flyingcheesehead
Touchdown! Greaser!
We got to talking about this on another thread, but @MIFlyer suggested that I post my "brain dump" on 310s that I wrote up for my airplane partner, rather than wait for @Ray Jr to start a thread about it. I'll keep the first post edited with any other information that is added/corrected.
This information was gleaned from conversations with @Ted DuPuis, some of the great info in Twin Cessna expert Jerry Temple's "Temple's Tips" (there's a lot of info on the other Twin Cessnas there as well), The Twin Cessna Flyer's 310 prospective buyer page, reading the POHs (I posted a 310R POH PDF here), and lots of Googling and reading other articles from around the web. So, here goes:
The big split in 310s is the long and short nose varieties. Only the 310R produced from 1975-1980 had the long nose with baggage compartment. Between aft baggage, nacelle baggage, and nose baggage, you can haul a lot of stuff AND a lot of people. Useful loads are in the 2000-pound range, with maximum tankage being about 1200 pounds of fuel, so you can pack 800 pounds of people and stuff into it and go for 8 hours to dry tanks at around 185 knots. Without any nacelle tanks, full fuel would give you a payload of about 1050 pounds and enough fuel to go for a solid 6+ hours to dry tanks.
Fuel tanks:
The tip tanks are the mains on ALL 310s, and were always 100 gallons regardless of their shape. Early 310s had “Tuna Tanks” - They kinda look like fish on the wingtips. Starting with the 1962 310G, they moved to the modern “Stabila-Tip” tanks. (Gotta love Cessna’s marketing jargon.)
Wing aux tanks became available in 1958, and most planes were equipped with them. They held 30 gallons from 1958-1966, then 40 gallons from 1967-1972, and for 1973 and later could be either 40 or 63 gallons. The aux tanks are directly selectable, but the overflow from the fuel divider always gets pumped back into the mains. So, you start, take off, climb, and land on the mains, and the initial part of cruise is on the mains as well: 60-90 minutes at the beginning of flight must be on the mains, 60 minutes for the 40-gallon aux tanks or 90 minutes for the 63-gallon aux tanks), to make room in the main/tip tanks. At that point, you can switch to the aux tanks, and while you do burn fuel direct from the aux tanks, the mains will re-fill from the overflow line off the fuel divider. So, once your aux tanks are empty, the mains will be full again.
Finally, starting in 1968, nacelle locker tanks became an option. The nacelle tanks are accessed via transfer pumps that push the fuel out to the main/tip tanks. There may be one or two nacelle tanks, 20 gallons each. You burn the mains down to 180 pounds (30 gal) per side from 50, and then start the transfer pumps. The transfer takes ~75 minutes for the 20 gallons, so about 16 gph per side. There are also aftermarket nacelle tanks that are 18.5 gallons each that can be installed both where the factory put theirs AND in the nacelle baggage compartment, so you could potentially have up to four nacelle tanks with the aftermarket variety, for up to 240 gallons total fuel.
Where it gets weird is if you have a nacelle tank only on one side. For this example, let’s say you have a nacelle tank only on the left side. You start heavy on that side to begin with unless you put something in the opposite wing locker, and when you start the fuel transfer that wing gets even heavier because you’re pumping the fuel out to the tip. Plus, there’s less fuel on the other (right) side. So, you have to crossfeed with the right engine, which lightens the load in the left tip AND puts overflow fuel into the right main, which helps balance things out. But, since you’re crossfeeding, you’re burning fuel out of the left tip at a much faster rate than the transfer pump is putting it back in. So, say you burn the mains down to 30 a side and you have 20 in the left nacelle, then you start the transfer pump and switch the right engine to crossfeed, after 75 minutes you’ve emptied the nacelle tank, which would put 50 gallons into the left tip if you weren’t burning anything, but you’re burning 25 gph all out of that tank so you’re down to about 19 on that side, except with the fuel divider thing you’ve actually pumped one engine’s worth of overflow fuel back into the RIGHT tip, which still had 30 gallons in it when you started crossfeeding… Confused yet? You kinda have to crossfeed just part of the time, but I haven’t figured out exactly how much that would be to avoid creating an imbalance. I think that particular configuration is the one that has given Twin Cessnas a bad reputation when it comes to fuel management.
Seats and Baggage:
Early models were four seats. Six became an option with the 310G in 1962, but at that point the 5th and 6th seats took up the entire baggage compartment (seat backs are up against the wall in front of the hat rack). The cabin was lengthened and moved the last row off the aft bulkhead sometime between then and 1973, quite possibly in 1971 when the Q model, S/N 400 and up, also gained a rear window. It appears that the R model may have lengthened this portion even more. (?)
So, aft baggage with six seats was no bueno for a while… But, nacelle/wing locker baggage compartments were added in 1964 with the 310I. Those have a limit of 120 pounds each, or 40 pounds if a nacelle tank is installed as well. Without a tank, the dimensions are 50” x 25” x 8” or about 3 golf bags per side. (For six seats… Hmmm.)
The final model 310R extended the nose a whopping 32 inches, adding a huge nose baggage compartment with 350-pound capacity. So, the R model has aft, nacelle, and nose baggage.
Engines:
The 310s came from the factory with either an IO-470 variant at 260hp/side and a 1500 hour TBO, or for the R model, an IO-520 at 285hp per side with a 1700 hour TBO. The 470-powered ones came standard with two-blade props, the 520s (including the turbos) with three-blade.
The 520s have a bad rep in many installations which is mostly undeserved - It sounds like if we run them at 65% all the time that they should last just fine. Turbos became an option with the 1969 310P, and all turbos had 285hp TSIO-520s with a 1400 hour TBO. TBO is kind of meaningless in the real world, but when you’re buying and selling it’s a factor.
Both Colemill and RAM did engine upgrades. Colemill did the “Executive 600” upgrade which basically puts the R’s IO520s on the older short-nosed 310s, plus 300hp available for 5 minutes. For the R model, they did the “Bearcat” conversion, which replaces the R’s normal IO-520s with 300hp IO-550-As. Put those on the short nose and it’s the Executive II. You can still do these mods, but it’s not really worth it - They’re in the $130K-$150K range, and while that does include engines, that’s an awfully spicy meatball unless you already need two new engines! The Colemill upgrades have a 1900-hour TBO.
RAM Aircraft does engine mods and other work on most Twin Cessnas. On the 310, they only do the turbos, and the “RAM I” mod ups it to 300hp/side while the “RAM IV” ups it to 325/side. (I bet that’s fun on takeoff, but not so much at the fuel pump).
Turbos:
They didn’t put turbos on the 310 until the 1969 P model. The good thing is that they’ve got automatic wastegates. The bad is that they’re hard-mounted and thus subject to a lot of vibration, so it sounds like they can potentially be a maintenance nightmare. There’s also an exhaust AD requiring an inspection every 50 hours on the turbo models. One source said that 2/3 of the final year of production 310Rs were turbo.
Robertson STOL:
This system basically replaces the 310’s stock split flaps with nice Fowler flaps. Vmc is lowered, accelerate-stop distance is drastically reduced, ground roll is shorter, and it sounds like this mod can really increase safety margins. However, it’s not well supported. Robertson went out of business and Sierra Industries bought the STCs, and while that company still exists, but they mainly do Citation maintenance now.
De-ice systems:
There are at least two possibilities. FIKI certification wasn’t available until 1977, and that system has wing boots both inboard and outboard of the nacelles, tail boots, hot props, and a hot plate on the windshield. But, before that there was a system with only the outboard part of the wings booted, tail boots, hot props, and an alcohol windshield. That system is pretty well regarded too, but not officially approved for flight into known icing. The hot plate on the FIKI system is supposed to be very expensive to repair or replace, too (10 AMU range).
Other options:
A/C: It sounds like the Cessna factory AC is crap. Mechanically driven and hard to find parts for. The factory AC requires the right engine to be running, and precludes having a right-side nacelle tank (and probably shrinks the baggage compartment on that side, though I couldn’t find anything saying so). There is an aftermarket system that is considered to be better (“Keith A/C”) that is electrically driven and supposedly reliable. The Keith system is fully electric and thus can be plugged in and run on the ground prior to engine start.
Vortex Generators: These are pretty much a must-have, conferring at least some of the benefits of the R/STOL only with no moving parts and way cheaper. Kits are still available (from Micro Aerodynamics, BLR, and Knots2U), and they can be installed in less than a day for about 3 AMU, so well worth doing if you find a plane without them. Gross weight is increased by 150-180 pounds, Vmc drops nearly 10 knots (and is only 2 knots above stall in the landing configuration), takeoff speed also drops 10 knots, etc… It’s an excellent performance improvement. More info here: https://www.avweb.com/news/reviews/182564-1.html
This information was gleaned from conversations with @Ted DuPuis, some of the great info in Twin Cessna expert Jerry Temple's "Temple's Tips" (there's a lot of info on the other Twin Cessnas there as well), The Twin Cessna Flyer's 310 prospective buyer page, reading the POHs (I posted a 310R POH PDF here), and lots of Googling and reading other articles from around the web. So, here goes:
The big split in 310s is the long and short nose varieties. Only the 310R produced from 1975-1980 had the long nose with baggage compartment. Between aft baggage, nacelle baggage, and nose baggage, you can haul a lot of stuff AND a lot of people. Useful loads are in the 2000-pound range, with maximum tankage being about 1200 pounds of fuel, so you can pack 800 pounds of people and stuff into it and go for 8 hours to dry tanks at around 185 knots. Without any nacelle tanks, full fuel would give you a payload of about 1050 pounds and enough fuel to go for a solid 6+ hours to dry tanks.
Fuel tanks:
The tip tanks are the mains on ALL 310s, and were always 100 gallons regardless of their shape. Early 310s had “Tuna Tanks” - They kinda look like fish on the wingtips. Starting with the 1962 310G, they moved to the modern “Stabila-Tip” tanks. (Gotta love Cessna’s marketing jargon.)
Wing aux tanks became available in 1958, and most planes were equipped with them. They held 30 gallons from 1958-1966, then 40 gallons from 1967-1972, and for 1973 and later could be either 40 or 63 gallons. The aux tanks are directly selectable, but the overflow from the fuel divider always gets pumped back into the mains. So, you start, take off, climb, and land on the mains, and the initial part of cruise is on the mains as well: 60-90 minutes at the beginning of flight must be on the mains, 60 minutes for the 40-gallon aux tanks or 90 minutes for the 63-gallon aux tanks), to make room in the main/tip tanks. At that point, you can switch to the aux tanks, and while you do burn fuel direct from the aux tanks, the mains will re-fill from the overflow line off the fuel divider. So, once your aux tanks are empty, the mains will be full again.
Finally, starting in 1968, nacelle locker tanks became an option. The nacelle tanks are accessed via transfer pumps that push the fuel out to the main/tip tanks. There may be one or two nacelle tanks, 20 gallons each. You burn the mains down to 180 pounds (30 gal) per side from 50, and then start the transfer pumps. The transfer takes ~75 minutes for the 20 gallons, so about 16 gph per side. There are also aftermarket nacelle tanks that are 18.5 gallons each that can be installed both where the factory put theirs AND in the nacelle baggage compartment, so you could potentially have up to four nacelle tanks with the aftermarket variety, for up to 240 gallons total fuel.
Where it gets weird is if you have a nacelle tank only on one side. For this example, let’s say you have a nacelle tank only on the left side. You start heavy on that side to begin with unless you put something in the opposite wing locker, and when you start the fuel transfer that wing gets even heavier because you’re pumping the fuel out to the tip. Plus, there’s less fuel on the other (right) side. So, you have to crossfeed with the right engine, which lightens the load in the left tip AND puts overflow fuel into the right main, which helps balance things out. But, since you’re crossfeeding, you’re burning fuel out of the left tip at a much faster rate than the transfer pump is putting it back in. So, say you burn the mains down to 30 a side and you have 20 in the left nacelle, then you start the transfer pump and switch the right engine to crossfeed, after 75 minutes you’ve emptied the nacelle tank, which would put 50 gallons into the left tip if you weren’t burning anything, but you’re burning 25 gph all out of that tank so you’re down to about 19 on that side, except with the fuel divider thing you’ve actually pumped one engine’s worth of overflow fuel back into the RIGHT tip, which still had 30 gallons in it when you started crossfeeding… Confused yet? You kinda have to crossfeed just part of the time, but I haven’t figured out exactly how much that would be to avoid creating an imbalance. I think that particular configuration is the one that has given Twin Cessnas a bad reputation when it comes to fuel management.
Seats and Baggage:
Early models were four seats. Six became an option with the 310G in 1962, but at that point the 5th and 6th seats took up the entire baggage compartment (seat backs are up against the wall in front of the hat rack). The cabin was lengthened and moved the last row off the aft bulkhead sometime between then and 1973, quite possibly in 1971 when the Q model, S/N 400 and up, also gained a rear window. It appears that the R model may have lengthened this portion even more. (?)
So, aft baggage with six seats was no bueno for a while… But, nacelle/wing locker baggage compartments were added in 1964 with the 310I. Those have a limit of 120 pounds each, or 40 pounds if a nacelle tank is installed as well. Without a tank, the dimensions are 50” x 25” x 8” or about 3 golf bags per side. (For six seats… Hmmm.)
The final model 310R extended the nose a whopping 32 inches, adding a huge nose baggage compartment with 350-pound capacity. So, the R model has aft, nacelle, and nose baggage.
Engines:
The 310s came from the factory with either an IO-470 variant at 260hp/side and a 1500 hour TBO, or for the R model, an IO-520 at 285hp per side with a 1700 hour TBO. The 470-powered ones came standard with two-blade props, the 520s (including the turbos) with three-blade.
The 520s have a bad rep in many installations which is mostly undeserved - It sounds like if we run them at 65% all the time that they should last just fine. Turbos became an option with the 1969 310P, and all turbos had 285hp TSIO-520s with a 1400 hour TBO. TBO is kind of meaningless in the real world, but when you’re buying and selling it’s a factor.
Both Colemill and RAM did engine upgrades. Colemill did the “Executive 600” upgrade which basically puts the R’s IO520s on the older short-nosed 310s, plus 300hp available for 5 minutes. For the R model, they did the “Bearcat” conversion, which replaces the R’s normal IO-520s with 300hp IO-550-As. Put those on the short nose and it’s the Executive II. You can still do these mods, but it’s not really worth it - They’re in the $130K-$150K range, and while that does include engines, that’s an awfully spicy meatball unless you already need two new engines! The Colemill upgrades have a 1900-hour TBO.
RAM Aircraft does engine mods and other work on most Twin Cessnas. On the 310, they only do the turbos, and the “RAM I” mod ups it to 300hp/side while the “RAM IV” ups it to 325/side. (I bet that’s fun on takeoff, but not so much at the fuel pump).
Turbos:
They didn’t put turbos on the 310 until the 1969 P model. The good thing is that they’ve got automatic wastegates. The bad is that they’re hard-mounted and thus subject to a lot of vibration, so it sounds like they can potentially be a maintenance nightmare. There’s also an exhaust AD requiring an inspection every 50 hours on the turbo models. One source said that 2/3 of the final year of production 310Rs were turbo.
Robertson STOL:
This system basically replaces the 310’s stock split flaps with nice Fowler flaps. Vmc is lowered, accelerate-stop distance is drastically reduced, ground roll is shorter, and it sounds like this mod can really increase safety margins. However, it’s not well supported. Robertson went out of business and Sierra Industries bought the STCs, and while that company still exists, but they mainly do Citation maintenance now.
De-ice systems:
There are at least two possibilities. FIKI certification wasn’t available until 1977, and that system has wing boots both inboard and outboard of the nacelles, tail boots, hot props, and a hot plate on the windshield. But, before that there was a system with only the outboard part of the wings booted, tail boots, hot props, and an alcohol windshield. That system is pretty well regarded too, but not officially approved for flight into known icing. The hot plate on the FIKI system is supposed to be very expensive to repair or replace, too (10 AMU range).
Other options:
A/C: It sounds like the Cessna factory AC is crap. Mechanically driven and hard to find parts for. The factory AC requires the right engine to be running, and precludes having a right-side nacelle tank (and probably shrinks the baggage compartment on that side, though I couldn’t find anything saying so). There is an aftermarket system that is considered to be better (“Keith A/C”) that is electrically driven and supposedly reliable. The Keith system is fully electric and thus can be plugged in and run on the ground prior to engine start.
Vortex Generators: These are pretty much a must-have, conferring at least some of the benefits of the R/STOL only with no moving parts and way cheaper. Kits are still available (from Micro Aerodynamics, BLR, and Knots2U), and they can be installed in less than a day for about 3 AMU, so well worth doing if you find a plane without them. Gross weight is increased by 150-180 pounds, Vmc drops nearly 10 knots (and is only 2 knots above stall in the landing configuration), takeoff speed also drops 10 knots, etc… It’s an excellent performance improvement. More info here: https://www.avweb.com/news/reviews/182564-1.html
my 310.
