4 tanks in a 1948 170 ragwing

[mantry]

Howdy, I posted a followup in a previous topic but didn't get any replies so I'll try its own topic.

Friend has a 1948 170 that had 4 tanks in it when he got it as part of his rebuild project. He had the 4th tank approved via Field approval so it is all fine. The questions are: What is the total capacity on these 4 tanks? He added a fuel totalizer and as a result of that he drained all the fuel he could get out of it using the 2 wing sumps and then filled it up at the gas pump and could only squeeze 44 gallons in it. His biggest question is "Is all 44 of those gallons useable???" Can you get the same amount via the normal outlet as you can the sump? Right now his assumption is all 44 gallons is useable.

Thanks in advance....

[GAHorn]

Sounds like an arithmetic error.
The standard fabric wing 170 has three 12.5 gal tanks (totalling 37.5 gals) with the type certificate stating that only 34.5 is useable. (Useable fuel is that fuel which is available in all normal flight attitudes and all you should plan for until "flameout", although some folks have experienced slight differences.... it's ALL you can count on getting to the engine.)

The above statistics/facts seem to point to 1.0 gals being UN-useable from each 12.5 gal tank. Therefore if your friend has four 12.5 gallon tanks his total capacity would be 50 gallons (which he should use for wt and bal computations, including gross takeoff wt) but of which, he can only count on 46 gallons useable. (4X1=4 unuseable approx.)

It clearly would be prudent to be a bit conservative in estimating useable fuel in such a modified airplane, since the field approval did not take into consideration vagaries of altered design. (How would you know if the extra tank, instead of adding 100% useable fuel.... didn't actually provide a place for additional un-useable fuel (flowing from the original tanks) to be stored?
Since he could only drain 44 gals, I suggest that as a MAXIMUM he should ever count on until the engine quits.
Remember, a field approval is only that.... APPROVAL for the installation... NOT certification of any additional fuel computations. That fourth tank is not a certified (meeting CARs/FARs) design.

[mantry]

Thanks George, that is about exactly what we were comming up with. I think he does throw a little bit more of conservativeness in there and only plans for 40 gallons MAX.

[GAHorn]

Just make sure that he counts ALL 50 GALLONS when computing takeoff weight/empty wt/useful load. (The good news is that once he makes the calculation of empty wt (which includes unuseable fuel), and subtracts it from gross wt, then his useful load should remain constant.)

He's carrying 300 POUNDS of fuel but can only use part of it.

[cessnaford]

hello,

i too have a '48 170. the previouse owner has labled the fuel tanks on the fuel selector as the right tank being 10 gallons and the left tank 22.5 gallons. i am currently trying to get my fourth tank approved because i didn't like the idea of only having 32.5 gallons of gas. my stock inboard tanks look smaller than the stock outboard tank. so having my tanks out of the wings and being able to see them i believe that there is, and will be only 45 gallons of gas for the whole weight and balance issue.

i read the 170 history about using 3 C-140 tanks but i wonder about that. if you would like i could email you some pictures of the tanks, all four set up as they would be in the wings.

[GAHorn]

I'd love to see them and have any divergent data you might have for the library. Thanks.
gahorn146ys (at) hotmail

[48rwflyboy]

Has anyone ever determined (guessed) approximately how many 1948 ragwings got the 4th tank installation using the one-time STC using the Rex Labrie limited STC available in the MX Library? http://www.cessna170.org/forums/members ... wgs%20.pdf

Perhaps impossible to know but would be interested as I did mine back in 2000 and haven't met anyone else yet who has done it other than Rex himself and one other who is working on it now.

[canav8]

Just make sure that he counts ALL 50 GALLONS when computing takeoff weight/empty wt/useful load. (The good news is that once he makes the calculation of empty wt (which includes unuseable fuel), and subtracts it from gross wt, then his useful load should remain constant.)

He's carrying 300 POUNDS of fuel but can only use part of it.

I caution the owner/pilot about this arrangement and computation of fuel. The first thing that needs to be addressed is the Weight and Balance. Was a new Weight and Balance conducted with unusable fuel on the scales? If you cannot answer this then all errors will continue in the future computations. If the owner can not emphatically answer this question then a new W&B should be done before any labeling. You need to know what the true empty weight is and that includes unusable fuel. The only caveat is the aircraft may be weighed with full fuel and then a computed weight may be derived if you know how much of that fuel is usable. This is not a normal way of doing a W&B but I have seen paperwork with it done that way. I would highly recommend the owner/pilot start over from the beginning if the true empty weight is unknown.

[48RagwingPilot]

FWIW, the Seattle FSDO just rejected my proposed 337 for a fourth fuel tank using the Rex Labrie paperwork. The inspector said that while my 337 looked great, the FAA's new policy is that any mod to the fuel system requires data from a DER. So, if anyone gets an approval without involving a DER, please let us all know.

[blueldr]

In my considered opinion (I don't have any humble opinions left) the only way to really determine the useable fuel amount is to fly the airplane on one tamk, with the skid ball centered, until the engine quits, then note the amount required to top it up again.
If you're real serious about this, on a second flight, after the engine quits, run the ball hard over toward the center line of the airplane to see how much more time you have left before the crash.

[blueldr]

I think that if I had a C-170, and in the event that anyone asked, it would have ALWAYS had a fourth tank ever since I had it.

[48rwflyboy]

FWIW, the Seattle FSDO just rejected my proposed 337 for a fourth fuel tank using the Rex Labrie paperwork. The inspector said that while my 337 looked great, the FAA's new policy is that any mod to the fuel system requires data from a DER. So, if anyone gets an approval without involving a DER, please let us all know.

Yes, the new mindset at the FAA seems to be "NO" for almost any one time STC but fuel systems have gotten them in trouble in the past and even something as common sense as the fourth tank matching the right wing arrangement in the ragwing gets kicked to the curb. Have you asked them if their DER could look at the proposal?

[cessna170bdriver]

Long-time member Duane Shockey in San Diego has 4 tanks in his ragwing, and can probably tell you anything you need to know about the system. He's in the directory.

[blueldr]

Like I said, Why hasn't your C-170 ALWAYS had four tanks? Is there anything in your log book that says it only has three tanks? I would think that this airplane has had four tanks for the last sixty eight years. How old are you? It, and that fourth tank, may well be older than your daddy!

One should be able to realize that the FAA would simply be delighted if they could completely dispose of any responsibility for our type of general aviation,
For example, why,with all the four tank installations hhat have been done on C-170s over the last sixty five years or so, should someone noe have hire an expensive DER to justify another one.

[n3833v]

When I did my wings, I thought long and hard about the 4th tank. I decided that it would not be an advantage due to 2.5 to 3 hrs was long enough to be in the seat flying and I needed to get out. If you feel you need the extra fuel, it is more weight to carry and drain when needed. Good luck in your thoughts.

John