PA-12 Operating Specifications Info

Hi all,

I'm in the process of field-approving PA-12 wings and fuel system on a J-5A, and the ACO is requesting some info for my flight manual supplement, namely usable/unusable quantities for the PA-12 tanks. I believe they are 19 gallon capacity, but is it all usable? Specifically, what do the operating specs say? (that's what the feds care about) If some of you -12 drivers could clue me in, or better yet, get a scan/picture of the operating spcecs page that has this info, I'd really appreciate it.

Thanks!

http://www.luscombeassoc.org/tc/Piper/A780.PA-12.pdf

http://www.luscombeassoc.org/tc/Piper/A725.J-5.pdf

????????

Mike, thanks for the reply. I have the TCDS's, and I saw the fuel capacity on them, but my question is specifically regarding usable fuel vs. capacity. I don't see that info on the TCDS, but am I just missing it? It was my understanding that this information is listed in the operation specifications (aka flight manual) for the PA-12.

Before my rebuild I had an original bi-metal piper 19 gallon tank in my 12, it had 17.4 usable. While it was definitely not straight it wasn't dented in very bad but lost 1.6 gallons. Although it did not leak I replaced it during my re-do with a new Wagaero tank, (I see that the wagaero catalog calls the replacement 18 gallons) which was listed as a direct replacement, it has a 18.0 usable. My other tank is newer but I don't know its origin as it is not shown as replaced anywhere in my logs has a usable within .10 of 18 gallons. I have no header tanks and 3/8" lines

Surprised that the usable amount needs to be listed, I'd think it would be stated something like 'the manufactured capacity 19 gallons, actual usable amount will be determined during flight testing. As some say on this site', mileage may vary....

doug

When my PA-12 had the 19 gallon fuel tanks I was able to put 19 gallons into the tank after running it dry.
windy

Hey guys,
Years ago when these airplanes were built, the CAA used to require a form (I forget the number. 109?) which lists all of the operating limitations. This form is required to be carried in the aircraft at all times. The official unusable fuel may be listed on this form. Now with the newer planes this information is in the Aircraft Flight manual.

What ak49flyer needs to see is this original form for a PA-12. It will be a rather dog eared piece of paper tucked under your registration in the airplane.

Unusable fuel is determined during flight testing by flying the airplane in unusual attitudes until the engine quits. What ever amount of fuel is drained out after landing is called the unusable fuel. ak49flyer needs this number for a PA-12, which needs to be an official number not just a guess based on your experience.

skywagon8a said:

Hey guys,
Years ago when these airplanes were built, the CAA used to require a form (I forget the number. 109?) which lists all of the operating limitations. This form is required to be carried in the aircraft at all times. The official unusable fuel may be listed on this form. Now with the newer planes this information is in the Aircraft Flight manual.

What ak49flyer needs to see is this original form for a PA-12. It will be a rather dog eared piece of paper tucked under your registration in the airplane.

Unusable fuel is determined during flight testing by flying the airplane in unusual attitudes until the engine quits. What ever amount of fuel is drained out after landing is called the unusable fuel. ak49flyer needs this number for a PA-12, which needs to be an official number not just a guess based on your experience.

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I think it's form ACA-309. When it's been lost, I've duplicated it from the OKC records disc for the airplane. It's usually one of the first few documents in the airworthiness section. It's an obsolete form and no longer used b the FAA. Sometimes it's missing even in the records. I don't recall ever seeing unusable fuel on one but I ain't saying it isn't there. I would think the type certificate holder, FS2003, should have that info. Or the responsible FAA entity for the TC, ANM-100S Seattle Aircraft Certification Office Tel: (425) 917-6400, should have records with that info. jrh

Thanks for all the responses. Skywagon, yes, that's exactly what I need. N86250, incidentally, the fed who requested this info is located at the Seattle ACO- I've long wondered why these guys dont have this stuff at their fingertips, because it all came across an FAA desk somewhere, sometime to get approved in the first place.

Thanks again,
Josh

Since the type certificate belongs to someone, the ACO is not allowed to use it for another persons benefit. The best method is for someone here to give you a copy of his PA-12 ACA-309. Your other option is to either get the information from the TC holder or permission from the TC holder for the ACO to share the information with you. Who knows, there may not be any official unusable fuel? The 309 may satisfy the ACO. Good luck.


As an after thought, if you are unable to get this information, perhaps the ACO will allow you to perform the test after you get flying. Just do the test for one tank at a time using the other tank to get back to the airport. The ACO should have a representative witness the measurement. It is not a very time consuming procedure.

What difference does it make? Add a known quantity of fuel to your installation, put your plane into level flight attitude, drain through the gascolator. Any difference is unusable fuel. What a factory reported 70 years ago should be less important than what you can demonstrate on your airplane today.

stewart, That is not how it is determined. The purpose is to determine how much fuel is trapped when the airplane is bouncing around uncoordinated in rough air in the worst attitude. The ACO needs the information from a PA-12 certification because they need to fill all of the squares for installing PA-12 wings on a J-5. These are certification requirements. They need specifics not just "that's good enough".

Interesting. When I've drained my fuel as described in several different airplanes the unusable fuel reconciles with the airframe placards. In the case of a Piper I wonder what role the header tanks play?

I don't recall any unusable fuel placards or instructions in my own -12 when I had it. Since placards or instructions in the Operator's Manual were a requirement of CAR 3 it could be argued that the absence of instructions means all 19 were usable, at least in the original fuel system as installed by Piper w/ stock header tank(s).

§ 3.437 Determination of unusable fuelsupply and fuel system operation on low fuel. (a)The unusable fuel supply for each tank shall beestablished as not less than the quantity at whichthe first evidence of malfunctioning occurs underthe conditions specified in this section. (See also§ 3.440.) In the case of airplanes equipped withmore than one fuel tank, any tank which is notrequired to feed the engine in all of the
conditions specified in this section need beinvestigated only for those flight conditions inwhich it shall be used and the unusable fuelsupply for the particular tank in question shallthen be based on the most critical of thoseconditions which are found to be applicable. Inall such cases, information regarding theconditions under which the full amount of usablefuel in the tank can safely be used shall be madeavailable to the operating personnel by means ofa suitable placard or instruction in the AirplaneFlight Manual.

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Here's a link to CAR 3 for reference. Fuel system requirements start at part 3.440. Good luck, AK49.
http://www.navioneer.org/riprelay/Yet More Navion Files/car_part3.pdf

I just pulled up my ACA-309 form for my pa-12. No mention anywhere on that 3 or page form that mentions fuel in anyway. It has rpm's; minimum octane; normal vs utility manuvers; and weights. My records also have an ACA-305 form-again no relevance and ACA-308 again no relation..

doug

stewart,
Start reading here; 3.437 Determination of unusable fuel supply and fuel system operation on low fuel.

Thanks for all the responses- the ACO contacted me today and told me their research had turned up no official data on usable vs. unusable fuel, so I was told I could stop searching for information that didn't exist. After I get it flying, I'll figure out real-world numbers...

GOBSMACKED !!!

I'm afraid that inspector has NO FUTURE in today's FAA! Offering a LOGICAL course of action? LOL !!

John Scott

My thoughts exactly! A rare treat, for sure; I'll savor it while I can...:lol:

No flight manual in a PA-12. I agree with stewart, unusable fuel is for weight and balance purpose. It is fuel that cannot be used during normal flight conditions. It assumes you are flying in coordinated flight. If you need to, put a placard on the instrument panel. Some 12's do not have fuelflow in nose low attitude, you could run out of fuel in nose down with 20 gallons on board. Sometimes you need to educate the FAA on older aircraft.

The ACA-309 form is the operations limitations and is considered to be the same as a flight manual. Later regulations addressed having a flight manual in the plane. The ACA-309 form is common for those planes produced during the 40s and early 50s.

As an amatuer builder (in Canada), determining unusable fuel is as described above: aircraft in max climb attitude, known quantity added to tanks then drained through gascolator. The difference in volumes is unusable fuel.Nowhere in anything that I have seen or read tells you to "fly it til it quits" in a test flight regime.
Lets examine A/C other than cubs for a second: Ever try to restart a hot 185? Your unusable fuel test would turn into forced landing test pretty quick if you tried the fly it til it quits method. That particular airplane wont start hot when it's still tied to the dock, no way I would do it on purpose in the air

skywagon8a said:

stewart,
Start reading here; 3.437 Determination of unusable fuel supply and fuel system operation on low fuel.

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Just reread this section to try and make sure I had a fair grasp of it. It stipulates (pragraph (c)) that tests should be done with unusable fuelPLUS a maximum of .003 gallons per certificated horse power. Or 4.5 gallons (a half hour flight time) for a 150 horse cub. You are also using this portion of the test to determine proper fuel flow, not usable fuel (which is still determined on the ground, in max climb flight attitude, IMHO of course, as there would be no way to simulate a slip or skid in the hangar)

I have had one experience where determining unusable fuel was done for FAA certification purposes. It was in a high wing, fuel injected, twin engine airplane, which had one main fuel tank in the fuselage. The FAA had us install a small aux tank in the cabin to use to get back to the airport. We used an old automobile gas tank for the return home fuel. I flew the plane slipping, skidding, pitching up and down, in general sloshing the fuel in anyway I could away from the pickup tube. At the first indication of the engines stopping I shifted tanks. The first indication of engines stopping was the rising manifold pressure followed by intermittent stumbling of the engines drawing air bubbles. After landing the remaining fuel was drained out of the sump drain . As I recall there was 1-1/2 quarts remaining. The FAA test pilot rode with me to witness the test and to ensure that it was done correctly.

To perform this test in a PA-12 or -18 would be easy in that there are two tanks. Test one and go home on the other. Then repeat with the other tank.

Restarting a hot 185, I'll admit, does take practice. The procedure can be learned so that only occasionally does the frustration happen.

I agree - my 309s do not mention fuel.

I am delighted to hear that someone besides me has a bit of apprehension about hot starts on injected engines. In 11 years my Super D has never really let me down, but there are times when it seems like I shall run out of battery in some place far away from home.

bob turner said:

I agree - my 309s do not mention fuel.

I am delighted to hear that someone besides me has a bit of apprehension about hot starts on injected engines. In 11 years my Super D has never really let me down, but there are times when it seems like I shall run out of battery in some place far away from home.

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Bob,
Lycoming uses the Bendix fuel injection system and Continental uses their own system. Different animals requiring different procedures for starting. They both can be a pain in the derriere however if understood are not difficult.

So the J-5 that was/is the reason for this thread has been up and flying, with the PA-12 wings and fuel system field approved, for a few months and approx. 50-60 hrs. After putting some time on the plane, I have a few questions for those of you out there with -12 experience, particularly in regards to the fuel system. This airplane will reliably unport and the engine will die due to fuel starvation any time the fuel level is below 1/2-3/8 full (both fuel selectors ON), when in a descent lasting approx. 4-5 minutes or more. By slowing the plane and pulling the nose up and pumping the throttle and/or primer, the engine can be kept running and as soon as the lines get a chance to refill in 20 seconds to a minute, the engine comes back to life and all is well until another descent. Is this normal for the stock -12 setup? I don't own the plane, but I've had it happen a couple times when I've been flying and the owner is getting sick of it, and it's going to bite somebody sooner or later, so we're looking at installing a header tank(s) or front outlets on the tank(s). I installed the system per the Piper drawing for the -12 system (don't have the dwg. no. off the top of my head). This drawing showed no header tank anywhere, and I have seen and heard of -12's with and without them. So, did Piper ever put a header or headers in the -12 or were these added later? If you know anything about adding a header, where and how is it plumbed? I've seen one other one done that had a header under the panel essentially inline with the vent from the gascolater to the top fwd outlet on the tanks. Is this the way to go, or is there a better way to plumb one in? If so, how big? I have a few extra -18 headers laying around, but just one -18 header seems like it could still be run dry while in a prolonged descent, and, if I do happen to run the header dry, does it have to refill completely before the engine will come back to life? Lots of questions I know, but curious what experience is out there in regards to info on this topic. Thanks in advance!

I suspect you only have rear fuel outlets in both tanks. The answer is to put fuel outlets in the front of both tanks with the correct plumbing so fuel is always going to the carb no matter what the nose position. Cubs/pacers have this issue with the right tank (even with header tank). That is why they are placarded for left tank only take off and landing. Early Cessna 180 also have same issue. A header tank will help but it can still happen if in nose down descent long enough. If properly installed a header tank will pass fuel quickly, however, if not full you will have lower head pressure that may or may not effect the carb.

Bite the bullet and get front fuel outlets for both tanks figure, and out how to run the lines. If done properly you won't need a header tank or fuel cross over line.
DENNY

That does seem to be the most fool proof solution- no chance of running a header dry too- the plane has fabric interior so getting access to tie new lines in might be tricky, but would be worth it. If I do the fwd outlets, is 1/4" tube big enough or should 3/8 be used in the front as well? Seems 1/4 would flow plenty of fuel for the low power used in a prolonged descent... Just curious what other experiences have been- I had a Cessna 140 that only had rear outlets and it never gave one bit of trouble in this department. I

I added front ports in my 12's tanks, here's a shot of the plumbing system using a Dakota Cub valve (a great investment by the way with a left, right, both, off detentes). the rear pick up come from the rear (duh) with the right tank line crossing behind the baggage. the right front you can see crosses just behind the fire wall. I built it so that it would all be accessible from the interior or by removing that one metal panel behind the boot cowl. Dakota Cub has a good diagram on their website for tank plumbing, with or without their sight guages.

20 seconds to a minute sounds like a VERY long time for restart. I think something is very wrong with your plumbing to take so long for restart. If one tank is run dry in my -12 I get a restart in less than 5 seconds after switching tanks - probably more like 2 or 3 seconds.

My 12 never had a header tank, and does have a fwd port in the left tank only. 3/8 tubing for sure to meet fuel flow standards. I have never had any trouble with nose down pitch if left tank is turned on.

Wouldn't it just be easier to take the airplane experimental and then do whatever you need to do for the fuel tanks? Won't you still have all the same limitations of a J-5 no matter what you do? Lower gross weight and useful load, etc. It seems to me that if you took it Experimental then you could make your own common-sense decisions about all of that. No?