Mr Whee was right!... lightening hole fuel tanks

[way_up_north]

Dear gentlemen....

Bob Barrows has made a creation and shared it with the world...priced affordably...he answers all inquiries ..in the spirit of his generosity ...I'm deleting my posts in this thread..because the spirit of this thread does not align with what Bob Barrows is about...weve all delt with other companies...i dont have to go into it. The Bearhawk is a great bunch of people...not just the plane...

Mark is doing his best to bring to market a safe affordable plane.... that you can buy one bolt... or the whole kit and mold it to your mission...

Jared ...doing thankless job and his heart is in the right place....

the Bearhawk is such a great plane because so many builders have added their sweat into the dream...many nameless people now that have donated expertise to give us what should be a $80,000 - $100,000 aircraft....jigs, methods, shortcuts....even the factory build manuals ..for a $100.. That other companies would charge thousands and you'd have to travel to their builder assistant facility....

I`m not sucking up...I'm saying thank you for the $100,000 plane that's been dropped into my lap.....

the plain truth.. the Bearhawk is hands down...a gift

Bearhawks are in demand on the used market like RVs....The Bearhawk has arrived.

I`ll do my tinkering....id like to develop a procedure of creating bubble windows in your home oven....step by step process on the cheap to give the cabin some extra elbow room....and see if its possible to balance out a 3rd row...be it nose wing tank...header tank/forward tank or whatever....it was not a good idea to use this forum as a scratchpad...as some ideas need a few months to think through....then an educated proposal made...when I have something useful to add on those Ill let you know...




so...fellas...have a good day..doing whatever you do...

[whee]

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/42255-fuel-tank-in-front-of-the-spar-ideas-on-6-seats

I'm not sure that I'm on to anything or that will will actually ever install additional tanks but I think it could work really well as auxiliary tanks.

I never asked hotel whisky anything because custom tanks would required and I could have them made locally. I think I calculated 10 gallons in the tube that runs through the lightening holes and 2 gallons in the tip where the fill port will be.

[way_up_north]

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[whee]

I was thinking of taking this one step further...brainstorming an idea ..

lets call this the poor mans wet wing...

make your inboard 5 nose ribs(or any amount depending on tank size) out of weldable aluminum...

Make lightening hole size to match off the shelf tube size

insert during construction of wing

tack weld tube to nose ribs

you don’t need rib stiffener as tube welded to rib is a much stronger structure

only down side you cant reach some rivets to buck, need to use flush pop rivets in some spots

up side you could have a large tank to use when loads push cg to rear...

There could be off the shelf aluminum extrusions that are tear drop/oval shaped that could further maximize the size of the tank... just make the lightening hole shape to match

maybr welding gas tanks to an airplane rather then mechanically attaching it might be a bad idea... this whole plan might have a lot of Swiss cheese in it... I’m hoping the more learned on here can do some critiquing

Your thinking further outside the box that I am typically comfortable so there isn't much that I can contribute that may be of value. I don't like to get into structural modifications especially when I'm not familiar with the analysis of the structure in question. The changes you are proposing likely would have major consequences.

My initial thoughts:

Welding thin aluminum in a structure that moves and is in a high vibration environment is asking for cracking issues.

Flush cherrymax rivets are doable but far from ideal.

The tank isn't going to be large at least by my standards. I'd swag 15 gallons. So you'll still need the standard main tanks and 30gal of extra fuel is way more than needed and not worth the hassle to get it, IMO.

I looked down this road because:
1. I want to add aux tanks later only if I need them.
2. I don't want the empty tanks to negatively affect my CG
3. I don't want transfer pumps.

[fairchild]

"tack weld tube to nose ribs" THAT is a forbidden idea----- you CANT weld to any piece of 2024. (due to the copper content--and the heat treatment--
it cracks right beside the weld right away--) NOW--- you might make the tube out of 6061 and be able
to weld THAT somewhere.... but as soon as you do--- you can no longer slide it through the lightening holes. Maybe just have a bracket on the end caps.
Use some kind of anti-chafe around the lightening holes to hold it from moving. BUT- I gotta think THAT would be a recipe for the rib to eventually slice a cut
into the tube and leak fuel into the cockpit. Maybe better to fab a tank shaped like the LE and 3 feet long. Leave out those nose ribs and make a section of LE
skin removable there. Mount the tank to the front of the spar. Lay some narrow strips of felt in the tank and let the skin/cover wrap over it. Bad place for a filler neck
and cap though. maybe dont have one. (?) Maybe make the tank about a finger width smaller than the skin and come up with an aluminum spacer which could
be adjusted /fabbed to exactly follow the LE contour so the tank would not have to follow it so exactly (make building the tank shape easier )

Tim

[way_up_north]

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[fairchild]

I kind of like the idea of the leading edge shaped tank. You might have to get Bob's advice on how to bolt it to the spar. I think if I was doing it--- I would redesign the skin around the tank to have
a section of skin (probably with doublers for stressed skin) with riveted in blind nuts on the underside of the perimeter--- and flush screws in the edge of the removable panel. The KingAir has
lots of those covering the fuel cells so you can get in there when you need to. I would want it big enough that I could remove the tank easily if needed. Have to get Bob to draw out a design
of the perrimeter to preserve the linear strength of the skin there--- not sure what that should look like exactly----
You might look on the RV website to see if any of them have all ready done this--- since our wing is similar to theirs ( I understand---)

done any calculations of the volume in each bay ? I would think it wouldn't take much length to pile up 15 gallons...…
Tim

[way_up_north]

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[PaulSA]

the tanks are 300 pounds to 400 pounds behind the spar....depending if you have an aux tank........to move that 2 to 3 feet forward would....open up,some possibilities....

If you have to do a "zero fuel" calculation, surely this doesn't help?

[svyolo]

5 pax and more gas? Sounds like you are starting to want/need a bigger airplane.

[way_up_north]

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[Bcone1381]

I am curious the results of your Weight and Balance calculations due to the movement of the fuel to a new location.

[way_up_north]

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[jaredyates]

It is also important to think about the weight distribution laterally, meaning how far left and right the weight is from the centerline. It is fun to think about all of the diverse ideas, but don't underestimate the immense complexity of Bob's original design. Like airplane engines, the finished product seems so simple because extraordinary engineering went into simplifting it. Deviations from the original design can really detract from the usefullness of the airplane and really complicate its construction, often for very little, if any, gain. It is a great 4-seat airplane and a poor 5-seat airplane. Let it do what it does well and it will reward you by doing well.

Regarding the bubble window discussion, there has been another thtlread about it in the last week or two .

[way_up_north]

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[Nev]

anywyas...ill take my opinions and wild ideas and go over to the homebuilt forum...

Please keep posting them here as well, I thoroughly enjoy reading your ideas and the “outside the box” type of thinking. Jared and others raise a sensible of degree of caution to provide balance and that’s important too.