benefits and there are many ways to proceed. I will try to post in detail when I get more than the minute i have... For now, recognize your goal is not to just add room or widen things... it should be to add to the Cozy's overall safety and aerodynamics without an unreasonable penalty.
 
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cattflight

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Thanks, John. I love the Synergy program and I am excited to see the progress continue on that. Looking forward to your feedback on my slightly less ambitious concept! :)

Some other people I've shown it to have only expressed concerns for the "ripple effect" of some of the dimension changes....adding to it concerns for whether I will ever finish (which is exactly the part of the discussion I was looking to avoid). After a little deeper review and some comments about how the bottom of the Cozy fuse is intentionally flat to act as a lifting surface, I am considering merely bowing the sides and mating it with an only slightly wider than plans flat bottom.

Happy New Year!
-Paul
 

Aircar

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Perhaps you could discuss the proposal with a Cozy builder such as Chris Esselstyne who has extensively modified his Cozy (and is currently building a Schreder HP 18 and doing a beautiful job ) --he posts on the HP forum @ soaridaho but i don't have any other way to contact him off hand.

I wouldn't think radiussing either the sides or belly would have any effect on the stall behaviour much less induce deep stall (if anything it could reduce the flat plate drag at high sink rate and lessen any tendency I would guess ) Staggering seats even slightly can 'create' extra elbow room --there was a Cozy or Long Eze variant that did this and was in Sport Aviation.
 

Synergy

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Thanks for your patience, Paul. Having not studied the Cozy in exhaustive detail, I'm not sure how relevant my comments will be for you. Also, although unlikely, it is possible that fuselage sculpting could unload the canard somewhat if the fuselage becomes slightly more effective at creating lift in flight, or for other reasons. As always, proceed with greater caution and respect for the narrower limits of the canard configuration. 'Awareness' is probably the flight test word to consider and plan around, rather than 'concern' though. If it were my airplane I'd try to get rid of the drag sources altogether, and this is how I'd do it.

The way a Cozy canopy meets its flat-topped fuselage (with a 'shelf' all around the outside of it) is nothing but turbulence. That sharp inner corner can be thought of as a pipeline for back-flowing air, feeding the low pressure areas created wherever the airflow tries to take a sharp corner, as well as the turbulent bubble at the bottom front of the canopy. So in my version of a Cozy serious consideration would be given to a custom canopy that reaches farther forward and blends. One step below that ambition would be making an external fillet to smooth the intersection of canopy to fuselage.

As you've drawn it, the proposed curves of your mod could probably be added as non-structural and semi-structural items for only a few pounds net increase. (Keeping weight parity is easy, as well, but more demanding of your engineering skills) Since the perennial problem with canards is aft weight gain, I would probably consider a little extra foam and glass up front insurance.

How to do it? Frankly I'd build per the plans, then (properly) laminate a sheet or two of ordinary extruded sheet foam to the semi-finished outside surfaces. Shaping it to a surprisingly easily-discovered natural laminar shape takes literally minutes of roughing and a day or two of hard-block sanding thereafter. Your hand and your tool will quite naturally want to deliver non-disruptive and appropriately-accelerated results, which is what NLF is all about. 'Tuning in' to this process like a sensitive craftsman or sculptor would is as much a joy as an addiction. A layer or two of glass will harden it up enough to do its job. Then you can add micro to the inevitable, unwanted divots and practice your technique some more.

What is interesting next is the potential to carve into this space from the inside for space gain and utility. It may be possible to cut away specific areas and leave others, using a router. After that, a carefully considered layup of the same total structural materials could be glassed-in to the original interior wall and the new foam wall. (Leave it thicker than before though.) The key to whether this is OK or not will be the new route of load transfer and potential new stress concentrations, and you should get help with this or be prepared to stamp it yourself, on your life. Done wisely, you'll be stronger than ever.

An example is found in the way we cut the aft fuselage walls for Synergy out of 8" thick foam. After laying up the outside, it was a straightforward job to remove everything that didn't look like my desired interior while keeping a 2" thick core. Originally the armrest was shaped in place, but I got a blade behind it so that I could use that chunk to duct airflow to a strategically located eyeball vent and sculpt a panic grip for the less enthusiastic passengers. Our 'famous' cup holders will pop in nicely too.

From this you can see that the most extreme way to go would be to re-engineer a thick core monocoque forward fuselage, reducing or eliminating existing bulkhead dependencies and weight. Learning why my brain sort of starts there while I work my way back to a reasonable first advice for you (build to plans, then sculpt) is how a psychiatrist probably could have saved me a lot of money!

left interior bagged.jpgarmrest venting.jpgaft cabin wall.gif
 

cattflight

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How to do it? Frankly I'd build per the plans, then (properly) laminate a sheet or two of ordinary extruded sheet foam to the semi-finished outside surfaces. Shaping it to a surprisingly easily-discovered natural laminar shape takes literally minutes of roughing and a day or two of hard-block sanding thereafter. Your hand and your tool will quite naturally want to deliver non-disruptive and appropriately-accelerated results, which is what NLF is all about. 'Tuning in' to this process like a sensitive craftsman or sculptor would is as much a joy as an addiction. A layer or two of glass will harden it up enough to do its job. Then you can add micro to the inevitable, unwanted divots and practice your technique some more.

What is interesting next is the potential to carve into this space from the inside for space gain and utility. It may be possible to cut away specific areas and leave others, using a router. After that, a carefully considered layup of the same total structural materials could be glassed-in to the original interior wall and the new foam wall. (Leave it thicker than before though.) The key to whether this is OK or not will be the new route of load transfer and potential new stress concentrations, and you should get help with this or be prepared to stamp it yourself, on your life. Done wisely, you'll be stronger than ever.
Thanks John. Yes, that approach is similar to one I had considered after reading this Cozy builder's website. He essentially suggested building a standard Cozy and then apply a hollow treatment to the exterior (sides only) to cover the control linkage and the arm rest, above which he would cut out to allow more elbow and hip room. Not sure if he pursued this further.

Also, you say "it is possible that fuselage sculpting could unload the canard somewhat if the fuselage becomes slightly more effective at creating lift in flight". Is that to suggest a flat bottom aircraft has a higher lifting potential than a curved bottom aircraft? Thus, the less flat the bottom, the less lift it will create from the fuse? As such, the canard would not unload as easily, correct? I am probably misunderstanding the "lifting body" concept, but I thought someone suggested the Cozy design embraced the flat fuselage as a lifting body and that contributed to the positive flight charateristics.

Maybe I should just stick to the plans. Arg. :(
 

Richard Schubert

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but I thought someone suggested the Cozy design embraced the flat fuselage as a lifting body and that contributed to the positive flight charateristics.
This is wrong. Area forward of the CG is destabilizing at higher angles of attack, exactly what you don't want in a canard configuration, which can be susceptible to deep stall if loaded improperly. For more information, see the cozy newsletters.

Maybe I should just stick to the plans. Arg. :(
If you are not comfortable sitting in it, the plane is useless to you. There are a lot of modifications that have been flown to address the width issue.

In no particular order:

1. Extended strakes for more elbow room.
2. Fuselage width 2"=4" wider.
3. Canopy from Lancair 320-360. Wider and not pointed at the front.
4. The E-racer uses 2" thick pvc foam for the sides, allowing more rounded contours.
5. Narrower consoles for more hip room.
6. Staggered seating, 3 seat at standard length fuselage and 4 seat with lengthened fuselage.

For a good idea of what people are doing, try to go a canard fly-in, there is a good one in the fall at Rough River in Kentucky. Join the CSA and get back issues of the newsletter, a lot of this has been covered there.

P.S. Because of the reclined seating position, you need support under your legs. The cushion thickness necessary for this is higher than the bottom of the cutout, so you wouldn't gain anything by removing the lower portion.
 
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cattflight

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Modifying the plans without having access to the designer's engineering data never ends well.
With all due respect, I am looking for constructive feedback. Besides, I am reasonably certain Nat Puffer didn't have access to Burt Rutan's engineering data when he derived the CozyIII from the LongEZ.
 

Synergy

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"+1" from me on anything Mr. Schubert has to say.

...that approach is similar to one I had considered after reading this Cozy builder's website. He essentially suggested building a standard Cozy and then apply a hollow treatment to the exterior (sides only) to cover the control linkage and the arm rest, above which he would cut out to allow more elbow and hip room. Not sure if he pursued this further.
Yes! That looks like a good example of the idea.

...Also, you say "it is possible that fuselage sculpting could unload the canard somewhat if the fuselage becomes slightly more effective at creating lift in flight". Is that to suggest a flat bottom aircraft has a higher lifting potential than a curved bottom aircraft?
No. Any shape or body is capable of creating unwanted aerodynamic forces; round ones included. The cause however is always differential pressure, and some things tend to create it more easily than others. Trapped air, sharp edges, flat surfaces, and rapid variations are the usual suspects, especially when they serve to delay or impede the "pressure-equalizing flows" that are always happening on the surface in response to such things. (This is another way of looking at what turbulence actually is.) Your rounded body, even though wider, would probably reduce the less-predictable contribution to lift made by the Cozy fuselage, if any. Its contribution to drag is a different matter and depends almost entirely on what happens ahead of (and transitioning into) the new geometry. If you've already gone turbulent, a laminar shape will increase your drag, not reduce it. You'd be wise to shape the whole forward section as required.

...Thus, the less flat the bottom, the less lift it will create from the fuse?
The bottom shape can't be separated from the top shape- it's their combined disruption of the airmass that imparts an energy or momentum to the volume they forcibly occupy. In other words, if the centroid of the fuselage follows a path, the isolated effect of the fuselage will be as if we have moved a fuselage-sized blob of air up or down along that path during the time we were there. So as it relates to your question, the influence would likely be small and likely in a negative direction rather than lifting. The thing that makes it hard to evaluate is the region ahead of the canopy. Its behavior will change in response to a bottom surface change, but not in ways that are obvious to me. Probably not by much. It is possible to evaluate them if you have the geometry.

... I thought someone suggested the Cozy design embraced the flat fuselage as a lifting body and that contributed to the positive flight charateristics.
It is very difficult to evaluate lifting fuselage ideas, and that is why we do not see many of them. Designers are inclined to neglect their contributions altogether and to shape them to avoid surprises.

...Maybe I should just stick to the plans. Arg. :(
Yeah, but that's no fun. Once upon a time, people who didn't have a fraction of the information, experience, or tools available to all of us designed, built, and flew every plane you've ever seen. In less time than we take to debate design ideas on this forum, aviation once changed profoundly with each new specimen to learn from. Our modern fear is adequate, I believe, to keep us relatively safe in re-establishing that progress if we want to do so. I just hope they don't fret over departing from the cattflight-approved Cozy mods three decades from now.
 

dviglierchio

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I think you may be confusing me with Terry Schubert, same last name, but he is one of the canard guru's, I am but a lowly student of the breed.:ponder:
You're still correct R. Schubert. This guy has posted this on the canard sites and didn't get the back slapping he was hoping for so is now trying this forum to see if it is any more excited about his plan.

With as many successful and comfortable, happy, safely flying Cozy builders out there, if they don't have this figured out yet - then it's a lost cause. Just the bigger canopy, Cozy Girrrls strakes and thinner console alone make the plane much more comfortable and are proven improvements. But there are those that have to reinvent the wheel from scratch and sometimes, but rarely, it turns out good....! Mostly they agonize over redesigning every last detail of a proven design and never end up completing or flying anything.

"to add to the Cozy's overall safety and aerodynamics without an unreasonable penalty." The Cozy has a pretty good safety record already. Most, if not all, safety problems are with pilots not the design. The aerodynamics, if not completely tuned during the build with proven improvements, can be done later with testing and experimentation as I am doing. Excessive obsession with major, untried "improvements" to an already nice design prior to building just wastes time and almost insures you'll never fly it. There are two new Cozys in northern California and they are beautiful planes that the owners feel are perfectly comfortable.

A fellow nearby took over a Long EZ project that was widened, stretched and gosh knows what else. He completed it beautifully. It was very large inside, more than necessary for comfort, performed as well as a normal Long EZ, though a bit less snappy in the controls, and burned about half again as much fuel. He sold it right away........:shock:

Oh, I almost forgot the important disclaimer - Just my 2 cents!
 
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Synergy

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Hmmm... Terry's probably not gonna let me get away with that one, Richard. Thanks.

Something to mention on the blended winglet shown in the link is that the mode of failure in this type of geometry tends to be a delamination buckling on the compression side due to surface failure of the foam. This is a difficult issue to see coming and to analyze until it happens. I would not personally recommend adoption of this technique using the foam shown, even though they rely on the spar web. A Corecell foam would be a better choice but also ten times as expensive.
 

slociviccoupe

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good information to know about the blended winglets. but the intent of the post was to show the lengthening and rounding of the cozy. also the guy who did the winglets has a cozy or other canard going well over the max vne of the aircraft and has done a lot of work to eliminate flutter. but yes very true that this is experimentation and more than likely won't know of a failure till it happens. and most likely there were no windtunnel or load tests done to find out the destruction point. I do know that when at a machine shop i used to work at the blended winglets that were added on to passenger jets majority of it was titanium.
 

Aircar

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If what you want is extra elbow room then the simplest way to get it is to simply create a couple of external blisters where your elbows and forearm intersect the fuselage wall -- check the Brown Carplane website for an example shown on their animations and still pix - for extra headroom the simplest way is surely to jack up the canopy (if you have he uncut bubble or can get the untrimmed molding then you might be able to just use the oversize from stock bubble ) -actually what John Mc G says about the intersection and drag is correct and well known - it also applies to wing leading edge junctions or any place where a stagnation point exists --filletting the intersection with a generous radius will alleviate the issue (the 'horseshoe vortex' )

I'm sending this from a public access terminal in my local computer repair who just got back from holidays and have my bloody computer again to fix after it refused to open the internet at all --so I have been offline for a few days and will be again for a few more --maybe somebody has responded to one of my other incendary postings and wonders why I haven't riposted (a pun there...)

Any aerodynamic effects of the changes proposed to the Cozy would be in the 'unmeasurably small' category --the Gyroflug speed canard has long flown with a fully rounded fuselage -courtesy of the Grob Astir two seater or ASK 21 probably and has no ill effects -- both weathercocking and pitch instability of the more rounded nose would be lessened not increased . As to the radiused winglets - Chris Esselstyne is the originator of this Cozy mod I think and would have known about the radial load components and hs g flown his extensively after modding .
 

cattflight

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Thanks Aircar. "Blisters"? Yikes, that sounds UGLY! :ermm:

But generally, I agree this is a good option and John (Synergy) suggested something like that as well. Also seems it could make the build less 'custom' by only adding to the plans rather than re-designing the entire fuselage geometry.

However, in addition to the elbow area, the area I want more room is at the hips. In the Cozy, the arm rest accommodates the side stick linkage and I would like to get it further outside. Now I'm thinking of constructing a per-plans fuselage (or maybe only 2" wider) and then bond an appropriately-shaped foam core exterior treatment (more like a GOITER than a blister!) that encompasses the control linkage as well. Then I could incorporate an armrest above the controls that is actually outside the orignal wall location. If I decide to round the bottom,I may just do this by shaping the foam and adding a flat false floor in the limited area it'd be required. Maybe out of honeycomb integrating some slim storage for a cover or tie-downs.

If what you want is extra elbow room then the simplest way to get it is to simply create a couple of external blisters where your elbows and forearm intersect the fuselage wall -- check the Brown Carplane website for an example shown on their animations and still pix - for extra headroom the simplest way is surely to jack up the canopy (if you have he uncut bubble or can get the untrimmed molding then you might be able to just use the oversize from stock bubble ) -actually what John Mc G says about the intersection and drag is correct and well known - it also applies to wing leading edge junctions or any place where a stagnation point exists --filletting the intersection with a generous radius will alleviate the issue (the 'horseshoe vortex' )

I'm sending this from a public access terminal in my local computer repair who just got back from holidays and have my bloody computer again to fix after it refused to open the internet at all --so I have been offline for a few days and will be again for a few more --maybe somebody has responded to one of my other incendary postings and wonders why I haven't riposted (a pun there...)

Any aerodynamic effects of the changes proposed to the Cozy would be in the 'unmeasurably small' category --the Gyroflug speed canard has long flown with a fully rounded fuselage -courtesy of the Grob Astir two seater or ASK 21 probably and has no ill effects -- both weathercocking and pitch instability of the more rounded nose would be lessened not increased . As to the radiused winglets - Chris Esselstyne is the originator of this Cozy mod I think and would have known about the radial load components and hs g flown his extensively after modding .
 
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