I have a 48 C170 which had the extra 12.5 gallon tank added so I have 25 gals in each wing. During my last annual, the mechanic labeled the fuel valve 39 gallons useable. I asked him about it and he was not sure why he did it -- citing a possible AD. I'll follow-up with him but have searched the forum topics and can't find an answer. I think it's 23 useable in each set of tanks. Thanks.
P.S. It's a little academic -- I have a three hour or so butt.
Useable Fuel -- 170
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Bruce Fenstermacher
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The place to find that information would be the paperwork that approved the installation of the 4th tank and and ADs against the modification.
The TCDS says the unusable fuel is 4 gallons (37.5-33.5) on the original system of 3 tanks. Oddly the TCDS says the weight for the unusable fuel is only 19 lbs. which doesn't add up. (4 gals x 6 lbs. = 24 lbs.)
I can't say for sure and this is not the way to figure this but if 3 tanks had 4 gallons unusable or 1.33 gallons per tank I'd be surprise if adding the 4th tank increased the unusable amount to more than an additional 1.33 gallons or 5.3 total unusable gallons. My thought anyway.
BTW if I had a mechanic label something in my plane and he wasn't sure why he did it, I'd have to wonder what else he did but didn't know why. Hmmmm.
The TCDS says the unusable fuel is 4 gallons (37.5-33.5) on the original system of 3 tanks. Oddly the TCDS says the weight for the unusable fuel is only 19 lbs. which doesn't add up. (4 gals x 6 lbs. = 24 lbs.)
I can't say for sure and this is not the way to figure this but if 3 tanks had 4 gallons unusable or 1.33 gallons per tank I'd be surprise if adding the 4th tank increased the unusable amount to more than an additional 1.33 gallons or 5.3 total unusable gallons. My thought anyway.
BTW if I had a mechanic label something in my plane and he wasn't sure why he did it, I'd have to wonder what else he did but didn't know why. Hmmmm.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
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steve grewing
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fuel
The Ft. Worth ACO accepted 4.0 gallons unuseable on my '48 when I got the additional fuel tank field approved in 2005. I discussed it with the engineer and he agreed with the 2.0 gal unuseable per side. Fuel selector is placarded 23 useable on left and right tanks, total 46 gals. BTW it took 24.6 gal to fill the left tank to the bottom of the ring when I initially filled it.
Steve
Steve
Unuseable fuel is not to be utilized for flight planning purposes. It is for wt & bal calculations. (It relates to "undrainable" fuel)
Therefore it is possible (not likely....but possible)... to add additional fuel capacity without adding additional fuel endurance, however the additional weight of the installation (which includes undrainable/unuseable fuel) must be either calculated or determined by actual weight (the more accurate method.)
FAA has made an error in their Rev. 54 of the TCDS and I have sent them an email regarding this error. (I sent them one two years ago to correct their error regarding flap settings/versus serial numbers and that resulted in Rev. 54. Perhaps we won't have to wait so long this time.)
The correct weight and ARM for unuseable fuel for a 170, straight ragwing, is 24 lbs @ +45 )
Thanks Bruce for addressing this issue.
Steve, you're an extremely qualified person to contribute to this discussion and I can appreciate your comments regarding your aircraft, but...I suspect your inspectors opinion allowing for no additional unuseable fuel (regardless of additional total fuel) may not be properly documented and therefore not supported. While adding a 4th tank may increase useable fuel, it does not automatically result in an equal amount (per tank) of unuseable fuel as that in previously existing tanks. Just wanted to clarify that matter. The unuseable fuel per tank MAY remain the same....or it MAY increase or decrease. The point is that the additonal tank does not guarantee that ALL the additional capacity is useable ...despite the fact it must be included in useful load calculations.
Therefore it is possible (not likely....but possible)... to add additional fuel capacity without adding additional fuel endurance, however the additional weight of the installation (which includes undrainable/unuseable fuel) must be either calculated or determined by actual weight (the more accurate method.)
FAA has made an error in their Rev. 54 of the TCDS and I have sent them an email regarding this error. (I sent them one two years ago to correct their error regarding flap settings/versus serial numbers and that resulted in Rev. 54. Perhaps we won't have to wait so long this time.)
The correct weight and ARM for unuseable fuel for a 170, straight ragwing, is 24 lbs @ +45 )
Thanks Bruce for addressing this issue.
Steve, you're an extremely qualified person to contribute to this discussion and I can appreciate your comments regarding your aircraft, but...I suspect your inspectors opinion allowing for no additional unuseable fuel (regardless of additional total fuel) may not be properly documented and therefore not supported. While adding a 4th tank may increase useable fuel, it does not automatically result in an equal amount (per tank) of unuseable fuel as that in previously existing tanks. Just wanted to clarify that matter. The unuseable fuel per tank MAY remain the same....or it MAY increase or decrease. The point is that the additonal tank does not guarantee that ALL the additional capacity is useable ...despite the fact it must be included in useful load calculations.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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Bruce Fenstermacher
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George I agree which is why I prefaced my comment with it's not really the way to figure it out. We after all have now idea if the new tank is installed exactly as the second tank is on the side that originally had two tanks. But I suspect it is.
We also have no way (without further visual inspection) to determine how the unusable fuel is divided in the three original tanks. For simplistic purpose I just divided by 3 for 1.33 per tank.
What Steve is saying in actuality all the unusable fuel on the side with 2 original tanks remains in the lowest tank and or fuel line in which case the amount of unusable fuel would be divided in half. Assuming the new tank is installed same as the other side then the new tank would also not hold any fuel and the unusable fuel would not increase with the 2nd tank added.
We also have no way (without further visual inspection) to determine how the unusable fuel is divided in the three original tanks. For simplistic purpose I just divided by 3 for 1.33 per tank.
What Steve is saying in actuality all the unusable fuel on the side with 2 original tanks remains in the lowest tank and or fuel line in which case the amount of unusable fuel would be divided in half. Assuming the new tank is installed same as the other side then the new tank would also not hold any fuel and the unusable fuel would not increase with the 2nd tank added.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
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steve grewing
- Posts: 82
- Joined: Sun Sep 26, 2004 2:44 pm
Fuel
The ACO's engineer and I discussed the obvious error in the TCDS. It was his call to put it at 4.0 gallons. Which statement in the TCDS is actually in error (1. Gallons of unusable fuel in the "Fuel Capacity" section or 2. Weight of unusable fuel in Note 1.) neither he nor I knew. I suspect Cessna probably has that info in the salt mine archives of western Kansas. My personal limits for minimum fuel exceed the FAA's so a gallon or two are not an issue for me personally. It was a Flight Manual Supplement and placarding per approved data issue to properly dot an "i" and cross a "t" so an ASI could sign it off.
Also, I am not sure the different arm for the unusable fuel is incorrect. Certfication processes dictate the unusable fuel be determined in conditions anywhere from level flight, power off glide transitioning to best rate of climb, skids, slips, etc. and must be established at whichever condition is the more critical. I don't know how the engineers deal with it for weight and balance purposes. If the most critical is in climb do they set the arm for that attitude? I would not think so but I don't know.
Steve
Also, I am not sure the different arm for the unusable fuel is incorrect. Certfication processes dictate the unusable fuel be determined in conditions anywhere from level flight, power off glide transitioning to best rate of climb, skids, slips, etc. and must be established at whichever condition is the more critical. I don't know how the engineers deal with it for weight and balance purposes. If the most critical is in climb do they set the arm for that attitude? I would not think so but I don't know.
Steve
Re: Fuel
That view seems reasonable. The A and B model also have unuseable fuel at an ARM different than for fuel loading. (I also believe that since it's calculated at empty wt that it's derived during static wt & bal. as undrainable.)steve grewing wrote:....Also, I am not sure the different arm for the unusable fuel is incorrect. Certfication processes dictate the unusable fuel be determined in conditions anywhere from level flight, power off glide transitioning to best rate of climb, skids, slips, etc. and must be established at whichever condition is the more critical. I don't know how the engineers deal with it for weight and balance purposes. If the most critical is in climb do they set the arm for that attitude? I would not think so but I don't know.
Steve
Similarly it's possible that unuseable fuel is not necessarily at the lowest point in the system. Portions may very well be trapped in an upper/outer tank.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.