Removable Stressed Skin Fuselage Panelling

[blondefletch]

Hi folks,

I'm currently undertaking a fuselage design project for a UAV. My question relates to something I read in this textbook, link to paragraph: Unmanned Aircraft Systems: UAVS Design, Development and Deployment by Reg Austin (

http://bit.ly/zMaMaK).

I am looking at potential design solutions for incorporating stressed skin panelling, but that is almost completely removable around the fuselage. So far I see three solutions, using removable high tensile rubber seals around the panels, using a blended fit for the fuselage structure, or just having removable side panels with the top and bottom surfaces being placed under stress.

Discuss? Cheers,

Bradley

PS: Picture of solutions

http://imageupload.org/en/file/199360/dsc-0058.jpg.html

 

[KENAT]

blondefletch

Do you have any other requirements that might drive the solution such as low observability (stealth)? Or is it mainly aerodynamic considerations?

The page in that book you link to is blocked for me, though the proceeding page talks about needing mostly removable skin for access requirements - is this your main driver?

I'm not sure I follow the reasoning for your rubber seals per your attached sketch. The other option you show can sometimes be achieve by jogling/dimpling the skin, rather than machining thickness away.

(Just a warning, student posts for help on assignments are discouraged/banned as detailed in the links in my signature. However, leeway tends to be given for interesting topics of discussion etc. that doesn't get specific enough to be considered cheating.)

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[blondefletch]

Hi Kenat,

To clarify, this is a project based completely in my spare time, with the question more related to future projects.

Thanks for your response, it is solely structural considerations, just trying to prompt a discussion on what methods can be used to make stressed skin panels removable, as opposed to a modular UAV design or a truss structure.

Hope this helps to focus on what I am getting at.

Thanks

 

[GregLocock]

Your picture of a single screw holding two curved skins together is probably the worst solution imaginable. At least use a double row.



Cheers

Greg Locock


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[KENAT]

Another thing to consider, if you plan on using countersunk/flat head fasteners then due to tolerance issues (if nothing else) you'll probably need to use some king of floating captive nuts.

For removable panels you'd also need to worry about fasteners getting lost which may drive you to captive fasteners for frequently removed panels. However, these impose their own constraints.

I have to admit most of my relevant experience is on nominally single flight equipment not true aerostructures, hopefully someone with more directly relevant experience will feel like imparting some knowledge to both of us.

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[GregLocock]

I have never seen a solution that come close to the strength and stiffness of a continuous panel unless it involves fastening the skins to an underlying frame. I'm inclined to think it doesn't exist since it would be all pervasive if it were practical.

Cheers

Greg Locock


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[thruthefence]

"that is almost completely removable around the fuselage"

I would think if this is your goal, the added supportive structure & parts count, ie nutplates & threaded fasteners, is going to make this thing to heavy to fly.

 

[blondefletch]

Thank you all very much for your comments. Greg, the image I used was a patented design, in which I thought exactly the same as you. Good to get a technical peer appraisal, so thanks again. KENAT, regardless of the non-aero background, very useful stuff once again, thanks.

I'll be pursuing a reinforced shell for my semi monocoque fuselage, with top and bottom surfaces in stress, trapezoidal cross section and consequently with the side panels removable. Been scanning CAP 722/CS-25(Closest spec!) and looks like a viable solution.

Any closing thoughts please let me know, but otherwise, cheers for the input folks

 

[btrueblood]

"I have to admit most of my relevant experience is on nominally single flight equipment "

Kenat has aero background. Just not on repetitive-use structures. Mine was similar, and my suggestion would have been to use a primacord charge to seperate the skin...but that is a single-use solution too.

 

[blondefletch]

Meant to put in aero-structures for KENAT, apologies. Either way, thanks for your input