Fuel consumption/Relief tubes and related

I am considering buying a 337G and am trying to get a feel for its range. I do not have access to the Pilot's Operating Handbook. What would be the approximate fuel consumption in gph and TAS at 65% and 75% power at say 15,000 feet?

[SkyKing]

First off, the mission capabilities of a normally aspirated 337G would be most difficult at 15,000', as these units are not equipped with oxygen and they are normally aspirated.

Even with the dual centerline thrust TCM IO-360's, the airplane's Service Ceiling is 18,000' with both mills turning. Front engine only is 6,900' and with the rear only, 7,100'.

Cruise configurations for the 337G (1977 model year) using recommended lean mixture with fuel allowance for engine start, taxi, takeoff, climb, 45-minutes reserve at 45% and descent will net the following:

75% power @ 5,500' with 528 pounds of fuel: 545nm/3.3hrs

75% power @ 5,500' with 888 pounds of fuel: 990nm/5.9hrs

MAX Range at 10,000' with 538 pounds of fuel: 670nm/5hrs

MAX Range at 10,000' with 888 pounds of fuel: 1,235nm/9.3hrs

Takeoff at full gross: 1,000'; over 50' obstacle: 1,675'
Landing ground roll: 700'; over 50' obstacle: 1,650'

Stall speed: (CAS)
Flaps up, power off: 70 knots
Flaps down, power off: 61 knots

Rate of climb @ sea-level: 1,100 FPM

MAX WT:
Takeoff - 4,630 lb
Landing - 4,400 lb

Standard Empty WT: 2,790 lb; Skymaster II: 2,913 lb

SkyKing

[SkyKing]

Whoops... forgot the speeds:

Maximum at Sea-Level: 179 Knots
75% Cruise power @ 5,500: 169 Knots.

Now, if you adopt a P337, at 16,000' with 2400 RPM and 31" MP (67% Power), your cruise speed would be 191 Knots with a total fuel burn of 144 PPH (24 GPH).

I don't have the figures for the non-pressuried but turbocharged 337H (T337H) which was only manufactured in 1978, 1979 and 1980, but one of the members of this board, Don Campbell, has one and perhaps he can provide some figures.

Keep in mind the T337H has 210 HP engines and smaller blowers, whereas the P337 (or T337G) has 225 HP engines.

SkyKing

[Keven]

Skyking in right re: non-pressurized ac.

I've got a 337A normally aspirated, and it takes a LONG time to get to 15,000, and . . . of course, requires supplemental oxygen. However, sometimes, the winds are good enough up there on a long trip that patience and supp o2 is rewarded.

If you buy that or any other non-pressurized bird, my unsolicited opinion is that it's worth your money to buy supp o2 regardless because it just makes life easier, safer, and more flexible. Plus, anytime I go over 7000' on a long trip I use it towards the end of my flight just to knock the edge off and eliminate any "hangover" effect.

It's worth the $.

Keven
________
Suzuki Dr650 History (http://www.suzuki-tech.com/wiki/Suzuki_DR650)

Thanks to all for your good advice. I have now determined that the airplane I'm going to see is a 1973 P337 with Continental TSIO360CB engines. I was trying to determine the range for this specific plane, and it looks like I will be able to make a safe 800nm flight if my rear end can hold out. If I can make a TAS of 190 kts at 16,000' with a fuel flow of 24 gph and a fuel capacity of 123 gallons, I can

[SkyKing]

Dear "cbrsrceo"...

Here are the numbers for a 1977 P337 with 148 gal fuel:

Max speed @ FL200: 217 Knots
Cruise, 75% power at FL200: 205 Knots
Cruise, 75% power at 10,000 feet: 186 Knots

Max Range at FL200 with 888 pounds usable fuel: 1,155nm/7hrs
Max Range at 10,000 feet, ditto on fuel: 1,110nm/7.3hrs

Nominal Range @ 75% power at FL200: 985nm/5hrs

The nice thing with turbos, rate of climb is still 870 FPM at FL200 at full gross, and you'll always be climbing faster that the 337G counterpart.

Best of all, at FL200, your cabin altitude will be around 10,000. If everything is in proper operating order, the P337 should maintain a sea-level cabin up to 7,000 feet, and in between at say 14,000 feet your cabin will be down at 5,500 feet. There is also a distinctive quieting effect of pressurization.

The above figures are from the POH.

BTW, you'll want to be aware that most of the early P337's, say 1973 vintage, still had (or have) the TSIO-360C engines and a number of those had a potential problem of cracked cases, mainly on the rear engine position. The CB6 version seemed to cure that TCM 'defect'. Of course, this won't be a problem unless the plane has the original engines SNEW.

SkyKing

[kevin]

Just for another viewpoint, I own and regularly fly a 1973 P337 with 123 gallon tanks. Your calculations seem to have forgotton wind, reserve for taxi, runup and climb, potentially unusable fuel, and reserves. I flightplan 10 gals for climb to 16,000, and 25 gph for cruise. This is a bit too much, but seems to work out within a few gallons. Therefore, the fuel exhaustion time for my airplane is approximately 4 hours and 45 minutes from takeoff. I run at 65% power approximately 65 degrees rich of peak on the first cylinder to peak. I will in fact get a TAS of 190 kts at 16,000, but headwinds more often than not reduce this, such that I use 170 kts as a flight plan groundspeed. I try to land with 60 minutes of fuel left, therefore my max range is 3:45 at 170 kts, or in other words, 637 nm.

With no reserve fuel at all, I calculate the range for my airplane to be 807 miles, assuming a 170 kt groundspeed.

You might barely be able to make such a trip at a very low power setting, perhaps 45% power. You'd still have a 140 kt groundspeed in that 20 kt headwind, and you'd land with a bit over 30 minutes fuel. I can't vouch for this, I have never run the airplane at such a power setting.

If you need 800nm range, buy a later model Skymaster - a H model, with the 148 gallon tanks. I wish I had them.

Kevin

[SkyKing]

Kevin, et al...

The 'Big Tanks' for the Pressurized Skymasters came along in the 1975 model year. That's when Cessna went to 4-tanks per wing, bringing the total usable to 148 gallons. Standard tanks for the 1973 and 1974 models were 92 gallons usable, with a long-range option totaling 118 gallons and these model years had 3-tanks per wing. Not sure when the fuel was increased to 123 usable, as in your case.

BTW, a later year "G" model of the pressurized series will also provide 148 gallons usable. Type certificate "T337G" is a P337 for those unaware.

Serial number & model years for the P-models break down as follows:

1973 T337G: P3370001 through P3370148
1974 T337G: P3370149 through P3370193
1975 T337G: P3370194 through P3370225
1976 T337G: P3370226 through P3370257
1977 T337G: P3370258 through P3370292
1978 T337H: P3370293 through P3370318
1979 T337H: P3370319 through P3370341
1980 T337H: P3370342 through P3370356

All of the above are Pressurized Models.

SkyKing

[kevin]

Skyking,

Thanks for the info about later G models having the large tanks, I didn't know that.

As for 118 gallons, I have heard this number before, and I am curious where you got it. I am looking at the owners manual for my airplane - a manual for the for correct year and model (1973 T337GP). On the inside front cover, under total fuel capacity, it says 125 gallons. On page 2-1, first paragraph, it says "The fuel system is composed of three interconnected fuel tanks (369 pounds total usable fuel) in each wing and one sump tank in the lower portion of each boom." 369 x 2 = 738 / 6 = 123 gallons.

If it only has 118, I'd like to know that. If you have time, I'd really appreciate knowing where your number comes from...

Thanks,

Kevin

[Jim Rainer]

Kevin,

I don't know about the "P" models but I think the 118 gallon number is usable fuel in the normally aspirated models with the small tanks - but this should be in your FM!

[stackj]

Fuel range - approx 6 hours:)
Bladder Range - Just over 3 hours:(

Safety Factor - just under 100% :D

[SkyKing]

For those of you with later P-models with the Cessna 'advertised' long-range tanks (1975 and later - the 4-tank arrangement)... if you have a Roberston STOL kit installed, the outboard tanks have been replaced with a slightly smaller tank to accomodate the Robertson rigging mechanism that allows the ailerons to be lowered with the flaps... your usable fuel is 71.5 gallons per side, or a total of 143... not 148. You might want to check the overhead fuel selector switches and make sure they're correctly placarded.

And Kevin... that 118 gallon figure was just stuck in my memory bank, but since you have the 1973 POH, you're information is more probably correct. When I was searching the marketplace, I happened on to 1973 with R/STOL and for some reason I recall the owner telling me his usable was 118 gallons... that's where the figure came from. But since the earlier P-models only have three tanks, I wouldn't think there'd be any penalty of fuel since there's nothing out there in the wing ends to interfere with the R/STOL rigging.

In any event, it's nice to have 148, ahhh, I mean '143' gallons usable with our R/STOL equipped bird, but like it's been said, the bladder capacity keeps the range much shorter!

Besides range, one additional benefit of the long range tanks is to be able to 'tanker home' some cheap fuel... WHEN you can find a deal. I recall when we had our FBO in the 70's, we were selling 100/130 and 100LL for $0.62 a gallon... and lately we're having to fork out $2.30 a gallon... are we getting screwed now, or what? Geesh... from $14.88/hour to $55.20/hour just for gas!! (based on 24/gph)

SkyKing

[WebMaster]

We recently went down to Indiana, after reviewing AirNav, had breakfast at RCO. On the way back, we stopped at OXI, and filled up the tanks on $1.75/gal fuel, and flew it back up to MI, where the discount is $2.68/Gal. We have the long range tanks in our 69 337D, and I was able to take on 102 Gallons, meaning I had 27 useable left, or more than an hour. It was worth the trip, and we had a pleasant breakfast.

[FRED-E]

Now you have me wondering, is my 1967 337B the only one with a pilot relief tub?
BTW if your ever through Oklahoma, just below Wichita, stop in our fuel is $ 1.85/gal (F22) Cushing, OK.
And oh yes, we are having our annual fly-in this week end, saturday, 9/7/02. Come one, come all !!!!!!!!!!!!:D
Fred N358

[kevin]

My old '65 C337 (N2223X) had a relief tube. Disadvantage to the P models, which is ironic...

Kevin

(Sorry.)

[rick bell]

not with depends (#1&2 try that with a relief tube)

[Jim Rainer]

P models can have relief tubes - a little more complicated getting through the fuselage and you need a "receiving" device with a valve you have to push then the pressurized air forces it out! The valve maintains the pressurization when not in use.

[Jim Rainer]

I should've said I don't have a relief tube - I use empty milk bottles with the screw-on tops. Sporty's has a relief package that converts the liquid into a solid and works well for ladies as well - about $3. Slick!

[skymaster]

Our new 40 gallon tip tanks are allowing longer trips without stopping our 73 p337. Belive me its worth it. The bladder deal is a small inconvenience when you calculate cycles. We have a mp3 player plugged into our intercom. I look forward to listening to the audible books. The longer wings require some lookout. The increase 5100 lb gross is real. The tips flex up during flight. JCH

[SkyKing]

I sure hope the wing-tips don't flex themselves off... your long range will become a short trip.

SkyKing

[GMAs]

Ahh pressurized aircraft.. and relief tubes... smile.. well... sometimes it does.. and sometimes it doesn't... but, hey just think of the other uses it has... having the little lady vac the interior while at altitude... and oh that spilled drink.. why just use the relief tube... it will take the hair right off the cat...kinda thing... and for the emergencies... why nothing finer for clearing the air... Of course make sure the cabin alt is lower than what your at because if its not ... you could be in for a surprise... too.... just don't get stuck in the thing when you open the valve.. at altitude above 10000.... to clear it for that extra coke that you supersized... as the little well that they used... was made for midgets.. with small bladders... I can hear the panic now...my husband is having extream pain... and we have to land ...now... (tower) where is the pain coming from.... (Passenger) ahhh... well.... he got stuck ... ahhh in... aahhhh ... while everyone else flying is doing loops and laughing so hard...smile... and no its not a adult toy.... and sometimes you have to clean off the outside of the plane.. remember its corrosive to the alu too.... but, remember the bottles will sometimes implode when you land... or explode when you climb and decompress... too... something to think about... smile... maybe its just better to take a break every 3 hrs.. or so... GMAs....

By all means don't use those things if they are old, just used mines, and they were stored in the plane for about four years, it's really complicated to hold on to it for the rest of the flight if for whatever reason the liquid doesn't get converted into gel or solid as it's suposed to... yes you guessed it, it doesn't always work I CAN tell you about it. My wife wasn't too happy about holding it either, thank god we improvised a couple of bags and hanged the package to the small hanger thing on the rear seats.

I am going back to the old trustable milk bottle...

Regards,

Ignacio

BTW: I never new if the things worked when new, because never tries them.

[Bob Cook]

Skyking / Kevin

Mine is a 74 P s/n 170 and I have 148 gallons of fuel. Apparently some 1974's came out with the large tanks.

Take a look in the POH and there is an endurance of 17 hrs for the P 337. now you need more than a relief tube <G>

PIREP

5B2 (Saratoga Springs) has fuel for 1.90 and it is NOT self serve. They provided me with a nice car for the day (gratis) and besides changed out my brake shoes on a Holiday.

I consider this to be one of the TOP 5 CLASSY FBO's that I have been too. A solid "10". Great town to visit. Horse racing at it's finest. Oh... and a large red carpet to boot!

Sure beats the 3.35 a gallon at Nantucket and the " what you only wanted 30 gallons of fuel? Sorry we topped your tanks....". This was at OWD.

Second time at OWD I received the "2X4". Should have learned my lesson first time around paying 400 dollars for an oil change! Pretty crafty to say the least.


Bob

[Kevin McDole]

My $0.02 for those who plan to use a relief tube for the first time ...

Before you begin, confirm the tube is operational by pouring some water through it. This will confirm that it isn't frozen shut from the last time you used it. You certainly will have a problem on your hands if you start peeing into a blocked tube. <grin>

Also, when you're done, pour some more water through it to rinse out all the corrosive stuff you just sent down the tube. And then hold it open for a little bit to allow the air to clear out the liquid (so it won't be frozen next time you need it).

[GMAs]

well that is cold... what do you do if it is blocked with ice???? well leave the valve open and it won't because it will allow air to pass thru and keep it clear... but, wouldn't you know it your have to go.. bad... reach for the tube and its frozen... wow thats really cold... could that be considered a emergency???? would that warm cup of coffee... defrost the tube... or would it be better to drink it and smile...

I still say it makes a good vacuum cleaner hose... when it works... but, remember that rear prop is going to dice anything up that goes its way... smile...

Better to plan stops along the way... and enjoy the ride.... don't they have a pill that will plug you up...

[Jim Rainer]

Seems there is no good relief for all occasions. Bob Cook, I think that is 7 hours not 17 hours endurance for P models w long range tanks. That'd be 4.3 gph per engine to dry tanks and I think they burn almost that much at idle!

[Bob Cook]

Jim

Would I give you a snow job?

Sorry, it is 17 hrs max endurance and it is listed in either the front inside or the rear inside page of the POH / 1974 manual. 148/17=8.7 g/hr /2 = 4.35 gph/engine.

I don't have mine here but I am sure someone can verify it.

AT 20k ft you become dehydrated enough that a relief tube is almost not necessary. <G>

Skyking-- do you have your poh with you?

bob

[GMAs]

Yep.. yep.. 17 hrs is just a little too long for the normal tanks on a skymaster... I am glad that I wasn't the only one that caught that...

You have to watch that Bob... he, I think came from texas originally... and has a tendency to stretch thing a little thin.. and then claims that its old age and memory loss.. when you catch him at it... but, maybe that might be the new leaning of peak stuff that he is doing now...

I hear if you add some goofie MJ smoke to the tanks you can get a lot more mileage out of the old bird... by flying upside down... something about the vector forces... lift is alway less than weight.. so if you invert them you will have more in the up direction that the down... or is it ... hmmm.. ah... well bob can explane it...

Hello larry... is the expert here... but, lately his bird has been dragging around the sky... after the dog protested and claimed union wages or else....and the plane hasn't flown the same since (the weight shifted to the front the the dog gone CG is too far forward now and he is creating more parasitic induced drag) the dog went out on strike taking a non-union job and is now working as a security representive... some say his dog gone flying days are over.... smile GMAs

[CO_Skymaster]

I'm thinking of adding a relief tube duirng my next annual. I was looking at aircraft spruce for the equipment and it looks like the opening to the outside goes through a venturi discharge. For those who have one, I have a couple questions:

1. Where would be the best place to place the outlet, under the fusalage just before the landing gear doors is my first thought (but, is there a problem placing it there such and ice freezing the doors closed for example).

2. Since our aircraft are Skymasters, does the rear engine tend to spray the output all over the tail section? Someone mention corrosion problems. (The best way I think to protect myself is a good protection coating and spray off the aircraft after a flight where I used the tube).

Thanks for any insight,

Karl

[hharney]

Is there an STC or just field approval?