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

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cattflight

Well-Known Member
Joined
Dec 31, 2010
Messages
47
Location
Spokane, WA
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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