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Tank access hole at bottom of fuselage

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Jan 24, 2018 7:27 am Post subject: Tank access hole at bottom of fuselage

Dear forum members,



The kit I got (XS Mono) has a modification made in the canoe where the two small fuel fitting holes at the bottom where converted to a large single gaping hole (ugh!).



Not a fan of this modification since I am more about strength than convenience and I also think it will upset the fitting of the cockpit module some (bumps on the inside where glass was added to create a flange around the hole)



So my question is whether this is a documented mod (this is the US so it doesn't have to be a formal approved mod). But I am looking for size and how other people have built the flange, etc. as well as whether this mod is OK and being done out there (experiences, history).



Thanks and Best Regards,

Chris

AirEupora

Joined: 01 Nov 2009
Posts: 186
Location: Dixon, CA

Posted: Wed Jan 24, 2018 8:32 am Post subject: Re: Tank access hole at bottom of fuselage

I have seem a number of pictures from the group showing this enlarged access panel,  I have thought about modifying mine as the two small panel hole are just too small to do anything in this area.  I just went through the five year cycle of changing all of my fuel hoses.  This enlarged hole would have help a lot.  If you have it the now I'd kept it.  The cockpit module should clear it with no problems.  



Go back through the pictures from the old web site there are lot of pictures and you might find  one you need.  Also give Bud a call.  If you have a Tri-gear then there is also a panel that has been used by a lot of the builders where the mono tire was.

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Jan 24, 2018 8:57 am Post subject: Re: Tank access hole at bottom of fuselage

Thanks for the reply AirEuropa. I will look for the pictures but where is this old web site you refer to?



Chris

Rocketman

Joined: 07 Sep 2010
Posts: 87
Location: USA, Earth

Posted: Wed Jan 24, 2018 9:00 am Post subject: Tank access hole at bottom of fuselage

Our Tri-Gear has had the same mod since first flight.  Seamless 

installation with no interference anywhere.



Jeff



"I believe that forgiving them is God's function. Our job is to arrange 

the meeting."



-Gen. Norman Schwarzkopf



On 1/24/2018 10:32 AM, AirEupora wrote:

 	  Quote: 	
		   

 

 I have seem a number of pictures from the group showing this enlarged access panel,  I have thought about modifying mine as the two small panel hole are just too small to do anything in this area.  I just went through the five year cycle of changing all of my fuel hoses.  This enlarged hole would have help a lot.  If you have it the now I'd kept it.  The cockpit module should clear it with no problems.

 

 Go back through the pictures from the old web site there are lot of pictures and you might find  one you need.  Also give Bud a call.  If you have a Tri-gear then there is also a panel that has been used by a lot of the builders where the mono tire was.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=477531#477531

AirEupora

Joined: 01 Nov 2009
Posts: 186
Location: Dixon, CA

Posted: Wed Jan 24, 2018 9:02 am Post subject: Re: Tank access hole at bottom of fuselage

I found this on the web site:



sidsel.svein(at)oslo.onli

Guest



 

PostPosted: Tue Dec 13, 2011 8:42 am    Post subject: Bottom cut-outs 

 

Put it in the Search and you will see your answer!

AirEupora

Joined: 01 Nov 2009
Posts: 186
Location: Dixon, CA

Posted: Wed Jan 24, 2018 9:05 am Post subject: Re: Tank access hole at bottom of fuselage

Do you still have the Mooney?

davidjoyce(at)doctors.org
Guest

Posted: Wed Jan 24, 2018 9:31 am Post subject: Tank access hole at bottom of fuselage

Chris, I have never come across such a thing in this country or Europe and I would be amazed if the LAA would ever approve it. It seems to be asking to seriously reduce the strength in a fairly critical area. It might be worthwhile for you to send pictures to Andy Draper and ask for his views. Regards, David Joyce, GXSDJ 

   

 

On 2018-01-24 15:27, n7188u wrote:  	  Quote: 	
		    	  Quote: 	
		  --> Europa-List message posted by: "n7188u" <chmgarb(at)gmail.com (chmgarb(at)gmail.com)>



Dear forum members,



The kit I got (XS Mono) has a modification made in the canoe where the two small fuel fitting holes at the bottom where converted to a large single gaping hole (ugh!).



Not a fan of this modification since I am more about strength than convenience and I also think it will upset the fitting of the cockpit module some (bumps on the inside where glass was added to create a flange around the hole)



So my question is whether this is a documented mod (this is the US so it doesn't have to be a formal approved mod). But I am looking for size and how other people have built the flange, etc. as well as whether this mod is OK and being done out there (experiences, history).



Best,

Chris





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=477530#477530

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Jan 24, 2018 10:36 am Post subject: Re: Tank access hole at bottom of fuselage

AirEuropa,



Not anymore but had that Mooney for 13 years. Nice airplane but lots of work.



Regarding the location of such opening, I agree it's awful from a structural standpoint. But only in the longitudinal direction. Not much change laterally since the bottom already has two access holes in that direction.



But as the owner of an older partially built kit, I new some things would not be to my standard of quality and would have to be fixed. And I can assure you, it has been very educational 



As they say, the beauty of composites is that almost anything can be fixed! Now I know how.



BTW, hence my previous (unanswered) post asking to see if anyone knew the pre-preg materials used in the fuselage. Important info if repairs are to be made.



Chris

John Wighton

Joined: 18 May 2010
Posts: 241

Posted: Thu Jan 25, 2018 12:58 am Post subject: Re: Tank access hole at bottom of fuselage

As per David Joyce's response, this area of the fuselage is load bearing and is fairly highly stressed for symmetric and asymmetric lifting loads (from the empennage).  A large hole with a cover will likely pass load via the flange/fasteners - this is not good practice.  Without the cover the corner stresses will be very high, potentially leading to damage. The aircraft design philosophy for damage tolerance is 'no growth', requiring there to be sufficient strength for inherent damages (incurred during factory build and by individual users completion processes, plus in-service accumulation of damage) - so as not to compromise the original MS/RF calculated.



The two 'standard' access holes are small for a reason.



I continue to progress the loads and stressing work on the Europa, this is being done as a R&D side project in my business.  The aim is to fully understand the structural margins that exist in the XS structure and, if possible, show a modest MAUW increase (possibly aligned with the US commonly used MTOW). The project is being conducted as per a clean sheet design.  I intend to write some articles for the Club Mag.

_________________
John Wighton
Europa XS trigear G-IPOD

budyerly(at)msn.com
Guest

Posted: Thu Jan 25, 2018 8:39 am Post subject: Tank access hole at bottom of fuselage

John, 

I appreciate the time and expense for your service to the Europa community. 

  

In the States, I have used a 6 inch access hole in the rear fuselage for years.  It is using a reverse of the flange layup in chapter 23 which ties the two skins together with a flox corner then 4 plies of bid on the inside.  One can use  the hole cutout for the cover in this method, by reinforcing the edge with a fill of flox to stabilize the skin and support the screws.  Of course I use a 4 ply inner skin reinforcement of 8 oz bid and a tie between the inner and outer skin as Flight Crafters  initially did.  (Bob used a common sense approach used by Rutan that ties the skins together at the hole perimeter and add a flange of the same number of plies as used in the sandwich in that area plus two for nutplate attachments if required.)  These are  the techniques used in the Eze, Quickie and by Ken Rand in the KR clamshell wings skins.)  No problem with the flow of stress around the hole in any of these aircraft either.   

  

I did calculations on it years ago.  My calculations were simply based on the 45 ply orientation with a 2 inch overlap on the inner skin.  I worked up the vertical  (tail plane) force on a round cylinder of 1.5 foot diameter with a six  inch hole.  I just evaluated the shear loads (as all the strands are at  a 45 back there and very light glass).  I use 4 AN screws on the cover/flange and found the load to be acceptable with over a safety margin of two provided there were at least 4 layers  to support the countersunk nutplate rivets.  Many years of mild aerobatics and flying at 1370 pounds doing advanced handling with no cracks wrinkles or problems after 10 years and 300 hours in my old Classic.  This sized hole has been put in about 16 aircraft  without incident using this method.  It only opens the hole from 5 inch to 6 so a man can get an arm in and ties the inner skin to the outer.  For normal flight I fly at 1450 lbs. nearly all the time as the guys I fly are not the 170 pound FAA specimens.   Again, no problem.  (Also fly XC with the wife at 1450 pounds of mandatory wifely needed items) 

  

I am very sorry that all that was on an old computer that I can no longer find the file with the calculations.  I used the shear load of a cylinder using an example from “Aircraft Structures” (Perry I think) used by Boeing.  They have a  very good metal structure analysis of monocoque tube structure, then applied the stress sandwich load of Michael Niu who wrote Composite Airframe Structures.  Assuming the tailplane load at 1750 pounds and the hole at about the 11 O,clock position.  Enlarging  the hole to a size that is appropriate for a normal mans arm can be done without need for a stringer and rib in that area.  Again, I am just an aero guy and not a structural guy.  I found the exercise to be challenging using only the Rutan documentation, but  I was introduced to Niu back in the late 90’s and he has a great analytical book on molding and the use of fasteners in composite material as well as and structural repairs and how the stresses flow around access holes and damage.  Pretty neat for the early  90s. 

  

Keep us posted on your results.  Todays structural analysis programs are awesome and I envy you having access to such wonderful computing aids. 

  

Best Regards, 

Bud Yerly 

  

Sent from  Mail for Windows 10 

   

From: John Wighton (john(at)wighton.net)

 Sent: Thursday, January 25, 2018 4:02 AM

 To: europa-list(at)matronics.com (europa-list(at)matronics.com)

 Subject: Re: Tank access hole at bottom of fuselage 

 

  

--> Europa-List message posted by: "John Wighton" <john(at)wighton.net>

 

 As per David Joyce's response, this area of the fuselage is load bearing and is fairly highly stressed for symmetric and asymmetric lifting loads (from the empennage).  A large hole with a cover will likely pass load via the flange/fasteners - this is not good  practice.  Without the cover the corner stresses will be very high, potentially leading to damage. The aircraft design philosophy for damage tolerance is 'no growth', requiring there to be sufficient strength for inherent damages (incurred during factory build  and by individual users completion processes, plus in-service accumulation of damage) - so as not to compromise the original MS/RF calculated.

 

 The two 'standard' access holes are small for a reason.

 

 I continue to progress the loads and stressing work on the Europa, this is being done as a R&D side project in my business.  The aim is to fully understand the structural margins that exist in the XS structure and, if possible, show a modest MAUW increase (possibly  aligned with the US commonly used MTOW). The project is being conducted as per a clean sheet design.  I intend to write some articles for the Club Mag.

 

 --------

 John Wighton

 Europa XS trigear G-IPOD

 

 

 

 

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Thu Jan 25, 2018 2:04 pm Post subject: Re: Tank access hole at bottom of fuselage

thanks to all for the replies. I particularly enjoy the technical ones (I'm an engineer and enjoy the details).



However, the goal of this posting has been achieved in that I now know this is not a mod that is commonly used or documented (unless I hear otherwise). I know I will have to do something about it.



One option is to close the hole in a typical repair fashion. The other is to create a stressed cover to transfer bending and torsion loads to appropriate flanges in the fuselage (with enough thickness to allow proper bearing loads on MS24694 structural screws).



I'm inclined to do the later.



Best,

Chris

John Wighton

Joined: 18 May 2010
Posts: 241

Posted: Thu Jan 25, 2018 11:55 pm Post subject: Re: Tank access hole at bottom of fuselage

As Bud says, a suitably reinforced larger hole can be quite acceptable. His approach sounds thorough and considers the conservative stressing methodologies of Mr Niu et al.  He could also have mentioned Bruhn (the stressman's bible), NACA/NASA papers, Roark & Young and the implementation of those Gentlemen's work by Bill Gran, Richard Abbott, etc.  



There are dangers in using the numerical programs (finite element based), as with most tools they need to be used properly. I came into stressing in the early 80's became attracted to FEM/FEA techniques and taught myself Nastran, Patran and a lot of other programs since).  Having since used FE techniques to analyse many thousands of objects (from paper clips to A380 wings) there is still a risk of getting things wrong.  However, with careful planning, incremental implementation and a robust approach to V&V (verification and validation) a great deal can be gleaned from these simulations.



I developed the structure for the Europa tail dragger (McCallum/Flyer initiated in the UK), this was done with a partial fuselage FE model, using the factory layup (pre-XS days).  Material data from Martin Hollmann's books is conservative but good for basic strength calcs.  That design is flying now as G-MLXP (the LAA, as is normal, insisted on beefing up the optimal structure l had specified).



Going back 'on topic' l think the layup details Bud gives can be used as a guideline for reinforcement of a Europa fuselage access hole.  In the UK any deviation would need to be cleared as a Mod (preferably before it is applied to the aircraft).

_________________
John Wighton
Europa XS trigear G-IPOD

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