Bill E Posted June 27, 2019 Report Posted June 27, 2019 I bought a 1979 231 with the Rocket Conversion. The aircraft has inboard and outboard (extended range) tanks. I'm certain the outboard tanks are 14.5 gallon capacity and further understand the inboard tanks are 40 gallon tanks, giving me roughly 109 gallons total tank capacity. My problem is getting an accurate measurement of how much fuel is in the inboard tanks. After using approximately 16 to 20 gallons from the inboard tanks, there is no visible fuel. However, the shape of the wing tells me there is definitely a good amount of fuel left. The last time I fueled the inboard tanks there was no fuel visible, but the tank topped off after adding approximately 16 gallons. Of course I added the fuel in 2-gallon increments and measured the level in attempts to calibrate a fuel dipstick. How do I measure the fuel in the tank that cannot be seen and a dipstick will not reach? Any advice will be greatly appreciated. Thanks, Bill Quote
Hank Posted June 27, 2019 Report Posted June 27, 2019 The easy way is to fly a tank dry, preferably at 10,000 msl or less where the air is thick enough to restart quickly when you switch tanks. Or drain the tank on the ground (outside, not in the hangar, and with a ground strap on whatever you are draining into), fill slowly until you can see fuel, and record the base measurement. Then fill up and you'll know the capacity. Just remember to subtract the unusable fuel per your POH, since the conversion won't affect that number. 1 Quote
carusoam Posted June 27, 2019 Report Posted June 27, 2019 Bill, Study up on how your tanks work... and where your fuel level sensors are... Some people did not pay extra to move their outer fuel level indicator to the best spot for most accurate reading... This takes knowing the rules for fuel level accuracy at empty, and stretches them a bit... Some people think that the outer tank area empties first for some reason... it’s up hill, so it does go dry first. It takes a full test to understand how much useable fuel your plane has... it takes some research to understand how the fuel level sensors account for the fuel... And there are some better fuel gauges that can be calibrated and used to better account for the fuel used...and how much you have on board at the same time... Another interesting fact... fuel filler caps on Mooneys are not all in the same place... so when you look in the tank, and see a dry bottom... it won’t be the same amount as an M20C... On the O... There is about an hour of fuel that can’t be seen... two hours total... Installing mechanical fuel gauges in the wing inspection panels is a great way to measure the fuel... but that would depend on what STC you have for your extended fuel tanks... Sounds like a great question for Piloto the fuel tank guy... PP thoughts only, not a mechanic... Best regards, -a- Quote
FloridaMan Posted June 27, 2019 Report Posted June 27, 2019 29 minutes ago, Hank said: The easy way is to fly a tank dry, preferably at 10,000 msl or less where the air is thick enough to restart quickly when you switch tanks. Or drain the tank on the ground (outside, not in the hangar, and with a ground strap on whatever you are draining into), fill slowly until you can see fuel, and record the base measurement. Then fill up and you'll know the capacity. Just remember to subtract the unusable fuel per your POH, since the conversion won't affect that number. This, though running the tank "dry" is a better metric because you get a "real world" usable amount. Fueling the long range tanks in the Rocket is a bit of a chore. All while rocking the wing with my leg, I fill the inboard tanks to the flapper, then the outboard, then return to the inboard tanks and "nurse" them up to the neck of the tank, then top off the outboard tanks again. I believe the inboard tanks are supposed to be 37.8 and the outboard are 14.5 on mine. They're all a bit different with speed brake installs. I've burned 50 gallons off of one side before (according to the totalizer) and the engine didn't quit, but I haven't run one dry yet. Also, fun trivia: no Rockets that I know of have pressurized magnetos. Quote
Bill E Posted June 27, 2019 Author Report Posted June 27, 2019 19 hours ago, Hank said: The easy way is to fly a tank dry, preferably at 10,000 msl or less where the air is thick enough to restart quickly when you switch tanks. Or drain the tank on the ground (outside, not in the hangar, and with a ground strap on whatever you are draining into), fill slowly until you can see fuel, and record the base measurement. Then fill up and you'll know the capacity. Just remember to subtract the unusable fuel per your POH, since the conversion won't affect that number. Thank you Hank. Draining the tank and slowly refilling seems to be my best option at this time. Haven't had the Rocket very long and would rather not attempt inflight restarts just yet. My last aircraft was a Cessna 210 but have opted for a sportier plane now that we're empty nest and don't need the heavy hauler anymore. Didn't have this fuel measurement problem with the 210. Thanks again. Bill Quote
Bill E Posted June 27, 2019 Author Report Posted June 27, 2019 19 hours ago, carusoam said: Bill, Study up on how your tanks work... and where your fuel level sensors are... Some people did not pay extra to move their outer fuel level indicator to the best spot for most accurate reading... This takes knowing the rules for fuel level accuracy at empty, and stretches them a bit... Some people think that the outer tank area empties first for some reason... it’s up hill, so it does go dry first. It takes a full test to understand how much useable fuel your plane has... it takes some research to understand how the fuel level sensors account for the fuel... And there are some better fuel gauges that can be calibrated and used to better account for the fuel used...and how much you have on board at the same time... Another interesting fact... fuel filler caps on Mooneys are not all in the same place... so when you look in the tank, and see a dry bottom... it won’t be the same amount as an M20C... On the O... There is about an hour of fuel that can’t be seen... two hours total... Installing mechanical fuel gauges in the wing inspection panels is a great way to measure the fuel... but that would depend on what STC you have for your extended fuel tanks... Sounds like a great question for Piloto the fuel tank guy... PP thoughts only, not a mechanic... Best regards, -a- Thanks for the reply! I appreciate your thoughts. I understand the outer tanks drain into the inboard tanks and the levels can be deceptive. I may drain the tanks and measure as gradually refill. Last aircraft was a C-210L and didn't have this dilemma. I've never relied on the panel fuel gauges. The Rocket has a fuel management system that helps, considerably. Thanks again, Bill 1 Quote
Bill E Posted June 27, 2019 Author Report Posted June 27, 2019 19 hours ago, FloridaMan said: This, though running the tank "dry" is a better metric because you get a "real world" usable amount. Fueling the long range tanks in the Rocket is a bit of a chore. All while rocking the wing with my leg, I fill the inboard tanks to the flapper, then the outboard, then return to the inboard tanks and "nurse" them up to the neck of the tank, then top off the outboard tanks again. I believe the inboard tanks are supposed to be 37.8 and the outboard are 14.5 on mine. They're all a bit different with speed brake installs. I've burned 50 gallons off of one side before (according to the totalizer) and the engine didn't quit, but I haven't run one dry yet. Also, fun trivia: no Rockets that I know of have pressurized magnetos. I appreciate your advice, FloridaMan. I do have the speed brakes installed, too. I just had all tanks resealed so I may contact Bill at PropellerHead, who seems to be a tank expert as well. At this point, the concensus seems to be drain the tanks and slowly refill, making calibrated measurement as I put the fuel in. Thanks again! Bill Quote
Hank Posted June 27, 2019 Report Posted June 27, 2019 @Bill E, since you resealed the tanks, you should know their capacity. When I picked my C up from that job, the tanks were full to the caps and had sat at least overnight with no loss. The fuel bill was 0.3 gallons more than my stated capacity: 52.3 gal pumped into my 52 gal tanks, much less than your Rocket holds, but it still gets me 4:45 with 1:00-1:15 remaining--I don't want to fly that long again, much less any longer . . . . Quote
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