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  #31  
Old 10-14-2018, 11:29 AM
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Toobuilder Toobuilder is offline
 
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Location: Mojave
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Quote:
Originally Posted by RWoodard View Post
I’m thinking I can enclose the space in the wingtips and make a composite tank. Shouldn’t be more than about $50 in fiberglass and resin (have most of it on hand anyway), another $150 for some Jeffco sealant, a couple of fuel caps, some fuel line, etc...
I'd take a good look at how the shear load of that new tank is addressed. The L-39 uses a similar attach method for its 26 gallon tip tanks, but the fasteners going into the upper and lower skin are large, numerous and in double shear. In addition, there is a hefty lug that ties the Tank into the main spar.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #32  
Old 10-14-2018, 05:21 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by Toobuilder View Post
I'd take a good look at how the shear load of that new tank is addressed. The L-39 uses a similar attach method for its 26 gallon tip tanks, but the fasteners going into the upper and lower skin are large, numerous and in double shear. In addition, there is a hefty lug that ties the Tank into the main spar.
The L-39 is also designed for significantly higher aerodynamic loads.

I know you know that, I'm just sayin... sometimes overkill is appropriate caution, and sometimes it's just overkill.
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Greg Niehues - VAF 2018 dues paid
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Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
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  #33  
Old 10-14-2018, 07:43 PM
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Toobuilder Toobuilder is offline
 
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Im not suggesting a copy of the L-39, but hanging a wet tip off a bunch of #8 screws countersunk into fiberglass will take some careful study.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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RV-8 - Flying
1940 Taylorcraft BL-65 -flying
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  #34  
Old 10-15-2018, 10:44 PM
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RWoodard RWoodard is offline
 
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I've seen several load tests at fly-ins when uncaring/unaware parents use wingtips as baby changing tables! Those chubby infants with a full diaper have got to be pushing the weight of 5 gallons of 100LL!

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Rod Woodard
Windsor, Colorado (KFNL)
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  #35  
Old 10-16-2018, 07:24 AM
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Bullseye Bullseye is offline
 
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Quote:
Originally Posted by RWoodard View Post
Those chubby infants with a full diaper have got to be pushing the weight of 5 gallons of 100LL!
[Looks over at my chubby infant....calculator sounds in head...] Yup.
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  #36  
Old 10-16-2018, 12:13 PM
BobTurner BobTurner is online now
 
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Quote:
Originally Posted by RWoodard View Post
I've seen several load tests at fly-ins when uncaring/unaware parents use wingtips as baby changing tables! Those chubby infants with a full diaper have got to be pushing the weight of 5 gallons of 100LL!

They’d need to be really chubby:
5 gal gas = 30 lbs, at 3.8 g = 114 lbs.
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  #37  
Old 10-16-2018, 12:17 PM
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Bill Boyd Bill Boyd is offline
 
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Default Airliner-gentle? Some dim memory is stirring as I read this

whether it was here or on the Matronics list, I don't recall... a certain airshow RV pilot was stating that adding fuel capacity to the wings had no penalizing effect on aerobatic gross weight and might even lessen stress in the spar by bending it the other way when pulling G's - and Van's be darned if they disagreed with him. I was not so sure I agreed with the aerodynamix that were being propounded, but nevertheless, there it was.

Anyone else recall that?
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  #38  
Old 10-16-2018, 12:50 PM
rv7charlie rv7charlie is offline
 
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Don't recall that particular thread, but there are multiple issues; not just wing bending moment/gross weight. Yes, spreading the load out along the wing can reduce the bending moment at the root, *but* spin characteristics and control effectiveness can change radically. At least for me, that's the reason to keep the plane as close to stock as possible for acro.

edit: Not meant to say I wouldn't add aux fuel; I'm doing that on my -7. Just that I made every attempt to keep added weight to a minimum, and kept the ability to fly with fuel in only the original tanks when flying acro.

Last edited by rv7charlie : 10-16-2018 at 03:37 PM.
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  #39  
Old 10-20-2018, 08:19 PM
paszekj paszekj is offline
 
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Location: West Des Moines, IA
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I'm just getting started so maybe I'm way off base here but my understanding is the HW Aviation tanks function by pumping from a small auxiliary tank into the main tank via a bung in each main tank. They even sell the bung kits separately that you can install when building to make it easier to add extended tanks in the future if you so decide.
Would it be possible to install an additional bung in each wall of the fuselage with a hose leading to each main tank, then have a removable additional tank (like an RV12 tank?) that you could secure in the baggage compartment with a single pump and a fuel selector switch? Then have a hose leading to each of those bungs in the fuselage wall. You could install the tank and hoses when needed for long trips, then remove it if you don't need it or want to do aerobatics/spins. It would have the additional benefit of being able to visualize a volume gauge in the tank while flying to verify that the fuel has transferred to the mains.
Maybe there are factors I'm not considering but I would think it would be lighter and cheaper than two separate tanks plus the benefit of being able to remove it. Granted you would use up most of your baggage capacity with a full tank but maybe a vertical tank right behind the seats (e.g., like a briefcase shape right behind the seat) would help keep the COG a little more forward. crazy?
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  #40  
Old 10-20-2018, 08:45 PM
rv7charlie rv7charlie is offline
 
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What's the mission? If you're just doing solo distance record stuff, sure. But if you're doing it to tanker fuel and/or for travel with a friend, then as you said, you lose both baggage volume and payload, because all the bending loads are in the center of the airframe. You're also riding around with a lot of gas in a temporary, removable container in the cockpit with you. Even without fire, a leak could be overwhelming. And depending on your alternate choice of built-in tank 'method', it can be significantly heavier. My two leading edge aux tanks added around 30 gallons capacity at the expense of about 2 lbs additional weight (probably around 4 lbs total, including fuel lines).

Your choice on plumbing. Mine is (was, at the time) a bit of a special case. I knew I was going to be using automotive style injection, so the engine is fed from only one tank (ala turbines). The other three tanks are all aux tanks, and the fuel selector just picks which one transfers to the main. Downside: no backup tank (but *many* a/c have only one tank, or a header that's fed from selected tanks). Upside: no switching tanks and no need for a duplex fuel selector.

If you want behind the seats tanks, here you go:
https://www.smokingairplanes.com/products/
His tanks can be plumbed as aux tanks.
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