Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
It may be less than a gallon in level flight but CAR 3 required that unusable fuel be determined under the most adverse conditions.minton wrote:I think the 4.5 unusable per side was a type-O by the fuzz based on the C-170B number of 5 total. In real life it's less a gallon per side or so.
The same tank exists in the C-172 long range wing and the unusable fuel is 3 gallons total. Same exact wing/fuel tank/fuel feed design as the C-175. Check the TCD's and the parts books. I had this exact arguement with the Feds and having my ducks lined up I won. They got it wrong on the C-175 TCD which caused the one time STC's on some aircraft to be wrong and who knows where else.gahorn wrote:The amount of "UNuseable fuel" varies between the 175 and the 170/172 because of the increased size/capacity of the tank.
Since unuseable fuel is that fuel which is not available in ALL normal flight attitudes of the aircraft ...i.e. takeoff/descent w/ full flaps (some of the fuel cannot reach the tank-exit in those attitudes).... the larger total capacity means a proportionately larger amount of unuseable fuel. The 175 had a total of 52 gas with 10 gals unuseable, leaving 42 gallons available in all attitudes. The 170/172 has 42 gals total with 37 useable in all attitudes. I have on two occasions re-fueled and managed to install 42 gallons. Don't ask when/where/why.... but you can probably surmise how.
However in level flight...virtuall all the fuel including the "unuseable" is still available and will continue to feed the engine. (Just avoid extreme nose-up/nose-dn attitudes.)
n2582d wrote:It may be less than a gallon in level flight but CAR 3 required that unusable fuel be determined under the most adverse conditions.It seems to me that modifying the fuel outlet point(s) on the long range tanks to be more like the C-185 would significantly lower the unusable fuel that would be needed to meet the CAR 3 requirements. Maybe one additional fuel outlet in the rear of the tank would do the trick.minton wrote:I think the 4.5 unusable per side was a type-O by the fuzz based on the C-170B number of 5 total. In real life it's less a gallon per side or so.
You forgot the front lines in Iraqrunerider wrote:Operating out of confined areas, short strips, high density altitudes, barriers at the strip's end, with a sixty year old airplane with non self sealing tanks that aren't rupture proof doesn't sound all that safe to me either. Using a modern self sealing rupture resistance bladder secured in the baggage area that can be stored rolled up when it is empty weighing 3lbs is safe and a lot cheaper and easier than the hassle of changing tanks or wings. Were there any cabin fires or explosions with the javelin system? "but to each his own!"
minton wrote:The same tank exists in the C-172 long range wing and the unusable fuel is 3 gallons total. Same exact wing/fuel tank/fuel feed design as the C-175. Check the TCD's and the parts books. I had this exact arguement with the Feds and having my ducks lined up I won. They got it wrong on the C-175 TCD which caused the one time STC's on some aircraft to be wrong and who knows where else.gahorn wrote:The amount of "UNuseable fuel" varies between the 175 and the 170/172 because of the increased size/capacity of the tank.
Since unuseable fuel is that fuel which is not available in ALL normal flight attitudes of the aircraft ...i.e. takeoff/descent w/ full flaps (some of the fuel cannot reach the tank-exit in those attitudes).... the larger total capacity means a proportionately larger amount of unuseable fuel. The 175 had a total of 52 gas with 10 gals unuseable, leaving 42 gallons available in all attitudes. The 170/172 has 42 gals total with 37 useable in all attitudes. I have on two occasions re-fueled and managed to install 42 gallons. Don't ask when/where/why.... but you can probably surmise how.
However in level flight...virtuall all the fuel including the "unuseable" is still available and will continue to feed the engine. (Just avoid extreme nose-up/nose-dn attitudes.)
Go fly until the engine quits when you're in a nose-down descent with full flaps, i.e. a simulated final approach, then after the engine has quit, execute a go-around.minton wrote:Unusable fuel: Fill tanks, Go fly until engine quits on first tank, Switch to other tank, go land and fill empty tank, take note of number times two, subtract total advertised volume of both tanks= unusable fuel + or -
I may have told this story here or not? ? ? I bought a '61 C175 in El Monte CA some years ago. Dea Babe and I worked three days getting it cleaned up, new tires, new battery, rebuilt the nose strut, put on the Cleveland Brakes and got a ferry permit to fly to Payson Arizona. There it got a new headliner, new seat covers and carpet. We flew several hours around AZ and really enjoyed that. I scheduled a trip from Payson to Toledo Bend and planned one fuel stop. I hadn't really done a lot of investigation into my fuel burn but with the larger tanks I just let it go. The morning of my departure, my grandson took me to the airport. Sunrises in Arizona are sometimes almost as spectacular as their sunsets and this morning was a great one. I asked Chris if he wanted to see this area at sunrise and so off we went - - I estimated we flew around for less than an hour but who thinks about that when surrounded by such grandeur. Anyway I said my goodby to him and headed for El Paso area.minton wrote:Unusable fuel: Fill tanks, Go fly until engine quits on first tank, Switch to other tank, go land and fill empty tank, take note of number times two, subtract total advertised volume of both tanks= unusable fuel + or -
