Exp Cub fuel tank??

[Lowrider]

Has anyone used or looked at using pre-fab aluminum fuel tanks built for "hotrod" use? The size seems to be compatable with the Cub wing but I can't find a weight. I've used the spun aluminum tanks in cars before and they are fairly light but still pretty stout. They look to be about 1/3 the price of purpose built Cub tanks.

http://www.speedwaymotors.com/T-Bucket-Aluminum-Fuel-Tank-for-Channeled-Body,41788.html


Any thoughts?

 

[courierguy]

I have had two custom tanks built by rdsaluminum.com. One a pretty simple ferry tank, the other a complicated shaped header tank, so much so it exceeded my drafting capability. I made a mockup out of heavy cardboard and duct tape, marked where I wanted the fittings right on it, and then sent it off to them inside another box. 2 weeks later I got exactly what I wanted, very good work and very reasonable price.

I always keep it simple..... and don't mention it's going in an airplane, just saying.

 

[Bugs66]

Do the auto fuel tanks have baffles? I would question if they are overbuilt and heavy. It is not hard to make your own tanks. My web site shows how I made mine.

 

[Lowrider]

Don't know about the baffles. I made the ones in my RV-4 too but they were preformed and relatively easy but riveted and sealed instead of welded like most of the other ones I've seen. I'll check out your site and learn from that.

 

[courierguy]

If baffles were desired, rds will put them in, they do whatever you want. That's if you order something custom, like I did, don't know about their stock tanks. I mostly liked the fact the guy welding it does nothing but build aluminum fuel tanks all day long, day after day. The price seemed OK also. My very custom (lots of tapered angles etc.) header tank was a bit over 200 bucks. Only 3 gallons but exactly what I wanted, with a sight gauge and 100% useable fuel. Not that I plan on running down to a gallon or two, but I can if I need to and know exactly when it will "get quiet".

 

[Cub junkie]

There is no free lunch, adapting an overweight street rod tank to a cub type airplane would require changing the structure all around it. I know from your posts you are in the planning stage but fuel tanks for cubs are not difficult to build and they are even easier to buy. I live near Louisville KY and every year I see all these type parts in person at the street rod nationals. The only thing I ever come away with from their trade show is tools and sanding belts.

 

[Lowrider]

You're so right about the free lunch...I can't get my grown kids to buy lunch either.

I just posted this tank question to see if there are any in use or if there is any advantage to trying to adapt one to a Cub. It looks like the build your own or try RDS Aluminum or use commercial tanks. I did see a nice round 4 gal tank that might make a header tank if it's not too heavy.

 

[wirsig]

I was thinking of using Speedway tanks until I found some used piper tanks fairly cheap. When they showed up I was amazed how light they were. I could wad 'em up like aluminum foil with my bare hands if I wanted. The tanks from speedway are probably an easy 10x heavier. It's a strange transition from working on dirt and farm equipment to aircraft, but really fun!

 

[Lowrider]

Same thoughts I had when I did my RV-4...this stuff sure is light after working with trucks, tractors and jeeps!! I actually used a backhoe bucket to form some curves on the parts so the heavy stuff can be good to have around.

The fuel tanks are one of the areas I have thought it might make sense to go heavy duty just for crash protection, but I don't want to go to an extreme. I can't think of anything less desirable than ripping a tank open on a ground loop or something worse. I've never bent an airplane but that doesn't mean it can't happen to me. I think I'm willing to give up some weight in fuel tank construction for safety sake. Maybe I'm over thinking this fuel thing.

 

[qsmx440]

I don't think you can over think fuel stuff. I wish there was more detailed accounting of "tanks" in supercub crashes. Do the tin foil like stock tanks fold up but not crack in a crash? Can a tank be to UN-forgiving and just fail by bursting open? Seems the best setup would be a bunch of small 5 gal tanks suspended by bungees in each rib bay . Just joking. There was some talk on one thread about some filler you add to tanks to stop deluges of fuel running out in a tank breach.
"The only time you have to much gas is when your on fire" Bob Hoover.

 

[Cub junkie]

Just having the tanks in the wing takes away a lot of risk opposed to that 12 gal molotov cocktail in your lap like a J-3. Those street rod tanks are made with .080 material or thicker. When Speedway has those tanks made in China they aren't thinking aircraft.

 

[Lowrider]

Love the Hoover quote...so true and I used to use that with students.

A properly designed tank made from 0.080 should be pretty tough. I might even be able to weld that stuff. Weight penalty would be there but I think that's one of the areas I'd be willing to bite the bullet and eat some weight.

Wing tanks are certainly safer than the bucket of fuel in your lap but I saw the end results of a fatal ground loop where the left wing tore away from the fuselage and broke open the tank which ignited and burned the driver who later died from the burns. I see that plane every time I get into my C-170 and wonder if that would happen to it in ground loop. You can't make it completely safe but then I suspect there are few cases of fire as described.

 

[skywagon8a]

Wing tanks are certainly safer than the bucket of fuel in your lap but I saw the end results of a fatal ground loop where the left wing tore away from the fuselage and broke open the tank which ignited and burned the driver who later died from the burns. I see that plane every time I get into my C-170 and wonder if that would happen to it in ground loop. You can't make it completely safe but then I suspect there are few cases of fire as described.

What type of airplane had the wing torn off? I would want to analyze the entire installation before I placed the blame on the tank.

Also, if it were me, I would make my own tank to fit my installation. If I did not feel comfortable doing the welding myself I would find a good professional welder for the job.

 

[Lowrider]

It was a Cessna 120 or 140...not sure which and you are correct that the tank failure may have been incidental to other causes. I just mention this as a reason for me to be interested in having a strong tank and fuel lines. Since I'm building is it worth beefing up the fuel system? Again, I may be over thinking this and it is not a safety issue to worry about when using customary Cub parts and methods.

Which raises the question, does anyone use fuel lines made with braided stainless shield rather than aluminum tube and rubber hose? Is it worth the cost and weight? I've always thought the key to any liquid lines was to keep them from rubbing on something that would cause failure. I have that problem with my backhoe where the lines need to move with the arm and bucket and you can't make them rigid so the flop around as a result and get worn in spots. On the plane I plan to use lots of Adel clamps to solve the problem.

 

[skywagon8a]

It was a Cessna 120 or 140...not sure which and you are correct that the tank failure may have been incidental to other causes. I just mention this as a reason for me to be interested in having a strong tank and fuel lines. Since I'm building is it worth beefing up the fuel system? Again, I may be over thinking this and it is not a safety issue to worry about when using customary Cub parts and methods.

I do not remember what the 120/140 uses to brace that bay. A Cub is quite sturdy with the steel tube cross member.

Which raises the question, does anyone use fuel lines made with braided stainless shield rather than aluminum tube and rubber hose? Is it worth the cost and weight?

Not a bad idea. It would be strong and very flexible. I hard connected mine directly from the tubing to the tank. We will see what happens over time. I have plexiglass covering the wing root area so can always see the connections. This is the sight gauge, don't have a picture of the connections.

 

[Lowrider]

That's a great idea with the plexiglass cover...you can seal the area and still see what's happening behind it. Mind if I steal you idea?

I'll use a sight gauge too but I always stick my tanks when I drain and pre-flight just to be sure....I like having enough fuel and oil on board!!

 

[skywagon8a]

Be my guest. The sight gauge is only for in flight use.

 

[Randy]

Lowrider wrote....
The fuel tanks are one of the areas I have thought it might make sense to go heavy duty just for crash protection, but I don't want to go to an extreme. I can't think of anything less desirable than ripping a tank open on a ground loop or something worse. I've never bent an airplane but that doesn't mean it can't happen to me. I think I'm willing to give up some weight in fuel tank construction for safety sake. Maybe I'm over thinking this fuel thing.

Lowrider...I agree....seem like more than a few Cub wrecks where fuel gets spashed around....at least when you are experimental you can use modern technology to build more crashworthy fuel tanks, lines, and sediment bowls like STEVE'S.....
Also..there is fuel resistant foam that is installed in the tanks to keep the gas from sloshing around in a wreck....maybe somebody else on the site has built more crashworthy Cub tanks.
Here is an excerpt that I cut and pasted from a study of agricultural aircraft wrecks involving wire strikes speaking of the fire potential..

Wish I could get the text into a smaller space...just scroll down to read it....
Randy

Specific problems such as the postimpact

fire potential, specifically related

to the PA-25, were addressed. Extensive

studies (Department of Civil Aviation

[a]) were undertaken by the Australian

Department of Civil Aviation-now the

Civil Aviation Authority (CAA)-from

1961 to improve the fuel tank design

and crashworthiness. Many proposals

were put forward with, among others,

the insertion of a flexible rubber cell

within the existing fiberglass tank,

which was granted approval
in 1965. A

subsequent analysis of accidents

between
1974-1980 revealed that both

Piper and Cessna aircraft displayed

high post-impact fire rates (17% and

19.6% respectively), more than twice

that of the overall rate for CA aircraft.

Moreover, both showed increased fire

rates following a wire strike accident

compared to other types of accidents.

Photo
SASI

5

However, it was noted that the fire rate had improved with time for Piper aircraft, reducing from 24%

between 1969-1973 to 17% between 1974-1980. A further review of Piper aircraft accidents between 19691986

revealed that the post-impact fire rate on aircraft without the fuel cell was 65%, whereas that of aircraft

with the fuel cell was 38%. Following this, Piper Aircraft Corporation issued Service Bulletin SB 878

in
1988 making the rubber cell installation mandatory.. Also, late in 1988, a concession was granted by the

CAA to install a new improved crashworthy fibreglass tank.

 

[skywagon8a]

.. Also, late in 1988, a concession was granted by the CAA to install a new improved crashworthy fibreglass tank.

That is an interesting thought. How about making a tank out of carbon fiber? You could get the structural integrity with less weight.

 

[Randy]

Skywagon8a
I think the original design of the aircraft in the crash study was the Piper PA-25...which had a inverted triangular shaped tank in the nose behind the firewall...and it was made of fiberglas.
I'm not too sure if the intent of that was to have it seperate from the airframe in the event of a major frontal crash...or if it was just shaped that way for other more practical purposes.
It would be interesting to know what the design rationale was when the desinger Fred Weick and Texas A@M came up with the concept of the AG-3...the protoype of the PA-25.
http://en.wikipedia.org/wiki/Fred_Weick
Randy

 

[Lowrider]

That is an interesting thought. How about making a tank out of carbon fiber? You could get the structural integrity with less weight.

That takes me back to one of my original thoughts about a wet wing with a carbon fiber tank built into the tank bay as an integral part of the wing. I kinda threw out the idea because of concerns about flex and stress on the wing root that would be transferred to the built-in tank and could cause the tank to crack/break. I just don't know enough about carbon fiber construction to feel comfortable with using that material. I am fairly good at laying up fiberglass so I guess the process is pretty much the same.

I was fortunate enough to meet Burt Rutan last year at the Veteran's Day celebration (11:11 on 11/11/11) and I wanted to hear him speak about carbon fiber uses but events were overtaken by time and it didn't happen. Anyway, I'm sure there are folks out there who can answer the carbon fiber questions. It seems that there are those who believe the same weight and strength can be achieved using much cheaper fiberglass and kevlar.

 

[dukeair]

Randy Appling, owner of Plaschem Wassila AK has told me he has made several cf tanks for different aircraft including supercubs. I have not seen this product but he tells me they weigh about half what a stock tank weighs.